CEL P0306, Problem run through. (1 Viewer)

[Crawdad]

Bought my 97 2 months ago, had what I thought was a trans slip. Trans is OK when checked out. Went up a steep hill and tripped check engine light. Thought it was a loose plug wire, reset it and it went away for a week, then it came back and tripped CEL again.

Had troubles reading OBD2 on some readers, local tune up shop read the code as Cylinder 6 misfire. They checked spark and found it was OK, suggested I replace the injector. I had recently replaced plugs,, wires, cap, rotor.

Read up on the threads and ordered up a throttle body gasket, Plenum gaskets, new injector, extra injector seals and o-rings, etc...

Just to prevent unnecessary efforts, I ran a half can of Sea Foam through the brake booster vacuum line, lots of smoke but no change in engine miss. BTW runs smooth at idle, miss is most notable from 1000-2000rpm's.

Yesterday, I rounded up my buddy who is a cruiser wrencher, we got through the project and cleaned out the intake, throttle body, injector rail, injectors, checked all the vacuum lines, replaced a few, and replaced the #6 injector.

At the end of the day, cruiser ran like a champ. No miss, lots of power, cruised around town and on the freeway for about 15 miles. Drove it again later in the evening and it was still great.

This morning, my wife says the miss is back and CEL is back on. I got home from work and ran to check codes, P0306 again, Cylinder 6 misfire. Stumbling idle, rough early acceleration and then runs fine at operating speeds.

Just wondering what else i could be missing. I noticed that my #5 injector has a new wire (red wire in pics) from just after the connector on the injector running along the main loomb into the firewall, fried wires from egr heat? could cylinder 6 misfire be from a similar prob? should I wire a new hot lead to #6?



No oil in the water or water in the oil, no bubblinh, no smoke in the exhaust, ideas? Thanks in advance gurus.... I have my fingers crossed for no HG...... not up for that just now. (fingers crossed, cold beer in fridge just in case.. volunteers?)

 

[Pin_Head]

Uphill problem with #6 misfire could be due to water filling up plug #6 and shorting it out. This is consistent with it running great later after the water evaporates. Are you parking it under a sprinkler?

 

[landtank]

it could be a problem with the harness were it passes over the egr valve. Going up hill will require more power which will torque the engine and strain the harness.

Try putting the engine in drive and do a brake stand and see if the stumble appears.

 

[Jack G. Nichols]

I agree with Rick - when mine was doing this I found the harness over the EGR valve was partly cooked. Problem went away when I insulated that area.

 

[Crawdad]

Brake stand does cause the stumble. IF the harness is cooked, will insulation help? or should I consider replacing wires?

 

[Crawdad]

No water in the system on the hill failure, garaged every night and a dry day on the hill-climb.

 

[landtank]

I personally replace the harness. But it's a rather involved job and about 385.00 in parts.

Minimum I would remove the heat wrap that is there and inspect the individual wires and repair as needed and then re-wrap them again afterward.

 

[Crawdad]

Rick, thanks for the input. What is a good insulating wrap product for when I am done inspecting the harness? I would rather start there than run into an HG project that might be unnecessary.

Anyone have any luck getting to this harness without removing the entire plenum? maybe just the TB and EGR?

 

[Crawdad]

OK, Here's an update. After sitting in the garage for a few days. I started the cruiser and the engine light had turned itself off. This is a first as all other times I have had to remove the EFI fuse to reset the codes. I had reset it after reading the code but it tripped again before I got home.

The engine is not missing currently. I was able to reach #6 injector wiring harness and pull it out of the clip, routing it further away from the EGR tube and then wedged some insulating material between the EGR tube and harness. Let it warm up for about 15 minutes, still no miss. I think Rick was on to something.

Thanks all.

 

[Crawdad]

So that pesky P0306 code tripped again yesterday while my wife was driving. But different symptoms this time.

A few weeks ago, my rig would buck a little on the freeway while driving straight, and then it seemed worse when turning to the right at freeway speeds. Consensus was have the tires balanced. Drove a few weeks around town and no problem, got the tires balanced yesterday.

After the tire balance, my wife drives about 30 miles to SLC. On the way there, no problems. On the way back, the "bucking" i had previously described is back and getting worse along the route home.

By the time she gets home, no vehicle power and CEL is on. Bucking is tremendously worse.

My guess? Either there is a binding in the drivetrain, ie diff, U-Joint, or Viscous Coupler that causes the shudder/bucking at freeway speeds, and it shook the wire harness enough to trip that CEL light by exposing the harness to EGR tube heat, or I am losing my mind... but where to start.

We sold our Denali so the LC is our primary family vehicle. Gotta get it running right or we are a no car family.

Suggestions would be appreciated.

 

[elhombre]

Sorry to hear the problem came back. I would go back to the wire harness. Some , maybe all(not quite sure), transmission wires travel through the same loom by the EGR so the problem could still be there. It may be that the wires have melted more in the loom and now other problems are coming around. You never said that you were able to peel back the insulation and inspect all the wires around the EGR, only the #6 injector wires. (Maybe I am not reading your post right). Those wires are crammed together tight in that loom and if one of the wires had to be replaced already, evidenced by the #5 red wire, there most likely is more destruction in there.

I used Thermo-tec wire wrap, bought from Jegs, to re-wrap my wire harness after my HG. Had enough left over to further insulate the A/C lines and double wrap the wire loom.

 

[Tools R Us]

I hate to say it, but is it consuming any coolant? In my experience a P0306 is sometimes an early indicator of head gasket failure.

 

[Crawdad]

OK, Thanks to CDAN for some very helpful advice as well as all of you who chimed in on my little slice of hell.

I activated my CDL, pulled the fuse, shifted back to high, removed the front drive shaft, and then before I drove it, looked at the advice that elhombre suggested..... dang wire harness... My insulation had melted out that I had placed there and the harness had new torch marks next to the EGR tube.

Removed the harness channels from the firewall and re-routed the whole harness under the heater/coolant valve assy that runs under it, wrapped it all in Thermoshield "good to 2000 degrees", and then couldn't get the harness channels back on. Wire tied the *** out of it and bolted it all back together.

Drove about 40 miles with the front shaft off and no problems, no new CEL, no shaking. Put the shaft back on and released the CDL, drove another 30 miles and climbed a few steep hills under hard power to see if there would be any engine hesitation, nothing.

I really think that the whole "shuddering bucking" scenario was cylinder 6 misfire again.... I hope I have it all fixed for good.... the wire is in tact but cooked. When pinched into the harness and held from the heat, it works great... one day I will have to pull a new section of wire to injector 6 but not today.

Thanks all for the help, glad this resource is available, and that you guys are so generous with your advice and assistance.

THANKS

 

[Crawdad]

Also, glad to report that there still appears to be no HG problem.... crossing fingers, knocking on wood, praying to the Toyota gods that it is not that... can't get that done anytime soon.

 

[RescueU]

Great info, Crawdad!

I'm struggling with this myself.

Did you, or has anyone else posted up any pictures of the wiring loom to show what it looks like opened up, and which specific wire is for the #6 cylinder fuel injector?

Also really curious if there were any particular things to account for when rewiring the lead from the harness to the #6 injector (ie, gauge of wire, connectors, etc).

Any pics of end results after alternate wrap and rerouting of the wiring loom, to get it away from the EGR area, would be awesome.

Thanks!