Need engine help with 2002, Dodge 3500 van, 5.2

Once warm it throws fits of backfiring into the intake while driving at low speed driving, 35 MPH or so.
On highway it will feel like it shut off for 1/2 second or so mostly when transitioning to a slight up hill grade.
The loss of power and backfiring into the intake also comes with slight upgrade, (When depressing gas pedal just a hair)
I noticed that when cold trans will down shift with just this slight gas pedal depression but when totally warm, 30 min or more of driving, The trans does not downshift with the same small changes in gas pedal depression....
Here's what I have done.
Van has 119K miles.
Cleaned lots of ground wires,
Added new grounds from batt to frame, Body and engine.
New TPS, cap, rotor, wires, plugs, Cam sensor, crank sensor, Fuel pump assy,
Voltage is good, Fuel pressure good, Cat and both 02 sensors replaced by dealer 15K ago by previous owner.
It DOES NOT THROW ANY CODES and that really bugs me........
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What the heck am I missing?
Always idles smooth, When it starts it's bucking, If I floor it, The trans down shifts and I take off smooth with lots of power.
Intake plenum has no oil in it, So it appears to have a good gasket.
I also got the truck nice and hot till it did it's thing,, Engine PC was at 140*, So I pulled the PC and baked it in the oven the next night to 160* and installed it hot, Drove the truck and nothing,,,, Just like a cold truck, So PC should be fine.. Now I will say that the P.O. had expirenced this issue a couple times in sever heat,, But he also had the ignition switch replaced and he thought issue went away,,, Sold the truck to this sucker...
It just seems to me that the trans will shift to such a low RPM and if it does not immediately downshift for the small grade or slight depression of the gas pedal, It loads down with fuel and then the 02 sensors say " Hey lets lean way out" and then I start to buck....
Someone Please help!
I need to bring this van out to Kutztown to sell off enough radios to pay for all these small parts ! !! ! ! !
Also thinking of getting the PC reflashed, Would this be a wise choice?
OK, Nearly time to take Mom out for Mums day.
Thank you for any advice you may have!
Peter and Eileen

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I had a Dodge Dakota that was doing the exact same thing as you describe and it had the same engine. I can tell you that mine was two things, one I had dropped the #8 cylinder and the other was that the fuel injection system needed to be completely taken apart and cleaned. I had about 100000 miles on it when it happened. One of the reasons that after several Chrysler products I ceased buying them, not what they used to be.

Try these folks here:

Dodge Vans - DodgeForum.com

Pete

Have you checked the catalytic converter? I had a Ford that once it warmed up had some of the same symptoms. It turned out that the converter was plugging up when it got hot.

compression

Before doing anything else run a compression check on all the cylinders.
That way you either find the problem or eliminate a burned valve as the possible cause.

Bruce

The first thing that I would do is double and then triple chech the spark plug wires. Many years ago my brother had a similar problem in a 1971 Old Cutlass and the dealer found that he'd crossed 2 of the spark plug wires. Red faces all around for us shade tree mechanics who couldn't figure out the problem. Ever since then I've made it a habit to check the really easy stuff first. It makes it so much easier when you find that you've made a real head slapping silly mistake.

Something similar happened to someone I knew years ago. The gas cap has a teensy vent hole in it. If it gets plugged up, a vacuum can temporarily develop in the gas tank, making the engine cut out until more air seeps in.

Its easy enough to check - just test drive without the gas cap.

A dirty mass air flow sensor can also cause a variety of drive-ability issues including what you described with your engine and transmission. Most parts store carry a MAF cleaner. A lot of times a code wont be set because the engine has enough tolerance in fueling to cover for it most of the time. It causes weird tranny issues because the PCM uses the MAF to calculate engine load which is used by the TCM to determine shift points in non-wot conditions.

