I started with a leaking plenum gasket, no power, misfiring, etc. I tried just replacing the gaskets with Felpro, that failed badly due to the plate bolts being too long. The second time I used a Hughes kit and Felpro gaskets. At one point I thought the cat might be plugged so I removed it by breaking it apart and blasting it out. Yes I removed the O2 sensor first. I have more power than before but I get the 3 codes for 8,6 and random misfires. It idles rough but really stumbles when it shifts into OD. I have recently replaced the: coil, plugs, wires, cap and rotor. I have cleaned my PCV and the tubing that goes to the manifold. The fuel pressure is at 49. The resistance on all the injectors is the same. I swapped the 2 and 8 injectors with no change. The voltage pulse from the harness is the same at 2 and 8 also. When I unplug the 2 injector the motor slows it does not with 8. When I pull the plug wires I can get a consistent snap on the heat shields for 6 and 8. Compression on 6 and 8 is at 140 dry. The other cylinders are not far off either. I have run it with the O2 sensors in, removed and in but unplugged with no difference in performance. On the scanner they range from 0.12 up to 0.9. I have not looked at the cam or crank sensors yet and I didn't go as far as the timing chain. Any thoughts would be appreciated.

 

Hhhmmm.... the numbers look reasonable, those cylinders should be firing. Even with cracked valve seats, it should still fire.... What brand plugs did you put in? Might wanna pull number 8, and make sure it isn't cracked, fouled, or whathaveyou.

And: Welcome to DF!

 

The new ones are Bosch, I put my old regapped NGKs in and didn't see a difference. The Bosch have oil on them and the NGKs came out darker. I was guessing it was from it not firing.

 

Is your temp gauge accurate?

Two cylinders right next to each other misfiring is usually suspicious, but, on the dodge, those are the two cylinders that fail first when the plenum goes, and eats the cat. As your cat is hollow..... and you have ran all the tests that I would normally suggest.....

How does the spark look on 6 and 8 as compared to 1 and 3? It *might* be crank sensor related.... but, if the spark looks nice, that would kinda eliminate that as a cause.

Also wondered if the headgasket was leaking between 6 and 8... but, compression numbers don't really indicate that... (unless the rest were rather higher than those two...)

Valve springs?

 

Well you caught me on the temp sensor. I literally pulled the guts out of it (carefully) both times and placed it back in with instant glue. It doesn't seem to be reading too far off from before. I forgot to mention the new 195* t-stat. I will watch it more closely with the gauge and the scanner.
The spark looks relatively the same over all the plugs (except 7 I didn't reach for that one).
The compression numbers range from 125 to 160.
I also thought of the valve springs but I haven't gotten over the idea of pulling everything away taking the cover off and then having it leak once I check that the springs are OK.
In the mean time I popped the PCV and pumped propane in there for a bit but that didn't pick up the RPMs so seems like the valve seals are acceptable.
Lastly, thanks for your help on this Christmas Eve Eve.

 

Well.... according to Chrysler.. your compression numbers are out of spec. All cylinders should be within 10 percent of each other. But, the cylinders you are having issues with AREN'T on the low side.... so much for that thought.

You *might* have the rubber valve cover gaskets. Hence, reusable. If nothing else, I think they are like 20 bucks at the parts store....

Merry Christmas.

 

Thanks Hey You, I'll take a look in the next day or two.

Merry Christmas to you and everyone on the DF.

 

I would start with the standard Champion copper plugs as a lot of Ma's engines like nothing but. I would also go with the highest quality of cap and rotor that you can find, nothing Boshe. I believe Standard was a good brand for these. Good luck.

 

A leakdown test on 8 and 6 would tell for sure. Sometimes cranking compression numbers look okay, but on a running engine might be a different story. Obviously 8 isn't contributing. Stick with copper champion plugs.

 

Bosch plugs work just fine in these trucks get over it guy's. It's when you get into the Iridium plugs that's when things get iffy. I have used Bosch +4 with great success in my motors stock or built, I currently have Bosch super copper's in it and it likes them just fine.
I can post that my truck just hates the cheap *** Autolite plugs and it does, but many like them and use them.