DFI Question-Cars stalls when cooling fan comes on


May 24, 2001
I am using a batch fire DFI with a VIC. when I start the car and let it idle, the engine will stall when the cooling fan turns on.

I was monitoring battery voltage with a digital recording osciliscope and I saw a momentary voltage drop to 12.09 volts when the stall occurred. Running voltage is normally 14.20v or so. My battery is a new Delco with 850 CCA (problem occurred with the old battery too) so I car rule it out as the cause.

After the first fan cycle the engine would not stall on subsequent fan cycles, but the engine stumbles and Stall saver kicks in.

Has anybody run into this? If you have, did you fix it? How?

Dave Roland
The only experience I have had with a problem like that is when ANY load was put on the motor it would die. Like fans, headlights, AC or putting it in gear. But that was solved by adding fuel to the base fuel map in the idle cells. How warm is the engine on those subsequent fan cycles?
That is correct, you want to add some more fuel into the idle cells until the stumble goes away. The dfi relies on interpolation so the neighbouring cells will effect the actual fuel mixture slightly also. Try to increase these cells also a few numbers.

I have my cooling fan set to come on at 168 degrees. Calmap doesn't give you a Cooling Fan off choice. I didn't think about a lean condition causing the problem. I was thinking that a voltage spike or something like that was going on. I will try adding a few counts to the BFM in the idle area. I may look at the afterstart enrichment as a posible correction.

This condition doesn't really cause alot of problems because this is a race only vehicle. But it is annoying. I'll tune it out, If I can.



One thing that can happen is that when the fan(s) come on the system voltage pulls down momentarily (as you saw on the DSO), which makes the inj less responsive, which throws off the fueling. The idle fueling can be tough enough to begin with, much less suddenly changing the way the inj responds :)

So, many systems have a voltage compensation to counter this. When the voltage drops the commanded fueling changes to make up for the decreased inj response time. Does your DFI have a voltage compensation table?

Of course if you had a wb O2 FAST ecu you could see the a/f ratio spike in action :)

The DFI I am using doesn't have any voltage compensation tables. But that does start me thinking about how the voltage drop affects A/F ratio at idle. I was reading the Accel EMIC training manual (downloaded from their website) and although it doesn't address a cooling fan spike, It does give alot of good hints to correct idle problems.

They call it "load dump". It is basically when you shift the trans into gear or somehow load the engine. They suggest you watch the BFM and see where the cursor goes during that event. They suggest you richen the cell that the ECU goes to during the "load dump". Makes sense.

I have had a problem with stalling when shifting into gear (cold engine only). I think the two problems (fan and shifting stall) are related and can be fixed with the above mentioned techniques.

I think the answer to my minor problems are in the BFM.