Idle Low RPM Voltage Drops

[Logizyme]

Background: I'm a repair technician at a Ford Dealer. I've had my marauder for about 5 months. I've had my 2003 P71 for a couple years.

At idle my voltage gauge begins to drop. Depending on electrical load it may be subtle or severe. At night with all my lights on radio on and defrost going when I'm stopped at a stoplight the gauge can read as low as 11.5-12v. as soon as I let off the brake and start moving and get rev's off idle voltage will surge momentarily and return to normal. The surges can go as high as 15.5v but typically in the 14.5-15v range. At idle my tach reads a hair above 500rpm. PCM was updated to the lastest calibration after I purchased it. While driving around the voltage gauge reads normal at 14.4-14.5v.

Obviously 11.5 and 15.5v are of serious concern, and the brightness fluctuations of all my lights are anoying, so I decided to replace the aftermarket battery and the alternator. Battery was replaced with a Ford/Motorcraft 850/1000 CCA/CA and the alternator was replaced with a DB Electric OE replacement 130a (because discontinued and not available from Ford)

No change in symptoms.

Durring replacement of the battery I noticed the B+ terminal had some damage and wear from previous corrosion and while I know that alone is not enough to cause my symptoms previous corrosion could have leeched into the battery cables causing excessive resistance. So I decided to replace the battery cable assembly - (disconinued from ford) - so I decided to replace it with one from a Grand Marquis (95% direct fit FYI) available from Ford for 65$. I did check and confirm the B+ fusible links were of the same rating. The cable assembly also replaces the body and engine grounds as well as the ground terminal and wire.

No change in symptoms.

I connected the IDS, checked for DTC's - none found. Then I monitored datastream watching VPWR. Simultaniously I connected a DMM to the battery and monitored voltage.

My observations were interesting. What I noticed was that the voltage gauge in the car exagerated considerably, when VPWR was at 13.9-14.0v the gauge would read 14.4-14.5, when VPWR was at 12-13v the gauge would read 11.5-12v. Also I observed that B+ voltage was nearly always 0.3v higher than VPWR, so when VPWR read 14.0v B+ voltage would be 14.3v. I also monitored engine RPM to confirm accuracy of the tach. At warm idle RPM is between 550 and 600 - consistant with the tach readings. At cold idle RPM is 700-800 and I dont notice any voltage change like durring warm idle.

Anytime above 800rpm the VPWR/B+/Gauge would read 14.0/14.3/14.4 respectivly.

At idle (550-600) with high electrical load (low's fogs stereo defrost) voltage would drop to about 12.2/12.5/12.0 within 10 seconds, and after about 30sec to a minute would stabilize at 11.8/12.1/11.5. Durring this time there is no charge indicator(battery MIL) illuminated - which i did check to see if it worked durring KOEO self test and it does.

Coming off of idle after the voltage drop, the voltage surge, my maximum measurements were 14.2/14.5/15.5 which occurs momentarily and returns to normal voltage within 2 seconds.

So voltage flutcuation measurements of up to 2.4/2.4/4.0

based on all my measurements I can say with certainty the voltage gauge is not the most accurate way to monitor voltage but it does give a good indication of system state.

I know that voltage fluctuations from 11.8-14.5 are not good for any part of the car and the change in headlight brightness is quite embarassing.

With a new alternator, battery and cables, no charge indicator light and no DTC's I am at a loss and dont know how else to procede.

My best explanation is that the small 130a alternators just dont put out enough at 600rpm to handle the electronics and struggles to keep voltage up untill rpm increases.

The vehicle is 100% stock at this time, no underdrives, no electric accessories exept a phone charger plugged into the cigarette ligher socket.

The only repair I can think of is raising idle rpm, which is something I intend on doing when I have the car tuned in the late spring, at which time I will have it set to 800rpm or so, which would solve this problem.

SO IF YOU'VE READ THIS FAR THANKYOU AND HERE ARE MY QUESTIONS:

Has anyone else had this issue or heard of this issue, and how was it resolved?

Whats your idle RPM?

Any ideas what repairs or diagnostics that I have not already done?

