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Top 2GNT Technical Turbo/Nitrous Tech topic #106373
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Subject: "Is this Fuel Cut or... what?" Previous topic | Next topic
JMay-07-09 12:53 PM
Old School 2GNTer
794 posts,
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#106373, "Is this Fuel Cut or... what?"


          

I've been giving my baby a very good, much needed overhaul... most notably switching from a Craptech to SFMU and redoing all pipes/plubming/hoses. The SFMU is the only real difference in the whole setup. Well, right now I've got the car running extremely rich and getting it ready for the dyno one final time for actual tuning (took it last week), and...

While parked, in neutral, and not moving... If I slowly raise the rpm's from idle to redline (to check for smoothness), I consistently get an immediate drop at ~5200rpm's back down to ~4700rpm's each and every time. My fuel pressure is strong and unchanged, but my A/F gauge (at ~5200rpm's) goes from a steady 'all the way rich' instantly to 'all the way lean' until the rpm's (quickly) drop back down to the ~4700rpm's, and then resumes 'all the way rich' until ~5200rpm's again. I can sit there and do this all day long, and it's very precise and consistent on every try.

Now, if I go WOT and floor it, I can go through the entire range of RPM's without any problem (while still parked/neutral). It's acting just like a rev limiter, and I can see the fuel cut back it back down.

I had to leave this morning for work and didn't really get to try anything yet. I intend to check the voltage of the MAP sensor, clean out the ML, and see if it acts this way while in gear/moving on the road. SOoooooooo... Am I going nuts? (quite possible, never experienced fuel cut before)

DSM Registry:
http://www.dsmregistry.com/137

Setup in a nutshell:
MANUAL TRANSMISSION
8.8:1 block, 3 angle valve, port/polish
440cc injectors, Vortech SFMU, Walbro Pump
Apexi SAFC, Missing Link, Hallman mbc
HRC S16g, Greddy Type-S Bov, Starion FMIC

- J

  

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Replies to this topic

TuxdreamerxMay-07-09 01:30 PM
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#106374, "RE: Is this Fuel Cut or... what?"
In response to Reply # 0




          

Sounds like a fuel cut but im very unexperienced with turbo so wait for some other responses.

  

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420agreenvilleSCMay-07-09 02:04 PM
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#106375, "RE: Is this Fuel Cut or... what?"
In response to Reply # 1




          

possibly a misfire hard to tell. Start by checking gap and condition of plugs

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Outside of Corona: "That sucks, peace out..." (jamie walks away)... "Sweeet, what we doin?" -Zac
Tim's garage (prior to motor install): "Im gonna smoke real quick, that way if you fuck up I am already nicotined up" -Tim

  

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JMay-07-09 02:12 PM
Old School 2GNTer
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#106377, "RE: Is this Fuel Cut or... what?"
In response to Reply # 2


          

Originally posted by 420agreenvilleSC
possibly a misfire hard to tell. Start by checking gap and condition of plugs


New plugs, freshly gapped... besides, I would expect a misfire to be through the entire rpm spectrum. Instead, this is occuring at precisely the exact same rpm, and nowhere else. Am I wrong?

- J

  

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JMay-07-09 09:37 PM
Old School 2GNTer
794 posts,
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#106381, "RE: Is this Fuel Cut or... what?"
In response to Reply # 3
May-08-09 09:28 AM by J

          

Any other ideas? Am looking forward to the morning...

::updated::

I just wanted to take a moment to say a word about a certain fellow at the shop... I'm not sure when he was born (didn't take the time to ask), but he inexplicably died today shortly after confessing to screwing around w/ my SAFC. My car ran great through the entire rpm range, and now (low & behold) it doesn't.

- J emoji

  

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420a_powerJun-03-09 12:04 PM
Member since Mar 06th 2008
17 posts,
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#106583, "RE: Is this Fuel Cut or... what?"
In response to Reply # 4


          

hey i had the same problem when i was N/A but then i but the turbo on it and it ran fine...do u have turbo cams? do u have a turbo?

  

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