Have been home for a few days now and getting to spend some time in the garage working on long overdure projects. Next on the "to-do" list is diagnose and repair, if possible, the fuel quantity/bad gage issue in my son's 88 Fbird with 2.8L.

He has run out of gas several times (once in front of his school at 7:30am, read here TOTALLY EMBARRASED).

I've suggested we use the trip odometer method and it works when he remebers to set it and look at the mileage. But at 16 years old, he has other things on his mind.

At any rate, please provide any known troubleshooting methods. I am an airline mechanic and have virtually every available tool (multi-meters, pressure gages and more hand tools than a human should be allowed to have, etc.).

DO NOT SUGGEST "LIVE WITH IT!".

Good mechanics never blame the "engineer", they find solutions.

Remember, todays million dollar aircraft are designed by guys with PHD's, built by guys with Masters, flown by guys with Under-grad degrees, BUT MAINTAINED BY GUYS WITH HS DIPLOMAS AND AMT CERTIFICATES!

The solution is out there, we just have to find it.

Thanking you in advance.....

Later

 

Does it flat not work?? Or just read improperly, etc??


If it flat doesn't work, I would attempt to see if you are getting signal to guage. I belive if the plug buy the tank was dx, it would kill the pump to, so I doubt thats it.

I have also seen sections of guages just up n quit working. IF you have access and some small $, go buy a used cluster and see if that fixes it. if so, you might beable to combine the two and make proper milage/fuel pump fix.

 

Most likely it's the sending unit, which IIRC you'll basically end up replacing the entire fuel pump assembly. It could be that the float came off inside the tank. First check to see if you're getting a signal. If not, then prepare to drop the tank or cut a hole in the body of the car.

 

The joy of owning a mid-80's GM car! In the mid-late 80's, GM used a stainless steel wire element in the fuel level sensor. Problem is, eventually, the float "wiper arm" will wear the stainless steel wire down to nothing, like 40 grit paper on skin. I'm told that in the 90's, GM started using a carbon-fiber element that doesn't wear thru.

This happened to me once; fuel gauge pegged itself at "way-over-filled" for a week or so, so I started doing searches & asking questions & etc. GM will gladly sell you a new fuel gauge, and charge you $300 for it- it's the whole fuel pump assembly that hangs into the tank, minus the pump. (Might as well put a new GM fuel pump in there while you're at it, too.)

I barely had $3 back then, let alone $300, so another guy told me that I could go to a yard, and find a gas tank from a 90's-up GM car. He said the float element was the same dimension as ours. (It's a little rectangular box, about an inch by 1/2 inch by 1/2 inch.) He said I could remove the element from the junkyard car, and swap it with mine. Problem #1, it involves dropping down TWO tanks. Problem #2, this was before digital cameras, and I would've felt much better seeing proof of his. Problem #3, nobody's ever mentioned such a solution again- to anyone- that I've heard of.

Other idea that crossed my mind- buy a complete fuel gauge sender from JC Whitney for $15, for the GM 90-0 ohm gauges, and install that into my tank. Still involves dropping the tank, but all solutions require that.. and it's much cheaper than buying a $300 sensor. Problem: How to cut the tank without blowing myself sky-high! Fill it with water? I have no idea.

So luckily, the gauge fixed itself on it's own; presumably, it got stuck. But before, I used to always ride on 1/2 tank or below, after that, I started making sure to vary my fuel level so the wiper arm wouldn't just be wearing out one spot of that sensor wire.

Oh- one more solution, might be between the two in cost, but a hell of a pain in the ***- drop a tank down from a newer f-body in a junkyard, and swap it under your son's car. I hear the newer tanks, especially in the high-end model f-bodies (like trans am's), received special baffles to keep fuel from sloshing around. I think one guy on the tech forum even put a 4th gen F-body tank under his third gen!

But you might want to try probing the sensor wire at the tank-to-body-connector first, to make sure there's no short in the circuit that'd be easy to fix. That's one key about our 0-90 ohm gauges. For "full", the gauge needs to see 90 ohms... and (I'm sure you see where I'm going with this) if there's a break in the wire, that's infinite ohms, and the gauge over-pegs itself to "full". A short in the wire (for 0 ohms) should peg the gauge at empty. If your son's gauge is pegged at empty, it's probalby not the sender in the tank!

