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Old 07-06-2004, 02:46 PM   #1
Chav
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Default Figure this one out

Between 3500rpm and 4000rpm the engine will hesitate heavily. I have tried tuning the problem out (fuel/timing). I checked the wiring, vacum lines, and I have tried different injectors. I have also noticed that if I am cruising in that range the tach will wobble very slowly. After examining the datalogs I have noticed that the a/f ratio will go lean by about 2 points during this range, so I richened up the mix only to find that the hesitation is worse. After a year of trying to solve the problem on my own I have managed to smooth the problem down to the effect of a slight jolt, but I would love to get rid of it completely.

The only thing that works is to set the injector firing from sequential to group. In group mode the engine revs so smoothly, but I loose about 3-5 mpg. Group mode also smooths out the a/f ratio across the board.

I also have noticed much like a few other people that between 2000-2500rpm during light cruise the engine bucks slightly.

Has anyone solved either of these problems?

-Chav
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Old 07-06-2004, 02:50 PM   #2
White 2.5rs
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what fuel pump and reg r u runnin?
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Old 07-06-2004, 02:58 PM   #3
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You might be running too rich in the midrange there instead of too lean.

That is the problem with an A/F meter... you can never tell on odd situations like that. See, with too much fuel the engine will misfire and just blow it out the tailpipe. The A/F meter just sees the air go by and reads real lean instead of real rich like it actually is. I've run into that problem before, and it's frustrating as hell until you get the cahones to lean it out a bit.
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Old 07-06-2004, 03:11 PM   #4
Chav
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walboro (Ludespeed stage 2) with stock reg and parallel fuel lines.

8complex, I tried that as well. I smoothed out pretty well up until it started pinging at around 13:1 a/f (wideband). So I richened it back up in favor of the hesitation rather than nuking a piston.

A lot of the normal tuning thoughts to solve this problem would make sense if the problem didn't completely go away when group injection is selected.

-Chav
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Old 07-08-2004, 07:20 PM   #5
Chav
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Well I tried disconnecting the ribon (laptop connection cable) from the link plus (thinking it maybe an interferance problem), but that didnt help at all. Next I'm going to try hard wiring the fuel pump. If that doesnt work I'm going to wire it up to use antiphase group injector firing and hope for the best.

-Chav
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Old 07-09-2004, 12:44 AM   #6
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How long is your vacuum line running to the link. When i shortened mine up it cleared up a lot of the hesitation. Are you using map+tps?
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Old 07-09-2004, 02:25 PM   #7
Chav
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I have a gm map sensor in the engine compartment. Before I had a pretty long line going from the link to the engine, and thought that if I had a closer sensor it would improve response. It helped a bit, but it didnt do anything for the hesitation. I'm running map fuel schedualing because with map + tps sometimes with sudden throttle movements into boost the link wouldnt change timing fast enough and the engine would ping.

-Chav
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Old 07-09-2004, 05:06 PM   #8
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Bad o2 sensor?
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Old 07-11-2004, 12:55 PM   #9
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Hmm... how many pounds of boost are you running? I see you have an '01 so you are on the SOHC heads. Try dropping the gap on your plugs. As strange as it sounds, some people have issues with the plug firing getting blown out at those engine speeds at certain boost levels. FHI designed those cams to create LOTS of turbulence at cruising speeds to improve fuel economy. When your radically increase your flow velocity the RPM's in which this effect happens moves up. The increased flow velocity makes the turbulence get REALLY crazy. The fact that batch firing smooths things out a bit also makes me think this is the issue.

anyway... I've gone on long enough, try dropping your plug gap to something in the range of .025 and see what happens.
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Old 07-11-2004, 01:04 PM   #10
Chav
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no-coast-punk, i'm running 5psi in the mid-range and up to 8psi up top. Originally I had my gap at .40, after the hesitation I moved it down to .30. I will try to move it down to .25 and see what happens.

Thanks for the reply.

-Chav
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Old 07-11-2004, 08:40 PM   #11
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Down to .25 with no improvement.

-Chav
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Old 07-11-2004, 11:24 PM   #12
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What is your setup?
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Old 07-11-2004, 11:26 PM   #13
Chav
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ludespeed stage 2, 440 rc injectors, link plus, borla 2.5 inch cat back, borla headers, and the normal stuff like fuel pump, dual feed fuel lines that came with the kit.

-Chav
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