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BRAAPs L6 EFI-induction advice and tips.


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EFI system basic run down and simple tuning/drivability diagnosing tool;

 

These two links are invaluable to to Datsun EFI tuning and diagnosing;

http://www.atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf

 

http://www.atlanticz.ca/zclub/techtips/EFI&fuel.htm

 

 

 

1) Water Temp sensor; In altering the resistance of the water temp sensor circuit, this offers a linear AFR change across the entire RPM range under all conditions. More resistance is richer, less is leaner. The only way to get “leaner” mixtures with the OE EFI is to use the resistor/potentiometer in place of the water temp sensor itself, but then you loose the coolant temperature compensation. I’m sure a savvy electrical engineer could build an electronic doodad that reads the water temp sender and then alters that return signal to the ECU both above AND below that of the water temp sender resistance.

 

2) TPS; The OE TPS is like a single pole double throw switch. Throttle closed portion of the TPS is for Idle and decel injector shut off. WOT portion of the switch closes the other circuit which actually kicks in at approx ¾ throttle opening, not at WOT as one would assume, everything in between idle and ¾ throttle is “open circuit”. I tried a Bosch TPS for a Fiat years ago that closed the WOT circuit only at WOT, at above 3/4 throttle position, the engine surged and had flat spots till the WOT switch was closed, at WOT. Discovering that resulted in further investigation using a manual switch in the cockpit hooked up the TPS to see how the ECU uses that TPS switch under various conditions. i.e. the throttle no longer actuated the TPS I did with a switch.

a) The idle circuit is a richer mixture and will only allow the engine to rev up to 3200 RPM, then as the RPMS drop, the EFI kicks back on at 2800 RPM. This is a VERY violent rev limiter! Many of you have found this after washing your engine bay and the TPS connector gets wet. This is incorporated for high RPM, when you drop the throttle to closed under deceleration conditions, the ECU shuts off fuel delivery to the engine completely for emissions. If you have a very free flowing exhaust, and depending on how rich your AFR’s are to begin with or BCDD removed, you will notice a slight to moderate ”POP” in the exhaust as the fuel is turned back on as the RPMS drop down through 2800 RPM, but only at closed throttle during decel.

b) The WOT switch alters how much influence the AFM has on the fuel map and adds to the fuel mixture. Open circuit, mimicking part throttle cruise, the AFM has tremendous influence on the injector pulse widths. At WOT, it has substantially less influence and the pulse width is mostly based on the ECU dedicated map, though the AFM does still have an influence, remember, it is substantially less of an influence at WOT than it does at part throttle. Also, the when the WOT switch is closed, the base fuel map is fattened as well.

 

3) Thermo time switch AND cold start injector; The Thermo time switch function is to allow the cold start injector to dump more fuel into the intake via the cold start injector during start up only and only for a couple seconds, when it really really cold outside and the engine is really really cold. Without the cold start injector and/or Thermo time switch, if the EFI is in good tune and the out side temp is really cold, around the freezing point, and the engine is also cold, the engine may take a few more revolutions to fire off during cranking. That is the only side affect of eliminating the cold start injector and Thermo time switch. Personally, I prefer to remove that system for my cars and all my customers, Been doing so since the late ‘80’s here in Pacific Northwest temps rarely get below 20 degree F and no ill effect regarding cold starts.

 

4) Inlet Air Temp sensor; The IAT is in the front of the AFM, looks like little white pencil eraser of sorts. It reacts to VERY quickly to temp change. The ECU uses this to adjust for air density based on Temperature. The IAT functions just the same as the water temp sensor, and by altering its resistance has the same effect on AFR as the water temp sensor, just on a much finer scale, not as drastic as the water temp sensors affect.

