I'm About Done With The %**&ing Efi

[FastWoman]

I thought you had adjusted/confirmed your TPS.  If not, that's a very easy thing to do.  I'd check it (and most other things) from the point of the ECU connector.  The idle contacts should break as you depress the accelerator pedal very slightly, and the WOT contacts should make when the pedal is mostly depressed (maybe 2/3 of the distance to the floor).  Easy to check.  You are partially correct about the "what-ifs."  If the ECU sees constant idle position, it will run the engine a bit rich.  Your leanest running will be off-idle and not as far as the WOT setting.  Your richest condition will be after the WOT contacts engage.

 

Although the resistance checks on your AFM are now much better (with the wiper contact resistance issue now seemingly corrected), did you ever power the thing up and confirm smooth voltage changes as you move the flap?

 

Did you measure the resistance of the CTS and air temp sensors at the ECU connector?  You'll discover/confirm more by mearusing at that connector.  At that location, you will also be checking for bad connections, miswiring, shorts, wire breaks, and mystery stuff hidden inside your wiring harness (e.g. a fixed resistor that someone had wired in series with the CTS circuit in my harness).

 

FAIW, I don't think the '75 and '76 years had the lean drift issue.  I know the '75 has the Bosch ECU.  At some point ('77?), a transition was made to Hitachi manufacture (and possibly circuit redesign), and that's when the lean drift problem surfaced.  For all I know, there could be a rich-drift issue with the Bosch units, but I don't think so.  Regardless, if you rule out everything else, you might be able to lean out your mixture by altering the CTS circuit.  This would be done by wiring a resistor in parallel with the CTS.  Unfortunately, this would diminish the responsivity of your system to temp changes, running it too lean when it's cold.  I would use that as a last resort, but it will get you running at the right mixture if all else fails.  (But check/confirm "all else" first!)

 

Oh, and finally....  Does your engine run any better now, with the AFM potentiometer cleaned?  Or is it the same?

Edited March 22, 2015 by FastWoman

[240260280z]

This should help:

http://atlanticz.ca/zclub/techtips/efisystem/overview.html

and the picture below:

#1 only occurs when you crank and when it is cold outside. It is the Cold Start Valve.

#2 is your idle enrichment and it continues while the car warms up and when it is warm until you press the pedal and cause the TVS to move.

#3 is extra fuel added by 6 injectors when cranking

#4 is extra fuel added by 6 injectors when cranking and while the car warms up at idle

#5 is a blip of extra fuel when coming off idle. it will blip when you change gears too and take your foot off the gas for a moment.

#6 is the TVS at WOT position.

So your TVS controls the adding of extra fuel at idle, at WOT, and when you come off idle (blip).

[mjr45]

Fastwoman, I thought I had adjusted the TPS correctly and in looking at the contacts and the adjustment I made yesterday it still appears correct. The CTS checked out as reading correctly based on ohm #'s, but I guess it could still be off. I checked all the parts at the ECU connector. As far as runnibg better, its hard to say, the roads up here are all muddy and I don't take it in the mud, so I just drove about 800' and never got it up to running temp. I'll let you know tomorrow when I have to take her out fro a new exhaust, just hope the roads are dryer or I can avoid the mud bogs. Since I'm not a whizz electrical guy, what size resistor and exactly hwo would you wire it in. Bottom line is I'd rather have too rich than too lean.

 

Thanks Blue, I've seen that diagram in my FSM, but never paid much attention to it. So my question is, if the ECU is only seeing #1,2,3,4 section of the diagram, its running rich most of the time, correct?

 

Thanks again to all.

Mike

[Hodgimus-maximus]

Have you checked your water tep sensor, if that is bad or if the wires are broken then your ecu will always supplying fuel to the engine as if it were cold? Also check your cold start injector, it might be leaking.

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[rossiz]

just a thought - i believe you mentioned that you took the cold start injector out of the equation by removing the electrical connection, but if it's leaking that wouldn't solve the problem, it would continue to leak due to the pressurized fuel behind it regardless of whether it's getting a signal or not. you might pull the hose off it and block it off temporarily with a bolt and clamp to see if that helps. to test, you could pull it from the manifold (2 bolts) and pressurize the system without turning the motor over and see if it's leaking.

[240260280z]

Hi Mike,

The graph's bottom layers (coolant temp sensor and air temp sensor) seem to affect the richness the most.

I had a coolant temp connector come off once and my car lasted about 10min before the plugs fouled black.

