2001 Dodge Dakota Sport 3.9L auto trans Standard Cab short bed


First of all, here's a little bit of history about the truck: I bought the truck in 2009 from an old farmer who, basically, never spent a dime on maintenance and literally ran and abused the truck till it quit. I knew it had an engine problem when I bought it but I didn't know how severe it was. I was told that it probably had a blown head gasket. Apparently, the farmer kept driving it in this condition and kept adding coolant as needed. When I took it to my mechanic for diagnosis, upon removing the cylinder head they found that it had burnt a hole through the top of the piston in the cylinder where it was leaking. Rebuilding the engine was cost prohibitive so they suggested using an engine from a salvage yard. The engine was replaced with an identical one from a 2002 Dakota which had about 30,000 miles less on it than mine did. Since that time...it never really has run right.


Here's the problem I'm experiencing: I'll start the truck and drive it somewhere getting the engine up to operating temp. Park the truck, go shopping in the store for 30-45 minutes. When I re-start the truck to go home, it starts fine (every time) but as soon as I put it into gear and step on the gas pedal it will bog down and start popping or backfiring through the throttle body. When it does this, if I turn off the engine then immediately re-start it, it will run fine. When it first started doing this, it only did it occasionally. Now it does it EVERY time. I took it to my mechanic, he checked it out and recommended that I take it to a Dealership. I took it to a Chrysler Dealership, they had it for a day changed an O2 sensor and cleaned the fuel injectors plus they cleaned the valves and combustion chambers and said it was fixed. That didn't help at all. I took it back the following Monday morning, they had the truck all week and I picked it up just before their quitting time on Friday. They said it was running fine and could only experience a little hiccup from it. I started to drive it away and it did the same old stuff even before I got out of their car lot. I didn't take it back because it was evident that they couldn't fix it either. It would've been a waste of time and money. I was told by the guy that did the engine swap that the new engine was checked first to make sure it was compatible. So I'm just going on his word for that. He works at a reputable shop. Nearly every sensor has been changed at some time and I did a tune up with good parts (plugs, plug wires, dist. cap & rotor). Nothing seems to help. I've run out of things to check. There are no DTC's set. Maybe it's just full of gremlins...


Anybody got any suggestions?


Oh, I forgot to mention that after I got the engine swapped, I found out that I needed to get the tranny rebuilt. :-( I'm not looking for any pity, just a little help getting this truck to run right.

 

3 things come to mind after reading this..
1) timing(fuel sync) if its off,it will cause all your symptoms..
2) TPS voltage...if idle voltage is to high,can cause backfire though throttle body.
3) worn cam lobe or vaccum leak...

does the engine make any ticking noise?
check your plugs,see if one is fouled,that will narrow it down to what cylinder is causing issues,if all look the same id check into 1 and 2...

 

The engine runs quiet...no ticking noise. All plugs look identical...none are fouled. TPS voltage is normal.


I tried something different on the start ups which would produce the problem. I'd start the engine, but instead of immediately putting it in gear and trying to drive away, I would sit and let the engine idle for a few minutes. Right after I started the engine, it would idle down and after a few seconds it would start idling rough as though it was only firing on 4 or 5 cylinders. (It felt similar to when you'd actuate a manual choke on an idling engine.) It would run rough for about 20-25 seconds, then the idle would smooth out. Then I could put it in gear and drive away with no back firing. I've tried this several times and it has worked every time. But I shouldn't have to sit and wait for this rough idle to pass. I should be able to just start and go like all other cars and trucks.

 

I had the same problem with my 2002 Dodge Dakota V6. I also changed O2 senors, but it wasn't until I changed the Crank Positioning Sensor that the problem went away.

Now if I could just fix my brake problems.

 

Thanks. I think I'll give that a try. Good luck with your brakes.

 

Well, I tried a new crankshaft position sensor but no luck there. After searching all over the web and reading different forums, now I'm wondering if I might have an intake manifold or plenum leak. From what I read, the 3.9L engine was/is notorious for that type of leak. The engine has about 110K miles on it now. I've also noticed the smell of antifreeze when I park the truck in my garage. The antifreeze level never seems to change and I have no overheating problems. I never see anything leaking and it's always dry underneath the truck. (I was wondering if the smell might be coming out of the tailpipe?)
I'm really dreading taking the truck back to the dealer because I don't feel that they have anyone experienced enough to do a proper diagnosis.
I want to get the truck running right because I like the way it drives and rides and I'd like to keep it. At this point I'm not sure if it's worth spending all the money or putting up with the hassle of fixing it.
I've considered having the fuel sync checked but that would mean having to take it to the dealer which I'm only willing to do as a last resort. I wish those scan tools weren't so freakin' expensive.


Here is something new that it hasn't done before:


After starting the engine I was listening to it idle. It was idling a little rougher than usual. After sitting there for about a minute, the engine (all by itself) increased the rpm's to about 1600 for a few seconds then it gradually dropped back down to idle speed and was still idling rough. Also, while driving through the grocery store parking lot, when I lifted my foot off the gas pedal, the truck acted like it wanted to keep going as though I was still pushing on the gas pedal. I also noticed that when I got out on the road and set the cruise control it would keep on accelerating and finally set at about 5 mph over the speed that I was trying to set. This was getting scary.

 

My truck does that. I set the cruise about five under what I want then it'll bring itself up to speed.
I've noticed that if I hit accel it will speed up a couple mph.
If I hit decel it'll slow one.
Hard to set speed that way. Lol.

 

I just fixed my Plenum leak. My truck has 108,000 miles. It wasn't that hard to fix and I'm by far no mechanic. It took me about 6 hours and that's never doing it before. Make sure you get the after market Plenum Plate. I also found the easiest way to check for a Plenum leak is to use UV DYE in your oil. I never found a large amount of oil pooling in my intake by taking off the throttle body and looking in. It wasn't until I put UV Dye in the oil and waited a few days and looked in using a UV light. My entire intake was glowing UV Green.

I would also check your TPS and IAC for your idle and RPM issues.

 

Normally, when I hit the cruise "set" button it will set it at exactly the speed I want. I have an old (1989) Chevy Beretta that does like your truck...you never know what the speed will set at. I just figured it was because it was old and worn out.

 

Given the mileage that I have, I'm sure those gaskets need changed. Yeah, I saw an aftermarket plenum plate made out of 1/4" aluminum plate that's guaranteed to fix the leak and keep it fixed. I think it was from hughesengines.com. I also plan to replace every vacuum line I can find to try to eliminate any possible vacuum leaks. Did you have any trouble getting the distributor reinstalled correctly? Right now, that would be my main concern. The rest would be a piece of cake.