I have a new LS3 crate engine in my 55 chevy and the alternator that came with it is around 90 amps.

I just installed dual 13" Spal fans rated at 63A -12 volts each.

When the fans come on the relays start buzzing and the car sputters, shakes, and bucks. As soon as the fans shut off the car idles and runs perfect and the buzzing stops. I notice a small dip on the voltage gauge when the fans come on.

Are these fans drawing too much power for this alternator? what is making the car shake so much when they come on?

Lorne

 

What's you idle speed?

 

My idle speed is about 900 rpms.

 

So this is 63 amp for each of the 2 fans or, both total?

 

The same 63 amp - 12 volt label was on each of the fas so I am assuming these specs are for each fan.
Not sure if this is operating specs. or maximun output specs.

I have same problem if I only use one fan.

 

bump for this post....Im having the same issue with my ls3 crate engine..running fan control from the blue ecu fan control wire to a one 16in AFCO electric fan..... was wondering if anyone have found a fix for this? Thanks Guys

 

4 year old thread, hope he has an answer by now.

How did you wire the fans, can you post a diagram? My thought would be excessive voltage drop in a line causing low voltage to the ECU.

Probably not the size of the alternator. That would just cause the battery to go dead with time. Motor shaking is something interfering with the computer/ignition/injectors.

 

Im running exactly how the crate engine instructions say
"Cooling fan is controlled by the ECM. Control is set to turn on a 12V fan at 97 Deg C (207 Deg F) coolant temperature. The fan control wire (Lt Blue) is fused/relayed and must be connected directly to your fan."
So i have wired - lt blue wire from ECM to + side of cooling fan pigtail, and - ground is to the frame.

i have hooked up a cooling fan up from a 2001 camaro to test the system..... When it engages that fan it does not do the erratic idle, and hesitation. Pretty stumped at this poing possibly bad fan is my guess at this point bc the stock fan pulls more amperage than the AFCO

 

So, does this "pigtail" include a relay? You can't power any fan directly from the ECM. At least not for long...

 

No , I have yet to try that, as the instructions say it's already fused and relayed . I have also spoken to a gm rep. And said that it's not needed on the GMPP harness since it's built in using their fuse/relay box. Im curious tho if i were to install another relay, when the ECM finally kicks the fan on its giving the wire 12 volts.......how would i even go about putting another relay into this, anyone have a pin out , bc i know its suppose to be a ground switch, but in that case it already is and feeding the wire 12 volts? Keep in mind this is a LS3 crate GMPP using one relay, ls1 and ls2 setups are different from what I've been looking into.

 

Realize old thread - but maybe this helps someone else....

At 900 engine rpm, your alternator is likely spinning somewhere around 1800 rpm (pulley size difference). The 90A rating, however, is what the alternator is capable of putting out at a much higher alt-rpm, usually up around 6000 (3000 engine-rpm). Without having some sort of "soft start" feature for the fans -- for the instant they come on, 63A fans are "hitting" the system with 1.5-2 times the current -- 90-120A, and at engine idle speed, the alternator isn't capable of putting out anywhere near 90A. (I believe your 63A rating is for both fans, not each fan). No doubt, that's a helluva shock to the electrical system. Back when my car was Ford powered, I ran a 95A alt, temp switch/relay controlled fans and the dual 11" Spal fans (about 50A). Same thing - with lights, stereo on, when I hit the A/C (which turned cooling fans on) it would sometimes actually kill the engine at idle. I installed a 130A alternator and a Delta Current Control variable speed controller to 'soft start' the fans and only turn them fast enough to maintain the temp set point. 1000% improvement in control and operation for the fans and the alternator system.

Currently run a crate LS3 with an Escalade 145A alternator. I use the same variable speed (PWM) controller and fans. We built a "fan tach" out of an old engine tachometer to let me know how fast the fans are turning -- it's so seamless that without that gauge, from inside the car, I couldn't tell you when the fans come on or even IF they're on. My engine uses a 2008 Corvette ecu -- and it has two temp outputs (a ground) one in the 220-229F range, and one in the 230-236F range IIRC. If I wanted to use those to control 2 fans at different set points, I would need two relays. But having experienced a variable speed controller, no way I'd use relays to control big amp items like the cooling fans. I believe the later model ecu's have PWM fan control capability built into them --- someone else will have to chime in to tell you how to access that feature. Using that, you wouldn't need to add an external fan controller like I use --- 'course, I already had the controller before I went with LS power, so I just stuck with it.

I believe with that much fan(s) coming on all-or-nothing style and that little alternator you are gonna have charging problems at low engine speeds. I'd want both a bigger alternator and a more optimal way of controlling the fans.

 

Im running a CS130 160 amp already, however my warm idle is about 550, and the alternator seems to not even put out above 12.5-12.8 at idle,but when rev higher it starts to charge. I have a HP Tuner coming in this week to raise the idle to 850-900. Maybe thats where i need to start at first before guessing and replacing parts, and messing with the harness

 

May also want to do some pulley measuring and be sure that the alternator is being overdriven correctly.