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I have a 2003 Ford zetec 2.0 l four door car. For a while now I've been having an issue with the vehicle losing power and the check engine light coming on whenever I push the AC button or sometimes flip the headlights on. Sometimes the issue can be mild and caused a minimal loss in power sometimes it can be extreme causing the car to rapidly downshift into very high RPMs. This can happen while underpower and accelerating or hardly any power and coasting down a hill. The other thing that happens is that I immediately lose power to the radio when this event occurs . Everything on the internet said to replace the alternator so I have done that. This helped the problem but it did not resolve it . I then thought well maybe it's my spark plug wires or my ignition coil. I have replaced all of this now with very little change. I have had my battery load tested as well as my alternator while on the vehicle with it running. This was done at O'Reilly's Auto Parts store. The thing that really gets me is that it seems to have such weak electrical signal that sometimes when the windows are already rolled all the way up or already rolled all the way down if I keep pushing in the direction that they already are it seems to intensify an issue that you can see a warning bulb through the dash. I have gone through every single ground and made sure they were bare metal under the hood and applied Dielectric grease when reattaching the bolts. I then went into every electrical connection that goes to things like the mass air flow sensor and sensors on the engine and opened them all up and applied a very small amount of Dielectric grease on the tip of a toothpick to every pin in those connections. Nothing seems to fully cure the problem nor can I completely diagnose the problem. It would be wonderful if someone would chime in that's had a similar issue. The car has 163000 miles on it and it's just a daily commuter vehicle for work.
 

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A/C takes about 7-9 whp to work and Alt with A/C on , headlights and corresponding lights, cooling fans , inside blower fans the Alt will draw about 5-7 whp

I am assuming you have a ATX because it was down shifting so you could be loosing 12-16 whp thats 10-12% power loss at the wheels , yes you will feel that big time and your not the first to ask this over the years

Best thing to do is a few simple mods to gain some performance and it lessens what you feel

Tom
 

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Ok, new information. I thought I found the potential electrical issue last night which seemed like some crossed over wires in the back coming off of the knock sensor wer bare for the first half inch or so before they went into the thick sheathing. They were all so twisted and the copper you could see was criss crossed over one another making connection. I detach that sensor and drove the vehicle what does sensor not attached to the car at all and no engine light comes on and the car drove just fine. I had to wait several hours for the liquid electrical tape to cure so today I drove the car to work with that sensor off. The car drove just fine until I decided to check the electrical system by coasting and just flicking on the headlights. The car instantly downshifted and made me confident that I have not fixed the problem yet
 

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My gauge is also do the crazy dance when these type of symptoms are occurring. I have the factory radio in my vehicle and I lose it during this whole process also. Which makes me think it is a purely electrical issue and has nothing to do with the actual air conditioner. I mean I lose all power to the vehicle not just some horsepower but the lights Flash the gauges dance the radio goes off and all I have to do to promote this to happen is flick on my headlights or push the air conditioner button. I am leaning towards the ECM being bad. Any help would be greatly appreciated.
 

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My gauge is also do the crazy dance when these type of symptoms are occurring. I have the factory radio in my vehicle and I lose it during this whole process also. Which makes me think it is a purely electrical issue and has nothing to do with the actual air conditioner. I mean I lose all power to the vehicle not just some horsepower but the lights Flash the gauges dance the radio goes off and all I have to do to promote this to happen is flick on my headlights or push the air conditioner button. I am leaning towards the ECM being bad. Any help would be greatly appreciated.
Pigtail on back of alternator is bad.
 

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'I am leaning towards the ECM being bad.'

And where the unlearned commonly go..............the PCM 'rebuilders' (dust it off and apply a new sticker to make it 'new' again) love you for it.
 

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My similar symptoms

I had similar symptoms and when the battery and alternator proved good I started poking around. I found the ground connection on the left fender well to be bad. The lug on the ground wire was screwed down to the painted surface. I scoured the paint off and the improved ground fixed my problems.

Joe
 

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Discussion Starter #9
I have done this on both fenders and used light bulb grease to assist with the electrical connection and it has not helped much. If anyone has any thoughts or ideas I would love to hear them! I think it may be a bad ECM located behind the passenger front kick panel.???
 

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Check the cables to the battery. They can look okay but be corroded inside. Just slice the insulation up a few inches and take a look. If they're fine, tape them back down and move on. Fairly common issue on the early Foci.

And you haven't said if you've looked at the alternator pigtail.
 

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OP has not done other logical things as well. I find it hilarious that he describes engine light coming on over and over yet will not read the code posted causing it to happen, then wants any type of money losing advice he can get. We pay approximate $2.5K just to get a computer that tells us what is wrong with car then we don't use it at all. The schools are not putting them out smarter.

Vehicle clearly has an electrical issue that may not be tied to engine light at all, but until one verifies that they are still in the realm of car fixing the idiot way.

Go ahead, change that PCM, I dare you. You will likely not like the result.

More.........

'I have had my battery load tested as well as my alternator while on the vehicle with it running. This was done at O'Reilly's Auto Parts store.'

It is witless to say that and not give the result, maybe keeping it a secret will help you find the fix faster??? More evidence on the worth of schools now.

It's like OP wants to bask in all the self-created misery there. "I did all this and it still doesn't work", give us a break; if you are not going to apply yourself 100% to what is basically YOUR problem. Expecting us to do more than you is........well..... you'll get the point eventually.

Another one needing the owner fixed as much or more than the car.

Hostility switch now off. Maybe.

Check the battery terminals for loose at battery, they can be tight and you still turn them by hand. Crap cable design. The cables have to be good 100% of the entire way they run.

Alternator can be bad and test as good. You STILL haven't checked the pigtail, and the main cable connection can be bad too. That alt design is well known for popped diodes (2, 4, I've seen 6!) sapping charge intensity to create whopping problems like those here. Battery being bad tears alt up (diodes go first) and no result mentioned even though they 'got checked' and how one loses a fix there.

Grounds are not nearly the end of the list when checking for electrical issues which this most likely is. You have to chase down ALL possibilities, not just grounds which are where stupid people stop when done. You got tensioner and belt issues that can do the same and a whole list of other things. The alt changed may be just as bad as the one removed, I rejected one out of every five we tested when I did parts. Right out of the box.
 

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Voltmeter check on the battery, car not running and then with car at idle in park all loads off and warmed up. Give numbers including tenths. Needle sweep dance means the battery is super low and incorrect voltage applied to keep needles in place, they have lost memory due to low volts.
 
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