Cranking pulse widths correlation to carb accel pump shot

[fe3xclone]

Okay, this is probably a really stupid question but is there anyway to correlate how many pumps of the throttle you need with a carb to give an engine enough fuel to start with how many miliseconds you need for your cranking pulse widths?

I'm still having starting issues with my 455 and I've been trying to correlate the cranking pulse widths to just how much fuel is actually being put into the engine while cranking.

I had the 455 running with a carb on my engine run-in stand before installing it in the car and hooking up the EFI. This way I could set my base timing on the non-computer HEI and also make sure the engine ran properly.

I remember that it took quiet a few good healthy full throttle squirts from the accelerator pump to give the engine enough fuel to start. More so than what I was typically used to. The carb I used was a Speed Demon 750cfm vacuum secondary off my brother's car. I believe it has a 30cc accelerator pump. Whatever comes stock with them.

So if it took 3-4 full throttle squirts with the carb, is there anyway to figure out how to set my cranking pulse widths to match this as close as possible?

Thanks,

[Matt Cramer]

Theoretically, if you're running a TBI and the exact same manifold, you could take the volume your accelerator pump shot and create a priming pulse length long enough to send the same amount of fuel. TBI and port injection engines seem to need different amounts of cranking fuel for some reason - probably more of it sticks to the manifold in a TBI setup - so if you have a port setup, this isn't going to get you anywhere.

[msiddalingaiah]

Yes, I think it depends on your intake and injector placement.

I have a similar situation, but on a kick start motorcycle. I know if I hold the decomp lever and give it five kicks to squirt priming fuel, it will start with exactly one kick every time. It seems to require quite a bit of fuel even though it's effectively port injection. I haven't adjusted the priming pulse yet, but that's my plan. If I'm right, I should be able to avoid priming kicks and kick only once to get it started.

[fe3xclone]

so if you have a port setup, this isn't going to get you anywhere.

Hmmm...thanks. And yes I do have a port setup. I'm using the same intake manifold as I did when I had the carb running the engine. Fuel injectors are 42lb/hr.

Hopefully I can get some more seat time over the weekend and see if I can track something down.

My problem is that I'm trying to get the body work finished on the car and need to drive it down to my neighbors house so we can get the body into its first coat of primer. I didn't think this would be a problem as I had the car actually running and driving a few months ago and it seemed to drive somewhat decent as well as rev through the rpm range good, although it did seem pretty rich.

Videos:

http://www.youtube.com/watch?v=LU9cTyO7sz4&NR=1

http://www.youtube.com/watch?v=wwl21THDnis&NR=1

http://www.youtube.com/watch?v=CARIYTts ... re=channel

However not long after these videos were taken I started having the problems with getting it to start consistantly. I didn't change anything with the tune in the ECU, I just noticed it kept getting harder and harder to start and when it was running was backfiring really bad at idle. When I tired messing with it I ended up hydrolocking the engine while cranking it over.

So I pulled all of the plugs, changed the oil, squirted some oil into the cylinders and then put a new set of plugs in the engine. This was all over the course of 1-2 weeks. Once I finally had everything set I hoped back into the car and tried cranking it over and was able to get it to fire up and idle again although I had to play around with the gas pedal to keep it idling.

I left it alone for a month while I worked on the paint and body then one day decided to try starting it again. Nothing changed since the last time I started it but it just wouldn't start and now it's been like that ever since.

Obviously I think I'm fouling my spark plugs out which is one of my problems. Or maybe its all of my problem and I just need to get lean everything out more? I do have a wideband O2 setup through the Megasquirt and initially I had readings in the 9.0-11.0 range while idling. It was enough to fill the barn with a cloud of unburned fuel. I've leaned them out since then but now I've run into my current starting issues.

Just thought I'd throw that all out there. I know it's just about impossible to diagnose anything over the internet. Wish some of you guys were closer so I could pick your brain in person!

Thanks,

[fe3xclone]

Well, I did some more investigating today. Made a few changes to my tune and retried everything. Still no fire.

I got out of the car and turned the ignition key to the run position. You can hear the fuel pump activate and shut off after a few seconds like its supposed to. However my fuel pressure gauge on my fuel rail was showing barely 5lbs of pressure.
I cycled the ignition on and off quite a few times and the needle never moved. Tried adjusting my fuel pressure regulator and still nothing.

So I decided to disconnect my fuel line crossover between my fuel rails to see if I had any fuel at all. When I cracked the one open, you could hear a lot of air escaping and my fuel pressure gauge dropped from 5lbs to zero. However there was no fuel at all that came out.

I then disconnected the fuel line at the back of the fuel rails and nothing came out there either.

So next I'm going to move on to the fuel filter and replace it. Question is, how do you know if you've got a bad fuel pump or regulator? Right now I'm thinking I have a clogged fuel filter since I'm getting now fuel into the fuel rails. Does that sound logical?

Thanks,

[fe3xclone]

Okay, disregard that last post. Turns out it doesn't matter what your cranking pulse widths are if you don't have any fuel in the tank!

Looks like I need to look into why my fuel gauge isn't reading correctly now...