possible bad ECM - what to buy - what is compatible

[sperold]

The ECM wants to know engine temperature. The fans are part of it, but a small part. The gauge on the dash uses another temperature sensor located near the one that runs the ECM. That gives you an idea of how important it is.

 

[rubydist]

if the pcm does not see engine coolant temp, it assumes it is cold and runs rich for up to 20 minutes in open loop before reverting to closed loop control. you do not want that, so you need to replace and reconnect the ect.

ircm is another term for ccrm.

 

[wespiece]

You guys are the *******! you were totally right. three digits codes pushed me in the right direction. here is my results

118 - ECT sensor is/was high or open - fixed by running fresh wire from ECT sensor to ECM. Connector i was using may have not been the right one on the harness, Could not find a connector with a green/yellow wire in it. Code cleared

519 - PSP switch/circuit open - Power steering pressure switch - you could possibly jumper this or plug in a switch that goes to nothing. A non issue either way with your buggy - still present but may fix later

551 - Intake Manifold Runner Control (IMRC) solenoid/circuit - whole circuit is still in place, just replaced the solenoid for $22 from autozone. Dorman 400-600 4x4 control module. Code cleared

556 - Fuel pump relay primary circuit fault - Likely due to the CCRM being removed - may fix later

564 - Fan Control (FC) circuit failure - makes sense as you said the CCRM has been removed - may fix later

We drove around the block several times today and it seems to be much better - no more die'ing/stalling. One thing i did notice is that the check engine light was off when we first started but then came back on after driving for a few. I checked the codes again and now I'm down to just 519,556,564 - will all of these codes trigger the check engine light? would like to focus on clearing anything that causes the light to come on at this point next.

We will also make a longer road trip once the weather clears up and double check everything now that we appear to much closer to perfect.

Thank you again for all the help - glad i don't need an ECM after all, Was not looking forward to dropping another $150+ on something that i wasn't sure was going to fix my problem.

 

[wespiece]

rubydist - when you talk about closed loop vs open loop - it that fuel or ? ?? pardon my stupidy - I'm still learning about these motors.

 

[rubydist]

something else is still going on, because none of those 3 remaining codes (519, 556, 564) are supposed to turn on the check engine light.

open loop v. closed loop: when the engine is first started, the pcm controls the engine in an open loop mode. that means it is using a predetermined table for the amount of fuel it is injecting into the cylinders, based on ambient temp, load, rpm, etc. it is not looking at the oxy sensors to see what they are saying. there are several reasons for this, including the oxy sensors need to warm up, engines need to run more rich when cold, etc. after the coolant temp starts to come up, it switches to closed loop control, where it looks at the oxy sensor readings and adjusts the fuel up or down to cycle across the 14.7:1 tip point. you care about this because the SHO motor is set up to run pretty rich in open loop, and too much fuel creates issues like not passing emissions (which you don't care about) and washing the oil off the cylinder walls (which you should care about). when the pcm doesn't see the coolant temp come up, it stays in open loop mode for (iirc) 20 minutes before it decides that it must be warm by now. that is way too long...