 

5) AFM; This complex electro-mechanical device is a well engineered, durable, intricate piece of antiquated equipment, and performs its intended job VERY well! It functions is tell the ECU how much “volume” of air the engine is ingesting, hence the name Air Flow Meter, (MAF stands for Mass Air Flow sensor and MAF’s measure the MASS of the air the engine is ingesting, which is more accurate as the engine actually needs fuel added based on the mass of the air, not the volume. The terms MAF and AFM are not interchangeable physically or in terminology in technical discussions). At WOT, the AFM actually tops out, full open between 4000-4500 RPM! After that, all fuel delivered to the engine is based on RPM, water temp, and air temp. The AFM has NO affect on the injector pulse width above 4500 RPM at WOT. The air flow flap opens as the “volume” of air pushes it open against the return spring and then passes around it on its way into the combustion chamber. Attached to that flap at 90 degrees to it, (see pic below), is the damper flap which is cushioned by the air space above it. Engine acceleration enrichment is delivered by the “over swing” of the flap in the AFM. The flap is also counterweighted. Altering the damper flap by drilling a small hole in the upper flap and/or removing mass from the counter weight, will allow the flap to over swing further, thereby fattening the acceleration enrichment. Loosening the AFM return spring also has the same effect, but also richens the mixture within the operating range of the AFM. Of all the L-series OE EFI tuning I have ever done, I have not found a need to alter that acceleration enrichment of the OE EFI above and beyond what adjusting the return spring for good cruise AFR has delivered.

 

 

Tangent; Back in the mid ‘90’s I had the wild idea of eliminating the AFM from the air stream altogether. I sacrificed an AFM and cut up the body, connected a bicycle brake cable to the damper flap with holes at various points away from the pivot for varied actuation rates. Bolted this AFM to my intake manifold plenum and connected the other end of the cable to my throttle linkage. The idea was to use the AFM electrically so the ECU thought it was in use, but actuate it with the throttle, not the air stream! Also had the TPS switch in the cockpit so I could manually trip the WOT circuit during this testing. WOW what a learning exercise that was! To drive the car without the engine stalling completely or at least drive it somewhat smoothly, the throttle pedal had to follow the RPM. With the TPS in cruise condition, open circuit, that range of pedal position to RPM was a very narrow range. With the WOT circuit closed, I had much more leeway in the throttle position to RPM range before the engine would let me know it didn’t like it, hence the WOT circuit not relying on the AFM so much for calculating fuel delivery. Also, just to drive the car I had to accelerate the same at the same rate all the time and finding that constant cruise condition to maintain a given speed that the engine would like was, oh so difficult. Tried the other holes I added along the length of the flap to alter the rate at which it was being actuated which just altered the rate I had to actuate the throttle to keep the engine running.

 

In short, I found the AFM works as originally designed and works INCREDIBLY well, and due to the narrow range that it functions, which is only below 4500 RPM and mostly under cruise conditions, the only tuning or alterations I perform to the AFM is to adjust the spring tension, but only after the WOT tune is set by altering the water temp sensor resistance. Oh, one other point. My particular L-28, with the water temp resistance first set for max WOT performance, then the AFM adjusted for best cruise conditions, while at idle, the CO adjuster would not allow the flap to close enough to allow a lean enough mixture at idle. I used a Dremel tool and ground a small trough in the floor of the AFM just under where the flap rested at idle to allow even more air to enter the engine and not be registered by the AFM, just as the CO adjusting screw does there by allowing the AFM flap to close a little more leaning out the mixture, but only at idle. One other down side to that mod is if the fuel switch is in the AFM, (early EFI), sometimes the AFM would close just enough at idle to turn off the fuel pump. Fuel pump triggering had to be hard wired to the ignition or with the later Z oil pressure style fuel pump trigger.

 

AFM1Medium.jpg

 

AFM2Medium.jpg

 

 

 

 

 

 

 

Here is a mixture controller I built a little while back that I gave to RTz. This was my “tuning/diagnosing” box for the OE EFI. It gets wired in series to the water temp sensor, (or for diagnosing the water temp circuit or other drivability issues, can be used in place of the water temp sender). The dial is linear variable resistor/POTentiometer and is 0-1000 ohms. I also included a single pole double throw switch that in one direction utilized just the POT alone, in the other direction added another 1000 ohms to whatever the POT was set at for quick and dirty rough/coarse testing/tuning. Middle position of the switch is open circuit, infinite ohms and will flood the engine, not useful. For seat of the pants tuning, with POT at say 250 ohms, you can then flip the switch at WOT and feel/hear/see any difference in how the car ran in real time. You would just narrow down the resistance value to what the engine likes best using that method and then once you narrowed it down, you would just add a resistor with that value in series the water temp sensor. After that WOT tuning is done, only then do you move on to fiddling with AFM spring tension for part throttle cruise. On the dyno, just turn the dial till the engine makes max power. Simple.

