Wondering if anyone can shed some light on this. I purchased a beautiful 2002 Dodge Dakota 4x4 quad cab with a 3.9L about a month ago. The truck ran great, but about a week or so after I bought it I noticed a slightly rough idle on a cold start and then the engine light came on. Did the turn the key on 3 times truck and found a P0304 code. I pulled the plug and found the previous owner was running some funky E3 brand spark plugs but saw no sign of an issue with it. I decided to replace all of the plugs with the original equipment anyway as I was unfamiliar with the brand and ended up replacing the wires as well as I was unable to get a couple of the boots off without breaking the wire. The truck ran great and I blamed the code on the E3's. A few days later, same thing. Cold start, very slight misfire, P0304. Checked intake and throttle body and lines for vacuum leaks with propane and found nothing. Pulled the injectors and cleaned them and ran a heavy duty injector cleaner through the gas tank for 2 tank fulls, truck ran beautiful. A week later, same thing happens again. I had ordered a CAI on eBay and installed it right after the code set, reset the code. Truck ran even better. I also ordered the upgraded injectors but hadn't received them yet. A few days later, code set again. The injectors arrived, I installed them, cleared the code, truck ran amazing. A few days later I decided to have a flow master installed, truck ran better than ever. Ran home, went back out to go pick up dinner, start the truck, very small misfire, check engine light back on, P0304 code. Other than the times the light comes on, the truck absolutely purrs, the misfire only lasts for a short time and it idles as smooth as a baby's butt. I couldn't be happier with it, and it's only gotten better with each thing I've done. I just have no idea what's causing this problem. Any thoughts?
Tiggeroni
Check your plenum gasket; it may be having an intermittent failure.
Easiest way to see it's bad is to look down through the throttle body (with the motor off!) and seeing if there's any oil in the bottom of the plenum. If there is, that gasket has failed.
You can just swap the gasket, or replace the belly pan with one that thermally matches the rest of the intake; that's what Hughes and others sell with their plenum repair kits.
RwP
Easiest way to see it's bad is to look down through the throttle body (with the motor off!) and seeing if there's any oil in the bottom of the plenum. If there is, that gasket has failed.
You can just swap the gasket, or replace the belly pan with one that thermally matches the rest of the intake; that's what Hughes and others sell with their plenum repair kits.
RwP
I suspected it could possibly be that, but most of the info I've read says it's usually a warm engine issue rather than cold. I'm trying to decide whose ported throttle body I want to buy and I'll probably pull the manifold when I put that on. I'm not sure if I wasn't to mod the manifold though. I've heard it can effect bottom end and I definitely don't want that
The plenum fix from Hughes doesn't mod the plenum; it's just a different material (same as the intake), so it expands/contracts at the same rate.
Currently the intake is aluminum, the plate steel, they expand and contract at different rates, and so it destroys the gasket with time.
RwP
Currently the intake is aluminum, the plate steel, they expand and contract at different rates, and so it destroys the gasket with time.
RwP
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