98 C5 PCM "no comm"
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From: Andrews AFB Maryland
98 C5 PCM "no comm"
So I've been battling this electrical gremlin for quite some time now.. The PCM reads "No Comm" when I try to read codes with the on board system, as well as a handheld scanner. Anyway, after months and months of trouble shooting I've come down to this.. The only time I can get the pcm to actually work and have comm is when I unplug any 1 of the injectors. I plug it back it, immediately no comm. What could be causing this? Do all the injector grounds combine into 1 wire, and then go into the pcm? Or do they each have a ground going into the pcm? That's really the only thing I can think of that could be causing that to happen
Last edited by Ppags; Jan 16, 2015 at 06:47 AM.
Le Mans Master
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From: Columbia SC
I answered that for you before. Each injector has a separate ground wire going into the PCM. The injectors are always powered when the ignition is ON or in START. The PCM grounds each injector in sequence to activate them.
I am still waiting on you to tell me if the car will run when you have one injector disconnected.
I am still waiting on you to tell me if the car will run when you have one injector disconnected.
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From: Andrews AFB Maryland
I answered that for you before. Each injector has a separate ground wire going into the PCM. The injectors are always powered when the ignition is ON or in START. The PCM grounds each injector in sequence to activate them.
I am still waiting on you to tell me if the car will run when you have one injector disconnected.
I am still waiting on you to tell me if the car will run when you have one injector disconnected.
Le Mans Master
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From: Columbia SC
10-4. The PCM No Comm issue has me stumped. I wish that 2nd PCM had been a good one. You previously mentioned you were going to send your PCM off to see if it is the issue. Cardone is one along with NEC and some others.
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From: Andrews AFB Maryland
Yea I found a guy on eBay that had great reviews and spoke with him, he said he could at least try to pull the tune off it and save it to eliminate that headache if the pcm goes completely, as well as try to see what's wrong with it. But I want to try to find someone local to bring it to. I'm not a big fan of sending things like that through the mail.
Last edited by Ppags; Jan 16, 2015 at 12:25 PM.
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From: Andrews AFB Maryland
So I'm looking at the pin outs on my PCM, here's the link: http://corvetteforum.shelor.net/Corv...tor_Pinout.htm
on the red connector what injector wires are the ground? anybody happen to know?
on the red connector what injector wires are the ground? anybody happen to know?
Le Mans Master
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From: York PA
So I'm looking at the pin outs on my PCM, here's the link: http://corvetteforum.shelor.net/Corv...tor_Pinout.htm
on the red connector what injector wires are the ground? anybody happen to know?
on the red connector what injector wires are the ground? anybody happen to know?
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From: Andrews AFB Maryland
Woooow. I completely misread the diagram. I was reading "ignition control" as injector control, and was wondering why in the hell is there 16 injector control pins? Well played sir
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From: Andrews AFB Maryland
Well I got the car back, but the battery is completely dead and most likely frozen bc it's only 20 outside, and was left on the truck overnight. So it needs some time to warm up before I can try to charge it. The garage said they put in the new ignition switch I sent to them, but it's still new in the box sitting on my seat so I dunno what the hell was going on with them, so I guess that could still be my problem, and they only put 3 lug nuts back on my damn passenger wheel, and left the wheel well hanging by 1 screw. Exactly why I hate having other people touching my cars
Le Mans Master
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From: Columbia SC
I don't think your ignition switch is your issue. You can put it in or we can just check voltages at the fuses it feeds to confirm if it is bad.
Please disconnect your dead battery if you charge it in the car. I can explain later about square DC waves and electronics.
Sorry about the shop issues.
Please disconnect your dead battery if you charge it in the car. I can explain later about square DC waves and electronics.
Sorry about the shop issues.
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From: Andrews AFB Maryland
Yea it happens I guess. The battery is still on the trickle charger going on 24 hrs now. It was completely drained. Im gonna mess with the car tonight once my daughter goes to sleep, maybe I'll get lucky
Le Mans Master
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From: Columbia SC
If you charge a dead battery in the car DISCONNECT the negative cable first. Normal car chargers produce DC square waves that can pound the electronics and damage them. A really dead battery cannot filter these. If a battery is just a little low there is no concern.
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From: Andrews AFB Maryland
The battery is completely out of the car sitting on the shelf while it's charging. I checked on it earlier and I think my charger fried overnight. It won't turn on anymore. Can't catch a break with anything lol
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From: Andrews AFB Maryland
Battery is still charging on my little 8 amp charger. I don't think it should take this long though, I was thinking 10 hrs or so charge time. So I might need another battery, if so I'm gonna go with an optima I think. Yesterday I had a little time and took the pcm out and checked all the pinouts. There was a little sand in the red connector, so I cleaned it out. Didn't find anything else wrong, rechecked all the grounds, and put the new ignition switch in as well. Guess we'll see what happens when I have a good battery to put in.
Drifting
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From: Bahama North Carolina
Battery is still charging on my little 8 amp charger. I don't think it should take this long though, I was thinking 10 hrs or so charge time. So I might need another battery, if so I'm gonna go with an optima I think. Yesterday I had a little time and took the pcm out and checked all the pinouts. There was a little sand in the red connector, so I cleaned it out. Didn't find anything else wrong, rechecked all the grounds, and put the new ignition switch in as well. Guess we'll see what happens when I have a good battery to put in.
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Cheers!
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From: Andrews AFB Maryland
Battery is charged,I did have it tested last night to be safe. I put it in real quick this morning before leaving for work, same problems, no comm, reduced engine power. I didn't have time to pull the injectors to see if it ran, I'll do that later. I did notice when I tried to roll the Windows down, that I couldn't control the passanger window from my driver side panel. and the memory for the seat doesn't work anymore. If the pcm is really the problem, would it cause the bcm malfunction as well since they are all tied together?
Le Mans Master
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From: Columbia SC
You may ask yourself then why does my computer power supply not damage the electronics? Good question. It is because the power supply is much more complex and actually makes a virtual true DC current. At least as close as possible.
Mr. Sam P. E.