[Marauderjack]

My idle is set at 850 RPM's in my blower tune and I don't remember the "stock" idle RPM......been awhile!!:shake:

Sounds to me like bumping the idle up will help??:beer:

Have you checked all frame grounds?? Some folks have had corrosion problems resulting in whacky voltage problems!!:eek:

Good Luck and Happy 2014!!:D

[martyo]

Sounds to me like bumping the idle up will help??:beer:


That'd be my vote as well.

[ctrlraven]

Do you know if the car has underdrive pulleys?

[fastblackmerc]

Are there under drive pulleys installed?

[martyo]

Do you know if the car has underdrive pulleys?


I was really curious about this too, but he said:


The vehicle is 100% stock at this time, no underdrives, no electric accessories exept a phone charger plugged into the cigarette ligher socket.

[fastblackmerc]

I was really curious about this too, but he said:

True, but he isn't the original owner and it's very hard to see the difference between under drive and stock pulleys.

[martyo]

True, but he isn't the original owner and it's very hard to see the difference between under drive and stock pulleys.

I completely agree with that.

[jwibbity]

he can measure them to see right??

[ctrlraven]

I didn't see where he said there was no UDP since he wrote so much I started to skim through it.

It's a good chance that the idle screw on the TB has been lowered or messed with before.
I know 600 rpm in gear (r, d, 1, 2) seems to be the normal on a stock car. Mine is at 750 in gear and 800 in Park/Neutral. I have a tune and UDP, sitting at idle in gear I can only run windshield defroster or rear window defroster one at a time, if I run both at the same time, my voltage will drop to 12.5/7 from 13.8.

I plan on to do the Big 3/4 sometime soon before I do my motor swap.

[babbage]

Any MM at night with: low, beams, defrost, heat and stereo will read low.

The defrost is the killer drain. This is normal.


Suggestion: Get a DB Electrical 160 or 220 AMP Alternator.
I got underdrives and get 14.1 at 750 Idle.

[Vortech347]

The RPM on a Marauder is WAY to low. Even stock. Really needs to be around 750-800. Go measure the crank pulley and see what its diameter is vs a stock one. Can't go off anyone's word. The measuring tape doesn't lie. :)

[babbage]

The RPM on a Marauder is WAY to low. Even stock. Really needs to be around 750-800. Go measure the crank pulley and see what its diameter is vs a stock one. Can't go off anyone's word. The measuring tape doesn't lie. :)


I think a Ford master tech would know what a stock harmonic balancer looks like...
:poke: -> :D

[fastblackmerc]

I think a Ford master tech would know what a stock harmonic balancer looks like...
:poke: -> :D

You would hope so......................

[Logizyme]

I assure you guys my car does not have underdrives. Seems like the concensous is that this is normal operation and my only bet is to up idle speed with a tune or get a higher output alternator.

Btw there is no idle screw on our throttle. Idle speed is controlled via an idle air control valve powered by a pcm controlled motor. The stopper screw on the throttle body is only there to set the closed position of the throttle body and is set at time of manufacture of the body and should not be adjusted. Even if it were adjusted you could not change idle rpm using it without causing other significant problems
Thanks everyone for the input and help.

[Vortech347]

I think a Ford master tech would know what a stock harmonic balancer looks like...
:poke: -> :D


You would hope so......................

Just because they have that designation doesn't mean they know their stuff. I'm shade tree level and I've had to fix things for friends after a dealer messed it up. Most of the time when I take my own vehicles in I have to tell them what to fix or they mis-diagnose it. I'm dealing with that right now with my F'n Escape. The steering rack knocks/pops like a MOFO, the tech decides its the sub-frame bushings!? Now on my 3rd trip back with it...


I assure you guys my car does not have underdrives. Seems like the concensous is that this is normal operation and my only bet is to up idle speed with a tune or get a higher output alternator.

Btw there is no idle screw on our throttle. Idle speed is controlled via an idle air control valve powered by a pcm controlled motor. The stopper screw on the throttle body is only there to set the closed position of the throttle body and is set at time of manufacture of the body and should not be adjusted. Even if it were adjusted you could not change idle rpm using it without causing other significant problems
Thanks everyone for the input and help.

A higher output alternator may not be the solution. Most higher amp ones require the same if not a little more idle speed before they start charging. I believe Jason (2,4shofast) had this issue with his higher output. Have you checked to see what the actual AMP and volt draw is at idle?

