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niceguy

My last report

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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) 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

post-31469-0-34465600-1369985111_thumb.j

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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) 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

Interesting testing sequence; that said, your alternator voltage looks too low at times, which is indicative of a weak voltage regulator or diodes. I would pull the alternator and have it load tested at either an alternator repair shop, or a parts outlet that do these tests for free, if for no other reason than to eliminate it.

You also have cable issues based upon your measurement of 0.7 ohms (this test should have been run with the cable ends disconnected so you are only looking at the cables), the cable resistance is also too high, which is a very common phenomenon on these cars (if memory serves, Porsche released a TSB on the subject as well as updated parts). Cable resistance should be much lower:

The resistance, R, of a length of wire is described by the expression:

  • [*]R = ρL/A

where

  • [*]ρ = resistivity of the material composing the wire,L = length of the wire, andA = area of the conducting cross section of the wire.

On that basis, a new "0" AWG battery cable would have a measured resistance level of 0.09 ohms over a length of 1000 feet, you are seeing 0.7 ohms across a couple of feet.

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Hi JFP,

Thanks a lot for your informative reply :)

I think I might have made a big mistake in my original post. The resistance across all those no. 1, 4, 24, 28, 17 and 19 should be 0.07 Ohms, not 0.7 Ohms. It is because before I started the 4 tests that I conducted, I measured the resistance of my newly bought three-meter-long 4 gauge cable and the resistance was the same as all those in the car, almost close to none. I know it would have been better to have measured each cable end disconnected, but I simply do not have the skills and knowledge to take each of them out. But, however, I did disconnect no.1 (battery -ve lead) and no.24 (alternator to starter lead) to measure resistance on their own and the results were the same as those measured connected.

My main point is that with the engine running at idle with full load (a/c on, all lights on), I did still see the full 14.0v when I measured from the back of the alternator to -ve alternator case, engine case, transmission case and fuel filter case whether the engine was hot or cold. The only time I saw 12.0-12.8v was when I measured the back of the alternator to the car's chassis, such as the airfilter bolt, the actually chassis, the cross member under the car and the silver door latch, all only showed 12.0-12.8v. I think I located the engine to chassis ground, no. 36, and the reason why I did not have any measurement for that was because my hands and tools could not reach it even with the wheel off and car on jack stand. But, I could see about 1/3 of that cable's plastic shield had been sliced open for some unknown reason. Does this sound like a bad engine to chassis ground to you?

Moreover, my car starts every time and the engine turns quickly every time.

Could you advise if no. 36, the engine to chassis ground is the one shown in the attachment? If so, how can I get to the top of engine bolt of that ground cable from under the car? Or, can I only approach it from the top without lowering the engine? 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 help again.

James

post-31469-0-49189400-1370028182_thumb.j

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Hi JFP,

Thanks a lot for your informative reply :)

I think I might have made a big mistake in my original post. The resistance across all those no. 1, 4, 24, 28, 17 and 19 should be 0.07 Ohms, not 0.7 Ohms. It is because before I started the 4 tests that I conducted, I measured the resistance of my newly bought three-meter-long 4 gauge cable and the resistance was the same as all those in the car, almost close to none. I know it would have been better to have measured each cable end disconnected, but I simply do not have the skills and knowledge to take each of them out. But, however, I did disconnect no.1 (battery -ve lead) and no.24 (alternator to starter lead) to measure resistance on their own and the results were the same as those measured connected.

My main point is that with the engine running at idle with full load (a/c on, all lights on), I did still see the full 14.0v when I measured from the back of the alternator to -ve alternator case, engine case, transmission case and fuel filter case whether the engine was hot or cold. The only time I saw 12.0-12.8v was when I measured the back of the alternator to the car's chassis, such as the airfilter bolt, the actually chassis, the cross member under the car and the silver door latch, all only showed 12.0-12.8v. I think I located the engine to chassis ground, no. 36, and the reason why I did not have any measurement for that was because my hands and tools could not reach it even with the wheel off and car on jack stand. But, I could see about 1/3 of that cable's plastic shield had been sliced open for some unknown reason. Does this sound like a bad engine to chassis ground to you?

