Hi, I have a 94 z28, with a 6 speed. It has some problems, and it may be different problems, i'm not sure. Anyhow, the motor will stumble, (miss at around 5k, maybe pop out the intake too). If I gradually push the pedal down, it doesn't seem to do it. And it is a random problem. It seems that the motor doesn't want to idle (1500) right when I start it, it takes a bit, and I have to be at a stop and sit till it idles down. Then it seems fine. I also noticed that sometimes the tach and speedometer needles jump all over the place at times. They only do it for a few seconds (they jump 3/4 of the scale a couple times, then back to what seems the correct value). It seems to get warm pretty quick also, but it does go down when the car is moving. so I'm not sure where to start on this. I have cleaned some of the ground and positive connections, (the one's I can find). New cat, muffler, pcv valve, air cleaner, thermostat, recently passed emission check, no codes... Any ideas?

 

Have you checked the fuel pressure? How long since the plugs and wires were changed? The fuel filter is something you should change every twenty five to thirty thousand miles.

 

I just purchased the car a few weeks ago, so I haven't a clue what has been done to it. I will start with your suggestions and see what happens. What would be a good fuel pressure reading?

 

Mine stays around the low 40's. Can't remember the exact specs.

 

Hi John,
Since you found the previous owner(s) had "punched out" the cat, I wonder what other "mods" they did to that car. Is it possible to contact the previous owner and ask more questions about the cars history? the tach AND speedo needles jumping around IS a wierd combo of symptoms. With all due respect to mrmint, I sincerely doubt fuel pressure or plug wire issues would cause your symptoms (I'll certainly agree plug wires could cause a stumble, but BOTH guages...??)
You might try looking at Shobox, Bret and Injuneers web sites for troubleshooting guidance.
My suspicions would focus on some wire connections that have been tampered with. Has the acr had aftermarket electrnics added to it? Might check to make sure the installer hasn't tapped into an inappropriate place for power. Does electrical load have any affect on the symptoms? Any particular consumers that affect the symptoms? If tehre's any otehr symptom diagnosis info you can post it will help the bright minds on this board offer suggestions.
again, good luck and please post your findings for us to learn from

 

You should clean the maf sensor with the cleaner made for it. How does your voltage look? Seems like something electrical going on. Check your opti harness for corrosion also.a

 

Here's a little update, I put new plugs, wires, coil and fuel filter. Fuel pressure is at 38psi when at idle, 42psi when the ignition is off and I run the fuel pump. Pressure seems to stay for quite a while before it starts going down. Still has the stumble. I cleaned the maf sensor already. When I first got the car, it didn't want to turn over to start, so I cleaned every positive terminal and grounds that I could find, and this seemed to fix the starting problem, and the cruise control started working also. There is an aftermarket radio, and speakers put in the car, maybe they tapped into something there... I'm still thinking maybe a bad ground, or the computer could be at fault, opti?

Both gauges gets me too. Yesterday, the gauges were acting up for probably 10 seconds, this time the abs light and some other light was on too. The car was running bad for these few seconds at this time. I have been looking at shobox for some info or ideas.

 

Check your opti harness connection next. Here someone with a similar issue that I found searching.
https://www.camaroz28.com/forums/lt1...rt-now-867137/

Rob says it could be your voltage being to low in the thread above, when you get random gauge lights. I would have the battery and alternator tested and see if they are the problem. Might unhook the stereo equipment and see if it makes a difference. Low voltage can make the fuel pump, injectors and many other ignition parts not work properly.

 

I had a 93 do the same thing it was the distribiter cap and button

 

Watch the fuel pressure as you drive, rev the motor, or do a WOT run. Spec is 43.5psi.

-Dustin-

 

Here's an update.
A couple weeks ago, I was driving home and the gauges acted up and different lights came on, but this time the engine quit and I coasted to a parking lot. The car would not turn over. I had it towed home and took the starter off and it was shot. It looked like the solonoid was stuck with the motor running and the armature and brushes were toasted. I replaced the starter and it fired right up. Then a couple days later the solonoid stuck on the new starter and I had to unhook the battery to make it stop turning. So back to autozone and got a replacement. So far the starter seems fine. I also took out the aftermarket radio, and disconnected the mess of wires that someone had put in. I replaced the radio with a stock one and spliced the wires the correct way, with a stock plug. I done this a couple weeks ago and I haven't had a problem with it missing or with the dash gauges messing up. Hopefully the problem is fixed. I will keep you posted.