Electric fan and RPM issues

66FSTBCK · 10-21-2012, 09:36 PM

Lately when my e fan kicks on it pulls my rpms down to where the car nearly dies. Then they will begin to be erratic. I can see my volt gauge drop too when the rpms begin to vary. No problems when cruising. Fan is hooked in with a relay and I am using a one wire 100 amp alt. problem just started recently. I checked the grounds and everything looks good. Bad relay possibly??

gearheadmb · 10-21-2012, 11:02 PM

I would start by getting the battery and alternator tested. You can also check the amp draw of the fan but i dont know what the proper amp draw should be.

66FSTBCK · 10-21-2012, 11:09 PM

Thanks for the info. Amp draw on the fan is 13.5 amps. I will test the battery and alt tomorrow. Seems wierd that this just started happening because the fan doesn't run much now that the weather has cooled down.

66FSTBCK · 10-23-2012, 08:29 PM

I tested the system with my multimeter tonight:
-Battery tested at 12.75v with car off
-Car running w/o fan on 14.95v
-Car Running w/ fan on 14.87v
-Car running w/ fan and headlights on 14.00v
-Battery tested at 13.33v w/ car off after running

These numbers all seem normal and the car didn't stutter or seem to want to die at all when I tested it tonight. I wonder if the carb is starving for fuel or something? The fan kicks on at 195* so engine hardly ever gets over that. Any thoughts??

gtonavy · 10-23-2012, 08:53 PM

Ok, I am going out on a limb here.

Do you have electronic ignition? Where do you get the power for the fan and the ignition?

If they are sharing a terminal, you could be pulling the voltage to the ignition down.

Its a stretch.

66FSTBCK · 10-23-2012, 10:03 PM

I do have an electronic ignition but my American autowire kit has dedicated wires for the ignition and fan. Fan is on a relay.

bartl · 10-23-2012, 11:28 PM

Maybe you need to snag a hot idle compensator off a 2V model. It creates a small vacuum leak in the PCV line which raises hot idle which, in turn makes the water pump and alternator spin faster. Later models with A/C and P/S used electronic idle speed plungers to bump up the idle when the A/C compressor cycled or P/S pressure was high. Other than that, I would suspect bad grounds somewhere.

2manyhobbies · 10-23-2012, 11:28 PM

Any luck tonight? does it just die when at idle or does it die when going down the road?

papamustang · 10-23-2012, 11:43 PM

I would check the relay and amperage. My idle drops when my fan kicks on. I assume that has to do with the amp draw at startup. If the draw is abnormally high because of a failure in the fan motor, that could be the problem.

66FSTBCK · 10-24-2012, 12:09 AM

Hasn't died yet but come close. The other day at a stop light the engine rpm dropped and then kicked back up and did that same thing a few times. I had to keep my foot on the gas at the light for fear of it dying. No problems when cruising. Checked all of the grounds and they seem good.

4mustangs · 10-24-2012, 11:15 PM

13.5 amps at 12.5volts is only about a quarter horsepower. That load reflected back thru the alternator shouldn't slow a 400 horsepower Stroker at all. You can eliminate that possibility by running the engine on the battery with the alternator completely disconnected. I think you need to look at your voltages and grounds back to the battery to all engine systems with the fan on and with it off. Bad connections are not limited to grounds, they also occur in the hot side of wiring. I wish I had more to offer but I don't have a clue.

Sorry, Ron

66FSTBCK · 11-20-2012, 12:59 AM

I'm still stuck on this. I let it idle in the driveway the other morning until it got to operating temp and ran fine. The second the e fan kicked on at 195* the rpms started to become erratic. Never died though. Based on my numbers in an earlier post, they all seem normal. Grounds appear good. I guess the next step is to replace the relay?? Then test the e fan motor itself??

CrackrStang71 · 11-20-2012, 02:29 AM

How can you test grounds by just appearing at them? I had this problem and my ground for the fan was located to close to the ground for my electronic ignition box. I'm assuming it was electrical interference. When I ran a ground to the battery for the fan, it fixed my problem.

Chaz

09Frank65 · 11-20-2012, 06:24 AM

Do you have underdrive pulleys?

The alternator output will drop signinicantly at idle vs. at speed.

I had a similar problem with underdrives in gear with a C4. The battery looked fine while measuring voltages but when the car was inspected the shop said it should be replaced. Put a new Optima battery in and problem went away.

With the underdrive pulleys my voltage will drop from 14.2 to 13.5 while in gear and idling with the fan on. As soon as I get above 1200 RPM it pops right back to 14.2.

ScottsGT · 11-20-2012, 07:17 AM

Quote:

Originally Posted by 09Frank65

Do you have underdrive pulleys?

The alternator output will drop signinicantly at idle vs. at speed.

I had a similar problem with underdrives in gear with a C4. The battery looked fine while measuring voltages but when the car was inspected the shop said it should be replaced. Put a new Optima battery in and problem went away.

With the underdrive pulleys my voltage will drop from 14.2 to 13.5 while in gear and idling with the fan on. As soon as I get above 1200 RPM it pops right back to 14.2.

Excellent point, but this sounds like something that has just started out of the blue. Unless he just installed UD pulleys.
I've got them on my '95 and I lose my dash lights (LED) at traffic lights.
But it could be a sign of a cell going out in his battery. On another forum I'm a member of a guy has a Chrysler minivan that started acting up. I told him to replace his battery, and that fixed his ECM issues.