electrical or pcm problem?

[papanino77]

Hi everyone, this is my first post so bare with me.... heres whats going on. i bought my truck,99 ram1500 5.9 auto, about 4 months ago. the guy that i got it from told me it would stall out once in a while and get no bus. i know that theres a million threads on this. heres my issue(s). driving the truck in the cold seems to be fine. never had any problem. now when driving at any temp above 65f is where it gets tricky. i was driving one warm afternoon and that was the first time. next morning took her for a drive and she went fine. i shut her off and just out of curiosity i tried to start her but nothing. cranks but wont turn over. i let her cool off. after i got her started i went to the pcm and wiggled the wires and sure enough she died. after experimenting for a few days i began to realize that you could wiggle the wires in the morning while it is still cool and not have any problems. it you wiggle while the truck is warm she stalls. so i got myself a reman computer off ebay(it looked like ass and I'm not sure this company even rebuilt it) and had the same problem. I have another pcm coming from a different company and hope it helps. Any suggestions??? Thanks in advance

 

[LB3711]

check all the connectors and all your grounds. Must be a loose connection somewhere especially with the age of the truck.

 

[HolyRamBatman]

Welcome to RF.
^^What Matt said. This will take some time to do but it has to be done.
Check every connection in the pcm harness to make sure that each one is grabbing and holding the pin it is attached to. Possibly a broken wire in the harness. And then last but not least check all grounds in that area.
Good luck

 

[papanino77]

thanks for the reply. i've checked almost every ground i can think of or see. but would a bad ground effect the truck no matter what temp it is. it seems to only do it when warm. i drove the truck for 3 months in cool weather, no problems. i even took it for an hour drive when i first got it in feb to try and reproduce what the original owner claimed was happening to the truck (mind you he stopped driving it in JUly of last year when its hot as hell) and was fine. now that the weather is getting a little warmer here in Boston the problem has surfaced. i just wanna figure this thing out for obvious safety issues. thanks for the help. any advice is welcome.

 

[LB3711]

go thru everything and clean everything. could also be corrosion on something. Hard to say without being there.

 

[papanino77]

Welcome to RF.
^^What Matt said. This will take some time to do but it has to be done.
Check every connection in the pcm harness to make sure that each one is grabbing and holding the pin it is attached to. Possibly a broken wire in the harness. And then last but not least check all grounds in that area.
Good luck

how can i check the harness connections and pins?

 

[LB3711]

unplug them, make sure nothing is loose or broken then get some contact cleaner and spray both sides and plug back in and make sure its connected solidly

 

[papanino77]

go thru everything and clean everything. could also be corrosion on something. Hard to say without being there.

all contacts have been cleaned really good. and i uses some dielectric grease on the contacts. i dont think i metioned that once the truck dies it wont turn on until it cools off for a few minutes.

 

[HolyRamBatman]

The easy way would be to take a pin from the old pcm and push into each spot on the harness. If any are loose try to squeeze the connector so it gets a better connection. To do this you will have to be willing to tear open the old pcm.
If you can find a pin of the exact same size the would work also.

 

[HolyRamBatman]

Stupid question, never heard of it just thinking, by chance do these pcm's have a thermal cutout/switch?

 

[papanino77]

Stupid question, never heard of it just thinking, by chance do these pcm's have a thermal cutout/switch?

not that im aware of. the rain just stopped for now. so im gonna try and do as you suggested. i'll keep you posted. thanks for the tips

 

[papanino77]

so today i let the truck run for about 15 minutes. i popped the hood and instead of wiggling any of the plugs I pressed on them to make sure they were snug. and the truck died. i unplugged the one closest to the drivers side and then plugged it back in. and she fired right up, but then died on her own without me touching a thing. any thaughts?

 

[Ocelot]

Everything you're describing points to a bad pin in the harness. The PCM is probably fine since you tried replacing it and hat the same issue.

What happens is that metal (wires, pins, etc) expand and contract with temperature changes. at different rates with different metals. That's one of the reasons aluminum wire is outlawed in house wiring. The wires would expand and contract and you would end up with loose connections sparking and causing fires. The copper in cars is much better.

Unfortunately those types of problems are the hardest to find and fix. You need to narrow it down to which one of the connectors causes problems when touching it

I used to work in electrical engineering for a barcode scanner company.
Many times it isn't the visible pin itself, but the back of the pin where the wire is crimped to the pin. the pins are usually removable from the back with a needle pressed alongside the pin to compress the tab. It isn't fun and I don't recommend it unless you've worked with connectors before

The best way to fix it is to determine which connector is the culprit and replace that harness.

Ray

 

[papanino77]

Everything you're describing points to a bad pin in the harness. The PCM is probably fine since you tried replacing it and hat the same issue.

What happens is that metal (wires, pins, etc) expand and contract with temperature changes. at different rates with different metals. That's one of the reasons aluminum wire is outlawed in house wiring. The wires would expand and contract and you would end up with loose connections sparking and causing fires. The copper in cars is much better.

Unfortunately those types of problems are the hardest to find and fix. You need to narrow it down to which one of the connectors causes problems when touching it

I used to work in electrical engineering for a barcode scanner company.
Many times it isn't the visible pin itself, but the back of the pin where the wire is crimped to the pin. the pins are usually removable from the back with a needle pressed alongside the pin to compress the tab. It isn't fun and I don't recommend it unless you've worked with connectors before

The best way to fix it is to determine which connector is the culprit and replace that harness.

Ray

wow thanks. that make total sense. do you know if these plugs are rebuildable? or where i can find that connector? or should i just cut one off at a bone yard and connect it? thanks for the info

 

[LB3711]

pull lightly on each one till one comes out or is looser than the others

 

[papanino77]

does anyone know how to replace the pcm harness plugs?

 

[HolyRamBatman]

does anyone know how to replace the pcm harness plugs?

Cut and splice each wire? I have never done this. Don't sound fun at all.Maybe someone else has knowledge on this.

 

[Ocelot]

Connectors like that arent usually field replaceable. In fact I doubt a dealer could do it either. If you had to, you could get a cutoff from a junk yard and splice, solder, and heat shrink every wire. But that's a lot of them.

I'm not sure what your harness looks like, but I think if a dealer were to repair it, they would replace they whole harness that has the bad connector.

Ray

 

[papanino77]

ok, i narrowed it down to one if the three connectors. but i cant reproduce the stalling with the individual wires. i went to a junk yard and cut off a harness connector and can hopefully get to splicing the 21 wires this week. man this sucks. i hope that thats all it is and i can end this once and for all. its driving me nuts. thanks for all the help everyone!

 

[papanino77]

i also noticed the truck will die after running for about 15min at idle. im wondering if it is the pcm. i ordered another one last week and it should be here any day now. i think im going to wait on splicing anything until i try the rebuilt pcm. any thaughts? i feel like im running circles in my head. it so strange how it happens. if the truck is cool i can wiggle the wires and its fine. as soon as it warms up and i play with the wires it dies. and now dies even without touching anything. wtf?