P0171, P030x 1999 Prerunner 3400 Diagnosis

I'm attempting to repair a 1999 Prerunner with the 3400 Motor. California engine sticker.

I'm getting P0171, P0300, P0303 and P0306. I clear them, they come back. Sometimes soon, sometimes a bit slower.

The truck seems to run great until I get it up to operating temp. Even afterwards. Until it throws the CEL. Sometimes it flashes, which I have been led to believe is "fix it before the Cat is ruined.
".

I put in new plugs, wires, sealed a vacuum leak.

At this point I want to see if we can diagnose it without throwing parts at it. I'm willing to do my part. I've spend a few weeks reading threads here and other sites P0171 and the P030x codes.

Live data is showing the TPS sensor at 5% before I turn the key. Should it show 0% or close ?

I read the rear 02 sensor sticky about it not affecting anything. It's voltage seems to stay under .09 unless I give it fuel, then jumps to 0.9...then back under 0.1. Not much middle of the road voltage.

LT FT was -11% two drives ago. Last drive it pushed 60%. Seems strange that it was way rich and now way lean...

Anyhow, I'm ready and can pass along live data, graphs etc.

 

I don't see any replies or suggestions...have a broken some sort of protocol here on TW ?

 

When do you get the flashing light? Does the truck not go over any certain RPM? When was the last time the spark plugs/wires were changed?

 

My suggestion is start to move stuff to see if the misfire goes away.

Bank 1 lean means the MAF is likely ok, as the bank 2 would show lean as well, what is the data on LT% for both.

You could have a misfire from coil pack #3, it shares with #6, this misfire could be spark related or injector related. Swap coils first.

I'm tired right now but this is a start.

 

I think you are listing those codes wrong.

PO446 or something similar? Are you sure they are 300 version codes.

 

Lower power and misfires. Wires and plugs done maybe 6 weeks ago.

 

Yeah . P0300 - Random Misfire - P0303 is cylinder 3 and P0306 - is cylinder 6.

 

MAF cleaned. Seems ok. I see g/s.

Haven't smoke checked the vacuum lines yet. But fixed one leak.

Yeah, I thought I'd checked...the coils but never hurts to double check. I've missed things before.

 

Swap out the coil packs between cylinders and see if your code moves.

Also, if you can't seem to get over a certain RPM and the engine light flashes at that point, you likely need a new catalytic converter. But check out my first suggestion before you do that.

 

I didn't see where you wrote the mileage on the engine so I assume it's pretty high. Could be that your injectors are on the way out.
At about 95K miles one of my injectors went belly-up and another was on the way. I replaced all of them with six rebuilt injectors for $180 from Motorwest in Canoga Park, CA and that fixed the problem.

Check what bishop84 says to check. Could be that the coil pack for the #3 cylinder is going out. That would explain the P0303 and P0306 codes.I would swap the #3 coil pack with the #5 coil pack. Reset the computer and see if the problem moves. Prolly have to drive an hour or so for the computer to catch up. If the problem moves from cylinders 3 and 6 to 5 and 2, then replace the coil pack. See the image below:

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If swapping the coil packs doesn't change the symptoms then I would prolly replace the injectors. All of them. Timmy the Toolman uploaded a video he made to his Youtube site that explains in detail how he replaced his injectors (and in excellent detail, I might add). Check it out.

Can't help you with the other codes.

And don't worry about the slow responses. Takes awhile to recover from the weekends .

 

I bought it used two years ago. Probably to the month. Looks like it had some coil packs and injectors before I got it. One injector was leaking at the the o rings. I put in new o-rings.

New cat about a year ago. I think I threw it at it for a slight misfire/ping in the exhaust Still get the "ping in the exhaust" once in a while.

178k current miles. I maybe put 15K on over two years. My Camry is my daily.

I appreciate the help from everybody. I chased a "won't start" on a 2k S-10 for six months (replaced entire fuel and electrical side) because of a replacement distributor built 22 degrees out. Which is why I'm taking this one slow ... I'm not against replacing things, but not into throwing new parts in where the old ones are fine

I'll swap coils this afternoon, reset the computer and see where we end up. And I'll follow up.

 

Swapped coils. Drove at various speeds for two hours. Weather moderate. No code. (Yesterday)

30 minute drive today. Hot weather. CEL came on - same codes.

So ... fuel side ?

 

If you still have codes = P0300-P0306 then you should think about injectors.

 

basics first... the PCM is telling you it is running lean and you are getting misfires overall and specific cylinders. Spray some carb clean around the brake booster and where the brake master cylinder bolts up. This is an often overlooked vacuum leak. Does brake fluid seem to disappear? If so there is a possibility that the fluid is sitting in the bottom of the booster and has rotted the rubber diaphram. Pull the hose, plug it and watch your fuel trims.

If this is your everyday transportation that is going to make some checks difficult as she needs to be mechanically sound first meaning checking the compression, valve clearances, vacuum hoses etc. You can go through all of that and have it end up being a flaky front 02 sensor or a dirty MAF.