 

That little box is a great tuning and diagnostic tool. It can be used in series with the existing sensor or it can be used to “bypass” the sensor.

 

 

BlackboxMedium.jpg

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CAMS and the OE EFI system;

 

The OE EFI will NOT tolerate larger than stock cams, (large enough to make any difference one would spend money and time to swap out), and there is no “reasonable” way around it. If you desire a cam for EFI L28, do yourself a favor and steup to aftermarket Engine management which will allow you to tune around the new VE curve the cam delivers and also delete the AFM from the air stream. The stock Z car EFI isn’t tunable enough to compensate for an altered VE curve. I’m sure someone could hack the resistors and caps in the ECU, but with Mega Squirt being so inexpensive and readily accessible now…

 

The OE EFI will barely tolerate extreme exhaust mods and minor head work, (those two items with the stock cam and stock EFI intake manifold don’t alter the VE curve too much and what they do alter we are able to compensate for with a variety of methods). The OE EFI will not tolerate freer flowing intake manifolds. Both of those alter the VE curve drastically enough that there is no reasonable way to keep the part throttle cruise AND WOT in balance. You will have to sacrifice one for the other and at that, if you spend too much driving around in the compromised region of the tune, the tune could be far enough out to actually foul plugs, which means that when get back into region that is correct for the engine, it wont run right due to fouled spark plugs.

 

In summation, if you have the stock EFI, keep the stock cam and stock intake manifold. If you desire an intake manifold and/or cam change be sure you also have an alternative engine management system that allows the end user to tune and make use of what the cam and intake manifold brings to the table in performance gains.

 

 

Paul

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Intake manifolds, runner sizes;

 

 

Of the factory OE EFI intakes used on the L28, they are very similar from a “power producing/air flow” stand point, (we are not discussing the visual aesthetics here).

There are two style of plenums, full length open box style for the early N/A and Turbo intakes and the necked down plenum for the later N/A plenums, necked down toward the rear of the plenum. Another difference is webbing between the runners. Early intake had no webs, later intakes have the webs. The Jury is still out if the webbing acts as a heat soak affecting IAT or acts as a heat shield reducing IAT, too many variables between different L-6 installations, engine bay air flows, exhaust manifolds and heat shielding etc for there to be a definitive answer. Regardless of the webbing, due to the restrictive runners of the OE EFI intakes, the discussion of which OE EFI intake is most ideal for performance, in my not so humble opinion is inconsequential. I say either use the one you already have or find the one that you like to look at when the hood is open and will still pass Emissions, (if you need EGR or not), and use that one.

 

Seat of the pants you will NOT feel any difference switching between open plenum and necked down plenums with the N/A manifolds. The runners are so choked down that any difference the plenums could/would yield in how then engine produces power is negated, not being realized. On the dyno, the necked down plenum vs open plenum N/A manifolds will perform the same! With runners capable of allowing the engine to breathe, those plenum differences would be small, and the consensus seem to favor larger Plenums, though there is some argument for smaller plenums in some applications.

 

Now the Turbo intakes have just slightly larger ID runners, (see information below), and as has been covered elsewhere on the forum, the runner ID of the factory EFI intake manifolds is only 53% the cross sectional area of the intake valve itself, ie.. the runner IS the restriction and any other changes including larger than stock throttle bodies will not yield any gains, till the restriction is no longer a restriction, i.e. the runners of the manifold! The Turbo runners are only slightly larger than the N/A runnners and should yield approx 2 maybe 4% more power over the N/A, again, nothing you could feel seat of the pants, and there is FAR more power to be gained in dialing in the tune, i.e. AFR’s, ignition timing and getting the ignition system up to snuff, i.e. Quality wires, (Taylor plug wires are NOT what I'm referring to when I say quality wire. Jacobs, Nology, and Magnecor ARE!), NGK spark bolts with projected tip for N/A engines.

