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Slight popping/sputtering sound


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From around 1700rpm on up there is a slight popping/sputtering sound while accelerating from 1/2 throttle on up and it gets worse with a load. The first thing I did was install a fuel pressure gauge to help diagnose/ eliminate possible causes. The results are as follows:

 


Idle: 22psi
2500 RPM (no load): 38psi
Pressure never drops below 20psi while doing a WOT run.

This is the truck's current setup:

*100 plate and AFC full forward. 
*Stock injectors that were cleaned, pop tested, and shimmed a couple years ago. 
*1st Gen air filter (was on the truck when I bought it, been meaning to do a BHAF). 
*Stock HX35 in good working order, minor amount of play and zero contact with housing. Will boost to 38+ psi but keep it at 32psi and under. 
*Timing set to 16.5 degrees.
*Valves adjusted to spec. 
*4 1/2" DP, 5" the rest of the way including stacks.
*Built 47RE
*4.10 gears. 
*35/12.50R16 tires. 

There are no leaks anywhere on the pump or from the injector lines. The truck starts fine, hot or cold, and idles smoothly. I'm starting to suspect the governor springs because the truck falls on it's face right around 2k RPM. When I say "it falls on it's face" I mean this:

Imagine your taking off from a dead stop and you floor it, then at about 50mph (for example) you let off the throttle to maintain speed. That's what happens around 2k rpm, except I'm not letting off the throttle. 

 

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Air in the fuel? Hook up a clear line and loop it on the windshield and see if there is any air or foam being generated. I'm fighting that problem now on the 1995 in my yard. Losing prime and rough starting. What I've done is grease the fittings on the AirDog and it made a temporary improvement.

Edited by Mopar1973Man
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Governor springs will cause what you describe with the de-fueling.  But what I hear in the video sounds like a typical 12 valve with a free-flowing exhaust.  You can look at exhaust leaks around the manifold and turbo connections.  If you put the throttle to the floor, how many cranks does it take to start?

 

Mike, The red line in this picture is a common point for air to get in when it's sitting.

 

screenshot_1.png

 

 

Edited by Cowboy
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With the pedal to the floor it only takes half a crank before it pops off. 

Just got back from the local stealership. Went to have my PCM flashed so I could use a lockup switch but was told they can't flash it, after charging me $60 :mad:

Edited by The_Hammer
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With you still having stock injectors I would say its sucking air somewhere, most common placed are the fuel heater and the formed hose going from the fuel heater to the lift pump and the steel tube going into the sender on top of the fuel tank.

 

I had a similar problem to what you are having only mine would only do it in free rev and 1st gear, once it got some load it would clear up. For me it started after I went to 5x.014 (roughly 100% over stock) injectors and after some hard thinking about how everything works etc. I decided it was due to lack of fuel after I eliminated any possibility of air in the system, so I put bigger delivery valves in my pump and that was the end of the problem for me.

Edited by bjytech
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  • 4 weeks later...

Forgot to update this.

First, I do NOT have a first gen air filter, I have no idea what it's actually for but it does work. Second, even though the filter looked ok I went ahead and replaced it with great results. The truck runs better and pulls hard right up to 2000 rpm, then falls on it's face. Next upgrade will be a 4k gsk and 60lb valve springs.

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