Fuel Guage not working

I have a 90 YJ Sahara 4.2 L with about 70K miles. The fuel guage just stopped working. It always reads zero or almost zero.The rest of the guages working OK. My guess is the sending unit. Any other likely possibilities. The dealer wanted nearly $250 for A new sender (not including installation) This seems a bit high to me, more like the price for the FI unit that includes the pump. Is there anyway to isolate the problem to the guage itself rather than the sender. If it is important, the guage does move slightly to the right when the power is turned on, but only gets to empty.

So assuming it is the sender and I can find one, any tips on dropping the tank. Also is there any way to tell the difference between the 14.5 gallon tank and the 20. Pretty sure I have the smaller tank, but I never let it get very low, so I am not sure.

Aloha from Maui Joe

Reply to
Joe and Joann
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Reply to
L.W.(Bill) Hughes III

The sender unit consists of a float attached to a moveable arm, that moves a variable resistor. The electrical resistance at the sender unit terminals will change as the arm is moved. I can tell you right now, that the Haynes Automotive Repair Manual that I have, part number 50030 (1777), for the 1987 through 1995 Jeep Wrangler, does not contain the resistance values, that you need to test the sender unit. :o( A cursory scan of that section of the manual indicates, that it may be useful for removing the tank. I suggest removing the tank, to inspect the sender unit. :o(

The sender unit is tested electrically, by moving the arm with a DVOM (Drive Vehicle Off Mountain or Digital Volt Ohm Meter, I can't remember which) attached to the sender unit terminals. The resistance should change smoothly as the arm is moved. Lacking the specifications, I can't tell you more. If the float is saturated or full of fuel, it will feel heavy or make a sloshing sound.

Other suspects are a faulty electrical connection at the fuel pump/sender unit connector, a fault in the wiring to the sender unit, and a bad gauge. If you can identify and access the wires to the sender unit (Haynes wiring diagrams are pretty bad too) then you can check for voltage to the sender unit with the key on. We used to short the terminal to ground, and watch the gauge go to full, on some older vehicles, but I do not know whether this is recommended for your vehicle. The Haynes manual is short on troubleshooting tips in this area.

It does sound as if the price quoted, is for a sender/fuel pump unit. They appear to be a single unit. On vehicles with a 20 gallon tank, the fuel pump/sender unit is mounted with eight screws. The fifteen gallon tank has a lock ring. The Haynes manual says "if the ring is difficult to remove, tap it loose with a wood dowel or brass punch and a small mallet (DO NOT use a steel punch, or you could cause an explosion!)" They show a steel screwdriver being used.

The behavior of your gauge is consistent with a flooded float, but not a

100% indication. On my old Plymouth Valiant, this was a fifteen minute job, if the tank was below one quarter full. Things sure have changed. My advice is to get some penetrating oil on the tank mounting bolts, a couple of days before you try dropping the tank.

Earle

Reply to
Earle Horton

Thanks Earl Since I have the carb 4.2 L with the mechanical pump, I sure don't need the in the tank pump used on the FI model. Hard to believe that price isn't for the combined pump/sender unit as you said. Thanks again for the ideas.

Earle Hort> The sender unit consists of a float attached to a moveable arm, that moves a

Reply to
Joe and Joann

The unit should cost under a hundred, you are either being quoted for the wrong part or are getting ripped off.

Here is a good diagnostic page for your gauges:

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If I remember right, the ground for the sender is just a black wire screwed into the frame. They get ratty and fail.

I recommend soaking all the tank bolts and nuts with penetrating oil for several days before starting the job.

Tank size.... Hmmm I 'think' it is mostly a depth difference in the tanks. I think the small tank has a square back and the larger one is cut on a 30 deg angle for the Jeeps departure angle so the tank doesn't tag the ground.

Supposedly I have a YJ skid plate here. It measures 5 1/2" below the rear cross member. The 20 gallon tank measures 8 1/2" below the cross member.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

Sorry, but this Haynes manual is terrible. That range of model years had a number of significant changes, and the manual doesn't even discuss the possibility of a fuel tank without an electric fuel pump in it.

If you have a saturated float, sometimes they can be repaired. If you have another vehicle, it would be good to identify for sure which part is busted, before spending $250 on a sender.

Earle

pump/sender

Reply to
Earle Horton

For that year of a YJ, the Haynes CJ manual is excellent. That YJ uses the CJ engine controls and the CJ underhood wiring harness.