Even though that screw should not be adjusted. You can datalog the TPS to see if its in the correct range. Its possible the previous owner of the car screwed with it. This can be done with ANY Ford SCT X2 tuner and a laptop. I'll bet at least a few techs at your dealership have a tune on their cars and a hand held. I've used my X2 from my Marauder to log my dad's F-150 before.

[Dre1842]

I had to jump in.....I have the same exact issues.
Can this also cause the car to crank slow?
Cold start crank is strong, but thereafter it's really weak.
Batteries and alternator are fine and udp's are on car (with stock alternator pulley)

[martyo]

I assure you guys my car does not have underdrives. Seems like the concensous is that this is normal operation and my only bet is to up idle speed with a tune or get a higher output alternator.

Btw there is no idle screw on our throttle. Idle speed is controlled via an idle air control valve powered by a pcm controlled motor. The stopper screw on the throttle body is only there to set the closed position of the throttle body and is set at time of manufacture of the body and should not be adjusted. Even if it were adjusted you could not change idle rpm using it without causing other significant problems
Thanks everyone for the input and help.

Do you have a tune in your car?

[Smalldogg/03mm]

Clean the idle control and the mass airflow system .... And while u at it the k/n if u have one


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[fastblackmerc]

I had to jump in.....I have the same exact issues.
Can this also cause the car to crank slow?
Cold start crank is strong, but thereafter it's really weak.
Batteries and alternator are fine and udp's are on car (with stock alternator pulley)

If the battery and starter are good.....

Check all the battery connections and grounds. Make sure they are clean and tight.

[Logizyme]

Have you checked all frame grounds??
Major frame and body grounds have been checked. Replacement of the battery cable assembly also replaced the engine-to and body-to-battery grounds.


I think a Ford master tech would know what a stock harmonic balancer looks like.
Just because they have that designation doesn't mean they know their stuff. I'm shade tree level and I've had to fix things for friends after a dealer messed it up.
I never said I was a master tech. I only said I am a technician at a Ford dealer. In fact I have no Ford certifications, only because I'm too lazy to sit through online training for things I already know. I am plenty competent and many of the other certified techs come to me for help frequently. I will not claim to know everything and I learn new things everyday. Vortech I would appreciate if you kept such opinions on dealer service to yourself, perhaps you should try another dealer or just stick to servicing your own vehicles, but myself and the technicians at my shop are the best in the buisness with the best equipment, and while we're not perfect and no one is, our track record for sucessful repairs are far higher than your average forum surfer or backyard mechanic.



A higher output alternator may not be the solution. Most higher amp ones require the same if not a little more idle speed before they start charging.
I agree completely and this is a far less ideal way to attempt a repair. But in a situation where a tune is either not possible or desired this seems like the best bet for proper operation.



Have you checked to see what the actual AMP and volt draw is at idle?
I have listed all relevent voltage measurments taken. I have not performed any amperage measurments, and while this could give additional information, I believe it would only reinforce the conclusion we have already arrived at.



Even though that screw should not be adjusted. You can datalog the TPS to see if its in the correct range. Its possible the previous owner of the car screwed with it. This can be done with ANY Ford SCT X2 tuner and a laptop. I'll bet at least a few techs at your dealership have a tune on their cars and a hand held. I've used my X2 from my Marauder to log my dad's F-150 before.
I use IDS's and Genesis' at work which are far more powerful than the SCT tuners, and just to humor you I did monitor TPS voltage and % through the full range of motion and compared it to specification and it was normal. There was one other tech in my shop who had a tune on his focus before he totalled it last month, now I'm the only one, I have a tune on my P71 using an SCT and I would not use it for datalogging or code reading unless I did not have access to any of my other diagnostic tools.


Do you have a tune in your car?
No tune. Car is 100% stock at this time. PCM was updated to the latest calibration from Ford a few months ago.


Clean the idle control and the mass airflow system.
IAC, intake and MAF were all cleaned as part of basic maintenance shortly after I bought the car. KAM has been reset multiple times.

