Good afternoon, I have a 1999 c6500 with a 3126 cat that is currently a crank no start. It has been noting short of a nightmare. To start it had a bad low pressure oil pump ( 20psi at 2000rpm and down to almost 0 at idle). put pump in and have 48 psi of oil pressure on crank now still a crank no start. test ipr and it is good. test the wiring to the ipr and have 12 volt with multimeter and 2volts under load. remove the harness from ecm and test wiring between ipr and ecm and wires are good. no oil pumping out of injectors, dead head the pump and instantly 5000psi. hard wire the ipr and get oil pumping out of injectorsbut no start still. Have fuel returning out of fuel pressure regulator so I know i have good fuel pressure. So currently have adequate oil pressure at injectors and fuel pressure but still a no start. given the voltage under load issue on ipr wiring I am assuming the ecm is bad. can anyone confirm or think of something i missed. Thank you in advance.
Have you verified all your power and ground to ECM? Usually there are 2 or 3 constant 12v and a keyed 12v plus a couple grounds. In my experience ECM’s are rarely the issue. It ends up being power, ground or a harness issue. I’ve run into a couple engines with harness issues so bad it will pass multiple click tests with the injector harness unplugged. I have a test harness I can plug in on the truck side of the ECM and run an engine. It’s a quick and dirty way to isolate which side of things the issue is on. It’s also gotten more than one truck off the side of the road in a jam.
I verified that I had good power and grounds. Notsure if I was missing any as I cannot find a wiring diagram Or a service manual for this engine
Try posting an engine Serial Number for an electrical schematic. Engine manuals for troubleshooting may also be available based on that same number.
7as80366. 3126.
I’m not online right now so cannot download a copy of the schematic. Search the web for Cat Publication RENR1368. It covers all 3126 engines of 7AS prefix.
99 should be a 70 pin ECM. I’ve yet to see anything truck that had different pin outs. A quick google search will give you basic pinout for 70 pin or the older 40 pin to verify power and ground.
It sounds like you have two of the three basic requirements for life. The last one is speed/timing sensor input. I'm not sure how you can easily verify that without ET. Also with ET, you can confirm that the IAP sensor is reading correctly.
It is a 70 pin.
I agree with @Cmark You really need ET, or some sort of scan tool, hooked up to it so that you can see parameters in real time and look at Diagnostic Codes. Here’s the schematic.
A good thread on this from the archive. HeavyEquipmentForums
Those things are a diagnostic nightmare. OBDII and ADEM II ECM with GM programming. The flash files are unattainable. Except for a few guys that forward thought about saving copies. I found a guy in Seattle that can program them. Your mileage may vary.
couldnt agree more. only has an obd2 plug under dash. Scanner wont connect even thou it has power to it. tell me failed to connect.
Scanner wont connect. only has an obd2 plug that i can find. plug has power to it as well
The OBDII doesn’t connect to anything useful. You have to make a jumper harness with a breakout to connect ET to. Or, buy one from EBay.
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When I had trouble with my (same) truck, a local mechanic had a laptop with an OBD II adapter to heavy equipment plug that allowed access to the engine puter via the OBD II.
I recieved my breakout harness and got my cat et hooked up to the ecm finally. Here are my results.
Can you post the images any bigger.? I can't get them to open separately so they can be enlarged. Also need to see the menu bar at the top of the screen that is cut off in the first of your two photos.
If you still have access to the ET can you download a Product Status Report from the ECM and post it up please.
Active codes are a result of the ecm not being plugged into motor harness at current time. I pulled the ecm this evening from truck.
Do you have an image of the ECM Configuration screen.?
All six injector current fault codes tell me there is a bad ground somewhere. I’m probably wrong. Couldn’t be that simple.
I think this may have something to do with it.
On the basis of all those screen captures you posted above, which don't really show anything of note, I think you need to verify this.........
Was that image above from ET while the ECM was still installed on the engine.?
Yes
I take it the engine was not running at the time, as your OP indicated a crank/no-start condition.?
That is correct. I noticed that engine speed appears a little low from desired
Were you actually cranking the engine at the time.? If yes then the cranking speed seems a little on the low side to me. Normally I would look for an absolute minimum of 150 RPM and preferably getting up to somewhere around 180 RPM while cranking over on the starter.. If you were not cranking the engine then there appears to be something wrong with the crankshaft speed sensor output signal. The speed should (obviously) read 0 RPM when the engine is stopped.
It’s got over 200 and was 190 in this pic. So I guess that is normal.