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Discussion Starter · #1 ·
I have a 93 dakota, 2WD. The issue(s) I seem to be having are specifically after I've parked it at random times it likes to scavenge, Some days more severe than others. It will also idle at around 1k rpm to 1500 rpm and hold steady, Sometimes blipping the throttle takes it away and others it just remains high. And seems to be scavenging at lower rpms while driving, Below 2k rpm mostly. I have watched videos, Read forums, and can't seem to find my specific issue. I have replaced the TPS, MAP sensor, checked and fixed a part of my vacuum line, checked all hoses, breathers to no avail. There is definitely something going stupid and I dread electrical but if that's something I need to check then so be it. Any recommendations? My next buys are going to be a nee EGR valve and IAC as everything seems to be original under the hood for the most part.
 

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What do you mean by "scavaging"? This is the first I've heard of that save as an effect of the exhaust tuning.

RwP
 

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Discussion Starter · #3 ·
What do you mean by "scavaging"? This is the first I've heard of that save as an effect of the exhaust tuning.

RwP
The rpm will flucuate between the regular idle speed and 1k rpm, I know there is a different and probably better term for it but I can't think of it right off hand. It doesn't do it all the time, But after driving for any amount of time seems to agitate it.
 

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Discussion Starter · #4 ·
The rpm will flucuate between the regular idle speed and 1k rpm, I know there is a different and probably better term for it but I can't think of it right off hand. It doesn't do it all the time, But after driving for any amount of time seems to agitate it.
 

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The rpm will flucuate between the regular idle speed and 1k rpm, I know there is a different and probably better term for it but I can't think of it right off hand. It doesn't do it all the time, But after driving for any amount of time seems to agitate it.
It's hunting due to a vacuum leak (usually).

Have you checked the plenum gasket on it? That's a common failure in the Magnum 3.9/5.2/5.9 motors.

And the term is "hunting" usually; it's hunting a stable idle.

RwP
 

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Discussion Starter · #6 ·
for ease of myself before I confuse myself and everyone else, It revs up and down between idle and 1k with no throttle input, as I said sometimes it seems to be at random but happens more often then not. After being driven any amount kf time it agitates it or so it seems.
 

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After reading Ralph's reply, you could probably try spraying water or carb cleaner around the base of the intake manifold with the engine running. If your plenum gasket was leaking, a water spray should make the idle drop off while carb cleaner should make the idle increase. I suppose a water spray should be recommended as I guess it would be safer.
 

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for ease of myself before I confuse myself and everyone else, It revs up and down between idle and 1k with no throttle input, as I said sometimes it seems to be at random but happens more often then not. After being driven any amount kf time it agitates it or so it seems.
Yep, that's hunting.

With the motor OFF, remove the air cleaner cap, then open the throttle body and look down into the plenum chamber.

If it's wet oily, your plenum gasket is blown.

Other things are vacuum lines (ALL of them!), the PCV valve and lines, and even the EGR valve possible.

But, TBH, vacuum lines and plenum gasket are the most common failures.

RwP
 

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I guess I didn't have an accurate picture in my mind's eye of the plenum pan on the 3.9/5.2/5.9 engines. Basically it is what is referred to as the "valley pan" on other engines?

So I took a look in my (unfortunately still) Haynes & also on Rock


and I guess what happens when the gasket leaks is that the vacuum leak is not from the outside but from the crankcase/lifter valley.

Just two (probably stupid questions) on that: as long as the intake port gaskets are not leaking . . . ?

And why not put a gasket on both sides of the plenum pan?
 

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Discussion Starter · #10 ·
I guess I didn't have an accurate picture in my mind's eye of the plenum pan on the 3.9/5.2/5.9 engines. Basically it is what is referred to as the "valley pan" on other engines?

So I took a look in my (unfortunately still) Haynes & also on Rock


and I guess what happens when the gasket leaks is that the vacuum leak is not from the outside but from the crankcase/lifter valley.

