'04 Random Idle Misfire (in gear)
#1
07-21-2023, 11:41 PM
'04 Random Idle Misfire (in gear)
Hi everyone,
I've been working on my new (to me) '04 discovery for a little over a month now. It's got a p38 4.6 swapped into it from a previous owner, and had been running decently but I recently tore a lot of it down to fix a good amount of leaks, and replaced the lower intake gasket, upper intake gasket, injector seals, water pump, timing chain, oil pump, oil pan gasket, and harmonic balancer. Along the way I also swapped in a new y-pipe and 4 new walker brand oxygen sensors. Since I had the intake off and the vehicle came with the parts when I purchased it, I also installed 2 new coils, all new wires, and new champion double platinum plugs. I finally got it running and driving today, and the engine feels great under load when moving, but it's got a random misfire at idle when in gear. The CEL hasn't come on, but i have a pending random misfire, cylinder 4 misfire, and cylinder 8 misfire code. Again, my butt dyno tells me that there's no misfire once above ~1000 rpm, but sitting and idling I can feel a sporadic misfire.
Right now, I'm hoping it's just a vacuum leak, and I'll be doing a smoke test first thing tomorrow. I'll also tidy up my plug wires which are touching one another on both sides, and could potentially be causing a misfire? though I saw no arcing. Regardless, I need to take care of that.
I wanted to see if there is any other direction I could head in diagnosing this issue. It ran a little rough at idle before I performed all the work, but I never got any misfire codes and just assumed it was due to my dead o2 sensor on bank 2. I've seen other people clean their IACV, which I'll probably do as well since it's just the cost of carb cleaner and a little time.
I'll keep this thread updated with anything I find in solving the issue, and any help is greatly appreciated!
I've been working on my new (to me) '04 discovery for a little over a month now. It's got a p38 4.6 swapped into it from a previous owner, and had been running decently but I recently tore a lot of it down to fix a good amount of leaks, and replaced the lower intake gasket, upper intake gasket, injector seals, water pump, timing chain, oil pump, oil pan gasket, and harmonic balancer. Along the way I also swapped in a new y-pipe and 4 new walker brand oxygen sensors. Since I had the intake off and the vehicle came with the parts when I purchased it, I also installed 2 new coils, all new wires, and new champion double platinum plugs. I finally got it running and driving today, and the engine feels great under load when moving, but it's got a random misfire at idle when in gear. The CEL hasn't come on, but i have a pending random misfire, cylinder 4 misfire, and cylinder 8 misfire code. Again, my butt dyno tells me that there's no misfire once above ~1000 rpm, but sitting and idling I can feel a sporadic misfire.
Right now, I'm hoping it's just a vacuum leak, and I'll be doing a smoke test first thing tomorrow. I'll also tidy up my plug wires which are touching one another on both sides, and could potentially be causing a misfire? though I saw no arcing. Regardless, I need to take care of that.
I wanted to see if there is any other direction I could head in diagnosing this issue. It ran a little rough at idle before I performed all the work, but I never got any misfire codes and just assumed it was due to my dead o2 sensor on bank 2. I've seen other people clean their IACV, which I'll probably do as well since it's just the cost of carb cleaner and a little time.
I'll keep this thread updated with anything I find in solving the issue, and any help is greatly appreciated!
#2
07-22-2023, 11:16 AM
Update:
My disco seems to love swisher sweets. I disconnected the intake pipe from the maf and put a rubber glove on the end, and then ran a few cigars worth of smoke through the PCV inlet on the intake manifold (I have done the best4x4 pcv mod) and had a decent bit of smoke coming from the brake booster line and a massive cloud of smoke coming from the bottom of the intake flex pipe. Since this is after the MAF, I am getting a concerning amount of unmetered air into the system. Hoping this is my issue. the bottom of the pipe has a tear, so I will attempt to repair it today and reinstall and am also looking into sourcing a new (used) pipe. Will update if my repair is successful and if this resolves the issue, or if I will be digging deeper.
If anyone is interested in my vacuum leak setup, I can make a separate post. I hate cigars, but a swisher sweet fits perfectly into the end of the hose on the el cheapo harbor freight transfer pump, and the other end of the hose fits perfectly over the pcv nipple. Makes it easy to pump a large amount of smoke into the intake, and each test is cheap (~ $1 per cigar).
My disco seems to love swisher sweets. I disconnected the intake pipe from the maf and put a rubber glove on the end, and then ran a few cigars worth of smoke through the PCV inlet on the intake manifold (I have done the best4x4 pcv mod) and had a decent bit of smoke coming from the brake booster line and a massive cloud of smoke coming from the bottom of the intake flex pipe. Since this is after the MAF, I am getting a concerning amount of unmetered air into the system. Hoping this is my issue. the bottom of the pipe has a tear, so I will attempt to repair it today and reinstall and am also looking into sourcing a new (used) pipe. Will update if my repair is successful and if this resolves the issue, or if I will be digging deeper.
If anyone is interested in my vacuum leak setup, I can make a separate post. I hate cigars, but a swisher sweet fits perfectly into the end of the hose on the el cheapo harbor freight transfer pump, and the other end of the hose fits perfectly over the pcv nipple. Makes it easy to pump a large amount of smoke into the intake, and each test is cheap (~ $1 per cigar).
#4
07-22-2023, 12:03 PM
#5
07-22-2023, 06:41 PM
Another Update -
Managed to successfully repair the intake pipe and eliminate all vacuum leaks from the system. I also got my plug wires separated, and cleaned my IACV. I still have a weird random miss at idle, it's hard to notice unless you're sitting in the car and feel it or if you're standing behind the tailpipe, but its definitely there. I just took it for a drive and didn't get any misfire codes (pending or confirmed) but do now have the SAI p1412 and p1415 codes, which sucks since I just vacuum tested the entire system and don't have any vacuum leaks that I'm aware of. I'll try and test my solenoid later tonight to see if its operating properly (I am looking there first since I dropped it on the ground... oops).
I assume I'll get a misfire code at some point, but we'll see. In the meantime I'll also run a bottle of chevron injector cleaner to see if that helps clear anything up. If anyone has any other ideas for things to look at resolving the misfire (or SAI codes) please let me know. I'm at a loss at this point.
Managed to successfully repair the intake pipe and eliminate all vacuum leaks from the system. I also got my plug wires separated, and cleaned my IACV. I still have a weird random miss at idle, it's hard to notice unless you're sitting in the car and feel it or if you're standing behind the tailpipe, but its definitely there. I just took it for a drive and didn't get any misfire codes (pending or confirmed) but do now have the SAI p1412 and p1415 codes, which sucks since I just vacuum tested the entire system and don't have any vacuum leaks that I'm aware of. I'll try and test my solenoid later tonight to see if its operating properly (I am looking there first since I dropped it on the ground... oops).
I assume I'll get a misfire code at some point, but we'll see. In the meantime I'll also run a bottle of chevron injector cleaner to see if that helps clear anything up. If anyone has any other ideas for things to look at resolving the misfire (or SAI codes) please let me know. I'm at a loss at this point.
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