[Vortech347]

I never said I was a master tech. I only said I am a technician at a Ford dealer. In fact I have no Ford certifications, only because I'm too lazy to sit through online training for things I already know. I am plenty competent and many of the other certified techs come to me for help frequently. I will not claim to know everything and I learn new things everyday. Vortech I would appreciate if you kept such opinions on dealer service to yourself, perhaps you should try another dealer or just stick to servicing your own vehicles, but myself and the technicians at my shop are the best in the buisness with the best equipment, and while we're not perfect and no one is, our track record for sucessful repairs are far higher than your average forum surfer or backyard mechanic.



If I pay the premium for a newer vehicle with a full warranty am I a bad person for trying to utilize it? When its not out of warranty then yes. I will service it myself. :D

After all, you're posting on here for help even with your tools and massive knowledge base at your finger tips. Just goes to show sometimes the dealer doesn't know everything. :)

Hopefully you find the fix you are looking for. Could be something as simple as a bad connection on the battery terminal. I had to replace my factory ones because they started to corrode quickly and didn't have much material on them.

[martyo]

No tune. Car is 100% stock at this time. PCM was updated to the latest calibration from Ford a few months ago.

If you want to try a tune out to see if simply raising the idle would help, and are interested in keeping it simple I could put a tune on a chip instead of a handheld which would save you $250.

[Logizyme]

If I pay the premium for a newer vehicle with a full warranty am I a bad person for trying to utilize it? When its not out of warranty then yes. I will service it myself. :D

After all, you're posting on here for help even with your tools and massive knowledge base at your finger tips. Just goes to show sometimes the dealer doesn't know everything. :)

Hopefully you find the fix you are looking for. Could be something as simple as a bad connection on the battery terminal. I had to replace my factory ones because they started to corrode quickly and didn't have much material on them.

Your not a bad person for utilizing your warranty. Your a bad person for complaining that a free repair did not fix your car the first time. From a technicians standpoint there are many hoops to jump through and difficulties with any warranty repair. Many warranty complaints have to go through specific warranty diagnostic pinpoint procedures which are not always effective or accurate in diagnosis. Warranty labor times are far lower, anywhere between 25% and 90% of what they should pay, so we have to work quickly to maximize our effeciency. Warranty will not always pay for all the parts or labor we would like, just the bare minimum, which does not always make a complete repair. Many repairs don't have warranty labor operation codes so we must flag actual time and hope Ford does not decide to kick it back. To top it off we have to look up parts, labor to ensure their covered and get manager approval which we are not paid for our time.

I came here asking for help because I was looking for some Marauder specific knowledge that might have lead to a different conclusion, and did I get any useful info here? No. I got talk of idle screws and Ford tech incompetence.

I already said I had battery terminal corrosion damage which is why I replaced the battery cable assembly.

[Logizyme]

If you want to try a tune out to see if simply raising the idle would help, and are interested in keeping it simple I could put a tune on a chip instead of a handheld which would save you $250.

I appreciate the offer, but I am preparing some spring mods which will require a tune so I will tolerate this issue until then and reduce how often I drive it to prevent damage. I hear good things about your tunes but I was not particularly happy with my mail order tunes and was leaning twords a local dyno tune, but when the time comes I will consider you.

[Vortech347]

Your not a bad person for utilizing your warranty. Your a bad person for complaining that a free repair did not fix your car the first time. From a technicians standpoint there are many hoops to jump through and difficulties with any warranty repair. Many warranty complaints have to go through specific warranty diagnostic pinpoint procedures which are not always effective or accurate in diagnosis. Warranty labor times are far lower, anywhere between 25% and 90% of what they should pay, so we have to work quickly to maximize our effeciency. Warranty will not always pay for all the parts or labor we would like, just the bare minimum, which does not always make a complete repair. Many repairs don't have warranty labor operation codes so we must flag actual time and hope Ford does not decide to kick it back. To top it off we have to look up parts, labor to ensure their covered and get manager approval which we are not paid for our time.

I came here asking for help because I was looking for some Marauder specific knowledge that might have lead to a different conclusion, and did I get any useful info here? No. I got talk of idle screws and Ford tech incompetence.

I already said I had battery terminal corrosion damage which is why I replaced the battery cable assembly.