Moreover, my car starts every time and the engine turns quickly every time.

Could you advise if no. 36, the engine to chassis ground is the one shown in the attachment? If so, how can I get to the top of engine bolt of that ground cable from under the car? Or, can I only approach it from the top without lowering the engine? 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 help again.

James

#36 is a chassis ground strap, which unfortunately is not accessible from underneath the car. To get at it from above requires pulling some components from the engine, such as part of the intake system.

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Hi JFP,

Thank you for your reply again. Do you think my problem now sounds like the chassis ground strap? Can I go ahead and replace it with two 4 guage cables and try if it solves the problem before ordering one from the factory?

Is there anywhere that I can add more chassis ground strap to the engine and chassis? Will it bring any benefit to the seemingly small stock chassis ground strap?

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Hi JFP,

Thank you for your reply again. Do you think my problem now sounds like the chassis ground strap? Can I go ahead and replace it with two 4 guage cables and try if it solves the problem before ordering one from the factory?

Is there anywhere that I can add more chassis ground strap to the engine and chassis? Will it bring any benefit to the seemingly small stock chassis ground strap?

As mentioned earlier, even Porsche recognized the ground straps and other cables were problematic, they are common weak point on these cars. Replacing a questionable cable is always a good idea, they cause no end of issues (codes, strange MIL lights with no basis, poor hot starts, diming lights, weird audio issues, etc.). We have found that just replacing the questionable cables is sufficient to putting an end to the problems; we have also never had to add any extra cables.

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I plan to have a go in replacing the chassis ground over the weekend. I am rather weak at DIY. The best I managed was to replace the alternator with my limited tools. Could you please advise what other tools I will need to remove enough in order to reach the chassis ground?

First, I tried searching on the Internet for 30 mins but did not find any post about how to DIY removing the engine/chassis ground on the 996tt. I can remove the airfilter box and the black y-shaped intake manifold but everything on the passenger side of the silver hydraualicoil bottle seems to be new to me. Do I have to remove the black engine oil filling tube? What are those components sitting below the engine oil filling tube that I will need to remove?

Thank you very much for your reply and assists again :notworthy: :notworthy: :notworthy:

James

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Here's a view of the ground strap with the engine remove. I think JFP is talking about this one...(correct me if I'm wrong). The frame attachment can be seen above the right turbo and the other end is beside the fuel pressure regulator just under the air pump. I think it is possible to reach and to facilitate the job you should lower the engine about 4 inches .... Lowering the engine is easy especially if you got access to a floor jack. See attachment....

I did not read all your post on Rennlist and 6speed but have you check the power consumption at rest which is suppose to be .6 amps maximum ?

Secondary air pump removal can be seen in the repair manual page 641.

post-29683-0-86627900-1370035486_thumb.j

post-29683-0-23228600-1370035497_thumb.j

Edited by jpflip

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Here's a view of the ground strap with the engine remove. I think JFP is talking about this one...(correct me if I'm wrong). The frame attachment can be seen above the right turbo and the other end is beside the fuel regulator just under the air pump. I think it is possible to reach and to facilitate the job you should lower the engine about 4 inches .... Lowering the engine is easy especially if you got access to a floor jack. See attachment....

I did not read all your post on Rennlist and 6speed but have you check the power consumption at rest which is suppose to be .6 amps maximum ?

Secondary air pump removal can be seen in the repair manual page 641.

That is the one, always fun to get at.

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Thanks JFP, I should replace it when I had my engine out...May be next time :thumbup:

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Thanks a lot jpflip!! Your info are great, I will try to remove the air pump to reach that bolt of the engine/chassis ground strap. Is there any danger in removing the air pump and the engine oil filling tube?

