[Gmecm] 7747 stumbling acceleration when cold

Thu Dec 2 15:51:29 UTC 2010

Lower BPW did not help.  I decided to install the closed air cleaner with
heat riser though and that seems to have helped a lot.  It has warmed up
some here, so I'll try it for a while longer before I give my final
verdict.

The factory air cleaner is an ugly beast on a dressed up engine.  I hate the
two part design with the spacer.  My engine didn't originally have this
exact setup, so I really have no idea how they routed the hose from the
spacer without it interfering with the throttle cable. I got part way down
the street and realized I could only open the throttle part way.  I have a
hose on the spacer trying to get over to the driver's side valve cover.  I
know this isn't EFI related exactly, but can anyone explain how the factory
routing goes for the engine breather?

On Tue, Nov 30, 2010 at 8:22 PM, Charles McDowell
<charles at taildragger.info>wrote:

> Well, I loaded up a new bin with BPW=122.  The engine isn't cold so it's
> not a real big test, but it seems to run fine.  The BLMs were higher, but
> not super high on my short test drive.  The range was like 123 to 140.  I'm
> going to let the engine cool off and see how it works in the morning...
>
>
> On Tue, Nov 30, 2010 at 6:00 PM, Charles McDowell <
> charles at taildragger.info> wrote:
>
>> Interesting.  Somehow I got myself to 132.  The standard ASDU is 135, so
>> I'm a little confused,  I'm sure I originally scaled it like 135*(55/65),
>> but maybe I found the BLMs to be running away or something....  I think I'll
>> try again and double check.
>>
>>
>> On Tue, Nov 30, 2010 at 3:14 PM, Scott Peitzsch <jlg-sep at comcast.net>wrote:
>>
>>> The 9C1 Caprice TBI injectors (aka Cop injectors) are nominally
>>> rated to flow 68#/hr @ (I believe) 12PSI.  The correct BPWs for
>>> them are:
>>>
>>> BPW on a 305 = 107
>>> BPW on a 350 = 122
>>>
>>>
>>>
>>> ----- Original Message -----
>>> From: "Aaron" <aaron at creativeoverdrive.com>
>>> To: <gmecm at diy-efi.org>
>>> Sent: Tuesday, November 30, 2010 3:11 PM
>>> Subject: Re: [Gmecm] 7747 stumbling acceleration when cold
>>>
>>>
>>> I've not seen "cop" injectors, but a quick search shows them to be 65
>>> lbs/h.
>>> But to calculate a correct BPW you MUST know what they flow.
>>> And the rated flow is based on a steady fuel pressure, so you'll need
>>> that
>>> as well.
>>>
>>> It's been so long since I've looked at the hack for the 7747, I can't
>>> remember what you should check next.
>>> I've always started with a bin that was close.
>>> Maybe Allen will pipe up soon. He's better at this than me.
>>>
>>> From: cmcdowell12 at gmail.com [mailto:cmcdowell12 at gmail.com] On Behalf Of
>>> Charles McDowell
>>> Sent: Tuesday, November 30, 2010 12:02 PM
>>> To: Aaron
>>> Cc: gmecm at diy-efi.org
>>> Subject: Re: [Gmecm] 7747 stumbling acceleration when cold
>>>
>>> I can check in the log file tonight for the items you asked about. I was
>>> having major grief when I first installed this because I was given 305
>>> injectors by mistake. I examined every tiny detail of the install so I'm
>>> pretty sure I don't have any air leaks. Also bear in mind that it all
>>> works
>>> fine when warm. I know things expand when they warm up, but it sure can't
>>> be anything major. The thing idles and cruises fine when cold too. It
>>> really seems like an acceleration thing.
>>>
>>> Does anyone know for sure what things need to be changed when using a
>>> larger
>>> injector size? All I changed was the BPW to account for "cop car"
>>> injectors. Are there other things too?
>>>
>>> Thanks.
>>> On Tue, Nov 30, 2010 at 9:19 AM, Aaron <aaron at creativeoverdrive.com>
>>> wrote:
>>> We have discussed the adapter plates before.
>>> They are notorious for creating a vacuum leak were the TB and IAC gasket
>>> go
>>> over one of the bolts.
>>> The IAC sometimes even hangs over the adapter plate, so there is no seal
>>> to
>>> the gasket.
>>>
>>> What is the IAC position at idle open loop and closed?
>>> Map voltage?
>>> TPS voltage?
>>> Fuel Pressure on the supply side?
>>> Fuel Pressure on the return side?
>>> Have you looked at the fuel spray pattern from the injectors?
>>> I like using a dial back timing light to strobe the spray to see it
>>> more clearly.
>>>
>>> From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On
>>> Behalf
>>> Of Charles McDowell
>>> Sent: Monday, November 29, 2010 3:09 PM
>>> To: Eck, Joel
>>> Cc: gmecm at diy-efi.org
>>> Subject: Re: [Gmecm] 7747 stumbling acceleration when cold
>>> 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.
>>>
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>>>
>>>
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>>
>>
>
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