EFI relay unplugged

[rcb280z]

Hmm....funny you say that. I was just thinking the same thing early this morning. If I have a vacuum leak it is probably going to be hard to find because it goes away so fast. I know it takes longer than that for the intake to heat up enough for the metal to expand. I think you meant intake to head connection though. I'm contemplating a compression test. Looking for possible valve (s) not seating right because although it might smooth out after warm up it doesn't idle as perfectly smooth as it should. I did a cold adjustment about 2 months ago and didn't find anything out so....? My vacuum gauge shows a reading of between 18-18.5 in Hg so if I had a vacuum leak do you think it would show up there? Guess I should hook it up during a cold start and see if I get a different reading. Wish I had a spare good known AFM. I could easy change it out to see if there was a difference in fuel delivery when it's cold. I have a fuel gauge in line and the pressure is good. Guess I'm grasping at straws here. I will keep plugging away at it. I want to try Fastwomens vacuum leak test. I will have a buddy of mine blow smoke into the intake...he smokes I don't.

Edited February 8, 2012 by rcb280z

[240260280z]

the CO may have nailed it. A quick way to check would be to "finger the AFM" upon cold start. If you rotate the AFM away from the stop, it will add more fuel but not air. If it is a lean condition then adding more fuel should bring your idle up. Unfortunately AFM's usually age and add too much fuel due to a weaker spring.

To clarify the BCCD tests above, what I meant was to do the cold morning start then hit the brakes if you don't normally do this to see if there is a difference but alternatively if you did hold the brake on start, then don't do it and see what happens... sort of a probing... but I think I now recall the bccd may be controlled by vacuum and electricity.

[rcb280z]

I will try the AFM next. I was going to try that before and forgot to. I know with the cover removed you can rotate (ever so slight) the counter weight CW or CC to lean and richen it. Remember when I said I was going to remove the plugs to see if they were fuel fouling? That's because I thought I was running rich at start up (fuel fouling the plugs).

[Captain Obvious]

If it is a lean condition, I'm not sure that it ever does go away. I was theorizing that it isn't as noticeable once the engine is warm. It may still be lean even once warm, but just not enough to cause a drivability issue.

And I know that you know... There are plenty of other ways to run lean other than by having a vacuum leak.

AFM problem.

Throttle position sensor problem.

Coolant temp sensor problem.

Intake air temp sensor problem.

Fuel pressure problem.

Fuel filter clogged.

Injector(s) clogged.

ECU drift problem.

And probably others that the experts can come up with!

And not to forget... Any air leak anywhere between the AFM and the pistons. On either side of the throttle butterfly is a problem. Basically, if it doesn't go through the AFM, the ECU won't account for it.

(Yes... I meant intake to head. I've clearly got a lot to learn!) :stupid:

[rcb280z]

I have a lot to learn also Captain Obvious! I have been able to fix everything else on the Z but this problem has been challenging. I like challenges and know that with the help of this forum we will find it. With special thanks to Blue for staying on this with me and everyone that has taken time out to help. I think I just found out that I have an AFM from a 76 280 on my 77. It has the anti backfire valve in the flap. I'm not 100% sure but I think the 77 and 78 didn't have that valve. Not that it matters but I know it's old and might be time to rebuild it or replace it if it warranted. The only thing I haven't checked out of your above list is the ECU drift. What are the symptoms?

[Captain Obvious]

FastWoman is the guru who coined the ECU drift concept. In theory, if the electronics in the ECU drift over time, then you could end up running either rich or lean, but in FastWoman's case, she ended up lean.

Here's the two main threads of the saga:

http://www.classiczcars.com/forums/showthread.php?40234-Purs-like-a-kitten

http://www.classiczcars.com/forums/showthread.php?42429-Update-on-EFI-mod-potentiometer-on-coolant-temp-sensor-circuit

I don't know if there are any differences in AFM's over the years.

[rcb280z]

Okay, here is a promising update! Decided to start the car this morning and with my list of tests I wanted to run in front of me I started with #1. That being; as soon as she fired and started her low unstable idle I moved the AFM counter weight forward...stumbled more. Moved the weight back (CW) and she perked right up and idled where she is supposed to on a cold start! So she is running too rich on cold start up due to AFM. I tightened the spring about 8 teeth (sound familiar?) and she idled around 1300 until she started to warm up and then slowly dropped to around 800 which is OK with me. I'm going to run it for a couple times to see if she likes the adjustment. If not I will go from there. After reading several threads, posts I'm wondering if my ECU is "floating" so to speak. A positive step in the right direction huh?

[240260280z]

yeah! You got it. I'll ring you now.

[FastWoman]

Wow, I apologize for getting in on this thread so late. I saw you already had the best folks in the forum helping you, and I was really busy making a new (to me) house ready for move-in. (We still haven't moved in, but we're getting closer.)

Your ECU could indeed have drifted. However, most linear circuits tend to drift in the same direction from copy to copy. I could be wrong, but the drift problem seems to be towards leaner, not richer. Ztrain, on the other hand, has described how his ECU had a solder joint fracture on one of its PC boards (I believe where the main connector was soldered in). A solder joint failure could happen almost anywhere in the ECU, with any number of consequences. I wonder whether that might be your problem. I know it's not a very refined diagnostic method, but what happens if you kick/bump/knock your ECU while your engine is running? Does that affect the running in any way? It might also be worth trying a different ECU. You can sometimes find them pretty cheap. I bought a spare for my '78 off of Ebay for $20.

If you have a fractured solder joint, you can of course re-flow it with a soldering iron. Of course you could re-flow all the joints, one by one, in the (likely) event you can't actually find a cold joint visually. Just allow the solder from one joint to re-solidify before moving to the next joint, lest you'll have a resistor drop off the board or something. Be careful to locate wire attachments. When you re-flow one of those, hold the wire to keep it from dropping out of the hole. It's a tedious process, but it might fix the problem.

[FastWoman]

Also just a theory: Perhaps the PO violated the calibration of the AFM, dialing it in richer (8 teeth?) to compensate for some other problem like a vacuum leak. (It wouldn't be the first time.) Then the problem was corrected, and the AFM remained dialed in rich. Have you tried Blue's patented beer-can method for calibrating the clock spring?

[rcb280z]

Yes Fastwomen you are correct, I do have the best of the best helping me out. Even after reading as much as I have in this forum and the FI system being as simple as it is there still are so many things to consider. The "8 teeth" adjustment is just the beginning. I'm going to attempt a fine tune session tomorrow on the AFM. It was actually a mechanic friend of mine that messed with the clock spring...he adjusted it lean because he thought it would need it to pass CA smog (and it didn't). So after the smog he adjusted it to where he thought I would like it. So if what you say is correct about ECU drift then mine could be considered "drifted lean" right? If it was adjusted richer because that seemed right then that would mean a lean condition correct? I will tap on the ECU to see if there is a difference. I have read about all the things you speak of on this site. Which BTW I am so happy to be a part of. I am considering Blue's calibration technique if I can't fine tune the AFM. I will have to read it again. Will keep you posted. Thanks to all.

[rcb280z]

Fastwomen, I sent you a PM regarding fuel injectors. That's a good looking Z you have there. Sometimes I wish my Z was all original. It is mostly, just exterior (minor) changes. I guess I would be happy with the one I have and one that was all original also. Wonder what my wife would say to that. Thank god she is understanding. I have spent quite a few hours lately trouble shooting the EFI. She knows just how rewarding it is for me to fix the problems though. I think I have it figured out now. Tomorrows AFM adjustment will tell. Again, I will post what I find.