What setting should I use on the multimeter in order to measure the power consumption at rest which is suppose to be .6 amps maximum?

But, I dare not lower the engine because I am really very weak with DIY jobs...

respect to all those help and advice again :notworthy: :notworthy: :notworthy:

Edited by niceguy

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No danger in removing the oil filling tube. The amperage reading should be done with the positive battery cable disconnected and your multimeter (selected to amps) in series between the positive cable and battery positive. Of course you do this with the engine not running.

Edited by jpflip

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Can you use a jumper cable to make a "parrallel connection" with the ground strap to see if you get improvements?

To test the ground strap, you could just let the engine run and turn on some heavy accessories. Then measure the voltage drop between the engine and the chasis close to where the ground strap is bolted on. If your previous measurements were correct (quoted below), you should see about 1.2v to 1.8v (which is WAY too high).

"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) "

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Ok, looked at your tests more carefully seeing how methodical you are, I would guess you are an engineer :)

A few comments first. Forget about measuring the resistance since the problem may be (and most likely) are at the connection points so even if the cable itself is perfect, you lost voltage across those bad connections. If you remove the cable, you lose the chance to detect those bad connections. Besides, a regular digital voltmeter (200ohm range) will not be able to measure the low resistance accurately. The resistance of the measuring probes themselves may be in the same order of magnitude.

So focus on the principle of applying a high current on the segment you want to measure and then measure the voltage drop between the ends of the segment in question.

I suggest you turn on the a/c and headlight (like you did) then measure the following. You should see close to 0v and not even 0.1v

- voltage drop between alt +ve terminal and engine +ve terminal (#29) - this will verify #28

- voltage drop between alt casing and the airfilter bolt - this will verify #36

Use the same principle to trace upstream all the way to the battery for different +ve segments from the engine to the battery. None of the segments should have a significant voltage drop. I would say 0.3v max....

Hang in there and I'm sure you're getting pretty close already. Again, try to focus on measuring voltage drop and not the resistance.

For reference, when a/c and headlights are on for my car, the alternator puts out ~40A and I measured almost 0v for those two set of test points I suggested above.

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Thanks Ahsai for your replies!!

I will carry out the amp measurements tonight and report back the readings.

But, I'm sorry for my stupidity that I do not understand what I have to measure for the following

- voltage drop between alt +ve terminal and engine +ve terminal (#29) - this will verify #28

- voltage drop between alt casing and the airfilter bolt - this will verify #36

Am I supposed to measure voltages for the following?

1. engine on

2. a/c on, heading lights on, +ve alt term to -ve alt case (I measured it and it was = 14.0v)

3. a/c on, heading lights on, +ve engine term to -ve alt case (=13.9v)

4. a/c on, heading lights on, +ve alt term to -ve airfilter bolt (measured = 12.1v)

5. a/c on, heading lights on, +ve engine term to -ve airfilter bolt (12.1v)

The voltage drop between alt +ve terminal and engine +ve terminal (#29) = 0.07-0.10v, this verifies #28 is normal.

But, the voltage drop between alt casing and the airfilter bolt =1.8-1.9v, this verifies #36 has a problem.

Moving upstream towards the battery, should I measure

the Volt between +ve transmission term to -ve engine case

the Volt between +ve transmission term to -ve chassis near the ground strap

I have the Vdrop result for this too and it is exactly 14.0v with engine case but 12.1v with chassis near the ground strap.

Does these Vdrops mean my problem is in the engine chassis strap, no. 36?

OR

I have done it incorrectly, please advise me if I am wrong.

Thanks again for your help and assistance.

James

Edited by niceguy

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James, what I was saying is turn on the cold engine, a/c and headlight and let it idle. Then set your multimeter to DC 2V range.

Test A for #28: Put the red probe on the "+ve alt terminal" and the black probe on the "engine +ve terminal (#29)". The meter should read very close to 0v if #28 is in good condition. If you see +0.3v or higher, you know #28 and/or its contacts are questionable.

