AFM adjustment for more fuel

[z-ya]

I did a search, but couldn't locate the answer I am looking for.

 

I'm building a 1mm over 10:1 NA 280Z motor for my wife's 78' 280Z, so I'm going to need the enrich the mixture a bit. I'd like to run stock fuel pressure, and keep the EFI looking stock (except that I plan on running a non smog manifold). So I'm thinking that there must be a way to modify the AFM to fake out the EFI computer, with the result being the ability to adjust mixture. I know about the adjustment screw in the AFM, but from what I hear, there isn't enough adjustment to compensate for modifications like increased CR.

 

Any help or suggestions appreciated.

 

Pete

[SleeperZ]

I'm not sure adjustments are necessary purely to compensate for increased compression. The AFM simply moves in response to a given airflow, and provides an injector duty cycle appropriate for the amount of air. A hotter cam should move more air and the ECU should supply more fuel. On the other hand, the n/a injectors are pretty wimpy, so a conversion to turbo injectors may be in order, and possibly to a turbo AFM. Then you can tweek the tension spring inside the AFM to get you the mixtures you are after.

[Brad-ManQ45]

Compression and cam don't require new injectors, and probably no change to AFM.

 

Your octane requirement has changed though - you need more.

[Nismo280zEd]

I disagree... the AFM is the heart of the 280z EFI fine tweaking can give considerate performance gains, as i speak from experience. is what you want to do it is pop off the black over... and inside there are two screws... if i remember right.. you want to loosen the one that holds a geared wheel on a spring. I believe you loosen the spring to enrichen. BE VERY CAREFUL TO NOT LET THE SPRING UNWIND!!!! OTHERWISE IT IS A B**** TO GET BACK TO NORMAL.

when you are done seal it up with some silicon or gasket maker to keep water out.

-Ed

[280Zone]

Can't you adjust the mixture by the external screw? I just can't remember which way is richer, tighter or looser.

[Nismo280zEd]

no, the external screw you are talking about is for idle sets how much air bypasses the flap at idle.

-Ed

[technicalninja]

Changing the spring tension can be used to "tune" the F.I. but at the stock 280 Z engines max flow rates it is almost fully open anyways and cannot be considered as a good method to increase total fuel delivery.

I have your basic engine in my 78 280Z 10.5:1(flat top/N42) medium cam and I increased my total fuel delivery by placing a variable ratio potentiometer in the return wire from the coolant temp sensor.

This critter is basically a variable resistor with a range of 0-1000 ohms and was dirt cheap at Radio Shack (.99). You have to determine your return wire from the CTS and splice the unit in (Unit has two posts- cut CTS return wire and apply unit in series). I cut CTS wiring near brain and added 2 wire speaker wire up along dash, tucked it behind A pillar trim and left the end at top of trim panel. Soldered unit to wires, soldered wires to cut wires. The unit is a small blue box with a small common headed screw coming out of it and is un-noticeable at top of trim panel.

Adding resistance to this circuit basically tricks the brain into thinking the engine is cooler than it is and this lengthens the injector open time thus delivering more fuel.

Through trial and error I found 350 ohms to be the setting my car runs best on. I can vary the AFR easily with a tiny screwdriver.

After finding the best full throttle point I then vary the AFM spring setting to retune my midrange.

Adjusting the AFM-

First carefully cut the silicon seal that holds the black plastic cover on the AFM.

The spring tension is adjusted by loosening the bolt which locates the black plastic spring carrier, rotating the carrier, and retightening bolt.

It is a good idea to mark the original location by scribing a line in the black plastic carrier adjacent to the bolt before adjustment. You do not have to loosen the bolt very much to be able to re-index the carrier. The carrier has teeth around the outer perimeter which mesh with the locater tab held down by the bolt. Make sure that the teeth mesh with the locater tab or you can break the carrier when you tighten the bolt down.

The original location has spring tension against it. When you loosen it it will try to release the tension by rotating so hold on to the carrier when you loosen it.

Adding tension reduces midrange fuel. Decreasing tension adds fuel.

Reduce tension by 5 teeth then drive car.

Increase tension by 2 teeth-drive car. Continue tightening by two until you feel a flat spot when flooring car from 3rd gear 3000 rpm cruise. After you find the lean flat spot reduce tension 1 to 2 teeth.

You can re-silicon the cover on but I use a fat rubber band to hold mine on.

 

My car ended up (after much messing with) 3 teeth tighter than stock (this is with the above mentioned CTS modification installed).

Having a AFR gauge would make this process easier but it can be done with out one.

