2000 3.3 suddenly runs very rough

[PArabbit]

My kids' 2000 Grand Caravan with 3.3 V6 (70,000 miles), which has been running as smooth as could be, suddenly made a thumping sound at top of a hill, like hitting something or tire going flat, now runs very rough and engine shakes, like missing on several cylinders. No check engine light, front 3 plug wires putting out spark, but disconnecting middle one has little or no effect on rough idle and running. All plug wires are attached.

OBD II diagnostic tool picks up no recorded codes and engine light is not on. Running in capture mode produces no meaningful results unless timing is off and I don't read it as so.

Nothing looks amiss under the hood, or jarred loose. As an older guy who can usually diagnose and fix most anything, I don't have a clue. It starts up with difficulty, because of rough running.

Does this engine have a timing belt or a chain? If belt, could it have chewed a single cog and jumped time? My previous timing belt failure experiences always involved total belt failure.

I don't have a manual, which would help.

[GTP Dad]

The 3.3 has a chain not a belt. I had 165K on one with no timing chain problems. Have you done a compression check. It sounds like you might have dropped a valve although that probably isn't the case I would check the compression to make sure. I would pull the number 2 plug to check it to see what it looks like. Don't really know what would cause a problem like this.

[Cobra_Sam]

Originally Posted by GTP Dad

The 3.3 has a chain not a belt. I had 165K on one with no timing chain problems. Have you done a compression check. It sounds like you might have dropped a valve although that probably isn't the case I would check the compression to make sure. I would pull the number 2 plug to check it to see what it looks like. Don't really know what would cause a problem like this.

I am going through the same thing right now and have changed the timing chain and gears because I thought it was worn, changed the fuel pump and fuel filter because I thought maybe there is not enought pressure, then changed the cam sensor, then the crank sensor, then the wires and plugs and it is still doing it. The van runds rough like it's running on 2 maybe 3 cylinders. All that is left to change is the SMEC ( single module engine controller ) and the computer.
I wish you and I both find a cure. I am contemplating buying a scanner it may save my sanity.
Sam

[GTP Dad]

Did either of you gentlemen change the coils. I don't have my T&C anymore but it sounds like the coil has failed on one bank. You could still get spark when you test the plugs but it may not be strong enough to fire under compression. I would check this before going any further before going to the expense of a computer.

[Cobra_Sam]

Originally Posted by GTP Dad

Did either of you gentlemen change the coils. I don't have my T&C anymore but it sounds like the coil has failed on one bank. You could still get spark when you test the plugs but it may not be strong enough to fire under compression. I would check this before going any further before going to the expense of a computer.

I did test it individually with a wire and plug and got spark from each one. But I will look into testing it properly. Thank you for the info.
Sam

[dno36]

Just a thought....

I too had a sudden rough running 3.3 without warning. A fellow poster here, about 4 years ago, suggested I check the wires to see if I had a bad 1, and check the post on the sending unit for glazing, as this seemed to be an intermittent problem.
I did find 1 plug that was not firing, and when I changed the wire with no improvement, I saw the post had a little white tint to it, so I fine sanded it and whaa-laa no more misfire.
Just a note, we have had a timing chain problem with any 3.3L's even with over 400K.

GL

DNO.

[PArabbit]

Dealer tested all external issues, pulled plugs and found two drenched in oil, with no compression at all on those.

Says the PCV valve is stuck in open position, allowing extra rich running and ultimate contamination of crankcase oil, which they say has gas in it.

This has resulted in two cylinders scoring, and a knocking rod bearing.

They are recommending engine replacement- either a reman. Chrysler one or a salvage engine w/11,000 miles on it. Both are pricey solutions.

Wouldn't stuck PCV valve or over-rich mixture turned on the check engine light? It was off, and I pulled no codes from it.

Does anyone have any thoughts on this or similar experiences, and would a faulty PCV valve (stuck open) result in this kind of damage?

Thanks!

[who fan]

I would have to wonder about a head gasket blowen. Aluminum heads, iron block could be.I wouldn,t think a pcv valve could have gone unnoticed to cause this kind of damage. Especially with this low mileage and sudden failer.

[GTP Dad]

Anything is possible but I doubt a PCV caused all that damage. If it did why then did it only effect two cylinders and not the entire engine. If it was as bad as the dealer says then you should have gotten a code of some kind in the computer since there should have been an emissions malfunction somewhere. If I were going to fix this I would go with the salvage engine, you should save a couple of thousand bucks by not purchasing a reman from Chrysler.

[nose-gobblin]

have the knock cencor replaced its when the engine is under strain it needs to adjust the timing and if the knock sencer is broke it wont advance/ retard the timing hence the knocking at the top of a hill, becuase the compression is fighting the piston movement, hope this helps