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Discussion Starter · #1 ·
Hi guys!

My '02 S4 has a cooling problem. As soon as the left fans "kicks in" I have an idle issue with erratic RPM causing the engine to die. If I manage to keep the engine running with the throttle, the problem only gets worst as the second fan comes on. If I disconnect the fans, the engine gets hot but no RPM problems and idles perfectly.

So I thought that maybe the fans draws too much amp.(but the 7.5A fan fuse is still good) and then the ECU has less voltage than necessary to do his job with the fuel map.

I have changed the battery for a brand new one, so I wrote that off as a potential culprit.

I've connected each individual fan directly to a 12v power source and they both run really good. So I think that the fan by themsleves are in good working order. So I kind of think of a bad ground wire on either of the left or right fan electrical circuit. What's your guess?

I noticed that the two fans have a different part number. In a troubleshooting procedure idea; can I switch the right and left fan to see if it changes anything?

Do you guys have any ideas to where or what I should look in order do find the problem and (hopefully) fix it?

Thanks in advance
 

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I'm willing to bet you have a fan blade touching a wire and it has worn through it partially and it's making a short. Or you have a fan wire partially worn through somewhere.

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I had the same on my 2002 S4. Found a splice that was bad with a big voltage drop. I think it was the voltage supply to the injectors. From memory I had about 10v to the injectors. I just added a new wire and all was good. I will have a look tomorrow if I have time.

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Discussion Starter · #5 ·
What's the voltage across the battery terminals at idle, before and after the fans kick in?
I'm quite busy with work right now, but as soon as I can test this; I'll post the numbers.

I had the same on my 2002 S4. Found a splice that was bad with a big voltage drop. I think it was the voltage supply to the injectors. From memory I had about 10v to the injectors. I just added a new wire and all was good. I will have a look tomorrow if I have time.

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And your problem occurred as soon as the fan kicked in ? Hum.... looks like I'm in for a deeper dig than I thought...
 

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If the fan is pulling alot of current, then their is a voltage drop across the area where the resistance has increased. I had this problem with my starter motor on my old Monster 900. There was a junction of wires just off the positive battery terminal. When I would hit the starter button and the starter relay would close, the large current draw of the starter motor would flow through the wire junction which had high resistance due to corrosion. The high resistance and high current would cause a high voltage drop V=IR (Ohms Law). This voltage drop would be seen by the entire electrical system. I put a volt meter on the battery terminals then try to start the bike. The bike would turn over but would not start. The battery voltage would drop below 9 volts. This voltage is too low to run the ECU properly. I noticed that the spark plugs would not fire when the battery voltage got too low. I replaced the entire starter circuit with the MotoLectric starter kit. This time, the voltage only dropped minimally when the starter button was actuated. Plugs fired properly and bike started immediately.

As someone said earlier, check the battery voltage when the fan goes on and see if it draws down the battery. If significant, it could affect the ECU function.

Also as mentioned, check the wire insulation for breaks.
 

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It's easy to check. Disconnect the front ignition coil and measure the voltage with engine running. Do like this. Start the engine and run it warm. Disconnect and measure. Run the bike again and now very hot so fans start. Measure again. You should have at least 12 volts.13 is even better. Mine was down at about 10 volt even if the measurement at the battery was 14.4 volt.

Jocke.
I'm quite busy with work right now, but as soon as I can test this; I'll post the numbers.



And your problem occurred as soon as the fan kicked in ? Hum.... looks like I'm in for a deeper dig than I thought...
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Discussion Starter · #8 ·
Ok I finally could spend a few hours on this...

What's the voltage across the battery terminals at idle, before and after the fans kick in?
With the key at OFF : 13.03v
With the key ON : 12.6v
Cranking to start : 11.7v
Idling : 14.53v
When the 1st fan started, it dropped a to 13.22v

Not what I expected. I thought it would drop much more than that. I couldn't keep the bike running 'till the 2nd fan comes on... so I went with ducatimike testing

If the fan is pulling alot of current, then their is a voltage drop across the area where the resistance has increased. I had this problem with my starter motor on my old Monster 900. There was a junction of wires just off the positive battery terminal. When I would hit the starter button and the starter relay would close, the large current draw of the starter motor would flow through the wire junction which had high resistance due to corrosion. The high resistance and high current would cause a high voltage drop V=IR (Ohms Law). This voltage drop would be seen by the entire electrical system. I put a volt meter on the battery terminals then try to start the bike. The bike would turn over but would not start. The battery voltage would drop below 9 volts. This voltage is too low to run the ECU properly. I noticed that the spark plugs would not fire when the battery voltage got too low. I replaced the entire starter circuit with the MotoLectric starter kit. This time, the voltage only dropped minimally when the starter button was actuated. Plugs fired properly and bike started immediately.

As someone said earlier, check the battery voltage when the fan goes on and see if it draws down the battery. If significant, it could affect the ECU function.