This modification should cost less than 5 dollars and will give a fair amount of adjustability to the stock system.

The CTS modification adjusts the basic fuel delivery, The AFM adjustment tunes it in midrange/acceleration.

All of the above assumes the stock F.I. is in good shape with proper injector patterns.

If you don't know the age/condition of your injectors remove them and send to a shop specializing in F.I. repair. Normally these shops don't work on whole car- you have to bring them the injectors separate. Have the injectors patterns checked/injectors cleaned.

All 6 of my original injectors were bad/had poor patterns so I replaced them with Beck/Arnley "rebuilt" injectors. I compared the "new" Beck/Arnley injectors with the "rebuilt" and the was no difference just boxes. I cannot believe that it is cost effective for the manufactor to use my old injectors and the price difference is just a sales gimmick.

New were $55 each, "rebuilt" were $30.

Hope this helps

Rick

[Nismo280zEd]

Where the hell where you when i had my EFI!

what an ingenious idea. too bad i have triple webers now. I ended up putn' a 90 psi fuel pump in and running about 50psi for performance gains... runs really really smooth at that psi too.

I'll print this for future use eventually i plan on owning a 911 could come in useful.

[technicalninja]

Most 911s had a type of F.I. called CIS (constant injection system) this "bugspray" F.I. works on totally different prinicples but it can be "Played" with to, just the above modifications are not applicable.

I neglected to advise how to find the "return" wiring from the CTS. The CTS has two wires going to it. Unplug harness from sensor under thermostat cover, turn ignition to "on" one wire will have a 5 volt reference voltage applied to it, that wire is what I call sensor feed. The other wire is the one you want to splice into and you can put potentiometer in engine compartment but it is a cleaner install and easier to adjust in interior. Potentiometer will actually work in either wire but a basic rule is to make your modifications AFTER the sensor. Reduces strange F.I. issues.

Old shop technicain slang for 911 is "Super Chicken" for the SC desigination on most of them-just don't let your customer hear you refer to his car this way- they don't understand! get bent outa shape.

[Nismo280zEd]

very true, i was refering more to the K-jetronic system very similar to the Z even uses many of the same pieces even an AFM.

But with the money the Z is worth i'll only be able to buy a triple weber carbed 2.4L 73 or older 911. Although owning the 3.0 or 3.2 L 911SC sure would be nice.

[z-ya]

Thanks a bunch for all the responses. I'll be copying this into a document to have near by when I start tuning it.

 

All this reminds me of this Impact Parts modification that I found an installtion manual for in a 280ZX I stripped. The kit was basically what you described, a pot, connected in between the proper CTS lead to fake the computer out.

 

Thanks again,

 

Pete

[technicalninja]

K-Jetronic is CIS. In its most recent forms its appearance is very similar to the L-Jetronic (electronic pulsed injection) but it still is vastly different animal. Much info exists on its modification and tuning throughout the Internet.

Now about your wish for a 911.

Z food normally is comprised of Camero, Mustang, Vett, and Honda but a nice fat 911 is a tasty treat every now and then. I just love the look on their face when the "Old Raty Z" screams by. Newer 911s are not to be messed with (YET).

Having owned both makes I can honestly say the I will always have a Z and I may never own another P-Wagen. Parts are drastically!!! expensive and the cars are harder to work on than the Zs. Not much faster than a z in stock form the 911 also has an interesting added entertainment feature- Trailing Throttle Oversteer. Gauranteed to terrify both the passenger and the driver for years to come.

Back to the post- Z-Ya,I have three suggestions which you may already be doing

60 MM throttle body, either aftermarket or Nissan KE motor(240SX,Stanza

Cold air system (Motorsport style- Building it your self would not be hard)

Good header/manifold 2.5 inch exhaust. Motorsports is cheap and fits pretty good.

Just suggestions but they "bring out the" motor and are not very expensive

[Guest dawg95_2000]

I am intrigued by your mod, Techninja, and have purchased the potentiometer you mentioned. I am almost positive I have located the cts off the thermostat housing and have found a good place to splice in. My question is how do I hook it up? It has three posts. Also it says this on the box- (15-Turn). Does that mean one turn adjusts it 15 ohms?

[technicalninja]

Need to go look at my car, cold and dark out there now. I did it years ago and cannot remember. What is range on your pot, it should be 1-1000ohms. 15 ohms per turn doesn't sound correct- more like 100 per turn on mine. I will look at car tomarrow and repost but you should be able to figure it out with a DVOM - Put it on 2k Ohms scale- attach leads to two of the little post-see if meter reading changes as you turn screw. Change leads around untill you find the adjustable set. 1 of the post is usually a reference and will not be used in this application. It is also possible to just use a normal resistor ( I would start with a 300 ohm one) but is not adjustable.

