Focus Fanatics Forum banner

1 - 20 of 23 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter · #1 ·
Back ground info:Car died while driving on the highway. Batt lite came on and car died. Towed to local shop diagnosed with bad alt. They replaced the alt with reman pos. Drove car two days card died while driving again. Same shop puts in another reman alt but can't get it to charge. They diagnose bad pcm. Towed to my house discover smashed alt pig tail and ripped cv boot ( they dropped the alt on it). Replace pig tail and install new ford alt. Runs great for one day then batt lite comes on at start up. Unplug hatch harness and disconnect battery. Alt comes back so I repair harness.

This is the new part. Batt lite comes on during test drive. Back in the driveway disconnect battery and hatch harness. Alt does not come back to life. Check engine grounds-all are dead- read over limit on ohm meter. Clean replace and add engine to chassis and bat to chassis grounds. Alt still dead,did resistance test in car about 180K ohms. About to pull it and give it proper resistance test. Think I fried another alt! What else should I check before I fry another alt?
 

·
Vince your Moderator
Joined
·
5,074 Posts
A dead or dying Alt will kill your battery as well and that dead battery will kill your Alt in return. Have the battery load tested.
 

·
Registered
Joined
·
17,490 Posts
Are you disconnecting battery while car is running?

'Alt still dead,did resistance test in car about 180K ohms.'

A waste of your breath unless you quantify what you tested, alts test like 20 different things, no one thing tells you good/bad like that except volts while running.

Using alt to charge back up dead battery will spit alt guts out very quickly, the warranty is voided doing that.
 

·
Registered
Joined
·
28 Posts
Agreed, if your battery is dead or heavily worn, can and will burn the alt out rather quickly. You should load test the battery and in cases where it has been throughly discharged (but not past the point of no return), it should be charged using an external charger before use in the car again to reduce the alternators load.

This is what kills these things, they are meant to recharge the amount used to start the car and perhaps support a modest accessory load, a standard alternator isn't meant to totally recharge a battery from the proverbial empty >_<.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #5 ·
AMC 49-To answer your questions, pin#1 to alt body=180K ohms. No I have never pulled the pos bat cable while the car was running. When I said dead I meant batt voltage below 12.5 volts and falling with engine running.As far as using the alt to charge a dead batt, the lowest voltage I asked the alt to charge from is 11.5. I don't know what the shop did to the other alts.

Sorry to assume you all know what I am thinking. I do appreciate all the help.

New info-I resistance tested three ground leads. All tested out of limit. Cleaned the two in the negative batt harness and they tested at zero or less than 1 ohm. The one from the bracket attached to the valve cover (by the alt) to chassis has square rubber part built into it (what is that?). No amount of cleaning will get any continuity through it. Ordered a new one from Ford. Oh yeah Ford is being cool and going to warranty the alt. I added two more grounds one engine to chassis and one battery to chassis. As for the battery, I charged it once (at 2 amps) am letting it rest over night then another charge cycle and I intended to load test it. I have only owned this car since may so I don't know the battery's history.
 

·
Premium Member
Joined
·
44,595 Posts
That small wire to black box to ground is a harness ground with an RF interference capacitor (the black box) inline.

Can't test a capacitor with a multimeter.


Haven't guessed what you mean by pin #1, main positive connection possibly? That shouldn't have continuity to ground... Diodes for one way current in that circuit.
 

·
Registered
Joined
·
17,490 Posts
................gack...........................see the next one..................
 

·
Registered
Joined
·
17,490 Posts
'...the lowest voltage I asked the alt to charge from is 11.5.'

Don't use the alt to charge the battery AT ALL other than normal slight topping off in normal operation. These put out quite a bit of amp and will overheat regulator to fail it if you insist on charging low battery. Ford says absolutely NOT and every rebuilder in the universe void warranty upon knowledge of that, the paperwork says so. Just because the unlearned prevail upon part maker to exchange it does not mean they didn't tear it up to begin with.

