de-fueling issue after 1/2 hr running
 

Hi all,

98.5 24v with the following issue(s). During my daily commute I've been experiencing the same issue every day. About 30 minutes into the drive on the way in I start to experience what I would call a slight de-fueling. The truck feels similar to hitting a head wind. It is fairly sporadic, but exists. On the way home, again about 30 minutes into the drive, the truck starts to feel like it is running out of fuel. The effect is much more noticeable then on the way in. (I'm driving around 64 mph.) If I step on the pedal it goes away, but once back to cruising speed it defuels again.

I changed the fuel filter last Wednesday and also removed the MAP sensor to check condition. I gave the MAP sesor a shot of carb cleaner although it didn't look dirty. Truck ran fine both Thursday and Friday. On Sunday I installed a fuel pressure gauge. Monday the issue started to return. Today it is back in full force. Pressure gauge shows 19-20 @ idle and never gets to under 10 under acceleration. Anyone have similar issue/suggested fix? I am getting no codes from my code reader. Thanks.

I've also noticed when I hit a bump around that thirty minute mark or so, sometimes the rpms will rev up for a second, then return to normal. I assume this might be a lose wire. Anyone know where to look?

Thanks for your help!

Have you ever done any trans service? Only reason i ask is the "free rev" thing. Thats kinda weird. Where are you measuring fuel pressure at?

I bought the truck with 125K on it. Previous owner said Trans (auto) was rebuilt. Carfax verified a trans "service" @ 107K. The truck has 175K on it now. The trans thing IS wierd. It isn't like a slip or anything. I hit a bump and the tach jumps 2 points for a sec, then back to normal.

I am reading fuel pressure from the clean(inside) port on filter canister. It appears good and is not fluctuating when experiencing the problem.

Other info about the truck: 3500 quad cab 4x4. 4 in exhaust, K/n air filter. Was running an Edge (whatever the basic box is called) and took it out last week.

Sounds like your VP44 injection pump.

Now why does everything around here sound like the VP44 injector pump? Surely someone out there's going to give me some good news?

Seriously, if the VP was on it's way out, what would be some other symptoms? If it was going down, would it respond to light acceleration, or would it continue to feel like it was running out of fuel? And any clue to the consistency of being 30 minutes into my commute and the fact that it is much worse on the way home than on the way to work?

Is there a test to be sure it is VP44?

Thanks for your help.

I was thinking the same thing... An issue after running steady throttle but not when accelerating, or starting... I cant speculate though because i don't know JACK about the VP44, although i NEED to learn!

Yeah, I don't know Jack about the VP either, but I am going to know Jack about Jack Daniels if I can't get this figured out soon. I'm leaning toward a wiring/map sensor issue for two reasons: 1) It was the only other thing I touched when changing the fuel filter and it seemed to fix it, although it was briefly. 2) I'm trying to be optimistic that I don't need to throw another stack of cash at this thing.

I think I just need some guidance on some tests I can do. I want to be sure a part is bad before I replace it.