james55

My 96 Camaro Z28 has a problem with rough idle and the car shakes at lower RPMs whether moving or stopped. Problem appears to be getting worse. One day it was running fine, next day..... this.
Magnaflow exhaust sound when driving / accelerating is bad.

Yesterday I replaced the ignition coil and ignition control module and it did not fix the problem. I really can't afford to take it to a mechanic. My research on different forums has led me to considering replacing the opti, plugs, plug wires, fuel pump.

I have ECMPro Scan software and I am not pulling any codes, current or stored.

The problem appears to get worse as the engine warms up.

Please help.

Thanks,

James

shoebox

If not been done in a while, plugs and wires is where I would go, first.

Injuneer

Who tuned it for the cam?

What power adder do you have (N2O, blower???) to generate 743 ft-lb of torque?

james55

Thanks for the replies.
Sorry, I guess I should remove that. I used the Dynometer in ECMPro Scan and did a dyno run, but don't think I got a full run in and when I let off the throttle it showed 743 ft-lbs of torque and about 300 hp. I never really reached fulled throttle for an extended period of time. No N2O and no blower. Just the cam, 58MM TB, 4" CAI, headers, Magnaflow exhaust. Solomon, at www.lt1pcmtuning.com did a power tune on the car which really did improve performance.

Back to the issue. I forgot to mention the car is hard to start when cold. It takes 2 or 3 cranks sometimes to get it started. A performance shop mechanic that had looked at the car a couple of months ago told me he "thought" the fuel pump was going bad.

The plugs and wires were replaced when the engine was rebuilt, about 1000 miles ago, but I had problems with bad fuel injectors, car running very rich, so the engine shop replaced the fuel injectors. Not sure if the plugs could go bad due to the problem I had with the fuel injectors.

Injuneer

If it was running rich, the plugs may be fouled, and once that happens, it will just get worse. As each cylinder misfires it dumps air into the exhaust, the PCM reads the O2 sensors as "lean" and starts pouring even more fuel into the system.

That cam is fairly mild, and the tune should be OK.

When is the last time the O2 sensors were changed? Does your scanning software indicate they are working correctly (varying rapidly from 0xx - 9xx mV) in closed loop? Does your scanning software indicate the coolant temp sensor is accurate?

james55

The O2 sensors are brand new (Delphi). From what I remember from the diagnostic scans the O2 sensors are registering / working properly. I didn't notice what the coolant temp sensor was registering? What should it register. I'll have to scan it again.

Thanks

James

james55

My scanning software does not allow me to scan the coolant temp sensors individually. That's a bummer since it costs $365. The software was showing the overall coolant temp to be almost exact the same as the temp gauge on the dash. I have a 160 degree thermostat.
The software shows no cylinder misfires on 1-8 and the O2 sensors are working fine.
The timing is being retarded from about -34 to -47 depending on if I'm idling or accelerating. Also shows the ignition voltage reading at apprx 13.5 volts.

shoebox

Any scanner or software is only going to give you one temp sensor's input, since there is only one sensor that delivers that information to the PCM. The timing you see is advance-not retard. Timing is BTDC, so most scanning registers will express it in negative degrees (which is correct).

james55

Ok, since everything else appears to be ok per the scan software, I and a mechanic from Goodyear corporate think I have a bad / clogged catalytic converter. I have read where a bad cat converter can cause the exact symptoms of rough idle, rough running engine. When I got headers and Magnaflow exhaust installed I did not get the cat converters replaced. Before the engine started running rough I was returning from home, pulled up in the garage and smelled a rotten egg smell like new cat converters have. I shut the engine off, the smell went away and the next time I tried to drive the car I had the rough idling, rough running engine. I'm taking it to a performance muffler shop on Monday. I think I will go ahead and get both cat converters replaced instead of just one.

shoebox

If the headers have AIR fittings, you can test for excessive backpressure. No need to replace something on a hunch.

Injuneer

Or pull a pre-cat O2 sensor and measure the pressure there.

james55

No offense.... , but I am not really replacing something on a hunch. I have read all over the internet where a bad cat converter can cause the exact symptoms my car is experiencing. Everything else is checking out - no cylinder misfires, correct ignition voltage, correct coolant temp sensor readings, vacuum fittings look intact, running 93 octane gas, O2 sensors functioning as they should, etc, etc. I will be taking my Camaro to Southwest Muffler here in Houston where they will test and diagnose the problem for free. I've got a feeling they won't lie to me, because I don't think anyone would want to change the cat converters out on a LT1 engine unless they really are bad. Especially the one on the driver's side that is mounted almost vertically 100%. But I could be wrong. These engines are about the hardest engines to work on or troubleshoot I have ever dealt with, but I love'em. Well kind of a love / hate relationship....

bw_hunter

Good luck...that's the last second to last thing to fail. the PCM is the last thing to fail.

There are a whole host of problems that will cause those exact symptoms. If it the cats you have to find the underlying cause or you'll ruin the next pair as well

james55

How about 179k miles. Sometimes things go bad because they wear out.... right?


I have no reason to believe the PCM is bad from the scanning and testing I have done.


Like I had pointed out earlier, I drove the car and when I parked it in the garage I smelled the rotten egg type smell like only a new cat converter gives off, not one with 179k miles on it - unless it goes bad. Then I got in the car the next day and it was idling and running rough.


Come on guys, give me a break. I'll let you know it's fixed when I get it back from the muffler shop.

slick1hunting

Its kind of sad when people ask for help and are getting it and then take a stance that very well might offend those that are helping. Shoebox and injuneer both suggested a test for the cats and bw is pretty much saying its probably not the cats and if so what caused them to fail will likely cause new ones to fail. All of that advice is incredibly helpful. I for one appreciate it. I have had cat failure and muffler failure in my truck. I personaly feel your plugs and plug wires are a greater chance even though they are low miles. I do feel your cats could be shot or at the end of their life but the chance of them failing based upon mechanical issues are greater than failure of wearing out. Many people with headers wipe out a plug wire and never know it until car is running so poor they get desperate enough to look at plugs and wires. If they weren't quality wires many fail shortly after install without even cooking on the header. If its a plug wire left unrepaired long enough can warp valves. If your muffler shop or anyone you know has a temp gun I would examine the heat going out each cyllander and you would have even more info at solving any problems.