Started stumbling at acceleration and have P0300 code(s) (1 Viewer)

[robertaleon]

Hey folks,

Just got back from our first trip to Nevada and the the 80 got us home! Drove approximately 700 miles with 500 of those towing a small dirtbike trailer which weighs about 2500 pounds. We drove out the 250 miles with no heating issues or acceleration issues except over the sierras but of course these are not speed machines and nothing I would say is a problem, 2nd gear in 4H on some of the grades.

The problem starts about 20 miles into a trail after I got 6 gallons of gas from a questionable source in the middle of the desert. We start to climb a graded road to the top of Fairview peak outside Fallon, NV and come across a herd of long horn sheep practically jumping over my hood. I stop and let them pass and get going again. Keep in mind that this grade climbs 3500 ft in about 2 short, twisty miles. So I get going again and then hit what feels like a rev limiter at 3K so I stopped again. Then I couldn't get started forward again, just stutter and stall. I had to back down the mountain with family in tow. Nerve racking to say the least. Still no heating problem according to the stock gauge, no funny smells, and no milk on oil cap. From the base we drive 10 miles on graded road back to camp - everything still checks ok.

Yesterday my wife was towing the small trailer back and came to a stop sign after driving about 50 miles. Upon acceleration the truck stutters so my wife backed off the pedal and slowly got the truck going. Runs fine another 100 miles from Carson City to Ione, CA where it does this stutter acceleration constantly at every stop but no heating problems per the gauge.

We get home and unload the kids. I hop back in the truck and drive around the block a few times with no problem. Finally after about 5 minutes of driving the stutter problem returns. I drive back to our house and the CEL blinks a few times and then stays on. Park the rig in the garage and pull codes (yes these have been posted before):

1. P0300 - General misfire
2. P0301 - Cylinder 1 misfire
3. P0306 - Cylinder 6 misfire

Now is where I turn it over to the experts here on the forum. The trail conditions were dusty. 6 gallons of fuel from small desert town, no heat issues per se, and problem got progressively worse. I figured I will start with the basics of

1. cleaning and replacing the rotor and cap,
2. inspect plugs 1 and 6 against others,
3. recently replaced wires with new Toyota wires.
4. Investigate source of small (5ml) of coolant near the base of the block drain plug, I hope it's a hose!

My greatest concern is #4. Is there an "acid test" for a 1.5 mechanic to validate an HG problem beyond a compression test, and bubbles in the coolant reservoir? Any other thoughts?

 

[Ebag333]

I would check the main engine wiring harness, directly behind the engine. Fair chance that it's toast, and wires are shorting or grounding, which will cause exactly the behavior you describe.

Double check the spark plug wires, when it's dark run the vehicle and lightly mist them with a spray bottle. Look for blue sparks, which would mean they're shorting to ground.

Check for water in the dizzy or spark plug tubes. If the boot that keeps the spark plug sealed has failed, there could be water in there.

 

[elhombre]

What came to mind while reading your post was maybe the transmission fluid is low. When it is low enough, it will foam up and cause the shifting to become erratic. This does not explain the codes, but it is an easy thing to check.

In my humble opinion, pulling spark plugs and comparing them is one of the best ways check for cylinder problems. Post pictures and Good Luck.

 

[robertaleon]

I checked prior to departure yesterday after the truck cooled a bit and the transmission fluid was right in the middle of the hot and cold marks. I will take another look and get pictures up of the plugs and such.

 

[7schulz]

Trans fluid should be check a operating temp, truck running in park on level ground. Not that I think that is your problem but that is the proper way. If you want to check the cold level, start the truck and check it running cold.

 

[robertaleon]

Trans fluid should be check a operating temp, truck running in park on level ground. Not that I think that is your problem but that is the proper way. If you want to check the cold level, start the truck and check it running cold.

Just for the record - I do comprehend the proper way of checking the fluid levels but this was out in the field. Now that it's in the garage, all checks and tests done by the (FSM) book.

Anyone have any fear of an HG issue? I'm thinking of picking up the Napa head gasket test kit for $50. PO claims that it was done and by the looks of things (hose clamps, PHH replaced, valve cover seal is black not grey) I would presume it was.

 

[Toyo Boyo]

What milage is on the truck?

These things are notorious for the front O2 exhaust sensor going around 100,000 miles. Mine did and threw some strange acceleration issues until I replaced the sensor. Toyota main dealer diagnosed the throttle position sensor as the issue (wrongly), MUD pointed me in the right direction.

Test - does it idle OK, accelerate = BIG STUTTER, wide open throttle also OK? (sensor is not used during idle and WOT).

Just remembered, when the sensor is starting to fail, the issue is intermittent, but gets progressively worse over time.

 

[robertaleon]

Mileage is at 212K. Idle is ok but mild acceleration is troublesome (stutter) and once started and WOT everything seems normal.

Not sure if I'm going to get into tonight - late night with the kids, etc.

Thanks everyone for the input.

 

[timer00]

I have a O2 sensor out on my 94 and have a stutter until full warmup (idle fine, WOT fine) that seemed to have got worse since the sensor went out. I am getting it replaced this next week along with a tuneup etc so hopefully that makes some improvement

 

[robertaleon]

ok here are the spark plugs (left to right) #1, #2, #6 since I was getting a P0301 and P0306 as well.

 

[Ebag333]

There are other people that can speak with more authority than I, but those plugs look okay to me. The center one looks a little on the whitish side, but as long as there is no powder/ash/flaking it's probably fine. Most likely just the flash throwing the colors off slihtly.

Did you check the other culprits?

