2000 Mountaineer 4.0 SOHC P0174 backfires when in gear accelerating

[wherestheswitch]

I just replaced all of the O2 sensors. Still having problems. I drove it 20 miles (needed to check transmission fluid). The check engine light only came on at the end of my trip when I hit the gas pretty hard to make it downshift to speed up. The only codes it gave me were misfires on 5 and 6. I could be mistaking a popping sound of an exhaust leak as back firing. I kind of assume it was backfiring in the intake because of the lean code but to me it actually sounds like the noise I hear comes from under the vehicle maybe around the catalytic converters. It sounds like a lot of popping (not incredibly loud but definitely noticeable) only when sort of heavily accelerating. You can manage to get it to not make popping noises if you are really easy on the gas. I did run live data at the end of the trip idling in the yard in closed loop. It still got higher fuel trims on bank 2. My line of thinking is maybe whatever damaged the first catalytic converter (gas exploding maybe) possibly damaged the exhaust pipe around the converter material causing a leak and making the downstream O2 read too much air, which is why I hear the popping down there. Obviously that is purely speculation at this point. I do know that before I took off the intake the first time to check the injector this truck ran just fine I was just trying to get rid of the misfire code (at the time you couldn't tell it was even skipping at all)... After putting everything back together and running the seafoam this truck started popping and what not. I never noticed any loud bangs that could have been the cause of the cat damage (that I recall). I am reluctant to look into the timing just because there was never any heavy load put onto the engine to cause timing issues. They are chains instead of belts so there are a bit more rigid, plus there's no rattling of any kind going on. The timing advance on the code scanner at idle (low at around 650 RPM) is around 17.5 degrees whatever that may tell you. Just wanted to give you guys an update. Starting to think maybe I am just an idiot who has no place trying to fix a vehicle lol.

 

[koda2000]

I just replaced all of the O2 sensors. Still having problems. I drove it 20 miles (needed to check transmission fluid). The check engine light only came on at the end of my trip when I hit the gas pretty hard to make it downshift to speed up. The only codes it gave me were misfires on 5 and 6. I could be mistaking a popping sound of an exhaust leak as back firing. I kind of assume it was backfiring in the intake because of the lean code but to me it actually sounds like the noise I hear comes from under the vehicle maybe around the catalytic converters. It sounds like a lot of popping (not incredibly loud but definitely noticeable) only when sort of heavily accelerating. You can manage to get it to not make popping noises if you are really easy on the gas. I did run live data at the end of the trip idling in the yard in closed loop. It still got higher fuel trims on bank 2. My line of thinking is maybe whatever damaged the first catalytic converter (gas exploding maybe) possibly damaged the exhaust pipe around the converter material causing a leak and making the downstream O2 read too much air, which is why I hear the popping down there. Obviously that is purely speculation at this point. I do know that before I took off the intake the first time to check the injector this truck ran just fine I was just trying to get rid of the misfire code (at the time you couldn't tell it was even skipping at all)... After putting everything back together and running the seafoam this truck started popping and what not. I never noticed any loud bangs that could have been the cause of the cat damage (that I recall). I am reluctant to look into the timing just because there was never any heavy load put onto the engine to cause timing issues. They are chains instead of belts so there are a bit more rigid, plus there's no rattling of any kind going on. The timing advance on the code scanner at idle (low at around 650 RPM) is around 17.5 degrees whatever that may tell you. Just wanted to give you guys an update. Starting to think maybe I am just an idiot who has no place trying to fix a vehicle lol.

Has anyone suggested you double check your spark plug wires to makes sure they are installed correctly? It's pretty easy to mix the wires up (I've done it more than once). Maybe cly 5 and 6 plug wires are crossed? If you've got two spark plug wires crossed you would likely be dumping raw fuel onto the cats and perhaps igniting it in the exhaust. Catalytic converters don't just die. They are murdered.

2000 4.0L SOHC firing order - 1-4-2-5-3-6 (coil and cyl layout below)

You don't need to hear a large bang for a SOHC timing chain to jump time. When the chains wear and stretch and the hydraulic chain tensioners weaken with age it can and has happened.

 

[wherestheswitch]

I referred to the loud bang as the possible cause of a possible exhaust leak...not so much the timing. An update: I still have the same issues. I took off the upper and lower intake and took out the injectors and replaced the seal adapters. I am waiting on some injectors to come in and ill go ahead and replace all of those. while I had it apart I also replaced the egr tube o-ring and PCV valve. I wanted to check the crankcase breather but id have to remove most of the sensor connectors to move the wiring harness out of the way and as Im just fixing this in my yard (its been raining alot lately) I feel like I will get stuck with the top end exposed during the rain and im trying to avoid that if possible. I am in the process of trying to close a deal on a house with a garage as well so theres the possibility of being able to have it apart for longer in the near future. I tested the coil and theres a couple resistance values im concerned about but also not completely sure as the haynes manual is vague. Ill post those up soon and see what you guys think. Ill make sure to triple check the order of the plug wires too when I can verify the coils condition.

 

[wherestheswitch]

So, as koda2000 suspected, I managed to mix up the coil wires. Feels bad man. It runs great now though so you can close this one down. As always I greatly appreciate all of your contributions. Im going to go headbutt a wall for making this much of a headache for myself.

 

[koda2000]

So, as koda2000 suspected, I managed to mix up the coil wires. Feels bad man. It runs great now though so you can close this one down. As always I greatly appreciate all of your contributions. Im going to go headbutt a wall for making this much of a headache for myself.

Don't feel bad. We've all done it. Glad you got it sorted out.