cold start w/ FAST

[foxspy]

Hey Everyone,

I have a question about cold starts w/ the Speed-Pro computer. When it's cold out, and I haven't started my truck for awhile, it takes a long time for the motor to finally start. I went in and enrichened the fuel mixture at colder coolant temps, but now every now and then I get a pretty large backfire when it first starts. What would I adjust to make it start quicker and not backfire when it's cold and hasn't been started in awhile??

Thanks for your help.

 

[foxspy]

Anyone??

Do I increase pulse width? Enrichment? What should I adjust?

Thanks.

 

[bobc455]

I'll add my two cents, even though I'm not sure it will help a ton.

In my opinion, the amount of fuel going into the motor is the most important parameter to adjust to get reliable starts. Play with this on the appropriate table- sounds like you've done this already.

The other thing that I tried to do is to get the engine speed right after I start to match the idle speed at that temperature. In other words, the engine didn't overshoot or undershoot the idle speed. To do this, I would play with the IAC motor adjustment by watching where the IAC motor would go just after startup, then adjust the IAC starting parameter to match. For example, if my idle speed was 1300 RPM and the IAC typically went to 100 to hold this speed just after the engine started (to maintain 1300 RPM), then I would adjust the IAC starting parameter to around 100. If the engine speed shoots up to like 2000 RPM then backs down, then I'd back off your IAC motor a bit. After you've played with this adjustment, you might have to go back and finagle with your fuel curves just a bit.

I don't know what is causing the backfire, but I suspect if you get your engine to start using this philosophy, you probably won't get a backfire.

Let us know if this helps!

-Bob Cunningham
bobc@gnttype.org

 

[55Belair]

Does it do this if the vehicle has NOT been sitting for a while?(Like a couple of days). You may want to increase your pump prime time. If you have a weak regulator that is allowing the fuel to drain back down to the tank, then it may take more than a few seconds of pump prime to refill that line and get up to pressure.

 

[ChrisChow]

Increase enrichment and make sure the IAC is nearly closed. Sometimes the IAC starting position is set incorrectly at 0% TPS and also why it's very important to have the TPS adjusted so that when your foot of off the throttle you get as close to 0% (with the gas pedal mashed to the floor you have 95% throttle or greater).

Originally posted by foxspy
Anyone??

Do I increase pulse width? Enrichment? What should I adjust?

Thanks.

 

[foxspy]

At idle my TPS is at 13%, I adjusted it down to 0%, but when it's WOT it only goes to 80%. Now w/ it at 13% at idle, it goes to 93% at WOT. If I clost the IAC at idle, wouldn't it die when I put it into gear cause of the catching of the motor/tranny.

 

[ChrisChow]

Oftentimes, the TPS must be adjusted (on the tabs) until you get the best of 0 and 99%. You must move the mounting tabs around until you get the values required. Sometimes this requires cutting off the end tabs of the TPS.

If you close the IAC at idle, it should kill the motor without dropping it in gear. The stall saver feature prevents the motor from stalling when you put in gear by opening the IAC in incremental steps. These steps are programmable thru the lap top...as you probably already know.

Originally posted by foxspy
At idle my TPS is at 13%, I adjusted it down to 0%, but when it's WOT it only goes to 80%. Now w/ it at 13% at idle, it goes to 93% at WOT. If I clost the IAC at idle, wouldn't it die when I put it into gear cause of the catching of the motor/tranny.

 

[HighPSI]

IMO: I would leave your TPS settings right where you have them (13% & 93%). They aren't that critical with a FAST setup as long as you get over 80% at WOT(Clear Flood mode). Just set the "Max TPS at idle" correctly in the idle parameters table. Once the truck is warmed up in park (least load on the motor), adjust the throttle screw until the IAC is nearly closed.

Your startup problem can probably be fixed in the cranking fuel table.

 

[HighPSI]

Originally posted by Zed_six
If you close the IAC at idle, it should kill the motor without dropping it in gear.

How are you closing the IAC? If you close it by putting more throttle in it, it shouldn't kill the engine. Just be sure to redo the idle parameters. Please explain.

 

[ChrisChow]

To be more clear, I meant selecting for lower idle speed via software that you lower idle speed, it will close the IAC. Also, throttle follower. Sorry for the confusion.

Originally posted by HighPSI


How are you closing the IAC? If you close it by putting more throttle in it, it shouldn't kill the engine. Just be sure to redo the idle parameters. Please explain.