Test B for #36: Put the black probe on the "alt casing" and the red probe on the "airfilter bolt". Again, it should read very close to 0v if #36 is in good condition. If you see +0.3v or higher, it means #36 and/or its contacts are questionable.

You can repeat tests A and B when the car has warmed up.

Also, you can do another 2 tests described on page 14 here http://www.autoshop101.com/forms/h8.pdf Same principles.

Edited by Ahsai

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Oh, I am so sorry for my stupidity.

I will do that right away and report back in an hour or so when I get home to my car.

Just curious, what if both of them are at 0v meaning #28 and #36 are fine?

Will Test C be?

Put the black probe on the "+ve alt terminal" and the red probe on the "+ve transmission terminal". Again, it should read very close to 0v if #24 is in good condition.

I am not good enough to remove things in order to reach the starter. Will that limit my testing ability to finding the ultimate culprit?

Edited by niceguy

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It does look like the ground strap is the culprit but I still want you to verify with test B above, where you should see 1.8-1.9v shown on the meter. Actually the quickest way is to do the two toyota tests in the link I sent above. Then you immediately isolate whether you lost the voltage (~1.8v) on the +ve branch of the circuit or the ground branch or a little bit on both.

Lets see what you get first before thinking about test C...so far everthing points to the ground branch. The only thing I cannot reconcile is why your jumper cable connecting the engine and the chasis did not help.

If the problem is trully in the ground branch, i dont see why you need to gain access or touch anything on the +ve branch (i.e., starter and transmission).

Edited by Ahsai

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Will Test C be?Put the black probe on the "+ve alt terminal" and the red probe on the "+ve transmission terminal". Again, it should read very close to 0v if #24 is in good condition.

Exactly, you got the idea now :) basically hunting where you lost that 1.8v between the alt and the battery.

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Thks fir the confirmation. I m home now working on my car.

I guess the jump leads creating the extra ground did not work because those leads did not allow sufficient amount of current to flow thu them.

I will do the Toyota tests n test b and report back in approx 20 mins

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Toyota test done according to p.14 of 21

1 man operation so readings at idle with ac and headlights

Results

open circuit - insulated side = 0.33-0.40 ( avg 0.35)

Ground side = 1.20-1.52 ( avg 1.35v)

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Would the voltage drop values that I measured have dropped or risen if I had managed to raise the engine rpm to 2000rpm?It does look like the ground is questionable. According to my understanding, there are only 2 grounds in the car. First is at the battery -ve lead and the other is from the engine to the chassis. I had used contact cleaner n carefully cleaned the battery ground lead and it's chassis connection bolt last week before I took all my pervious readings.

Edited by niceguy

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I lost 1.2-1.5v at the ground and that is exactly the sum of 1.35v of what I lost at the battery 1.35+12.2v (during the measurement) = 13.75v with ac and headlights

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All right! I think you're zooming in. Test A result is too high at 0.22v for such a short cable (#28). Your total vdrop on the insulated side is 0.33-0.4v and that's over the whole length of the car between the alt +ve to the battery +ve term and you lost 2/3 of that on cable #28, which is only a foot long. So I think you have to address that sometime.

Let's fix the ground side first since that's the biggest drop. Can you do the following Test C?

Vdrop between airfilter bolt and engine side of ground strap (#36)

Vdrop between engine side of ground strap and chassis side of ground strap

Vdrop between chassis side of ground strap to chassis side of #1 (battery -ve cable)

Vdrop between chassis side of #1 and -ve battery terminal

If you see any big drop, you found your problem. Then try to add a jumper cable to short out that problematic section.

If you want to see another confirmation of ground problem, you can use a jumper cable to short out the -ve battery terminal and the airfilter bolt and you should see immediate improvement. Try to use gauge 8 or fatter jumper cable. Good luck!!

Edited by Ahsai

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