Voltage drop and idle speed drop during warm up

[robrike1]

Hi,
I am stumped by a rather odd issue. My 2004 F250 6.0 has a drop in voltage from 13 volts to roughly 11.3 during a cold start warm up. I know this is the glow plugs cycling off and on however it also causes my idle to drop up a d down as it does this. Maybe 400rpm or so.

I was thinking the cycling of the glow plugs only lasted 2 minutes on a cold start, say 30 to 40 degrees type cold start. I'll plug it up for a few hours below 35 degrees just to be kind to the engine.

Alternator puts out rouggly 13.5 volts to battery at idle. I just replaced both batteries with Walmart group 65 850CCA. Prior to that I was having very low charge if left undriven for 3 or 4 days and voltage drop would go to 10.3 volts when plugs cycled on with engine running. Interior lights dim a lot when plugs are cycling so now wondering if it could be a grounding issue somewhere among the many grounds causing this weird rpm drop and lights dimming.

I have also noticed cycling lasting 3 to 5 minutes instead of the 2 minutes I've heard is supposed to happen. I'll clean and check my grounds but could a failing GP relay or controller do something like this and is the 2 minute cycle time set in stone? It rarely goes below 20 degrees here in Eastern part of TN. Everything on truck is stock including the pitiful 110amp alternator.

Just wondering if I'm on right track with grounds? Batteries were definently going so replacing them was a bit helpful in that voltage doesn't drop to 10 volts. I have an Edge cts monitor. FICM voltage is always a solid 48 volts even when things drop down with the cycling GP's. I'm thinking about a higher output alternator like a Bosch 140amp. I don't have any crazy high current draw items on the truck.

Thanks for any tips or suggestions. I searched for this issue but found nothing saying idle dropped when lights dimmed from the cycling.

Robert

Sent from my SM-G955U using Tapatalk

 

[TooManyToys]

Depending on the alternator, several different voltage regulators could have been installed. If the VR is one with a higher voltage setpoint than 14.4v, even with a lower output current alternator, you could get the GPCM to cycle on and off due to the voltage.

The details from the service manual how the system works, and three graphs showing the voltages you can expect from different setups you've mentioned.

 

[robrike1]

Thank you for that information. I'll have to check into that. Perhaps it is time for a new alternator or at least a very thorough check of my present one. I think a higher amperage alternator is going to be in my future just because.

Sent from my SM-G955U using Tapatalk

 

[robrike1]

I've had very little time to deal with knocking this issue out but what I have found so far is that my frame to body ground strap was green and both eyelets snapped off while unbolting it to replace with a cable. I had tried running a battery jumper cable from the passenger negative post to the frame and at that time after starting the surging wasnt quite as bad but was still fairly noticeable once everything stabilized which takes 4 to 5 minutes before idle quits dropping in unison with voltage dropping and rising. I'm assuming glow plugs cycling longer than they should.

Once the cycling stopped I measure voltage at battery and alternator and never got higher than 13.1 volts from alternator post of either battery as alternator was charging. Today I replaced the cable that was corroded and also undid the passenger negative to engine connection and cleaned it with wire wheel and coated in di-electric grease and reinstalled. Did not get to either frame ground yet. I didn't get to drive it as I am at work and won't get off till tomorrow morning.

I would think after a cold start once the alternator kicked into action to charge I should see voltages higher than 13.1. I even tried 2 different voltmeter just to be certain. I'll clean those frame grounds off the 2 battery negative terminals and see where I'm running but I have a feeling a new alternator is coming. Never get a battery light and it does work with KO-EOFF.

I'll post more when I have those other grounds cleaned up. If anyone thinks my alternator is on the way out based on lack of 14+ volts from alternator post I'd love to here from you. The 13.1 volts was with my engine steady at 1250 rpm also.

Thanks,

Robert

Sent from my SM-G955U using Tapatalk

 

[6_Riders]

I've had very little time to deal with knocking this issue out but what I have found so far is that my frame to body ground strap was green and both eyelets snapped off while unbolting it to replace with a cable. I had tried running a battery jumper cable from the passenger negative post to the frame and at that time after starting the surging wasnt quite as bad but was still fairly noticeable once everything stabilized which takes 4 to 5 minutes before idle quits dropping in unison with voltage dropping and rising. I'm assuming glow plugs cycling longer than they should.

Once the cycling stopped I measure voltage at battery and alternator and never got higher than 13.1 volts from alternator post of either battery as alternator was charging. Today I replaced the cable that was corroded and also undid the passenger negative to engine connection and cleaned it with wire wheel and coated in di-electric grease and reinstalled. Did not get to either frame ground yet. I didn't get to drive it as I am at work and won't get off till tomorrow morning.

I would think after a cold start once the alternator kicked into action to charge I should see voltages higher than 13.1. I even tried 2 different voltmeter just to be certain. I'll clean those frame grounds off the 2 battery negative terminals and see where I'm running but I have a feeling a new alternator is coming. Never get a battery light and it does work with KO-EOFF.

I'll post more when I have those other grounds cleaned up. If anyone thinks my alternator is on the way out based on lack of 14+ volts from alternator post I'd love to here from you. The 13.1 volts was with my engine steady at 1250 rpm also.

