Phox00

Hi everyone, been lurking for a couple months and I figured it was time to join the ‘club’. I hope to learn a few things and maybe I’ll be able to help someone else learn.

So, I have had the CEL and traction lights on for a couple months now.
It keeps throwing P0301 (cylinder 1) misfire code. I usually clear the code every day or two for the added traction because the roads have been snowy/icy here. If I don’t clear the code for several days (4+ days) I also get a cylinder 7 misfire.



My vehicle:

2005 GX 470 w/ 130k

Besides the CEL you would think nothing is wrong.....

Runs great (Sometimes a slight hesitation on start-up)
No leaks
No smoke
No oil or antifreeze consumption
Regular oil changes w/ Pennzoil full synthetic
Premium Gas - Always – Sunoco or Mobil
Gas mileage seems low @ 16.2mpg (Mostly highway)
Slight exhaust smell

The issues & things I’ve noticed:

Cylinder 1 misfire (Only seems to happen at idle or very low rpm, under 1500)
Cylinder 7 misfire (I have only gotten this code a couple times and it’s only when I haven’t reset the CEL after several days)
Bank 1 Long term fuel trim (LTFT) is approximately -15(rich) at idle, but seems normal under acceleration
Catalytic Converter temperatures seem good but I haven’t verified this extensively

What I’ve replaced :

Cylinder 1 ignition coil (I’ve even swapped the coils around to verify the new one was ok)
Fuel injector
Bank 1 pre-cat 02 sensor
Spark plugs (8)
PCV Valve
Crankshaft position sensor
Air Filter

What I’ve checked:

Smoke-test performed (no leaks)
MAF - it seems ok. I was going to clean it but it looks brand new inside



All help is appreciated, I might have missed a few things but I am at a loss with this….

chiph9

You've done all the things I would have done. Running rich means the air/fuel mixture is wrong, or it's not getting ignited. You checked the latter. And it's not a direct-injection engine, so not a stuck injector (otherwise you'd see a lot more misfires from multiple cylinders). I think you need to do a leak-down test and check the valves.

Chip H.

Booyah

You have done allot and spent good $$$$----I say take it to Lexus and give them the list of all you have done and have them do a diag, they should be able to pinpoint it down to the part(s) it needs, this will probably cost you 100-125 for the diag fee and whats wrong, then you can decide if you want them to do the work as well

Phox00

Chip9h,
I will try and get my hands on a leakage tester, at the least it needs to be ruled out.

Booyah,
I actually took my vehicle to Toyota a month ago, the nearest Lexus dealer is 2.5 hours away, and for $100 Toyota diagnosed a bad fuel injector. They wanted $400 to replace it and had to order it from Lexus. I bought the Denso injector online for 1/4 the cost. Obviously that wasn't the problem. Sometimes it seems like these mechanic's throw a dart at possible causes. But I have thought about taking it back after everything, since then, that I've replaced and checked.
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edvinas

Hey Phox00,

I have attached a file for diagnosing P0301 from Chilton's manual (I think it's just a reprint of Toyota/Lexus service manual). Hope that helps!

Phox00

edvinas,

Thanks for posting the manual, it has some interesting information and has helped me look at a few other things....

Bought a spark tester and everything seems ok on cylinder 1.

I still haven't completely ruled out the MAF which, I believe, also houses the IAT (intake air temperature sensor).
With my reader i noticed the IAT sensor was a 25-30 degree difference compared to the outside temperature. Currently the outside temp is 13° but the IAT sensor was reading 39-41; Not sure how much of an effect this would have, just something i noticed.
Also, I performed the test from page 22:
MAF at idle rpm: 4.0 to 8.0 g/s (shift lever is in N position and A/C is OFF)
MAF at 2,500 rpm: 10.0 to 20.0 g/s (shift lever is in N position and A/C is OFF)

In my driveway the MAF numbers were within the above ranges.While driving they seemed to be in the same ranges mostly, a few times i noticed it spike up to 40-50 g/s.

DiabloX22

The MAF will always look clean, I would get some CRC and clean it. Obviously dont touch the wires. You went this far, it wont hurt. From the readings you posted its off, clean it, or replace it. Let us know!

Phox00

Cleaned the MAF with MAF cleaner and no difference.

A few things I noticed today....

The downstream(post-cat) 02 sensors seem high, with bank 1(@ .820+/-) always about .100 higher than bank 2(@ .720+/-)
A few sources I've read seem to associate high downstream 02 voltages with ignition problems.
Intermittent engine misfire analysis
fuel trims and downstream O2s
With the ignition coil unplugged it immediately throws a P0351 code.

While misfiring at idle, I can make it stop misfiring by slightly increasing the load; Anywhere from 1300-2000rpm

All of the sleeves to the fuel injectors on bank 1 have been sliced open and #5 injector has new wires(different color than the others) and connector(cleanest of the 4)
Also, I used a 12v test light at the connector of injector #1, at idle only, and it is pulsing.

**edit**

So I drove to work tonight(mostly highway)trying to monitor the live data. It's difficult to see everything going on because it only displays about 7 things per page. Everything seemed fine, 02 sensors all seemed good, fuel trims were good, IAT, we're all spot on. As rolled into work and parked of course the fuel trims for bank 1 started going more into the negative and it started misfiring. I also noticed the IAT was 40-45° higher. So I wonder if this is a symptom of whatever is going on, or the cause.

DiabloX22

Good question. Did you ever figure out what was going on?

Phox00

Ugh....Finally took it back to Toyota today, the worse news, they diagnosed low compression in cylinder #1, 70psi.
They guesstimated over 20+ hours @ $100/hour just to tear it down to fully diagnose the cause, i.e- ring, valves, gasket, etc... Then, parts for the fix, labor and putting it all back together I can easily see $4-5k+.....
The vehicle is in excellent condition, interior and exterior, everything works. What to do next?

Dallasguy1

Sell it at first offer and get something else, not worth spending 4-5k on the engine.

FrankT

Thanks for posting your story Phox00 ...
If it were me I would replace LH head or bank1 head; cyl. 1,3,5,7 with a used head and call it a day.

Good luck

sheikhmax

With that kind labor charge and 20 plus hours, you are better of getting a whole new motor from a salvage yard.. Here is what a quick google search shows:

http://www.carmonkeys.com/2004-LEXUS-LEXUS-GX470-Engine-Assembly-4-7L-VIN-T-5th-Digit-2UZFE-Engine-1-Year-Warranty?utm_campaign=google&gclid=CPn93JHFl9ICFVWBswodA2UEFw




Here is another one:

http://www.ebay.com/itm/03-04-TOYOTA...3D361858615055

tz693

Did you replace the ignition coil? Maybe you want to give it a shot.