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My 2002 4.7 tundra got towed home from the gas station last week and I'm hoping some of you fine folks can help me troubleshoot this down a bit more.

I know misfiring questions come up often, but I'm hoping I've compiled enough information that someone will be able to help narrow it down a bit more or maybe suggest something different entirely.

I've been doing repairs for a couple months now and I don't know what, if any, of the issues I'm seeing are connected so I've included some background leading up to getting towed just in case it's relevant.

Background:
I've had the truck about a year. At time of purchase, it was almost due for its 2nd timing belt/water pump and was throwing a CIL for o2 censors. I (at the time) didn't have a code reader of my own and opted to not clear the codes.

I ran it like that for almost a year (not daily) before changing the timing belt/water pump a couple months ago. Except for a broken crankshaft sensor connector, that job went well. I drove it for a few weeks before it overheated going uphill with a bed-load. I didn't notice until it was already in the red. No leak visible on ground or under hood and the dipstick looked fine but smell of coolant was in the air.

A passer-by in a 2nd Gen Tundra suggested burping the coolant system, something I didn't do after timing belt job. Got it home, burped system and truck stopped overheating but the faint smell of coolant remained in the air. Never smelled inside the cab, only outside and reservoir level looked fine. Ran it for a couple weeks before coolant started dripping onto the ground.

Followed the leak to an O-ring at the Water Inlet Assembly. Part of the ring pushed through and was visible. This ring was new, replaced during timing belt job. I found at least one bolt loose. I must not have torqued enough when attaching water inlet assembly or maybe too much anti-seize. Replaced o-ring and torqued down plenty. Leak stops and the smell of coolant at operating temperature also goes away. Used truck to haul a trailer with 6 grown pigs on a route with hills and has no problems.

All the while this is going on, the pipe connecting the resonator (16” After-Market tube shape) to the muffler had completely separated where the resonator and pipe met. It was loud but seemed fine otherwise. I had the parts, just not the time.

The Problem At Hand:
A couple weeks ago, on a particularly cold morning, I went out to start the truck and it sounded real rough and loud. Louder than just the broken exhaust. As I started driving, the CIL started blinking. I drove about an 8th of a mile to where I was going before pulling over and shutting it off. Waited a few moments and turned it back on. It still sounded rough but the CIL stopped blinking. I let it idle and as it warmed, it seemed to come out of it some. Drove back home the 8th of a mile without the CIL blinking and sounding fine (lower RPM) so I assumed it was cold related somehow.

I had to drive to town the next morning (10 miles round trip). I start the truck and it sounds rough again. I let it warm up for a few minutes, assumed it'd be like the day before and head out to the store. The first couple miles are mostly downhill at 35 mph. I can tell its still not right, but it seems to be coming out of it again. Pull out to a flat main road and the truck doesn't want to go over 40-45. The closer I get to the store, the slower the truck wants to go. As I pull into the parking lot, it barely has enough power to make the turn. As I crawl into a parking space, the truck stalls completely and won't start.

Get myself and truck home and borrow neighbor's code reader. I get the following codes in this order (All appear twice)

PO300 - Random/Multi-Cylinder Misfire Detected
PO301 - Clyinder 1 misfire
PO303 - Cylinder 3 misfire
PO304 - Cylinder 4 misfire
PO305 - Cylinder 5 misfire
PO115 - Engine Coolant Temp Sensor Circuit
PO135 - o2 Sensor Heater Circuit Bank 1 Sensor
PO155 - o2 Sensor Heater Circuit Bank 2 Sensor
P1305 - Manufacturer Control (Faulty ignition Coil #2)
PO300 - Random/Multi-Cylinder Misfire Detected
PO301 - Cylinder 1 misfire
PO303 - Cylinder 3 misfire
PO304 - Cylinder 4 misfire
PO305 - Cylinder 5 misfire
PO115 - Engine Coolant Temp Sensor Circuit
PO135 - o2 Sensor Heater Circuit Bank 1 Sensor
PO155 - o2 Sensor Heater Circuit Bank 2 Sensor
P1305 - Manufacturer Control (Faulty ignition Coil #2)

After writing them down, I cleared/deleted the codes, added more dry-gas than necessary for a ¼ of gas and then tried to start the truck. Truck still did not start.

