P420

Started by Newbie57, August 7, 2026, 20:48

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Newbie57

#50
Yesterday at 18:33
Took some reading off the MAF
Air flow at idle 2.2 to 3 g/s
At 2.5k revs unloaded 8.3 g/s

Newbie57

#51
Yesterday at 20:13
More investigation tonight.


B2s1 shows consistent high reading a 4k revs. Not cycling as before

Long term fuel trim 10%
Short term at idle -2.7% & -4,3% at idle
Max min voltage on b1s1 b1s2 show fail on diagnostics

shnazzle

#52
Yesterday at 20:36
That looks ok, based on my vague memories.

But...just going back through the thread..I noticed something..

Would you be able to post your short and long term fuel trims for the 3k-4k range?
...neutiquam erro.

shnazzle

#53
Yesterday at 20:37 Last Edit: Yesterday at 20:42 by shnazzle
Quote from: Newbie57 on Yesterday at 20:13More investigation tonight.


B2s1 shows consistent high reading a 4k revs. Not cycling as before

Long term fuel trim 10%
Short term at idle -2.7% & -4,3% at idle
Max min voltage on b1s1 b1s2 show fail on diagnostics
Is that 10% positive ? Or negative


Basically I'm starting to suspect injector or something upstream and the cat is just struggling to fight the overfueling.

If it's constantly trimming fuel...then there's your answer. It IS rich. But why...?
Probably injector
...neutiquam erro.

Newbie57

#54
Yesterday at 21:17
Quote from: shnazzle on Yesterday at 20:37Is that 10% positive ? Or negative


Basically I'm starting to suspect injector or something upstream and the cat is just struggling to fight the overfueling.

If it's constantly trimming fuel...then there's your answer. It IS rich. But why...?
Probably injector

10% is positive

shnazzle

#55
Yesterday at 21:25
Quote from: Newbie57 on Yesterday at 21:1710% is positive
Damn.
That's that theory out the window.

Hmm...

Ok next theory. Air leak near throttle body.
Unmetered air causing lean condition, so it's dumping in more fuel.
Why is the trim negative at idle you ask? Well, at idle, vacuum is highest, and what you can see is that that vacuum sucks the leak shut. Now because your overall trim is positive, it has to trim fuel down at idle when the leak is shut.

So... Same test as before with the exhaust, spray EGR cleaner or MAF cleaner by the throttle body and the joins by the intake
...neutiquam erro.

Ardent

#56
Yesterday at 21:33
I have little to contribute to these threads but love reading them. The ROC collective working to solve a problem they are miles away from.

Gaz mr-s

#57
Yesterday at 22:40
I mentioned intake as an aside earlier on......I think in my mind I was believing it had already been done.....  ???

Carolyn

#58
Today at 08:05
Pull  the sprk plugs nd see if one is obviously running rich.  If one is, that isolates the issue to an injector.
Perry Byrnes Memorial Award 2016, 2018.  Love this club. 
https://www.mr2roc.org/forum/index.php?topic=63866.0

shnazzle

#59
Today at 08:09
Quote from: Carolyn on Today at 08:05Pull  the sprk plugs nd see if one is obviously running rich.  If one is, that isolates the issue to an injector.
Which the OP already did earlier...all sparks looked fine.
So I guess back to Gaz:s intake leak
...neutiquam erro.

Newbie57

#60
Today at 08:20
Quote from: shnazzle on Yesterday at 21:25Damn.
That's that theory out the window.

Hmm...

Ok next theory. Air leak near throttle body.
Unmetered air causing lean condition, so it's dumping in more fuel.
Why is the trim negative at idle you ask? Well, at idle, vacuum is highest, and what you can see is that that vacuum sucks the leak shut. Now because your overall trim is positive, it has to trim fuel down at idle when the leak is shut.

So... Same test as before with the exhaust, spray EGR cleaner or MAF cleaner by the throttle body and the joins by the intake

From memory I think short term at 4k revs was +14%
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