Help! Chronic Misfire Issue - 99 UZJ100

[blkwrpp]

Hey all, hoping I could get some advice here on a chronic issue I have had on my 99 UZJ100.

Vehicle Stats:

Purchased: April 2014 - ih8mud listing
Current Mileage: 266,682

I have meticulously kept up maintenance on the vehicle and only now am I having trouble with diagnosis and solving the root issue of my truck's cylinder misfires.

Please see the service history below for reference


I originally had replaced all spark plugs and #7 coil pack in 2017. This was the first time having to replace plugs and coil packs as the truck's owner. This lasted for a few years until I decided to do preventative replacement on all 8 cylinders. It seems as though these fixes last for a summer, but as soon as winter in Colorado comes, the issue comes back. In fact, it seems to really be triggered by snow/cold weather.

After a full replacement, the plugs/coils lasted for a year, then like clockwork, started misfiring again. Cylinder 7 on 12/01/2021 was promptly fixed.

Then Cylinder 1 and Cylinder 2 only a month later. I had shrugged this off as either poor work done by the mechanic shop, or poor quality parts (ECH Ignition Coil - IC336).

Fast forward another month, and Cylinder 1, Cylinder 2 and Cylinder 7 begin to misfire AGAIN. At this point I started to worry about an oil leak or a head gasket issue so I took the truck to a Toyota specialist who only focuses on 4x4 Toyotas. I had them run a compression test and the truck came back with flying colors. The mechanics had noticed water sighting poor sealant by the previous mechanic. All 8 plugs (Denso 673-1303) and coil packs were replaced and the truck ran fine throughout the summer.

Once again on a snowy day in January, the truck has begun to misfire. P0300 (Multiple misfires detected), P0301 (Cylinder 1 misfire), P0302 (Cylinder 2 misfire), and P0307 (Cylinder 7 misfire).

There is certainly a pattern here, why would it only be those 3 cylinders constantly? I will certainly keep replacing plugs/coils/etc, although I shouldn't have to do it 3 times in 3 months as I am having to do now. I am having tough time figuring out the root of the problem.

The next steps are to run the truck through a series of tests that are seemingly simple but expensive at a mechanic. Ex. Water off the windshield.
Will also look again for oil in spark plug wells, look for faulty connector/wires, check for blown fuses etc.

I am at a loss, so any help would be MUCH APPRECIATED!


Misfire Related Service History:

P.S. There has been an extensive amount of work done to the vehicle. Above is simply related to the issue.

 

[Mauser]

My only guess, is either a cam or crank sensor.

 

[neoworm]

OEM coils?

 

[SteveH]

Can you move the bad coil packs to different cylinders and see if the problem follows - just to be sure the truck is properly reporting the problem? DENSO coils should be reliable, but who knows.

If you think high voltage (over time) is killing the coils, I would think a shop could watch voltages for each cylinder and see of some weirdness is taking place.

 

[hxidynsxge]

Hey all, hoping I could get some advice here on a chronic issue I have had on my 99 UZJ100.

Vehicle Stats:

Purchased: April 2014 - ih8mud listing
Current Mileage: 266,682

I have meticulously kept up maintenance on the vehicle and only now am I having trouble with diagnosis and solving the root issue of my truck's cylinder misfires.

Please see the service history below for reference


I originally had replaced all spark plugs and #7 coil pack in 2017. This was the first time having to replace plugs and coil packs as the truck's owner. This lasted for a few years until I decided to do preventative replacement on all 8 cylinders. It seems as though these fixes last for a summer, but as soon as winter in Colorado comes, the issue comes back. In fact, it seems to really be triggered by snow/cold weather.

After a full replacement, the plugs/coils lasted for a year, then like clockwork, started misfiring again. Cylinder 7 on 12/01/2021 was promptly fixed.

Then Cylinder 1 and Cylinder 2 only a month later. I had shrugged this off as either poor work done by the mechanic shop, or poor quality parts (ECH Ignition Coil - IC336).

Fast forward another month, and Cylinder 1, Cylinder 2 and Cylinder 7 begin to misfire AGAIN. At this point I started to worry about an oil leak or a head gasket issue so I took the truck to a Toyota specialist who only focuses on 4x4 Toyotas. I had them run a compression test and the truck came back with flying colors. The mechanics had noticed water sighting poor sealant by the previous mechanic. All 8 plugs (Denso 673-1303) and coil packs were replaced and the truck ran fine throughout the summer.

Once again on a snowy day in January, the truck has begun to misfire. P0300 (Multiple misfires detected), P0301 (Cylinder 1 misfire), P0302 (Cylinder 2 misfire), and P0307 (Cylinder 7 misfire).

There is certainly a pattern here, why would it only be those 3 cylinders constantly? I will certainly keep replacing plugs/coils/etc, although I shouldn't have to do it 3 times in 3 months as I am having to do now. I am having tough time figuring out the root of the problem.

The next steps are to run the truck through a series of tests that are seemingly simple but expensive at a mechanic. Ex. Water off the windshield.
Will also look again for oil in spark plug wells, look for faulty connector/wires, check for blown fuses etc.

I am at a loss, so any help would be MUCH APPRECIATED!


Misfire Related Service History:
View attachment 3210503

P.S. There has been an extensive amount of work done to the vehicle. Above is simply related to the issue.

CAM sensor?

 

[blkwrpp]

UPDATE

I was able to pinpoint the issue down to faulty fuel injectors. It turns out that cylinder 1 was simply soaking the spark plug causing the misfire which also carried over to cylinder 2. Cylinder 7 had the same issue.

I replaced all 8 fuel injectors and have not had a single misfire for a few hundred miles now.


One piece that seemed to cause another issue the amount of ethanol mixed in at most gas stations. The ethanol certainly contributed in soaking the spark plugs. I was able to clear the tank and add red Heet.

I appreciate all the support and trouble shooting!

 

[bmwjnky]

Glad you fixed your issue. My first thought before even getting to the end of your first post was an injector issue. I don't know why, maybe it was the almost 30 years working on cars, but fuel system/injector was my first thought. Make sure to change your fuel filter every other year or so, they are not that expensive for genuine ones and fairly easy to access under the hood.

I would also run a bottle of Red Line injector cleaner once a year. Of all the injector cleaners I have used over the years as a tech and shop manager, even the uber BG stuff, the Red Line one is the only one I have had work for cleaning up the fuel system. Their other products I'm so/so on but for fuel system clean-up it's my go to. You can usually get a 2 pack on Amazon for $25-30 depending on the seller.