Fan causing bucking in my LS2 FD
11-24-2015, 11:33 AM
#1
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Fan causing bucking in my LS2 FD I currently have my car running on a standalone harness, I have no chassis wiring yet so I have a fan hard wired to a switch. I originally had the fan grounded to the chassis, but now I have it straight to the battery. What's happening is the car runs and drives great, plenty of power. As soon as I hit the fan it starts cutting out and bucking, making it un-drivable. I'm pretty un skilled electrically so I'm stumped, I thought for sure it was the fan ground causing the problem. Any ideas?
11-24-2015, 11:43 AM
#2
I'm going to guess that there is electrical feedback / noise coming from your fan OR perhaps your fan has some shorted windings or high current draw. Do you have a spare fan to test with? Also, what is the current capacity of the switch you're using (i.e. 20 amps, 40 amps, etc).
Is there a fuse in-line with the fan? I suspect if there was one, it would quickly burn out. You probably have a bad fan.
Is there a fuse in-line with the fan? I suspect if there was one, it would quickly burn out. You probably have a bad fan.
11-24-2015, 12:03 PM
#3
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It is a SPAL slim fan, no fuse in-line, wiring does not get hot at all after running the fan for 15-20 min. Switch is a 30 AMP. I have 2 fans, I'll try swapping over to the other one and see what happens. I have a Odyssey battery. I should also note the fan work perfect with the engine on or off, only the bucking/stalling.
Last edited by LS2FD3S; 11-24-2015 at 12:09 PM.
11-24-2015, 12:19 PM
#4
for what it's worth, I've got a JY fan which pulls about that much amperage at start, a tiny battery, and 40 amp relay. I don't notice anything when the fan start unless I'm sitting idle. When that happens, the engine dips about 50 to 75 RPM from the extra load on the alternator, but that's it.
My wiring route is: Fan > relay > alternator post > starter > battery.
You can see the battery and wires to/from the alternator in a pic I just posted to the "New Hooker 2nd-gen F-Body LS swap components" thread.
My wiring route is: Fan > relay > alternator post > starter > battery.
You can see the battery and wires to/from the alternator in a pic I just posted to the "New Hooker 2nd-gen F-Body LS swap components" thread.
11-24-2015, 02:15 PM
#5
TECH Resident
I'm guessing the fan is spinning inductive feedback (noise) back in to the computer?
Is the ground and 12V+ feeds for the computer totally separate from the fan's?
I might try running a heavy gauge ground (say 8 or 10 gauge) to make sure the computer has a good clean ground source. Batteries are very good filters for things needing clean 12V. I also ground the computer's case.
Doug
Is the ground and 12V+ feeds for the computer totally separate from the fan's?
I might try running a heavy gauge ground (say 8 or 10 gauge) to make sure the computer has a good clean ground source. Batteries are very good filters for things needing clean 12V. I also ground the computer's case.
Doug
11-25-2015, 03:21 AM
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Right now the harness is grounded to the head. I have a -4 ground from the head to the block and a -4 ground from the block to the chassis. Fan is grounded to chassis. I don't have the ECU case/body grounded, I'll try this and also check my voltage at the alternator with / without fan running. Thanks for the tips!!
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11-25-2015, 06:35 AM
#8
Important place to check voltage will be at the ECU, maybe at the injector's. I've seen high electrical loads screw up EFI before and that's what this sounds like. Low power can screw up injector response and change fueling from what the ECU expects.
11-25-2015, 10:46 AM
#9
TECH Resident
run the computer ground back to the battery ground. do the same for the constant 12V.
I bet that will solve your issue.
Motors put off a lot of noise. The battery will act as a filter.
Doug
I bet that will solve your issue.
Motors put off a lot of noise. The battery will act as a filter.
Doug
11-25-2015, 09:05 PM
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Engine grounded to chassis, trans grounded to chassis, fuel pump grounded to battery.
Car is just set up to run standalone , the chassis harness is a few months out waiting for a shop to free up some time. I have it running like this to do some testing, make sure everything is mechanically sound, want to solve this bucking so I can put some hard passes down. I can get one or 2 now and I have to shut it down, at idle it's no big deal with the fan, dry and drive and it starts cutting out.
11-27-2015, 10:15 AM
#12
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Right now it's battery > Starter > Alternator.
Engine grounded to chassis, trans grounded to chassis, fuel pump grounded to battery.
Car is just set up to run standalone , the chassis harness is a few months out waiting for a shop to free up some time. I have it running like this to do some testing, make sure everything is mechanically sound, want to solve this bucking so I can put some hard passes down. I can get one or 2 now and I have to shut it down, at idle it's no big deal with the fan, dry and drive and it starts cutting out.
Engine grounded to chassis, trans grounded to chassis, fuel pump grounded to battery.
Car is just set up to run standalone , the chassis harness is a few months out waiting for a shop to free up some time. I have it running like this to do some testing, make sure everything is mechanically sound, want to solve this bucking so I can put some hard passes down. I can get one or 2 now and I have to shut it down, at idle it's no big deal with the fan, dry and drive and it starts cutting out.
Andrew
11-27-2015, 07:28 PM
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I'm saying I don't have a main power distribution point, the alternator is only hooked up to the starter. Everything else is wired straight to the battery with basic 4 wire hook up.
Fuel pump is running through my speartech harness relay, grounded to the battery.
I don't have very good electric lingo, I'm not electrically skilled which is why I've done the bare minimum until the shop can wire the chassis and hook everything up permanent.
Fuel pump is running through my speartech harness relay, grounded to the battery.
I don't have very good electric lingo, I'm not electrically skilled which is why I've done the bare minimum until the shop can wire the chassis and hook everything up permanent.
11-27-2015, 07:33 PM
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11-28-2015, 01:13 AM
#17
Without the sense wire you are likely getting low output voltage which would explain why when heavy draw accessories are used the engine has issues, likely due to low voltage. I seem to recall reading that if the sense wire isn't hooked up the alternator defaults to lower output?
11-28-2015, 02:20 PM
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