Voltmeter/Fuel Gauge Issues

[Michael7810]

Hi - I'm new to the 944 forum and recently bought an 87 951. The dash voltmeter is reading very low (like 10 volts) and the gas gauge reads low as well. I don't have any problems starting or other electrical issues that I know of. I checked the battery voltage with car running and AC and headlights on and it read 13.1V. I revved it up to 3K and it stayed right at 13.1V. I moved the negative lead from the voltmeter to the firewall end of the negative battery cable and it read the same. I moved the negative voltmeter lead to the engine block and it read the same 13.1V (+on the battery and - on the lifting hook). I shut the engine off and while the fans and turbo pump were running the voltmeter read 12.1V. After the fans stopped the voltage was 12.4V. Seems like I have a ground problem. I've not had a 944 long enough to know where the gremlins live. Thanks in advance for the help.

[9FF]

If you are only getting 13.1v across the battery with the engine revs up your voltage regulator is likely toast. It's located on the alternator and it's an easy and cheap fix. It could be your alternator itself but you won't know for sure unless you swap out the regulator.

The alternator +ve goes directly to the battery +ve so as long as your battery ground is good you should be reading alternator voltage at the battery which is about 14.7v with the engine running. Without the engine running you should just see battery voltage of just over 12v, which it seems you are getting.

[bumflick]

Is the voltage regulator really a $90 part? If the Nissan quest alternator is only $120, wouldn't that make more sense?

[smudo]

Originally Posted by Michael7810

Hi - I'm new to the 944 forum and recently bought an 87 951. The dash voltmeter is reading very low (like 10 volts) and the gas gauge reads low as well. I don't have any problems starting or other electrical issues that I know of. I checked the battery voltage with car running and AC and headlights on and it read 13.1V. I revved it up to 3K and it stayed right at 13.1V. I moved the negative lead from the voltmeter to the firewall end of the negative battery cable and it read the same. I moved the negative voltmeter lead to the engine block and it read the same 13.1V (+on the battery and - on the lifting hook). I shut the engine off and while the fans and turbo pump were running the voltmeter read 12.1V. After the fans stopped the voltage was 12.4V. Seems like I have a ground problem. I've not had a 944 long enough to know where the gremlins live. Thanks in advance for the help.

It seems that I have the exactly the same problems. My tank gauge is showing 1/4 less at all levels. Have not looked in to the reasons for that.

Also my a voltmeter gauge is showing only 12 - 12.5 V with engine running. It seems that I need to change the voltage regulator or rebuild the alternator.

[Michael7810]

Seems like I have 2 problems (at least). Low voltage from the charging system and the dash voltmeter is not reading correctly. I'll fix the charging system first. I'm going to check the positive wire from alternator to the battery to make sure it's OK, then start with the Voltage Regulator. Can I change the regulator without removing the alternator? The VR is out of stock on this site but I'm not in a hurry because it's too hot in Phoenix to work in the garage and I'm not planning to take it out of town until September (and I'll fix the charging system before then). Then I'll look into the gauge issue. Thanks

[AaronM]

The first thing to do with weird gauge issues is to clean all the grounds.

The fuel gauge reading low could be either the gauge or the sending unit. Instructions for how to test it (and how to clean the sending unit) are here: Fuel Level Indication Problems / Repairs

[Michael7810]

I figured the gauge problems might be bad grounds (I have a 914 so I know all about bad grounds). I just bought this car and have not worked on a 944. Is there a list or diagram of where I can find the grounds on an '87?

[944 Ecology]

The ground points are shown on the wiring diagram, which is included in the factory service manual.

[DannoXYZ]

Originally Posted by Michael7810

Seems like I have 2 problems (at least). Low voltage from the charging system and the dash voltmeter is not reading correctly. I'll fix the charging system first. I'm going to check the positive wire from alternator to the battery to make sure it's OK, then start with the Voltage Regulator. Can I change the regulator without removing the alternator? The VR is out of stock on this site but I'm not in a hurry because it's too hot in Phoenix to work in the garage and I'm not planning to take it out of town until September (and I'll fix the charging system before then). Then I'll look into the gauge issue. Thanks

You can replace the VRM with Transpo # IB372A. It's adjustable so you can set it on the high-end (about 14v) to get maximum brightness out of the lights. Available many places on-line for about $40. Actually some suppliers in Phoenix somewhere. Or you can get the factory replacement for $10.

On a 944NA, you can replace the VRM without removing alternator. I haven't figured out a way on the 951 because the rear of the alternator is blocked by the downpipe. So the rear-cover on the alternator can't be removed. Check first though, some 951s have had their rear-covers removed and left off.

Yeah, and check your grounds. Especially the one for the dash. I typically add two supplemental grounds. Between the factory battery-ground bolt at the firewall to the cam-tower (replace bolt with longer one so you can attach additional nut on the other side). And one at the front between the body and one of the bolts near the alternator. This really helps with current flow for the headlights.

[Michael7810]

Thanks Danno for the great tips.