Electrical Idle Stumbles When Radiator Fan Turns On

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Hello All,

I'm looking for some troubleshooting pointers on this issue where my idle will stumble/drop when the radiator fan kicks on. After a moment the idle will return to normal. Then once the fan turns off the idle will jump a bit and then return to normal. Sometimes (but not very often) the engine seems like it will stall when the fan comes on.

I think this has been going on since I bought the car 6 years ago, but it has been getting markedly worse in the last year.

We're dealing with a 1999 Mustang GT.
  • 177k miles
    • Runs well (except for this issue and A/C needing attention).
  • Alternator replaced at 148k miles 4½ years ago due to constant charge light.
    • Replaced with a 110A from O'Reilly Auto Parts.
    • Charging system and battery tested ok at Interstate battery.
  • No codes.
  • Radiator fan is original (as far as I know).
  • Stock pulleys. Good tensioner and belt.
  • Electrical mods:
    • Sequential rear turn signals.
    • Modest LED strip lighting in trunk.
    • Modest LED strip lighting in all foot wells.
    • Fog light mod to have lights on without parking/headlights.

Here are 2 videos showing the event. In the first one (which also shows running voltage at the battery) try to ignore the lifter noise and concentrate on the deeper exhaust note. That is where the idle drop is most noticeable.


Radiator fan kicks-on (and engine bogs down) at 0:02.
Then fan shuts off at 0:29.


idle stumble with radiator fan tach

You may need to turn-up your volume to hear when the engine bogs down, which happens at 0:05.
Fan shuts off at 0:31.​

I look forward to any help you guys can offer.
 
  • Sponsors(?)


Sluggie24

Member
Apr 8, 2017
92
15
18
44
When an extra load is put on the electrical system, rad fan, the alternator increases its output which puts an extra load on the engine. The computer will usually compensate for this quickly via opening the air bypass valve more. If your idle is dropping too much for too long then the bypass valve could be the issue. Does the idle jump up properly when the AC is turned on?
 

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Thanks Sluggie24.

As best I remember the idle does jump up when the A/C is on, but it does it the same way as when the radiator fan kicks-on: the idle drops low first (sometimes almost stalling for a moment) and then comes up to a bit higher than an idle without the A/C or radiator fan being on. I preface this response with "as best I remember" on account of the A/C not working properly for the better part of a year. I remember a few times where the engine did stall when the A/C was turned-on at the same time the radiator fan was running.

The load placed on charging system by the radiator fan seems like it could be excessive. If this engine was a 1.0L like in my wife's Fiesta I could understand that, but to bog a V-8 this much has me thinking my radiator fan might be going. However, I would like to test something before getting into the part-swapping method. :)
 

Sluggie24

Member
Apr 8, 2017
92
15
18
44
It's possible that the air bypass valve has crud built up inside it that is causing the valve to stick. Try taking the valve off and cleaning it out really well with gumout or similar cleaner. Also clean out the passages to it in the T body and even the t body plate if they look bad. If you're careful removing the bypass valve the gasket should stay in one peice and should be reusable.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,366
417
164
Houston Texas

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
As Sluggie24 suggested, I cleaned-out the IAC with B12 carb cleaner, Q-tips, and compressed air. It had some soot in there but not clumps of stuff or anything that bad. Also cleaned-out the TB passages which were just slightly sooty. End results: no change.

I'll do the charging system voltage drop test next, per the sage WMBurns. I'll also look at accessory bearings. I hadn't noticed how prominent that noise was until I watched the video.

Thanks again everyone for your ideas.
 

robertsa

Well-Known Member
Apr 22, 2017
159
44
58
34
San Antonio
Yar. Sounds just like my alternator bearings when they crapped out recently. That coupled with the your other symptoms makes it and a possibly on the way out battery make the most sense. Failing alternators can kill good batteries and vise versa.
 

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
So just finished the voltage-drop test that WMBurns pointed me to and the short report is -
Will take alternator to be tested.​

Testing details -
upload_2017-7-9_21-50-5.png


The voltage-drop measurements when the fan was on show the reading when the fan first started and then once it was running. Since the full-load voltage drop was so good I wonder if the voltage drop readings for when the fan is on points to a problem with the fan pulling way too much current.

