Tricking your engine to idle up and electric radiator fans

[colinnwn]

 

I got the valve cover gaskets redone on my Pathy. It is running even smoother than it has in years. I assume that is because they found and replaced some more vacuum hoses that were brittle and leaking. A side effect has been that when my electric radiator fan kicks on, the engine idle RPM drops by about 250, and seems like it is stumbling for a second until the IACV can catch back up. It never did this before. But I imagine that is because there were enough air leaks the IACV didn't need to do much, and the ECU just fed the engine a bit more fuel.

 

It is fine to leave as is. But its one of those things I'd like to improve if I could. The first thing I thought is if I could tap into either the signal from the air conditioner or the power steering pressure sensor that signals the engine to idle up right as the fan is turning on, that would help. Has anyone done this? I'm going to get out the FSM wiring manual and look through it.

 

As I was writing this, I thought maybe an easier solution would be to just put the radiator fan controller inline with a capacitor, like they do with high power amps. Maybe that would smooth out the initial surge current enough to give the IACV valve more time to recover.

 

 

[Sjackson2]

Is your battery up to snuff? Have you done the idle volume relearn? Cleaned out the iacv? I would do all these before I started trying to mess with the idle 

[colinnwn]

The battery is good as best I can tell. It is approx 2 year old Optima and starts the truck fine. It has been abused because my old alternator overcharged it to 19 volts, and then the replacement alternator was obviously undercharged it for several months until I realized what was going on. But at no point did it ever fail to start the car, or drag the starter significantly.

 

I haven't done the IACV relearn or clean the IACV. I was hesitant to do that since this problem is only related to starting the radiator fan, and otherwise the idle is very solid and stable. But I guess I will try that. I'll research the process to do the IACV relearn. Do you know if it requires the NISSAN CONSULT?

 

[Sjackson2]

Failing to start the car, and still having sufficient voltage are two different things. Get it checked. 

No it does not require a consult scanner. Depending on the year of your vehicle there are two different methods

[colinnwn]

I can watch the voltage pretty much constantly on my Scan Gauge, and I have a "Battery Bug" that monitors voltage constantly including during starts, and the voltage is within normal range. The battery bug says I have 70% battery life (not battery charge).  I would trust that testing in-situ more than the crappy battery load testing equipment at most auto stores. So I'm fairly certain it is fine.

 

I did some research and found this on the relearn process

https://www.nissanhelp.com/diy/pathfinder/projects/2001_2002_nissan_pathfinder_idle_air_volume_learning.php

 

Based on that, I don't have the pre-condition to need an idle volume relearn. The shop I took it to for the valve cover replacement has a stellar reputation. It is idling so smoothly now, I wouldn't be surprised if they actually did the relearn. If I didn't have an electric fan, this wouldn't even be happening. It's the surge of electric power demanded by the fan startup, potentially exacerbated by my rebuilt alternator that can supply more power to the battery to replace it, at the expense of the engine power surge.

 

It is also possible my IACV motor is getting marginal or clogged. But it is very strange this occurred suddenly and exactly after a shop visit, where everything else related to engine idling smoothness improved so drastically at the same time.

 

I was vaguely aware that if the IACV ingested coolant as it aged and died, that it could burn out your ECU. So I had been wondering about replacing it proactively. It is a little expensive to do that. The cost is similar to an ECU repair if it did fry it, the only downside would be waiting on the turnaround of the ECU repair or trying to do it myself.

 

When the weather is better I will probably remove and inspect the IACV. I also found this thread where someone recommends putting a 1-5 amp fuse (I assume it would need to be a fast-blow fuse) inline with the IACV and it might prevent it from frying your ECU if your IACV ever does go out.