Its not free if I paid the premium for the warranty. :lol: Isn't it cheaper to get it first the first time rather than 3-4?

Myself and others gave you some great suggestions. Problem you need to realize we don't know EVERY little thing you've done. Nor do we see the car with our own eyes to verify certain things. :D I never said YOU were incompetent. I said some can be. Get some thicker skin. It was never my intention to hurt your feelbads.
:alone:

If it were me I'd see what the key on/engine off was drawing amp wise. See if anything is pulling more than it should.

You gotta admit. Its pretty humorous when the designer/maker/supporter comes to us lowly internet DIY'ers and shadetree mechanics for help. (your opinion) :flamer:

[RF Overlord]

OK, can we please stop the bickering and try to help the OP?

Logizyme, 2 things come to mind:

1) You said your idle speed is 500 RPM...that sounds low. I can't find the exact spec but I bet it's higher than that.

2) You said you have access to an IDS...can you not use that to raise the idle speed and see if that corrects the issue?

[Logizyme]

Logizyme, 2 things come to mind:

1) You said your idle speed is 500 RPM...that sounds low. I can't find the exact spec but I bet it's higher than that.

2) You said you have access to an IDS...can you not use that to raise the idle speed and see if that corrects the issue?

Its at 550-600, which seems to be the same as everyone else, and it idles smooth as hell. I also could not find a specfication. I can manually change it using IDS while datalogging but no I can't program the car to do it itself.


At idle my tach reads a hair above 500rpm.


I also monitored engine RPM to confirm accuracy of the tach. At warm idle RPM is between 550 and 600 - consistant with the tach readings.

Durring cold idle 700-800rpm I do not have voltage issues.

[Logizyme]

Its not free if I paid the premium for the warranty. :lol: Isn't it cheaper to get it first the first time rather than 3-4?

Myself and others gave you some great suggestions. Problem you need to realize we don't know EVERY little thing you've done. Nor do we see the car with our own eyes to verify certain things. :D I never said YOU were incompetent. I said some can be. Get some thicker skin. It was never my intention to hurt your feelbads.
:alone:

If it were me I'd see what the key on/engine off was drawing amp wise. See if anything is pulling more than it should.

You gotta admit. Its pretty humorous when the designer/maker/supporter comes to us lowly internet DIY'ers and shadetree mechanics for help. (your opinion) :flamer:

Since a warranty comes with a new car free of charge, and you can't really buy a new car without one, you must be referring to an extended warranty, which you paid "Premium" for yet you don't like taking your car to the dealer. got it.

Sure it's cheaper to fix cars the first time, but bueracrats running warranty administrations also think its cheaper to cut back parts and labor too.

What great suggestions? Not even half of the responders told me what their idle RPM was. And while this thread has confirmed my theory that this issue is normal operation and should be solved with a tune, I'm no closer to a repair than I was in my OP. I'm NOT trying to say I expected to find some magic repair that I had'nt thought of yet, but sometimes forums can contain some specific knowlege of a car that can help, this was just a hail marry. I DO appreciate the effort put forth by several responders, but too many responders did not even fully read the OP, did not respond to the questions written on the first post, asked me three times if I had UDP, then questioned wether I knew how to tell, then asked two more times if I had a tune, meanwhile I got people talking about idle screws, cleaning my MAF, and complaining about the service they recieve at Ford dealers, none of which helps me get to a repair.

You never hurt my feelings. People like your are just annoying. Starting arguements over stupid crap on forums.

Since I have no aftermarket electronics, and my car is not on fire, its pretty safe to assume amperage measurements will only confirm what we already know, and I'm done doing pointless diag for you.

Humorous? ehh, maybe a little ironic. But no not really. I said that I don't know everything, and I don't expect that you guys know the solution, but you might. I guess I'm a little more open-minded than you are.

[Vortech347]

Damn. You're right. My warranty was free. No way it was factored into the price of a new vehicle! Nothing in this world is free.

Doesn't need to have aftermarket electronics, its a 10 year old car. All sorts of problems can happen with OEM parts. Otherwise you wouldn't have a job. You are thinking in the box that everything Ford doesn't break. I've found numerous drains from things doing this. Including one on an 05 Mustang that kept killing the battery. The stock radio worked fine. But was pulling 4 amps for some reason with the Key OFF. Swapped out the deck and dead batteries were no more! This was after 5 dealer trips and 3 motorcraft batteries under warranty.

