DII Misfire problem

Aug 20, 2007
2,727
45
Nashville TN
04 DII was running rough , and would occasionally stumbled when first driving when the engine is cold.

Had these codes:
p1300 random misfire
p0305 cylinder 5 misfire
p0307cylinder 7 misfire

I also have live feed code reader connected to my phone. two O2 sensors reed between 0V and .4V. I believe they are supposed to be at .4V.

After replacing coil packs, plugs and wires (8mm magnacore and champion platinum plugs) I now have these codes:
p1884 low output MAF (after cranking it with the MAF unplugged on accident)
p1300 random misfire
p0303 cyl. 3 misfire
p0305 cyl. 5 misfire
p0307 cyl 7 misfire

All the wires are routed correctly. I checked multiple times before installing and compared to the coils that were in there (we had numbered them when we redid the heads about 30K miles ago). The engine seems to run smoothly and there's no noticeable stumbling.

I do have one little vacuum hose on the passenger side that connects to the SAI pump that has broken off. Would this small vacuum leak be enough to be causing these misfires? I also lost the gas cap last time I filled up.

The engine does seem to be running a bit better, but it will idle either really low at first (300 rpm) or really high (1500 rpm)

Any Help is seriously appreciated. I'm getting pretty tired of working on this truck without being able to enjoy it. I've probably spent 30-40 hours on it and have only driven it maybe 10 times in the past year. The rover is not been my DD since January, but we sold my wifes car so we need to use it for our daily commute (7 miles each way)

I pretty much always ran the truck on regular gas, and would seafoam it every once in a while. The truck sat for a year, and I filled it back up again with regular a few weeks ago. is it safe to drive my commute (7 miles each way).

Thanks,
Michael
 
Last edited:

kcabpilot

Well-known member
Mar 26, 2006
334
1
California
Well it's a little late now but when you had the plenum off to replace the coil packs you probably should have cleaned and tested the injectors and replaced the o-rings. A random misfire code can't tell you whether it's fuel or ignition, it could be either.
 
Aug 20, 2007
2,727
45
Nashville TN
It wouldn't be the end of the world to take the plenum off again. I'm going to clean the Throttle body and see if that helps the idle and go form there to check the injectors again. I'm also going to compression test soon as well.

Any other suggestions are still greatly appreciated!


Well it's a little late now but when you had the plenum off to replace the coil packs you probably should have cleaned and tested the injectors and replaced the o-rings. A random misfire code can't tell you whether it's fuel or ignition, it could be either.
 

ezzzzzzz

Well-known member
Apr 22, 2010
604
7
SE Va
All 3 misfires are on the driver's bank. I'd pull those plugs to look for sooting and probably change out the Bank 1 forward O2 sensor.
 

kcabpilot

Well-known member
Mar 26, 2006
334
1
California
Also D2 has 9.3:1 compression ratio, you're supposed to use premium, although this is not related to your current issue.
 

SMLE

Well-known member
Aug 21, 2014
107
2
GA
All 3 misfires are on the driver's bank. I'd pull those plugs to look for sooting and probably change out the Bank 1 forward O2 sensor.

This fixed my problem when I had the exact same codes and soot...
 

Hubacek

Well-known member
Apr 28, 2015
88
0
Dallas, TX
04 DII was running rough , and would occasionally stumbled when first driving when the ingine is cold.

Had these codes:
p1300 random misfire
p0305 cylinder 5 misfire
p0307cylinder 7 misfire

I also have live feed code reader connected to my phone. two O2 sensors reed between 0V and .4V. I believe they are supposed to be at .4V.

After replacing coil packs, plugs and wires (8mm magnacore and champion platinum plugs) I now have these codes:
p1884 low output MAF
p1300 random misfire
p0303 cyl. 3 misfire
p0305 cyl. 5 misfire
p0307 cyl 7 misfire

All the wires are routed correctly. I checked multiple times before installing and compared to the coils that were in there (we had numbered them when we redid the heads about 30K miles ago). The engine seems to run smoothly and there's no noticeable stumbling.

I do have one little vacuum hose on the passenger side that connects to the SAI pump that has broken off. Would this small vacuum leak be enough to be causing these misfires? I also lost the gas cap last time I filled up.

The engine does seem to be running a bit better, but it will idle either really low at first (300 rpm) or really high (1500 rpm)

*************
THIS REALLY JUMPS OUT AT ME. MORE THE REASON TO FIX OR REPLACE ALL VACUUM LINES (they are all brittle) AND REPLACE THE MAF SENSOR ...or at least get a good, known-working unit from another truck to test on yours. I have read where you can unplug the MAF harness and if it is faulty the misfire possibly will cease temporarily BUT this is NOT a fix, just leaving the MAF sensor unhooked, indefinitely. Don't do that. You can first try cleaning your original unit but that MAF cleaner is $10 a can. I swabbed mine with a Q-tip and rubbing alcohol too, but I wasn't having and issues or P-codes with it. I honestly don't even know how or what goes out, there isn't a whole lot going on inside that little MAF tube but a delicate strip and even more delicate sensor tip or 2.
***********

Any Help is seriously appreciated. I'm getting pretty tired of working on this truck without being able to enjoy it. I've probably spent 30-40 hours on it and have only driven it maybe 10 times in the past year. The rover is not been my DD since January, but we sold my wifes car so we need to use it for our daily commute (7 miles each way)

I pretty much always ran the truck on regular gas (WHY) and would seafoam it every once in a while (WOULD THINK SO = REG UNLEADED FUEL?)The truck sat for a year, and I filled it back up again with regular a few weeks ago. is it safe to drive my commute (7 miles each way).

