87 auto 101000 miles-I've had that miss just at 1700-1800 RPMs-and the dash lights were going crazy-jumping around. Thought the dash was do to battery and Bad alternator (alternator was bad only putting out 1.5 amps) replaced battery and alternator (new-not rebuilt). Replaced plugs (it was due) coil, rotor, had ignition module tested (good), checked fuel pressure-good 41-42 psi, only dropped to 37 in 15 minutes, pressure holds while running-checked for vac leaks-none I could detect, checked plug wires for arcing-couldn't see any.Can't see any lose connections-haven't checked starter connections yet! Plugged EGR-test drive-no difference.

Dash still going crazy NOT all the time though.
Miss still there.
No Codes

Starts great-idles great, pulls strong.

Need your ideas-thanks again

 

No 1 ?

 

Is there a connection between the time the dash acts crazy and the miss? If so, I'd suggest that either the main wiring harness may have an intermittent ground/short issue, or the ECM may be acting up. You might also have a ground issue inside the digi-dash that is the cause of your problem. The digi-dash is notorious for this. Check out Bryan Thompson's repair page at: http://www.batee.com/corvette/index.shtml

I had an intermittent drivability issue in my 88 that was real hard to figure out. It kept going into "limp home" mode and setting a code 33. After trying all kinds of fixes, I finally bought a laptop based scan tool and started driving around waiting for the problem to reappear. After a few miles, sure enough the stumble and code showed up. My Ease scan tool showed that I got 5 codes simutaneously. Since I had completely checked the wriing in general, and the 5 codes were for different areas, it appeared to me the sole connection between them was the ECM. I replaced the existing unit with a NAPA rebuilt GM ECM and have not had a problem since.

So, are you getting any codes? What exactly do you mean by the dash goes crazy?

You replaced the plugs and checked the plug wires. Did you do a resistance check of the wires and flex each one some to see if vibration had any effect on their resistance?

Have you double checked the battery cables? I mean pull on them and hand twist them. Make sure that they are clean and tight on both ends?

 

Thanks Mike,
there seems to be no connection between digi and miss, in fact miss was there for some time(didn't have time), the dash started acting up after I let my battery go down-went to have battery checked-wouldn't hold a charge-alternator proved to be bad.Replaced both. The digi will act up mostly at idle-like holds 700 RPMs-but the 3000 RPM mark will flash, but no real change in engine RPMs-some of the other functions-mostly on the tach side of display will get jumbled-almost stabilizes while driving.

No-I'm not getting any codes.
haven't checked plug wires for resistance or done an ohms check-not to good with an ohm meter.

Battery side of cables are clean and tight.

Plan on checking starter connections when I can get someone to watch as I go up the ramps-probably tommorow.

I'm interested in getting a laptop set up like yours-can you fill me in and let me know $$

thanks.

 

I had the same problem on my 87 when the fuel pump was on the way out. Have you done a fuel pressure check with the guage taped to the winshield while driving. The other area you might check is the fuel sock in the tank.

Seems like you have the spark area covered, I would definately check fuel delivery.

hope this helps

 

Since it flashes incorrect values, the digi-dash problem sounds like an improper voltage/ground issue to the dash controller. More than likely it is due to a bad ground which is covered in the DIY repair article I posted earlier.

Either that or the signal(s) from the ECM/sensors are off. It could be in the wiring from the ECM or the sensors to the digi-dash, or it could just be that the ECM is starting to get "flakey". If the digi-dash and miss appeard to be related with respect to frequency I'd guess that the ECM need testing. Since they don't appear to be related, it is most likely 2 seperate issues that happen to be occurring at the same time.

I'd follow the recommendations in the digi-dash article for the dash and look in the FSM for the definition of the type of "miss" that you are seeing. There should be a troubleshooting chart that is pretty specific to your probelm conditions.

 

My vote is plug wires. My dash did some silly stuff when the wires were arcing off the headers.

 

Thanks cmontel1727-fuel pump and sock are about 2-3 yrs old, 41-42 psi on schrader with key on, drops to 37-38 in 15 minutes-holds 41 while running.So I think the fuel is OK.

Mike-88z51, thanks again, the digi problem only started when the battery got low and the alternator died-and it doesn't do it all the time.
I am beginning to wonder about ECM though-just need to check starter connections first.

spankyellow-thanks-even though I did not see arcing in the dark-I will check again-if I can figure out my ohm meter, I think there supposed to ohm at about 5000 per foot.

I did look through the FSM and can't pin point anything that fitts-mostly this and that say replace cluster, and I don't think the cluster is bad.