So, I started picking away at the list. Fixed the exhaust with a new 20” resonator from ebay, a couple of lap joints from amazon and some exhaust temp sealer. Replaced those two o2 sensors (PO135 & P0155) and installed a new coolant temp sensor (PO115). A salvage yard had 4 ignition coils for about $10 ea. I bought all 4. Replaced the Cylinder #2 ignition coil (P1305) with the best looking of the 4 salvage yard coils. Decide to try replacing the #1, #3 & #5 coils with the three remaining salvage yard coils (PO301, PO303 and PO305). I label the three I pull. One of them looks almost new.

Turn key and truck hesitates for a moment but starts running. Engine sounds smooth and no CIL. I let truck idle for at least 10 minutes and still sounds good. No CIL. I decide to rev the engine a little bit. The CIL starts blinking immediately and truck starts running rough again. My brand new code reader gives me the following.

PO300 - multi-misfire
PO301 - #1 Misfire
PO303 - #3 Misfire
PO305 - #5 Misfire
P1325 - #6 Ignition Coil

So replacing the #1,#3 & #5 coils did nothing to fix those misfires and now I got a different ignition coil coming up bad. I decide to replace all the spark plugs. I don't think it's the problem, but I gotta rule it out. Put in new plugs, clear codes and start the truck. Truck starts but then quickly starts running rough and flashing the CIL. It gives me the same 5 error codes.

I switch out the #6 coil (P1325) with the best looking coil of the three I pulled and labeled from before. Clear codes and start truck. Truck sounds like it might be OK for a moment, but then quickly starts misfiring again and flashing the CIL. Code reader shows...

PO300 - Multi-misfire
PO301 - #1 Misfire
PO303 - #3 Misfire
PO304 - #4 Misfire
PO305 - #5 Misfire

So P1325 is gone but PO304 returned. I switch out the #4 coil with the #7 coil. Clear codes and start truck. CIL flashing and code reader shows same list of misfires. Switching #4 & #7 coils changed nothing.

Now that I've sat down and started really thinking about it, I can recall at least two other times where I thought the exhaust was suddenly louder than normal. It did it while driving and while in park. I assumed it had to do with it getting colder along with the break in the exhaust...but maybe I was getting sporadic misfires that I was dismissing as noise from a broken exhaust. I didn't notice a loss in power, it wast enough to make the CIL flash and it rarely lasted after a few minutes of driving...until that one cold morning a couple weeks ago.

Had I checked a code reader, instead of assuming it had something to do with the cold, maybe I would have seen 1 or 2 misfires. But, because I waited till the CIL was flashing, it looks (to me) like they all happened at the same time. But maybe it was more gradual and I just didn't notice since the CIL was already on for months because of the bad o2 sensors.

Based on threads Ive read so far on this site, Ive got some ideas on what to try next, but I feel like I'm really just stabbing at the dark at this point.

My next move, I guess, is to start switching around fuel injectors to see if the misfires follow them, but I don't feel confident that's the problem....is it strange to have 3 or 4 injectors go like that around the same time?

I thought maybe the driver-side fuel rail could be causing #1,#3 &#5 to misfire but if that was the case, wouldn't the #7 be misfiring as well? And that still leaves the #4 misfiring for some reason. I can't tell if there is a single issue causing all four misfires or if there are two (or more) separate issues causing multiple misfires.

Maybe there's some component/electrical issue at fault? I've seen the MAF sensor get mentioned a few times...could a bad/dirty MAF sensor cause misfiring like this?

I added the dry-gas but maybe it's still a bad gas issue?....maybe adding some fresh gas and letting it run for a few minutes would help?....or would letting it run misfiring like that for any period of time cause more harm than good?

So, if you were able to read through that and have any other ideas, suggestions or thoughts, I'd be open to hearing them. Like I said, I know you folks must get misfire questions a lot but I'm hoping there's something here that might help narrow down the list more than I've already done. Its cold and snowy outside now so any information that could save me from spending more time than necessary outside would be greatly appreciated.
 

