88 Ranger running rich when hot

[2trux]

My sons Ranger started running rich after the engine warms up. It runs great when cold. When it is hot it runs rough and often dies when you come to a stop. The fuel mileage dropped to about 8-10 MPG. I changed out the temp sensor and the connector. many of the other sensors I have swapped with my 89 and there was no change.
The only thing that seemed to make a difference was putting the ECM from my 89 into it. It still doesn't run perfect but it is much better and doesn't die at stops. The idle seems to be closer to what it should be and more stable.
The only change running the 88 ECM in my 89 is the idle moved up to around 1000-1100 RPM.
How much difference is there between these two computers?
Both trucks are 4x4, 5 speed , 2.9 engines.

Thanks

 

[rusty ol ranger]

Shouldnt be any difference between the 88 and 89 ECMs.

Pull codes on the 88. Also when you changed the temp sensor did you change the sensor (2 prong plug) or sender (1prong plug)?

If you did the sender all it does ia control the gauge. The sensor feeds the ecm info

Also, check the vacuum hose running to the FPR for fuel. Regulators are a known 2.9 weak spot.

 

[2trux]

I changed the 2 prong sensor and connector. I checked the fuel pressure and it looked good, the regulator was replaced recently.
I had no codes KOEO and 41 during KOER.

 

[2trux]

Just to close this out. I replaced the ECU, the MAP sensor, and the O2 sensor all at the same time and the truck is running great.

 

[thorsranger91]

I get the fun of doing much of this myself. The previous owner put a cherry bomb in place of the cat assembly so it needs that too