Hey guys...

My brother has a 1999 Dodge Ram 1500 4x4 that I'm trying to help him fix. It's down on power and not shifting that well. I'm a pretty good mechanic, so I've got a few ideas but I don't know what the usual suspects would be on this truck.

It's got a 5.2L V-8 and it had a vaccum leak. I thought that might be the problem because those can cause power losses. One of the vaccum lines that goes from the manifold to the transfer case (the white one) was completely burnt through. I changed it out and the 4x4 axle and vents started working again but the power loss was still there. I thought maybe it was a fuel filter but that's an in-tank deal and usually don't go bad.

Here are the ideas I had:

Clogged Cat Converter (the truck has almost 180k miles)
Transmission needs service (it has a lot of trouble shifting but the engine sounds okay)
Bad gear ratio (truck is lifted and is a 1500 4x4, I've heard that these axles might have trouble pushing larger tires)

I'm open to other ideas, too...

 

Has the plenum been fixed? Those tend to go bad on these trucks.

 

No idea if it's been changed before.

Could be it, though...

How do you diagnose? Spray carb/choke cleaner around the intake runners and look for smoke and/or change in idle?

 

There are several ways to check for the belly pan leak....

Pull the air cleaner, get a bright light and look through the throttle body into the manifold. If you see oil pooled up in there you might have a leak. This could also be a leaking PCV valve so don't rely completely on this check.

There's a TSB procedure to check for a failed belly pan gasket which involves a vacuum gauge, pulling the PCV breather tube and checking for vacuum pressure.

My personal favorite is to get the motor up to operating temp, pull the oil cap from the valve cover and put a piece of paper over the hole. If the paper is held against the oil fill hole you have a vacuum leak from the belly pan. Works every time....

 

Thanks man...

I'll give the oil cap trick a try.

I'd think that if this was the issue, the truck might smoke, or idle rough, or something else in addition to just the power loss. Is that typical of this issue, or are there other symptoms that are clues to this diagnosis?

 

I've seen rough idle, burning oil, fouled plugs and loss of power. The belly pan may not be the problem....but it's certainly the most suspect of the potential problems.

If you have access to a Scangauge or AutoTap you can run real time diagnostics on the truck....check for vac leaks, idle, etc... This may save you some time and money.

 

Thanks for the tips, man! Much appreciated..

As far as the gaskets go, I've been reading that the APS kits are the preferred replacement parts. Is that still the consensus, or has that changed?


...just hit me; has this been documented somewhere else on here? I don't want to keep bumping it up to the top if I can go to a "Sticky" thread, or something. I don't want to keep pestering you all.

 

There's a Hughes Plenum Kit that a lot of the guys use to permanently fix the issue. They run about $80 and should come with everything... if this is your problem. I'm ordering one and throwing it on this fall as I too think I have the belly pan leak. I have weak power below 3000rpm and oil in the intake. Never heard of the paper towel over the oil cap thing before. I'll do that before I buy the kit.

 

Keep in mind, if the PCV system is operating as it should, and is still hooked up when you run that test, it will hold the paper there every time. Well, unless your rings are REALLY bad......

 

Thanks for catching my omission that's in the mental check list but didn't make it to the fingers. Disconnect the PCV system first. Hook it back up when done.