tjbreen

I finally got around to checking out my 3/4 when full problem by checking the forums and doing some testing. Many posts suggested moving the needle. This seemed like it would fix the symptom but not the problem.

I tried one thing I had read in one post - to see if the ground wire was seeing too much resistance. I built a jumper plug and grounded the pin to the body. The needle immediately jumped up nearly the 1/4 I was missing on a full tank. Thinking I solved the problem I went looking to find where that wire led to but could not find it anywhere in the car.

Can anyone tell me where the fuel level sender ground wire attaches to ground?

Skip

what year/model?

[edit] - looks like all models except for 924S run the ground all the way to the fuse/relay board on the firewall.

t/s info - http://www.tech-session.com/kb/index...x_v2&id=72&c=4

Clark W

tjbreen, Did you jumper to ground at the gauge or the sender? Sounds like you jumpered at the gauge, but wanted to make sure.

I've had this problem for 16 years on my '89 s2. I've tried it all it seems. Last attempt was to clean the grounds up front under the dash which I believe I verified as the gauge grounding point. All to no avail.

The jumper sounds like a promising diagnostic.

clark

tjbreen

I jumped the ground pin at the sender in the rear of the car. I bent a thin copper wire in a U-shape and put the connector back on with one leg of the U jammed in the with the ground pin. I then attached a alligator clip to the other leg of the U and grounded to the chassis ground between the rear tail lights. I could easily see the fuel needle jumping about 15 degrees up and down as I touched the ground. The needle never bounced off the top pin but did manage to touch the bottom edge of the full line with the old sender, which showed a resistance of 4.8 ohms full (Skips article says it should show 2.8).

I have a new sender on order from Paragon. I expect the combination of the new sender and good ground to put me well into the full area.

Granite 944

I highly recommend Skip's link. Its a good way to test it out ( I just need to get myself a "decent" poteniometer for future use. Any suggestions where I can get one to cover 0-300 ohms for this sort of thing?) . I've done my cars, and know its the senders in my cases ( I think ). Each one of them I've dismantled and looked at, the inside wires had worn down into the float tab connections, creating what I believe, to be a sticky situation (but still not 100% sure of that either. I'll know for sure within another couple weeks). One I can live with, the other, well, like tjbreen, I've got one on order from Paragon. (Thanks again Chuck!)

One other thing to look at is the connector to that cluster unit, and make sure the pins/sockets are clean and tight also. I also used a smear of dielectric grease on 'em. Good luck!

Skip

I've been using the same Craftsman digital auto-sensing multimeter for about 8 years. Works great on everything I've ever had need to measure.

Granite 944

Oops, I got your site mixed up with another that talks about also using a fixed resistance in place of the sender values, added to the wires to test out the gage itself, not just what the sender is reading out at any given time. The digital multimeter I have, and I have some crappy old trim pots, and much higher (and harder to adjust in) poteniometers (sp), that got me by long enough to test out the gage function, using those resistance values as the fixed values for a gage check. And your stated values did check out fine for checking the gage, but not when coming from my sender (hence the needed sender). It all works out in the wash pretty much the same however, I believe.
Thanks.