[Guest smoov280zx]

Hey ninja, have you had your AFR checked, or did you just adjust by seat-of-the-pants? I'm just curious what ratio you went to after your tuning.

[technicalninja]

I did it by "seat of pants". The engine was originally just slapped together. .30over L28 flat top (incredibly strange-all other overbores I have seen were .20 or .40-could not buy replacement rings-no supply) . I reused all original bearing, rings, etc. N47 non-prepared cylinder head. Basically cleaned and regasketed everything- spent like $100. With the stock cam the engine pinged badly on 93 octane. I did the fuel mod and added resistance untill I lost my detonation then did some plug checking runs. No one ever talks about reading plugs anymore! it actually works pretty good as long as you seen plugs from lean,correct,and rich motors before.

Plug check method- Car should be fully warmed up before completing this test.Drive car "briskly" and have the last part of your run a 2+min high engine speed/mid throttle run (usually 2nd and 3rd gear-on freeway 3500-5000 rpm. Pull plugs and inspect 15 seconds after you turn car off-don't idle car for any time after run. It is important to have already applied antisieze to plugs and have the plugs installed lightly in the head(keeps from destroying cyl head).

Look at insulator of plug- Rich will apear brown to black and some times its even sooty, Correct will look slightly off white (kitchen appliance white- almond). Lean will be extremly white and may appear shiny or glazed,sometimes with little specks on the insulator-obviously has been HOT. I removed a set once that appeared to be glowing white and watched as the "glow" faded out of the plugs in about two minutes. This is why I pull plugs immediatley to check and do not idle car for longer than nec. The "color" of the plugs changes (probably just a little) with time.

After getting nice off-white plugs in sport mode I then drove car at normal freeway settings and rechecked plugs still were same color. I could vary the plug color with the pot by the time I was finished (ended up getting a feel for how much 1 turn was worth on the pot). I have since had the car inspected and the inspection showed 13.7:1. I do not believe the inspection procedure accurately mimics the road(especialy my driving habits) but the numbers were closer to stoich than I expected.

One note- The stock cam in this engine produced compression values (Snap-On comp gauge) between 240 and 250 PSI. Adding a performance cam dropped readings to 175-185 and seems to have solved any detonation issues. The stock cam had tremendous low end power but was going away by 5800 rpm. New cam is much better on top end(still has decent low end). Original cam could leave stop sign in 4th with out lugging the engine(won a bet with this cam 0-100 without shifting or clutch slippage $20). Fuel injection was well dialed in.

I guess I spent 5 or 6 hours over 2 weeks playing with settings. I had it very close by the second hour although. I do have 20+years experience as a professional import car tech and and knew what I was doing. I would think a someone who has never done anything like this would take twice as long playing around with it before they mastered it.

The new cam required a minor fuel add (plugs got a white again). Have not retested it since.

Still haven't gotten out to look at potentiometer-life to busy.

Hope this helps

Rick

[Guest smoov280zx]

Yeah, it helps alot. I never thought of tuning by plugs, guess I've been around computers too long. Thanks again for the info man.

 

Mitch

[Guest bastaad525]

You WILL need to supply more fuel for increased compression to avoid detonation, I definately did, HOWEVER, I have heard and read a lot of info that suggests that running a hotter-than-stock cam can keep the detonation from occuring.

 

When I built an L28 with flattop pistons, N42 head, roughly 10.5:1 compression, stock cam, bone stock EFI, I had a LOT of ping above 5000rpm at WOT. Adjusting the AFM spring had NO effect on this... on the dyno, no amount of adjusting the AFM spring affected top end (above 4k or 5k rpm) fuel mixture, lending more credence to the theory that the stock AFM flap is fully open at WOT by about 4000rpm. By the way this is on 91 octane (all I can get ... reasonably anyways). The simple solution was to get an adjustable fuel pressure regulator, turn up the fuel pressure a few pounds, you can then TIGHTEN the AFM spring to compensate for the richer running from the higher fuel pressure, yet the top end will remain richened... and play with the timing some, I ended up backing it from stock 10* to 8* BTDC, upped the fuel pressure by about 3psi, and tightened the AFM spring like 1/4 or 1/8 turn (I forget as this was some 3 years ago) and got my peak power and torque along with retaining great cruise driveability and just about the same mileage I had with the stock motor.

