I am having a nagging misfire on my 94 318 Magnum Ram. On tip-in for acceleration it will misfire and sometimes backfire thru the intake at right around 2100 RPM.

It has new plugs, wires, cap, and rotor. The misfire seems to have killed my MSD 6AL box, so I am running on the stock ignition.

I thought that may be the TPS was giving faulty readings so I changed that, with no improvement.

Around New Years, it lost power and I thought it was the plenum gasket, so I changed that to no avail. The throttle body and intake were cleaned. That power loss turned out to be a broken down catalytic converter clogging the exhaust.

Still the misfire is there. The plugs look good and it idles smooth. I put a timing light on it and at 2000 RPM it looks to be advancing about 30-35 degrees, but it does dance a little bit.
About 60,000 miles ago, I put a Cloyes double roller timing chain on it, so I don't think the chain has jumped.

No codes have been set.

The backfire and bad cat make me think it is running rich...How do I tell? Is there a way to check for a funky injector?

Anybody got any experience on what the SBEC computer is doing?

Any help will really be appreciated...

My guess would be a misplaced dist (180 deg off),

or a faulty sensor, I tried to use an ignition box in my 94 too, but fried the cam sensor....

Check the crank sensor.

Dan

Oxygen sensor.

on my 97 ram 1500 with the 318, there was a TSB about a special way to route the spark plug wires since the firing order was so close and the wires, if touching, could jump wires and cause a misfire.

got a diesel injection place nearby? Take your fuel rail and set of injectors in and for ~$15/each they will flush and test them; fuel injection's equivalent to a "carb rebuild"
You WILL notice a difference after! I wouldnt be surprised to hear that you have 1 or 2 partially plugged. (or shorting out)
I happen to have such a place about 6 mi from me.

Thanks guys. I have a spare fuel rail around somewhere and will try to swap that out. I hate to mess with the injector o-rings as they always seem to leak on me afterward.

Also, I think the crank position sensor may be worth a look and possibly the oxygen sensor.

However, the stumble will happen when the motor is cold or warm. I was under the impression the motor was in open loop when cold and not reading from the O2 sensor until warmed up into closed loop. Can anyone confirm or deny this?

The distributor has never been out of the motor. But, that does bring to mind that years ago my father was doing a lot of towing with the truck and experienced a lot of ping. He took it to the dealer and had them retard the timing...I wonder if a mechanic rotated the distributor and screwed up the sync for timing / fuel maps....

I ran the code check again and came up with a 37.. but that code isn't listed in the service manual. Anyone know what it is??

I dont remember but a "non issue" I remember that code coming up alot; and it was meaningless alot of the time..... something like computer not seeing a command for AC (and this was on non AC trucks... I guess the comp on all was programmed to "look for" it.
Better put a scanner on there and check the dist for "sync"; ping is a sign of a bad plenum gasket

The motor hasn't pinged in 100,000 miles since I changed the plenum gasket the first time.

After reading, this it looks like the back firing is caused by the distributor sync.
Camshaft Timing and Setting Fuel Sync.pdf

It looks like a trip to the dealer to hook to the scantool.

Thanks for the ideas.

I really doubt that ! But do keep us informed of the end issue....

Dan

I would check to make sure cat is not plugging up and also check the oil pump drive and bushing as they had issues with both of them. The oil pump drive bushing when bad will cause a fairly bad miss/stumble around 2000-2300 rpm.

Thanks for the TSB. I will check the play and sync.

It looks like the bushing and drive gear may be causing the issue. My hot oil pressure will fluctuate between 30 and 50. I have replaced the sending unit in past, but that didn't make a difference. It's worth a check to see if the two are related.

How long ago did the rotor get replaced?
I had one like you describe, it was the rotor had burnt a hole thru the center.

Make sure the EGR is working properly. Put vacuum on valve and make sure it does not bleed off. I would not waste your time on the injectors I have never seen one fail like you are describing you can run a resistance check on the injectors as a generic test. Have you replaced the igntion coil? Try spraying the cap, rotor, wires, coil with a solution of salt water and see if you can induce a misfire anywhere.