HELP Kenworth T-800 electrical problem

[PNECAT]

I have a 1994 Kenworth T -800 with a Detroit 60 series 12.7
So my truck wouldn't start with some old batteries or jumped. I went and bought 3 new interstate batteries and put them in the truck. It rolled over like it should but no fire. I checked to make sure that everything was hooked up right after installing the new batteries and it checked out good. Made sure I was getting fuel and that was good. Found 2 fuses blown up by the fire wall that came from the ECM power plug (Red wires). Replaced the fuses and fired right up. Cool problem fixed. Well I went down 2 days later to fire the truck up and it did the same thing as before I replaced the batteries. Rolled over and no fire. Fuses where all good and had power to the ECM. Found a plug with only 2 wires on the plug to the ECM that you could mover around that would make contact and fire up and run. So I got it to run. With the old plug and bought a new one to replace it. Well during the time I had bought another new plug it stopped running again and I could not get it to fire back up on the old plug. Bought the new plug and installed it in the ECM. The truck will no longer start. All of my fuses are good. Batteries are all fully charged. I have no clue what to check anymore. I have fully charged batteries so the ECM should have the power it need some to see to start. Could I possibly have a bad ECM?

 

[Mike L]

Whem you turn the key on does the check engine light come on? If it does then you have power to the ECM. If not then check the wire from the battery to the ECM.

 

[PNECAT]

Mike L .Yes I have a green check engine light come on. I have 9.8 volts to the power plug on the ECM so I'm getting about a 2 volt drop from my battery to the ECM. The plug that gave me the problem has been replaced with a new plug and it only has 2 wires on A and B pins.

 

[kenh]

IIRC some car ECMs will not function under 10V. (maybe the same for bigrigs?)
Possible under cranking load your voltage is going even lower.
Can you jumper direct to the ECM?

 

[JNisbet]

Sounds like you have checked out the basics for trouble shooting a 60 Series no crank issue. I typically at this point would start pulling the loom off of the ECM wire bundle and find where the broken wires and Fuzzy Green Stuff is at. Especially since you have the excessive voltage drop to the ECM.

Have you checked the Starter Solenoid yet? Or are you getting absolutely no power to the electronics/ECM?

 

[PNECAT]

I haven't checked the starter solenoid yet but yes i am getting power to the ECM. It is only getting 9.8 volts from the batteries which test out at 12.8. My meter has a 129 battery test setting on it and it checks (Green good). I got to the power plug on the ECM and test it while rolling over the engine and it drops to 9.8 and my meter goes yellow basically saying that it's lose of power? I did run 3 new power wires and spliced them into the existing power plug. And still got the same volts and cleaned up the main grounds. I will see if I can get move voltage to the ECM? Keep checking out the wiring. Thanks for the help

 

[overworked]

How is your battery voltage? If your batteries are run down cranking voltage will be low. Double check connections at batteries.

 

[PNECAT]

The batteries are fully charged with 12.8 volts. I took them out and charged each one 24hrs. The connections are good and tight aslo. I will double check everything I have read on this page to make sure it's good.

 

[mitch504]

Have you put a voltmeter on the battery studs or posts directly while cranking? I bet your battery voltage is dropping when you hit the start button.

If the voltage on the posts stays good, try it on the battery cables. wherever the voltage drops, there is a high resistance between there and the batteries.

 

[overworked]

Not to beat a dead horse, are the power and ground hookups for ecm in battery box, I once put new batteries in a freightliner and hooked all up, even fused pwr for computer, got a call truck would shut off when hitting bumps, the ground fell behind a battery and laid against the box, grounding it , until you hit a bump,

 

[PNECAT]

Mitch504 yes I have a voltmeter. I have not checked the power on the batterie terminal yet while cranking over the truck. That's an idea I can test. Then I will check the battery cables and get back with you. Thanks

 

[PNECAT]

Overworked yes the power and grounds cables go directly back to the battery box. The hot wires go directly to the positive terminal and the negative wires go to a relay inside of the battery box I believe. The big thing to remember is that the truck ran exactly how it is wired as it sits even after I replaced the new batteries it ran once I found the lose plug in the ECM.

 

[overworked]

Can you post a pic of the plug?

 

[PNECAT]

Yes I will when I get a chance to get one this weekend.