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I think you should check your timing belt. just disassemble enough to pry the timing belt covers away from the cams, put the crank at 0 and check you cam positions. my 02 sequoia timing belt skipped a tooth or two twice and you get the multi misfire and flashing cel. it's hard to imagine another failure that could affect so many coil packs at once or both fuel rails or so many injectors spontaneously. if it went from running great to flashing cel with 6 or 7 cylinders reporting misfire, i'd look at timing. did you have mouse nest debris in your lower timing belt cover area?
 

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Have you checked the catalytic converters? If they are clogged or broken apart they will throw a misfire code aswell 02 sensor code. You can check with a live feed scan gauge. The front 02 sensor should be bouncing all over in voltage, while the rear 02 sensor behind the cat should stay steady at a certain voltage. If the voltage is bouncing all over the like the front one then your cat is not working.
 

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Here is the quick answer since I have been on a similar road with my 2001 Sequoia with 200K miles. Remove all you fuel injectors and have them professionally tested and cleaned. It cost about $20 per injector if you pull them out yourself. I had all eight of mine done and all of them tested with low fuel flow. One injector completely failed and needed to be replaced. The results after replacement? Amazing performance! The rig feels like its brand new and accelerates with amazing power that I never knew it had.

So go pull out the injectors and get theme tested and cleaned, you won't believe the difference!
 

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Discussion Starter #5
I think you should check your timing belt. just disassemble enough to pry the timing belt covers away from the cams, put the crank at 0 and check you cam positions. my 02 sequoia timing belt skipped a tooth or two twice and you get the multi misfire and flashing cel. it's hard to imagine another failure that could affect so many coil packs at once or both fuel rails or so many injectors spontaneously. if it went from running great to flashing cel with 6 or 7 cylinders reporting misfire, i'd look at timing. did you have mouse nest debris in your lower timing belt cover area?

I pulled a nest out of the air box this past July but nothing like that in the timing belt when I did that a few months ago.

I went back and forth on this possibility when it first happened...especially with me just changing the thing a few months prior. One of the things I came across online when I was first researching stuff mentioned that 2005 and newer 1st gen tundras (and sequoias?) had something that could potentially cause a belt to jump, but that the tundra's prior didnt have that problem. I'd sort of ruled it out when the codes started showing just 3 specific misfires (1,3 &5). Im going to do a compression test. If that shows good, then my plan was to start swapping around fuel injectors....but maybe Ill double check the timing before I do that. Thanks!
 

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Discussion Starter #6
Have you checked the catalytic converters? If they are clogged or broken apart they will throw a misfire code as well 02 sensor code. You can check with a live feed scan gauge. The front 02 sensor should be bouncing all over in voltage, while the rear 02 sensor behind the cat should stay steady at a certain voltage. If the voltage is bouncing all over the like the front one then your cat is not working.
Nothing beyond a visual inspection (they look ok) but this possibility is on my radar as well. I've bounced my problem off a couple other folks and one guy with more skills than mine made an argument for the same thing. If that's what it is, then I don't think I'm seeing any other signs other than those 3 misfires in the 1,3 &5. Exhaust looks and smells fine and the o2 sensor codes haven't thrown since I replaced the sensors....but maybe if I was actually driving it around and not just starting it and letting it idle in the driveway that problem would be more obvious. I'm not familar with a "live feed scan gauge". Any idea if this is something I could check with an ohm meter with long leads? Thanks!
 

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Nothing beyond a visual inspection (they look ok) but this possibility is on my radar as well. I've bounced my problem off a couple other folks and one guy with more skills than mine made an argument for the same thing. If that's what it is, then I don't think I'm seeing any other signs other than those 3 misfires in the 1,3 &5. Exhaust looks and smells fine and the o2 sensor codes haven't thrown since I replaced the sensors....but maybe if I was actually driving it around and not just starting it and letting it idle in the driveway that problem would be more obvious. I'm not familar with a "live feed scan gauge". Any idea if this is something I could check with an ohm meter with long leads? Thanks!
Well I replaced the cats and still the problem exists. I'm now think is my throttle positioning sensor. From what I've been reading that controls everything the engines needs to run right. I have an appontment at toyota tomorrow to tell me exactly whats going on, but I cant get over 20mph now.
 
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