Misfire Codes after headgaskets

[KingKong8247]

Last summer I swapped the 4.0 out of my 98 Discovery for a Bosch 4.6. Used the Frankenrover website to pretty much guide me through it. So basically it is a 4.6 block and heads with everything else from the 4.0.

She ran fine after it was all said and done except the head gaskets started to leak. Never overheated. I could see the leak towards the front of the heads. So I brought her to a shop to have the head gaskets done. Unfortunately she had to sit for several months before I could pick her up from the shop. They would occasionally drive the truck for me in the mean time.

Fast forward to now and maybe 1000 miles after the headgaskets and the truck has these codes:
P0300 - Random Misfire
P0308 - Misfire cyl 8
P1314 - Misfire Catalyst Damage, bank 2
P1313 - Misfire Catalyst Damage, bank 1

Replaced all spark plugs NGK BPR6ES and wires 8mm Magnacore. Originally had magnacores that looked beat so replaced with NGK's I had laying around until the new wires came in and still got the codes. Cylinder number 1 plug had excessive gap, >.050, when pulled but all plugs looked fine.

Truck appears to run just fine without stumbling or rough idle. Even gets 13 mpg on hwy with roof rack lift and HD bumpers. I also didnt have these codes before the headgasket job. I put a few hundred miles on the engine after the swap.

Thought possible bad gas clogged injectors so ran full bottle of seafoam in gas, always 93 octane.

Cats have under 50k miles but could have gone bad from driving around with the apparent misfire.

I am going to check the tabs on the flywheel in the inspection plate to see if any of those are bent.

I have not checked compression yet.


Any other thoughts?

 

[yoseffby]

Did you ever find a solution? I have about the same symptoms.

So far I have P1313, P1314, P1316.

The truck smells like its running rich most of the time. I have observed that I get nearly no spark or a weak spark on 2-4 of the valves intermittently. From the same two coils. I replaced all four coil packs with a set from British Atlantic and the issue has persisted. Looking at the O2 sensors output the two upstream sensors were pretty much zero all the time and all had some sporadic 1 and 0 readings. Replaced all four O2 sensors. Now the readings are still pretty extreme. A lot of the time its at 0 or 1 and I noticed that when the engine is running rough it will often go to zero and then 1 when it kicks back with spark on all 8. I checked the wires running from the coil pack to the ecu and those all test good. I also replaced all the plugs, wires, MAF, and Crank Speed Sensor.

 

[mastercamper]

Are your O2's new? I had issues with a bank misfiring and the o2 sensor plug had oil in it.

 

[yoseffby]

I did replace the 02 sensors. After a couple days with the new Crank Sensor I haven't seen any codes and the O2 sensor readings are much better (staying in the .7-.95 range) BUT the truck is still loosing power and misfiring. I'll see if I can get any new codes after driving it some more....

 

[ERover82]

Had the same issue with a GEMS 4.0 rebuild. Never figured it out. Last theories were bad cam, cam gear, lifters, or rocker assembly (all were cheap parts), or glazing of cylinder wall due to break-in with synthetic. Got sick of dealing with it and moved on.

 

[yoseffby]

New codes P1371 and P1376. Haven't been able to find anything concrete on P1376. Actually these were showing up a while ago but turned into P1313, P1314 and P1316 which all went away when I replaced the Crank Position Sensor and now these have returned. Would really appreciate any good info on 1376 or the general situation. Thanks!

 

[discostew]

I cant find the P1376. But I did find p0376. "timing reference high resalution signal B too many pulses" I've never seen that code before either. Usually the 1 in front instead of the 0 means that it's intermittent.

Those other codes are pretty weird too. The P1371 is early activation of coil#1(cylinders 1 & 6. I think I would be looking at whatever modification you had to make to get that crank sensor to work in the wrong block.

 

[yoseffby]

The truck started running worse again and I hooked it up to my reader, same codes showed up and I noticed one of the rear O2s was reading 0. Funny since I replaced them with new ones a couple weeks ago. A few minutes later the engine starts running better than I can remember in recent memory. It has stayed running great now for a couple quick drives, starting up and running very smooth and powerfully, its a dream. The interesting thing is that all four O2 sensors are now reading 0 constantly, sometimes .02 or something like that but never near the normal range.

 

[yoseffby]

I cant find the P1376. But I did find p0376. "timing reference high resalution signal B too many pulses" I've never seen that code before either. Usually the 1 in front instead of the 0 means that it's intermittent.

Those other codes are pretty weird too. The P1371 is early activation of coil#1(cylinders 1 & 6. I think I would be looking at whatever modification you had to make to get that crank sensor to work in the wrong block.

Also, I'm not sure what you meant by this modification. I replaced the crank sensor one to one with a new part. No modifications needed.

 

[discostew]

I thought you said it was a 4.6 Bosch block. I was under the impression you would have to change the crank sensor mounting boss. I've never done that so I really have no clue. Somebody here probably does.

 

[discostew]

I wonder if you have s cam sensor problem going on. I think it's like a 1 in 6 chance that fuel injection is timed properly on start up when your cam sensor is not working. Since it's sequential it needs to know what injector to open when.

 

[yoseffby]

o2 sensor readings are back in the normal range and the truck is running horribly again. I ordered a replacement cam sensor and will try that next week.

 

[discostew]

I'm not saying I would go buy a cam sensor. I would check it out. You have some kind of correlation fault it looks like. I have really never seen or heard of these faults till I went looking for you. For the car to be picking on the early activation of coil#1 extra pulse from the other code is maybe a clue. You have a scope you could put on your crank sensor signal? I kind of think you would have a cam sensor code if that was the problem.

 

[yoseffby]

I have a multimeter I can put the car up and check the crank sensor (new part), is that what you're suggesting? I was thinking that maybe I have some bad tabs on the reluctor ring but that's why its so weird when it comes back for a day or 30 sec and works great. I like the cam sensor idea because it definitely runs rich when it runs bad. Thanks for your help!

 

[yoseffby]

Checked the crank sensor reading, its consistently good and the reluctor tabs look good. I'm wondering about the throttle position sensor now...