Oh and one more thing, if you haven't already, post (or search) at the main tech board and the TPI board and TBI board; all fuel injected thirdgens share the same fuel pump hanger/sender assembly and gauge wiring.

 

Thanks Dale, Ovrclck350 and as always TomP.

Update on troubleshooting:

Situation is the gauge is all over the place with no discernable pattern. I do not drive the car (except when my son needs a mechanic) so I have no real idea on what it's doing 100% of the time. I do know that when it's empty, the gauge says so too.

With fuel tank at 1/2 to 3/4 full, gauge reads 3/4 full before start.

After start, gauge will vary from 1/2 to 3/4. I searched through 12 pages of previous posts and I can duplicate the sloshing fuel syndrome on start and stop (lower readings when braking, higher readings when accelerating). After routine city driving the gauge will begin to lower it's readings as far down as 1/4 full even when the tank is actually 1/2-3/4 full/

Put car on stands and disconnected the 3-wire lead to fuel tank.
Cleaned the connection thoroughly with aerosol electrical contact cleaner.

Using the center wire (pink/purple) and the black wire (Gnd) got a reading of 28-30 Ohms with tank about 1/2-3/4 full/ It's not exactly 50% of 90 Ohms (45 Ohms) or greater, but it tells me there is some resistance back on that circuit. Without knowing what the publishd standard is for the whole circuit, I must assume the actual gauge in the cluster is functioning properly since it is showing complete sweep movement at various times.

Therefore, I have to begin to question the resistor in the quantitiy indicator unit in the tank. TomP is probably right when he says that "the float 'wiper arm' will wear the stainless steel wire down to nothing".

So, some day when there is no snow on the ground, the temperature is above 35F and I have nothing better to do, I'll drop the tank and investigate TomP's suggestion. I also suspect the previous owner had this car "sitting" longer than she stated. She had purchased a 2000 Tahoe and "did'nt drive the Firebird" much? When things are not used, they still break. Sometimes faster than if you did use them.

That's my story and I'm stickin' to it!

 

Can you send the gauge 0-90 ohms? Like with a $5 100K potentiometer from Radio Shack? Could probably hook the pot up right at the tank connector, and as you (or your son) turns the pot, someone watches the dash to see the levels. I'll see what my '86 GM book has to say about the digital dash; I think all Firebirds used digital dashes starting in '87. For '86, as Dale helped me find out, you only got a digital dash if you got the full gauge cluster. I'll double check on the 0-90 ohms bit, too...

 

I remember my guage would peg at way below empty if I did a power turn and was around a 1/4, then it would come unstuck during a refill.

But before the car left me; one day the gas guage pegged itself way over full, so I just figured it was a bad ground, but what you said makes sense. I might go visit the guy who bought the car from me and see how he is doing, and if he has not fixed the guage yet, suggest that too him. I replaced the tank shortly before I sold it, so all bolts are lubed up and easy to take out, so he might as well fix it now, rather then wait for it to rust in.

Back to the topic, from what you said AA88Fbird the guage moves erradically while driving, my tach did that, would jump slightly up and down at lower RPM's, I discovered it to be a lose bare spot in the wire. So you could try testing the guages wire that runs behind the rear seats and under the carpet and see if it is consistant, or maybe breaking up and losing contact.

 

More great ideas! Keep them coming. I'll print this thread after a few days and keep it to provide an outline for troubleshooting.

Will also provide feedback on solution (or at least what did not cure it).

 

I'm too lazy to read the rest of any of this thread, but correct me if I'm wrong when I just read that you asaid that all firebirds after 87 had a digital dash?

Mine doesn't.

 

I think he means electronic. As in the Speedometer runs off a sensor rather then a cable etc.

 

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OK. Then he's right, but it started earlier in the Trans Am's. THe base firebirds finally got them in 87, but the TA's had them earlier.