DFI79MC

iTrader: (1)

Little background-

Accel Gen 7/Dual Sync/ProRam running on a hydraulic roller 406 SBC. It runs awesome, cold starts awesome, just doesnt like to warm start. If I shut it off and try to restart it before it cools down, all I get is a couple cranks then a hiccup. At that point I need to hold it wide open to get it to start. All the tunes I've seen had the starting fuel coefficient very low. I've over doubled that table in the warm area and it didnt seem to make a difference. Is there something I'm missing? Am I adjusting the right area?

Any thoughts would be much appreciated. I'm soooo close to having this thing be a closed deal!

jmanley

Have you tried upping the "prime" time for the injection system. I have mine set to 6 seconds, and I turn the key enough to engage the fuel pump but I don't crank until I see fuel pressure at full climb.

Any thoughts if it's too rich or too lean when this happens? There is a table where you can adjust fueling by coolant temp. Have you tried changing it dramatically to see what happens? On my tune, when I look at Starting Fuel Coefficient, I have 280.0 at -40F, sloping down to 80.0 at 180F, then level at 80.0 until 230F, then back up to 90.0 at 245F. Hope that helps. Oh, and I have a 408, so should be close.

DFI79MC

iTrader: (1)

I'd have to run out and look again, but I believe the prime time is set at 5 seconds currently. I never crank until the pump stops either.

The lean or rich thing is a little confusing to me. Everything I've read points at it being lean, but that doesnt explain why I need to hold the throttle wide open for it to start... or does it? Things I read said if it was rich at start up it would just smoke and stumble till it cleaned up. It almost seems like its not getting enough air for a warm restart. Not really rich, just not enough air.

You are exactly right about the starting fueling. All the tunes I've seen have it set around 80 at typical warm starting temps. I cranked mine up over 170 there and it didnt seem to make a difference.

DFI79MC

iTrader: (1)

I was doing some poking around in the instructions and figured out something to try. I noticed my starting prime pulse is disabled, so I'm gonna enable it just to test something. The starting prime pulse is like pumping the gas on a carbureted vehicle. You need to pump the gas pedal twice within one second on the DFI for it to be active. Its designed to add fuel for a very cold start, but I'll try it when hot to see if it helps or hurts. That should be a simple way to add more fuel and determine if its rich or lean.

jmanley

While that is a band-aid in cold weather, you sid that you had problems starting when the car was warm. I'm thinking that you may be too rich and/or your timing is off at idle a bit. Before you goof too much with prime pulse (Mine is set at about 18, btw), why not try locking the timing in a few different spots to see if that makes it easier; i.e. try locking it at 10*, 15*, 20* and see if that helps.

Mine is hard to start if I have less than 16* timing at start.

DFI79MC

iTrader: (1)

I totally agree that the prime pulse is a band-aid, I just figured it would be a good way to shoot in some extra fuel to determine whether its rich or lean. I have a pretty aggressive timing table also, there are no cells below 20*. Its a fairly choppy cam and always idled a ton better with more timing.

The more I think about it, it acts like you took a warmed up carb engine and tried to start it with the choke closed. You get a couple cranks, a huff, then it doesnt want to start. I should go through the IAC settings again with a fine tooth comb. The only other settings I'm not 100% sure about are in the idle control configuration page. The integral, proportional etc. Would those apply here?

jmanley

Ok, yes, it would be a good way for an extra shot of fuel at startup. Maybe you have too much timing right around idle. Pull off 4* right at your idle speed area and see what happens. Maybe you have so much timing that is making it hard to start. I have a HUGE cam and I'm idling at 19-20*. If you get too agressive on idle spark, btw, you can actually lose HP in the transition zone between idle and mid-throttle application. If you have a huge cam, screw the "smooth idle", you gave that up with the cam - go for the HP that you want, which might mean backing off the timing a bit down there.

Let me know what you find. I think it's something easier than you think. Not in all the sub-tables. This should be able to be fixed with the master AFR/Base fuel map/timing tables since you say it's a warm-start issue.

Oh, but that does bring up a good point, what AFR are you using at idle? If I may suggest, make it a little richer than normal because you have a reversion problem with big cams. I'd suggest going to about 14.2 or maybe even 14.0, but don't keep it at stoich. That, with pulling some timing out should help a bunch.

I run mine at 14.2:1 in the idle area, then go to 14.5 in the "highway" speed area, but then as rich as 12.8:1 at WOT at peak torque, then go leaner to 13.2 at RPM's above peak torque (above 5400 rpm in my case).

Try some of this "easy" stuff before you get too carried away. Let me know and I'll try my best to help.

DFI79MC

iTrader: (1)

I'll try pulling out some timing around idle to see if that helps. Its really not that the cam is so big (234/238@.050), its the 108 LSA that makes it choppy.

Ever since we put this engine together with a carb, it liked fuel. Right now I idle at 13.5 AFR and cruise at 14.0. It would idle in park leaner than 13.5, but the idle in gear would surge so hard it almost pushed through the brakes. Once I have everything absolutely dialed in, my plan is to slowly lean it out everywhere until it gets unhappy and surges. On the dyno it wasnt picky at all for WOT AFR though.. anything from 12.5 to 13.0 didnt make any more difference than a standard pull to pull variance. Same thing with WOT timing.

If the rains ever quit I'm gonna get out there and tinker a bit. I'll pull some timing and report back how it acts. Thanks again for the help.

jmanley

No problem, let me know if I can help more. Did you start with a good base fuel map of a similar setup to yours? If not, you can request those from Accel. They have a great set of them.

iroc90dfi

Hi

Just ran across your post, did you ever get the issued figured out? I just installed GEN 7 in my 1990 Iroc a couple of weeks ago. I am having the same issue. The car starts up fine when cold and idles great, once its warmed up and I turn it off it will not start up again. I have to keep the throttle open to get it started but it will not idle. Let me know if you got yours figured out.

Thanks

DFI79MC

iTrader: (1)

Its been too long since an update, I apologize to those that helped out here. Its still not 100% perfect yet, but its way better than it was. I pulled timing out in the idle (and below idle) cells, and also took some fuel OUT and its much better. I'm almost bottomed out (leanwise) in those fuel maps, so I still need to go over everything else to make sure its not starved for air at all (IAC?). Being a car I tend not to run errands with, I tend to put the fine tuning on the back burner because it runs so good otherwise.

Its sleeping for winter now, so its really not an issue for awhile