Hey guys.

I just dropped a new motor in my S4. I also replaced the battery and alternator (105 amp buick alt, have had it for over a year). I have the e-fan wired with a thermoswitch, and I've never had problems with it before. I have a taurus 2 speed fan installed, always on low speed.

When the car gets hot enough to turn on the fan, my idle sucks and becomes erratic. It fluctuates between 600rpms and 800rpms, and it's very rough. I have no idea what is causing it. As the fan is kicking on, sometimes it will almost stall the car out. Like I said, I never had this problem until I installed the new engine.

Also, possibly related, my radio will cut off when the bass hits if I have it up too high.

Any ideas?

 

If you still have your BAC on, it might be dirty. If you dont, its because of the draw on the alt thats dropping your idle.

It sounds like you are saying though that it's been on there for a long time, and it's just started happening recently, so I'm not sure? Has your sound system been in there a while too?

 

Yes, my sound system, buick alt, and e-fan have been in the car for over a year now, running the same series battery, and with no problems whatsoever. It has only started acting up since the install of the new engine.

 

The BAC is supposed to compensate for electrical loads, which it does by monitoring various inputs to the ECU from aircon / heater / lights / fogs / rear demistor / power stearing pump. If you switch off all these loads, then unplug the BAC and start switching them on - you'll get pretty much the same effect. If you are not using one of those inputs to the ECU you can use it with the E - fan instead and have the engine compensate when it comes on.

If you don't have a BAC valve then there's the problem. If you do - it could be dirty, or the connectors are damaged, or you have no airflow path to the BAC. It normally takes a feed off the pipe that comes off the turbo compressor, and is fed with metered air.

 

I do have the BAC on. I will clean that asap. Unfortunatly I am using all of those inputs. That would be a good idea to have the BAC compensate for the e-fan though. If I could figure out another way to do that I would do it.

 

I think that you could piggyback two inputs to the ecu via a relay. Piggyback the efan onto the defroster input. Use a relay to allow either the efan or the rear defroster to signal the ecu. I haven't looked at the wiring diagram, but it should be doable.

Other things you can do to help. Verify that your TPS is adjusted absolutely correct. Increase your idle speed to 900-1000 rpm. I had a similar bounce after I adusted my TPS and then set idle speed from 900 down to 600rpm. At 900, I got no bounce at all with the efan. At 600, the idle is stable with all the accessories w/BAC inputs, but not when the efan runs. I am planning to set my idle back to 800 or 900, whichever it takes to make it idle well.

 

Hm... That might be going a little further than my electrical knowledge will allow. I will just clean the BAC and see how that affects everything.

 

poor grounding?

 

Or just bump up the idle a little. On a rotary, 900 rpm idle is not a big deal. Make sure you jumper the idle speed set connector before you adjust the idle speed set screw. It is located on the passenger side shock tower, typically a yellow or faded to nearly white 2 spade female connector. Jump it, set the idle where you want, then un jumper it. Done!

 

From the engine replacement? That might be a factor as well. Try cleaning the grounds on the 'new' engine.

These are cheap (free) fixes.

 

Sounded like a ground issue to me. Let us know

 

get your battery tested/deep cycle/charge your battery.

 

It's brand new.