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#3615514 - 04/20/17 05:26 PM 1999 Mercury Grand Marquis Intermittant Alternator
jgedmin Offline
Stranger

Registered: 04/11/17
Posts: 5
Loc: New Lenox IL
Hello. I’m new here, but I’ve been lurking around a lot lately for info on a car that has been really giving me a hard time. What started off as a quick alternator swap has now turned into a month long exploratory surgery that has still not turned anything up.

The car is a 1999 Mercury Grand Marquis LS 4.6L with about 175000 miles. Completely stock.

There were a couple issues happening all at once, and all have been remedied expect for the intermittent alternator operation.
Right off the bat, the alternator was dead… brought it to AutoZone and verified this on their bench test. I picked up a reman alternator and installed it. It still wasn’t charging, so I brought it back. Tested on the bench and it failed. Ok… chalk that up to bad luck. Reman alternator #2 goes in. Verified the power cables, fuseable links, ground cables and straps are all in good order with no shorts. Battery also checked out fine with load tester. The car seems to be working fine for about two weeks, then it cuts out again. This time it has a P1299 overheating code. Remove and bench test the alternator, it checks out ok, but for sure it wasn’t working fine on the car so AZ swapped it out for me with a “NEW” alternator. Everything appears ok now, and I addressed the coolant leak that caused the low coolant. Replaced thermostat, gasket, RTV’d the crack in the t-stat housing (for now…) and new surge tank pressure cap and new coolant. The P1299 code I guess kicks in a high temp protection mode that turns the fan on high speed, even at idle. I noticed the current draw was pushing 90A even at idle when the headlights were on and the fan kicks into high speed, so I figured if this has been happening, sure it will kill the alternator. I pulled the fan high speed relay to keep it from overworking the alternator at idle if it did overheat again. I personally drove the car for the next week and a half with no issues until it dropped out on me on my way to work. The radio dropped out, then the dash, and it was running very rough, but luckily I made it to work. I checked the voltage… no output from the alternator. I jumped it at lunchtime and it was now charging 13.5V… drove it for 20 minutes and figured I would make it home. Went out after work, started the engine… 11.5V. I threw my laptop in the trunk and slammed the trunk and heard the engine whine a bit and magically it was charging 14.0V. Drove it home with no problem. Brought the alternator back to autozone, tested out ok but still swapped it out with another “NEW” alternator. So now with alternator #4 still acting intermittently, I decided it was time to get a good visual look at the power and ground cables. Pulled them all out, unwrapped, and they all look great. While I was at it, I found a random butt splice in the harness on a green w/ red tracer wire (same color wire that goes to ‘I’ terminal on alternator! I also found one of the pins on the alternator had been stretched out by a multimeter probe… obviously a rookie had been trying to work on this thing at some point. With the engine running I was able to get the alternator to fire up by pushing in on the connector so I pulled the pin out of the connector, squeezed it back together, reinstalled and boom… 14.3V. I figured that I finally found the problem so I pigtailed the alternator plug with a new one from AutoZone and replaced the random butt splice with a soldered and shrink wrapped joint. All the wiring was back to how it should be. I even replaced the battery terminals just for good measure. Fairly confident the “NEW” alternator is functional. It shows battery voltage at the "A" pin, but the "I" pin voltage varies from 0-10V which seems odd. The schematic I have shows this coming from/going to the charge indicator on the instrument cluster. I looked into getting a cluster, but I can only find junk from ebay that I’m not willing to spend $100 on a cluster that a.) might not be any good to begin with or b.) might not be the issue.

I'm going to try wiring the "A" pin direct to the battery, and run the "I" pin through a test light to the battery and see if that gets the alternator to fire up...

Any ideas or suggestions would be appreciated.

Thanks,

Jason

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#3615602 - 04/20/17 06:17 PM Re: 1999 Mercury Grand Marquis Intermittant Alternator [Re: jgedmin]
bigROC209 Offline
Over the Hill

Registered: 04/11/12
Posts: 2163
Loc: Stockton, CA
I had similar symptoms on my Tahoe. Ended up being the ignition.
_________________________
2002 Marquis LS Precision Trac, new engine @ 125K, GT Wheels, HP tires, SCT Xcal 2, 91 Octane tune from BOC, Traction Locker w/Ford Racing clutches, 3.55's, Police D/S, Ford Racing IM @114K, 75mm TB, Trick Flow Plenum, Ziptube, GT MAF, P71 Rear Coils, Summit Racing UDP's, HPP Sway Bar, Gas KYB's, J-Mod, 2-1/4" Dual Exhaust, Thrush Glasspacks & 18" tips, MSD COPs, NGK TR55's & Grey Injectors, Pinstripe removed, Disc changer, 2400 watt Pioneeer amp & 6x9's, Kicker Comp VR 10" DVC subwoofers.

Bottle in the trunk coming soon!


