Engine Missing

[tomtom72]

Don, it looks to me that it is possible that there are actually two issues.

And, Yes if there is an SES light the secondaries are canceled till repairs are made. Anything to do with fuel, oil psi, coolant temps, ignition boxes, and a vacuum failure in the secondary port throttle system results in no secondaries usually.

I don't mean to be out of line here, but we have to settle on what exactly we are dealing with; as I see it there are two separate issues: ignition system issues and a fuel issue/O2 issue.

One easy ( maybe not exactly correct if you are a real Tech ) check is to swap a known good ECM into your car. If the codes come back then there must be something with the ignition and fuel pump. I'd do that because I'm some knuckle head back yard type! You don't have a spare ECM?

The fuel pump relay could be gone, ckt 120 open or shorted to ground, ckt 2 open,open or short in ckt 490, you get the idea. I only ran down about one half of one side of a two sided diagnostic tree under 54. You can guess that the other codes have similar diagnostic trees.

You could check all the grounds at the bell housing and any other grounds you can find for good connections. The rest is very difficult to do over the forum in real time. I'm not throwing you under the bus, but I don't have a scanner that I could use to e-mail you the FSM pages.

Tom

[c4zr1]

I decided to take the Z out to see if anything changed. I disconnected the battery for about 5 minutes hoping to clear the codes. It did not. When I started the car the SES light was on. I drove about 4 miles with the SES light on. Pulled up to a stop sign and the SES light went off. I took off and the car was running very good. It was hitting on all cylinders and the secondaries were kicking in.
I am beyond my testing ability. Should I start replacing parts? I am still getting several codes. 42, 43, 44, and 54. My next step is to get it to a shop I guess.

[gbrtng]

Don:

I had a similar problem with wifey's 91 L98. Several unrelated codes and intermittent. Turned out to be a bad ECM which I replaced and all OK for many moons. Put out an APB for a loaner replacement you can try out rather than throwing parts at it.

[tomtom72]

Originally Posted by c4zr1

I decided to take the Z out to see if anything changed. I disconnected the battery for about 5 minutes hoping to clear the codes. It did not. When I started the car the SES light was on. I drove about 4 miles with the SES light on. Pulled up to a stop sign and the SES light went off. I took off and the car was running very good. It was hitting on all cylinders and the secondaries were kicking in.
I am beyond my testing ability. Should I start replacing parts? I am still getting several codes. 42, 43, 44, and 54. My next step is to get it to a shop I guess.

Don, No, emphatically NO. The last thing to start doing is throwing parts at it. It isn't cost effective with these computer cars.

Do you know anyone that has an ECM that is a "known good unit" that you can hit up for a loaner?

If not let me know as I have one in my parts inventory. I just do not have any EPROMs for other model year cars as mine is a 90.


Tom

[XfireZ51]

A code 34 says the MAP voltage is too low at anything below 700rpm which is why he's getting SES at startup. I would replace MAP sensor or test the one you have with a DVM and Mity Vac. Having a scan too would be nice. If the MAP is reading incorrectly, it could cause the lean condition and affect correct timing. Also a code 42 says the ECM isn't doing the "handshake" with the DIS module and taking over timing after 400rpm. Could be using bypass mode.
Start with the MAP sensor.
As for the ECM, if you turn ignition to ON and get the SES blink, that's the ECM self test indicating ECM is good. If it stays on and no blink I would suspect prom first, then ECM.

[tomtom72]

Don, listen to Dominic ( XfireZ51 ) Trust me on this. I know that when there are many voices talking at you it gets a bit overwhelming. Trust me, listen to Dominic....if I knew what he forgot about the electronics on these cars, I'd be a top Tech!

Dominic, thanks for bringing your knowledge to this thread!


Tom

[XfireZ51]

Originally Posted by tomtom72

Don, listen to Dominic ( XfireZ51 ) Trust me on this. I know that when there are many voices talking at you it gets a bit overwhelming. Trust me, listen to Dominic....if I knew what he forgot about the electronics on these cars, I'd be a top Tech!

Dominic, thanks for bringing your knowledge to this thread!


Tom

Tom,

Just adding my $.02. There are several other members here with much more experience than I. I appreciate the confidence and I hope this helps.

[c4zr1]

Tom,

I took your advice. I had a freind that has a 91 ZR-1 so I asked him if I could borrow his ECM. I put my prom in his ECM and did a swap.
No codes. I think I found the problem. Bad ECM.
Where is the best place to buy a ECM?

Thanks for everyone help.
Don

[XfireZ51]

Originally Posted by c4zr1

Tom,

I took your advice. I had a freind that has a 91 ZR-1 so I asked him if I could borrow his ECM. I put my prom in his ECM and did a swap.
No codes. I think I found the problem. Bad ECM.
Where is the best place to buy a ECM?

Thanks for everyone help.
Don

Swap the prom back into the old ECM one more time to double check or use another prom.

[Kb7tif]

Originally Posted by XfireZ51

Swap the prom back into the old ECM one more time to double check or use another prom.

Yes double check old pcm, might of had a unseated/dirty connection on one of the 4 main connectors!! Hope thats all it was