[Gmecm] 7747 stumbling acceleration when cold

[Aaron]

YES , BUT 


The closer you are, the less other settings must be changed.
For instance, if the BPW is on target, you may not need to change the VE
fuel table to get a BLM of 128 for most driving conditions. Then spark table
would be closer based on the starting rich / lean condition, the accel
enrichment would not need to be changed, followed by the enrichment vs
coolant temp and others.

Most of my experience is in installing TBI not the tuning.
I was hoping Mr. Allen or someone else could provide a step by step.
IIRC the first step is the basics of the installation.
1. Supply side fuel pressure set to 9~13 psi (or 13~18 psi depending on who
you ask).
2. Return side fuel pressure verified to be less than 1~3 psi.
3. Idle speed based on the throttle position screw with the ALDL A & B
Terminal grounded.
4. TPS voltage set by moving the sensor to 0.5 volts.
5. Confirm MAP voltage with Key On Engine Off to match your altitude.
(Columbus Ohio at 1200 ft is 3.6~5.3 volts)
6. Confirm Map Vacuum signal is manifold vacuum and NOT port vacuum.
7. Confirm throttle cable / gas pedal pull far enough at WOT to get the TPS
to read ~5 volts.
8. Confirm IAC counts at idle. I prefer 50 as it gives you room to move both
ways.


From: cmcdowell12 at gmail.com [mailto:cmcdowell12 at gmail.com] On Behalf Of
Charles McDowell
Sent: Tuesday, November 30, 2010 3:17 PM
To: Aaron
Cc: gmecm at diy-efi.org
Subject: Re: [Gmecm] 7747 stumbling acceleration when cold

Let me ask my dumb question.? Why does the BPW need to be anything other
than "close enough"?? If it's off by, say, 10%, wouldn't the BLM pull it
in?? 

I just scaled off the spec flow rates, isn't that what a factory bin would
do anyway?
On Tue, Nov 30, 2010 at 1:11 PM, Aaron <aaron at creativeoverdrive.com> wrote:
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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