[Gmecm] 7747 stumbling acceleration when cold

[Scott Peitzsch]

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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