Jughead

Here's my first post about my recent engine miss.

http://forums.corvetteforum.com/showthread.php?t=915441

Well I replaced the plug wires and the coil....no change. Then I noticed that the engine began to miss right after my spal fans "kicked-on."

I was baffeled. So I disconnected the fan wires leading to the temperature switch....miss is gone? Engine runs great. I connect one of the leads back to the sending unit....no miss! I connect the other wire to the same sending unit and I start getting a miss???

Any ideas? Should I have two separate sending units and have each fan have it's own sending unit?

munday

closest i can guess is gremlins, can you use the same power supply for the other fan?

trotter73

I'm wondering, are the fans wired to a relay? I'm not an expert ( so don't anyone jump on me), but I was wondering if they were wired to a relay maybe that would help. I had an electric fan hooked up once and my buddy wired it through a relay that had 4 or 5 connections

w1ctc

I would check the voltage running the ignition system when the fans go on. If there is a large drop, find another source for the fan supply.
Bob

70BBvert

Are you running the stock 42 amp alternator? Maybe you're exceding the capacity of the system. What kind of current draw are you experiencing with both fans running and what does the voltage dip to?

I will be installing the same setup & maybe electric headlight operators. I also plan to upgrade to a higher output alternator.

Jim

CGGorman

I'm running dual Spals with both gray leads connected directly to a single sending unit with no problems. The orange leads are connected to the ignition switch. The yellow leads are connected directly to the battery. The red leads are connected to the fans. The black leads are connected to the engine PS head. None of the wires were spliced or cut. I just crimped connectors on the ends of the wires and fastened them down. I'm not even using an alternator...yet. Heck, I'm even running MSD w/a HVC coil. If it's a matter of current, mine should be doing it too!

You got me...

Bobchad

Does it do the same thing if you connect the fans in the reverse order? Or does it start to miss when you connect that one fan. I guess I'm trying to determine if it is a power draw issue or an issue with that one fan and/or its wiring.

Jughead

Fans are running thru 2 realys.

The alternator is SB stock, don't know the amp.
This setup worked great when I had my SB in there. I think the SB put a voo-doo curse on the wiring and the BB before it left the car.


I have the red wires going directly to the fans.

The yellow wires are running to the 30A fuses and then the outer most starter terminal.

The orange wires I have running to a red wire which I believe runs off the winshield wipers.

Like I said this setup worked great 2 months ago.

What's that Italian curse....Scala-ma-gooch? Maybe I got some of that too.

It felt good though, going foward about 10 ft over and over again.

CGGorman

What kind of ignition are you running? The outermost terminal on the starter goes to the coil on the stock systems. My MSD doesn't use it, though. I left it unused. Perhaps you have some noise getting into the coil from the fans. Try connecting the yellow to the big dog on the starter.

Jughead

Stock ignition.

Outermost = passenger side.

Both yellows? I gotta wait until the behemoth cools down.

Jughead

It was a while ago that I did this, but I think I narrowed it down to just being affected with the one fan lead to the temperature sender.

I could be wrong, I'll try again later.

Boofers

This is the most likely cause. Monitor the voltage at the alternator - if you notice a significant drop when both fans come on (maybe 3 volts or more) your alternator is not able to supply enough current.
This would explain your miss because the drop in voltage would be seen throughout the entire car including your ignition system. Either your alternator is worn out or it just doesn't have a high enough current generating capacity. Your battery may be contributing to the problem if it is weak.
Good Luck & thanks for keeping us posted this is an interesting problem.

humiliategravity

I would be surprised if it's the alternator. A lot of racers take their alternator off completely without consequence to the engine... my understanding is that it's just to keep your battery charged.

I think it's a strange enough problem that your test is worth repeating. Make double-sure that it's the second temperature switch lead that causes the miss. If it is, then maybe the minimal current draw from the switched-on fans triggers a larger current draw from the battery (I assume the fans are directly hooked up to the positive battery terminal or starter?) and diminishes the voltage output from the distributor.

Try your temperature switch lead test while jumping the battery - that will tell you if it's a current output problem.

Good luck!

Dave

Jughead

Last week when I was trying to get the engine running I noticed that a few times, the engine just quit! I now think it was shutting off just when the fans kicked on?

Steve's74

Get a voltmeter and check the system voltage. At idle your alternator isn't spinning fast enough to put out lots of current, and I bet those fans pull a lot. If you have the stock alternator, running at idle the voltage could possibly drop low enough to affect the ignition.

Steve

MN-Brent

Alternator-
If you go to electric fans, you need to upgrade your electrical system also IMHO for longevity.

Your ignition has a voltage tolerance spec, and with the dual fans, you are going beyond the alternators power limit and going out of voltage regulation.

Get an 85Amp alternator, the 85Amp belt (its longer and you'll need it) and a good battery like an Optima. Check out Parts America.com for the belt and alternator part numbers.

My guess is troubles will be gone.

Wiring should direct to battery for fans power also so there is no pull from the circuit that provides power to your ignition. This would cause a drop in voltage to the ignition module and could even cause a fire if the wiring overheated.

Brent...

SanDiegoPaul

HAVE THE ALT REWIRED. I just had mine changed from a 62A to a 94A and now all of a sudden, my A/C runs full speed at idle, and my lights don't dim at night ....

PRESSURERAT

That stock alternator has got to go! Remember, that 42(or 62 or whatever it is) amps is at 2500 rpms and up, not at idle. If it is a low speed only miss, that is probably your problem. More power captain!

71coupe

Glad you found the problem. Why don't you install a mech eng-driven fan? A reg flex fan works good for 427hotrod Jim - should work ok with your BB too.

GaryS

There should be a number stamped into your alternator giving the amps. Maybe some electrical guru can tell you if a low amp alternator will drag the engine down. Sounds logical.
Gary