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Speed density engine rich at idle

  • Darren
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17 Oct 2020 02:07 #43817 by Darren
Speed density engine rich at idle was created by Darren
1az-fe Toyota Speed Density Engine
-24% STFT at idle
0% STFT after WOT snap and then back to -24%
high idle (1100 rpm, 900 when hot)

Car starts fine and road tests ok (a little sluggish on acceleration). STFT reduces to zero at various rpms during driving.

possible causes I can think of is

Faulty MAP system (reading high)
Faulty O2 system (reading high)
Fuel pressure (Too high)
Leaking/dribbling fuel injector/s
Faulty air intake/engine temp sensor
Timing???? would timing cause such drastic negative STFT?

What else could contribute to severe negative STFT on a speed density engine?

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17 Oct 2020 07:02 #43819 by Tutti57
Replied by Tutti57 on topic Re:Speed density engine rich at idle
If it has an EGR valve, and it's leaking, that additional air going into the intake would increase manifold pressure and fuel.

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  • Darren
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17 Oct 2020 07:45 #43820 by Darren
Replied by Darren on topic Re:Speed density engine rich at idle

Tutti57 wrote: If it has an EGR valve, and it's leaking, that additional air going into the intake would increase manifold pressure and fuel.

Nissan Technician


Agreed, but it will not max out fuel trim into negative?

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  • Chad
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17 Oct 2020 09:20 #43821 by Chad
Replied by Chad on topic Speed density engine rich at idle

What else could contribute to severe negative STFT on a speed density engine?


The last one I battled was a 2002 Dakota 3.9L. The EVAP vent hose was twisted and kinked.

"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer."
The following user(s) said Thank You: Darren

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17 Oct 2020 18:59 #43828 by Tutti57
Replied by Tutti57 on topic Re:Speed density engine rich at idle
I guess it depends on how big the leak is. Is there anything you can pinch or block off to test it?

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18 Oct 2020 10:42 #43832 by guafa
Replied by guafa on topic Speed density engine rich at idle
Hello,

I think you first should stay focused on that high idle.

Maybe PCM strategy priority is to keep target rpm.

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  • Darren
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24 Oct 2020 12:05 #43952 by Darren
Replied by Darren on topic Speed density engine rich at idle
Thanks guys. I've been quite busy with this one on Iatn, there are a lot of very interesting feedback in there concerning this engine.

I'm looking now at the possibility of backlash on the camshaft based on the waveform I captured on the CAM sensor (Cylinder head over skimmed and/or stretched timing chain). I also think my timing is a bit retarded as well.

members.iatn.net/forums/search/search.as...orum2&ft=1&fv=4&qv=1

I'm going to try and post the wave forms in jpeg in this post, hope it works!
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