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No start, No Tach, No WTS, no PCM communication

16K views 12 replies 6 participants last post by  Jared4454 
#1 ·
I have searched through a ton of threads and have tried many different things to figure this out. Looking for some input from someone. I had the truck die on me while driving last week. No hesitation or running issues, just cut out and no restart. I had no pcm communication with scanner, no tach and no WTS light. I came to the conclusion that PCM was bad. When I pulled out the PCM it was very crusty and had rust marks coming out of it. I got a rebuilt PCM and hooked it up, charged batteries to max and still no start. I took the fuel filter cap off just to see if it was full and found out it was. Put it back on and then tried to start it again. Got WTS this time and truck fired up. Let it run for 5 minutes and then died. Did this 5 times, runs fine and then dies after a few minutes. After doing some searching I found that the IPR tin nut(STUPID) was loose and solenoid was moving around. I put a real 1/2-20 nut with thread locker on it and truck fired right up, ran good for 15 min and then took for a ride. I made it 1 mile down the road and the truck died just like it did the week prior. Could not get it restarted, and the truck is doing the same thing, no WTS, tach, communication. Really hoping the PCM is not fried again! Any input would be greatly appreciated!!
 
#2 ·
First thing to check would be the #22 fuse in the underhood fuse box. If the fuel heater is still connected, unplug it. You don't state what year the truck is, but it will be a Red wire with Light Green stripe about halfway down the driver's side of the filter bowl. It has a funky-looking spade connector that pulls straight out from the bowl. After that and still no WTS, I would check for 5V at any of these sensor's Brown with White stripe wire with key in RUN position: BARO, ICP, CPS, TPS, EBP, or MAP. If any of these sensors has shorted it will cause the same symptoms (EBP sensor is one of the more common ones to short). I would also suggest checking your PCM connector's condition (damaged pins, corrosion, etc). Cheers!
 
#6 ·
ERM100, you must have missed this from my post above:
After that and still no WTS, I would check for 5V at any of these sensor's Brown with White stripe wire with key in RUN position: BARO, ICP, CPS, TPS, EBP, or MAP. If any of these sensors has shorted it will cause the same symptoms (EBP sensor is one of the more common ones to short).
Those are it as far as the 5V reference voltage goes (trans doesn't use it). Cheers!
 
#3 ·
Thank you! My truck is a 97' F250 7.3. I removed the fuel bowl heater over a year ago and the fuse is good. I checked my new PCM on a buddies 96' F250 and she fired right up so thats good! I am really thinking there is a bad wire somewhere. Not looking forward to hunting it down. The one thing I had to do to get it fired up after new PCM was installed was to tighten IPR nut. I had to remove fuel bowl to do it. Maybe me just moving the fuel bowl harness around was enough to make a good connection until I went for a drive and it started to heat up and poof. The IPR seemed to be able to turn the WTS off when connection was bad. Is it possible for an IPR solenoid to go bad if it was loose for awhile? Whatever it is, as soon as that WTS comes on it fires right up. Is the PCM diode in fuse box known to go bad. With key on I can remove diode and when I put it back in I can hear pcm relay click and gpr click. Good sign i guess. I know that cranking the engine a lot will sometimes empty the HPOP. Is there a sensor on HPOP that will keep the engine from firing if its low?? Thanks again!
 
#4 ·
Just got done messing with the truck. I found that I have no 5 V ref on any of the sensors with the brown white wire. When I unplug the big harness plug right by the fuse box towards engine on fender well and turn the key on the wts light comes on. Haven't seen that in awhile! Not sure if its a short in the wire or a sensor thats killing the ref voltage. I found brown white wire on map, ebp, cps, icp. What else uses this wire? trying to test the wire from the closest sensor to the furtherest to see where problem is. Any sensors know to be problematic???
 
#5 ·
I would disconnect everything that uses 5V VREF, see if the WTS comes on then. If so, then start reconnecting until you lose the WTS. Off the top of my head, along with the above, there's BARO, APS (on the pedal), IAT, EOT. Automatic or manual transmission? Automatic MIGHT have a 5V VREF.

