My '02 7.3Ltr has been giving me trouble, running rough while cold, running good when hot, and throwing an IDM code (just a general code, nothing specific). I have tested the crap out of everything and finally took it to a shop. They diagnosed a bad IDM and replaced that, then 2 bad injectors and replaced them, then 1 intermittently bad injector. I was done with them at this point. After $3000 I told them I would take it somewhere else. Once you loose trust in the shop it's over. I took it to a guy in another city. I like them. After hearing my story he asked if anyone has checked the compression. I said no. Well he checked the compression one No. 1 and No. 2 (because No. 1 injector on his equipment had a High to Low Open showing). The compression came out to 320 psi on No. 1 and 360 on No. 2. He didn't go any further. He said that for everything to run smooth and clean it had to be 400psi. Am I being shellacked? I told him to go ahead with the injector and button it up.

I am too old to be rebuilding a big *** diesel. The truck has 233+,000 miles. It has been taken care of, but in Texas we drive the crap out of everything we own (unless you live in Austin, the San Francisco of Texas).

I need to figure out what is true and then decide on rebuild, buy new engine or just buy a new truck (NOOOOOOOOOOOOO!).

 

Those numbers are a little on the low side if I remember right, but low compression will not cause a high to low open code, or any other circuit code. The only code low compression should cause is a cylinder contribution or misfire code.

 

Well the cylinder contribution test completed successfully and there were no codes for that. The no 1 injector had that code before we ran the cylinder contribution. BTW, what the hell is "Cylinder Contribution?" They are putting the truck back together with a new no. 1 injector. Hopefully I can pick it up this afternoon.

I have an Autoenginuity computer. I would love to figure out how to run some of these tests. I ran the Cyliinder Contribution test from the testing tab and waited while it did something. That came up with Test Completed Successfully message. He ran the same test at his shop. Same result. I guess I'll start a new thread with the problem (if it still exists) and see what I get for guidance.

Thanks for your response.

 

You really need to do all the holes on the compression test just to see how close they are. That will also tell you how good his equipment is. Low 400 are good on a warm motor. Lots running in the high to mid 300 and are just fine. I'd say if the rest were high 300's or even 4 hundreds then the one 320 mitt wearing a bit. Some equipment reads higher then others. Ten percent difference in cylinders is considered good.

 

Cylinder Contribution Test is pretty literal: It measures how much each cylinder contributes to the cause of spinning the motor. If you have a hot or cold injector, or one cylinder with low compression - the delay in the rotation of the engine is measurable from cylinder to cylinder. The procedure is to get the Engine Oil Temperature above 140 degrees, turn your heater or A/C completely off, put it in gear with the brake on, and start the test.


I fire up AE and look at the Cylinder Rotational Velocity for all 8 injectors - in gear and out. Very telling stuff right there. The truck can pass the CCT, but the CRV tells much more.

 

Thank you both for your responses. I'm going to hook up AE this afternoon and run that test. See if I can get the little bugger to tell me anything.
I still have the IDM code. Apparently it is there to stay. I forget the actual code, but the translation is "General IDM..." Nothing specific. I notice that when I am cruising and I let the accelerator off, for example, going down a hill, the check engine light goes out until I accelerate. When I check the code it's that damn IDM code. The shop I had it at couldn't clear it either.

Oh well. Test and look and test and look. One day I'll either find the REAL problem or just get a new truck.

 

Ah... IDM code. There are three tests to help pin that down:


KOEO (Key On Engine Off) - conduct that as the acronym states.


KOER (Key On Engine Running) - same instructions, but don't be shocked when the truck sounds aggressive for a few seconds.


UVCH test from the link in my signature.

 

Scott, hang in there. There are a lot of guys on this site who have chased problems and solved them.
Larry