Checking the easy stuff is always good advice. I would like to know what kind of vacuum this thing is making at idle, while it is breaking down and whether or not the needle is steady or dancing??? If the vacuum gauge has a pretty much normal reading and the needle is steady I would start looking for a bad injector or two. It is at that point in it's service life where it could be many things. There are alot of things that can go wrong and not set a trouble code or even worse...set of a bunch of codes that are incidental. Is it using more fuel or is the mileage about normal??? Poor or reduced mileage is another indicator of a few bad injectors. Good or normal mileage with the symptoms you are having suggest a vacuum leak or problem in the valve train. As stated in another post a compression test would be helpful too.

Lean backfire, did the fuel filter get changed at 100K? Fuel pump could be getting weak. You should have the fuel pressure checked under load. Some of the vans had a returnless system with the fuel filter in the tank, if thats what you have, install the pump while the tank is down.

I'm no expert, but I have to agree with the post mentioning vacuum problems. Some of todays rigs have a gazillion vacuum lines and i do know that the vacuum changes when the engine gets warmed up to operating temp.
Peace,
gordon

Have you checked the coil?

Cam Shaft Positioning Sensor did it to my Dodge. Thing was driving like I had just put bad gas into it, unfortunately I had just filled up (turned out to be just a coincidence). Once the van quit running a short time later I had it towed...

I just replaced the fuel pump this weekend, Yes it is a returnless system and was a pretty easy job to do.
BUT issue is still here.
I am really leaning toward the intake plenum gasket which is known to leak, I was asked to look down into the intake for oil which I did and I didnt see any oil in there, BUT I am thinking that this may be an issue, It would make some sort of sense with the engine only doing this while hot,,
The wires are new and are routed correctly, I install and service heaters and AC units in a commercial environment and I have tried to teach other techs that 99% of the time it is always something simple....
I even went and heated up the engine PC to 160* to test it under engine heat, All was OK......
I have to take it for a run Fri morning and I will have a vacuum gauge hooked up for the ride,
What exactly should I be looking for?
I will also be installing a new speed sensor and a MAP sensor before the run, I doubt that they will do anything, But I will try.....
$1000 reward to the one who comes to my house in Phila and fixes this issue...
I will go dig up a good vacuum gauge tonight.
Thanks all.
Anything else I should look at?
Peter

If it is indeed a 318 then the plenum gasket (valley cover) has been a forever problem. It was made out of fiber or card board. One of the reasons I got rid of my 2001 Ram PU.

Yea I am thinking the Plenum gasket.
Have too much to do this week, But it is on the block for next week.
Or shoot the dang thing with my 44 mag. (S&W) 629.
Peter

If it is a leaky plenum gasket, the IAC reading will be minimum and the idle will be slightly high. The idle air motor will close down attempting to control idle speed. This really requires a scanner and the knowledge to interprete it to keep from throwing parts at it. A code reader is not sufficient. Most vacuum leaks can be found using a length of vacuum hose with one end stuck in your ear. Use the other end to trace around the intake plenum and any other suspect areas. Sometimes a piece of metal tubing slip into the hose will make it more usable.

I'm starting to think you have spent way more than a proper repair shop diagnosis and repair would cost. Reflash is for specific problems, usually emission related. I would not recommend parts store parts over OEM, if you end up in a repair shop they may remove aftermarket parts and install OEM.

Since it has a distributor, I'd recommend checking the timing. Timing chains stretch, so checking the base timing should be part of the standard diagnostics done for this condition.

sar4937 said:

I'm starting to think you have spent way more than a proper repair shop diagnosis and repair would cost. Reflash is for specific problems, usually emission related. I would not recommend parts store parts over OEM, if you end up in a repair shop they may remove aftermarket parts and install OEM.

Click to expand...

Previous owner had it it the dealer 2X with NPF and I had my mechanic with code scanner drive the truck for a week, It never stumbled, I did speak to the local dealer and he said that unless it did it's thing on the shop floor, He would not be able to find the issue, You really need to get out and drive the thing for a while to get it to act up. Usually in the 40 MPH range going up hills.
SSOOooo at $114 an hour for dealer to diagnose and not drive the thing I think I would be wasting my money.
IS there something that they can do at the dealer that can determine the exact issue?
Thank you
Peter