Hi guys,

I'm trying to get my combo to start a little easier. Right now, it requires a little bit of throttle feathering to get it to fall in line.

If anyone has some good table data to use as reference, it would be helpful. This is with 60# injectors on a 441ci. Big cam, big single-plane manifold.

I've played a bit with the crank fuel PW modifier vs temp, crank pw modifier vs crank pulse, etc. Also played a bit with the IAC park position. Just looking for something that has worked well for others in this area.

Many thanks,
-Craig

 

I have no idea if this will help or not, but..

on my 71 with it's 406 and 240/248 cam (@ 0.050), it will NOT start at a base timing of 6*-8* unless you held the throttle open.

As you know, a stock $8d setup cranks at the 6* of advance that the dist is set to, and no more.

I re-set-up the dist in my 71 for 20* base timing, and only 12-14* of total mechanical advance (no vacuum adv). Starts to the touch of a key now with no throttle help.

big cams need more advance to fire up easily - there is more compression leakdown when you're cranking, and the spark is just too late at only 6* BTDC to do much good/develop much cylinder pressure. A stock cam doesn't have nearly as much overlap and there's still good cylinder pressure at cranking speed.

Thus my recommendation is you might try burning a chip with the initial spark advance value increased by say 10*, and then advance the dist 10* mechanically. This gives ya no net change to your running timing, but gives you 10* more while cranking up.

I know lots of folks don't like messing with the 6* base timing, but the difference for me was very large.

beware that if any point on your timing curve falls below whatever your new initial advance is, you'll observe a timing increase to the new initial advance. I.E. if you're at 6* now, and you increase it to 16*, and somewhere your timing curve only calls for 14* timing, it can only go as low as 16* now ....

 

That's a good idea, thanks!

Wonder if it can be done via code hack? Say have a crank spark adder or something slick like that? Hmm..

 

I believe there is a value something along the lines of "minimum RPM for ECM controlled spark advance" and i believe it's default is 400rpm.

if you set it down much lower (say, to 100rpm) then in theory you could control the timing right in the ECM at crank speeds (well, presuming they are above 100rpm, which they should be).

disclaimer: haven't tried it, can't confirm it.

 

Referring to this?

L801A: FDB 3277 ; 300 RPM, START UP RPM
; ARG = (65536*120)/(RPM/NUM CYL)

That's all I saw that matched up I think.

Also, I've got a FP regulator that tends to bleed down when pump is off. Wonder if I can find a variable for the on-time cycle for the FP and set it up to like 10 seconds. Stock is like 1 second or so. That'd also be nice.

 

You can key on and off a few times to prime it. Or try a jumper at the ALDL - fuel pump pin. Of course this is just diagnostic stuff, to try to find the root cause of your problems, not permanent.

What's your base timing at now?

 

Base timing is at 6 degrees, idle timing is around 40-43. I guess I can try diddling that parameter listed above down to 50-100 or so and see what happens.

In the other scenario, I can do as suggested and set my base timing up to 16 degrees or so and pull up the base timing parameter in the bin to compensate, and see how that does with crank timing at 16 degrees. The thing idles rock-solid once it kicks off, and fueling either +/- doesn't seem to make it happy, so the timing must be what it needs (makes sense). Running 110 fuel too, so that needs even more timing to light off.

Yeah, been doing the key on/off thing a couple times for a while, ready to have it a little nicer. Was going to rig up a switch to keep the FP hot whenever the ignition is on. I have it running a 30A relay common with the electric water pump now. It's an Aeromotive A1000, not sure if it's pump slip or regulator bleed-down. Either way, better to have it running throughout the startup to ensure proper pressure.

 

What about a check valve in the fuel line? May not help if the regulator is leaking by, though.

 

The output to the relay is controlled by U13 and is (I believe) interrupt driven to set the output state. Uses the DRP to set the FP relay on for each pulse. Timing must be within that chip??. Can't find any delay or length of counter setting that could be changed in code for that bit.
The EST bypass operates from the same location so from what I'm guessing, the counter interrupt signals the outputs somehow because that output can be controlled by the counter as to when to go on. There is no info out there on that chip to really know what its doing.

 

There is a GM 'hot start' module that was used in the HD vans and trucks. It would run the fuel pump for 20 seconds at key on. IIRC it was used in the '87 to '92 time frame with the '7747 ECM. Could actually be used with any ECM.

RBob.