Since I have found the voltage difference between the engine terminal and the battery to be 0.3v consistently, does it mean that my long positive cable that runs from the alternator to the DME and battery under the car to be fine?

If after I replaced the alternator to starter hardness and still it doesn't fix the problem, would the only possible culprit be left on the engine ground strap or the DME?

The car has been starting very quickly and normally every time hot or cold. Could this be an indication of a good starter and ground?

Let me list out the possible problems with my low voltage symptom.
1. battery (new)
2. alternator 997-603-012-06 TIP (new)
3. regulator (new, comes with item 2)
4. alternator pulley (new, comes with item 2)
5. alternator to starter hardness 996-607-03-204
6. engine ground strap 996-607-034-01
7. battery ground lead 997-611-09-100
8. alternator to battery, the long positive cable that runs under the car (I'm guess this is the 996-612-044-00?)

My question is, is the DME located between the alternator to the battery cable (item no.8)?

My car's voltage now ever sees higher than 12.5v during driving whether it is highway or city. Is there anything other than the 8 items listed above that could go wrong to give me that constantly low voltage of 12.1-12.5v during driving?

Cheers

James

 

Having spent hours of research and jacking the car up and down, I will call this my last report because I've had enough of test car and that’s it if I still cant get it fixed by next week.

Last night, I carried out the final voltage and resistance tests with cold & hot engine using the multimeter based on the 996tt electrical diagram attached.

Let me list out the possible problems with my low voltage symptom.
1. 85A battery (new)
2. Bosch alternator 997-603-012-06 TIP (new)
3. regulator & alternator pulley (new, comes with item 2)
4. alternator to starter hardness 996 607 03 204 (no.28 ) Test 1
5. engine ground strap 996 607 034 01(no.36) Test 2
6. –ve battery lead 997 611-090 00 (no.1) Test 4
7. +ve battery lead 996 612 090 09 (no.4) Test 4
7. long cable from starter to ECU 996 612 044 00 (no.19) Test 3
8. engine terminal to transmission terminal 996 607 033 02 (no.24)

So I focused on testing on no.24, 28, 36, 1 and 4. Not, 19 because I cant actually see it. According to the diagram, I assumed no.29 = +ve engine terminal and no.25 = transmission terminal.

Test 1 (to prove alternator to starter hardness no.28 is OK even with the engine HOT)
With the car hot or cold, battery +ve & -ve unhooked
Resistance @ 200 Ohm setting
+ve engine terminal (no.29) to +ve transmission terminal (no.25) = 0.7 Ohm
+ve engine terminal (no.29) to +ve battery lead (no.4) = 0.7 Ohm
+ve transmission terminal (no.25) to +ve battery lead (no.4) =0.7 Ohm
-ve airfilter bolt to –ve battery terminal lead (no.1) = 0.7 Ohm
-ve airfilter bolt to –ve chassis /door latch= 0.7 Ohm
-ve airfilter bolt to –ve Hydraulicoil body/engine/gearbox/alternator case = 0.7 Ohm
–ve Hydraulicoil oil body/engine/gearbox/alternator case to –ve chassis = 0.7 Ohm

Voltage
+ve directly from alternator (I fitted an independent lead from the alternator)
-ve Hydraulicoil oil body / engine / gearbox / alternator case
=14.0v (hot/cold)

+ve directly from alternator
-ve airfilter bolt / chassis / door lock
=12.2v (hot) or 12.8v (cold)

+ve transmission terminal
-ve engine / gearbox / alternator case
=14.0v (hot/cold)

+ve transmission terminal
-ve airfilter bolt / chassis / door lock
=12.2v (hot) or 12.8v (cold)

Results
1. Voltage always 14.0v if –ve are measured from engine/gearbox/fuel filter casings. Voltage always 12.2-12.8v if –ve are measured from chassis (airfilter bolt/door latch/chassis metal).
2. But, resistance of no.28 is the same hot or cold, it seems to be in good order.

No.28 seems to be fine and the problem seems to be on the chassis ground. So, I conducted Test 2.


Test 2 (to test engine ground cable, no.36)
Hooked up 2 thick truck-grade jump leads from engine case (-ve) to chassis (ground) and door latch (ground) = nothing happened to all voltage measurements (same as unhooked)

Cold measurements, idling
At battery 12.9v (cold)
On dash voltmeter 12.9v
+ve engine terminal to airfilter bolt 13.2v
+ve directly from altern. to altern. case / Hydraulicoil oil tank body / fuel filter 14.0v

Hot measurements, with aircon and headlights on:
batt multimeter 12.1v (hot)
dash voltmeter 12.1v
engine terminal 12.4v
alternator terminal 13.9v

Results
Adding extra engine to ground leads did not do anything or helped the stock engine ground cable. So, no.38 is in good order, too.

Test 3 (to test no.17 & 19)
COLD voltage
+ve alternator terminal to airfilter bolt (chassis ground) = 13.2v
+ve batt to –ve batt = 12.9v

HOT voltage
+ve alternator terminal to airfilter bolt (chassis ground) = 12.4v
+ve batt to –ve batt = 12.1v

Results
No.17 & 19 are using or losing 0.3v because there is always a 0.3v difference between the back of the engine to the front of the car. I can say theses 2 long cables are in good order because how far voltage has to travel here.

Test 4 (to test no.1 & 4, hot and cold engine)
Took them off the car, measured resistance before cleaning them and they never got hot even after 30 mins of driving. Always 0.6 Ohm

Results
No. 1 & 4 are in good order.


It seems to me all the cables are in good order. Who can help me to solve this my low voltage problem?

a million thanks

James :worship: :worship: :worship:

 

You've pretty much gone thru the entire charging system by the looks of it. Does the battery show 12 VDC with the power off after a long drive with the lights/AC on? If the alt. voltage sufficient to keep the battery charged, you could just monitor it and live with it for now. If this is not an option, pull the alt. have it checked at an electrical speciality shop. Was intesting to note that you mentioned 14 volts at the VR contacts with the wire you added but only 12 volts (approx.) with connector installed.

 

Yes, the battery shows 12 VDC always after a long drive and short drive with full load, too. I used to see 12.6-12.4 when the battery was brand new 3 weeks ago and it has been dropping and stopped at 12 VDC. The reason why I cant drive the car for much longer without this problem fixed first is because when the voltage is as low as 12v, the oil pressure gauge shows much lower values, sometimes lower than 1 and I am really concerned about the unsolved issue.

I am a DIYer with limited tools at home and at where I live, there is no shop that will bench test my new and old alternators.

Thank you very much for your reply and help!

James

 

niceguy,

I going to assume you read the post "low charging voltage" 5-27-13 on Rennlist related to your charging issue. May be of some interest to finding out what's causing your low charge voltage.

 

Thanks mate, I am now enjoying the read. I will report back after I have read it.

 

Niceguy,

What is the status of your voltage regulation issue? Did you remove and replace the voltaqe regulator? Just curious to find out if you resolved the problem.

 

Hi Gillrich,

Thanks for your concern. In the end, I realised it was only the problem with the engine to chassis ground because I could see that it was loose on the engine end. So, I replaced that and I am seeing 14v cold start and always around 13.8v with headlights n air con on.

James