Hi, I have a 1992 z28 5.0 TPI I’m working on. It recently had issues where wouldn’t crank, dialed it in to being the pickup coil. So new coil and whole new distributor and it finally runs great. It STILL runs great BUT I recently noticed if I go and start the car, shut it off and start it again it just won’t start, I can get it to start but it runs really bad. It ONLY does it in that matter. I can literally daily drive the car A long as I don’t have to move the car quick or hop in and out of it it’s fine. Hadn’t done a second crank in less than 10 minutes till now and now is when I notice I can duplicate it everytime. It has fuel and spark, so I’m betting it’s a computer or sensor issue. The service engine soon light does come on when it goes into that phaSe. I have to check the codes but I imagine have to duplicate it again so I’ll try that next weekend. Mean time, any ideas? Could it be the MAP sensor? Not sure how to post a video here but I have videos.

Just a guess it could be a bad ecm. Do you have injector pulse when it doesn’t start. Is the tach moving, assuming you have a tachometer.

Yup tach moves. I verified with video. It’s just weird as like I said before when it doesn’t do it(which is most of the time) it runs great!
smooth and powerful. It’s crazy!

Was very close to making this car a weekend or weekday driver but now I’m having some major concerns with it. May just throw her in garage until I can LS swap it! Lol! Really wanna enjoy the car as is though.

Went to check the codes and it just blinks once, then twice...over and over same pattern

do you have injector pulse when it won’t start ?
have you checked for spark when it just cranks ?
fuel pressure ok when it just cranks ?

I can hear injectors ticking, I have spark, and yea the tach moves. I run codes and only get code 12 repeated over and over. I can get the car to sort of almost start if I give it throttle but I backfires and/or stumbles. I adjust timing and the changes are minimal so don’t think it’s that. It’s gotta be electronic. Car went from started up perfect running fine, I shut off to step away for one minute or less, go crank and nothing. Hasn’t started since. Fuel pump was replaced recently and I can hear it so somewhat rule that out. Plenty of pressure at the rail too.

Yea that’s next, gonna remove it and clean the plugs and make sure all the pins are intact nor loose. Maybe throw some dialectic grease on them as well.

dialectic grease is not needed on the ecm connections.
I would advise not using it.

Thanks for the tip! Just figured the south Florida humidity and possible leaking t-tops would cause moisture down there. I’ll just make sure connections are good then.

Came across a few posts online of similar issues of the code 12 just repeating over and over and it lead to a burnt ecu. But some weren’t even camaros just obd1 cars. So that left me skeptical.

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So isn’t the computer by the passenger side kick panel? I thought it was remove panel and it would be right there but all I see is a plug. Regardless I wiggles it and same thing. It just cranks and jumps like it’s almoat about to start but just doesn’t. It’s like if it was completely out of timing or something. I think I’m gonna order another distributor!

The ecm is in a holder under the dash. Passengers side under the dash speaker accessible under the dash.

Checked out the plug on ecm everything looks unharmed or burnt. Looks almost brand new actually all the wiring and etc. Damn car was definitely stored well, always surprises me the shape it’s in on the inside lol! Too bad now it don’t run worth a damn!

I continue to get the code 12 when I try to run diagnostics. Any place I can maybe send the computer out to for them to check it out that you guys know of? I saw hawks has some computers but I don’t imagine they fix them. Just don’t want to go and buy another for it to do the same thing. Or worse it’s sometbing else that is burning up the ecm and it’ll just burn the new one.

I don’t know of anyone who does refurbishing on the ecm. I do have a good working ecm for your car for $55 shipped in the states. I just don’t know for certain that’s your issue.

I am willing to try that out but my worry is it’s something shorting the ecm out and then I install a new one and ruins that one too.

It sounds like the ecm is resetting. Just a guess I’m not positive that’s your problem.
if the ecm was shorted out with a 5v reference line the car would run horribly.
The code 12 is normal but if I’m reading the first post right the check engine light stays on at times?

Would never come on at all before. But now the car won’t run and if I get it too run by giving it gas it does indeed stay on. It’s also stays lit and blinks while I try to start it. Things I never saw it do when it ran fine.

So still at the issue. Car won’t run. I changed the distributor. Took me a while to get a warranty. Same problem. I’m getting spark I’m getting fuel cuz I can smell it. Just don’t understand what’s going on.

Now I’m smelling fuel, I can hear the ticking but it’s not a constant tick pattern. Thinking it can be injector issue. Which what controls the injectors? The ecm right? The injectors themselves should be ok, they were running nice and smooth before why a bunch go bad now all of a sudden. I definitely have spark although the wires don’t seem that old they are flimsy and probably cheap ones. So I’ll order a nice set anyways but highly doubt it’s the spark wires.

Sorry for so many responses just troubleshooting the thing. I tried unplugging the tps and the IAC and that helped but still no idle. So plugged them back in and removed the vacuum that goes to the canister on the driver side and now the car idles. High, but it idles!! So now what? I’m confused. Could it be the IAC valve?

Unplugging the iac and tps isn’t going to diagnose your issue. Making a large vacuum leak is helping the idle. Have you set the minimum idle speed ?
is the check engine light still on but no codes available?
there is only one injector driver so all the injectors pulse the same width.
if they sound different you might have a few bad injectors. You can always ohm them with the engine warm.
If they are the original multecs they are junk and should be replaced. The coils are notorious for failing.

Well now that the engine is cranked and running. No check engine light. It’s literally running perfect but with that massive vacuum port open lol! I went ahead and ordered the IaC valve as it was nasty and I’m gonna clean the throttle body let’s see if that helps.

