9/26/11: I just bumped this thread back up to go along with my "Interesting spark problem" thread, because i think the two are related.

To recap: I'm getting a weak and intermittent spark on certain cylinders only, and it seems to have nothing to do with anything downstream from the coil.

This thread contains a lot of posts about the kegger mod/plenum repair, which I have not yet done, but which has nothing apparent to do with the intermittent spark problem I know I'm having. Kindly ignore anything having to do with the plenum/kegger. Thanks.

End of foreword - original thread follows.

******

Still having a stalling problem that's been driving me nuts for a couple of YEARS now.

Clues:

Only happens when it's cold out
Happens mostly when I start to accelerate from a stop
Also happens when the engine has been idling for a few minutes
Engine will "lope" at idle, revs rising and falling lower and lower until it dies

Fuel pressure is 41 psi. It should be 49 +/- 5 psi. Is this low enough to cause stalling?

What else could it be? I've replaced (or tested) just about everything but the CPS, CKPS, and PCM.

Idle air control replaced, new O2 sensor, complete tuneup, all the usual suspects ruled out.

Ideas anyone? Thanks.

 

What brand O2 sensor?

Fuel pressure is correct for your year. They bumped it to 49 later in life.

How many miles on the truck?

Have you fixed the plenum?

Kinda sounds like a vacuum leak......

 

Hi Brian -

Not sure what brand of O2 sensor; just one I got at NAPA. I think it was a Bosch, but I couldn't swear to it. What brands are good, and which are bad? Dealer item?

No, haven't looked into the plenum. I've seen references to problems with the plenum, but never pursued it. I will now. I'll search it, but in the meantime, what's the plenum story in a nutshell?

About 150,000 miles on it, engine is still very strong. (It's a van actually, hence my recent little joke about how I don't see what the big deal is with getting at the distributor).

I've done a lot of looking for vacuum leaks; inspecting hoses, spraying various volatile substances around the intake manifold listening for changes in idle speed; I'll look some more, and put a gauge on it. Sure does sound like a vacuum leak, doesn't it ....

Thanks for the reassurance about the fuel pressure. That didn't really fit anyway since it goes like a bat outta hell at higher rpm's.

And thanks for the reply - you are incredibly helpful and knowledgable.

 

The prefered 02 Sensor(s) is NTK(NGK) or OEM from Dealer. Bosch and or any other brand don't seem to last as long or play as nice.

On the plenum, spraying fluid to notice idle changes doesn't always work. Its not like tracing down a "traditional" vacum leak. At 150k on the clock, and no mention of it ever being replaced, I am 99% sure its blown.

Do a search on "plenum" there is a TON of information on it

 

Plenum in a nutshell: Steel plate that seals the bottom of the intake manifold. Take off your air filter housing, crack the throttle all the way open, and have a look down in there with a flashlight. Chances are REAL good you are going to see oil pooled in there. The gasket tends to let go, and the intake will suck air/oil right out of the engine valley..... leads to things like fouled plugs, unstable idle, and other fun things associated with vacuum leaks.

 

OK - looked inside, and the intake has definite signs of oil. Not pooled, but a moderate coating of gunky residue that smells like waste oil. I'm definitely going to do the plenum thing.

So, next questions:

Is it worth it to do the Hughes thing, or is a simple gasket replacement sufficient? I'm not going to have this van forever, but is the original design so bad that I shouldn't just replicate it?

Checklist of items to replace while I'm in there? Injector o-rings, fuel hoses, throttle body gasket ..... ?

Other things to do at the same time? Clean the injectors, do anything to the throttle body .... ?

Lastly - does the "Kegger mod" apply to the '94 5.2L? I've seen references to "keggers" being on Magnum engines, but I have a hunch this isn't a Magnum; or do all the Dodge engines of this vintage have "keggers"?

As always, thanks.

 

If your manifold looks like a beer keg.... that's the kegger.

Kegger mod moves the power band up a bit, and allows a bit better breathing at higher rpm. How much it changes from stock? I don't have a clue, my plenum was REALLY bad when I did mine, so, any improvements due to just the kegger were hidden by the other stuff I did at the same time.