 

[robertaleon]

So I started digging in a bit deeper. Found that the DS of the heater valve (above wire harness) is leaking coolant; but first things first. The wiring harness wrap was charred a bit but just the face towards the EGR plumbing; who the hell designed this!? I also looked at the cap and rotor, not great, not bad BUT the bottom bolt was completely backed out so this could have contributed to misfire.

tightened things back up and cleared codes. Let her warm up in the garage and revved in neutral - no problems, no hesitation, no codes (wasn't expecting any this early). I did receive emission warning but as the computer states - these have not had time to pass the "has run" mode. Let her run some more and tried touching the harness but had no affect. I then proceeded to stand on the brake and rev for about 2 minutes and no problems, no hesitation, no codes; emissions still yellow "has not run"

Have not tested or OHM'd out the wires, these are new (2010 stamped) and appeared in good condition

Now that the petrol tank is nearly empty, here are my thoughts:

1. Replace fuel filter
2. New cap and rotor since this was open at bottom and cheap PM (again)
3. Injector Cleaner (Techron, etc)
4. Road and load test at least to clear emissions

Please provide criticism (constructive or otherwise) and/or feedback.

 

[Ebag333]

The wiring harness wrap was charred a bit but just the face towards the EGR plumbing; who the hell designed this!?

The harness could be damaged more than is easily visible. Sometimes you have to look it over extremely carefully to see the problem, difficult since it's in a hard to reach spot.

The EGR pipe being there was a bad design. I disabled the EGR system on my truck, need to do the same to the as her harness wrap is starting to go.

I did receive emission warning but as the computer states - these have not had time to pass the "has run" mode. Let her run some more and tried touching the harness but had no affect. I then proceeded to stand on the brake and rev for about 2 minutes and no problems, no hesitation, no codes; emissions still yellow "has not run"

The emission status showing as good/green takes multiple drive cycles. Some of them are a huge pain to do, the O2 sensors and EGR systems especially. It could easily take a month of normal driving to get those to flag as good.

1. Replace fuel filter
2. New cap and rotor since this was open at bottom and cheap PM (again)
3. Injector Cleaner (Techron, etc)
4. Road and load test at least to clear emissions

Not sure I'd bother with the fuel filter. Many people have changed theirs and found there was absolutely no reason to. Some people have changed theirs and been glad to. I'm planning on changing mine when I hit 300k miles, unless there's a problem that forces me to earlier. Do you live in an area where folks often need to change their fuel filter due to contaminates in the gas?

New cap and rotor is a good idea. Also replace the O ring on the dizzy while you're in there.

 

[robertaleon]

Regarding bad fuel.....in my first post I mentioned that I picked up 6 gallons of petrol at an old Pony Express stop; they limit your purchase to 5-7 gallons. The buggies we were with regularly use this gas and use it in my dirt bike but it is not the best gas. I just thought it was either ironic or coincidental that I started stuttering after this purchase. Probably just anecdotal and I haven't swapped the fuel filter myself and PO didn't know.

 

[robertaleon]

Got some free time to knock out some work on the cruiser. For anyone that doesn't use their 80 as a DD and can afford to be down for a while, grab a buddy and a wife and take the hood off. It's almost orgasmic to do work with all that overhead room and being able to climb into the engine bay. Almost!

1. Cleared CEL codes
2. Replaced rotor and cap with OEM including dielectric grease and used blue loc-tite for the cap since my bottom screw had backed out during our trail ride.
3. Cooltape installed on main wiring harness where it passes from firewall to slightly past cylinder 6. Found no wire damage (no melted insulation, wires not sticking together etc, and did not create hesitation when wiggling harness).
4. Performed the PHH metal pipe bypass over the brake booster and under the steering using Napa 5/8" gold stripe which matches the Gates green stripe 2 ratings. Napa Gold Fleetflex $4 a foot.
5. Also replaced FHH hoses and every other hose that I didn't get during my radiator swap.
6. Coolant flush - obviously since PHH came off.
7. Also ran with radiator cap off for a while to see if any bubbles were coming up, no bubbles! (bowing to HG gods)
8. Drove around the neighborhood in first gear for 15 minutes, let things heat up - no new codes, no hesitation
9. Left with yellow emissions alarm light on scanner but only O2 and EGR are tripping so I'll wait those out.

I'm gonna throw the hood on tonight and see what happens.

Thanks for everyone's input.

 

[robertaleon]

Anyone else wrap the EGR pipe with header tape for added protection against the wiring harness fiasco? I have about 3-4 layers of Cooltape on the wiring harness but want to make this thing even more bullet proof.

 

[OGBeno]

Anyone else wrap the EGR pipe with header tape for added protection against the wiring harness fiasco? I have about 3-4 layers of Cooltape on the wiring harness but want to make this thing even more bullet proof.

Yes, many people have (including myself) and it's almost SOP at this point.

 

[Offroads4x4]

Yes you should be able to wrap the EGR pipe as well. I know its a tight area to work in but it can't hurt.
I have heard some of the guys have made a heat deflector and hose clamped it to the EGR pipe also.

Just some food for thought.

 

[robertaleon]

Bolted the hood on, checked the fluids and drove like a bat out of hell - no hesitation, no codes, and only the "CAT" emissions light on the OBD scanner and better yet - no leaks on the bypass.


I'll be driving it to work tomorrow and hopefully rid that "CAT" code.

 

[robertaleon]

Done for now

Closing out the work for this thread. Ran around for a total of 100 miles and the CAT and 02 emission alarms went out. Temperature and performance all seem fine even with some minor offroading down in some deep river rockbeds. Basically the high-level tasks performed were:

1. Replaced cap, rotor, and o-ring with OEM
2. Rewrapped main wiring harness behind EGR

The stumbling I would probably attribute mainly to the distributor cap being loose (bottom bolt) and that increased resistance causing ignition problems.

I learned even more about these rigs (yet again). Heading up to Fordyce Lake and Signal Peak (easy way) next weekend.