8.1L swap engine stumbles when warm

[1984dually]

Installed an 8.1 into my 1984 Dually last summer/fall. Have put on about 5,000 miles on it since with no problems until recently. Starting out cold it runs normal. Gives no problems until I stop. When I start it back up it will stumble and run like crap for a couple of minutes. When it clears up it will run fine until I stop again. Don't feel like it is loading up and it doesn't put out any black smoke. Any ideas?

 

[HotRodPC]

So is this a Carbed motor, or did you install all the ECM and wiring harnesses?

 

[MadOgre]

sounds like a quadrajet with leaking fuel well plugs

 

[HotRodPC]

Or improper set accelerator pump and why I asked if it was carbed when most 8.1's are ECM Injected and dizzless ignition.

 

[1984dually]

Total electronic 2004 8.1/4l80e. Giving the indication that an injector(new) is leaking but no black smoke that is usually present when an engine is flooded.

 

[HotRodPC]

NO codes huh? Being that it runs OK when cold and doesn't start acting up until it's warmed up, makes me think it's ECM related as in a sensor or something connected to the ECM.

The ECM's give different instructions when the engine is cold. Once it's warm enough, the computer system will go into full closed loop operation and read all sensors and give all instructions and starts tuning for efficiency, performance and even more emissions.

 

[1984dually]

No codes as of yet.Could be a sensor giving a false reading. May replace the cam sensor which seems to be a problem sometimes. Also need to ck the fuel pressure to see if it is leaking off. This is the type of problems I was not wanting when I did the swap but with help it will get figured out.

 

[HotRodPC]

It would probably be expensive, but if you could find someone with a true scanner that reads all the sesnors, you'd be able to pin point if any ECM related item was failing. If they don't fall into their milivolt ranges, or ohms, then you know where the bad part is.

 

[1984dually]

Have a scanner. Got time to hook it up and read the sensors. All look ok. Thinking the fuel might be boiling when engine is warmed up. Going to drive it tomorrow with a fuel pressure gauge hooked up and see if it reads anything funky.

 

[1911fool]

Pull the plug on the coolant temp sensor when its running bad and see if it straightens up. If it does replace the CTS.

 

[1984dually]

Cked fuel pressure under load and it was dropping to around 40 psi. Went back to 58 when not under load. Changed fuel filter/reg and pressure went to normal under load. Still stumbled. Had a coolant temp sensor so I changed it. Took off the A race an Sacramento CA(300 miles) and it did it again the first time I took off hot. Let it idle before taking off after that and it never did it again. Never does it pulling hills hot or cold.

Ran c gas on a 9.60 index. Went to the final in a 16 car field. Lost on a double breakout.