 

https://forums.nicoclub.com/idle-air-control-valve-iacv-replacement-diy-for-2001-pathfinder-t607957-30.html?sid=ad4c250f17e7c09848e838cf13fa93b7

 

[QuasarDecimari]

Wow, this is a lot of stuff I haven’t heard of doing before with the IACV, I’ll be keeping an eye on this thread for sure...
I noticed you were talking about putting capacitors in line with the radiator fans to help with the initial current draw, I’ve been actually thinking of doing the same thing, I just need to figure out what size of capacitor to run because some of those bigger radiator fans draw quite a lot of current initially, so a cap with good capacitance will be needed to really make a difference... maybe I’ll toy around with it myself, since I have access to some pretty cool supercapacitors at work.

[Sjackson2]

1 hour ago, colinnwn said:

I can watch the voltage pretty much constantly on my Scan Gauge, and I have a "Battery Bug" that monitors voltage constantly including during starts, and the voltage is within normal range. The battery bug says I have 70% battery life (not battery charge).  I would trust that testing in-situ more than the crappy battery load testing equipment at most auto stores. So I'm fairly certain it is fine.

 

I did some research and found this on the relearn process

https://www.nissanhelp.com/diy/pathfinder/projects/2001_2002_nissan_pathfinder_idle_air_volume_learning.php

 

Based on that, I don't have the pre-condition to need an idle volume relearn. The shop I took it to for the valve cover replacement has a stellar reputation. It is idling so smoothly now, I wouldn't be surprised if they actually did the relearn. If I didn't have an electric fan, this wouldn't even be happening. It's the surge of electric power demanded by the fan startup, potentially exacerbated by my rebuilt alternator that can supply more power to the battery to replace it, at the expense of the engine power surge.

 

It is also possible my IACV motor is getting marginal or clogged. But it is very strange this occurred suddenly and exactly after a shop visit, where everything else related to engine idling smoothness improved so drastically at the same time.

 

I was vaguely aware that if the IACV ingested coolant as it aged and died, that it could burn out your ECU. So I had been wondering about replacing it proactively. It is a little expensive to do that. The cost is similar to an ECU repair if it did fry it, the only downside would be waiting on the turnaround of the ECU repair or trying to do it myself.

 

When the weather is better I will probably remove and inspect the IACV. I also found this thread where someone recommends putting a 1-5 amp fuse (I assume it would need to be a fast-blow fuse) inline with the IACV and it might prevent it from frying your ECU if your IACV ever does go out.

 

https://forums.nicoclub.com/idle-air-control-valve-iacv-replacement-diy-for-2001-pathfinder-t607957-30.html?sid=ad4c250f17e7c09848e838cf13fa93b7

 

I would not use the fuse. Just bypass the coolant line to the throttle body and you’ll never have to worry about coolant leaking into your iacv. And definitely clean it out. 

Edited February 17, 2019 by Sjackson2

[Sjackson2]

and I’d look into testing and getting a new alternator before I put caps iine to the fan 

[colinnwn]

The alternator was disassembled and tested by an alternator shop before I put it in a couple of weeks ago. I asked him to check the brushes and test diode ripple specifically, because I was hoping to not do another alt swap on this vehicle. It is a generic Malaysian 13900 I got at a junkyard but the guy said it looked new or freshly rebuilt inside.

Until more out of place symptoms appear, I have no other reason to believe anything is wrong with this alternator.

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[colinnwn]

Interesting on the coolant bypass. You think it is unlikely to cause problems by bypassing?

What specifically about the fuse do you think is a bad idea? Just another potential failure point?

I sorta have the same concern about the coolant bypass. But if others have done it successfully, then I guess it is worth doing. If I ran into icing in the valve, I should be able to get it underway with some careful manipulation of the throttle pedal if it dawns on me what is going on.

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[colinnwn]

Just to play around with options, I do have a 88-108 mfd 250 vac HVAC start capacitor laying around.

I've never wired up my own capacitor circuit. But from doing some research, it looks like AC capacitors should work fine with DC. I could wire one side of the capacitor through a bulb like a 194 to the negative battery terminal to control the recharge rate. Then off the other capacitor terminal run one wire to the positive battery terminal, and another wire to the fan controller positive input.

