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Old 05-07-2007, 12:53 PM   #1
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Default Tech help - 4000rpm stumble on accel

Hey folks,
I have an acceleration problem that I need some help trying to solve.

Problem: when accelerating at full throttle the car stumbles badly between 4000-5000rpm and then accelerates fine up to redline.

If I accelerate hard up to 4000rpm, then back off but still accelerate slightly (50% throttle) I can get past 5000rpm and nail it again.

I mostly tracked the car last year so I just kept the rpms above 5k and would be good, but I am daily driving it now and trying to get it fixed plus it's not healthy to leave this uncorrected.

This happened after I swapped my engine last year. I had the same setup, just swapped a new 1.6 and the problem started.

I played around with the LINK settings, not much change. Re-loaded FM defaults and re-tuned slightly, no change.

Relevant notes on car:
-1.6 Turbo with piggyback Link (not full LINK)
-single injector at throttle body
-O2 signal modifier (olderguy)
-new O2 sensor installed recently
-just installed a bunch of ground wires in case it was bad grounding
-changed over the TPS, temp sensor and rad switch from old to new engine


Stumped...

Ideas:
- any other sensors I should check?
- re-wire the piggy?
- was suggested I adjust the O2 clamp settings?

I assume it has something to do with the piggyback ECU taking over from the OEM computer since the transition is around 4000rpm where the OEM ECU would go into open loop (or is that full).



Any ideas more than welcome.

Thanks in advance,

Andre
Ottawa, Ontario
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Old 05-07-2007, 12:57 PM   #2
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what are the plugs gapped at?
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Old 05-07-2007, 01:07 PM   #3
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Quote:
Originally Posted by Braineack View Post
what are the plugs gapped at?
I believe I gapped them down to .030" (.75mm) Any bigger makes the stumble worse.

Plugs are relatively new also and 1-2 ranges colder than stock (NGK's)
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Old 05-07-2007, 01:27 PM   #4
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Try new plug wires
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Old 05-07-2007, 02:09 PM   #5
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Last year, I swapped out the wires and coils from my spare engine and no change.
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Old 05-07-2007, 02:18 PM   #6
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o2 clamp voltage? ..but u probably already have one or something else that eliminates that
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Old 05-07-2007, 02:24 PM   #7
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I got the "olderguy" O2 clamp installed last year as I figured it could fix my problem but no. Perhaps it is out of adjustment?

From what I understand, this only regulates O2 sensor voltage up to 4000rpm, beyond that the ECU does not use this signal.

If my problem is at 4000-4500rpm, doesn't this rule out the O2 clamp?
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Old 05-07-2007, 04:20 PM   #8
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are the secondair injectors working???
fuel and power????

The piggyback just adjust timing where you want it, and add fuel above 0 psi.
(that's why you don't have any readings in the lower zones)

I suggest a fuel problem....
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Old 05-07-2007, 04:34 PM   #9
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Sounds like a lean/rich spot to me. Get a wideband on it and see what's up.
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Old 05-07-2007, 06:32 PM   #10
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I ve run a greddy set without fuel enrichment....(i know) and got the same problem... Search into your fuel...
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Old 05-07-2007, 06:53 PM   #11
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probally not getting enough fuel...or too much...
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Old 05-07-2007, 08:03 PM   #12
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stumbles are going to be lean spikes, rich spikes will be less harsh; if anything just doesn't feel like you have enough umpf.
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Old 05-08-2007, 10:17 AM   #13
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Thanks for the responses everyone.

I think I will re-wire the Piggyback LINK in case there is a problem there. This also sounds like perhaps the 5th injector is not working or wiring is messed up, as my plugs and O2 sensor indicate the car is running lean while the LINK "settings" are not set lean at all.

I'm only running 3psi for now until I get it sorted out so no danger of hurting the engine, plus I'm not driving it hard until it gets solved.

Will re-wire and see what happens and get it on the dyno/wideband and check it out further. (and check out the O2 clamp settings too)

Thanks again,

Andre
Ottawa, ON
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