Thanks,

Robert

Sent from my SM-G955U using Tapatalk

13.8~14.0 would be normal. Make sure the charge cable, at the alternator, nut is tight. Also double check the charge cable, at the battery, for corrosion.
Upgrading the battery to frame to engine ground cable on the passenger side.... And upgrading the battery to frame ground and adding a block to frame ground on the driver's side battery.... These help. I ran a new (additional) cable from the alternator to the driver's battery and upgraded my positive cables too.
I think the alt to bat and all/any ground cables are the best things to do.

Sent from my Redmi Note 9 Pro using Tapatalk

 

[TooManyToys]

That's a more poor condition cable than I would ever imagine.

Cold, the alternator post to alternator frame reading should be in the 14.2 to 14.4v reading. It can drop per design to 13.8v with the underhood heat.

Putting a clamp-on ammeter on the glow plug fusible links should show the ON timing as well as checking a glowplug votage, but you are reporting a longer than normal time. Three minutes is the program maximum, but in NJ, I don't ever remember seeing that.

Any chance you have dual alternators?

 

[robrike1]

That's a more poor condition cable than I would ever imagine.

Cold, the alternator post to alternator frame reading should be in the 14.2 to 14.4v reading. It can drop per design to 13.8v with the underhood heat.

Putting a clamp-on ammeter on the glow plug fusible links should show the ON timing as well as checking a glowplug votage, but you are reporting a longer than normal time. Three minutes is the program maximum, but in NJ, I don't ever remember seeing that.

Any chance you have dual alternators?

I have the single alternator setup. After replacing the crumbled ground cable yesterday at work and cleaning the passenger negative post to engine ground thoroughly I woke up this morning and went out to start it and to my surprise there was still a slight hunt during idle but here is the surprising part, the surge or hunting stopped after a couple of minutes with my coolant temp at 84 degrees Fahrenheit. Usually that wouldn't show signs of stopping till 140 degrees at least. Voltage on my Edge CTS showed at between 12.9 and 13.2 from there on out till I arrived at home.

I am going to test alternator voltage properly later today with a voltmeter and report back my results. I think I have made quite a bit of progress on this issue just by checking body to frame ground and cleaning passenger negative to engine ground thanks to info on this forum. I still have passenger negative post to frame to clean and then driver negative post to frame but so far I am pretty positive feeling about the results this AM.

Thanks to everyone for all the valuable info on this site. I bought this truck used in 2014 (2004 F250 King Ranch) with 104,000 miles on it. Dealer had replaced blown head gaskets and oil cooler before my purchase and it has been pretty trouble free since. They also replaced alternator then because 2 days after purchase battery light was coming on. Aside from a rear end that was covered under extended warranty this has been my first real issue with odometer at 136,000 now.

I'll update this once I get voltmeter readings and again when I get those other grounds cleaned up.

Robert



Sent from my SM-G955U using Tapatalk

 

[TooManyToys]

Your reported OBD2 voltage can be up to 0.5v lower than at the alternator/batteries, depending on the channel.

If your one ground strap were really bad, you would have started on most, if not one, battery. Without ground on the other battery, it's just a positive terminal connection with no battery contribution.

 

[robrike1]

Hey,
sorry I have not posted more info. I came down with walking pneumonia last week and with it being so cold here I have not messed with the truck. Hoping this weekend if it doesn't rain to clean my 2 frame rail grounds up and see where I am at then. So far with the new frame to cab ground strap and the ground from passenger battery to engine block I can tell a big difference. Still get hunting where alternator kicks in and out while glow plugs cycle but the gp stop cycling after 2 to 2.5 minutes instead of taking 5 or 6 minutes back before my ground repair and cleaning.

Will update as I get into it further. Really flirting with idea of a newer more powerful alternator as well. Just for good measure.

Thanks,

Robert

Sent from my SM-G955U using Tapatalk

 

[robrike1]

Well, I can update this thread finally. I am fairly certain my problems were alternator related all along with grounding issues a secondary factor. Last night I was moving my truck to the back yard to load some brush up to haul off and noticed my Edge Monitor was showing 11.5 to 11.8 volts several minutes after truck had been running. Took a voltmeter to alternator terminal and it too showed 11.6 Volts. Weird thing is battery light wasn't on. Maybe there is a threshold it hadn't quite hit to trigger light. Light comes on on KOEOFF. I'm gonna try my luck with the Bosch 140 amp alternator. I'm thinking maybe the voltage regulator has been on the fritz awhile, mostly when cold causing all the cycling of alternator on and off.

Hopefully new alternator is the cure. Will let you guys know after I get it.

Thanks,

Robert

Sent from my SM-N986U using Tapatalk

 

[robrike1]

Got my Bosch 140 amp alternator installed. Truck is doing great presently. No crazy surges similar to ac compressor kicking in and out. Those are gone. Voltage after startup and glow plugs off showing 13.5 at idle and 13.9 to 14.2 while driving. I've got the overdrive pulley on order. Had another issue with glow plugs not coming on last 2 starts with old alternator. I reseated gpcm plugs while swapping alternator and so far so good.

I really think old alternator voltage regulator was failing. Don't know if that can cause trouble for PCM and mess with signal to glow plugs. I'll keep an eye on glow plug operation. GPCM is new so makes me wonder if problem was alternator even though it is off during GP operation or wiring issue somewhere. I ohm'd all plugs and had 0.7 ohms roughly on all of them so they check out good.

Hopefully done with all the electrical issues. Time will tell.

Robert

Sent from my SM-N986U using Tapatalk