TPS Question

[Ph34r]

I have an odd issue, did some searching here and didn't find concrete answers. So I figure I'll pose the question for the masters to ponder.

 

So...

When I go WOT on my 79 L28e it feels like its starving for gas... BUT!

I got under the hood and was looking at all the things I read to look at. I adjusted the TPS, cleaned the TB. Opened up and refreshed the MAF.

 

Still no go juice...

 

So in frustration I unplug the TPS and the damn thing runs like a bat out of hell.

 

Any ideas on what could be doing it?

 

And one other thing...

I have several TB's from 240sx's and want to do the swap.

Do I have to run any special wiring to the TPS or is it pretty much plug and play?

 

I have the spacer machined and I am in the process of cleaning out a plenum for it.

 

Thanks again...

 

Ph34r

[Daeron]

what did you do to adjust the TPS? How did you "refresh the MAF?"

 

 

Don't forget, you are talking about a throttle position switch (two contacts, three positions: idle, cruise, and WOT) not a sensor, and you are also dealing with an air flow meter, and not a mass air flow sensor.

 

TPS also stands for throttle position sensor on newer cars (think volume knob) which is a totally different animal. The L28 EFI doesn't talk to throttle position sensors.. the only potentiometer it understands is the air flow meter.

 

An air flow meter is another volume knob hooked up to a flap in the air stream. More air flow, more flap deflection, more "volume" from the knob. A mass air flow sensor is a pair of hot wires, which can get dirty and crudded up over time; cleaning a MAF "refreshes" it but cleaning an AFM doesn't do anything unless it was REALLY dirty, and in that case you would likely run rich at idle, lean at WOT.. but not very much of either.

 

Do a search for EFI bible and you can find the answer to all your stock EFI questions.

[m4xwellmurd3r]

sounds like something is making your engine run rich when the tps goes to its WOT enrichment setting. Have you cleaned your water temp sensor?

[Ph34r]

There is a writeup that shows you that there is a carbon "Trail" that the Air flow meter uses to send the signal. And that over time it can wear down.

http://www.geocities.com/jfairladyz/AFMrebuild.html?1144191577198

But I think that someone has messed with the AFM (It was sealed up with silicone and badly I might add). So I am looking for a new, untouched one to try

 

And to adjust the TPS I used the FSM to properly adjust it.

 

I understand how it all works, just trying to narrow down the problem.

 

And no, I have not checked/cleaned the water temp sensor. Would that be affected by the fact that I run super cool all the time? I have a 16inch flex-a-lite and a turbo radiator... car rarely gets over the first line on the thermostat and I am in Florida.

 

Thanks again... and if you ever need tech/computer help... let me know...lol. I am A+, DCSE and MCP. And I owe you guys whatever help I can offer.

[m4xwellmurd3r]

if there is ANY corrosion on the water temp sensor and the wires going to the ecu, the car WILL run rich and will have that problem where the wot enrichment causes the car to bog.

[Ph34r]

Baller... since I am running at lower temps, would getting a low temp thermostat help this too?

[Daeron]

no and no to your temperature issues.

 

And, sorry if I was a tad condescending with my last post, just had to make sure you knew what you were tinkering with the throttle position switch/sensor thing is a hang up for lots of people who know what they are doing with modern FI but don't recognize the antiquity of what they're looking at under the hood of an L-series Z... and the MAF/AFM confusion.. well, it just let me believe you might've made those mistakes

 

The coolant temp sensor in question is JUST for the ECU for fuel enrichment purposes while cold. Its a standard thermistor, and low temp = high resistance... SO, corrosion leading to increased resistance makes the ECU think the car is always running cold, so it enriches the mix to a point where it CAN be problematic, when other enrichments come on board, (ie WOT AFM enrich) when hot.

 

Three ideas come to mind first... CTS check is the first, and the second is a repeat of your TPS adjustment. You set it so that the idle contacts, contact at idle, and the WOT contacts, contact at WOT, I presume..... BUT what I want you to try is the exact same instrument check, at the ECU end of the wiring harness. Find the FSM for your year, find the pinout, and check those circuits to make sure that somehow, some wire is not crossed, leading to a false WOT signal making it into the ECU when in fact, your TPS is not sending that signal.

 

The third shot would be to check the calibration of the AFM. One old school tuner tweak for the stock EFI involved advancing the potentiometer in the AFM ahead of where it actually should have been; since you say it had already been dickered with, theres a good chance someone did that to fould you up.

 

If push comes to shove, I should be able to lay my hands on a spare AFM to ship you... but the parts are my uncles, they're at my uncle's place, and while they aren't exactly going to be used anytime soon.. I can't promise something that isn't mine right now. Let me know if you really want one and I will try to find one and see what can be done.

 

HTH and again, sorry if I was being an ass

[Ph34r]

LOL, I have had my fair share of vehicles with VAF/AFM whatever you want to call them. I'll check the CTS today.

 

I am gonna go get the AFM from the 81zx that is in the yard here and try the and see if it makes any difference.

 

Appreciate all the help!

