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VY L67 Flat Spot/Hesitation ONLY when cold on acceleration.

mechanic

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Use your O2 sensors to monitor fuel ratio during the flat spot.
 

Immortality

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Great idea, the only problem is the flat spot is only during a cold start when the engine is operating in open loop mode and the factory NB O2 sensor won't up to operating temp to give accurate readings.
 

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I may have found a possible cause for this issue. I’m not sure how I’ve never noticed it before, but the lcd screens for the trip computer dim a little while stuttering. As such I’m thinking it could be my quite old battery. This might also explain why the stutter is worse when it’s cold.

Coincidentally I was planning on getting a new battery tomorrow as I’ve had it go flat from little use a few times now. Hopefully it’s a two birds one stone situation, but there’s so many things that could cause the stutter so I’m not holding my breath.
 

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That's an interesting observation. I've started down that rabbit hole. I have good battery and alternator and get good voltage at the battery however if you put the dash in diagnostic mode the voltage displayed is normally less by about a volt. There is definitely a voltage drop somewhere between the battery and the dash/pcm but I've not found it yet.
 

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New battery is in but stutter is not gone. Screen flicker while stuttering is gone though. Next step will be to do some more detailed logging for any indication as to what it could be.
 

krusing

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Next Chapter:

Well I replaced the Plugs and Leads this morning, with OEM Plugs Part # 92143093, & OEM Leads Part # 92142486, ;)
and put the leads on the drivers side in separate flexible conduits
[in the even the spark was leaking/jumping between leads, shouldn't think it would being new leads, but just to be sure, to be sure].
I did notice it has a bit quicker acceleration, :D
But,
the Damn Flat Spot is still there, :confused:
Next will be a new DFI.
I have scanned it numerous times, but its not producing any DTC's :mad:

Side Note:
The Spark Plugs that were removed all looked the same,
and in fairly good condition, apart from probably needed re-gapping.
 
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krusing

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krusing

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Update:

Curiosity got the better of me, :confused:
I replaced the DFI this afternoon with a new OEM one [Delphi model], that I had on the shelf as a spare for a rainy day,
And waited till the engine was cold from this morning,
didn't take long though, and it felt like 8deg most of the day. :eek:
And you guess it, o_O
The Damn Flat Spot is still there when cold under acceleration. :mad:
Oh well, one would say, back to the drawing board. :rolleyes:
 

Lex

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Update:

Curiosity got the better of me, :confused:
I replaced the DFI this afternoon with a new OEM one [Delphi model], that I had on the shelf as a spare for a rainy day,
And waited till the engine was cold from this morning,
didn't take long though, and it felt like 8deg most of the day. :eek:
And you guess it, o_O
The Damn Flat Spot is still there when cold under acceleration. :mad:
Oh well, one would say, back to the drawing board. :rolleyes:
Have you inspected the DFI plug?
Have you inspected any part of the DFI wiring loom?
 

krusing

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Have you inspected the DFI plug?
Have you inspected any part of the DFI wiring loom?

Yes,
Checked the Plug and loom, in case it had a damaged, burnt pin or socket.
I did that this afternoon after I pulled the DFI off, which gave be a bit of room to check the plug and wiring.

Were it NEVER misses a beat when warmed up, it actually runs perfectly.
 
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