RockoFTN

Hi guys,

My 94 Z28 starts up and runs pretty good (not 100%) when its cold. However, after its warm and is started: The ABS inop light comes on right away and the engine runs really rough, almost like a fuel injector has failed. A few weeks ago it had a coolant leak from a coolant line right above the Opti, so its possible that some coolant got inside the Opti. I put new plug wires and spark plugs in, but cylinder #4 has a weak spark (voltage is low in the wire).

Has anyone ever seen something like this before? Any information would be helpful. This was the first car I've ever bought. I bought it right after I joined the military back in 2001, I took it all over the world with me and I don't want to let it go.

Thanks

RockoFTN

Also, when its started cold, there is no ABS inop light.

belac350

The ABS systems looks at the third brake light, so if its burnt out you will get ABS INOP, first place I would check, after that check the reluctors in the from wheels, and the one in the rear as yous is a 94 so 3 channel ABS.

RockoFTN

Thanks, I checked the 3rd break light and its working fine. I changed out the cable from the alternator to the battery (it was corroded) and that seemed to restore the engine's power that it was lacking. I think the Opti and the fuel injectors were not getting enough voltage to run properly. I also have a crack in the air induction elbow which is allowing un-metered air into the intake, so I'll order a new one and replace that and see how she runs after that (still some hesitation when I punch the gas). I'll look at the reluctors and see whats going on with that. Thanks for your response.

Injuneer

Put some duct tape on that crack in the inlet elbow, while waiting for the new one. No reason to drive it with air bypassing the MAF sensor and screwing up the long term fuel corrections. That will often cause the stumble on throttle application.

RockoFTN

Thanks for the advice. The replacement Bellow arrived yesterday and I swapped out the cracked one for the new one, the new one also had the portal for the resonator tube blocked off already. The engine is performing better, but sometimes the ABS light comes after ignition and the engine doesn't seem to run as smoothy and the idle oscillates between 1000-800 RPMs. The times when the ABS light does not come on, the engine runs very smooth with a constant idle of 1000 RPMs. Any idea what could cause this? My third tail light in the rear spoiler works, so its not that.

Also, I have a OBD 1 scan tool that I'm having issues with. The LT1 is not the stock engine, the previous owner replaced it with a new LT1 after he blew it in a drag race. I'm not sure the year on the LT1, it could be a 95 LT1 in a 94 z28. So the engine serial number does not match the VIN. I've tried scanning by selecting 1994 as the year and received 10 codes, and when I try scanning using 1995 as the year I receive 26 codes... I removed the PCM batt fuse to reset the computer codes, I will install it again in the morning and fire it up to see what codes I get.

Does anyone know what to do with a scanner in this situation?

mrmint69

Are you saying you checked the spark plug wires out of the vehicle and one of them is bad?

Check your brake fluid level, negative ground on the passenger side inner fender & Check wheel/differential sensors connections. Possibly from plug wires being to close to abs wiring. If it happened after tune up, I would bet your wire routing is the cause. Wiring can also get burnt on aftermarket headers.

RockoFTN

No, I had a bad alternator cable, I replaced that. The corroded cable was causing a voltage drop of 4-6 volts, sometimes more. After replacing that cable, the engine was receiving 12-14 Volts again, instead of 8-10 Volts.

I'm curious why the ABS light would affect the engine idle. I'm not seeing a connection between the two. But I will definitely check your suggestions and see if its something as simple as a bad ground or low break fluid.

bw_hunter

Does your cruise control work? If not, check the third brake light bulb...

I think you need to get the car scanned to see what's causing the ABS INOP light. It's likely to be a bad sensor at a wheel.

I can't see the connection between the ABS and the rough idle.....bad wires, sure. Large plug gap, certainly. Wire routing near an ABS wire but otherwise OK? Not so much to me.

Do the right diagnosis for the symptoms you have without jumping to the conclusion they're related. Check fuel pressure. Check plug gaps and condition. Change the fuel filter. Clean the throttle body. Check the plug wires. Check the EGR.

Check the ABS separately....

Guest47904

Wheel sensors are only an issue once the vehicle starts to move. If you get the code sitting still, it's not them.

You need to locate a scanner that works.

If I understand the running rough issue, it occurs after hot. So disconnect one of the O2s and see it it runs better even after it gets hot. If so, you have a control problem in closed loop since disconnecting an O2 will force it to stay in open loop.

Wires from the ABS that are close to a miss firing plug wire will throw an ABS inop light.

You didn't say if you replaced the rear spoiler with one that has LED's. If so, they need a relay or some other coil to load the tail light circuit down. LED's by themselves will not work and the ABS and cruise will shut down.

Roddy

Just bought a 2002 Camaro with ABS and ASR. Booth lights are on. It appears that the rear was swapped out at some point with one with a sensor on the rear pumpkin only and not both wheels. Understand that ASR won't work with only 3 channel but at least want ABS to work. Anybody have any sugestions on how to make ABS work?

shoebox

You hijacked a thread that has nothing to do with your particular problem. I suggest making your own thread in the proper forum.

Andrewmac124

Just signed up but I was having the same issues. Check your mass air flow and mass air censor. I found a small leak in the air hose cause it wasn't connected to the throttle body all the way causing it to idle high and run terribly and not start. Now she runs like a champ

Fatdog2

Also check to make sure that the bulbs are the EXACT ones recommended by the manuf.Sometimes folks throw anything in there.My02.If that doesn't work,then might replace the brake light switch under the floorboard.My02.

Injuneer

If you have low system voltage or a bad ground, it can cause the ABS system to shut down and cause problems with the way the engine runs. The ABS light isn't causing the rough idle. They are both symptoms of your electrical problem.