my 85 has a miss in her when she is cold.. she also back fires.. when she is warmed up she runs great. change the plugs, wires, and the distributor cap... any helpful tips would be greatly appreciated.

thanks $300vette

 

is the check engine light coming on?

 

No it has not been comming on...We put her on the computer and it is comming up with no answer...


Thanks $300vett

 

My best guess would be the coolant temperature sensor. It can cause rough running at cold temps.

Try pulling codes again, mine doesn't ever light up, but stills stores a trouble code. Instead of using the computer, get a paperclip and bridge the a and b ports on the connector under the drivers side of the dash. a and b are the top right ports. After this, turn the key on, but don't crank. Your check engine light will flash once, then twice for a code 12 three times. After the third code 12, it will read out any other codes. a code 36, for example, would be flash, flash, flash, pause, then six more flashes.

 

Thanks a million. That help out a lot but I still have a small miss when she is cold...Still no codes are comming up.... Don' know what to do next....

Thanks $300vett

 

Start it up cold with the scan tool on it watching the air flow numbers. If the MAF is having a problem (either with ambient temperature or with the air temp compensation circuitry) you'll see erratic or low (compared to Warm idle) air flow values. If the air flow numbers at idle are the same cold as when hot, and are Stable, your problem likely isn't anything to do with the MAF.

As suggested, coolant temp is the Next most likely - you can also watch That sensor value on the scan tool from a cold start and see if it makes sense.

After that - are you sure it isn't in the ignition? Looked for a miss with a timing light or scope? Any of the ECS module, ignition module or coil can be effected by temps, particularly if they are dying slowly. Usually it's Higher temps that will cause the item to act out, but nothing says it has to be that way... I've seen bad coils cause weird problems when cold - hard starting, misfire at idle, etc., and still run Fine once warmed up or off idle. It happens.

Also could be other, less obious stuff like EGR or AIR valves that aren't sealing well, AIR isn't real likely (it's putting air in downstream of the combustion chambers, after all), but a goofy EGR valve (or control solenoid) could be doing this. (Backfiring is s symptom of Lean, of course, and an open EGR valve will do that..)

Also the Knock sensor - does a timing light show any timing retard being dialed in when it's mis-firing? Does the motor have a cold "knock" or rattle that that goes away as it warms up a bit - something the ESC is seeing and then messing with the timing for you?

Hmmm - thinking about it - have you checked the fuel pressure? Injectors? Again, anything there wouldn't normally be expected to be worse cold than warm, but anything's possible..