P0304 Misfire fixed (Injector) to P0171 System Lean CEL.

[tkc74]

Alright, long time lurker, first time poster (or 16th time i guess...)

1996 Toyota 4Runner SR5 V6 3.4L Automatic ~ 290km (180k miles)

About a month ago I noticed I was idling pretty rough, however at higher RPM's it seemed to run fine. CEL came up so I ordered an OBD II (with Torque App). The rough idle got worse, when I got my OBD II set up I pulled the code, P0304 - misfire in cylinder 4, oh great!

I pulled the plug, didn't seem too bad, brown on one side which I thought was weird, replaced that one (and the rest), cleared the code and ran the vehicle, seemed okay for a short bit but the rough idle came back. Dang, never that easy.

Next checked the wires and coil packs with an ohm meter. The wires were a little off and never replaced so I got new ones, the coil packs were right within spec according to the Haynes manual so neither of those. Great!

I knew this had to be the injector, so I got a refurbished one and went for it. Managed to replace without too much trouble. Tested the faulty one with an ohm meter with the refurbished one and they were wayyy off so it had to be it. Got the plenums back together, reconnected the battery (cleared the CEL) and lo and behold that was it, CEL stayed gone...for a while.

Drove it about 50km, got home, went to throw it in reveres into my garage, looked back to back up and when I looked forward again the CEL was back on... fak!

Checked the code, but this time it was now P0171 - System too Lean (Bank 1).

Not sure what this could be now, something I messed up when replacing the injector perhaps? (I replaced my O2 sensor nearest the cat about 1 year ago if that matters at all)

Looking for any insight into why this code is coming up, which has never happened before, right after swapping an injector. It is not idling high/rough so I don't think I connected any hose/tube incorrectly....I think...

Regards,

tKc

 

[Doc2012]

So, it could be a variety of things.

I chased a 171 code for MONTHS before I got it figured out.

I tested EVERYTHING per the FSM, and it all checked out fine.

Replaced EVERYTHING from the fuel pump forward; pump, filter, FPR, gaskets, MAF, 4 out of 6 injectors, both O2 sensors, plugs, wires, packs.

Still had the code. Put a nice dent in my fender because of it.


Started to look into having the injectors cleaned and rebuilt. 26 bucks per injector. Not bad, but didn't have the cash.

Got an email from Amazon, and they had an ultrasonic cleaner for 40 bucks. Snagged it.

Two days later, they had an injector tester for 20. Snagged that. Basically it pulsed the injectors so you could test flow rate.

Ran the injectors in the cleaner for a couple days (probably overkill), then ran them while pulsing.

No more code.

I will mention, I had NO drivability symptoms. NO misfire code, NO trouble during acceleration, NOTHING.

I'm not saying that's you're issue, but if everything tests out fine, I would consider it.

Since you have TP, you can look at the O2 sensor live read data, as well as some other stuff that might help you out.


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[Buckaroo]

I agree with Doc that it could be an injector balance issue. You replaced one that is now flowing like new versus the other 5 where perhaps flow has degraded over time. I recently had an injector which was intermittently failing which involved a P0171 and a cylinder specific misfire. I replaced the failed injector with a rebuilt one and had the other five cleaned/rebuilt by witchhunter. The other 5 were not visually fouled , found not to be leaking & coil resistance was good (very good I thought for 235,000 miles but I try to run Top Tier fuel). The flow rate on the five old injectors increased on average by 1.3% with a single injector increasing by 3.2%. Also replaced the MAF - had been cleaning it periodically for 10 years and thought it was time. Resolved the issue......

Buckaroo

 

[tkc74]

Since you have TP, you can look at the O2 sensor live read data, as well as some other stuff that might help you out.

I don't drive often but I will set this up and try to monitor it as much as possible, thanks for the advice.

Just out of curiosity, how does the system determine if it is running too lean or rich? With the addition of a new injector, the system now sees that this injector is inputting more fuel than the others and determines that the rest are not putting out enough? Why not the other way around and say it is running to rich and that new injector is running too high comparatively to the rest.

Also, if the rest are running below standard, why was the CEL not on earlier saying the system is too lean (i.e. why did it take a new one for this to appear)

Regards,

 

[Doc2012]

Bank 1, Sensor 1 O2 sensor is what determines lean/rich condition.

In Cali emissions (99-00) trucks, and all 01+ trucks, this is a Air/Fuel ratio sensor.

You could try replacing the O2 Sensor, but don't think it'll fix it.


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[Brveagle]

In my opinion, you are barking up the wrong tree. I am betting that you pinched a gasket, left a hose unhooked, or hooked something up wrong when you put the intake plenum back together.

Did you use all new gaskets? Go over all your connections, check for any loose clamps, etc.

 

[tkc74]

Bank 1, Sensor 1 O2 sensor is what determines lean/rich condition.

I had replaced the O2 Sensor about 1 year prior, so I think you are right and don't think this will fix it.

I am betting that you pinched a gasket, left a hose unhooked, or hooked something up wrong when you put the intake plenum back together.

I was worried about this prior to changing my injector, so I purchased a spare set of gaskets for the 3 injectors along the same fuel rail I would be replacing. I only changed the top gasket on the fuel rails as that would be the one that would get pinched from the moving of the fuel rail, the rest remained the same, so I don't think so? Do you still think it is a possibility?

Also, would the CEL not appear right away if a tube was connected incorrectly rather than 50km later (30km of highway)?

Regards,

 

[Manic]

If it's in the injectors, shoot me a PM, I have a extra set that I just had cleaned and flow matched that I'd part with for what it cost me to get them cleaned. $10/ea.

Hopefully it's just a loose hose connection.

GL!