Big drop in idle when fans kick on???

[Pman1961]

Doing my final sorting of my new engine tranny swap in my SPF. I have one issue left to resolve. I have a 445w big hydraulic roller cam. Car idles great at 1100rpm start to go any lower the motor gets to sounding a little lazy. Anyhow, when the fans kick on it will slowly pull the rpm down to 750 or so which sounds as though the motor could quit and never seems to regain the 1100rpm idle when the fans kick off unless you press the accelerator some. If I bump the idle up another 50 to 100 rpm more it seems to take care of the rpm drop. I'm considering a dashpot at the carb wired so that it will activate when the fans run to bump the idle up some. Tomorrow I'm going to fine tune the carb and maybe play with the timing which it is currently set a 34degrees full advance. With the higher idle when you shut the car off especially when warm it may diesel a few seconds and makes a wheezing sound as it stops. Is this the typical nature of the larger cams or does anybody have a suggestion that does not require disassembly of the motor?

[elmariachi]

Timing must always be set before messing with the carb. If you are in doubt, talk to the builder of the engine for timing settings. And just because you have total timing set, if the resulting base idle timing isn't right then you could be feeding advance into your idle. Trying to tune a carb with that going on is futile. So once you get the timing sorted out, then you can tune on the carb.

There could be a few things going on with your fan issue. You don't say what fan or alternator you are running or how its wired but it is possible that you have a fan that demands a lot of amps and the alternator isn't up to it. I would confirm that the fan is going through a relay and make sure you have a solid power source with a big 12V+ wire for that relay. You could also have a bad ground on the fan circuit. Might be worth taking the car to a parts store as-is and having them check the alternator and battery and see what their charging diagnostic equipment shows when the fan kicks on.

[ratsnst1]

put a volt meter on the alternator, see if it drops when fans turn on, I run a 140 amp.

[Dana E.]

Perry,

What's your initial timing set at to get your 34 degrees total?

With a big cam, set the distributor up with 18-20 degrees initial and 34 degrees total adavance and see how that works.

Dana

[Pman1961]

With the previous 351w 385hp crate motor I did not have the issue of the idle dropping when the fans kicked on. Maybe a few rpm but not noticeable. My current motor was built and run on a dyno at KCR with total timing set 34degrees advance. I don't know if anything to curve the dizzy was done and will call to discuss Monday. Dana, I've got limited experience messing with distributors. Can the curve you mention be achieved with different spring rates or do I need to take to a Engine Builder that can curve the dizzy? My purpose to adjust the timing was I would think retarding a few degrees may help preventing the run-on when shut off. I did have some old gas and that may be a culprit as I put fresh fuel in today and seemed okay but never got the car to full temperature before shutting off. Elmariachi thanks for the good advice. I'll test and make follow up tomorrow. By the way my car is a 2006 Superformance with a factory ford alternator. I'm sure nothing special but I've always noted that when the lights are turned on the ammeter takes a big hit. Never a problem with the battery though. I'll check the voltage drop on the alternator also. Any idea what I should expect and what are the pro's and con's of running a higher amp alternator? Thanks guys!

[Dana E.]

Perry,

You need to limit the amount of mechanical advance in the distributor. Different manufacturers use diferent methods accomplish this: bushings, adjustable stops, or electronically. The springs change how fast the timing is advanced.

If your initial timing, at idle, is set at say 8 degrees to get that 34 degree total and you recurve the distributor so your initial timing is now 18 degrees, and the same 34 degrees total, the idle speed will now be higher with the extra advance. Now you can close the throttle plates by backing out the idle speed screw and that should take care of the "run on" problem. If you retard the timing, you will have to open the throttle plates more to get the motor to idle and that will make the "run on" problem worse. After you get the timing sorted out, you can readjust the idle mixture. Do all the mechanical timing checks with the vacuum advance disconnected.

Depending on which distributor you have, getting the curve you want can be fairly easy, or a pain in the a$$. What distributor do you have and do you have the instructions that came with it? You can probably do the distributor mods yourself and not have to send it out.

Let me know what distributor you have, what your timing is at idle and at what rpm your advance is all in.