Also as mentioned, check the wire insulation for breaks.
I putted a multimeter lead on the positive terminal of the battery and the other lead at the positive wire of the 1st fan connector. When engine was running I had a small normal consuption, but when the fan started it jumped at 10v and higher!

My thinking is that I have the same kind of problem that Ducatimike had. I have an higher than normal resistance on the positive circuit. But how to narrow it down ? I don't have to go through every little wire, on each and every circuit of the motorcycle!!

I putted the key at the ON position and with a multimeter lead still on the positive terminal of the battery and the other at the fan connector, I pulled every fuse one at a time expecting to see a different reading on the mulimeter and then target the default circuit, but no go... Should I do this test with the engine running ? Won't it die when I pull the fuse??

Then I went from the positive terminal of the battery to the relay of the starter and the reading was what I expected on both of the terminal of the starter relay (0v - 12.5v and when I pushed the start button; 0v and 0v and the starter motor started the engine flawlessly)

So I'm kind of lost here on what should be my next step??

Thanks in advance!
 

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With the key at OFF : 13.03v
With the key ON : 12.6v
Cranking to start : 11.7v
Idling : 14.53v
When the 1st fan started, it dropped a to 13.22v

Not what I expected. I thought it would drop much more than that. I couldn't keep the bike running 'till the 2nd fan comes on.
All your voltages look very good. The fan-start set-points and ignition coil triggers are under the control of the ECU. Since the there's an ignition interaction with the fans starting, I'd suspect power and/or ground to the ECU — maybe the ECU itself.
 

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Discussion Starter · #10 ·
All your voltages look very good. The fan-start set-points and ignition coil triggers are under the control of the ECU. Since the there's an ignition interaction with the fans starting, I'd suspect power and/or ground to the ECU — maybe the ECU itself.
I found the voltages to be in correct specs. But not being an expert myself, I always have a doubt.

But, your assuption to be the ECU itself scares me a lot. I do have a power commander (III) unit installed. Since it "plays" with ignition, should I remove it? I know that these units don't interact with the fuel map below 3k rmp (or so) so it shoudn't be a problem, but...
 

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You are using the right techniques but need to do voltage drop on ecu and coils when running. Use paper clip with one end straightened to back-probe connectors. I suspect you have voltage drop on positive side to injection system relay but I would check earth just to be sure. Probably what is happening is fan is pulling current and it's causing voltage supply to injectors and coils to drop because of restriction in common supply. This is the big injection fuses.
 

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i've seen a few that have a low voltage at the fuel pump/coils/injectors relay, and at idle (and with the extra fan load probably) they will be 2v or more lower than battery. ime it leads to them dropping the horizontal cylinder, but not the vertical. wacky.

i usually run another relay to supply power into that relay to fix the issue. but going right over it couldn't hurt.
 

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I am a little confused and not understanding what you are finding. Did the battery voltage drop low when the 2nd fan came on? If so, it sounds like the 2nd fan is drawing too much current, which could mean the fan motor is bad or the connections to the fan are corroded. If the problem occurs only when the 2nd fan goes on, then it sounds like the problem has to do with the 2nd fan. What am I missing?
 

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Discussion Starter · #15 ·
I am a little confused and not understanding what you are finding. Did the battery voltage drop low when the 2nd fan came on? If so, it sounds like the 2nd fan is drawing too much current, which could mean the fan motor is bad or the connections to the fan are corroded. If the problem occurs only when the 2nd fan goes on, then it sounds like the problem has to do with the 2nd fan. What am I missing?

I couln't get to the point where the 2nd fan comes on. The engine dies pretty fast after the 1st fan comes on even when I try to keep it running with the throttle. The battery did drop, but very little, this is the part that confuses me.

Check and clean ground to the ECU
I can't seems to find where the ECU gets its ground. I searched closely and haven't seen any wire going at the screws of the ECU (see photos attached), as it should be if I refer to the wiring diagram of my model/year.

So where does the ECU gets its ground??
 

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Discussion Starter · #17 ·
Hello guys!

Sorry for the delay in my update, I've been really busy by work lately.

Nevertheless, I finally succeded in resolving my issue.

After multiple test in positive and negative voltage drops ( battery, Battery to main fuse, main fuse to fan fuse, fan fuse to fan, fan to ECU, ECU to battery) I finally found that the major drop was from the ECU to battery; about 1.7 volts (I even had .3 volts without key and .7 volts with key ON).

I removed the ECU, cleaned everything with brake cleaner and no results.

The ECU external case is ground via its mounting bolts.
That I couldn't figure how it did and then decided to add a wire from the negative born of the battery to one of the mounting bolts of the ECU (as showed in the workshop manual), and VOILA; problem solved!!

So thanks everyone for all your inputs, it has been really appreciated!

No let's ride, even if it's warm outside :wink2:
 
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