[luvemfast]

Is there any difference between n/a and turbo afm's?

If so, would it be better to run a turbo one on a n/a car when upgrading throttle body and intake (like Justin Olsons custom design)?

Also, who would send one down to Australia? (as we didn't get turbo cars here)

[Daeron]

luvemfast: there is a trick whereby you can swap the entire circuit board from the datsun AFM into the body from a Toyota Cressida AFM, and the Cressida AFM has a larger cross-sectional area...

 

 

...but AFMs are old-tech, and are only used with the stock ECU. The stock ECU is as limiting on power as the stock intake hardware.. in other words, if you are replacing your entire intake tract with higher-flowing equipment, the ECU won't really be able to take advantage of all that, so you really may as well switch to standalone EMS (most of which use MAP sensors instead of AFM/MAF) or the 300ZX engine control system, which uses a MAF.

 

phear (i refuse to use numbers for letters): the ZX AFM should do you fine.

 

Regarding the turbo AFMs, I really don't KNOW but I see them listed on ebay as "turbo AFM" and "turbo TB" so I presume they must not be identical... but it probably isn't an upgrade, its simply different.

[Ph34r]

Update...

 

NEW CTS, NEW OEM Thermostat, MSD Blaster 3 and an optima redtop...

 

 

bat out of hell...

 

 

Thanks again guys, worked like a charm!

 

Jason

[Ph34r]

Ok...

 

Still an issue... What I have done made it better....

 

 

there is always a but...

 

I hooked up a A/F tonight http://www.knfilters.com/airfuelmonitors.htm

Was running at the top of the chart 13.2-12.1 with the TPS hooked up and a bit leaner with it disconnected.

 

I am stuck... gas mileage still blows nuts and there are serious performance issues. My only ideas are the AFM and the ECU itself being shot. I will linetest the system tomorrow. And I'll start the search for a new AFM. (Anyone want to sell a good one? Or want a tweaked one in partial trade?

 

*Using the search tool... *

I found that the vac line to the FPR may be an issue so I will check that too...

 

Any other ideas off the top of your head?

[m4xwellmurd3r]

what does your fuel pressure look like

[Daeron]

Have you found the EFI bible yet?

 

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

 

I think that page also has step by step instructions on re-calibrating an AFM to stock specs.

 

You *need* to test the AFM for proper output range.. it is as simple as checking resistance versus a chart at various openings, just like adjusting a potentiometer-type throttle position sensor. When the TPS on the L-EFI is unplugged, the computer simply reads that as "cruise" instead of "WOT" or "Idle." A better test to "lean it out" would be to short the two wires that complete the "idle" circuit to falsely cut into ECU idle enrichment levels, at real speeds. Don't know how catastrophic this could be, but as long as RPMs are kept low and you don't go drag racing with a jumper like this installed you shouldn't grenade any pistons.

 

The ECU is virtually a pass/fail device. There is a sequence of tests to run upon diagnosis of a rich condition, in the EFI bible. Run them. You could possibly have a sticking injector, malfunctioning fuel pressure regulator as mentioned above, maybe even something wild like a dropping resistor outputting slightly high voltage and opening the injectors too far, who knows. The EFI bible runs through the process of pinpointing where the error lies.

[Ph34r]

Thanks again, I'll get to that today and see what pops up.

[Ph34r]

Ok, new AFM in... no luck, but I think I my have found an issue...

Of the 6 injectors... 3 are black, 2 are yellow and one is green...

[m4xwellmurd3r]

that'll only cause an issue if they're all rated differently. different manufactures produce the same rated injector in different colors.

[Ph34r]

Just to be sure, when the new intake mani gets here I am going to get 6 new ones and a new rail. Next is replacing the ECU... Do I need a 79 specific or will 79-83 NA work?

[Daeron]

You could take the injectors out, and set them up with a dropping resistor (or a DC power supply at the right voltage) and a fuel pump, and measure the flow of each and inspect the spray pattern as well...

 

You could even do it on the car, since the dropping resistor supplies the appropriate positive current with the relay energized and actuates the injector by grounding the circuit. I am not 110% positive what all you would need to do to guarantee that the ECU has +VDC going to them, but once you get that all you have to do is jump a wire to ground and it will spray, if there is fuel pressure.

 

I mention it because it could save you some money. (At least short term, if you want to replace them later.) I've got scads of stock NA injectors hanging around from a parts hoard, and "one of these days" I plan on building a wee rack to test, clean, and flow check each injector so that I can set up six, nice, matched injectors to go on my car, and if I can assemble any sets of 4 or 6, then also for sale (cheap, think $40-50 for six). Ideal? no, but better than nominal or unknown (the state of the injectors on my car now) or potentially mismatched, like what you are dealing with.

 

Heck, you are in St Augustine.. shipping between us should be almost nil, and should be quick. I had this plan, and it was low priority.. but if you would be interested in a set of 6 flow tested and verified matching, but used and unguaranteed injectors..... Well, if you are interested, just PM me and we could work out details. I wasn't in a rush to do any of this, and I am not trying to sell you something... but the offer is there.