I wish I had a clamp-on ammeter like Eric O (from South Main Auto video in link WMBurns provided) to confirm the alternator output is weak. But with how the idle dipped in synch with the hazards flashing I think that may also be what I'm dealing with here. That and the alternator pulley movement doesn't sit well with me.

So if for nothing else other than entertainment purposes, I'll keep you all posted.

Thanks again.
 

Attachments

Last edited:

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Correction to a couple measurements (decimal troubles). When the radiator fan is on the voltage drops are:
+ : 0.090
- : 0.065​

I retested tonight and the voltage drop measurements were the same under full-load with the radiator fan on. So I feel pretty confident there isn't a voltage drop issue.

Nope...haven't tested the alternator yet. :)
 

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Well...the alternator tested good (off the car) at Advance Auto. It was pretty quiet in their test bench, so I'm no longer concerned about the little clunking I was hearing.

This brings me back to suspecting the radiator fan pulling too much or maybe the IAC is "off a bit" (if that's even possible).

So would anyone have some more troubleshooting suggestions?

Thanks.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,366
417
164
Houston Texas
But with how the idle dipped in synch with the hazards flashing I think that may also be what I'm dealing with here. That and the alternator pulley movement doesn't sit well with me.
^^^This can't be a good thing. IMO this is a huge symptom. The fact that a fairly small load such as the hazard lights could affect the way the motor runs is.....bad.

Well...the alternator tested good (off the car) at Advance Auto. It was pretty quiet in their test bench, so I'm no longer concerned about the little clunking I was hearing.

This brings me back to suspecting the radiator fan pulling too much or maybe the IAC is "off a bit" (if that's even possible).
IF your only problem were the fan's drawing too much power then how do you explain the idle dip in response to the hazard light load? Have you ever seen any other "normal" car do this?

Does the voltage at the alternator change in sync with the hazards lights? It would also be interesting to measure the voltage at the motor's ignition VPWR circuit. Pick any of the COP or injector power lines to test.

Which alternator does your car have? The 6G alternator has a plastic cap covering the rear bearing.

I have never met an alternator where the input shaft had large amounts of in/out play. From my experience rebuilding two 6G alternators the shaft is constrained by the front bearing. The bearing is sandwiched between the pulley and the rotor. Soooooooo if the shaft has a ton of in/out play then either:
  • The pulley is loose (bad)
  • the inner bearing race is loose or heavily worn (bad)
  • the outer bearing is not fixed to the alternator case or the bearing has spun (bad as this will erode the alternator's case).
Nor I have ever met a good working charging system where you could easily see the system voltage making large voltage changes in response to changing loads. Normally any voltage changes are tiny and infrequent.

If you are certain that the alternator is not part of the problem (I have doubts), then my gut tells me that you have a bad ground someone in the car. Likely affecting the PCM. Perhaps repeat the voltage drop tests using the PCM at one test point and the battery negative as the other.

OBTW, good work on covering the basics! I wish more people would follow this example.
 
Last edited:

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Thanks for the time and thought towards this issue, WMBurns...it's greatly appreciated.

I checked voltages in a variety of scenarios and short answer: the hazards aren't having that great an effect on the charging system or engine idle (details in chart below). I found that the idle was actually steady and it was the alternator making a cycling whine that was almost at the same pace as the hazards. So things are good there. I also made measurements at cylinder #6's COP (each wire to ground), which were the same as what's in the table below.

upload_2017-7-11_20-30-46.png


As for the alternator it's a 6G 110A. Closer examination of the pulley found VERY little end-play. In fact, with the alternator hot there is no play.

To do the voltage-drop test for the PCM's ground I'll need to fabricate a good-sized (length and gauge) test lead extender and get back to you on that.

Now...there is a new twist to all this. About 4 times over the last few months my car will have quite a noticeable hum that goes away after about 5 minutes. While the car is humming there isn't much else different except the idle seems to hunt a little bit. Fortunately, it happened this morning, so with troubleshooting still fresh on my mind, I gave the front passenger fender some caresses and it was purring right along - can't spell CCRM without 'purring'. After 5 minutes it stopped and has been quiet all day. So I suspect I should I check the ground and other wires connecting to the CCRM for damage. Any other tests I should perform?