Mike

Earle Hort>

Reply to
Mike Romain

Aloha Well, an interesting thing happened. I had refueled yesterday and the guage still didn't move off empty. Today I was driving and the guage went up to full and has been working steadily since then. Thanks to all who replied. I am saving a copy of this thread so that when it comes back I will be ready.

Meanwhile I will continue trying to track down a replacement at a reasonable price. The Mopar parts on line shows one sender for 1990, but it does't differentiate between the 20 and 15 gallon tank, nor FI or the carbed I6. So I don't have a lot of confidence in that one. Its price is $150 or so, at least better than the dealer.

The problem could be a bad ground, but it seems rock solid now. I would think an intermittent ground would give more unsteady readings, but who knows. Maybe the float was somehow stuck on empty.

By the way Mike, the tank is 51/2 inches below the rear cross member, so itis the smaller tank.

Aloha from Maui and thanks Mike, Earle and Bill for the ideas

Reply to
Joe and Joann

These guys

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are good. Both new and used parts.Send them an email if you don't see it on their site. Earle

Reply to
Earle Horton

Reply to
L.W.(Bill) Hughes III

That sounds like a connection issue. When the sender up and dies, it doesn't fix itself. If it was 'stuck' then it might be like Bill mentions. That still wouldn't call for a replacement, just an adjustment.

Mike

Joe and Joann wrote:

Reply to
Mike Romain

My opinion is that the highest probability is that the wire leading to the sender is open. Next, that the sender (potentiometer) is open. I would make a resistance measurement at the sender with the wire disconnected. If you don't read a very high value (perhaps in the MegOhm range) then don't condemn the sender, I would look for the open wire from tank to gauge.

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Reply to
Professor

The fuel gauge meter movement is heavily damped and gets its signal voltage intermittently by design, so an intermittent open ground probably won't be noticeable unless it stays connected for several seconds. The sender ground line in earlier CJ's runs from the sender to a self-tapping screw driven into the frame cross member just forw'd of the fuel tank, driver-left of center, I'm guessing that yours is the same. You /might/ be able to see it if you pull the left rear wheel and look into the space above the front part of the fuel tank, but you won't be able to reach it with your hand. Hurm. There might also be a quick disconnect for the hot side of the line where it comes out of the wiring harness in the wheel house (again, driver-left side of the Jeep). It might have gotten grotty inside and isn't conducting. Pull it apart, clean or replace as needed, pack with silicone bulb grease when reassembling to prevent further corrosion.

Mike: Does anything other than the fuel sender take its ground from the frame? I think everything else grounds through the body sheet metal or engine block. Perhaps the ground strap from the block to the frame is missing or broken. On 1970s-80s CJ I-6s it was a #8AWG cable that jumpered the left engine mount, dunno about other engines. Joe: It can't hurt to add one (universal mesh straps are available in the "Help!" sections in retail chain auto parts stores) if the frame ground is missing then the only one the sender can get is to "steal" one through the body mount bolts and random places where the frame hits the body. It would be a good idea to eyeball the engine mounts anyway. They're 16 years old and probably getting soft or broken.

I'm wondering if the weight of the full tank has shifted something just enough to restore the ground. But I'd drop the tank and check the wires before ponying up a wad of cash for a new sender. Beware of two things, though: If your `90 is like the earlier CJ tanks you can't can't remove the sender from the tank for inspection without replacing the lock ring and gasket (it _will_ leak), and the threaded stud welded to the strap that crosses the top of the tank from fore to aft will probably twist off when you turn the nut (the center nut at the rear cross member.) You'll either need a replacement strap or weld another stud onto the strap. If you're not especially handy with tools or unlucky, expect to spend the whole day at it.

Joe and Joann wrote:

Reply to
Lee Ayrton

Ah, well, that's some useful info you're providing there, Perfesser. Nice of you to take the time to share your guess^W opinion.

If Joe finds that his sender is reading even a decade north of 100 ohms, let alone anywhere within sight of "the MegOhm range", the part is farked. A definitive answer wasn't forthcoming on Google, but his YJ fuel gauge wants one of these three sets of ranges:

Empty Full 73 Ohms 8-12 Ohms (`76-`86 standard, perhaps YJ*) 0 Ohms 88-90 Ohms (`89 YJ, perhaps others)

According to this** the FSM for the `91 YJ specs: 105 Ohms 5 Ohms.

The gentle reader will note the reversed ranges. Mixing senders across models but will result in reversed gauge readings, as those who swapped their ugly YJ dashes for manly CJ dashes found.

* **

Professor wrote:

Reply to
Lee Ayrton

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