Had this truck for 3 years and has been fine up until the last few weeks. I hate to sell it but I'm ready to dump this turd on some unlucky dude!

2002 Dak/SXT/3.9L. Automatic with just a tad over 100k on the odometer.

First noticed a drop in mileage, then my wife started complainig it was randomly going dead on her at stop signs. Nothing major, but enough to get annoying. It has steadily gotten so bad that we cant drive it anymore.

Heres the annoyances:
-Gets ~15 MPG... previously getting better than 20
-Dies at stops after driving for 20 minutes or so (after it heats up).
-On restarting, the IAC whistels, it shakes and rattels then dies out again
-The further we drive, the worse it gets (up to the point it won't stay running at all)
-After it cools off, it starts up fine.
-No codes whatsoever

What I've done:
-New air filter
-New plugs (no platnium crap, just what the book recommends)
-New Cap and Rotor
-Cleaned the IAC valve and IAC port
-Fuel injection cleaner ran thru last tank
-Ran down the vacume lines and can't find any leaks

Is this commom to these engines?

I'm not looking to spend a ton on this thing and I am very capable of fixing these type problems on my own. I've been a GM/Ford guy all my life and never tinkered with any Dodge stuff.

Anyone here had any of these problems and found the fix? Throw me a bone guys.

 

It wouldn't cost too much to replace the IAC. I'd try that first. What kind of shape are the catalytic convertors in? I have also heard about O2 sensors going bad or getting lazy but not setting a code. If the cats are OK you might try replacing both of the upstream O2's and see what happens.

Jimmy

 

maybe a clogged cat? also, try re-setting your PCM.

 

when its trying to die, if you lay your foot on the gas pedal just a little bit and crack open the throttle, up to about 1000 rpm, does it stay running. if so, replace IAC with either mopar or SMP brand and reset pcm. avoid autozone or advance/GP brand iac's i've had a terrible time with those. while iac is off, stick a small screwdriver or wire through the iac port and make sure its open and clean.
https://dodgeforum.com/forum/2nd-gen-ram-tech/140607-why-does-the-iac-fail-so-frequently.html

 

my cherokee is experiencing this right now and i think its the cat in that because im pretty sure the rattle it has is the cat in piece i would check into that too, i believe they can do a back pressure test or something to test to see if the cats bad but the iac replacement doesn't sound like a bad idea either

 

I feel dumb now, somehow when I replied on this one I had the idea there were 2 cats, I know there is only one. Duh...

But I do know that when you clean the IAC pintle you have to be very gentle with it or else it gets ruined. I'd still get a new one and be sure you don't drop it, and handle it very carefully. Check the cat, they way I learned it is if you hit it with a soft face hammer or your fist and it rattles like it's full of gravel it's bad. You might still need O2 sensors, but I would try a new IAC first. I would also say remove the throttle body off the manifold when you install the new IAC so you can really clean the IAC port and the TB too. You know it already but don't forget to get a new TB gasket.

Jimmy

 

check ur o2's might be running really rich, and once it warms up it will die... Check for codes...

 

maybe it has something to do with how the computer enters/responds/adjusts to a closed loop when it at OT.

 

Updates...

Finally got the chance to stop at the parts store to check into O2's and IAC.

I haven't actually looked but they (O'Rielly's) said there are 4 O2 sensors. One before and one after each cat converter. (I do have 2 cats). Each was rouchly 55 bucks each so I laughed and headed out to do more homework.

As my luck would have it, the truck would not start...right there in the parking lot. I had driven about 50 miles or so and the engine was cooking hot. Then finally...a code!

P0320 Crankshaft position sensor. Went back in and asked about that part and they said the Cam position sensor can cause that code too.

I'm feeling like this is turning into a mouse hunt.

What the heck?!?!?

The key complaint I have is that the truck runs fine when cold then gets progressively worse as it heats up. When fully at Operating temp, it always dies at idle.

Is this the symptom of a bad Crank position sensor?
Is this a cam sensor problem?


Any ammo you guys might have would be awesome

 

Code 320 means the Crankshaft position sensor reference signal cannot be found while the engine is cranking. The crankshaft position sensor is in back of the passenger side cylinder head and goes into the trans bellhousing. The code you had is caused when the crankshaft sensor fails 3 times. Usually when it is bad the truck will buck and bog down as if not getting any fuel, but not die out completely.

If this were my truck I would replace both upstream O2 sensors AND the crankshaft position sensor. At the mileage you have it's good preventative maintenance to replace the upstream O2's. The downstream ones have a lot less problems and can usually be left alone. I would not use the Bosch O2's sold at a lot of parts stores. They don't work very well with the 3.9. Either go online and order NGK sensors or get new ones from the Dodge dealer. I think NGK is the supplier for the OE sensors anyway.

Take a look at the crankshaft sensor. See if the grommet has worn out and allowed the sensor end to get rusty. If so, when you replace the crankshaft position sensor be sure to get a new grommet for it and use the original bolts that came off the old one to reinstall the new one. They are precison machined to be the exact length to go back into the bell housing without causing problems. It's a lot easier to get to the sensor if you remove the right front wheel and the inner fender liner. Just be sure to get about a dozen new plastic fasteners from the parts store to reinstall the liner. The plastic fasteners are a one-time use part and have to be drilled out.

If you want to save money on this one, try replacing just the O2 sensors first. I have heard that lazy O2's can inhibit the signal from the crankshaft position sensor and cause this kind of problem.

Jimmy