Heater Causing Drop In Revs....

[SGILWHITE]

hi guys, got a weird problem....

had what i thought was an idle problem...car slowing the revs drop too low and engine rumbles before revs flick back up again. changed camshaft sensor, crankshaft sensor, idle control valve, throttle sensor and done an ecu reset.

today just for investigation sake, i sat in the car, engine cold, started the car, turned on heater. with it turned to full heat, the idle would drop and rumble, a clear click can be heard which im sure is the fan switch, the revs would flick up and the click can be heard again. this would continue until i turned the heater off. it will also do this when i turn on the air con. if i have it on cold without the air con it doesnt do it. only does it do the rev drop, flick and click (as i call it) when the heater is on or the air con.

anyone had this before and/or know what the problem is? dodgy relay? faulty switch?

weird i know.

[simcor]

Putting any load on a car will cause the revs to dip very slightly as the alternator has to produce more power for the extra load being required, certainly at idle. Once you request extra load the revs should come back up to normal.

When you are idling does the rev counter fluctuate a reasonable amount? I.e is it noticeable movement of the needle say 100rpm or so any more and I would say there is a problem.

Fluctuating revs can be caused by many things, a bad air to fuel ratio or electrical gremlin for example a dying alternator could cause issues.

Does the car behave when you have nothing turned on, so just the engine running everything else like lights, heater and stereo off etc? If it only becomes a problem when running several electrical items then I suspect either a poor alternator or air to fuel ratio problem.

I do suspect your alternator is probably weak, and the request of the extra load is making the revs drop and the car attempts to rectify the revs and causing the fluctuation.

[SGILWHITE]

tried a quick test to check if alternator by putting on dome light above seats and opened the drivers door to see if it dimmed and it didnt....uploaded video clip to youtube of clicking....

take a look...

[artscot79]

The air on sounds like its needing topped up that's what's clicking not the alternator either it needs topped up or one of the switches is at fault.....all cars revs drop at idle with load on then increase as it compensates you may have thrown money at it for no reason the more load you put on at idle the alternator is spinning at idle speed it isn't running fast enough to keep up that's normal also

[SGILWHITE]

really? but the revs drop and i can hear the clicking as per the video when the heater is on...although thinking about it, the air con could of been on aswell as the heater. i thought it was strange for the alternator to click...it must be the fan clicking on as normal when the air con is trying to work, then when it doesnt the fan clicks off again, and so on and so on. as above i did a quick and easy test with the light inside the car to see if it dimmed and it didnt. ive not heard that noise before.

thanks matey.

[TomsFocus]

If the air con is on the engine fan is on as well, this is what draws the large load and makes the revs drop. Mine drops quite low as well which surprised me with a 'smart' alternator. With the heater on in low temps you may also have a supplemental electric heater that draws a load of current.

[SGILWHITE]

well, the rev dropping never happened until about 3 months ago...now i feel i cant have the heater or air con on because of the low revs it causes, aswell as the clicking on and off of the fan.

i want to get this sorted. it never used to be normal to have the revs dropping so low. i did another ecu reset which has returned the idle a little higher which is great. but i put the heater on to see and the low revs started again. do i change the alternater? the lambda sensor? switch? relay?

[artscot79]

You need to do the dash test and see what it says it could be the battery.....battery without engine running should say 12.5v min running 14.4v with lights and heater on 14.2v then look at the idle speed it should be anywhere from 760-800 rpm now put heater on it should dip momentarily then be within the above figures ......you need it diagnosed is it aircon with a faulty sensor a faulty fan switch causing the aircon to click on and off or multiple things don't change anything till its been looked at as the alternators rarely fail its just misdiagnosed as an alternator

[SGILWHITE]

what do i need to do this test? the battery is about 8 months old and has a 400-500 load on it. plus its got an indicator that says its fully charged.

i thought it might be a relay but the fan is working at both speeds so a relay cant have gone otherwise it wouldnt come on at all?

[steveo3002]

did you ever fix this , i have the same problem :( 

[FatHead1979]

Start off (if you haven't already) by checking the alternator is capable of outputting stable power with all the electrics turned on i.e. all lights including main beam and hazards, heater on full heat, AC on, full fans, all interior lights, radio on, rear heated screen on and front screen on if you have it fitted.  Even with everything turned on, a SmartCharge alternator should be capable of powering everything without the car nearly stalling.

Google the "Focus dash trick" if you're not familiar once the screens you can cycle through will tell you what voltage the ECU is reporting, it's probably not 100% accurate but if it's below 14v volts with the engine running and all the electrical systems turned on, I'd suggest the alternator is not delivering the power it should be.

Even if this ends up being the case, alternators are pretty robust and don't often fail (they do wear out eventually though), there are a number of other elements which make up the SmartCharge system (wiring looms, sensors, connectors etc) a failure in any of these could cause a perfectly good alternator to not perform correctly.