I have never had a chance to "play" with an EFI Z and my A/F sensor but hopefully I will this summer and I can map what the A/F changes are. I'll finally be able to quantify the EFI components.

For your car if you tighten the AFM spring it should eventually start leaning out the overall mixture to get you out of the deep end.

[mjr45]

Thanks Blue for all your help, I may just have to adjust that spring to get it to lean out. It doesn't make a lot of sense to me as to what could be going on, AFM, CTS are checking out good, which means maybe the injectors, FPR and CSV are leaking, but I don't think they are(they are all new), but also not sure how to check except by the rail pressure, the rail right now does not hold pressure for more than a few minutes, I'll try clamping off the CSV to start and go from there.

 

rossiz, I replaced the CSV because it was leaking, same with the FPR(wouldn't hold any vacuum) so maybe I'll try claping the CSV fuel line and see what happens.

 

Thanks for all the help.

Mike

Edited March 22, 2015 by mjr45

[Zed Head]

Here's something I just went through to pass emissions in Oregon.  I have non-stock injectors that flow a little higher than stock and I failed my first time through.  I tried my usual tuning tricks and failed two  more times.  CO was high,which means too much fuel for the oxygen supplied.

 

So I dropped my fuel pressure by a few psi  (I have an adjustable FPR) and turned the idle air bypass on the AFM out until I heard a change in idle quality.  I had intended to lean things out until I got a lean miss, then dial it back up, but didn't get that far.  But I did notice a distinct change in idle quality at a certain point, beyond which not much happened.  So I left it there, went back and passed.  

 

My point is, I guess, that you could dial that AFM spring wheel tighter until you hit that idle change point, and try that.  I just posted a thought on the spring in another thread, that I think is right, but I may be off.  Since fuel is mostly low air flow at high RPM, the spring adjustment could be a big part of your mpg problem.

 

I think that adding a resistor in parallel with the coolant circuit will change the slope of the curve and might really make things weird.  It would make every temperature lower resistance (leaner), but have very dramatic effect at low temperature, where resistance should be very high, and little at high temperature where resistance is very low.  Could get confusing.  It might barely run cold because things look hot.  You could put it on a switch maybe and only put it in-circuit when the engine warmed up.

 

 

[Patcon]

My only contribution here is to the new injector issue. I hopped up a 95 Suburban years ago. It was throttle body injected and I had to try several different sets of injectors to find one that delivered the right amount of fuel. One of the sets I got had a bad injector right out of the box. Unless you are sure the injectors don't leak and flow correctly you are possibly overlooking the root cause.

Charles

[240260280z]

If all plugs are sooty then problem will be common to all.

[mjr45]

Charles, you could be right, I never had them flow tested or checked when I bought them new. Maybe I'll just slap the old ones back in and see what happens.

 

Zed, I'm not real I want to mess with resistors and switches quite yet. I had the Z out to warm it up and check some fuel rail pressures, ata idle with vacuum 32-33PSI, if I clamp off the in line, pressure drops to 10 in about 90 seconds then slowly bleeds down to 0. If I clamp the return line pressure stays up as long as the line is clamped on release goes to 0, if I clamp the CSV line pressure drops much more slowly but goes to zero, if I clamp both in and return line, pressure very very slowly bleeds down. I'm not sure what all that tells, bad FPR bad CSV whole thing is bad, what? Unfortunately my assistant had to go to town for a massage so I couldn't work three or four clamps at the same time.

 

Blue, yep all the plugs look relatively the same, sooty black.

Edited March 22, 2015 by mjr45

[jonathanrussell]

FYI, Zed Head I agree with your concern about adjusting the AFM spring tension, and what you wrote in your new thread. I know that many smart folks on this forum adjust the spring tension to correct mixture problems. I personally can't wrap my brain around that being a good path to success. Just my opinion though. I agree with what Zed Head wrote about the effects on tension throughout the flap movement cycle. 

 

mir45, I have read your entire thread. Sorry for the frustrating problems you are having. I have two comments that I am sure you have already considered but maybe something will help you stumble on an answer.

 

1) One time, my 75 AFM ended up in a situation where the flap was getting stuck (bent a bit due to a backfire probably). In reading your situation, I wonder whether your flap is stuck about 3/4. If so, you could be rich most of the time but lean at WOT. I seem to recall you writing that your flap is not sticking. Are you certain?

 

2) Are you sure that your injectors are not the problem? Especially if you have original injectors (can't remember whether you said yours have been replaced), more often than not, I am finding that poor running 280zs end up getting solved with new injectors (of course assuming other sensors and wiring are working as they should). Are all cylinders firing?