[Gmecm] 7747 stumbling acceleration when cold

Mon Nov 29 20:08:52 UTC 2010

I'll double check my logs, but I think my temp is good.  Bear in mind that
it's not like this thing ran well once and stopped.  It never worked well
since I installed it.  I have an Edelbrock performer quadrajet carb manifold
with an adapter for the TBI.  Thanks.

On Mon, Nov 29, 2010 at 12:10 PM, Eck, Joel <Joel.Eck at hp.com> wrote:

>  You can select ?reply to all? instead of just ?reply?, and it will
> include the gmecm mailing list as well as the last poster.
>
>
>
> Is your coolant temp sensor reading properly/remotely close? What kind of
> intake are you running, stock TBI, aftermarket TBI, some sort of carb
> manifold with TBI adapter?? Checked for any potential vacuum leaks while
> cold?
>
>
>
> Thanks,
> Joel Eck
>
>
>
> *From:* gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] *On
> Behalf Of *Charles McDowell
> *Sent:* Monday, November 29, 2010 11:58 AM
>
> *To:* gmecm at diy-efi.org
> *Subject:* Re: [Gmecm] 7747 stumbling acceleration when cold
>
>
>
> No, I have no park/neutral switch.  I datalogged this morning and the
> problem was very pronounced since it was fairly cold (40 degrees).  I
> noticed that the "old high gear flag" was on when it was in closed loop but
> not before.  It wasn't on in open loop.  The problem was, if anything, worse
> in closed loop.  I have a heated O2 and go closed loop pretty quick.  Anyone
> know if the high gear flag thing indicates anything important about the fuel
> delivery?
>
> Did I mention I have "cop car" injectors?  It seemed like a fun idea at the
> time I got them, but I wonder if it's part of my problem.  I adjusted the
> BPW to account for them, but maybe there are other things that need
> adjusting as well?  I'm tempted to just get stock injectors so I can maybe
> use a normal bin without so many mods.  I originally had 305 injectors
> without knowing it and of course nothing worked.  I went straight to the cop
> car ones, so I've never actually used the regular 350 ones.
>
> Thanks for the help.
>
> By the way, this list always wants to reply to the individual poster
> instead of the whole list.  What's the easiest way around that?  I'm in
> gmail and all I can figure to do is cut and paste the list address over the
> poster's after I hit reply.
>
> On Mon, Nov 29, 2010 at 9:48 AM, Mike Wilson <mwilson at bwarch.com> wrote:
>
> Do you have a functional park / neutral switch? I know it acts differently
> when it thinks it is in park. With no VSS and no heat riser with an open
> element air cleaner and headers there could be enough off in the tune to
> make it stumble when cold if it thought the trans was in park still.
>
>
>
> Just a thought.
>
>
>
> Mike
>
>
>
>
>
> *From:* gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] *On
> Behalf Of *Charles McDowell
> *Sent:* Sunday, November 28, 2010 3:32 PM
> *Cc:* gmecm
> *Subject:* Re: [Gmecm] 7747 stumbling acceleration when cold
>
>
>
> Thanks for the replies.  This is a transplant onto a carb engine and it has
> never really run great.  Good enough for daily driver, but with quirks in
> cool weather.  I've tried various tunes over the years so I'm sure it's not
> the same, but I tried to start it one morning when it was cold soaked to
> about 15 degrees and it simply wouldn't start.
>
> I have headers, so the heat riser thermac thing is going to be cheesy at
> best.  The headers do have a little tube for thermac, but there's not much
> to it.
>
> Anyway, I datalogged some this morning but it was too warm to have the
> problem really show up.  I have a heated O2 and I go closed loop pretty
> quick.  I think the problem persists after going closed loop.  I noticed
> that the rich flag is almost always on.  It only turns off during constant
> cruise, but the BLMs aren't terribly far off.  The table had ranges from 118
> to 138 for a short drive.
>
> I also noticed the "old high gear flag" was on all the time.  Does it
> matter?  I tried searching for info on it, but I can't tell if the ECM
> changes anything as a result of that flag.  I don't have anything hooked to
> the ECM from my trans.  No VSS either.
>
> I'll try to get some data logged on a colder day too.
>
> Thanks.
>
> On Sun, Nov 28, 2010 at 2:56 PM, Scott Peitzsch <jlg-sep at comcast.net>
> wrote:
>
> Even with your caveat below, I'd suspect this is directly related to the
> lack of a
>
> properly functioning Thermac system.  Without a well regulated source of
> warm
>
> air, basically every 7747 I've ever tuned with an open air cleaner exhibits
> the
>
> symptoms you describe below.
>
>
>
> I'd suggest either returning to a stock style air cleaner and intake with a
> fully
>
> functional Thermac system, or consider switching over to a 1228746 ECM.
> The
>
> 8746 is pin-for-pin compatible with the 7747, and adds IAT capability,
> which
>
> should go a long way towards solving your issue.  I've used this solution
> with
>
> excellent success on a few recent trucks I've tuned.
>
>
>
> -Scott
>
>
>
>  ----- Original Message -----
>
> *From:* Charles McDowell <charles at taildragger.info>
>
> *To:* gmecm <gmecm at diy-efi.org>
>
> *Sent:* Sunday, November 28, 2010 12:09 AM
>
> *Subject:* [Gmecm] 7747 stumbling acceleration when cold
>
>
>
> I'm hoping someone can point me in the right direction of what to change in
> my BIN to solve a bad cold acceleration issue with a 7747 TBI.  The truck
> runs great once warmed up, but when the engine is still warming up (and
> worse on colder days) it stumbles through it's acceleration, sometimes even
> backfiring.  It sort of comes off the line decently, then bogs down and
> gradually works its way up to speed.  Any pointers on what I might change to
> fix this?
>
> Not sure if it matters, but this vehicle has an open air cleaner and no
> heat riser stuff.  I don't think that should be the issue since this happens
> even when it's 55 degrees out, but I thought I'd mention it in case.
> Thanks.
>   ------------------------------
>
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