Re: Disappointing day at the dyno... Advice needed!

From: William H. Hiatt III (william@hiatt.net)
Date: Sun Nov 17 2002 - 22:53:14 EST


Well, I hooked up my OBD-II scanner on my laptop, and read the short term
fuel trim. It seems to be running rich (Average was about -12% for bank one
and -11 for bank 2). I would however constantly see -18% or so on both
banks, with peaks of -25% on the banks. I can't read the long term fuel trim
(It's at 0) because the PCM hasn't learned yet.

The reason I bring this up is after about 200 miles after the PCM learns,
the truck will start to surge about 200RPM here and there while driving not
under acceleration. Then it'll throw a a few 20X codes (Injector control
malfunction)

Could this be because it's running way to rich? I do have those 21# FMS
injectors, coupled with the extra fuel in the LEACH PCM flash, minus the
extra timing in the flash?

I'm going back to LEACH on Tuesday, and Tom is going to flash my box and set
the timing back up to 28.5 (Where he sets them all). Is the extra 3.5
degrees enough to burn the rest of this fuel causing the truck to run rich?

Thanks
william

""news.verizon.net"" <wE@.com> wrote in message
news:ar1i83$dr9$1@bent.twistedbits.net...
>
> Well I had a disappointing day at the dyno today. Only gained 1.4RWHP and
> 5RWTQ, this is after the HO cams. This brings me to 225.4RWHP and
283.5RWTQ.
>
>
>
> My guess is that 3.5 degrees of timing out of the PCM is making a big
> difference! Also, you can see a steady decline after 4400 RPM of the of
the
> TQ/HP curve.
>
>
>
> Changes between this run and last run:
>
>
>
> - HO cams
>
> - 21# FMS injectors
>
> - (-3.5) degrees timing on the PCM
>
>
>
> Other things that may make a difference between this run and last run:
>
>
>
> - I have a bolt in cat for the third cat now. There is a minor leak around
> where the cat bolts to the exhaust. I can tell this because water leaks
out
> from where you bolt the cat in (I got ripped on the install job I had this
> crappy shop do)
>
>
>
> - I'm running a Robertshaw 330-180 thermostat. The problem is it's such a
> HIGH FLOW tstat, the truck doesn't warm up a lot of the times, and trips a
> check engine light. I'm thinking I should change it to a GT755-180
> thermostat? Could this be affecting HP/TQ?
>
>
>
> Here are my questions:
>
> 1) I think I need to get that timing put back in! 3.5 degrees must make a
> big difference
>
>
>
> 2) HO intake?
>
>
>
> 3) I'm going to remove third cat, and weld in some pipe between the Y pipe
> and muffler. My question is, should I go 3" between Y pipe and muffler, or
> go 2.5" to like halfway to the muffler. I DO NOT want to loose any more
> power, and I know our engines aren't that large, so we need to be
> conservative on pipe size. Is this even worth doing?
>
>
>
> 4) Anything else you can suggest based on my mods. Do I need to change my
> exhaust?
>
>
>
> Again, my mods are as follows:
>
>
>
> - Mike Leach PCM (With 25 degrees of timing instead of 28)
>
> - FMS 21# injectors
>
> - HO Cams
>
> - 4" Z-tube
>
> - Magnaflow 3" IN 2x2.25" OUT exhaust
>
> - F&B Throttle body
>
> - Robertshaw 330-180 Tstat (180 degrees)
>
>
>
> Sorry for the long post, this whole thing was kind of frustrating.
>
>



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