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Alternator/charging

It's still dropping voltage just running the fuel pump which is on a separate 10ga wire and switched on with a relay. I've had two batteries and MTX1000D with 3 subwoofers in the car years ago with a large capacitor. It always worked well.
 
How many millivolts voltage drop did you get on your cables!!!!?

For example, I measure from battery positive to an under hood fuse block positive on the trucks I work on, crank, no more than 200 mv should read on the meter. On the ground side I measure from battery negative to the furthest engine metal away from the battery, then crank, 200mv is the most I should see here too. If more, replace the cable.

I had another vehicle that was a no crank. From negative terminal at battery to chassis I was already reading 1.5 v without even trying to crank. When hitting crank, the meter went all the way up to 11.5v!!! NO ground!!!. Found the ground wire loose buried deep under fuse block, etc. Couldn't see it.


Ok point is, learn to do voltage drop testing. Look it up! It's a measure of millivolts, NOT how much your 12v is dropping down.

It may not be the cause, but these cars the crimps go bad on the cables and may look fine but will likely fail voltage drop tests!!!
 
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Had a similiar issue on my 240.

I crimped a new ring terminal onto the exciter wire when I switched from a Bosch to a Denso 100A. When the Denso started failing, I switched back to a Bosch. (Kept my old Bosch and put in a new voltage regulator).

When I put the Bosch back in, I was only getting 12.8 volts or so at the battery. I checked and had 12v at the exicter wire, so then went through all the usual diagnostic checks and cleaned all the grounds. Still only 12.8 at the battery. Double checked all the connections again. Turns out the ring terminal that I had crimped on for the Denso was too big, and not making a good connection with the Bosch.

Crimped a new, smaller connector and that solved it. 14.1V at the alternator (B+ to Ground), and 14.0 at the battery at idle.
 
It maybe, today it ran 13.8v at the dash 13.2 when blower was on full 12.9 with head lights were on normal and 12.8 with the stereo was on. I took it to autozone and it passed the charging system test. I'll spend sometime in the near future testing.
 
Battery is probably 2 weeks old. It's charged fairly well now. No cranking issues. It did die on the highway two weeks ago and I bought a new battery to get me back home. I had the battery checked Friday and it was good but needed charged.
 
Those drops are still too low with that much load on the alternator. If you are exceeding the rated current draw then you want to consider a more powerful alternator.

Also I have had weird things happen with the 80 amp bosch alternator. I had one that put out less voltage due to a bad diode in the warning light circuit than what the B+ terminal voltage would be. Created a problem where the dash lights were always lit dimly since the alternator was charging at slightly over 14v but the charging lamp circuit had 12v.

Check around for more voltage drops. The fuse box can get dirty terminals because it is right near the door. If your windshield ever had a leak in that area you can get corrosion in the fuse box. Also be sure the fuses are the brass and copper type and not the white metal crap. They corrode and will cause their own set of problems when they age.
 
There is corrosion around the terminals in the fuse box. Some are the white metal fuses you talked about. I'll take a wire wheel on my dremel and clean them soon. I cleaned the terminals on the speedo and the battery terminals yesterday. I'll keep at it and keep checking. Thanks again for the info.
 
What were the results of the voltage drop tests??!

Using a multimeter, one lead to battery positive and the other to alternator positive. I wouldn't want to see much more than 200 millivolts. Then put one lead to alternator case and one to battery ground. If you get a high reading, you have a bad connection!!! This is with engine running.
 
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I'm waiting on set of alligator clips from Amazon. I have to remove my wastegate to get to the positive terminal on the alternator. I'll report back... it was busy weekend with drag racing and family events,lol.
 
I'm running a 100 Amp Volvo/Bosch alternator from a 92 940. No voltage or amperage issues. Before that I was running a Denso 80 amp alternator from a 91 740. Only difference noticeable between the two alternators was 13.8 volts for the 80 amp, and 14.1 volts for 100 amp.

This is on a 88 765T with plenty of space available for a large alternator. The 100 amp Denso alternator is supposedly smaller in size.
 
I'll check those out in the future. I have two good alternators that I have a voltage drop somewhere it's looking like. The 80amp should be enough for all the standard accessories .
 
12.25 at alternator at idle blower on alternator positive, light and radio on. 12.11 at battery.

It was both showing 14.1 @ idle and the B+ was showing the same. The car passed the charging system test at autozone.

b+ was identical to alternator output.

I cleaned terminals and fuses with wire wheel on dremel. No changes... I'll keep looking.
 
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You can get higher voltage set point regulators to bring up the system voltage. But fix the issue first. Once you get the test leads you can look around the wiring harness for voltage drops. I get the feeling you need to upgrade the grounds in various places and fix some voltage drop issues on the positive side of the electrical system. The greenbook wiring manual has a listing of the various locations of grounds in the car.
 
I got the test leads now. I was able to measure the alternator voltage with them. Can I test with the car not running? The battery drops voltage from 12.6 to 11.8 when the accessories on.
 
There is .2 Volt drop on the alternator to positive battery terminal with the blower, lights, heat warmer,radio and wipers on. There is less than .05V on ground terminal to the motor and alternator. There is a .05V drop to the distribution to the inside of the car on the left fender. I ordered a new positive cable and will replace the alternator positive cable and test again.
 
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To test cables you prevent the car from starting, crank , and measure max voltage drop. It's usually more of an intermittent no crank if the cables are bad, rather than a low charge. I just diagnosed a truck that was intermittent no crank with 500mv drop on both the positive and negative=way too much.
 
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The car starts right up. I changed out the power wire from the battery to starter, starter to alternator. Still dropping voltage with all accessories on. I'll have to wait till the car is cold to check the voltage drop from the positive to the alternator. It's drops .8 volts if I turn the headlights on. .5 volts if I turn blower on. .2 volts if I turn the radio on. .2 volts if I turn the seat warmers on. It dropped to 11.5 volts with everything but AC and rear defroster on. I pushed a 8ga wire from the ground terminal to the body and didn't change anything. I'll check the alternator ground again.
 
The bushings are fine. The belts are fairly smooth. They are only a year old. I'll mark them and crank pulley to see for some reason that could be rotating. The belts should run evenly. I just checked the voltage drop from the alternator to the battery terminal with everything on. The battery voltage was at 11.7v with everything on.

.053V alternator body to negative battery terminal.
.052V positive alternator to positive battery terminal.
 
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