Troubleshoot tips. Battery loosing voltage.

Mattias

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Hi there

Have been a proud Viper owner since 2006 when I bought my 2001 RT10 from the US and imported it to my location (Sweden, Europe). I have had a lot of fun with the car and it has never given me any trouble. I have used it only in the summer time from 2006 to 2010 when we got our first child. I put the Viper in a warehouse 2010 until times allowed me to use it again. Unfortunately, time runs fast and it took me 11 years (!!) before I got it out again a few weeks ago. Did oil/filter and battery change and the beast fired right up and everything seemed fine. a minute or two later the battery lamp came on. Power dropped slowly but I managed to take it home and did some further investigation.
Have searched the internet and especially this forum but didnt find a clear way to proceed...
Heres what I came up with, all tips are more than welcome.
- Checked battery - OK
- Checked all cables and connectors from/to alternator. - OK
- Did voltage drop test on + and -. - OK (0,02V)
- Checked the battery temp sensor. - OK
- Measured B+ and got the same reading as from the battery, slowly dropping
- Disconnected battery + pole when engine was running. Engine died directly (normally it should run if the alternator is ok, or??)

Thoughts, further ideas and questions
- Is there a fusible link from B+ (black/white wire) from alternator to the connector on engine bays left side? Can I measure if it is damaged with an ohm meter (will it burn right of??). My thinking is that if the alternator was charging, I would be able to measure 14V-something directly on B+ on alternator connector (or?)
- From what I have read, the PCM (Power control module, is it right mentioned..?) is located inside the ECU (Engine control module..?). Meaning this car does not have a common charging relay...? Has anyone went down this road? If yes, what would be my next step...? Im figuring, either buy a new alternator and swap it just to check if it helps. If not, then I wonder if there is a way to mount an external charge relay OR if the only way is to exchange the ECU?

Ideas of what has happened that damaged the charging system
- During the years in the warehouse, the Viper has had its battery from 2008 installed. It has been moved every other year or so. After a few years the battery was completely dead (didnt use any charger). If I recall it right, the first years I jump started it and drove it to move it. Last summer, I recall that we had to have the "jumper car" connected all the time to move the Viper. As soon as the jumper cables were removed, the Viper died. That time we had it running for 15 minutes, or more, connected to the jumper car. Could it be, that the longtime-jumper-running has damaged the charging system? My guess is that the old battery from 2008 had a short ciruit after some time in the warehouse.
- Have had european cars stored for a while before without any charging issues afterwards. Have had a corvette stored where the alternator broke down afterwards. Are alternator issues common on american cars?

All ideas, suggestions and support is more than welcome!
 
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Chad Spackman

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Suspicion of the alternator is reasonable. But so is ECU control over the charge current. See the following general description. Such a problem could be the field control wire(s) continuity from alternator to ECU, ECU itself, or alternator. A way to test the alternator is given with some cautions.

https://autoprollc.com/wp-content/uploads/2016/12/5-RemyTechnicalBulletin_July_web.pdf

Ground continuity to alternator is also critical of course
 
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Mattias

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Thanks alot Chad
This helps me further. Very useful info there. I have brought the alternator to a repair shop who should test it. On Monday I will check with them if it’s broken or what. Also if it’s not working I guess there is a separate “exchangeable plate” where “carbon sticks” (don’t know the proper name for them) and electronics can easily be switched. Or is it better to buy a complete alternator...? I guess I will have to order it directly from the US. If the alternator only exists in vipers, I guess it’s impossible to find over here. If there are other cars using a similar alternator. please let me know since it will increase my possibilities to find one quickly over here.
 

Chad Spackman

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RE: The link I posted regarding Chrysler generator testing: I have a gen 1 and the ECU doesn't have any control over charge current/voltage. Its done in a standard way with the regulator internal to the alternator and and 3 pins; (IG - ignition, S - Vsense, L - lamp, I only have the gen 1 shop manual. You have a gen 2 as I recall. If the alternator checks out, figuring out how the regulation is done is the next step.
 
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InTheZoneAC

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I would say swap to a new battery before pulling the alternator. Unless it was stored in a humid area the only things that may go bad for an alternator just sitting there is the bearings or cables, but you already checked the cables.