 

As of late, there has been a few members here making an effort to improve air flow with EFI manifolds, building their own manifolds and also carving up OE intake manifolds in an effort to open up the runners to allow the engine to breathe more freely. Those folks are on the right track.

 

 

One particular discussion regarding perceived advantages of the Turbo intake over the N/A intakes fired me up to spend an afternoon measuring a few EFI intakes that we have laying around the shop and posting those results. Mind, you I only measured 4 manifolds. 2 of them are Turbo intakes, the other two are N/A. One of the N/A is a non EGR P-82 off a friends 280-ZX, the other is a NON EGR N-42 intake manifold. I have no idea what years the Turbo intakes are, sorry. I’m sure measuring all the EFI intakes that Nissan used would be more accurate, but I strongly feel the results I acquired are good enough for the intent of this thread, i.e. I don’t think measuring them ALL will reveal anything not found here.

Also, keep in mind, these are cast parts, and as such, there are some pretty drastic differences between manifolds, let alone within each runner due to the casting molds etc. I started out also measuring the runners horizontally as well as vertically, but the casting part line was skewing the measurements so much, and being as the runners are, for the most part round not oval, I just used my vertical measurements.

 

In summation, yes the Turbo manifold has ever so slightly larger runners, yet that difference, in my not so humble opinion, is not worth any effort to replace any other existing OE EFI intake that you may be already using. (I take back all the statements that I made previously in other threads in regards to the Turbo intake manifolds being a worthwhile upgrade). ALL of the OE EFI manifolds ARE restrictive, period! No real gain in power will be had using one over the other. There are much bigger performance gains to be had in just dialing in your ignition timing and Air Fuel ratios than switching to a Turbo Intake manifold. If a real marked performance gain is your goal, make sure that none of the OE EFI manifolds are on your engine. They can be made to look real pretty and will perform respectably, but more power can and will be had by switching to an aftermarket manifold with larger than stock diameter runners.

Extrude hone is an option as well some of the extreme preparation others have done to open up the stock runners. I would agree that if the runner could be safely opened another .100” using that process, that would help. Realistically, opening it up another .200” would make it worth while, but I’m not sure there is enough material in the runners to safely remove that much using the extrude hone process. Also, the cost of extrude hone for a little gain is something that you’ll have to weigh against your bank account. For some, it might be more cost effective to spend a little more for a custom intake which would allow the rest of your performance parts and modification to do their job to the fullest, not just partially.

 

 

Here are the details of the afternoons measuring session on these manifold runners.

 

I measured all 6 runners of all 4 manifolds and I measured each and every runner in 3 different locations along the length of the runner. I was using my machinist snap gauges and Mitutoyo 0-12” dial caliper. First measurement point “A”, is 4 ½” from the head flange. Point “B” is 2 ½” from the head flange. Point “C” is at the head flange, ¼” in from the flange surface.

 

 

Top pic shows the manifolds that were measured.

 

Second pic shows the locations at which the measurements were taken, “A” “B” and “C” respectively.

 

Third pic is each and every measurement taken at all three points in all runners of all 4 manifolds, to within .005”. Average runner diameters per location, avg per individual runner, and avg overall. At the bottom is the square area of the averages and the % of difference between the two N/A vs the Turbos, (I used 1.308” Sq/in for the Turbo Reference).

 

ManifoldsMedium.jpg

 

DSC_3535.jpg

 

SpreadCustom.jpg

 

 

 

Keep in mind, if using the stock ECU and wanting to take advantage of what larger intake runner has to offer, much like bigger cam, the stock ECU will not play well with a freer flowing intake.

