Camp

I'm stumped and hoping you guys have some ideas. I've got a '95 12V with an NV4500 behind it. I've had the problem since I got the truck about a year ago. The truck was stock when I got it and nothing we have changed has changed the flutter at all. Basically, above 2500 rpm, in 1st through 3rd gear, the truck pulls but you can hear it flutter. Originally, the truck had 4.10 gears and we set the timing at 17 degrees. We have put a towing cam in it, ported and polished the head, 3000 GSK, changed the turbo to a HX35/HX40 hybrid turbo, 4" exhaust from Summit, replaced the stock injectors with a fresh set of rebuilt stock injectors, run both a number 10 and number 100 plate in it, put the ATS exhaust and intake manifold on it, adjusted the valves multiple times, pulled the timing back to 15 degrees, and installed 3.55 gears. No changes in the flutter. The mods were not all done at the same time.

The truck kind of flattens out on the top end once it starts to flutter but, you don't hear the flutter in 4th and 5th gear where it would see more load on the engine due to the higher gear.

I do not have a fuel pressure gauge on it so, I cannot current verify that there are no issues with the injection pump but, there are no air or fuel leaks and we have checked multiple times. Smoke does not change when it goes to fluttering but, this truck does not have heavy smoke at any point in the rpm. The smoke it will produce is closer to a blue than a black and is very light. My last truck, '04.5 CR, would smoke like a coal train so, I'm fairly familiar with what it should look like with a lot of fuel.

Any ideas or suggestions on what this might be?

Rare1

It might be nothing. You have gone the second mile with your tuning. I would feel proud to drive that truck. It is perfect. What bothers me is why anybody feels the need to rev to 2500 rpm under light load, max torque is at 1500 rpm. No flutter in higher gears. My guess is you feel the gear teeth bouncing from front to back.

gorms

I'd say throw at least a temp fuel pressure gauge.

Camp

I do need to throw a fuel pressure gauge at it. I'm wondering if it is having any trouble with the delivery valves, causing this flutter. It is not gear teeth making the noise.

The truck is really not all that fast, the high rpm happens when I have to pull out in traffic and get on it. As for max torque at 1500 rpm, with the current set up, lots of go pedal anywhere below 1500 rpm chugs and/or barks the turbo.

After we installed the cam, done at the same time the head was ported and polished, we put it back together with the same fuel plate and waste gate settings we had before hand. We did add the ATS intake horn at the same time too. The truck had unreal throttle response and was spiking the turbo at just about any change in throttle. It would also smoke upon letting the clutch out, no throttle. We pulled the plate and the AFC housing back and have moved it around a few times now so that when I'm climbing the mountain west of Denver, I can pretty much accelerate at any speed I want, usually running around 80, never getting above 1200 deg. Currently, at constant cruising speed of 80 mph, I'm at about 2200 rpm and 975 degrees, pre turbo and 26 lbs of boost. I haven't towed since we installed teh 3.55 gears but, with the current plate setting and 4.10's, I could tow around 6500lbs across the mountains from Denver to Vail running about any speed I wanted without heat issues. Currently the truck pulls around 32psi climbing, loaded.

I suppose I should mention, this truck only gets around 16 mpg, with 4.10's or 3.55's on the current set up.

infidel

Don't even consider other problems till you check the FP or at least clean the prefilter.
Instructions> http://www.cumminsforum.com/forum/94...-12-valve.html

Camp

Thanks, I'll give that a whirl.

sabercat

my 94 does something like that, like when I'm in 1st gear, plowing my drive, but after a bit it does'nt do it as bad, if at all, I thought it was not fully warmed up, does it in the summer also.