Random missfire (NO CEL) (1 Viewer)

[sandcruiser80]

1997 LX450 with 390k on the clock.
Over the past few weeks I have been experiencing a random miss fire. It started slight, I could barely notice it on cold starts and progressively gotten worse. It happens on cold starts for the first 15-30 seconds, run fine for a second a miss and then fine and miss, I loose about 100rpm when it misses but if I rev it, it’s fine. I can still drive the truck but it’s most noticeable when I let off the gas. If I go from a stop and give it consistent gas, no miss. If I feather the gas off while driving, it misses but only once, maybe twice. I did put in a gas treatment and the problem will go away for a few days and then come back. It’s definitely getting worse and I attached a video of it happening as I know how to make it happen now. Iv gotten NO CEL the entire time. Iv cleaned the MAF, checked the O2 sensor connectors for water inside and checked the distributor and rotor. I even pulled out the fuel pump and changed the sock. I’m going to pull the fuel filter and dump it and see what kind of stuff comes out as I think it’s fuel related because when I put treatment in it, problem goes away. I don’t want to pull and have the injectors tested as this is my daily driver and the job is a pain. Anyone have more ideas that don’t break the bank?

 

[sandcruiser80]

1997 LX450 with 390k on the clock.
Over the past few weeks I have been experiencing a random miss fire. It started slight, I could barely notice it on cold starts and progressively gotten worse. It happens on cold starts for the first 15-30 seconds, run fine for a second a miss and then fine and miss, I loose about 100rpm when it misses but if I rev it, it’s fine. I can still drive the truck but it’s most noticeable when I let off the gas. If I go from a stop and give it consistent gas, no miss. If I feather the gas off while driving, it misses but only once, maybe twice. I did put in a gas treatment and the problem will go away for a few days and then come back. It’s definitely getting worse and I attached a video of it happening as I know how to make it happen now. Iv gotten NO CEL the entire time. Iv cleaned the MAF, checked the O2 sensor connectors for water inside and checked the distributor and rotor. I even pulled out the fuel pump and changed the sock. I’m going to pull the fuel filter and dump it and see what kind of stuff comes out as I think it’s fuel related because when I put treatment in it, problem goes away. I don’t want to pull and have the injectors tested as this is my daily driver and the job is a pain. Anyone have more ideas that don’t break the bank?

 

[sandcruiser80]

Just took off the fuel filter and shot some brake cleaner through it both ways and this is what came out, no big chunks of anything but I’m pretty sure it’s not supposed to be black/brown. Filter probably has 80k on it

 

[sandcruiser80]

Well I have my answer, cleaned the filter but now the misfire is worse and I noticed when it missed, I was getting a little puff of of white smoke. I smelled the exhaust pipe after I shut it off and it definitely smells sweet like burning coolant, pretty sure my head gasket is shot. Luckily I caught it early enough that I think I can just replace the head gasket and nothing else is damaged. The coolant is still clean and red and the oil is not milky. I think the gasket blew and was seeping coolant into the combustion chamber and it was burning off after warming up but now it’s definitely seeping in after it’s hot. Iv rebuilt this motor once so it shouldn’t take me to long to do it again and I don’t think I’m going to pull the motor out of the truck this time. Wish me luck…

 

[Old Nick]

Well I have my answer, cleaned the filter but now the misfire is worse and I noticed when it missed, I was getting a little puff of of white smoke. I smelled the exhaust pipe after I shut it off and it definitely smells sweet like burning coolant, pretty sure my head gasket is shot. Luckily I caught it early enough that I think I can just replace the head gasket and nothing else is damaged. The coolant is still clean and red and the oil is not milky. I think the gasket blew and was seeping coolant into the combustion chamber and it was burning off after warming up but now it’s definitely seeping in after it’s hot. Iv rebuilt this motor once so it shouldn’t take me to long to do it again and I don’t think I’m going to pull the motor out of the truck this time. Wish me luck…

Sorry to hear that you're dealing with this, but also glad that you've found out what the matter is and can fix it.

 

[sandcruiser80]

I have been running sea foam through the fuel system, that probably accounts for the white haze on them but not one gives me a idea of what cylinder may be blown..