Rule #1 is always start with a KNOWN GOOD BATTERY fully charged and load tested at PROPER CCA, testing too low because they cannot tell what the CCA is is a mistake the parts guys commonly make and can fail the alt again, the catalogs show what CCA should be but they often won't lift a finger to consult them.

Just what do you expect to see at your 'pin 1' test? NONE of the pins are ground (ground is through the case) and they all go into regulator which cannot often be checked good/bad like that. The pin use moves around and if you are probing the PWM circuit from the PCM then you could easily be torching the regulator with your meter. The PWM circuit can only be checked by operating it, what the alt tester does.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #12 ·
To AMC49- So this is my someting new for today. Didn't think asking the alt to charge from 11.5 volts was a no no. Thanks for the info. I saw the pin test in a different thread here (can't find at the moment). It gave ohm values for #1 pin to alt body as 1.2K-1.6K=good >60K=failed alt. I have not disconnected the batt with the car running and have not probed the pcm at all only the alt. I suspect my issues are bad grounds and low batt voltage. I am waiting for the new alt and ground lead with capacitor to come in. I have charged the batt again and will let it rest over night. Then load test or maybe just replace as pm. Does anyone think there is someting else I should check so I don't fry another alt?
 

·
Registered
Joined
·
17,490 Posts
The alt grounds through the case. The only true extra ground you can run there is from alt case directly to battery negative post at battery.

Battery is pretty much dead past 12.0 volts, they give trouble at 12.3 or so. Max charged will be like 12.8. Ford says it takes 8 hours running to fully charge battery that's dead, the regulator will torch way before that. The warning to their guys to not do it.

When checking alt pin to case you are talking going through so many different pieces of circuit there is no way you can tell good/bad that way in my view. The makers of the regulator say you must ramp the PWM duty cycle up/down to check the entire thing or testing one is worthless. Meaning complete assembled alt test is only way to be sure.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #14 ·
So the only way to check the alt in my car in my driveway is a simple voltage check across the battery with the engine running? What else would you (amc49) check if you were replacing an alt? Received the new alt and ground lead from ford today. Will install tomorrow, then load test/replace the battery.

Sometimes I long for thedays when cars did not have computers!
 

·
Registered
Joined
·
17,490 Posts
I look for 14.0 volts or higher at idle after waiting for it to ramp up maybe 30 seconds and all is right in my world then. Measure across the battery.

Have them run test on alt at store and look specifically at RIPPLE to make sure it's even and low, that is a diode check. Diode connections fail easily on these, it then takes out the regulator.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #16 ·
Have them run test on alt at store and look specifically at RIPPLE to make sure it's even and low, that is a diode check. Diode connections fail easily on these, it then takes out the regulator.[/QUOTE]

By them do you mean my local parts store? And are you suggesting I install a ground wire between alt body and batt neg?
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #17 ·
OK so we have brand new ford alt, new from ford alt pigtail, new from ford capacitor ground lead, new interstate battery. Cleaned three ground leads and added three more (alt mounting stud to batt neg, engine to chassis, and batt neg to chassis). Start the car...30 seconds of 14.5 volts then 12.0 volts and dropping.

The only thing I can think of is PCM.
 

·
Vince your Moderator
Joined
·
5,074 Posts
Sometimes, the blue sensing wire corrodes further up the wire than is expected causing problems. 2ft or so of wire is much more cheaper than an ECU.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #19 ·
I will check that wire. If I amgetting battery voltage across B+(at alt) and ground (alt body) is it correct to assume that pos bat cable is good?
 

·
Registered
2004 Focus Wagon, Zetec DOHC, Auto
Joined
·
1,612 Posts
I will check that wire. If I am getting battery voltage across B+(at alt) and ground (alt body) is it correct to assume that pos bat cable is good?
To check positive battery cable, check voltage from alternator positive output to the positive terminal of the battery. Depending on charge current, it should be less than 1 volt.

EDIT: Check with car running.
 
1 - 20 of 23 Posts
Top