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#3615658 - 04/20/17 06:33 PM Re: 1999 Mercury Grand Marquis Intermittant Alternator [Re: jgedmin]
GrandMarq9807 Offline
Over the Hill

Registered: 05/10/10
Posts: 3933
Loc: Virginia
You are on right track, the I terminal excites the alt, won't charge if this circuit is open or shorted to ground... The test lamp to battery will bypass all the normal circuitry, unless shorted should definitely charge...
_________________________
1998 Grand Marquis LS. 77K mi.
2007 Grand Marquis GS. 78K mi.
1996 F-150 XLT 5.0 E4OD 189K mi
1988 Turbo Coupe 331 AOD & 3.73
1969 Fairlane Cobra 428CJ 4-Speed
1972 Comet GT - 306 C4 <<< Under Hood



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#3615994 - 04/20/17 11:58 PM Re: 1999 Mercury Grand Marquis Intermittant Alternator [Re: jgedmin]
jgedmin Offline
Stranger

Registered: 04/11/17
Posts: 5
Loc: New Lenox IL
Update...

I fired it up again after work... still no alternator. I decided to bang on the instrument cluster for the heck of it, and it would fire the alternator up for a second or two. Then I started pushing on things... when I push on the little display below and left of the steering wheel for the TRAC CTL light, the alternator fires up as long as I'm pushing it in. I guess I'm ripping that out tomorrow to look for a loose or corroded connection or something. Why some pea-brained engineer thought running the alternator through the cluster is beyond me. Now I almost feel silly for spending an hour writing up my first post :-/

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#3616314 - 04/21/17 10:02 AM Re: 1999 Mercury Grand Marquis Intermittant Alternator [Re: jgedmin]
1 Adam 12 Offline

Over the Hill

Registered: 07/04/01
Posts: 1748
Loc: Glendale, AZ
I'm sure you have another issue going on, but I thought I would throw my .02 in and tell you what you've already discovered with the dead out of the box first one: Autozone electrical parts, including Alternators, are trash. Someone did an article awhile back who saw how they "remanufacture" the items. I suggest getting a Motorcraft unit next time if you can.
_________________________
~Chris~

2007 Smokestone LX HPP - 17.5K miles 1/2016
'05 PI Airbox/Ziptube, BOC 91 Octane Tune, PowerSlot F&R Rotors, Raybestos Police Patrol Pads F&R, 260A Mechman Alt w/OAD & Big 3, Ported Intake Plenum, Adco Front & Rear Swaybars, Metco Control Arms, Metco Watts Link, KYB Police Struts/Shocks F&R, Arnott HPP-spec "Limo" rear bags, Walker Quietflow 3's w/Resonator delete, 3.55 TracLoc conversion, 180 T-Stat, 22C Plugs, GY Eagle Sport AS Tires, Kenwood DNN992 Nav Headunit & Speakers, Viper 5901 Alarm/Remote Start & Street Guardian Dashcam

MY ARTICLES

Pulleys for Police Alternators | Replacing Door Weather Barriers | Exhaust Dampers and their importance

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#3616586 - 04/21/17 03:04 PM Re: 1999 Mercury Grand Marquis Intermittant Alternator [Re: jgedmin]
GrandMarq9807 Offline
Over the Hill

Registered: 05/10/10
Posts: 3933
Loc: Virginia
Originally Posted By jgedmin
Why some pea-brained engineer thought running the alternator through the cluster is beyond me. Now I almost feel silly for spending an hour writing up my first post :-/

Basically they've been wired in that configuration since the advent of electronic regulators... The lamp circuit triggers the alt and has a parallel resistor that's supposed to turn on alt if lamp fails, but if there is a bad connection all bets are off... Originally the resistor was 500 ohms but I noticed in my '98 EVTM it had been reduced to 390 ohms...

Mechanical regulators had built in resistors that were in relay circuits, one of the relays pulled a contact open to turn light off when alt was charging...
_________________________
1998 Grand Marquis LS. 77K mi.
2007 Grand Marquis GS. 78K mi.
1996 F-150 XLT 5.0 E4OD 189K mi
1988 Turbo Coupe 331 AOD & 3.73
1969 Fairlane Cobra 428CJ 4-Speed
1972 Comet GT - 306 C4 <<< Under Hood



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#3620137 - 04/25/17 01:22 AM Re: 1999 Mercury Grand Marquis Intermittant Alternator [Re: jgedmin]
jgedmin Offline
Stranger

Registered: 04/11/17
Posts: 5
Loc: New Lenox IL
Thanks for the sanity check guys. After opening up the instrument panel I found some more shotty wiring. Someone really took some effort in hiding it, so it has obviously been in for this problem in the past. Someone bypassed the wire that usually runs to the alternator from the cluster... which is why I was getting strange readings on it. The "new" wiring checked out, but I don't trust the connection at the cluster. After removing the shotty wiring, I ended up splicing a wire, diode, and indicator light into the keyswitch power that runs to the fuel pump relay and ran that to the "I" terminal on the alternator directly. So far no problems and consistently charging 14.2VDC... even with cluster removed from the car.


Edited by jgedmin (04/25/17 01:23 AM)

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