As always, thank you very much for the help.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,366
417
164
Houston Texas
To do the voltage-drop test for the PCM's ground I'll need to fabricate a good-sized (length and gauge) test lead extender and get back to you on that.
^^this is not totally true. While you will need to extend a VOM lead it does NOT need to be a heavy gauge wire. Why? Because there's no real current flow through the VOM. So any common piece of scrap wire will do the trick.

Rebuilding your own alternator:
https://www.stangnet.com/mustang-forums/threads/higher-amp-alternator-how-much-higher.897392/#post-9044147

I recently rebuilt the alternator in my 2000 GT because the alternator's voltage was almost always in the 13.8 volt range. I never saw it go into the low 14's. What I found was even though the alternator would PASS the auto store tests the battery life was being adversely affected. I was replacing batteries every 9-18 months.

During the rebuild I found one of the slip rings deeply worn. The wear pattern looked very much like the examples given in the rebuilderinabox video (see about 10:00 into the video) . The slip ring brushes were also very short with little (if any) life left.

After rebuild with new slip rings the voltages were into the low 14 volt range. It's a little too early to declare the short battery life issue resolved.

Bottom line. At 13.8 volts your alternator is towards the lower end of "acceptable". Note, an alternator voltage of 13.8 would be considered OK if the battery were deeply discharged and needed a heavy recharge current. This is clearly not true in your case as the battery voltage is indicating a full charge.

I also went back and watched again your original video. One thing noted is when the radiator fan kicks on the voltage drops down to 12.6 volts. This is battery voltage. When the voltage kicks back up the motor can clearly be heard responding to the change in load. This says to me that one possibility is that the alternator is dropping out with the large step load change and then kicking back in.

I'm not saying that the alternator is the problem. BUT I'm a big believer in Occam's Razor. Occam's Razor would tell us not to over look the simple and common things things before looking at every increasing complex "possible" solutions to a problem.

I also understand that technically your alternator tests OK. As such the auto parts store that sold the rebuild is not likely going to offer a new unit. But it won't hurt to ask would it? Another possibility would be for you to just replace the regulator as likely the rest of the alternator is OK given the history.

How to change the Voltage Regulator on Ford 6G Alternator
View: https://www.youtube.com/watch?v=JuKCrnoe_Vs


https://en.wikipedia.org/wiki/Occam's_razor

>>https://www.autobatteries.com/en-us/battery-testing-and-maintenance/car-battery-voltage-and-testing
When Fully Charged, How Many Volts Should A Car Battery Have?
Fully charged automotive batteries should measure at 12.6 volts or above. When the engine is running, this measurement should be 13.7 to 14.7 volts. If you don’t have a multimeter to tell you the voltage of your battery, you can do a test of your electrical system by starting the car and turning on the headlights. If they are dim, that indicates the lights are running off the battery and that little or no charge is being produced by the alternator. If the lights get brighter as you rev the engine, it means the alternator is producing some current, but may not be producing enough at idle to keep the battery properly charged. If the lights have normal brightness and don’t change intensity as the engine is revved, your charging system is probably functioning normally. If you’ve been experiencing problems with your battery system and the headlight test checks out okay, you should check whether or not the battery is holding a charge, or if something on the vehicle is discharging it.
 
Last edited:

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Sure enjoyed those alternator rebuilding videos -thanks. They've got me wanting to rebuild mine now. Before going that route I'll check with O'Reilly Auto about doing me a solid on the alternator. I just found out that they no longer carry the model I got from them. The one I have now is 4½ years old with 29,707 miles on it - rebuilt in China. But like you said, no harm in asking.

Since you didn't mention my humming CCRM does that mean I should get the alternator/radiator fan load issue sorted-out first before taking a closer look at the CCRM?

One last question (for now): I've read about the radiator fan having a low speed. When is that normally used? All I've heard my fan do is run on what has to be high speed.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,366
417
164
Houston Texas
Regarding the use of high speed verses low speed fan.

The default fan speed is the low speed. When the AC is on, the low speed fan is forced on (Yes that is correct. LOW speed fan).

