Ok guys I need a little help. I finally got some time to do some tuning after replumbing the TB's ( parrallel) and repairing a hard drive crash on the laptop. I got the BLM's pretty close now (they were way rich as I expected) and idle is fairly good. Problem I have is a RPM flare up after restart. This is after the engine is warmed up and has been idling for sometime at 750 rpm. It normally flares up to around 1300 rpm and comes down to 1000 rpm and stays there until I put it in gear. Then comes down to 750 and stays there after I shift it back to neutral.
I have adjusted the following with little to no changes.

BTW this is a 7747 ecm prominator/HAM equipped in an 82 vette (crossfire intake with dual TB's).

Park position @ 0x5c2
Park to run delay @ 0x5c3
Coolant vs Temp @ 0x5f5
Delay @ 0x5e7
Filter coefficient @ 0x5e4
Throttle follower @ 0x5f0 and 0x5f1

Any other places I need to look into?

Thanks,
Ed

 

Anyone?

 

With the stock '747 code this can not be corrected. The flair can be reduced by decreasing the park steps. However, this is at the mercy of cold startup stalling.

You may be able to find a happy median by changing the park position (used at startup), the park to run delay, the kickdown delay, and the kickdown steps.

I eventually added a startup IAC position table. In this manner at key on the IAC will move to a position dependent upon the coolant temperature. Works nice. . . Will be available in the Ultimate TBI code.

RBob.

 

Make sure the kickdown steps are larger (by 1 if needed) than the IAC vs. coolant table at the highest temps. The idle speed will hang up if kickdown steps are lower.

 

Thanks for the suggestions. I'll play around with it today and see if I can get her to settle down.
Don't know if this matters but I parrallel plumbed the TB's, removed the compensator and FPR and am using an areomotive regulator in it's place. Also using two equal sized injectors instead of the staggered stock ones.

Ed

 

The IAC is the one thing that drives me crazy, I have tried with lots of burns to get it to work, but with only limited sucsess.

 

OK so I am starting to make some progress here. I've adjusted quite a number of the IAC controls and now dont have the flareup problem. Still trying to stabilize the idle. Was at 1200rpm but have it down to 900 now. A little more tuning and I should have it to normal. Thanks for the help and direction to go in.

Ed

 

The kickdown steps are at address 5D8. This value in steps must be larger than the IAC vs. coolant table in all normal temp range. For ex. a stock ASDU bin has 24 steps at 56 deg. C and higher. The kickdown steps in the same stock bin is 25 steps. Via a Romulator, I found that if the kickdown steps are lower than the IAC steps, the idle will hang up. RBob's paper on IAC function hints at the importance of the kickdown steps so I played with it to see what would happen. Then I checked all the stock bins I could and found this to be consistent.

 

I'm curious though, how does the Crossfire handle IAC? Do both TBIs have an IAC or is the IAC only on one TBI and is somehow routed to both TBIs?

 

Each TB has it's own IAC (2 total) on the crossfire setup. I have been playing with the Kickdown steps and have kept it just one count higher than the IAC steps. Seems to be working out OK so Far even though my IAC steps are very low now.

 

Can somebody post a link to Rbob's idle acrticle mentioned above? I can't find it, though I will continue looking in the meantime

 

http://www.diy-efi.org/gmecm/papers/

 

Here is another parameter to play with:
This controls the rate at which the timing is changed from the base timing (used during crank) to the run timing (once engine is running).

The smaller the value the longer it takes to move from base timing to run timing.

RBob.