MrDcomby

A buddy was drivin my truck while I was out of town.. At about 60 he was getting fluctuating rail pressure, she surged and dropped to 0 And died.. First thing, I went to the fuel filter, put a new one in....
this was 5 months ago..
started idling normal but when you get going and get some pressure she jumped from 6000psi to 25,000.. got a brand new rail with RPS and PRV, Runs better but still not stable.. Idles good, but while cruising at 35 you get into it rail pressure jumps starting from 15k-20k then all over the place...

the last month:
the truck runs fine cold, she doesnt give me a hard start, smoke or anything, and no codes... you could kick the truck sideways when shes cold, and idles good.. after a few mins of running after it warms up, the truck starts bucking on me, steady speed or accelerating.. i cant get the truck over 40 mph.. if i stay a steady 40mph the truck seems like a miss but its intermittent, if i come to a stop and go to take off again i get back bucking to the point of having to let off the accelerator to keep it running.. after this problem i park and continue to idle the truck will intermittently stumble on itself at idle with RPM drop like its a fuel delivery problem, i cracked the wingnut on the airdog at idle and tightened it back up and within a min or 2 the truck would kill itself and i would get a hard start, if the truck dies out at a stop sign it takes a little bit to get it started but problems persist after i start it back up

List of items i have done to try to fix the problem:
x2 fuel filter and water seperator
x4 motors from josh at airdog
x2 wiring harnesses from josh at airdog
Sinister tank fuel sump
Industrial Injection 33% over CP3
New Rail with RPS and PRV
re-tourqed injector feed tubes to 37ft-lbs
new ECM
2 brand new batteries

I got a new Fuel Pressure gauge in the mail today, i will install it tonight and see what pressures im getting cold and warm, idle and while driving and see where i get... this thing is breaking me down and winning the battle, ive asked around the cummins forum and talked to multiple diesel 'experts' at Alligator, XDP, ECD, Thouroghbred, and even friends.. maybe someone else has more input, any help would be appriciated

Thanks, MrDcomby

MrDcomby

the fuel pressure gauge is on, but it only reads on initial start up when you can hear the airdog pumping.. you can see the pressure and when the noise goes away so does the pressure within a few seconds.. the truck will start but the pressure gauge will be sitting on 0.. its in line about a foot away from the cp3, could this possibly be a lift pump or injector/connector tube problem?

StealthDiesel

1st off, stop throwing parts at the problem.

How are you monitoring rail pressure?


If you don't have at least 5psi input to your CP3 while the engine is running, you need to fix that before anything else.

MrDcomby

Hard not to throw parts when your on the edge of throwing tools with no direction..

i have an auto meter rail pressure gauge. Delton at ECD said it sounds like a low end pressure problem since the gauge isnt reading right so this weekend or early next week im going to be checking the suction side fittings and doing a bucket test

StealthDiesel

Throwing parts or tools never solves anything. A logical, systematic approach to problems will always yield better results.

Install the low side fuel pressure gauge and that will tell you what your next step is.
If you can hear that the Air Dog lift motor stops running there is no need to be checking the suction side fittings or doing a bucket test or anything like that.

For anyone else reading this, this is an example that shows gauges are well worth it for diagnosing engine issues and will pay off for themselves easily.

Boost gauge, pyro, auto trans temp, a real oil pressure gauge, low side and high side fuel pressure gauges, all worth it.

MrDcomby

I have a low side pressure gauge about a foot from the cp3.. The gauge as previously stated will go up while priming and right after the truck is started the gauge will slowly drop to zero and sit there

The airdog seems to still be running but my trucks so d**n loud that its hard to tell.. I'm just stuck on what the next step should be

StealthDiesel

1. What are the actual readings on the low side fuel pressure gauge?

2. If you have any doubts about the low side fuel pressure gauge, temporarily install a mechanical fuel pressure gauge.

3. If the low side fuel pressure is going to zero after the truck starts, check for 12V directly at the Airdog lift pump.

4. Your voltmeter will tell you if you have a voltage issue or a lift pump issue.

MrDcomby

Here's the deal after checking this morning.. 11.09 volts until the wait to start light kicks off.. When it kicks off she jumps up to 11.95-11.97 then with the truck started jumps from 11.80-15.02 at its highest and everywhere inbetween..

The low pressure gauge reads 24 psi at prime and slowly drops to 0 after being started or if waiting long enough after wait to start goes out