 

An example of a custom built larger runner intake;

http://forums.hybridz.org/index.php?showtopic=51825

 

 

 

 

Just a little food for thought. In researching intake manifolds and power produced from those that have ran their cars on the Dyno, was able to find quite a few for the Turbo guys, and a handful for the N/A guys. Essentially all of the Turbo guys running the OE EFI intake manifold are making great torque numbers, but the HP to Torque relationship is reminiscent of the mid ‘80’s GM TPI engine or like turbo diesel HP and torque numbers. Huge torque, but it falls off early in the band. Others that are running similar set ups with the only difference being a different or altered intake manifold, their HP numbers fall in line with the torque numbers respectively, i.e. if they are making 500 ft lbs of torque, they are also making in the neighborhood of 500+ HP. The OE intake guys making similar torque figures are typically making mid 300 to low 400 HP. For the N/A EFI crowd, a similar situation holds true. You will find that the fast EFI N/A guys are running some intakes other than the OE intake! (hmm… seems to be a trend here… ) The throttle valve being used, whether it be OE or the monster 90mm Q-45 unit is irrelevant.

 

 

 

Good read for designing induction systems;

http://www.themotorbookstore.com/engine1.html

 

 

Good source for intake manifold and EFI fueling components.;

http://www.rossmachineracing.com/

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Big mouth/Large bore Throttle bodies.

 

As mentioned, the stock EFI manifold port runners have only 53% the area of the L-28 intake valve!… Even armed with this knowledge, some guys are still fixated on wanting to install larger throttle bodies on their EFI L28 as a first mod. You spend all the money, time, and effort you want on big throat throttle valves, but until those restrictive runners are opened up, exhaust system opened up, optimize the ignition system including advance curve, you will NOT be realizing the engines full potential with any over sized throttle body. :wink:

 

Braaps recommendations on where to concentrate ones efforts for building more power from their L6 engine in order of priority…

 

1) Exhaust, Ignition, (quality spark and “tuned” mech curve), Induction, (including getting rid of that AFM!)

 

2) Cam, (but ONLY after exhaust, ignition, induction upgrades including an aftermarket standalone EFI)

 

3) Light weight flywheel.

 

4) Head work.

 

 

 

In regards to HUGE throttle valves, here is a thread that discuses the details with good arguments from both camps;

http://forums.hybridz.org/index.php/topic/54034-big-throttle-bodies-why/

 

 

 

Hope that helps...

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Datsun OE EFI intake manifolds

 

 

 

 

 

 

Cleaned up, shaved and customized L6 intakes.

 

 

Start out with my personal list of items that I typically delete and retain;

 

This example is an intake swap with a 60mm TB conversion I completed recetnly for a local customer. Local customer sourced a non-EGR N-42 intake, 60mm TB, Pallnet fuel rail and TB spacer kit then dropped those goodies and the car off for me to install and tidy up similar to what we have done for many others, including rerouting the EFI harness along the firewall and under the fuel rail instead of over the middle of the plenum, A/C delete, etc. After the intake swap and clean up, the car runs great, just as it did when it came in, other than the deleted air flow regulator as described below. Other than that, no different! :2thumbs:

 

This is a bone stock L-28 EFI.

 

Items deleted;

1) EGR, (This is a ’75 car registered outside of CA)

2) Air Flow Regulator (for a cold idle speed that the engine will idle on its own without holding the gas pedal, a "warm" idle speed has to be approx 1000-1200 RPM on a properly tuned L-28. If a warm idle speed of 650-800 is desired, then you’ll have to hold the gas pedal to keep the car running when cold till the car warms up, or reinstall the Air Flow Regulator.)

3) Coolant by pass that ran under the Air Flow Regulator.

4) Cold start injector and Thermo time switch. Tapped the cold start injector hole for 1/8" NPT, brass pipe plug installed. (left the Thermo-time switch in the thermostat housing, just deleted the wiring.)

5) A/C equipment in the engine bay.

 

Items rearranged; but still functioning as OE!

1) Carbon Canister vacuum line has new port drilled and tapped into the back of the plenum and vacuum line rerouted along passenger frame rail and across the lower firewall.

