ntanzi

So running a yellow light I missed a shift and over revved my stock L98 for a second. Nothing seemed wrong with the car until I came to the next light a few miles down at which point the car stalled out. I managed to get the car home by restarting and maintaining high revs around 2,000rpm. The next day I scanned the car receiving a few codes:
42 electronic spark timing (EST) circuit grounded
44 oxygen sensor lean exhaust
45 oxygen sensor rich exhaust
54 egr system failure or fuel pump circuit low voltage
55 a/d converter error or pcm not grounded or lean fuel or frounded reference voltage
67 a/c pressure sensor circuit or a/c clutch circuit failure
68 a/c compressor relay circuit failure

The bold ones are the ones I am worried about. I will be putting a new exhaust and A/C in the upcoming weeks.

I reviewed my service manual which said 42, 54, and 55 all may be ECM and/or MemCal. I have since replaced the ECM and attempted to burned my own chip to replace my MemCal. I am not sure if my chip is working correctly so I recently bought a 'hypertech super chip' from a member here (still waiting for its arrival) which is just a stock chip with the thermostat lowered to kick on the fans earlier.

With the new ECM and my chip the car starts, but fails to run as before. I will be replacing the spark plugs, wires, and distributor cap this weekend. By then the Chip should be in so I can use the hypertech chip with the new ECM.

Is there anything that I am missing or should check on? What does the EST grounded really mean? is there a plug that has popped out?

Cliff Harris

You will get an error code 42 if you open the EST (Electronic Spark Timing) connector to set the timing. That said... Some or all of the other error codes could be transient codes that will go away with an ECM reset. I don't know how you got some of the error codes you list, because your ECM doesn't recognize/use error codes 67 & 68. You have a 1227165 ECM, which was used on '86 - '89 Corvettes. The error codes for that ECM are shown here:

http://home.earthlink.net/~cliff_har...Misc/misc.html

In general, these older ECMs are REALLY STUPID and the error codes are on the order of "this circuit is shorted" or "this circuit is open".

You should reset the ECM to clear the error codes and then proceed from there. Drive the car to see what error codes show up.

Open this connector to reset the ECM (a few seconds will do it):

ntanzi

After taking the ECM out I noticed that it was a refurbished replacement could it be a newer ECM with more codes? but I was going off a site from what codes I remember. I am currently at work without my list of codes in front of me. I just remembered getting two codes involving my A/C which doesn't work so I was not surprised with them and the rich/lean exhaust which gives me a reason to get a new cat-less/sensor free system anyway.

When I got the car home I disconnected the negative side, it appears that the diagram has the ECM power on the positive, should I remove the positive instead? would it make a difference over the neg? The car didn't run but starts when I reconnected the neg. How long does the care have to run to pull new codes after I clear them?

Thanks for your help!

ntanzi

I have changed the ECM and used the new chip I bought from a member. The car started, but shortly after the start cycle RPMs drop off and the car stalls out. I erased the codes then re scanned here are the codes I received:

Code 42 - (page 6E3-A-58) EST fault (Electronic Spark Timing - bypass circuit open)
Code 43 - (page 6E3-A-60) ESC fault (Electronic Spark Control - knock sensor or ESC module)
Code 45 - (page 6E3-A-64) Rich exhaust indication (O2 sensor bad or O2 sensor circuit open)
Code 51 - (page 6E3-A-70) MEM/CAL fault
Code 54 - (page 6E3-A-68) Fuel pump voltage low

Could this be a timing issue?

ntanzi

So when working on the car today I decided to take of the Mass Air Flow sensor. It turns out it was bad.... I don't know why I did not get any of the MAF codes... but regardless my car runs once again. Thank you for your help!