The high speed fan kicks on IF the motor's temperature exceeds a set point or the AC head pressure exceeds a set high pressure point.

For the GT it's vital for the fan to work on both speeds. When helping people with fan problems I will always recommend testing the fan by jumping directly from battery to confirm operation on both speeds as the first trouble shooting step.

The fan turns off IF the motor's temperature is below a set point or the car's speed is above 45 MPH.

Regarding the CCRM humming. IDK what to tell you as of yet. In my experience CCRM's either work or they don't. Clearly the CCRM is working or the motor would never start. It's just as clear that the CCRM isn't dropping out as the motor would die out right if true. If you go back to how I recommend to perform trouble shooting. Cover the basics first. Gather information. Test. Then repair/replace.

I'm also a big believer in a through visual inspection. As such if this were my car I would be inspecting the CCRM very closely. Looking for evidence of bent/pushed pins or over heating wires and terminals. I might even take the CCRM apart to see if there's anyting inside that might explain the noise. Who knows. I might even replace it just to be sure (would depend upon how fat my wallet was this week).

I'm also the type that might find out which CCRM relay is making all the noise and perform a PC level board replacement. It can be done! Note, truth be told if this were my car I would also perform some quick voltage measurements at the CCRM to confirm there isn't something wrong external to the CCRM that could explain the noise.
 
Last edited:

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Thanks again for the more good stuff.

Just for the sake of testing (if nothing else) I took some resistance measurements on the fan motor and fan motor connector (unplugged). Below are the results of that. I think it's safe to say the connector and wiring aren't the issue. As for the fan resistance measurements, I'd be very curious if others have similar measurements (perhaps a separate post). I may just find a local new motor and just take measurements at the store.

I also jumped the fan directly to the battery (low- and high-speed). Video of the results are here -

I'll be pulling the fan later to see if that scrapping sound is part of the fan or the motor. I also jumped the fan with the engine running (fan unplugged) and that made the alternator whine and the idle dip. At least it's consistent.

upload_2017-7-17_23-36-6.png

Hope this is as nearly entertaining for you all as it is for me. ;)

Thanks.
 

Attachments

wmburns

SN Certified Technician
Aug 14, 2009
5,366
417
164
Houston Texas
Your Ohm tests would indicate there's nothing obviously wrong with the fan. Following Ohm's law P=(E*E)/R. (13.8*13.8)/1.4=136 Watts. In general a cooling fan should be around 150 Watts. At 136 Watts your fan is well within "reasonable" values.

At 150 Watts and 13.8 volts the current flow should be around 10.86 amps (I=P/E). Again a "reasonable" value should be in the 10-12 amp range.

Here's another way to think about the fan's current flow and how it compares to the alternator's capacity. The Mustang GT Ford Stock alternator is 110 amp. Therefore the fan's draw of 10 amps represents slightly less than 10 percent of the alternator's rated capacity. Sooooo only a 10% step load change causes your alternator to lose it's mind.

In my area I have bought several salvage yards alternators usually paying about $35. I suggest buying a salvage yard 6G alternator for your car from a local salvage yard. The Mustang GT's alternator is stupid easy to change. So for a small amount of work (swapping the alternator) and a relative modest cost ($35) could offer a quick way to rule out/in the alternator as part of the problem.

Choose a 6G alternator so that it opens up the options to re-build your own alternator on the bench without it being time critical.

Of course if this were my car I would be cleaning the block mounting points as well as all of the other electrical connections at the alternator just to give the greatest chance of success.
 
Last edited:

cjcoburn

Member
Aug 25, 2011
54
0
7
Denver, CO
Ahhh...good old Ohm's Law...gotta love it. What I really appreciated was your knowledge of what our radiator fan motor should pull in terms of watts and amps -very encouraging. It really seems like we've zeroed-in on the alternator.

The next trick is finding a yard here that has usable Mustang parts. I haven't had to tour a yard for Mustang pieces yet. :)
 

wmburns

SN Certified Technician
Aug 14, 2009
5,366
417
164
Houston Texas
Don't need a Mustang specific alternator. Ford uses the same alternator in several different 4.6 applications. Try Car-part.com for a searchable list of salvage yards in your area.