jocamino

I changed plugs & wires on my 93 because it had a miss in it. So after changing them it has a hesitation really bad @2000 rpm. But it runs great the first 20-30 miles then it starts running like it has 3 plug wires off. I pulled TB and cleaned it and it ran great for 25-35 miles then right back to running like craps. Any ideas?

Z28Freak86

So the car runs fine for the first 25-30 miles, then it starts to stumble/hesitate? Did this problem exist before the plug and wire change? My only thoughts is its heat related... If you shut off of car and restart it after this 25-35 mile trip, does the problem continue?

Heat related problems could be the ICM, an easy way to test this is once it starts to run poorly, give it a few taps to see if the hesitation gets any better... Another easy way to try and fix this is to add a washer or 2 behind it to keep it away from the head so it doesn't heat soak anymore. They dont fail very often, but it is known to happen.

Does your car throw any codes? Id be surprised if it didn't at least throw a lean code on one side. Just my two cents

jocamino

No it doesn't have any codes.And no it didn't do this before plug & wires change. It started the next day. The car only has 45,000 miles

Z28Freak86

Well the only common denominator here is that it started after the plug and wire change. So lets focus this on the plugs and wires. Start up the car in the dark and look for any arching between the plugs and the cylinder heads (has to be very dark). It may be hard to spot, but just look closely at the end boots of the plugs on each cylinder and the plugs themselves to see if there is any arching at all going on. If you have a friend that is willing, have him give the car a little gas or put a small load on the motor to see if it will arch then. Did you also replace the coil wire when you did the plug change? I've had trouble with that wire long time ago, but it was more of a high rev miss then a stumble at 2000 rpms. So double check those plugs and wires for any arching.

jocamino

I'll give it a try. Thanks

jocamino

Ok still working on this thing. But I have a question about optic spark. I figured since I've done plugs and wires I might as well do a cap &rotor. So what is the best cap & rotor to use with GM opti? Car only has 45,000 miles so I'm hoping all it needs is cap and rotor.

Z28Freak86

Best ones for our cars is going with oem replacement or MSD for the entire unit. Cap and rotors aren't as important as having a good optical pickup. But MSD makes a good one, especially for your year. Since you do not have a vented opti, MSD does make a replacement opti that will make your year vented. But do a forum search here and see what others have used and what works for them.

Fatdog2

Sounds like when my water pump was going out.It would leak down onto the opti occasionally and drive me nuts.Are you loosing any coolant?

jocamino

no I'm not losing any antifreeze. I changed out the EGR valve and EGR vacuum solenoid and that didn't help at all.

jocamino

I'm still thinking it's a EGR valve problem. Not the valve or solenoid but the vacuum to it. The valve doesn't move in or out at idle or different rpm's. So how much vacuum does it take for egr valve to work and how much vacuum should I be getting at intake port?

Injuneer

EGR system is does not operate at idle, not at WOT, not above 3,500 RPM. You won't see/feel anything move at idle.

At idle, take the two lines off the solenoid, and hook them together. If the engine stumbles and stalls, you have vacuum. Or, with lines connected to the solenoid, take the harness connector off the EGR solenoid, and apply 12V to one pin on the solenoid and ground to the other to open it. Engine should stumble and stall.

The vacuum port for the EGR solenoid is a full vacuum port, so you should see about 20" Hg at idle on a vacuum gauge, or if you can scan the ECM, about 10" Hg on the MAP sensor. Very unlikely that the port is plugged. Could have leaking lines. But I don't think its an EGR problem. Why would is only appear after 20 minutes or so?

Heat soak can affect the ICM and the optical cam position sensor module in the Opti. If it's the Opti, I do not recommend the MSD. It has problems.

Best thing you can do at this point is download Scan9495 (also works on the 93 ECM), get a cable, and run a data log, saving the results when you have encountered the problem. I can review the data log for you.

https://www.camaroz28.com/forums/com...95-lt1-874306/

jocamino

So what opti do you recommend if not msd? I'm going to take to dealership and see if they can run scan and just tell me what's wrong.

moparman

Delphi is the opti to get. Check Rock Auto and Amazon.

Injuneer

Hope you have a "dealership" that knows what they are doing. The average Chevy mechanic has probably never seen an LT1 engine.