Check Engine Light is on

[clanofwolves]

OK, the family and I are 400 miles from home in the mountains and the truck starts running rough followed by the check engine light appearing. Auto Zone's finest plugs in the box and tells me I have a mis-fire on #4. The wires and plugs are basically new; I pull the plug and run her and see a spark on the grounded #4 plug. I figure it's a fuel issue like the injector. So, we drive it home.

Today, I get it checked again and I get:
1) P0120 "Throttle/Pedal Position Sensor"
2) P0300 "Misfire"
3) P0301, P0303, P0304 (which are) "Misfire on #1, #3, and #4"

Just looking through the forum and it looks like the "old needle in the..." but I'm looking for the best first step. Any help is appreciated as I want to keep my hair.

Thanks!!

 

[FROGrunner]

I believe a faulty TPS can create a misfire condition. P0300 will almost always come on whenever a misfire is detected. Does it run rougher when you apply the throttle?

 

[clanofwolves]

I believe a faulty TPS can create a misfire condition. P0300 will almost always come on whenever a misfire is detected. Does it run rougher when you apply the throttle?

When parked, it is not rougher when throttle is applied. When driving, it seems to be roughest when driving with under 2K showing on the tach, but when it is over 2K, it is smoother.

 

[clanofwolves]

I just replaced the TPS and the roughness and the error codes for misfires on cylinders #1, #3 and #4 still show up on the AutoZone reader.

I'm thinking of swapping a coil-pack and seeing if the misfire cylinders change with them. Good idea?

Oh, and as far as the exhaust goes, I can hear a mis and I'm not sure, but it seems the smell is a bit more sulfur than usual....

 

[BrianSD_42]

Borrow / rent a compression tester tool from autozone and post each CYL compression here.

It's cheap and will help to identify or sort of rule out a mechanical a electrical problem.

 

[drdolittlerwc]

How many miles on it? Have you changed the timing belt?

 

[clanofwolves]

How many miles on it? Have you changed the timing belt?

190K and the belt has been replaced and it's within the recommended window of miles.

I swapped the rear and center coil pack and now I only get a misfire code on #4 as it was last week. I'm thinking fuel, like the #4 injector.

 

[clanofwolves]

Borrow / rent a compression tester tool from autozone and post each CYL compression here.

It's cheap and will help to identify or sort of rule out a mechanical a electrical problem.

Good idea, I'll check #4; what should it read on this motor??

 

[drdolittlerwc]

Good idea, I'll check #4; what should it read on this motor??

Generally, it's best to check them all and look for any major differences. I don't have my manual here for actual specs, but if it's compression you'll notice by comparing the numbers.

 

[clanofwolves]

Rough running problem solved!!

Interestingly enough, the problem is finally fixed!!

I'm not sure how much the first repair did, but I replaced the TPS and that code was cleared...but the engine still ran rough even though not quite as badly.

As a bit of history, the plugs and wires were replaced two years ago at the Toyota dealership (not in my possession at that time, but in the hands of a family member) and they certainly looked fine. Even so, I pulled the plugs and wires and gave them the once-over, but I didn't "really" inspect them beyond the eye test. However, after exhausting all my troubleshooting options yesterday and getting tired of removing, relocating and reinstalling items (coil packs, injectors, etc.) and then having the codes run again and again to look for alterations in the denoted "misfire" cylinders, I once again played with a wire or two and my oscilloscope. The real issue was the wires! The three wires on the drivers side (the only side with any) were somehow cross arcing just enough to throw the spark intensity off the cylinder that needed it and giving a little hit to one on an intake or exhaust stroke. It peeved me that this expensive "scheduled maintenance" item by Toyota was of such poor quality. Maybe it was just a bad batch of wires with an error in their shielding construction? In any event, with a set of replacements (that one would assume to be of less quality) from AutoZone, it purrs like a kitten now and shudders not.

Thanks for all of the help!! You guys rock!!

 

[TheDurk]

Interestingly enough, the problem is finally fixed!!

I'm not sure how much the first repair did, but I replaced the TPS and that code was cleared...but the engine still ran rough even though not quite as badly.

As a bit of history, the plugs and wires were replaced two years ago at the Toyota dealership (not in my possession at that time, but in the hands of a family member) and they certainly looked fine. Even so, I pulled the plugs and wires and gave them the once-over, but I didn't "really" inspect them beyond the eye test. However, after exhausting all my troubleshooting options yesterday and getting tired of removing, relocating and reinstalling items (coil packs, injectors, etc.) and then having the codes run again and again to look for alterations in the denoted "misfire" cylinders, I once again played with a wire or two and my oscilloscope. The real issue was the wires! The three wires on the drivers side (the only side with any) were somehow cross arcing just enough to throw the spark intensity off the cylinder that needed it and giving a little hit to one on an intake or exhaust stroke. It peeved me that this expensive "scheduled maintenance" item by Toyota was of such poor quality. Maybe it was just a bad batch of wires with an error in their shielding construction? In any event, with a set of replacements (that one would assume to be of less quality) from AutoZone, it purrs like a kitten now and shudders not.

Thanks for all of the help!! You guys rock!!

What brand did the dealer sell you? Sometimes they have OEM Sumitomo's and sometimes they sell Denso.

 

[clanofwolves]

What brand did the dealer sell you? Sometimes they have OEM Sumitomo's and sometimes they sell Denso.

They were tagged with "Denso" and on the outside they looked fine. For kicks I took one wire and lightly pulled it as I held a boot and the shielding wire came loose and pulled right out; the interior was crumbly. I think I'm going to contact Pinehurst Toyota and complain; these wires were only two years and 10K old. So much for a super cheap tune up deal...