And check the serpentine belt and/or tensioner as the tensioner may have lost a lot of tension and the alternator may be sensitive to those changes
 

Chad Spackman

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Yeah, what is the state of the battery and belt? And you said you measured B+. With it running? Or would it not run unless jumped

More bits of info for you: Various part numbers for the same thing. And this is externally regulated as the description notes. So if it's not the alternator itself (and we know battery state. Oh you said battery is new...ok), there is another line of trouble shooting which we can go down...

BECK ARNLEY: 186-6444 1866444
CHRYSLER: 4848662AB
DENSO: 1210004360 1210004361 121000-4360 121000-4361
LESTER: 13924
WILSON: 90-29-5631 90295631

ITEM DESCRIPTION: ALTERNATOR
UNIT TYPE: DENSO
VOLTAGE: 12
AMPERAGE: 125
REGULATOR: EXTERNALLY
GROOVES: 7
PULLEY: SERPENTINE
SPECIFICATIONS: SMALL OVAL PLUG
WEIGHT: 14 LBS
 
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Chad Spackman

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Happened to talk with my viper tech last night. Referring once again to this: https://autoprollc.com/wp-content/uploads/2016/12/5-RemyTechnicalBulletin_July_web.pdf

The gen 2 has a “dual field” type A oval connector. One of the pins on that oval connector will be tied to 12v, probably through the ASD relay. The other will be pulse code modulated through the ECU. The ECU will switch this pin on and off to ground to create and average positive charge current through the alternator’s B+ terminal.

Given you have a good battery and a good belt, you can test the alternator as described in the link above by removing the oval connector and momentarily placing 12v across the 2 exposed field pins on the alternator’s oval connector while monitoring B+. B+ should rise above the battery voltage. If it does not, then bad alternator. If it does, then faulty oval connection to 12v or ECU, OR bad ECU.

I’ve heard of ECUs as being at fault with charging issues but considered it unlikely with such an isolated problem. But I’ve also heard the ECUs are sensitive to over voltage as might occur when jumped by another car. If at all possible, I jump a viper by NOT starting the other car. That takes short, heavy, jumper cables to cover cable IR losses.
 

Mattias

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Hey guys!
I can not Thank you enough for all the tips and input provided!
I am on a business trip this week but will try to dig into troubleshooting once I get back home on Saturday. I will keep you posted on the progress.
went by the shop that had the alternator earlier and unfortunately they had been unable to test it (due to the fact that the regulator is not inside the alternator).
So the tests described above should definitely help me forward.
Thanks a lot!
//Mattias
 

Mattias

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Answers to some of the questions above:
1. Yes, battery is ok/new
2. All belt tensioning etc is in good working condition.
3. I have a gen II viper. (Also have a service manual for genII)
4. Yes I did the measurement of b+ with engine running. Tested at idle and also at slowly rising rpm up to 2500rpm. B+ stayed the same. After a while it dropped slowly in the same pace, to the same level as the battery +.
5. The car starts fine with the battery charged. It runs without jumper cables etc. since the battery is new I can run for 1hour (I guess) before the injection etc. shuts down, if I don’t run lights, stereo, AC etc.
6. One thing I noticed the other day is that the AC is not working properly. Used to be ice cold. Now it’s not making any cold air. Just the fan that blows. But that might be normal after sitting in a garage for 11 years...
 

Chad Spackman

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All sounds good. Battery is surely in good enough shape to check alternator via the aforementioned method

Re:AC. The ECU controls the AC clutch and in tandem, the ECU also controls the radiator fan when AC is called for. That fan draws several amps. It is quite plausible that if the ECU is trying to call for the alternator to supply charge current, and sees that voltage is not rising, it won't allow the AC and fan to be enabled which would more rapidly drain the battery if allowed. So I'd tick these things off one at time; alternator first. You may find the AC comes good with the battery charge issue addressed. If not, you can check refrigerant levels with an AC recharge can. The Viper will take R134a refrigerant and if pressure has fallen below an acceptable level it won't engage the AC clutch nor the fan until properly recharged.
 

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