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Discussion Starter · #1 ·
I had my son take a 94 12v to have it aligned. They drove it after setting things up,came back made a few adjustments & it would start,but only run maybe 15 seconds & stop. It would restart if you pressed on throttle pedal alittle, but wouldn't idle but 15 seconds.

I have replaced all the incoming fuel lines w/ Vulcan's rubber lines & removed the heater from the pre filter & resealed it w/ Cummins gasket. New lift pump,fuel filter & lines to the tank. When you press the prime button you hear a sound (hiss)& feel it vibrate the line coming from the return check vavle on the inj. pump. I see/feel no leaks from it. I replaced all these things before this happening today. I Have not replace anything on the return side .

After a trailer ride home & sitting less than 1 hour, it now starts & runs even under a load ( in the driveway). The primer still make a sound from near the return line from the pump & going down in the valley of the motor

What is the return check valves function? Could it be allowing fuel to exit the pump & loosing it's prime??

Sorry for the LOOONG post
 

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the 'return check valve' is actually called the 'overflow valve'. Its main purpose is to regulate fuel pressure on the low pressure side of the pump and to prevent the pump and lines from draining while the engine is shut off.

One thing i may note, those early p-7100s are known to warp the barrels and stick the plungers. This can cause everything from weird behavior to intermittent no-starts/stalls.
 

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Why won't my Wife's '96 start crisply like a lot of 12 valves traditionally do? Crank, crank, crank, crank, crank then it mulls to a start and idles fine. If I put my foot into it just a touch it fires up crisply but with excess black smoke out the tail pipe like if I pump the throttle while idleing.
 

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I would change the overflow valve or at least make sure it is sealing. I am sure someone may have one laying around you could try. Last time I bought one they were ~$40. Not real cheap just to try it. Try to tighten it down, maybe mess with it while it is running to see if you can get the hiss to go away.
 

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Oh her truck has 370's, -5 plate, cam, afe intake, 4" diamond eye exhaust, ATS Aroura 3000, Suncoast 47re w/ stock shafts but new everything else
 

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Hard 12v starting

Found leak on #4 injector line coming from the pump and cleaned it and tightend it but problem is still the same.:confused013:
 

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Why won't my Wife's '96 start crisply like a lot of 12 valves traditionally do? Crank, crank, crank, crank, crank then it mulls to a start and idles fine. If I put my foot into it just a touch it fires up crisply but with excess black smoke out the tail pipe like if I pump the throttle while idleing.
your idle is too low. bump it up. i like mine 850-900.
 

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Discussion Starter · #9 ·
Today started truck ideled fine let run for 10 mins took it for a drive was fine came back let idel a little more took it back out and when driving it started to sputter again then it would die. Restart it with use of pedal go for a little bit then die. Any thoughts?
 

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This sounds like the same problem I'm having right now. Does the throttle seem to get stiff/sticky when it starts to act up?
 

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I figured I'd put my version in, LOL. My truck is doing the same thing starts, idles, revs while cold, and then as soon as I get some heat starts missing, no power, pedal gets stiff. I took it to an international truck repair shop, and they tested the injection pump. I guess i need a new one
 

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Discussion Starter · #12 ·
Yes my pedal feels weired when it starts to act up.
 

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I figured I'd put my version in, LOL. My truck is doing the same thing starts, idles, revs while cold, and then as soon as I get some heat starts missing, no power, pedal gets stiff. I took it to an international truck repair shop, and they tested the injection pump. I guess i need a new one
If you're able to... get a 2nd opinion, an IP is pretty expensive and the P7100s aren't prone to failure. It does happen, but lots of times it could be something else... delivery valve, fuel shutdown, etc... and some shops may opt for the expensive part first. Just a caution.

Yes my pedal feels weired when it starts to act up.
Yah, same thing mine has been doing. Haven't figured it out yet, truck's at the shop... towed it the last 80km home the other nite and straight to the shop. In the process of installing a GSK, AFC Spring, and new overflow-valve, so going to check over all of the pump, fuel shutdown, etc... and see if anything shows up. Also replacing all my fuel supply lines, to eliminate all air leaks. Hopefully these fix my problems, and may help me to help you find yours.
 

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I am having the same problem. But mine will surge and start making a knocking sound from the pump after it gets hot. Then dies and will start and run for a few seconds then die. If I pour some ice water on the injector pump it starts and runs great.

It seems like there are a LOT of these same trucks with the same problem.

Could someone tell me the diagnosis of an injector pump going out.

thanks,
Mike
 

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I am having the same problem. But mine will surge and start making a knocking sound from the pump after it gets hot. Then dies and will start and run for a few seconds then die. If I pour some ice water on the injector pump it starts and runs great.

It seems like there are a LOT of these same trucks with the same problem.

Could someone tell me the diagnosis of an injector pump going out.

thanks,
Mike
Yours sounds like mine did before I replaced the IP, never tried pouring water on it but bet it would work.
Replace the injection pump.
Columbus Diesel Supply has the best deal with warranty and a great reputation.
Don't fall for some of the ebay deals, many reported problems.
 

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Did you install the pump yourself or have it done? Is there a how to guide? Mine is getting worse the hotter the outside temp is.

I put a fuel pressure gauge on and it is between 15-17 at idle in gear and 25 no load at 2000 rpm. The truck starts a pecking sound from the pump and you have to keep your foot into it to keep it running. Then the surging then it dies and sits until the pump cools down.
 

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Did you install the pump yourself or have it done? Is there a how to guide?
I did it myself using the factory service manual.
You really should have one if you want to do your own work, pays for itself on the first repair.
Only $59 here www.techauthority.com
Your's sounds exactly like mine did. The whole reason I installed a FP gauge 12 years ago was to isolate the problem. FP always stayed good when the truck was acting up, only thing left was the IP.

I limped along for several years by keeping the tank more than half full all the time.
More fuel provides more cooling for the pump.
 

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i think mines going too. At 1200 rpms the motor runs rough, so say when it shifts into 4th and bogs down to around 1200 rpms the whole truck bucks/shutters. My idle was sounding a little weird yesterday too.

i got my injectors and return and feed lines tested and they checked out. The pumps gotta be going.

any other sugeestions before i drop 1500 on my 3 week old truck?
 

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Install a dash mounted FP gauge so you can watch the delivery pressure while it's screwing up. Might pay for itself plus it's good to have anyway.
 

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Well your probably experiencing the same prob. then, Mine got to the point that I had to rip it off and replace it. I also put a new lift pump on just so I know it's all good, piece of mind for 80.00.
 
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