Jump to content
Do Not Sell My Personal Information


Engine Revving Up And Down


david295
 Share

Recommended Posts

Between the o and 1 or rev counter, there are 2 black lines, normally mine ticks over at the first line under the one.

If i switch on headlights it drops down to the first line just above zero, then jumps up to next one under 1, and just fluctuate's between them 2.

Link to comment
Share on other sites


as arts said, we cant rule out an alternator pumping the wrong voltage, but it could be anything as simple as the ICV needs cleaning and or replacing, or the air filter could do with being replaced. does it only happen with the headlights on?

if you have no electrics on but the engine runs, does it idle rough?

If you then switch on any other electrics (one at a time) does anything else affect it?

Once you have checked these it will help further...

Link to comment
Share on other sites

do the dash trick and go to engine rpm take a note of the speed then switch the lights on again and note the speed now the idle speed at idle with no electrics should be between 670-730 with a warm engine so first thing is to make sure that is what you are getting as the rev counter doesnt give exact figures it sits at 800 but the car doesnt idle at 800rpm

next switch on the lights and watch the dash readout the rpm should increase sometimes to about 800rpm then it should drop and settle it will fluctuate slightly but it should still be around 670-750rpm no higher on a warm engine note the figures now on the dash test go to battery voltage and see what it says i would expect it to be 14.1-14.3v with the engine running and lights off switch on the lights and watch the voltage it should go down then instantly back up to 14.1-14.3v again note the figures and post them up here if the revs when the lights are switched on go high and stay high for more than a second it indicates the idle control valve disconnecting the connector to the icv will show if the engine stays the same no increase or decrase in revs the icv is knackered if the revs do change its no the icv thats at fault but maybe a split or collapsed hose and blocked pcv valve

Link to comment
Share on other sites

as arts said, we cant rule out an alternator pumping the wrong voltage, but it could be anything as simple as the ICV needs cleaning and or replacing, or the air filter could do with being replaced. does it only happen with the headlights on?

if you have no electrics on but the engine runs, does it idle rough?

If you then switch on any other electrics (one at a time) does anything else affect it?

Once you have checked these it will help further...

Icv has been cleaned, air filter new, it happens with anything elctrical turned on.

Engine runs perfect on tick over with nothing switched on.

I have been told that I should have a 105amp alt, but the new one i have which is a Bosch recon, is only 80amp, the haynes manual states 80amp.

Whould it matter if i put a 105 amp one on

Link to comment
Share on other sites

do the dash trick and go to engine rpm take a note of the speed then switch the lights on again and note the speed now the idle speed at idle with no electrics should be between 670-730 with a warm engine so first thing is to make sure that is what you are getting as the rev counter doesnt give exact figures it sits at 800 but the car doesnt idle at 800rpm

next switch on the lights and watch the dash readout the rpm should increase sometimes to about 800rpm then it should drop and settle it will fluctuate slightly but it should still be around 670-750rpm no higher on a warm engine note the figures now on the dash test go to battery voltage and see what it says i would expect it to be 14.1-14.3v with the engine running and lights off switch on the lights and watch the voltage it should go down then instantly back up to 14.1-14.3v again note the figures and post them up here if the revs when the lights are switched on go high and stay high for more than a second it indicates the idle control valve disconnecting the connector to the icv will show if the engine stays the same no increase or decrase in revs the icv is knackered if the revs do change its no the icv thats at fault but maybe a split or collapsed hose and blocked pcv valve

Mine does not show the engine revs on the dash trick, it doesent even show speed, if i disconnect icv on tick over engine speed does drop, but yet again, if i disconnect alt completly, that is red power cable and 3 pin smart charge plug, i can turn on everything elctrical, and there is no change in engine speed, everything works perfect, if i start enging and run it off just battery and no alt
Link to comment
Share on other sites


all fords show this info using the dash trick mate if your car doesnt you have far bigger issues icv fine there wont be a change in engine speed if you disconnect the alt its not connected so theres no load on it to make the revs drop in the dash menu using the dash trick you will get the info required engine off press and hold trip reset and switch engine on with the reset still pressed it will say test release trip reset each press scrolls through the menu.

