Stumbling & Hesitation after Idling or Cruising

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BlueReaperX
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Stumbling & Hesitation after Idling or Cruising

Postby BlueReaperX » Wed Oct 10, 2018 4:50 pm

I have an Elite 2500 on my twin turbo Tundra (3UR-FE 5.7L V8). After the last tune up at the track last April I've developed an issue where it would misfire or hesitate (loss of power) when trying to accelerate but would clear up if I kept at it or tried again immediately after. Initially I though it was spark plugs, ignition coils, injectors, fuel filter, a vacuum leak, etc. All replaced/cleaned/fixed. The issue is still there.

Driving it for a few months and looking at logs I've noticed the following: If the truck sits idling for 5-10 minutes or cruising at a steady highway speed for about 20-30 minutes without any partial or hard acceleration it would start to sound as if it's having a hard time firing (gurgling). If I try to accelerate it would hesitate or misfire as if I was 2-stepping and eventually clear up and accelerate normally. If I rev it up in neutral it would also clean up not necessarily under boost. On the logs it would seem to be rich on one bank (10:1) and lean on the other (13:1) before clearing up. All the other sensors are reading properly.

On a highway where I know where all the trap speeds are I could drive for over an hour, decelerating at the speed traps and accelerating after without it ever hesitating once. As soon as I cruise for a few minutes and then try to accelerate again it would stumble and misfire before clearing up again.

AFR is 14.7 at idle all the time. Cruising it's between 13.5-14.5 depending on load/speed/TPS. I've replaced everything that could cause this mechanically, only thing left is if I messed thing up accidently while tuning last April (I was only adding more timing and boost and adjusting AFR for a 100 Nitrous shot as far as I can remember). Nothing I remember that would cause this. Is it possibly throttle body/TPS related? looking at the logs it seems DBW is working properly.

Last thing that comes to mind are the O2 sensors reading incorrectly causing one bank to misfire/flood. Has something similar to this happened to anyone else before? I have ordered 2 new O2 sensors in the meantime.

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HaltechMatthew
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Re: Stumbling & Hesitation after Idling or Cruising

Postby HaltechMatthew » Mon Oct 15, 2018 2:12 pm

Map and logs my friend

BlueReaperX
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Re: Stumbling & Hesitation after Idling or Cruising

Postby BlueReaperX » Mon Oct 15, 2018 6:19 pm

Sorry, forgot to post those. But I think I found the problem. I replaced the o2 sensors and it's still the same. Tried to replicate the issue as much as I could and it finally went into limp mode and threw a code. P1276, Bank 1 too lean. Turns out it's one of the injectors on Bank 1. Took all 4 off for cleaning/maintenance and will add some injector cleaner and see how it goes. If it happens again I'll try to capture it on a log.

BlueReaperX
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Joined: Tue Jun 19, 2018 8:29 pm

Re: Stumbling & Hesitation after Idling or Cruising

Postby BlueReaperX » Mon Oct 29, 2018 6:04 am

Well I cleaned the injectors and "fixed" some wiring that could probably cause such an issue but 3 days later it's happening all over again. As I said in my OP, this issue only happens if I idle or cruise for a decent amount of time. The first 3 days I didn't let it idle and I was driving it hard, thus the issue didn't show up. Today I waited at the gas station for a good 20 minutes and left the truck idling for a while to got something from inside the gas station. Drove off and its back.

I even tried switching around the o2 sensor signals but that just caused it to run extremely lean on one bank and rich on the other at idle.

I might take the injectors one last time to get checked and serviced at a more professional shop, after that I need to get new ones unless someone here can point me elsewhere.

I have attached two logs, the first one I let off early, at about 50% throttle. The second one you can see I kept at it and Bank one went all the way to 17:1 AFR before clearing up. The next two times in the same log the issue didn't show up just as I explained previously. I really hope it's not a mechanical issue.

3UR Misfire.rar
(259.02 KiB) Downloaded 10 times

BlueReaperX
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Re: Stumbling & Hesitation after Idling or Cruising

Postby BlueReaperX » Sun Nov 04, 2018 4:31 pm

Just wanted to update this thread since I found the problem incase someone faces something similar.

Since I've replaced/cleaned everything on bank 1 and it would still lean out, the only thing l haven't checked or wasn't able to was the fuel pressure on that side. My fuel pressure sensor is on the inlet of bank 2 and even thought it looks like its fine on the log, it was a little low at low boost (40 psi at idle -10 psi but only 47 at 1-2 psi) when the issue would show up. Until my auxiliary pump kicks in and then it would stabilize or should I say increase the pressure as required.

I enabled my auxiliary pump at idle which increased my pressure to about 43 psi. The issue was still there after a 20-30 minute idle. So on to my fuel system.

I had my fuel rail setup just like fuelab suggested in the image below:
Fuelab.png


-8 single feed line, splits into two -6 for each fuel rail and then to the regulator with a -6 return.

So thinking the issue was with the regulator not able to equalize the pressure between two banks, I closed off one of the inlets and used another Y fitting into a single -6 line between the fuel rails and the regulator. This insured both banks had equal fuel pressure and increased my fuel pressure before the regulator to about 45-46 psi. This reduced the issue dramatically. After a long drive, the issue only accord once and it was very minor. I then adjusted the pressure at the regulator to read 50 psi at idle. after about 4-5 days of driving the issue is completely gone.

For some reason fuel pressure was dropping on one bank. Probably because it had a shorter path of fuel line thus starving? I know, it doesn't make sense to me either but it seems to be rather a quick fix by simply increasing the pressure just enough to be stable.

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HaltechMatthew
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Re: Stumbling & Hesitation after Idling or Cruising

Postby HaltechMatthew » Mon Nov 05, 2018 11:08 am

Thanks for updating

BlueReaperX
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Re: Stumbling & Hesitation after Idling or Cruising

Postby BlueReaperX » Thu Nov 15, 2018 6:42 am

After a week of no issues, it came back. I increased the pressure up to 60 psi and it's still there. I went back down to 40 psi as it turns out pressure wasn't the issue.

After discussing with a local tuner, it appears to be a leaking or a stuck open/closed injector. My fuel system seems to lose pressure after switching off ignition. There is no fuel coming out of the regulator's return line, so it's either one of the injectors are leaking or the check valve in the fuel pump is not holding pressure.

Initially I thought it was bank 1 with the issue, but I think I was looking at things backwards. STFT on bank 1 was about 9-10%. Bank 2 on the other hand was over 20%.

Revving the engine I can see the AFR being more stable on bank 1 than bank 2 where it gets lean (17-18:1 AFR) for a few seconds before o2 control kicks in and goes back to normal. Where as bank 1 goes back to normal AFR immediately.

My guess is 1 of the injectors on bank 2 is not supplying enough fuel. Causing the 3 injectors on that side to pump more fuel to compensate. This fouls the plugs or floods the cylinders and causes bogging when trying to accelerate.

Revving at idle also blows out black soot and there is always a black spot below the tail pipe where I park.

Does my theory make sense or is a difference of 10-15% STFT between two banks normal?


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