Dana

[Pman1961]

Dana, thanks for the useful information. I've got a few errands to run this morning and will get on the car afterwards. It makes sense and I agree it seems as though I have a timing issue. One question another poster asked is the ignition advancing at idle? Note the timing at the 1100rpm idle and then maybe drop to 800rpm and see if the initial advance dropped? By the way it is a MSD ignition and I know when I purchased the car the dizzy had been modified by the previous owner. I'll get my papers out and see what it says and let you know. Thanks

[mreid]

What alternator do you have? Is it the same one you used with the old engine? Are these the same fans you used with the old engine? Your new engine has less torque at idle and the current pull on the alternator puts load on it and it can drag the rpms down. With an aggressive cam, it can stall the engine. Working with timing can help, however you don't want performance to suffer to fix this problem. Kind of like substituting one problem for another. A dashpot won't help. They are simply designed to cushion the return of the throttle to the idle screw position and were originally used in automatics were the torque converter doesn't allow the drivetrain to perform the same function. Worst case, you would need a throttle solenoid like those used with a/c. It bumps the idle up when the compressor is puting load on the engine keeping it from stalling. This is the problem you are experiencing only the load is coming from the alternator. Perform the checks listed above before considering this solution, but don't end up substituting one problem for another. Good luck!

[patrickt]

Pman1961 -- the very first thing you do is make sure your battery is 100% fully charged. The electric motor in your fan pulls a good bit of current -- maybe close to 20 amps. It will pull even more if your voltage is low, and a lot of our alternators don't do a whole lot at idle. So, before you start your diagnositics, it's absolutely imperative that your battery be healthy and charged to 100% or you will get mislead.

[Pman1961]

Thanks Patrick. I have a local recommend putting a 96amp alternator on the car. Probably has a 70 currently. I'll check that out first thing and let you know.

[Pman1961]

Before I go yanking battery and alternator off the car and I've got a few more errands to run this is my observance checking the voltage of the battery: 12.75 volts car not running. 14.86 running. Fans running 12.85. What's your opinion on the battery or alternator condition? Haven't messed with the timing yet as my timing light has malfunctioned.

[Jerry Clayton]

sounds like your fan is taking all the output of the alternator at idle--

[Pman1961]

Jerry would you recommend a higher amperage alternator as well?

[patrickt]

Originally Posted by Pman1961

Jerry would you recommend a higher amperage alternator as well?

Your alternator only needs to put out 20 amps at idle to handle this job. Here, I keep benchmarks on what my car is doing when it is running perfectly so I can go back and compare when something is amiss. When my battery is fully, 100%, charged I get a reading of about 12.7 volts. When I turn on all my fans (1800CFM puller and dual pushers) the draw is just under 23 amps and the voltage drops to 11.9 volts. I doubt your single big fan pulls as much as my three fans running all together. When I shut the fans off the voltage goes back to 12.7 volts in just a few seconds. And by the way, each pusher fan draws 3.7 amps at this voltage. Now I know you don't have an inductive DC ammeter, but if you could repeat this test and give us your voltage numbers it would make for a good comparison. All of this is done with the car not running, of course.

[FWB]

besides the alt. output......where are you picking up power for the fans?
fans should not be connected to the ignition switch or to a starter solenoid.
the appropriate size wire is also important. #8 or #10 depending on fan manufacturers recommendation. on my car the msd coupled with the draw of the fan made a 90 to 100 amp alternator mandatory.

[patrickt]

FWIW, an MSD ignition draws about 1 amp per each thousand of RPM....

[Pman1961]

Sorry for the slow responses. My dog Jack had a stoke about a week and a half ago and was getting better and I think he may have another last night. He's been to the vet but I don't know how much longer he'll be with me. Very sad at the moment. Anyhow, I have the typical dual Superformance cooling fans. Voltage with ignition off was 12.55, fans running 12.05 and after about a minute and a half voltage climbed to 12.47. Voltage was slow climbing back up. The battery more than likely is the original one when the car was completed in 2006. I've had it since Sept. 2008. It is an Optima. I'll take it to Autozone for a load test and purchase another one should it be bad and post the results. The car has been down for a year also. Eager to get the bugs out and enjoy! Thanks

[patrickt]

Originally Posted by Pman1961

Voltage with ignition off was 12.55, fans running 12.05 and after about a minute and a half voltage climbed to 12.47. Voltage was slow climbing back up.

That's pointing to a weak battery, but maybe all it needs is a really nice charge. But whatever you end up doing, don't do it until you have a healthy, fully charged battery in there. If you're lucky, a charge might make the whole problem go away.

[FWB]

holy crap patrick.....do you ever drive your car? there isn't even a flea turd on it...
my car gets dirtier in the garage than your ride WTF?

[patrickt]

Originally Posted by FWB

holy crap patrick.....do you ever drive your car? there isn't even a flea turd on it...
my car gets dirtier in the garage than your ride WTF?

Yes, from time to time. Mostly I use it as an excuse to buy cool new tools, like an inductive DC ammeter, that I don't really need but have a lot of fun playing with as I take my car apart and then put it back together again, all the while taking photos for posting here on CC.