Re. HPO reservoir level, no sensor for that function, it's just built into the design. Inadequate HPO, injectors don't fire.
 
#7 ·
Ok I have disconnected and checked every sensor with 5 v reference. They all have .2v on the brown white wire. And nothing on the other 2. I'm thinking the PCM is getting a bad ground and not waking up when I turn the key. I think all the black white wires at PCM are the grounds. What is the main ground supply for PCM? I'm tempted to try a new engine harness but don't want to throw unnecessary parts and money at it. This whole thing is REALLY starting to frustrate me! Thinking if I use a jumper with a probe I can add a ground to the black white at PCM connector and see what happens.(not probing through jacket) Also if I try to jump across big posts on gpr the relay just clicks really fast but the disc won't stay up??
 
#8 ·
You were getting the 0.2V with all the sensors disconnected at the same time? You still could have a short in the harness somewhere. I've attached the reference voltage tests for you.

Grounds are both Black with White stripe and solid Black wires. Pins 24, 25, 51, 76, 77, and 103.

Cheers!
 

Attachments

#9 ·
was getting that .2v on brown white wire when harness and pcm were plugged in. When all harness plugs and and pcm and sensors were disconnected I was getting a short to ground on the brown white wire. The harness was pretty beat up, broken plugs and corroded wire jackets from previous fuel leaks. I found a engine harness on Craigslist not too far from me and bought it last night. Came out of a 97, only difference is the oil temp sensor in HPOP res. I am just going to swap the pigtail from my harness. I am going to swap harnesses this weekend and hope I didnt burn up the pcm trying to find the short. Thanks for your help!
 
#10 ·
I had a similar issue with my 96 and ended up being the IPR connector wires were shorting together. At the plug where the wires go into it, they were chaffed and I pulled them apart cleaned and put a dab of RTV between them and perfect for over a year so far.
It would run good then just stutter and die.
Do you have software to run on the truck like Auto Enginuity?
I have also heard of a grounding issue from others and we replaced ground wires from cab to frame. Just used heavy wire like a battery cable or welding cable.
Good luck chasing down the electrical gremlin.
 
#11 ·
Thanks for reply. I had the same issue about a year ago. They sell new IPR pigtails so you can cut out bad wire and you get a new connector. I finally found the problem. I knew the 5v ref (brn-wht) wire was shorted somewhere. So I found a used engine harness on Craigslist. Guy said it was used but in "perfect shape", same as factory harness. So I drove 2 hrs each way and paid $150 for it. I got it home and took off the loom and started checking it out. The whole thing was covered in diesel fuel, all under the loom was dripping fuel. 2 injector plugs were completely fried, the main square harness plug was cracked, every single wire was cut and soldered 3" behind main plug. ****ty solder job with sharp metal sticking through shrink tube. 2 solders where not covered at all. he also had all the weather seals in a zip lock bag, he did this becasue the fuel made them swell up almost double in size. Harness was totally unusable. I called the guy back up and he played dumb and would not give me my money back. Total scumbag liar. So I removed my harness and found that the previous owner had pinched the Cam position sensor wires in between the EBPS tube and the block. Short found. Took and few good connectors off the scammers harness and replaced all loom and electrical tape and cleaned my original one. Installed everything and she fired right up. I spent about $650 to fix a 25 cent problem. What a pain in the ass. Thanks for all the help everyone!
 
#13 ·
Having your exact same issue after I installed injectors, HPOP, and new turbo. Idling like crap and found it was my ICP (which was brand new) reading wrong. I performed a key on engine off test and half way through the PCM shut down. No comms, no reset, nothing. I tried everything I could including disconnecting the entire wire harness on the engine and still nothing. I sent the PCM off for repair. Hoping that's all it is. I did just wrap the old wire harness when I did all the work but it drove ok until I ran that test. Should get it back this week and we'll see if that was the issue because I have doubts.
 
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