Alright, I just pulled the 081 TPI heads i put on my LO3 because the studs were pulling, so i got screw-ins put in and just finished reinstalling everything. Started it up for the first time and it ran perfect, flawless for about 3 days of normal driving, idled like a rock at 750 RPM, its now got a ZZ4 cam. I did a lot of tuning the PROM over the summer so it runs great with the new cam and heads.

Now, I had to replace the hose from the heater core to the intake manifold because the elbow I installed in place of the big heater valve was clamping as tight as I'd like. So i replaced it with a solid hose with a 90* bend. A little coolant leaked out of the hose when i removed it, I started it up again 2 days after installing the hose. It now runs absolutely terrible, it will not idle, and runs like its missing 2 cylinders. I cannot figure out what's causing it. I tried pulling codes, but it will not flash the codes, and my laptop in the ALDL port does not show any codes but the SES light is on solid.

There was a little coolant on the #6 plug so i removed it cleaned it, no difference. I then removed it and started it, ran the same as with it plugged in, so then I removed the #5 plug to see if it'd at least act like i just unplugged a spark plug, and it still ran exactly the same. Unplugged the IAC, same thing, the EST, same thing. Nothing seems to make any difference at all. Sorry for the long post, but if anybody has any ideas I'd love to hear them.

 

Sounds like it is running in limp mode. With the key off for at least ten seconds, key on and look for the SES blink.

That is, at key on the SES illuminates, then blinks off for about 1/2 second, then comes back on (don't crank the engine, just key-on). If the SES doesn't blink then the ECM isn't running from the EPROM.

Could be a bad ECM, improperly seated EPROM, bad burn on the EPROM, . . .

RBob.

 

Check the CTS connection as it is easy to break or pull out of the CTS while messing with the front of the engine. I have broken about 5 of them on various SBCs. Tend to break them installing the passenger side front intake bolts.

Have you tried reseting the ECM by removing the negative battery cable?

Also make sure that all the grounds on then engine made there way back and have a good connection. This includes the ground strap on the back of the head.

 

Figgure out the SES light first, then from there I say do a compression test and check the vacuum.

 

Thanks a lot for the suggestions guys, they're a big help. RBob I didn't realize that meant the ECM wasn't running off the EPROM, i thought only the rapid blinking meant that code 51. So..

Pulled the ECM down, the heater core leaked a little coolant from under the dash and the wires into the ECM were wet. I dried them off, opened up the ECM and cleaned it up real good, there was a little fluid on the case but none inside the case. But I still cleaned it up real good, now testing the key-on. The SES does not blink, but rather stays solid and occasionally flickers and I sometimes hear a clicking sound from the engine bay. Seems to me that the flickering is so sparatic that its some kind of grounding issue because it looks like the circuit is complete, then not complete. I'm running a PROMinator, I'm going to try to reburn a new .bin image and hopefully it will take. Or is this futile? Does it seem pretty obvious to you guys that the ECM is burned out? I think i'm going to pull the passenger valve cover and check the grounds back there, that's the only way i can reach them. Thanks, let me know what you think.

 

What I would do is to remove the ECM from the car. Rinse the harness connectors out with clean water, shake most water out, then dry with a hair drier or such.

Open up the ECM and rinse it out/off with clean water, shake and then dry. The ECM PCB is conformal coated, however the PROMinator, I don't believe this is. May need to take some extra care in drying out the PROMinator.

Once dry reinstall, reload the bin and try again. If the same then something is fried. Try a stock ECM just to see if the SES blink works. That will help in verifying the issue.

RBob.