[Gmecm] RE Tweaking Asynchronous BTW

Sun Sep 10 11:51:25 UTC 2006

    Where have you found that term? BTW? Sounds like a type-O. Asynch BPW makes more sense (Base Pulse Width). Asynch pulses are used during AE among other conditions. Setting asynch BPW to zero would at a minimum reduce the AE shot, and likely decrease it to 0 ms of fuel added. I without a better understanding of this table, I would play it safe and "leave it alone."

 27 Eproms? Consider that a good start. You might be into it for far more by the time you get done.

 Most of the fuel delivery calcs in the ecm are tied in with the injector constant. If the constant is adjusted, the fuel delivery calculations will also be adjusted. One function which is ignorant of injector size is the Acceleration Enrichment. AE is delivered as timed shots of fuel to help during transient conditions. AE is set up to prevent stumbles, bogs, and excess emissions by trial and error. If you alter engine airflow and response, as well as injector size, you'll need to re-adjust the AE to fit your engine and injectors.

 If you have a "low end" cam it will tend accelerate the engine faster at lower engine rpm. There will be less change in airflow at higher rpm. AE should follow, with greater fuel delivery at lower engine rpm. If you have a "top end" cam you'll get more effective cylinder filling at higher rpm. AE should tend to be higher at higher rpm.

 Larger injectors really affect AE the most. And larger injectors with increased fuel pressure are even worse. In the old days of Holley Carburetor madness it was tough to get too much AE. Not so today. Too much AE is very common now and the results are a squishy, saggy, hesitating engine which can run great under steady load, but will show rich O2 readings and can spew black smoke at the same load if it's after a rapid increase in MAP or TPS.

 If we're voting, I'm with Beau. Less AE may save the day.

 Zaphod

 -----Original Message-----
 From: matthew10_5 at netzero.net
 To: gmecm at diy-efi.org
 Sent: Sat, 9 Sep 2006 2:02 PM
 Subject: [Gmecm] RE Tweaking Asynchronous BTW

  Thanks Darryl.. 

 Maybe a bit more info would be in order. I built this engine 2500

miles ago. I put every thing new inside and out. It has been overbored

has a cam a little taller than stock. I thought that maybe one of the

new sensors might be bad , so one by one they have all been replaced

again. The wiring harness was replaced and the speed sensor. The TBI

unit is from a 350 cid and therfore has larger injectors . This larger

injector size facilitated an 8% lowering of the VE tables almost across

the board (so far). The timing tables have been tweaked only slightly

mostly to stop preignition. I had taken my van to a Chip maker to start

with because at the timeI was unfamiliar with reprogaming the ECM. When

the engine was first fired it would hardly run blowing clouds of

unburned fuel from the tail pipe. When I picked up the van it was

better and it would idle now but was still blowing black smoke under

what I now know as WOT. After taking the van back 3 times for the same

problem, and after an $800 bill, I deceided to try it myself even

though it didn't have the Dyno. Everything the shop did has been undone

except for the increased fuel pressure regulator. For some reason they

thought this was part of the problem. Anyway I bought all of the

equipment, (except the Dyno and Sniffer) and have burned 27 EPROMS so far.

 This is why I am now at the place it must be something else. All the

sensors and the IAC are working properly. The BLM is still low at this

point in Real time using a data logging program. I have extensive

records of in car actual driving conditions, even through the Rocky

Mountains.

Back to my ORIGINAL QUESTION , what is "ASYNCHRONOUS BTW" and how does

it affect the VE tables. Is it nessessary or should it just be disabled.?

If your reading this Steve, do you have any comments?

From: "dgilbert78 at juno.com" <dgilbert78 at juno.com>

Subject: Re: [Gmecm] Tweaking Asynchronous   BTW

To: gmecm at diy-efi.org
Message-ID: <20060908.105104.3679.893120 at webmail16.lax.untd.com>

Content-Type: text/plain

Hello: make absolutely sure that the MAP sensor is seeing proper

vacuum. No 

kinked hose, no mushy hose, no partially carboned map port in the TBI

body. 

Restricted (delayed) vacuum to the MAP will act like bad acclerator

pump in a 

carb. Make sure that is absolutely perfect befort re programming. May

have to 

remove TBI and rod out the MAP vacuum port, these become carboned and

gummed. 

Good luck. Spent many hours finding that one.

Darryl..

    Tweaking Asynchronous BTW

Date    :   Fri, Sep 08, 2006 10:04 AM

I have been unable to remedy the stumble problem with my 305 using

the 7747. I have readjusted the timing tables, the VE tables. 

Although the motor runs great it still stumbles on takeoff in open or

closed loop. The system goes rich under partial throttle between 800

and 1100 RPM without going into WOT inrichment. My question is about

the asynchronous BTW handles in three tables. One table is for Maximum

and one is for Minimum and still one is for RPM.

One blog that I ran across tells off fixing the stumble problem that I

have by setting one of these table values to "0". Can someone shed 

some

light on the asynchronous BTW modes? What is it, and does it overide

the VE table, or work with them, or none of the above? Which setting

would potentially remedy my problem. Any Thoughts?   Matt

Darryl..

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