I lose compression cant drive after 3-5 miles . athen the after it cools down it runs again for 3-5 miles, 7 yrs ago input on a used ECM and it ran fine until this again -?the same problem as then?
im n Santa Maria Santa Barbara Ca
i greaty appreciate any ones help 2-4-26

 

I'm not at all sure what you mean by "lose compression". Dying with the engine warm makes me highly suspect the Crankshaft Position Sensor.

 

On a 94-95 D1 3.9L V8 = 90% ignition amplifier or 10% Coolant Temp Sensor/Fuel Temp sensor. 96-99 GEMS 4.0L V8 could be a CPS, or the wiring insulation going to it. LR's aren't really famous for injectors getting heat soaked.

 

What do you mean by 'losing compression'? Does that mean losing engine power? If so, it could be several things from simple to more complicated...
- Idles Air Control Valve (my first guess)
- Crank Sensor (as Best4x4 wrote)
- Catalytic converters clogged

We'll need to know more about the circumstances. Will the vehicle idle for 10 minutes without the engine shutting down? What is the coolant temp across that time span?

Your 1996 should have an OBD port. My very first suggestion is to purchase an OBD dongle and get an app for your phone. This will allow you to see many of the inputs going to the ECM. That data will direct the analysis.

iPhone app = OBD Fusion
Android app = Torque

OBD wifi dongle = https://a.co/d/0hgcYlbP

 

so we did replaced the blocked Catyl Convertors, but i original problem still exists.Driving home ahout 4miles I lost power? engine ran very ruff back firing. Then over heating radiator. Towed home, Next day drove 1 mile no problem ,them home.
So I replaced tge Electronic Computer moniter 7 yrs ago with a used one 3000 miles ago,and a new crankshaft positioning sensor.7years ago,
and it ran good, It seems to have the same problem now? Should i just replace the crankshaft positioning sensor first? do i need any electronic equipment.Could insimply replace it n run the engine as the cheapest way?

 

Will the vehicle idle? For how long? What is the coolant temp after 10 mins at idle? What type of weather hot/warm/cold/freezing are you experiencing?

The problem you describe is too vague to suggest a solution.

 

Ides ok after 10 minutes , in a mild climate , 70s , can i exchangevthe crankshaft positioning sensor myself by just replacing it ? or do i need electric equipment to calibrate?

 

the crank sensor is heat sensitive and yes, you can replace it yourself. Use the search function of this site for added photos and thoughts.

The service manuals are in the google drive linked in my signature. They are very helpful.

 

Thank you.