A couple weeks ago, after running for about 3 min., my truck started idling weird (really low and now really high sometimes) and when you get to about 40-50mph, it feels like it has no power and if you use more gas, it does nothing but accelerate really slow. Then, if you let off the gas the revs drop waay low and sometimes it dies out. I got the CEL checked today and it was p0108, MAP sensor voltage high. I did a search and on one thread someone said it might be caused by the blown plenum. I have the kit, but my dad said he doesnt want to mess with it until we figure out this problem. Should it go away if we go ahead and fix the plenum?

 

Plenum should be fixed either way. A blown plenum can cause this issues you have. Reset the code, fix the plenum, an drive it a while see if it comes back.

 

Yeah, the trouble is finding time to do it. Would it still be okay to drive until i get a chance to do it though?

 

I wouldn't expect a blown plenum gasket to result in P0108.

The symptoms you describe are perfectly consistent with a vacuum leak. If it's one of the intake manifold gaskets that is leaking, then fixing the plenum might be the magic that cures it. The hot ticket is to buckle down and find the leak rather than replacing things *****-nilly -- you could conceivably introduce a second problem that could make things way too interesting.

 

This is the thread that mentions it may be from the plenum leak:https://dodgeforum.com/forum/2nd-gen...ems-p0108.html . But if its a vacuum leak, would all the new gaskets in the kit take care of it?

 

That guy had different symptoms, multiple leaks, at least at the plenum gasket and the EVAP canister, and maybe in who knows how many of the vacuum lines he replaced. It'd be illogical to pick just one of those many parts and call it the root cause.

Not if there's a big vacuum leak somewhere else. There's just no telling from where I sit... Can you tell me where the lighter I lost in my truck got off to?

Were it mine, I'd fall back to basic, disciplined troubleshooting. What you're looking for is a gross leak, so it should be easily enough found. I'd start with the things that are very likely and easily isolated, like disconnecting and plugging the vacuum sources for the EVAP system and testing. If doing that results in immediate improvement, you know that the next step is to isolate the leak in the EVAP system (or whatever other system you've isolated). If it doesn't result in improvement, then you put everything right back where it belongs and continue seeking the source of the gross leak. Never change more than one thing at a time.

If you haven't got it yet, grab the 2001 factory service manual from the FAQ/DIY section, and in particular read up on the Evaporative Emissions system. It should then become clear why I'm leaning in that direction. It's a few minutes into operation that the problem occurs, right? That's right around the window of time in which the PCM starts dithering the purge valve. So... what happens if you disconnect the electrical connector from the purge solenoid so it can't dither the valve? Find out.

If the three minutes you report as being the time after startup at which things go wrong is actually closer to one minute, then the upstream oxygen sensor is implicated and all of the above becomes moot. For that, I'd be looking at the sensor, the plenum gasket, and the catalytic converter. And looking quick, too, before that problem cascades into bank breaking failure.

The thing that sticks in my head is this: A plenum gasket that's so far gone that it presents a gross vacuum leak doesn't usually wait a few minutes to start leaking. That gasket might be shot, and it might be throwing oil into the combustion chambers, icking up the intake valves and clogging the catalytic converter, but it's still unlikely to consistently wait three minutes after startup to start leaking.

I wouldn't be driving the thing while it's in this broken state. There's no sense risking that a smallish problem will grow into a great big expensive one. Lots of guys, for example, have found out the hard way that driving around with a blown plenum gasket leads to catalytic converter clogging, which leads to cylinder head cracks.

 

Unreg. did you look under the seat for your lighter? Thats where I usually find mine.
JK . Thats alot of good info. Do you think we could make a flow chart for common problems?

 

I looked under the seats, in the glove box, in the center seatback, between the seats, behind and inside the instrument panel and its ductwork a couple weekends back... my favorite black Zippo is in the truck somewhere, but in none of those places.

Sure, go for it and post it up here when you're done. I'd love to have one myself.

 

The 3 min. was just the first time it started doing it, now its all the time from start-up till i shut her off. And there was some o2 sensor code, but I figured it was just from the gutted cat. I cant remember what code it was though.
It looks like I should have a weekend free to fix her up pretty soon and can probably do without her till then

 

With no delay at all, not even of about a minute? If that's the case, it's time to back up a step and look at the issue in light of this news.

And the cat's gutted, too? Another new dimension. All of these things that are news to me here are relevant, man, and should not be left unsaid!

Gutted cats are usually a sign of a blown plenum gasket in the truck's history. What do you know about that? And it's time to get the codes read again because the oxygen sensor might be failing in a way that's telling us something. Also: How many miles behind that upstream oxygen sensor?

More details about this truck are in order. What (ALL!) about the engine is no longer in factory trim?