Also. calculate pulley speed to determine the RPM the alternator is getting. Find out the operating range of that alt. Ford has screwed up numerous times with alternator speeds. 03/04 Cobra's are horrendously overspun from the factory and cavitate and do not charge after 4500rpm.

My Marauder with the factory tune on it idles at around 600. With the aftermarket one it sits around 800, raised slightly because I have an underdrive crank. However when it was a stock crank and stock tune the lights would dim and the volt meter would slam down to 12 if the defrost was on and the headlights were too. If you have all the fancy tools you boast, reflash the PCM to get an 800 idle. If you still have issues, you've obviously got a gremlin somewhere that needs to be found the old fashion way with a volt/amp meter at the fuse box.

[jwibbity]

:popcorn::popcorn:

[rexjet]

My 2003 randomly quits at idle, usually in traffic, batt light will come on and engine may or may not quit. If I put it in neutral and bring up rpm, all is well. A little disconcerting if I'm ( or worse, wife) making a turn as the power steering goes out ( obviously) anyone else having this problem? OBD has no faults and dealer says everything OK .

Thanks

[RF Overlord]

Clean/replace the IAC.

[SeanyCash]

Are the voltage regulators attached to a new alternator? can't remember if they are or not...... otherwise something to check

[martyo]

My 2003 randomly quits at idle, usually in traffic, batt light will come on and engine may or may not quit. If I put it in neutral and bring up rpm, all is well. A little disconcerting if I'm ( or worse, wife) making a turn as the power steering goes out ( obviously) anyone else having this problem? OBD has no faults and dealer says everything OK .

Thanks


Clean/replace the IAC.


I concur with the 'lord.

[racorcey]

I've been off for a while due to various activities that seem to keep me away from enjoying the digest here. However, I saw this one, and had to throw my 2 cents into the fray....

I have experienced the same problems as the original poster ever since I owned my car, virtually new at 11k miles, and, in addition, the dealer having replaced the alternator way back.

Being an EE, I own a number of good Fluke meters. What I found was that the car's voltmeter is as accurate as crap. Where you should be observing the voltage is at the battery terminals. The car voltmeter is attached at the electrical block where it enters the interior. It is subject to severe voltage drop, not to mention the natural inaccuracy of the meter itself.

In actual load measurements, at the same 500-600 rpm, I found the following:

Inside voltmeter reading ~ 11.5 to 12 vdc; actually reading at battery of 12 to 12.5 vdc. Not charging, but not discharging either.

Inside voltmeter reading ~ 13 to 13.5 vdc; actually reading at battery of 13.5 to 14.5 vdc. This is within the normal charging range of 13.8 to 14.5 vdc.

Any higher inside voltmeter readings did not translate into much higher readings at the battery.

That difference in headlight output is the result of only about a 1 to 2 volt change...not really that significant, just annoying.

So, assuming all things being equal, I wouldn't worry about it too much. If you see a lot of light flickering and the like, that means that likely the internal regulator is getting a bit old.

I did find, however, that raising the idle to about 600 rpm gets rid of the majority of the problem. That's just the nature of the beast...an alternator is not a very linear device, and will put out 80% of it's full rating between 800 and 1000 rpm.

I hope this helps a little.

[RF Overlord]

As the car's voltmeter was never intended to be a precision instrument, I wouldn't call being off by only 0.5V "accurate as crap"...

[racorcey]

As the car's voltmeter was never intended to be a precision instrument, I wouldn't call being off by only 0.5V "accurate as crap"...

RF - it depends on your perspective....

While you're correct as far as the voltmeter not being intended as a precision device, as an engineer, I have a tendency to expect more - especially when the device says "VDO" on it.

In terms of real numbers, the "off" range is 0.5 to 1 volt average at best. In terms of percentage, based on a 13.8 vdc bogie, that would be about 4 to 8%. Not bad, but "crap" in my world. And that percentage becomes worse as you stray from the center point.

Point is, regardless of the accuracy, it's not measuring the real voltage seen at the battery, which is the more important detail of this thread.