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OT - Diesel truck battery voltage drop and cable issues

V

viper

Titanium
Joined
May 18, 2007
Location
nowhereville
I am fighting a starting problem with a GM 6.5 TD truck. Been fighting it almost since owned. Bats sit at 12.6V with no load and pull down to 10V during starting which is a 400A load. It has dual 600cca bats in which one is new and the other is, well, not. I can test each bat for current, etc but everything I am getting from OEMs is the bats are just fine.

They say 400A on a bat system of 1200cca dropping to 10V is fine. IMO, that is a problem. Further more, the best I can tell, I have a 4ga copper cable from main bat to starter. That cable is seeing .9V drop. The HUGE cable coupling the batts is .25V drop.

So, if my bats are pulling down to 10V and I have .9Vdrop on cable, my starter is seeing near 9V. The truck turns over slow and as any diesel wrench knows, diesels gotta spin to get going. I am not sure that is all my problem but probably some of it...

Any experiences? Anyone willing to go unplug their injection pump and crank for 5sec and see what you get for Vdrop? Current? I am about to push this truck off a cliff....
 
Have you checked your grounding cable connections? What about upgrading the size of cables?

Has it ever failed to start, or does it just not crank fast enough for you?
 
IME most cranking trouble is from poor connections, not skinny cables. Solder all lugs. Measure volts while cranking at battery terminal on solenoid, also at starter terminal on solenoid, as contacts can go bad inside solenoid, too. There should be a mfr's spec on cranking speed, too.
 
Problem is the truck stumbles along and blows smoke for several seconds and usually takes 2-4 start attempts. Once running, the truck is fine. Cold starts are the problem. Glow plug system is guaranteed to be working perfectly. I really think the worn (reduced compression) engine coupled with slow cranking is giving some starting fits.

Well, lets just say I want to fix the cranking issue before I start really tearing into it. These trucks are known for a long list of IP and FSD issues but all testing has proved both of them fine at this point.
 
OH, forgot I had a vid. this was taken cold BUT with the coolant temo sensor unplugged which forces max fuel and IP pump timing. It started up better but you can still see what I am chasing. Note that it dies for no reason and failed to restart immediately. I had a junk FSD plugged in and it decided it was done for the day. When cranking with no smoke puffs, there is no fuel being injected..

http://www.youtube.com/watch?v=P541tZHUKto
 
How cold is it there? 12.6 volts is kinda low for batteries that are fully charged. A warm day and they should be sitting nearer 13.1 or more.
 
so,i had a friend with a gm diesel truck,replace batteries,cables,ecu and so on.was always hard starting-i said put in a starter.he had the engine rebuilt.i said put in a starter.he had the turbo rebuilt,i said put in a starter.he kept probing for info,as i was a red seal licenced automotive technician,he would not give my starter advice any merit,i politely told him to piss off and quit bothering me if he didnt want to put in a starter.
after almost a year,thousands of dollars,he put in a 250 dollar starter....guess what-it fixed the long cranking carryin on sputtering and starting.the computer would lose its mind during cranking due to low voltage.
just my .02 worth

Frank
 
Yep, I am never above installing a starter but before I do, I want to make sure the batts and cables are up to snuff. I know what you are saying about ECM issues. If the bats get too low during cranking, it will start but will stick in 2nd gear and I have to shut truck off and do a restart to get my trans back. Talk about scary the first time that happened.

I already replaced the starter once with a used one because I too had my finger pointed at the starter. 2 of the 4 brushes were gondie...

What I found moments ago I either caused or is on the right track to finding my issue. There is a water purge valve that hooks to the fuel filter housing somewhere. The line was split where it connected to the valve thus leaking fuel and might have been a fuel priming issue. Guess I will know tomorrow AM...
 
viper said:
OH, forgot I had a vid. this was taken cold BUT with the coolant temo sensor unplugged which forces max fuel and IP pump timing. It started up better but you can still see what I am chasing. Note that it dies for no reason and failed to restart immediately. I had a junk FSD plugged in and it decided it was done for the day. When cranking with no smoke puffs, there is no fuel being injected..

