'89 runs rough when at operating temperature

**marathon26** · 09-05-09, 05:57 PM

The '89 has a problem when it reaches operating temperature. It starts to run rough and sometimes dies. If it has not reached operating temperature by the time I reach my destination, when I come out it won't start until the engine has cooled down. I have replaced the control module inside the distributor and the coil. Since I was there and it was so much fun to work in that area, I replaced the distributor and the rotor. Prior to doing this I had the fuel pressure checked and it was on target.

Does anyone have any ideas?

**gmjunkie** · 09-05-09, 06:14 PM

Originally Posted by marathon26

The '89 has a problem when it reaches operating temperature. It starts to run rough and sometimes dies. If it has not reached operating temperature by the time I reach my destination, when I come out it won't start until the engine has cooled down. I have replaced the control module inside the distributor and the coil. Since I was there and it was so much fun to work in that area, I replaced the distributor and the rotor. Prior to doing this I had the fuel pressure checked and it was on target.

Does anyone have any ideas?

You need to check the Temp Sensor under the throttle body and see if it's sending the right temp to the ECM!!

They'll sometimes not be working within range and cause running problems Cold or Hot,and not trip a code!

You'll need a scanner that has a real time Data Mode!

**Schrade** · 09-05-09, 07:53 PM

Originally Posted by marathon26

The '89 has a problem when it reaches operating temperature. It starts to run rough and sometimes dies. If it has not reached operating temperature by the time I reach my destination, when I come out it won't start until the engine has cooled down. I have replaced the control module inside the distributor and the coil. Since I was there and it was so much fun to work in that area, I replaced the distributor and the rotor. Prior to doing this I had the fuel pressure checked and it was on target.

Does anyone have any ideas?

Was the FP test a dynamic test or static?

Static (motor off) test needs to include pressure bleed-down time.

Dynamic (motor running) pressure would not show weak injectors, since more fuel is pumped that gets used. This would mask weak injectors. AND, weak injectors atomizes fuel poorly, and a warm motor, in turn, does not burn excess fuel well. Cold motor STILL would start right away...

Is it loping idle at all?

**marathon26** · 09-06-09, 09:06 AM

Not sure how the fuel pressure test was run. I can only assume it was run properly. By loping idle, if you mean fluctuating between 6 and 700 rpm, the answer is yes.

**Curious George** · 09-06-09, 10:41 AM

If you did not check the fuel pressure yourself (or anything else), do not assume it was "checked" correctly. I would also check the fuel pressure regulator. Pull the vacuum line off of the regulater, if there are signs of fuel, then the diaphram has a hole in it and it is not regulating fuel pressure.

CG