jsbmct

On my 1985 L98 I am having an issue with a hard start and then it backfires and pops when I push the accelerator when it is cold.

When I first try to start it, I have to let it crank for about 4 seconds, turn key off, then try to start it again. It will start, but runs really rough for about 5 seconds then its ok. I know that I have good fuel pressure, as I have put the gauge on it and do not have any leak down of pressure.

If I try to give it any gas when it is cold (coolant temp below 190) it will stumble, pop and back fire. Once it warms up, no issue at all and revs just fine.

There was no SES light when I started it, i drove it down the street and back and SES came on - Code 43 & 54.

Any thoughts??

antfarmer2

1985-1991: ECM Codes
Code #12: Normal No Codes.
Code #13: Open Oxygen Sensor Circuit.
Code #14: Coolant Sensor Circuit Low.
Code #15: Coolant Sensor Circuit High.
Code #21: Throttle Position Sensor High.
Code #22: Throttle Position Sensor Low.
Code #23: Manifold Air Temperature Circuit High.
Code #24: Vehicle Speed Sensor.
Code #25: Manifold Air Temperature Circuit Low.
Code #32: EGR System Failure.
Code #33: Mass Air Flow Sensor High.
Code #34: Mass Air Flow Sensor Low.
Code #36: Mass Air Flow Sensor Burn-Off Function Fault.
Code #41: Cylinder Select Error.
Code #42: Electronic Spark Timing.
Code #43: Electronic Spark Control.
Code #44: Lean Exhaust indication.
Code #45: Rich Exhaust Indication.
Code #46: Vehicle Anti Theft Fault.
Code #51: Faulty Mem-Cal.
Code #52: Fuel Calpak Missing.
Code #52: (1990-91 Corvette Only): Engine Oil Temperature Sensor Low.
Code #53: System Over Voltage.
Code #54: Fuel Pump Circuit Low Voltage.
Code #55: Defective ECM.
Code #62: Engine Oil Temperature Sensor Circuit High.

jsbmct

Thank you antfarmer2 - I looked up the codes and provided them as a reference - hoping that they would help aid the diagnosis.

It seemed strange to me that the codes were not present when it was running bad at start up while cold and only showed up when the engine warmed and was running fine. There were no issues with the engine when driving it, but the SES light came on.

Any thoughts on if those codes would cause the hard start and backfire when cold?

antfarmer2

It controls your spark so either it's going bad or bad or dirty connections. I would clean and check connections then replace about $30 I think. Might check your knock sensors too.

Might be injectors dirty or bad ohm them don't forget the cold start injector first.

jsbmct

Thank you.

I check the connections to the ESC and it looks good - nice and clean. I need find a diagram that shows how to test the wiring to the ESC and the ESC itself - figure which one is at fault so I know which to replace.

I forgot about that cold start injector - That will be my next step - pull it off and take a look at it. Do you know if I can remove the cold start injector and tube without pulling the valve cover or plenum?

antfarmer2

I believe advanced auto can test it for you others may as well. Don't know about the cold injector.

Cliff Harris

The ECM tests the ESC system when the engine first starts by advancing the timing 20° and looking for knocks. If it does not see at least 2 knocks it will set error code 43. The problem could be the knock sensor, ESC module or the associated wiring and/or connectors.