I’ve spent about a year trying to chase down an overheating issue and after talking with a few people I think I may have a timing issue.
it’s a 95 with a 4.0l.
I know it’s controlled by the ECM/ ECU (PCM) and can’t be adjusted. I just don’t want to spend the money for a new one if this isn’t an issue.
I put a light on it today and at idle the timing is about 8 degrees BTDC.
when I rev the engine it retards significantly, like off the dial to what I can only assume is around 50 degrees btdc.
I’m thinking this isn’t normal and it should be somewhere in the 15-18 range at most?
I overheats when the rpm stays above 2500 for long periods and I’m guessing this might be why.
anyone else ever tested the actual timing on theirs? I can’t find a lot of info since it’s all electronically controlled.
is there anything else with the distributor that could cause this?
could This be caused by the MAP sensor, TPS.
how do I test those to rule them out?

 

I'm skeptical you have a timing issue. You've confirmed the fan clutch is good? The usual cooling system problems like clogged radiator, water pump vanes rusted away? Torque converter is locking up when it's supposed to and not dumping extra heat get into the radiator? O2 sensor isn't making it run lean? How's the mileage?

 

clutch fan, radiator and water pump have all been replaced. Torque converter seems to be locking up.
haven’t tested the O2 sensor yet.
milage is about 220k.
I had the head taken off and checked a few months ago and they milled it. Compression is about 120 on all cylinders.
I did figure out how to test the MAP, TPS and I take temp sensor and all seem ok.

 

Is the CEL on?
is the fan shroud in place?
have you confirmed the temperature gauge is accurate?
does the electric fan kick on?
Does the temperature slowly creep up or does it just shoot up and overheat quickly?
do you have a winch/light bar/lights or anything else blocking the grill?

 

I’m not familiar with the acronym CEL.
I’ve checked the block temp in several locations with a IR gauge and the temp gauge seems close.
electic fam kicks on. I’ve also tried jumping the relay on the fan so that it runs continuously.

if I stay below 2000 rpm, it doesn’t heat up. A few sustained minutes of climbing my a hill or accelerating/ driving at 70 on the highway and the temp climbs up. If I back off and turn the heat on full blast, I can get it to slowly come down.

I have a Smittybuilt winch bumper with a 5K winch that does block the front some but so to thousands of other people that aren’t overheating.

50+ degrees before tdc seems ridiculous to me. I’ve worked on a. Lot of older cars and adjusted ignition timing and I’m surprised it runs being that far retarded. I know that I’m general, the timing being retarded too far can cause overheating. How do I know if the ECU is bad and causing this?

 

CEL is the check engine light. Is it throwing codes?

Try a quality replacement thermostat.

 

50 degrees btdc would be very advanced not retarded. I'm assuming an automatic? As a quick test, while driving along at a steady speed in 4th gear, give the brake pedal a light press with your left foot. You should see the rpm jump a few hundred when the torque converter unlocks. If the torque converter is not locking, all that excess heat from the t/c slipping ends up in the radiator and can contribute to overheating under load. The common causes for the t/c not locking are a bad brake light switch (pre 91 it's actually a separate switch on the pedal), a bad t/c solenoid, or a bad throttle position sensor. A bad solenoid may not throw a check engine light on a pre-98 (98 added a front speed sensor that will catch the lack of rpm change when the t/c locks)

Try unplugging the O2 sensor and going for a drive as well. That should force the engine computer to stay open loop, which might help diagnose whether the O2 sensor is giving bad data. That will likely set the check engine light. If it's the original, it could very well be bad by now.

 

only throwing the 12 code.

thermostat has been replaced as well.

 

Torque converter is locking up as it should.
drove it with O2 disconnected.
no change.

 

when it starts overheating, turn the heater on full blast

This acts like a second radiator

If your engine temp falls, this usually means your radiator or its cooling fan are not to scratch

If it doesnt, it may be a failing water pump (or some other cause)

For other I6 engines I am familiar with, about 40 degrees of advance at 3000rpm is normal, they can go higher, but that is only at cruising speed with no throttle (like going downhill)