You might want to try this
http://www.iroczone.com/articles/eng...rol-iac-valve/

what did you set the timing to ?
did you do it with the est disconnected?

I ordered a new IAC valve gonna clean throttle body and start with that. Injectors are pulsing right and with the engine revving it don’t denote a rich or lean smell from the exhaust. Also the SES light went away, not that it was much help when it was on anyways. The injectors I have to doubt, it’s never low on fuel, the fuel pump is fairly new, and it always ran great. The problem is now just at idle. Adjusting the timing wasn’t helping, so I set it back to where it always was. Need to pick up a timing gun to dial it in, but engine revs up and runs really smooth. I’ll update soon. Valve should be in by Monday.

Well I installed the IAC valve after a good throttle body clean. And low and behold that was it. She cranks up every time now. I will dial in the idle now when I get a chance to continue working on it as I ran out of time. The timing is still a bit off so will need to get a gun to dial that in. Big headache is gone for now at least. One step closer to making it my weekend car and not a yard ornament lol!

Yea little by little. It’s still starting a little rough when cold. But I haven’t done a full reset to the idle. Gotta remove the factory cap on the throttle body as well. Want to remove the IaC valve and put a drop of oil on the stem as I only cleaned the throttle body and through it in. Didn’t even do the full reset by jumping the obd port and etc. I also timed it to the recommended 6 degrees. But I feel it running a tad sluggish. Read somewhere a few ppl advance it a bit for smoother power? Is that closer to the zero or further away like at 8-10°? Just got the ac working well luckily so that’s also another plus. I’m thinking for sure next year it’ll be ready to drive every other day haha. I also finally put some wheels I have been painting, gotta get fatter tires and the proper lug nuts tho. But feels good to progress the car a bit. Hard these days with a busy lifestyle!

Yea I was thinking of doing the that next as well as n oil change as the pressure gauge does fluctuate a bit more than I like. But before I bought the car the old lady that had it, had a mechanic give it a tune up so everything is new. The wires are new but the typical cheap auto parts so maybe even just doing the wires will suffice. Car does run great, but maybe before with the first distributor it was advanced a bit and felt more powerful not sure. Definitely doing Taylor wires, always used them, they’re great.

I am in Fort Lauderdale. Actually have a Wawa near me with rec fuel but it’s 87 octane. I’ll try that.

So so this morning I attempted to reset the IaC and set the idle....but weirdly enough after jumping the adld for 30 seconds then disconnecting the valve, I go to start the car and it just won’t idle down. It stays at like 1200-1500 rpms. So I did my best to tinker with it, and also timed it up to about 8°, it’s running and idling fine. It still has trouble cranking on second try’s but I’m starting to think it’s the mix of gas, shitty spark plug wires, and a weak battery.

Yea I definitely followed the stickies. I noticed that as well the changing in timing factored the idle a bit but the more I advanced the the higher it would go. BUT at 6° and now the 8 it seems to idle perfectly in drive. It’ll prop up to 1000 in park but kinda settle in. As I said in previous post trying to reset the IaC and adjusting idle manually didn’t quite work as i thought it would. Gonna try some new wires and fresh fuel and see how she behaves there. Gonna change the fuel filter as well although it looked pretty new last time I was under the car if I remember right.

Finally made some time and swapped out fuel filter which looked like the oem one. Was full of gunk. And also did spark plug wires, wow what a pain those last cylinders. Car is running much smoother. Now all that’s left is oil change. Oil seems a bit thin as it came from up north. So pressure at idle drops down more than I’d like. I drove it around a bit once it warmed up and runs very smooth. Good smooth power even through the shifts.

Now one thing I noticed is Speedo is not working. And I can’t for the life of me remember if it did or not. I do remember checking the miles making sure those worked since it has 92k miles wanted to verify that. And I remember that working. These come with an electronic speed sensor right? Because I don’t notice a tv cable either at the throttle body.

Woops gotta update that. It’s a 1992 Z28 5.0 TPI. I checked again and saw the cable, it’s just routed under the intake so didn’t notice it at a quick glance.

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Post 9
https://www.thirdgen.org/forums/elec...t-working.html
terminals b9 and b10

And where is C1 located? I read on a few posts it’s most likely the speedo as if it’s the ecu or the vss it’ll throw a code?

C1 is a optical signal. I’m not sure how to measure it hz maybe. The connector is at the ecm.
lack of Vss signal should throw a code 24. With a automatic transmission you will loose tcc lockup. The most common failure is the instrument cluster itself.

Yea that’s what I’ve come across a lot. Weird that just the speedo gives out due to that design. Is there a company that fixes them or have to salvage one and risk it not working too?

I’m not sure if there is a reputable company that does repairs.
You might want to post a ad in the classifieds wanted section.

There are a few places that fix speedometer/odometers on this thread. If your tach is messed up that’s a easy fix.
https://www.thirdgen.org/forums/inte...roken-but.html

https://www.thirdgen.org/forums/tran...ds-double.html

http://paspeedo.com/

http://www.scottspeedometer.com/

This one says all gauges work on the item description

https://www.ebay.com/itm/90-91-92-CH...ty!20876!US!-1

Wow thanks guys. I try to go on here as much as I can but I tend to disappear very busy. I ordered a speed sensor as it was about $30 to give that a shot. If I see no changes I’ll jump on a cluster. I have a dash pad to install there anyways so I’ll hold off on throwing it on that way I just use one whole day to take apart whole dash ha.