[Gmecm] '7730 Stumbles at cruise

[Programmer]

Provided fuel pressure, ignition, and everything else is fine,

Without VSS, the ECM 'assumes' a couple things related to IAC strategy...so 
you might want to get that working....even though its been flawless for 2.5 
year, you can make it even more flawless.

LW

----- Original Message ----- 
From: "Cowen" <captain_krill at yahoo.com>
To: <gmecm at diy-efi.org>
Sent: Tuesday, May 29, 2007 12:05 PM
Subject: [Gmecm] '7730 Stumbles at cruise


> Hello folks,
>
> It has indeed been quiet, so here's a question to generate some 
> discussion.
>
> I've got a stock '730 ECM from a 3.1 running, a 3.4, with injection parts 
> from a Fiero 2.8, with DIS.  This setup has been going almost flawlessly 
> for about 2 1/2 years now, and I love the power, mileage, low emissions, 
> and year-round easy starting compared to the carb it replaced.
>
> Unfortunately, it has picked up two small issues in the last 6 months or 
> so.  First, it stumbles a bit at very light cruise. I have no VSS yet, so 
> I'm pulling a code for that, but nothing else.  I have the (digital) EGR 
> vacuum plugged too, but I don't think it enables without VSS anyway.
>
> Secondly, when the engine is cold, the there's a bog coming off idle 
> unless it's revved up.  This feels like the IAC is closing in response to 
> throttle input.  I had this problem when I first got things going, because 
> the throttle plate was adjusted for a 2.8 and the IAC had to 
> overcompensate for the air in a 3.4, so properly adjusting the throttle 
> body completely cured it, until now.  I've tried increasing the throttle 
> at idle slightly (reducing IAC counts required), but it hasn't affected 
> the mild bog.
>
> I know my setup isn't perfect with no VSS (I'll be transplanting the whole 
> shebang again into an MGA next year anyway), but the thing is it didn't 
> have this stumble for more than a year of operation.  I've done a quick 
> check for loose connections at the TPS and IAC and they look good.  I 
> can't find any vacuum leaks and it still runs wonderfully otherwise.
>
> Any suggestions on what I should focus on?
>
> Thanks!
>
>
>
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