Link to comment
Share on other sites

On my sons 1.8 focus same year as yours at the back of the inlet manifold there are two white vacuum blanking caps (non renewable ) these had come adrift and caused an air leak taped them up and cured the problem might be worth a look to see if this is the same problem on yours .

Link to comment
Share on other sites

the 110 is the ideal output because the focus uses a smartcharge gem system which is going to ensure your car copes more appropriately. so it would be better if you could get the right output.

With regards to the dash trick, its been a while since I used it, but there should be an option on there as your scrolling to see the RPM in realtime as digits as well as dash... if you have a look at the "dashboard trick" thread at the top of the focus forum, that has a step by step of the entire self diagnostics...

Link to comment
Share on other sites

the 110 is the ideal output because the focus uses a smartcharge gem system which is going to ensure your car copes more appropriately. so it would be better if you could get the right output.

I believe it has the correct output 80amp alt, thats what is mentioned in haynes, the 110 is for diesels.

It has been to fords for a scan, and they say no fault, they say its normal for revs to drop when brake lights come on.

Now I do not agree, i have never had a car that does that

Link to comment
Share on other sites

revs do drop when the brakes are applied if you watch the revs on the dash trick and switch on electrics or press the brakes the revs and battery voltage momentarily drops on most cars you dont notice its because most cars idle at 800-850rpm the foci idles low at 670-730 for emission purposes so what they say is true and they all do it all of them

Link to comment
Share on other sites

Even if i take the brake light switch of the pedal, press it in start car let it tick over and release my finger off button, to make brake lights come on, there is a big noticable drop in revs, and the whole car starts shaking.

I do not believe for 1 minute that is normal.

Link to comment
Share on other sites

the dash trick will answer all questions

revs on a warm engine 670 to 730 itl bounce between these thats normal

switch on rear window heater revs should drop but not below 600 then go up to normal if the revs drop to 600 or less then its either the pcm values need updated or pcv valve sticking weak spring or icv valve or collapsed hose fords diagnostics will pinpoint it there should be a drop when using the electrics thats normal if the revs are 620 or more its fine

Link to comment
Share on other sites

Warm Engine

Tick over: 780 to 800

Headlights on: 770 to 775

Brake lights on: 770 to 780

Heater on full: 740 to 750

Rear Demister: 730 to 740

Everything On: 790 to 800

Voltage tick over: 19v

Everything on: 18v

Link to comment
Share on other sites

the voltage is way wrong everything is okay ie revs are exactly as they should be so they are not the issue if its putting out 19v either the battery is dead or faulty or It may be that the regulator is packing up and the alternator is going to max. unregulated output because of a bad battery output voltage (alternator input) connection between the battery and the alternator also the pcm regulates the voltage so if theres a pcm fault youll have this issue you need to take it to ford for an ids hook up they can check the alternator and do a pin test ide do it soon at 19v the battery will soon be fried the fuse to the alt will overload eventually it can fry the pcm module also get it in quick and avoid driving it till then

Link to comment
Share on other sites

I have today put another alternator on, and another ecu, that i know was working perfect, as i heard car running before i took it off.

Here are readings i am getting now using multimeter on battery.

Battery: 12.8v

Tick over: 14.5v : Smart charge disconnected: 13.9v

Everything switched on, on tick over: 14.0v

But yet engine still struggles and shakes when brake lights come on.

Link to comment
Share on other sites

they are indeed the correct readings so either it was the alternator smart charge or the ecu from youre own info the engine isnt struggling when applying brakes or electrics the readings are indeed correct the car will shake slightly its not an up to date engine add to that when you apply any electrics the car will adjust the idle and fuelling to give the lowest reading youre issue may be as said a sticking or weak pcv valve or a collapsed hose its not a battery or electrical issue as the readings are exactly what they should be it could even be as simple as incorrect spark plug gaps

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Forums


News


Membership