SDV 1157 - YouTube
Click to expand...

I'd say the starter is doing exactly what it's sposed to be doing...
But the engine sure sounds like crap right after it finally starts and never sounds "normal". Find out why...

Every diesel I ever had in cars and other is boats would start before I could get my finger off the start button and none of that long cranking on any of them... no smoke on startup and the only smoke it would make is if you goosed the throttle before it warmed up which you're not sposed to do anyway... why do you do that?.. want to ruin the engine fast??
 
Gary, you would lose count in 5 sec of how many people get in a diesel truck cold and go like the wind.

The truck was only being revved to half of redline.
 
viper said:
Gary, you would lose count in 5 sec of how many people get in a diesel truck cold and go like the wind.

The truck was only being revved to half of redline.
Click to expand...

YOU are abusing that engine and it sounds like it...I dont care if that was 1/2 or 1/4 the way to redline...
if you did that to my truck, you'd be fired in a New York second.
 
viper said:
Glad I don't work for you Gary. How do YOU break in cams anyway?
Click to expand...

Cams are precision ground and do not need BREAKING IN.... and If that's what you are doing then that POS TRUCK and it's LOUZZY ENGINE should be under a guarantee of some sort... TAKE IT BACK for service. It's clear you have no knowledge of how to fix it.
 
Whilst starting is clearly a issue how is the engine generally? Well maintained? Good compression (have you tested it?)? Clean air filter? Never hurts to rule out the basics and that white smoke on start up is not good. What ever way you cut it that looks like unburnt fuel leaving the engine and that should not be happening regardless of starter motor speed.

As to the engine, yeah does not sound good but then you tube does funny things to sound clips due to the compression they use.
 
the 6.5 sounds like shit from day one and run close to how they sound. This one has over 300K on the clock. Comp is still 375. Certainly not a new truck but I needed one I did not need to worry about. It has a sticky intake valve but other than that, it ain't too bad. I think I have to problem found and fixed but we will know more tomorrow.

Typical Gary throwing bullshit in the air with a shovel. I just hope someday someone will be born that is that smart... I would LOVE to dice with you ANY day on wrenching but it does not make any difference, Gary will always be smarter...
 
How long is that #4 cable? I'd want at least a #2 for that kind of load. It does crank slow to my ear, but the way it runs means there's more involved and whatever that is is contributing to the starting problem.
 
adama said:
How cold is it there? 12.6 volts is kinda low for batteries that are fully charged. A warm day and they should be sitting nearer 13.1 or more.
Click to expand...

Dunno where you get your info, but that is just plain wrong.

An AGM or GEL battery might reach 12.9-13.0v when brand new and fully charged, but a standard flooded lead-acid can be expected to do no better than about 12.8v when new.

Since we are talking about an old battery here (one old + one new = lowest common denominator) then 12.6v is about what I'd expect for an battery bank with some age on it. Either way, should be enough to get the engine cranking.

#4 wire is definitely suspect if you really are pulling 400A, as is a .25v drop across the jumper cable. I'd want to see 1-0 at least with that kind of cranking amps.

Conceivably the starter has a bad winding and is pulling too many amps even though it still manages to turn the engine over.
 
gnorbury said:
Dunno where you get your info, but that is just plain wrong.

An AGM or GEL battery might reach 12.9-13.0v when brand new and fully charged, but a standard flooded lead-acid can be expected to do no better than about 12.8v when new.

Since we are talking about an old battery here (one old + one new = lowest common denominator) then 12.6v is about what I'd expect for an battery bank with some age on it. Either way, should be enough to get the engine cranking.

#4 wire is definitely suspect if you really are pulling 400A, as is a .25v drop across the jumper cable. I'd want to see 1-0 at least with that kind of cranking amps.

Conceivably the starter has a bad winding and is pulling too many amps even though it still manages to turn the engine over.
Click to expand...

I think he might have been quoting surface charge numbers which will hover in the 13s after getting some charge.

I will have to go check my cable numbers again. I did fix a small issue with the ground cable but everyone has been tied up to get an extra hand on the pos cable.
 
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