I have an 89 Coupe, which has been one challenge after another for the last few months. I think I am finally making some progress. It runs fine and idles steady at 700 rpm. But the first time it is started after a few days it is difficult to turn over. When it does, it stumbles, back fires and occasionally dies. If I can get it running for even a few minutes, it warms up and runs fine even after it sits for a while. The timing is solid at 6 degree BTDC. Any thoughts would be helpful.



Thanks

 

Check injectors and FPR.

 

I just replaced the injectors with Bosch. What is FPR?

 

Fuel Pressure Regulator
Why don't you start off listing what you have done will make it easier to help

 

What is your fuel pressure with key on and engine off ? (after sitting for a long period)
Sounds like the fuel pump may be running off the oil pressure switch and not the fuel pump relay.

 

Okay, I have some more information. I got a fuel pressure kit from Autozone. When it is cold the fuel rail pressurizes to about 44 psi and it hold pressure well (4 psi drop after 15 min). Once started, it idles rough, a back fire or two and has about 40 psi with 16 lbs of vacuum @700 rpm. Also when I push the accelerator the fuel pressure bounces all over, dipping and spiking.

Once it warms up, a completely different story. The idle smooths out, pressure is rock steady at 48psi, still 16 lbs of vacuum @700 rpm. The fuel pressures remains steady at 48 psi on acceleration.

Any thoughts as to why it so idles rough when its' cold would be appreciated?

Thanks

 

Bbb

 

Check Coolant Temp Sensor signal - you'll need a Scanner. It's your choke and the cooler the Coolant temperature, the longer the injector pulse; ie the more fuel it gets. With the engine cold, the Scan should show ambient or something close to it. If not, you've probably found the problem and you'll need to find out if it's the Sensor, wiring or ECM. Or if you don't have a Scanner, blow 12 Bucks on another Sensor and simply plug it into the Harness when the motor is cold. If that fixes it, R & R the old one.

 

timing belt jumped couple teeth.

 

You said that it holds a steady 40psi when cold....and then drops off 4psi after 15 minutes........Is this all while it is running, or if you shut it off?

When you shut it off, it should also hold pressure.
If it doesn't hold pressure when you shut it off, then the valve in the fuel pump is bad, and you will need to replace the fuel pump. Also, if the fuel pump is not an AC delco or a good flowing pump then you may need a better pump. (places like autozone have been known to sell pumps that do not flow the same as stock for the high performance cars).

Is it backfiring through the plenum or the exhaust? Probably the plenum....which means lean...which means fuel.....which means your on the right track. The other members are also right to suggest the possibility of sensors being off. However, everyone of these sensors can be checked, for free, with a voltmeter and a repair manual that tells you how. I once had a similar issue with mine, and just went through every sensor from intake to exhaust.....then fuel pressure.

I wonder, is this normal for pressure to increase as the engine warms up? .....Although, it's only 4 psi difference. However, when you gently push the gas and it leans out, it sounds like the pump isn't keeping the fuel pressure high enough....but just a theory.

Fuel pumps usually go out quicker than anything else I've ever had to replace. I had an 89 GMC truck that used to do the EXACT same thing as you are describing, ran perfectly when warm.......it was the fuel pump.....it had the same pump on it that it had when bought new...and was just getting old and weak. Just a theory, hope it helps.

 

Great advice, thanks.

The 4 lbs presure drop was when the vehicle was off. I also noticed the electric fan comes on during start up. Shouldn't the fan remain off untill the car heats up? if so, that might mean the coolant temp unit is not working. But the fuel pump is probably orginal, I should look into both.

 

If your fan didn't normally come on during start up, your ECM may be in limp home mode.
Is the SES light on when running and have you tried to see if there are any stored codes in the ECM ?

 

Or that the ECM is seeing the threshold for fan operation from the CTS - 226 degrees - (assuming the a/c is off). Happen to me and several others, but you won't know until you scan it.

 

I just bought a scanner, waiting for it to come in.

Thanks