Hi guys, I have a 327 with an Isky 280 .485" lift 232@0.050 duration cam and a 6E MAF Stealth Rammed setup. This cam has a choppy idle but the MAF setup is very happy idling consistently with it with no surging or irregularities. However, when the fan is running I get a couple hundred rpms of slow up and down surging. As soon as the fan shuts off I'm back to normal. I have 7 steps added for fan anticipate right now. Is this value only to keep the engine from dying when the fan first starts and draws a lot off the alternator, and then it decays out and the IAC can do whatever it wants, or is 7 steps the minimum value when the fan is on and the IAC can only control on top of that? If this anticipate step value does not decay but rather remains through fan run time, do I have too little steps, or too many and it is overshooting? Its kinda hard to burn several chips when its cold out because the fan does not kick in very often = lots of run time waiting to see if I made a difference. I am running a Ford dual speed fan on high speed only, so there is more amp. draw than if I had a stock fan operating normally. I need to get my data link cable working again so I can see for myself what the IAC is doing.

 

I think I might be on to something based on a thought I had -- the factory bins all have the IAC keep alive learning max temp set 5-7 degrees below when the fans turn on -- I lowered the fan turn on temps by almost 30 degrees F but left the keep alive learning max temp way up. Maybe the IAC will be happier if it is not trying to relearn its keep alive routine during fan on -- we'll find out

 

Changing the keep alive temp didn't help. Is it possible that my idle is too lean and that when it is loaded down it surges? I know back when my open loop idle was too lean it would hunt just like this. My BLM's at idle max out and I capped them at 140 but I assume the idle is too rich because it smells awfully strong, although I suppose this could also be an excessive lean condition. Hmmmmm.

 

Electric fan? If so, and it's going lean, look at the injector PW vs battery volts table. The injectors are always + but the fan is a HUGE electrical draw on the battery and alternator. You probably just need to increase the pulse width at the lower battery volts to get it running smooth again.

 

The funny thing is I do not lose any voltage at all with the fan running -- I have datalogs. I normally see 13.7-13.8 battery voltage. When the fan kicks on, this drops to 13.0 for only a few samples (at 10 Hz sampling) and then is back to 13.7-13.8 within a second or two as the fan is running. I am running a brand new 105 amp factory 1987 alternator and it keeps the voltage constant even with the headlights on and the fan running.

 

Do you have a flat spot in your MAF tables for idle? The fan puts a little load on the engine via the alternator, and may just be in a bad spot on the MAF tables, or perhaps the spark table.

 

RednGold, I was just thinking the same thing. I do have a ramp up in the spark table where the fan may cause the load to reach at idle. I'm going to reburn and check right now.