Thanks,
Michael

See above notation first. Then read on at your own discretion.

Have you read the full def of P1300? Besides multiple misfire, it states "catalyst damaging level"
Meaning that after you finally diagnose and repair the culprit behind the misfire you will be replacing the cat-back assembly and that ain't cheap at all. No, you should not be driving the vehicle until it is repaired.

Replace the damn gas cap! I bought a new one labeled for a Toyota Camry or something for like $15 at Oreillys. Just another P-code that isn't necessary, plus it's dangerous and it jacks up fuel consumption. While you are in there, drop another $10 on a roll of vacuum tubing.

I think with vacuum leaks and low grade fuel you are chasing your tail. Do some searches on random misfires with vacuum leaks and reg unleaded in a premium designed system.

Also of note, a faulty MAF sensor can be directly responsible for misfire. You do have a fault code for the MAF sensor. I would replace that but only with the OEM Bosch unit. Do not buy a cheap aftermarket replica...they don't work. As stated by others, the Oxygen sensors can have an affect on misfire but since you do not have a P-code for the O2, start with the MAF. Fix the vacuum leak as this will cause misfire. If you don't have ALL 4 bolts secured in the coil pack bracketry, THiS will also cause misfire. A lot of people that neglect their vehicles or ignore manufacture specs will use the cheap fuel but maybe you haven't seen the 1-million posts about replacing the valve trains, rebuilding the bottom end, replacing the head gaskets, remanunfacturing the cylinder heads, overheating the engine to level of cracks, cylinder liners moving around, and so on and so forth. You don't have a real stout, gem of an engine, hell even when it rolled off the assembly line. Putting good gas in it and changing the oil MORE than regularly with one of the few makes/grades that almost everyone in the community recommends/utilizes, along with quality oil and air filters is the least you can do to prevent a catastrophic failure sooner than need be. No doubt your engine will seize or grenade sooner or later, but sheesh do the very least amount possible to squeeze what you can out of it. And if your coolant temp is over 200 at any time then you really aren't helping yourself. I bought a D2 thinking it would look great on a suspension lift with some steel accessories but here I am 1.5 years later still replacing shit but there is something that comes with owning a piece of junk (at the core) but having the ability to tag/register at any time and not starting the rig every morning to an ongoing flood of Amber warning lights in the gauge cluster and with doubts if it will get you to point-B and back.

PS even when you get the misfire resolved, the struggle never ends. Usually something with the steering. Not sure where yours grades on 1-10 of driveability but replacing the upper/lower ball-joints and the 2 steering rod assemblies will get it back to a 9/10 with healthy tires somewhere near factory spec in size. Don't know if you have done anything with the front driveshaft but that's worth a search if you don't know which little Disco-2 anomaly that I am referring to, but it ends with a destroyed transmission FROM the busted driveshaft. Rebuild or replace both of them at the same time. If you still have red coolant in it, that will also cost you. Could go on half the night about all the junk that takes a dive on these trucks after 15-years.
 
Last edited:

ezzzzzzz

Well-known member
Apr 22, 2010
604
7
SE Va
^ I didn't have O2 codes on my 02 D2 but I did suffer obvious misfires and similar, if not identical, P codes. Replacing the O2, and heavily sooted plugs, resolved the issue immediately. Mine went tits up to a point that driving it was not possible in only one day once the symptoms occurred and the MIL came on. The cat was not damaged but would have likely been if I'd continued driving it. As for octane ratings, I typically use only mid-grade fuel (in all of my vehicles) unless the deal is exceptional. I will use high test when trailering or heading to mountainous areas. There is no apparent difference in performance in the DD mode. I do use good oil and change it regularly though. As for engine failures I blame that more on unaddressed cooling system issues than anything else but to be sure this aluminum engine suffers from poor engineering and little to no upgrades over it's 50+ years of existence. I've only been driving LRs for 25 years so I probably haven't learned enough yet. I'm finally down to 9 and still looking to lower that number.
 

mlnnc

Well-known member
Mar 23, 2008
266
31
Charlotte
I can say from experience that a bad upstream O2 sensor can cause misfires without triggering O2 codes, so yes, change it as others said. Also, the upstream O2 voltages should bounce or switch back and forth between 0.1V and 0.9V.
 
Aug 20, 2007
2,727
45
Nashville TN
The more I think about it, the more it seems it must be the 02, and quite possible the cats needing replaced. I think I'll start with fresh driver side O2 sensors and go from there for now.

Plugs are brand new and the ones that were in there before were had a slightly rough texture on them. I'll replace the o2 sensors and get back to you all.
 
Last edited:
Aug 20, 2007
2,727
45
Nashville TN
I may as well go this route, too.


What are the no-doo-doo recs on new ones? I've seen people mention they've gotten them off Amazon? Or LR vendor?

I went atlantic british for $70 each. I saw them for $55 on amazon I think but wasn't sure if they'd be good or not.