'96 P300, P301, P302 Codes
 

I recently bought a used 1996 Dakota with 109,000 miles.. 4x4, auto, 5.2L.
It ran pretty rough and the engine light was on. Three codes as listed in title. (I dropped the leading 0)
I have tested the fuel injectors with my ohm meter and all showed 12.6 resistance.
I put on a new distributor cap, rotor, spark plugs, and wires.
I replaced the throttle position sensor and the idle air control valve.
I checked the compression and all cylinders are within a pound of 120.
I ran a full can of Seafoam through the power brake vacuum line and filled the nearly empty tank with fresh fuel.
I pulled the passenger fuel rail, pulled injectors #2 and #8. I cleaned up number two and switched them. I was thinking I had clogged injectors and that the error code would move to cylinder number 8.
After every step, I would clear the engine light and drive. After a few blocks the engine light would come on and the very same codes would be back again. P0300, P0301, and P0302, cylinder misfire on cylinders one and two.

So what do I do now? I am running out of ideas.
Thanks in advance.

My next step would be to do the "brake clean" check on the front of the intake manifold.

#1 and #2, with good compression, still misfiring, tells me that there's a problem at the front - and the common point is the intake manifold. If there's enough of a vacuum leak, then you could get misfires at the front.

One more thing - since it's a 1996, you can do a good OBDII reader and check the data stream. Try that and see what the ECU thinks is going on, that is, what are the short term fuel trims (STFT) and the long term fuel trims (LTFT) in case it's able to adjust out overall, but is running too lean on the front cylinders.

RwP

Ralph,
Great idea. Thank you for writing.
I am thinking I need to clear the computer and then drive it a bit. I have monkeyed around with it so much that the LTFTs must really be goofed up by now.
If I get the codes again after clearing the computer, I will indeed go to the brake cleaner.
Thanks again.

Yah, I don't KNOW that it's the intake leaking at the front causing the AFR to be bad on those cylinders. But equal pressure on compression (although I'd have expected > 120 lbs, YMMV natch and go with what the manual specifies!) means it's not a HEAD gasket, and likely not a bad valve.

With all the new tune up parts, unless you've got two bad new wires, I'd eliminate those also.

I did forget - at night, when it's nice and dark, take the truck, start the motor, and spritz the spark plug wiring with some (preferably distilled!) water to see if you get a "light show". If so, you may have bad wiring.

Also, be worth pulling the #1/#2 spark plugs and reading them.

RwP

I disconnected the battery and powered down the system.
Hooked it back up and I hammered it a few times and drove it quite a bit.
No codes.
Thanks for the LTFT clue. I think I have it now.
Now that it runs, I am contemplating the Mopar Performance computer. I guess having it running perfectly and on its way to being a daily driver just isn't good enough.

The saga continues...
Engine code after three days of driving. Sames codes as above.
After extensive reading I think the plenum gasket is blown. So it is an intake gasket problem, but not to the outside. I haven't owned it long enough to know that it had poor fuel economy or high oil consumption.
The good news is everything electrical on top is now new. ($$$)
Ordered kit from Hughes and hopefully this will fix it.

Thanks again Ralph. You were correct afterall. I just didn't realize there was a plenum gasket that could go.

Have u tested each one of the coil packs? It’s an easy test to do just need a straight pin (t pins work best) and an electrical tester (pin style). There are several videos on YouTube that show u how to test each one. Simple. My 05 Dakota had the same errors showing and low and behold after checking everything it ended up being a broken spark plug on cylinder 8. Replaced the plug and all codes went away.
Hope this helps.

No coil packs on a 1996, Angie Burk.

RwP

I'm currently dealing with the same issue as the original poster. I tried switching out the fuel pump relay with the air conditioner relay and the car started and ran for a day, and then died on me while I was driving. I'm getting the same no bus reading on my odometer. So I'm wondering, because google isn't giving me any help in this regard, can anyone tell me where the powertrain control module is?

Also what are the other items in the circuit I should check out?

If you're getting NOBUS, you don't have a Gen1.

Might want to check in the appropriate forum for your year Dakota.

RwP