Accel DFI Cranking Pulse Width

[Butch]

Guys, I am trying to get my LT1 engine started for the first time. It is stock internally with a slightly larger cam and ported and polished heads with bigger valves.

In order to get any combustion I have had to increase the Cranking Pulse Width up to around 55ms, the default was around 9ms. at 75 degrees.

It will occasionally run for about 1/2 second but nothing more.

Any ideas would be appreciated!

Butch

 

[64duece]

Sounds like something else is going on there. A BIG vacuum leak maybe? Take all that fuel back out and start looking for the culprit. I can only assume you've checked spark, fuel pressure while cranking..ect. Double check the grounds on ECM and IGN and fuel pump. What happens if you use starting fluid? Will it fire? Let us know what you come up with

 

[Butch]

I suspect a vaccum leak also. I have some holes in my intake plugged with plastic plugs temporarily. I will check that out.

Thanks,

Butch

 

[Butch]

Well, I can't find any vaccum leaks. Is it safe to experiment with starting fluid (vapor lock?) Someone also suggested a propane torch (unlit).

I was kinda hoping that someone would have a startup file from a similar Engine so that I can compare my setup????

BB

 

[64duece]

I would try a small shot of starting fluid and/or carb cleaner to see if it fires. When it begins to die..shoot another shot in to see if it will stay running. I use propane or carb cleaner to find vacuum leaks. My reason for the fluid, if it fires easily...you may have a supply issue. Even if there is a big leak [which I have seen them run @ 50% load (about 5" vacuum) and higher @ idle] It would still stay running, just needed alot of fuel in the map to keep it running (like IV of 60) Of course that is way to much fuel, but again, this customer had a huge vacuum leak. A base map with 20% more fuel should get it running and keep it running, but the #'s you have indicate something else is amiss.

 

[Racetronix]

Chances are you are running low impedance injectors with this setup. Certain models of the DFI cannot run eight low impedance injectors at once (batch fire). Total parallel impedance is 0.25 ohms.

We have seen this on a few occasions where the car will sputter and die out.

Unplug two injectors, one on each side of the motor and set the cranking fuel to around 8-10ms. You should get it to start on 6 cylinders. This is assuming your after start and base fuel map are in order.

 

[Lance]

Low impedance injectors should not typically be a problem for the DFI box. That unit has four, 4 amp peak/1 amp hold drivers and injectors are typically paired on a driver. A standard 14 ohm injector would reduce to 7 ohms when paired and draw about 2 amps at 13.5V. This is not enough to cause the driver to foldback into "hold" mode so the injectors will operate saturated. A 2 ohm injecter paired, will be about 1 ohm and will want to draw about 13.5 amps at 13.5V. The injectors will never see 13.5 amps as the driver will fold the current back to 1 amp as soon as the 4 amp peak threshold is reached. This equates to about 500mA for each injector and should still be sufficient for most injectors.

Where (I think) the problem comes in is when using MSD or Rochester low impedance injectors. The magnetics for this type of injector have always seemed to be a bit strange to me. I was never able to put my finger on it but this seemed to be the application that was always the problem. Nevertheless, problems did not seem to occur when the injectors were not paired on a driver.

Just FYI for anyone interested.

Lance

 

[Butch]

I am using the stock LT1 injectors!

Butch