leaderman

I'm hoping some kind soul would help me diagnose problems with my car (1994 Camaro Z28)... It has been stalling out on me and then the check engine light comes on so I purchased a OBD1 cable and was able to pull 3 DTC's from the vehicle. The codes are as follows:

Code 16 LO RES FAILURE
Code 36 HI RES FAILURE
Code 42 EST GROUNDED

It does have a new MSD distributor in it but it ran GREAT with the new distributor for almost a year so I'm PRAYING that's not the problem?? I was thinking it may be the alternator but I put a multimeter on it and it seems fine?? Not to mention the alternator isn't that old (140 CCA alternator).. I'm hoping some pro knows where I should start looking?? Damn car just has 50K on the odometer and I purchased it brand new so I know it isn't abused?? VERY FRUSTRATING... Thanks for your time and Happy Holidays...

shoebox

Those three codes would indicate the opti or opti harness. 42 often accompanies the other two.

Injuneer

The first two codes are for the optical cam postion sensor in the Optispark. Check the Opti harness connector for corrosion, bent pins or being loose. Clear the codes (pull "PCM BAT" fuse for 30 seconds) and see how fast they come back. You have to scan it periodically, even if the SES light isn't on. The opti codes don't turn on the SES light.

leaderman

Thanks so much for your time!! I just ordered a new high temp opti wire harness because now that I think about it I should have done that when I replaced the distributor for the MSD one. I'm praying the harness is the culprit?? Sometimes on short drives the car is fine with no SES light whatsoever?? But usually as I'm driving the engine will try to stall and then the SES light comes on and it runs fine again (sometimes it stalls again even with the SES light on but usually when the SES light is on then there's no worries).. I've been driving with this problem for about a year (don't really drive it that much).. but finally last week the car wouldn't start at all for me?? (and I was away from home).. I went to pick it up the next day (ready to flatbed it) and it cranked over no problem after it sat there all night.. Hopefully the harness won't take long to come in?? I just scanned it finally the other day (had to wait until the SES light finally came on) and that's when I was able to pull those 3 DTC's from the car... I just hope it's that harness and nothing else?? (a little worried that you said the opti DOESN'T trigger the SES light??).. But I know that wire harness is old and should have been replaced anyway. Thanks again for your time... Both of you.. I will let you know if that worked when the harness arrives.. Maybe a week?? Happy Holidays all.. You guys are SAVIORS... I forgot to tell you that I couldn't pull any DTC's only until the SES light came on?? I figured the codes would still be present in the memory, but ONLY after the SES light comes on??

-Chris

Injuneer

You don't have to wait for the SES light to come on to scan it. There are numerous codes that don't even turn on the SES light. And the codes are "stored" for a fairly large number of driving cycles, even if the problem does not recur. Eventually, they will self clear. Scan it at any time, and the active and stored codes will show up.

When DTC 16 sets, the PCM shuts down the fuel system - pump and injectors. Without the low res pulse signal from the Opti cam sensor, it can't time the spark and injectors to the correct cylinder.

my1994z28

The Msd opti has the harness"bult" into the opti..atleast the one I have does..it only has the one plug on it that plugs into the engine harness

Injuneer

Then that would be the place to look for corrosion, bent pins or a loose connector.

Rashiki

My MSD opti failed very quickly too Production run issues?