Just two (probably stupid questions) on that: as long as the intake port gaskets are not leaking . . . ?

And why not put a gasket on both sides of the plenum pan?
Thank you for your knowledge, I have yet to be able to take a look at it with work but that's kind of what I was thinking as well was plenum gasket. Idk why they decided that would be the best design but I think someone was smoking something that wasn't cigarettes lol.
 

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Discussion Starter · #11 ·
Yep, that's hunting.

With the motor OFF, remove the air cleaner cap, then open the throttle body and look down into the plenum chamber.

If it's wet oily, your plenum gasket is blown.

Other things are vacuum lines (ALL of them!), the PCV valve and lines, and even the EGR valve possible.

But, TBH, vacuum lines and plenum gasket are the most common failures.

RwP
Ahhh hunting, Thank you! I'll have a look when I get back to the house. Thank you for the help!
 

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I guess I didn't have an accurate picture in my mind's eye of the plenum pan on the 3.9/5.2/5.9 engines. Basically it is what is referred to as the "valley pan" on other engines?
It's not a valley pan.

It's the bottom of the intake.

Chrysler did a 2-part intake instead of a one-part casting to make it easier to machine the inside of the casting.

RwP
 

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It's not a valley pan.

It's the bottom of the intake.

Chrysler did a 2-part intake instead of a one-part casting to make it easier to machine the inside of the casting.

RwP
Thanks, Ralph.
Yeah, last night I was still thinking I wasn't quite seeing the big picture quite right on that; so being as this may apply to me some day, I watched a pretty good video and now it became clear to me.
To get sound from my computer I have to screw around a little bit more than I felt like doing last night, so if the Youtuber that made the video talked about it, I didn't hear it, but is there a recommended replacement gasket for that? One that holds up better than apparently OEM does?
 

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... is there a recommended replacement gasket for that? One that holds up better than apparently OEM does?
Not so much a recommended gasket, but two things you can do.

1) Take the factory bolts, hit the tip and take off a fraction (say 1/32" or so), and reassemble with a good gasket (Fel-Pro or Mahle seem to be good ones).

2) Pick up the Hughes (or a competitor's!) aluminum plate and gasket.

The problem is two fold.

1) Aluminum and steel expand and contract at different rates. But the total difference isn't very much.

2) The bolts that Mother Mopar used are JUST perfectly the right size; so when the gasket gets older, it starts to gap. And you torque them against the bottom of the bolt hole, not the clamping force.

RwP
 

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Thanks, Ralph!
Between you and Old Marine I learn a thing or two every day.

After reading a couple more articles related to this subject, I am getting that it is not IF it start leaking (& sucking vacuum) but WHEN.
 

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Thanks, Ralph!
Between you and Old Marine I learn a thing or two every day.

After reading a couple more articles related to this subject, I am getting that it is not IF it start leaking (& sucking vacuum) but WHEN.
Pretty much, yes.

RwP
 

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Pretty much, yes.

RwP
I live up in the Rust Belt & the Salt Season will soon be here. I don't drive my Dak during the Salt season, so I think I may go proactive this winter & fix it before it breaks.
I quote you,
"2) Pick up the Hughes (or a competitor's!) aluminum plate and gasket."
although I'll still need to get new intake gaskets & injector o-rings, I assume from that, that Hughes wants you to use their gasket for this repair.
 

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The Hughes kit comes with a gasket, but I think it's the Fel-Pro one you'd buy to reseal the factory plate.

Mancini Racing also sells the Hughes kit ... Hughes Engines Plenum Repair Kit (manciniracing.com)

There's a few other sources also.

RwP
Beautiful
and it looks as if it comes with the intakes, the O-rings AND the bypass hose!
For $157 + tax & shipping that looks decent.
I read in the product description, and again I quote,
"Don't want to weld the cover to the intake?"
no, I don't particularly wish to do that, but it kind of seems like maybe it would have been nice if Dodge would have done that.
 
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