2) Fuel Pressure regulator relocated to the firewall, fuel rail plumbed in a pseudo dead head style arrangement, (before anyone jumps on the “dead end EFI fuel systems cant be done” bandwagon, SEARCH! It can, has, and is still being successfully done, by the OE and tuners such as myself with NO ill effects NO vapor lock etc). Vacuum port of the FPR also has its own new dedicated vacuum port added to the back of the plenum next to the canister port.

3) PCV is now drawing fresh air, K&N filter on valve cover. (This caused the engine to ingest "false air" as the air being drawn in through the PCV system is no longer being measured by the AFM, yet the engine is breathing that air, i.e. “false air”), as such I will be fine tuning the part throttle tune with a combination of the water temp resistance and AFM adjustments, todays project. For those new to the stock EFI or EFI in general, just leave the valve cover breather plumbed to any port between the Throttle body-butterfly and the AFM and you’ll be just fine!

4) Removed the EFI harness and removed the outer sheathing from the harness that resides in the engine bay. Deleted the Thermo-time switching wiring back to the splice, also deleted the cold start injector wiring. (Just leave the wires cut, but protected from grounding/shorting. The computer doesn’t know the difference nor does the engine.) Separated the injector wires and the water temp sensor wires of the AFM and TPS wires into two separate runs. Retaped those as 2 runs. Reinstalled harness, routed the injector and water temp wires along firewall and then under the fuel rail, (can’t even really see them in this photo below, but they are there) and routed the AFM and TPS wires back in the stock location.

 

Customer wasn’t ready to for a shaved intake, so this one was just painted and installed. Original fuel pressure regulator port plugged as well as a couple other deleted vacuum ports.

 

Here is the picture, below that is a diagram of the dead-head fuel rail system.

 

Boot between TB and AFM is not secured in picture, it needs to be secured!

Running.jpg

 

Returnless.jpg

 

 

 

 

Here is brief run down and how I tackle cleaning up these intakes.

 

With the intake removed from the car and ALL the ancillary parts removed, I jet wash the manifold, (just take it to your local automotive machine shop and ask to have it jet washed or tanked, they’ll take care of it from there). Now for the aggressive removal tactics. Mark ALL the bosses that you won’t be using and wack them off. You can use a Saws-all, hack saw, cut off wheel, or you can just gnaw them off if you have really good dental insurance. I prefer to clamp the intake down on the table of a milling machine and use a ¾” end mill and just GO FOR IT!!! (My oldest daughter enjoys performing that machining operation for me). Then I use the die grinder with assorted non ferrous carbide bits to “rough in” what’s left. Then I use a finer carbide bit in the die grinder to smooth out the scallops left behind from the more aggressive bits. Then I’ll use a sanding roll in the die grinder to smooth out all the grinding marks.

Now, mark all the holes that will be getting filled in, i.e not used any more.

Now, depending on whether the intake is getting polished or painted, that will determine how I tackle the holes and divots left behind. If it is getting painted, I will tap all the holes for SAE pipe plugs and thread in solid brass pipe plugs into the holes and then carve the protruding remnants of the plugs down flush. I have been known to use JB Weld as filler in the divots left behind, but I won’t 100% admit to that.

If the intake is to be polished or the customer prefers the intake to be all aluminum, I’ll make small aluminum plugs from scrap billet that fit the larger holes and have a competent welder weld the plugs in their respective holes and also fill in all the remaining divots, (I don’t weld, so that portion is outsourced). When I get the intake back, I then get out the die grinder again, and start all over on the welds till the entire intake is somewhat smooth. Then I attack the intake with a D/A, then it gets a final cleansing and paint. If it is getting polished, I get it “roughed in” so to speak and take it to a polisher to let him/her finish the job. Oh, before it gets painted/polished, I will set the intake up on the mill and “face” the throttle body mounting surface and if the head mating surface received any damage, I’ll surface that as well. The Throttle body surface ALWAYS needs resurfaced if the cold start injector boss was removed/plugged, especially if the cold start injector boss was welded shut. When filling the holes that used to house the cold start injector, whether I use the pipe plug method or have it welded, the throttle body mounting surface will distort. Welding severely distorts it. Better off to just resurface it so there is no chance of a vacuum leak.

