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A little expert tuning help needed

983 views 11 replies 6 participants last post by  atasirudy 
#1 ·
I have a 94 2500 4x4 auto. I installed a #10 plate, 3000k springs and boost elbow. Other wise it is stock. I have pyro, fuel pressure and boost gauge.
Let me say I am not looking for a real fast truck, I just want to enter an expressway without getting run over. I want the power only when I need it that is all. When I first tried it out it ran great and pulled hard up to 3000 rpms. It has good fuel pressure usually around 17psi and the pyro don't go over 1100, the boost goes up to 30lbs. and it is not putting out any smoke, and I prefer for it not to smoke if possible. It has new fuel filter, new rubber fuel lines and prefilter has been cleaned. Today when I got in it there was a kind of flutter or miss and the power seemed to go away, there was a very slow rpm increase and it seemed to be holding back when it reached around 2200 rpms. What do you think the problem might be?

Thanks for any help
RH
 
#3 ·
Air in fuel lines maybe. Crack each injector open for at least 5 seconds each and tighten it up. Do this for every injector and then take it for a spin
 
#5 ·
I never bleed injector lines after I've had them off. The longest it's ever taken my engine to smooth out after starting is 10 seconds or so.

My guess without more information would be a sudden onset of boost leak or an air leak in the fuel supply lines. I mean no insult here, but how much fuel do you have in your tank? Less than 1/4?
 
#6 ·
My fuel tank is 3/4 full. I replaced the rubber fuel lines because it had a miss upon starting and they must have been leaking air in because it cured the miss. I also sealed the areas on the preheater electrical connections that could possibly be drawing air. I have not pulled the tank to check the lines there.
 
#7 ·
My fuel tank is 3/4 full. I replaced the rubber fuel lines because it had a miss upon starting and they must have been leaking air in because it cured the miss. I also sealed the areas on the preheater electrical connections that could possibly be drawing air. I have not pulled the tank to check the lines there.
I highly recommend deleting the preheater entirely. Take the prefilter off, then the heater puck either unscrews or slides off, then stick an allen wrench in the stud (8 or 10mm I believe) and unscrew it. Put the prefilter back on, prime, and you're done.

I also recommend pressurizing the tank (no more than 10psi). A rag on a blow gun stuck in the filler neck is all you need. This will force fuel out any leaks that would be drawing in air when the engine is running.

If you end up dropping the tank, a scissor style transmission jack and a couple 2x4s are worth their weight in gold. You may consider raising the bed if you don't have a goose or 5th wheel. Remove the front 6 bolts, loosen the rear 2, and lift from the front.
 
#8 ·
17 is the low side of idle pressure spec. Cummins' pressure specs are 17-22 psi at idle, 25-35 at 2500 rpm no load. Pressure should never drop below 15 psi under load for extended periods. You can check to see if you have an OFV problem or a lift pump problem by briefly clamping the fuel return line to the filter. If the pressure spikes you need an OFV, if there isn't a spike in pressure the lift pump is failing. I'm constantly amazed by the "air in the fuel lines" diagnosis.:doh::hehe:, however, deleting the fuel heater is good advice.
 
#9 ·
If anything is ever wrong with a p7100's its air in the fuel lines GAmes, you didn't know that? Lol
 
#12 ·
That test already proved that the ofv will fix the problem.
 
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