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94 Dodge 3.0 high HC at idle problem needs help

Folks, my son has a 94 Caravan with the 3.0 engine and it hits 1200 ppm HC at idle with the limit at 200. At speed it is just fine.

He has put new plugs, cap, rotor, wires, t-stat, TB cleaner and that 'guaranteed to pass' gas additive and nothing have made it budge much. The air cleaner is new also.

It was at 1356 and it is now only at 1200.

The engine seems to run really nice.

Any ideas would be very much appreciated.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '09. Some Canadian Bush Trip and Build Photos:
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Mike Romain
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Have you had the timing checked?

Reply to
Doc

No, why would the timing suddenly change? It is an electronic ignition, not a set of points... This vehicle passed just fine last time and only flunks the HC's at idle.

I am thinking something isn't turning on right or isn't turning off.

There is some type of vacuum unit on the passenger fender that is ticking away at idle, we don't remember that from before, but...

Mike

Reply to
Mike Romain

try changing the oil. gas soaked oil can make hc go high.

Reply to
jp6867

OK, so the engine failed HC at idle because one cylinder, the front center one only has 50 PSI compression. The rest were all even and OK.

Do these 3.0's pop head gaskets or cook valves often? We haven't done a wet compression test yet, those were the garage's numbers.

Thanks,

Mike

Mike Roma> Folks, my son has a 94 Caravan with the 3.0 engine and it hits 1200 ppm

Reply to
Mike Romain

i believe that this is the Mitsu engine, common failure mode for this engine as I understand it is dropped valve guides which would explain high HC but not the low compression. I have not worked on one of these personally nor am I aware of a common ring/HG/valve issue, I guess you're just going to have to pull the head and see what there is to see.

If you're feeling froggy you could try simply putting that piston at the bottom of its hole and filling it up with some solvent for a couple days to see if you've got a stuck ring. Depending on how often your son needs to use this vehicle it might be worth a try. Actually if the intake valve guide is dropped it might have coked up the cylinder and a stuck ring could be a possibility - freeing it up might get you through the inspection but the issue will come back

nate

Reply to
N8N

Thanks Nate, I was thinking a good decarboning with a pint of ATF burned slowly and the solvent treatment sure wouldn't hurt this one. My son was driving with almost dead plugs and got a real jump in performance with the tune up so that also may have contributed to the fouling.

It is a daily driver and the garage gave him a conditional 2 year pass.

Mike

N8N wrote:

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Mike Romain

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man of machines

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