If you do 'just the gasket', get some bolts for the plate that are a bit shorter than what are in there now. 1/8th inch shorter would be adequate. Problem is, they are a bit too long, and bottom in the holes at the correct torque, instead of tightening on the plate itself. Washers would probably also work. Don't forget to use some loketite on 'em. Don't want 'em backing out, and dropping into the engine. The hughes plate is a permanent fix. Just doing the gaskets, new bolts or no, might not be..... if you plan on putting another 50K or so on the van, I would get the hughes plate anyway, or, one from any of the several guys here on the forum that are now making them.

For the truck guys, cap/rotor/plugs/wires are recommended at the same time. As you have a van, and just pulling the doghouse puts everything right in your lap...... (yes, I AM giving you a hard look. Yes, I AM jealous. ) Not as much of an issue for you.

Clean the crap out of the throttle body really well too. TB gaskets are two bucks and some change.

You don't have to pull the fuel rail off of the manifold to do the job.... unless when you are modding your kegger, you also clearance the injector ports some.... If you do, then go ahead and replace all the orings. If you simply don't like the ones that are in there, simply because of how long they have been in there, go ahead and replace them. They are a bear to get out of the manifold though.

You will need the neat little quick disconnect tool for the fuel line. 3/8ths is the size you want. (if you don't already have one.)

94 engine should be a magnum as well.....

Oh, afterthought..... replace your PCV valve too, get one from the dealer. The aftermarket guys tend to have too high of a flow rate, and will suck oil right out of the valve covers.

Watch the front two intake manifold to head bolts. They like to break. Bottoms of the bolts are exposed...... crap likes to accumulate there, and they stick.... TTY bolts, so they are not exactly 'high strength".... rear two are exposed as well, but, being at the back of the motor, didn't seem to get as much junk on them on mine. They actually came out, and didn't break.

 

Thanks a million Brian! Great info, as always.

Yeah, my intake does look "keggish", so I guess I'll be doing the mods to it. Pretty sure I know what to do; take maybe 1.5" off each runner (cut off square, not at an angle), and remove the divider. Forunately, I've got a bitchin' set of 1/4" shank carbide cutters for my air grinder, so the aluminum won't stand a chance. Hate to continually bug you, but I'm not sure how to modify the injector ports. I'm sure there are at least 100 posts on here about how to do it, but I have a feeling that A) there'd be about five different opinions about how best to do it and B) that your opinion would be the best. Lastly, do you concur that 1.5" off the runners is about right, or do you have another amount in mind?

Thanks again; your help is greatly appreciated.

And thanks Twisted Metal - it always did seem like a vacuum leak, and it always puzzled me why I couldn't seem to find one. I like the 99% odds that I'm about to make my engine run better.

 

John, there is an excellent DIY write up for the Kegger Mod in the FAQ section. And it was done on and EGR Intake so it will show how to remove the center divider too. 1.5" seems to be the widely accepted amount to remove off the runners. As far as opening the FI ports, I did mine with a small dremel wheel. Your looking to open up the back of the port to help get a better spray. Where you planning on using your current intake or picking up another one to mod?

 

I shaved my runners back flush with the rest of the casting. (on the side where the casting was..... wish I had some pics.... straight across from there.) Basically, what you are doing there is shortening the runners, and "unshrouding" them, if you will...... promotes better air flow, but, does move the power band up the rpm range a bit. (few hundred RPM, give or take) With the plenum fixed, and modded though, I STILL have MUCH better bottom end than I did previous to the repair. I LOVE the way my engine runs now. (though I DO wish it got better gas mileage..... but, its a truck, can't have everything. )

I did the timing chain at a later date, and just that 'fix' alone also made a noticeable difference in performance. (the water pump that was on there was relatively new, so, I didn't worry about that at the time of the intake repair. in typical fashion though, shortly thereafter, I developed a coolant leak at the timing cover..... so, since I had to pull the pump anyway, I just replaced it.)

Here is the link for the DIY for the kegger mod. Very good write up. Follow that, and you will be pleased with the results.

Keep in mind, space in there is at a premium. I used a dremel, with the fiber reinforced cutting wheels. They were MUCH more durable than the standard wheels. I would blow those apart more often than I would wear them down. Not so with the reinforced guys. They would wear to a nub before breaking. They were just a bit larger, and in some places, was a very tight fit... I would use them in more open spots to wear them some, and then go after the tight spots.