View Full Version : Accel DFI Tuning Question, hard to start

01-31-2006, 10:59 AM
My BBC 427 is equipped with an Accel DFI Superam system. The engine should produce between 575 and 600 hp. It has a Comp Cams 288/.653 solid roller cam, 10:1 pistions, and the usual performance upgrades.

I spent some time getting the timing set, adjusting the idle, throttle position, and a few others things. It idle good at about 850 rpm with the IAC position at about 9.5 when ideling.

The fuel injectors are only 30 lb/hr which should be about 42 lb/hr. Would that be the cause for poor starts? In the system configuration screen, I set the injector size to 30 lb/hr so I would think it would adjust the pulse width to compensate. Is it just not enough pulse width there for priming with that small injector? It does idle fine. There is a slight hessitation off idle when you rev it up. Nothing crazy yet, its only been running for a total of 30 minutes so far. I was able to pull it out and back into the garage under it's own power (for the first time since I bought it 8 years ago.) Should I just mess with the starting fuel coefficient until it seems to work? I am a bigginer at the fuel injection stuff and Jody says that it is a pain to cut your teeth on.

If anyone has a suggestion, I'm all ears.


01-31-2006, 12:12 PM
I'm not totally familar with the Accel software but it should have several startup parameters.

First test: does it start easier or harder if you give it a bit of throttle?

If it starts easier, you're likely too rich during cranking/startup.

1. Decrease the cranking injector pulsewidth. A general guideline is to set the cranking pulsewidth to be about 2X your typical fully-warm idle pulsewidth.
2. Open the IAC more during cranking to let more air in. I usually find that maxing out the IAC opening during cranking is helpful as it will result in a little rpm "flare" just after startup which can prevent the thing from dying or having to give it a bit of throttle manually to keep it running.

You may also have it starting lean. If it's more difficult to start with the throttle cracked open a little bit, that's likely the case. If so, do the opposite of both of the above recommendations.

You may also have to tweak the "afterstart" parameters if it tries to die just after firing.Typically you want it a bit on the rich side just after startup and have the additional fuel taper off slowly; you can taper it off more quickly when the engine is hot compared to when it is cold.


02-09-2006, 06:42 PM
In case anyone was wandering, I figured out what the problem was with my hard starts. It turns out that the MSD flying magnet pick-up distributor has a rising trigger input and a rising trigger output (this could be backwards, I can't remember off the top of my head). The latest DFI software assumes falling output trigger and it won't let you change it unless you get the Pro version. Jody mentioned in another thread how they dumbed down the software and this was part of it. I ended up reloading my 1.0 software that came with the system (its about 4 years old now) and it gives you the abilitiy to set the input and output triggers to rising or falling. I corrected the triggers and it now fires right up. Now that it is timed and idling on its own, it time to start tunning. I just wish the temp outside would rise above 40 degrees. It gets chilly in the garage with the door open and there's snow on the ground.

Thanks for the advice above, I'll reference it when I get to fine tuning the system.