Helloyall, I am a bit of a loss here.

I have a 95 Ram that has been running poorly since I got it. Very rough in idle, with a hissing noise whenever I turn the engine off (like air is releasing back up through the engine compartment somewhere. I took it to a shop that had a good recomendation from someone I trust, and they put it on a computer and found no warning codes - they said that there was something wrong internal to the engine and that it would have to be taken apart. Instead, we had a new Jasper 5.2 installed by a former mechanic. It still ran rough in very much the same way. He said it was the cat, but just this morning I got fed up and gutted the cat and left it open to try and run it - same exact problem - so now I guess its not the engine, not the cat, not the muffler (since the cat had a hole in the side still I assume the muffler was bypassed and hence not the problem)...so what is it? What else could it possibly be, some sort of sensor that was reused? Computer?

 

On a 1995 model 5.2V8
you have the exhaust gas recirculation (EGR) valve
at the back of the intake manifold
in a hard to see spot.

There is also a 'EGR Modulating' electric unit
right beside it.

Either of these can malfunction and cause the poor running you describe
and you should suspect them first.

Other items:
IAC may be dirty or bad
cylinders 7 or 8 may be cracked or head gasket blown
plenum plate under intake manifold may have bad gasket

Do you know how to on/off then on/off then on/off
and finally on
with the ignition key
so that you can then count the blinks of the check engine light?

This can be tricky
and you should repeat the whole thing at least three times for certainty
but it will give you the two number DTC code number
and tell you what your PCM computer thinks the problems are

http://allpar.com/fix/80s-codes.html

 

Thanks Hank, I have been lurking on this forum and you really seem to know your stuff.

Since my last post I've had the EGR checked - it was ok, had the check engine light come on which was apparently the O2 sensor, replaced that, still running rough though. IAC checked out ok. Since its a brand new motor and ran this way out of the box (and just like the old engine before it) I'm gonna ssume its not a cracked head.


That brings us to the plenum. Could my friend have taken the entire intake manifold off when he switched engines before, thus never disturbing the plenum, or would he have had to disturb that plenum gasket? Also he said there was a lot of oil pooling before and actually solidifying up in there (not quite certain where he meant), but from the core which I now have it looks like on top of the engine near the push rods oil has been solidifying. Would a plenum leak oil there?

This new engine has now been driven 1500 miles and it doesnt seem to be leaking oil, but it is still running rough - like it has a vac leak. Hoses all look good to me. The spark plugs did have a lot of soot on them, I think it may be running rich but I'm not sure. Can you make anything more out of this?

Thanks again.

 

I pulled the throttle body off this morning to look down into the intake. There is a little pooling of oil at the back of the intake, can't see all the way around to know just how bad it is. So yes the plenum is leaking. BTW, one time I pulled one of the sparkplugs in the rear of the engine and it was wet fouled badly with oil. So, is the plenum pretty much now sure to be my problem?

 

I've put the vehicle in the hands of a local mechanic, and after compression tests he we don't know...he is getting 120 psi on all the cylinders except #7 which is 90 psi. Did a leakdown test and it was inconclusive.

I did in fact see a little oil pooling on the plenum pan. But those numbers all sound really low and indicitive of the problem, although I have no idea what the solution is besides pulling stuff out.

So a couple questions; can a leaking plenum cause low compression numbers in any way?

Can the low compression numbers be caused by anything not relating to the jasper remanufactured engine?

All along I have denied the possibility that we might have recieved a defective engine based on the premise that its is running after the swap like it did before, and I thought the chances of recieving an engine with the same problems as the old one miniscule. Logic seemed to dictate that it was something other than the engine after the swap. But these cold compression figures are kinda hard to overlook.