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One thing I have not seen mentioned ( but I may have missed it) is that if a sensor (MAP,ICP or CPS (CAMP) sensor fail in a high impedance manner they can pull Vref (5v) in the PCM down to the point that it does not function. You can unplug all these sensors and see if the PCM behaves normally and boots up giving you communications with a scan tool.
Great point and I do not believe it has been suggested yet. I saw a MAP sensor do this on one of Scanner Danner's you tubes but it never crossed my mind that it could be happening here. Makes sense too because I believe his PCM tested Ok.
...You can unplug all these sensors and see if the PCM behaves normally and boots up giving you communications with a scan tool.
Jeez Steve... good one! In this test, I'd do as tdpower suggested and pull the 42-pin connector, isolating almost everything from the 5v. If that restores PCM communications, then it's just a matter of plugging/unplugging stuff until the culprit prairie-dogs.
I think the PCM supplies the 5v..., but I'd have to look to be sure.
You could take out fuses one at a time and see if any make a difference. Maybe you can isolate it to one circuit causing the problem. I would also check the wires down at the transmission. I had problems with mine deteriorating down there. Wires going over drivers side valve cover often rub and cause problems.
Finally some great suggestions. Im on it . will let you know. Its been in the back of my mind that a sensor could cause this , but not knowing how they work, I never pursued it. That said, BIG56 mentions the map sensor having caused a similar condition. Its the one I suspect, because its the only one that couldn't handle my built motor, and had to be modified. It used to cause a huge boost drop when I got to about 30psi because its only designed to function at 19psi. Says the tuner. So I had to tap and ground the green black wire I think it was. This stopped the map from sending the OH NO TOO MUCH BOOST" signal, solving the boost issue. Its apparently common when you add that much boost. THis trick or a regulator solves it. BUT, I suspect that wire is the VREF wire, and because its grounded the sensor may have failed and is now going to ground all the time rather than just at the high boost signal. That said, I have hit that high range several times in the days before the failure, during some 140mph drag races. SO its been in my mind I may have over worked my stock map and killed it, and my ground tap is causing the failure. I will do my best to get back on it asap. I hope to find time today. Still recovering from the big storm. What a mess.
There it is. By completely grounding the MAP signal, you change the impedence on the whole Vref line with high boost... bad juju. The MAP sensor will try to regulate the voltage to the signal line, but that direct short likely killed the MAP sensor and took the Vref down with it.
"Stinky's" previous owner put a voltage regulator on this line to prevent an overboost code, but the regulator failed and it took me a while to discover its existence.
To prevent the mess you have now and the one I encountered, I suggest not tinkering with the electrical signal. Instead, regulate the air pressure to the MAP sensor (OCR - Overboost Code Regulator) like the one I bought from Riffraff Diesel. You can see mine in the upper-left corner in the photo below:
The MAP max is right around 48 PSI (Barometric pressure plus boost). I know this because going over that limit broke mine and I had to replace it and install the OCR to prevent a repeat. Good thing I log everything when I drive... that's how I catch these nuggets.
Yes Tugly, That's what I suspect. Just need some time to investigate. Its actually worked fantastic for about a year since I did the build. But originally Jody told me to get a compressor regulator and set it to 21psi max, and install it before the map sensor. Had it almost all made up when I saw the post on the ground instead. I went with the ground. I hope its the problem. Easy fix. I still have the regulator set up, so I will change to that. Never knew Riffraff had one. Wish me Luck.
Thank You clem1226, and everyone else that helped me. Clem has solved my issue. I did what he said and I have computer communication back, and it almost started except my batteries were low. Its looking like the Exhaust pressure sensor has failed causing what clem1226 said the map would do as well. I disconnected the map and nothing happened, then the wasted gate one on the "Y", nothing, then the oil pressure, then the EBP sensor. Upon pulling the EBP sensor my fuel pressure gauge began to rise. I knew I had something. Plugged the rest back in and all held up. Did a code read. Hello!!! P0237,P0475,P0603. Kam is probably because I had the batteries disconnected and the pcm out for some time. EBP valve, must mean the sensor which is now disconnected. Will it run without that? Might be able to get one on sunday. We will see. I'm gonna try to start it though. Just charging right now. I will let you know. Going to do the map regulator too, even though its ok. I'm going to order one though. I hope this is it. Thank you to all who helped, and even the ones that cut me up. They got me mad enough to keep going. LOL. I will post final results soon. Thank you so much, especially clem1226. Nice job man.
Hmmm.... EBP.... I didn't see that coming. I can make one suggestion, though: Make sure there is no exhaust leak near the sensor. If exhaust gasses can escape very close to the sensor, it will burn the new sensor. This is the very reason for that tube... the sensor can measure the pressure while staying the hell away from the heat.
Ok everyone. I'm fixed. It was the EBPV sensor. I got a new one at NAPA. Over a 100 bucks. Ouch. But put it in, computer stayed up. I also splurged for two new batteries. The maintenance free ones so they won't leak that acid all over. Put them in, wow did it crank faster. Mine must have been weak for awhile. Anyway fired up and running like a dream. Thanks to all for all your help.
Hot Damn! I have been lurking here following this thread on baited breath ! Man now I know why I hang out here ! We have some of the best brains on this forum bar none!I am happy that you got your ride up and running again. Good luck and happy trouble free motoring!!
Glad you got it and I think a lot of us learned some things. Here is the Scanner Danner video of the case I was referring to, wished I'd thought about it sooner but anyway Clem came to the rescue.
Glad you got it and I think a lot of us learned some things. Here is the Scanner Danner video of the case I was referring to, wished I'd thought about it sooner but anyway Clem came to the rescue.
Glad you kept after it and everyone benefits from threads like this
Holy Cow that video would have helped two weeks ago. LOL. Funny how that works. Thanks. I learned a lot throughout this ordeal. That video is good learning.
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Man now I know why I hang out here ! We have some of the best brains on this forum bar none!