I'm not sure I will do this, as I don't quite trust myself to not let the magic smoke out.

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[Sjackson2]

34 minutes ago, colinnwn said:

Interesting on the coolant bypass. You think it is unlikely to cause problems by bypassing?

What specifically about the fuse do you think is a bad idea? Just another potential failure point?

I sorta have the same concern about the coolant bypass. But if others have done it successfully, then I guess it is worth doing. If I ran into icing in the valve, I should be able to get it underway with some careful manipulation of the throttle pedal if it dawns on me what is going on.

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I know it’s unlikely to cause problems. Unless you live somewhere very cold maybe. Tons of owners have done it, myself included. The only time the coolant does you any good is on startup anyways. And yes....I don’t like the idea of splicing into the wiring 

[Sjackson2]

I just think the capacitor is a band aid for a larger overall problem. There’s no reason that the factory alternator shouldn’t be able to handle the draw from an electric fan. Something else is going on and a capacitor will just mask it

[QuasarDecimari]

I highly suggest a bit of research on capacitors if you’re going to experiment, they can be rather dangerous, or you could hurt your circuit if you don’t wire it correctly. They’re a tad tricky if you don’t understand them completely, and an underpowered capacitor is just going to be useless if you don’t calculate the capacitance needed for the circuit.

[colinnwn]

I'll disconnect the coolant line.

 

The alternator is keeping up with the fan. It only bogs down the engine for 1 or 2 seconds each time the fan starts, until the IACV has a chance to add enough air to bring the idle speed back up to 750 and stable. In fact I think the fresh alternator is able to keep up too well, and that is why it is able to pull down the idle speed momentarily. The old alternator was probably letting the voltage sag during the fan start, because the regulator was tired and unstable and couldn't energize the alternator sufficiently.

 

I'll do more research on capacitors. I've replaced several of them on HVAC equipment. I understand they can be dangerous to people if not discharged, and equipment if miswired. I've just never designed my own circuit. It sounds like they won't blow themselves up if you connect them directly to a voltage source that is under their rated voltage. They just charge to the supply voltage and stop.

 

For example at first I didn't understand why people suggested putting a bulb in the negative line. Then I realized it was because if you didn't, the capacitor would try to recharge as fast as the current draw it was supplying, and there would be little net change in the inrush current, the whole point of the capacitor. The bulb slows the recharge rate of the capacitor.

 

I saw some formulas for how to calculate the right capacitor size. I figured I should do that. But I also figured that the power required of a 12 volt 18 amp radiator fan would be less than or equal to the compressor rating of a 9000 btu air conditioner rated for a 120 volt 15 amp circuit, so that capacitor should be good or slightly overrated.

[onespiritbrain]

You’d need a huge capacitor if you’re using it to supplement current that your battery can’t handle. Really you’d need a bank of super capacitors. Start caps in a DC motor circuit can help start a motor if the power supply is sized for the run current and the start current draw time is very short but your fans are supplied by the same battery that your starter is supplied by and your starter draws far more than your fans, by a lot.

I bet you have a poor ground somewhere. Go over every single +\- connection they’d have messed with during the repairs, or all of them in the engine bay altogether, and clean them.

[colinnwn]

I'll check the grounds. 

 

But I don't think the battery is having any trouble handling the fan. Even when the old alternator wasn't charging the car for the first minute or two, the battery was able to start and run the car with the voltage remaining around 12.5. This is approximately the same voltage that the battery bug captures as the lowest voltage during an engine start (which it assumes by watching for significant voltage swings.

 

I think the alternator is just trying to replace the used charge too fast and the IACV motor can't keep up with the increased demand. This is the same reason that ECUs command increased idle air at the same time they turn on the AC at idle, or sense high power steering pressure. I think I've even heard some cars do it that have factory electric radiator fans.