Temp guage is teasing me!

juVius · 09-02-2006, 06:12 PM

My temp guage is mad at me or something. it works, but
when i ground the tachometer the temp guage goes all the way up. Also goes all the way up when i turn my headlights on. I've read through the posts and didn't see anyone else who has had this problem.

i check the battery connections, cleaned and regrounded: ground by each headlight, the one in the back, and the ones at the engine block. i don't know where the rest of the grounds are.

if anyone knows how i can track this down, i'd appreciate it. I'm gettin burnt out on trying to figure it out on my own. it took me two days to figure out the above.

thanks in advance

Slam · 09-02-2006, 06:16 PM

On the early cars alot of the dash grounds are in series. I'd pull out the instrument cluster and check all the grounds there (brown wires) and then check and clean all the grounds behind the fuse block. You'll find a ring of ground wires there and sometimes they get corroded.

HTH

juVius · 09-02-2006, 07:02 PM

i'll check that in the morning. thanks. any other ideas on things to check if that doesn't fix it?

juVius · 09-03-2006, 03:57 PM

ok... i checked all the grounds and still the same problem. here's the symptoms: with tach ungrounded and lights off the temp gauge works, when i turn on the lights it dropped down to zero. then wether lights are on or off if the tach is grounded so the instrument lights will work the needle jumps all the way up and stays there till the key is turned off. This is the last known issue i have with my 84 944 and it's driving me crazy that i can't figure it out.

somebody please help me!!!

Mike B · 09-03-2006, 04:15 PM

I would add another ground from the body to the frame rail. It's cheap, eay to do and will probably fix the problem. If it doesn't you may have a failing alternator.

Best of luck.

juVius · 09-03-2006, 04:30 PM

i have tried that and same symptoms. Not questioning you, i just don't know anything, but..... how would a failing alernator do that? i'm just curious. and if that's the case i do happen to have another alernator in the garage for this car... thanks

juVius · 09-03-2006, 06:06 PM

is there any reason why the temp sensor wire goes through the tach gauge before is goes the the temp gauge?

SoCal Driver · SoCal Driver's Garage

First get the electrical schematics off of Pelican. If you have the Haynes do a circuit by circuit comparison. Trust the factory wirng over the Haynes.

The biggest problems as have been noted are the grounds at the gauges and where the ground connects to the chassis above the fuse and relay block.

I would clean the heck out of the wire connections at the positive battery terminal. Especially the large gauge red wires.

If it was only the temp that was acting up I suggest checking the sender connection and the wire from it. It's on the block behind the DME temp sender. A bit under the intake runner for cylinder #1. The connector is special for the button head sender so don't cut it off and try another. I've had to solder a new section of wire in between the connector and the harness to get rid of the green wire disease.

juVius · 09-03-2006, 08:20 PM

i think i'm gonna take the whole dash out so i can check all the wires and grounds. i did move the fuse box out of the way earlier, removed the screws holding the grounds and scuffed the screw hole and all the ground connectors with sandpaper then applied some greese lightening and screwed them all back on tightly. that didn't make a difference. Also, earlier today i unscrewed the sensor and cleaned it off and made sure the connector and wire were ok.. best i could tell they were fine.

i'm not going to give up until the car explodes...

tooter884 · 04:32 PM

My post may be a little late for you, but it does appear that you have a bad ground.

I would assume that my 83 and your 84 944 instrument cluster wiring are essentially identical. On the 83, the ground lead to the instrument cluster goes thru a round 12 pin connector on the back of the instrument cluster. The ground point originates at two grounding rings above the Central Electric Board, which is mounted under the left end of the dash. The Pin 2 ground is common to the Coolant Temperature Gauge; Fuel Gauge; High Beam indicator bulb; Parking Brake indicator bulb; Tachometer, Pin 4; Speedometer housing (display light bulbs ground); and the Light Switch display light bulb. If the gauges do not have a true ground reference, they will be erratic, and even more so when additional current is flowing thru this “ground,” which is what happens when the Parking Lights are turned on.

Since the light switch ground is common to the instrument cluster ground, you can check this ground by merely pulling the light switch, and checking the resistance from the Brown wire to the battery ground. If it is non-zero, you have found your problem. If this proves to be your problem, cut the ground wire at Pin 2 (only the wire going to the grounding ring) on the Instrument Cluster connector, and run a supplementary ground from a hard ground point (e.g., the Battery Box) to the spade connector ground point on the Speedometer housing.
The wiring diagrams are here for the Instrument Cluster http://www.pelicanparts.com/944/electrical/944_84_4_2.jpg and here for the Light Switch http://www.pelicanparts.com/944/electrical/944_84_2_1.jpg

hpaulb · 09-07-2006, 06:54 AM

On topic but a little off. I fear I have to work on my cooling system. New engine and harness. After installation the fans worked but now the cooling fan never comes on. Air fan comes on if I turn the AC switch. Temp runs between the second and third bar depending on traffic. Seems a lot higher than my last engine. Were should it be?

924RACR · 09-07-2006, 08:01 AM

Well, first off, your fans do come on when you turn on the AC, right? If not, I'd suspect a problem like maybe the fan relay - I've had them sometimes fail and only power one circuit. Especially when one fan dies! Overheats the relay.

YMMV. Anyway, the temp doesn't sound that off - my 87 924S ran at the first mark when I got it; new waterpump and t-stat later, it now runs at the middle, creeps up towards the 3rd when in traffic. It's just the normal t-stat, not a low temp one, that's why. Fans come on IIRC just before the 3rd mark - think it's a low-temp fan switch. I think at the 3rd mark is normal. I wouldn't worry unless they either don't come on with AC on, or don't come on and the temp is close to the red.

barlowj · 09-08-2006, 11:21 AM

Two follow-ups to this thread. First, a response to the temp range question, my 85.5 944 runs at the first bar (normal t-stat switch) but will rise to the next bar (I believe I only have two) at long idles. Fans kick in at that bar and it drops back down to the first bar.

Second part, the other day I was driving at night and noticed my temp gauge acting odd and then it dropped off (like it had no signa). I haven't driven it since or played around to locate the problem but looking at the replies, I am wondering if I have a bad ground that was brought to life by the extra current caused by the lights? No other gauges were acting strange.

gadgit · 09-09-2006, 06:28 AM

I've been dogged with this problem ever since I've had the car!!

One day its fine and then, all over the shop.#

My 944S2 has a big red light that comes on when its really hot, so it has a back up to the guage.

All through the cars history it appears to suffer with high temperature and I now believe that its been an earth causing it after reading this thread.

I'd replaced the sender, and resoldered the conectors to no avail, but now I'm off to check the earths and thanks.

Gadgit.

Slam · 09-10-2006, 09:28 AM

tooter884 has it, I think. If the gauges can't ground through their proper ground they'll ground through the light switch ground and put too much load on it. The things get really fun...