 

Anyways, now i'm running a turbo motor, though it runs on the same type of AFM setup. I'm very interested in technicalninja's method for tuning. The turbo EFI runs SUPER rich in the midrange, and it's not just my car, I've seen like 3-4 other people dyno and get the same results. I may be going back to the dyno tommorow and will be tweaking the AFM soley to try to lean out the midrange, and fully expect to find, again, that it will NOT affect WOT, high rpm performance or air/fuel ratio. I'm also most likely going to get an adj. fuel pressure regulator on this setup and use that to richen up the top end, and the afm to lean out the midrange, just as I did on my N/A Z motor. Though I may try technicalninja's setup first...

 

one question... I dont have a coolant temp sensor mounted in the thermostat housing, rather, my EFI just has the head temp sensor that screws into the head between the #5 and #6 spark plugs. Can I use this for mounting that resistor to? Actually... two questions... doesn't the ECU only have two fuel settings associated with whatever it reads from the coolant temp sensor? I thought it just has it's 'cold run mode' which is just a richer setting, until the temp reaches 180 degrees, then immediately switches to the leaner, regular running mode?

 

Then again, you really can attain this same result by just installing an adjustable fuel pressure regulator... use that to adjust your total mixture, and fine tune idle, cruise and low rpm mixture via the AFM tension spring.

 

There is an MSD adj. FPR with a vacuum/boost reference (just like the stock one) that can be had for about $50-75, and you can set up a pressure gauge with common hardware store parts for about $10 in your return line.

[Guest smoov280zx]

I'm putting together the same motor actually bastaad, and was going to use your method of upping the fuel pressure and adjusting the afm. I already have the aeromotive AFPR so I might as well use it, and also got a 260/270 .460 cam kit sitting in the garage too. Think i will use the N47 I already have stripped when i rebuild my bottom end or buy a longblock. I had heard about the variable resistior thing before but never from someone who had gotten it to work right. I did think about using the resistor, but I was worried that the injectors might not have enough pulse time to be able to supply enough fuel for the highcomp + bigger cam at the stock fuel pressure. I had always heard that higher pressure and better atomization through the stock injector gives a better mixture. I'm curious if anyone knows, I assume the stock injectors run at 80% of their capacity since thats what the bosch FI book says most are designed to do. Has anyone ever measured how close to capacity the non-turbo injectors actually run on a stock system at stock pressure?

 

About WOT, as far as I know, nothing affects WOT, except maybe modified fuel pressure. I think it's a preset map(open loop mode, I believe) as soon as the contacts meet in the Throttle Vane Switch. I believe the sensors only work below WOT.

 

I might be wrong, maybe someone can confirm or deny this.

 

Mitch

[technicalninja]

Stock Z injector (na) duty cycle is about 80 percent. The CTS mod can add additional fuel up to probably 95 percent duty cycle. This is a gain of 12+ percent total and will support mild to moderate standard displacement L28 engine mods. An adjustable FPR can support much much more(as long as the fuel pump can supply). The CTS mod is a super cheap tuning tool that can increase fuel supply a little. It will NOT be the answer to increasing fuel in a turbo situation where a FPR/RRFPR would help far better. The cost of the CTS mod can't be beat although.

Most coolant temp sensors work the same way. As temps heat up resistance across the 2 sensor leads DECREASE. The F.I. units vary the base fuel curve by what resistance the sensor is at. Curve has no settings;adjusts to any changes to resistance (no hot and cold maps-One base map varied by multiple inputs). Inputs in order of their ability to adjust base map (most changing first)-RPM signal from ignition, AFM, CTS, TPS,O2,ATS (air temp),baro(if equipt). RPM is not normally trickable.

AFM range is maxed at WOT by stock engine,CTS is first easily tricked sensor circuit. TPS can also be used but early Zs (pre 300ZX) have a tps with three positions (wot,closed,and anything in between)not very selective but WOT can be adjusted to turn on earlier in throttle range. Might give tiny midrange increase. The O2 sensor and baro sensor have such small impact on fuel curves they are not usually a good place to try.

Exceptions ALWAYS exist to ANY rule.

Either type of CTS sensor works on same principles and the mod is applicable to either.

WOT releases most EFI systems from "closed loop mode" and effectivley turns off signal from O2 sensor but all other signals still adjust fuel injector duty cycle. To verify just disconnect CTS(car thinks it -127 degrees) and try to drive car at WOT-may not run-WAY WAY rich-especially at all but redline. Then cross to leads in sensor harness (car thinks its 500 degrees) and try to rerun-may not run-WAY WAY lean.

Hope this helps

Rick