Can a Faulty Computer Set a P0304 Misfire Code?

[JMac101]

I have changed everything and clear the code and the it still returned. I swapped out: Coil pack, injectors, plugs, wires, fuel rail, fuel rail wiring harness, MAP Sensor, Throttle position sensor, egr valve. I tried reseting code and it still returned.
Symptoms: Rough Idle. Misfiring. Stumble on accerleration. Flashing MIL light followed by steady MIL light. No smoke from exhaust just extreme rough idle.
Can a Bad Computer cause a code?
I have a 2001 Dodge Caravan 4 Cylinder 2.4 Liter van with 138,000 miles on it with the original computer still in it.
I changed everything I could possibly think of and every part that was suggested for the P0304 code. My mechanic says the cat converter is fine. The only thing I havent changed was my 02 Sensor.
Will a back computer just be faulty and conk out and produce random codes or will a faulty computer generate its own code?
I have been battleing this code for 7 months.
Thanks

 

[punisher]

Well, you know it is not the PCM setting random codes, as you do indeed have a missfire, "Symptoms: Rough Idle. Misfiring. Stumble on accerleration. Flashing MIL light followed by steady MIL light." All your PCM is looking for is the time between sensor ring pulses from your crank sensor. It's hard for a PCM to accidentally interpret data to throw a code for one specific cylinder.

You have thrown a lot of parts at it. Might be time to dee if there is a base engine concern like low compression or bad/burned/bent valve, broken/loose valvetrain cam follower etc. Try a compression and/or leakdown test.

Anytime you get a missfire code for a specific cylinder, you worry only about component(s)that effect that particular cylinder. Example, an O2 sensor will not cause a missfire code for only one cylinder.

 

[DieselTech]

It's not a computer problem. Compression test would be a wise choice. It's just #4.

If it was the cat it would be a random misfire code. I know alot of those vans running around with junk compression. Too small of an engine in the size of vehicle. It was a major problem in those vans

 

[JMac101]

so you both so compression test it?
I was gonna pick up a compression tester and try it myself, will any compression tester work?
If it is a burnt or bad valve that would be located in the oil crankcase right?
If the compression is bad in that one cylinder, is there anyway to repair it? What if the valve is burnt or shot?
Costly repair?
Van was my dads and if I can get it repaired for a decent price Id like to keep it.
Thanks Guys

 

[mechtech2]

Any compression leak is a huge job to fix.

Sometimes an internal cleaning with Auto RX or Marvel Mystery Oil helps by freeing up stuck rings/lands.
But don't count on it to fix a real mechanical problem.

If you test the compression, the engine should be warm. Open the throttle fully. Disconnect the fuel and ignition. See how the gauge comes up, as well as the final. 4-5 cranks is enough for each cylinder.
20 cranks to try and eke out a few more lbs on the gauge is a false reading.

 

[Scott_Tucker]

I think a compression test would be a good idea. Although a bad driver in the computer could cause it, it would be an expensive mistake to just throw a computer at it. An O2 sensor would not cause a single cylinder misfire.

 

[brianl703]

Originally Posted By: punisher
Try a compression and/or leakdown test.


Would a vacuum gauge be useful here?

 

[Trav]

A vacuum gauge is not a replacement for a compression test.It can however provide information like sticking valves,blown head gasket,poor rings,worn guides,ignition timing issues etc.Interpreting the gauge properly is key to a proper diagnosis.

This gives so good scenarios of different gauge readings.
http://www.secondchancegarage.com/public/186.cfm

 

[punisher]

A vac gauge can show everything Trav listed. Main thing on a symptom like this, see how much bounce you have in the needle of the gauge. A bouncy needle would indicate a mechanical problem.

 

[Scott_Tucker]

Be careful how you interpret the results though. A cylinder that is not firing can show up as an oscillating needle too.

 

[punisher]

I should have said "BOUNCY, BOUNCY" needle.

 

[JMac101]

ok thanks guys.
If I was to buy a compression tester Friday, how would I go about performing the test?
I know hold the throttle open.
Disconnect the fuel and ignition.
Crank 4-5 times and check gauge reading.

Anything else I need to know?
After cranking 4-5 times will the gauge stay where it is so that I can get out of the van and check it or will pressure drop?

Thanks

 

[Trav]

The gauge has a little valve that needs to be depressed to release the pressure.Be sure to remove all the plugs for an accurate reading,after doing all cylinders use an oil can with motor oil and squirt it 2 or 3 times in the first cylinder and perform the test again.
Do the same for the rest of cylinders and compare the results to the initial dry test.

The oil will create an artificial seal on the piston rings,if the engine has worn or stuck rings the reading will be substantially higher (it is normal to have a minor 5-10 psi increase).

 

[DieselTech]

A misfire is something worse then just a stuck ring. There is a bigger issue. You can try an additve 1st but dont hold your breath

 

[JMac101]

ok well im going to buy a compression tester tomorrow and I am going to compression test it both wet and dry and see what happens.
I will record the PSI readings that I encounter and I will report them back to this post by Friday night or saturday.
Until then if anyone has any other comments or suggestions they would be greatly appreciated before I go ahead and compression test the motor. Once again thanks guys for you time and advice.