That about covers it. Each person will have their own techniques that work best for them, so use what works best for you if you so choose to do this on your own.

 

Die grinder and bits;

PorttoolsMedium.jpg

 

Intake ready for plugging;

P6180960Medium.jpg

 

 

Here is an intake pictured above just prior to paint. Note the Brass plugs and if you look close, you can make out some of the divots left behind from the old boss holes, grinding divots, etc.

Intake1Large.jpg

 

 

 

 

 

 

 

 

 

Component location;

 

The Fuel Pressure regulator is attached to the fuel rail itself.

 

1) Large is Brake booster, smaller is FICD, factory A/C controls etc.

2) Mount for A/C idle speed boost.

3) Fuel Pressure Regulator port.

4) Mount for Air Flow Regulator.

5) Port for Carbon canister.

6) Cold start injector.

7) Fuel rail mount pads.

 

 

comp.jpg

 

ManifoldsMedium.jpg

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I have paperwork in one of my "280Z" folders that contains detailed information about physically swapping out various resistors inside the ECU, and what effect they have on the various functions of the EFI.   If I get my scanner to work, I'll post them.

 

 

Very cool, looking forward to seeing that info. For the budget DIY crowd, especially in the era pre MegaSquirt, that sort of info opens up possibilities for tuning around cams and intakes. :blink::2thumbs:

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OK This report I have is from the stone age of the Internet.  I can't get my scanner to work and I don't know who published this information but it was someone with an electronics background for sure.  There are photos showing the locations of the resistors but they are not of high quality.  I believe that the resistors are all labeled on the board, so ID'ing them may be easily possible by opening up the ECU.  Resistors are located on both sides of the main board.  The article was written about the generic L-Jetronic system.

 

Here is a summary of what was done:

 

A CD player was used to simulate an ignition signal and a scope was used to read the outputs of the ECU while resistance values were tweaked. 100hz signal = 3000rpm.

 

 

 

 

Resistors and what they do:

 

R103  Low RPM Dwell limit  for injector pulse/ smaller R = higher limit on low-rpm dwell.  

 

R106  rev-limit  smaller R = time of pulse decreases and rev-limit raises

 

R237 & R239 voltage swing compensation during cranking

 

R616  off idle and Post cranking enrichment  - works with coolant temp sensor

 

R758  fuel cut-off speed

 

R621 Off idle enrichment max smaller R = more rich

 

R624 Off idle enrichment decay speed smaller R = faster decay

 

R306  timing of post start enrichment larger R = longer enrichment

 

R617 Post Start and Temp enrichment amount smaller R = less enrichment

 

WOT switch (TPS) fixes enrichment to about +9%

 

R345 Injector opening time compensation

 

Injectors open with about 4amps, after 0.5ms current is held at about 2amps by R408

 

3 Notches  in the AFM wheel gives about a 2% change in lambda.

 

 

This is take from a website that existed in 2/26/1997. I do not have the author's name.

 

http://proffa.cc.tut...24775/mods.html

 

 

Or you can try your luck here:

http://web.archive.o...24775/mods.html

http://web.archive.org/web/19970805035446/proffa.cc.tut.fi/~k124775/Injection.html

 

 

 

 

 

 

Edited by cygnusx1
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Howdy, comrades!

Braap, excellent write-up as usual- lots of usable info, concisely written.

I recently converted to a aftermarket rail (ebay one-off), rigged "dead-end" style. But

my stock pressure regulator only has two ports- in at side, out at bottom. with standard

vac fitting on top. I've got the fuel return line plugged/clamped off, but is this messing

with anything? Too much fuel? The tubes 16mm OD.

It runs rough and smokes, but that may be indicative of a laundry list of other problems. Bessie's

always been a sickly child....

Any thoughts?

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