I'm attempting to decipher the 'no fuel' problem on my 86GT. I aquired it knowing they had issues with this in the past and had replaced the fuel pump but they stated it was now getting too much fuel. The vehicle did smell of gas when he attempted to start it for me but the battery was weak and the attempt failed.

Heres a rundown of my diagnosis so far:
1 - engine fires and runs on starter fluid verifying spark
2 - ran a fuel pressure check... no fuel present, however fuel guage registers roughly ½ tank
3 - fuel pump fuse is good and hot on both sides with key off... not sure if this is the norm
4 - as the radio doesn't shut off and the radiator fan runs fulltime [or so I thought] I pulled those fuses and turned the key on... no pump noise.
5 - reinserted those fuses and seperated the 3-prong tank connector in the engine compartment at the firewall, turned the key on and went back to check for voltage on the loom side. none was present but as I was checking this, the fan shut down. The A/C is not on so that isnt why the fan runs. the fan seems to run for maybe 20 to 30 seconds before it shuts down.

My question is what is it that shuts the fuel pump down in the initial 'key-on' circuit? Is it a pressure sensor or is this a timed circuit? The reason I ask is could it be possible that the former mechanic swapped connectors at the relays, causing the fan to run for a short time and shut down? Checking for voltage at the relay is the next step for me while I wait for a reply. Another question is shouldnt I register a voltage at the connector for the fuel tank on the loom side on at least one of the prongs?

Thanks in advance

Steve

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Site: FieroMojo
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Remove your cigarette lighter plate to expose the ALDL connector:

Next, use your multimeter to check for a short to ground on the terminal marked FUEL PUMP TERMINAL in the picture. If no short, then run a jumper wire from the 12v power terminal off the cigarette lighter to the FUEL PUMP TERMINAL in the ALDL connector. Does the pump run? Can you hear it? If it runs, then check for fuel pressure. If no pressure, then the pump is fubar. If pressure, how much? Spec is 35-38 IIRC. If the pump doesn't run, then either the pump or the wiring at the pump is fubar. The ALDL terminal is a direct connection to the pump, bypassing the oil pressure switch and the fuel pump relay.

JazzMan

The ECM turns on the fuel pump for about 2 sec. when you turn the key on. After that the fuel pump relay is activated by spark pulses from the ECM. As a backup system in case of a bad pump relay the oil pressure switch will kick on the pump when the oil pressure reaches a certian pressure (6 psi I think).

to answer your original question--yes, the initial 'key on/2 sec fuel pump run up is an ECM initiated timed event. It is possible I guess to hook the fuel pump circuit up to the fan circuit relay, but you would have to go way out of your way to do it. The FP relay is in the eng compartment, on the left firewall-and the cooling fan relay is in the front of the car near the driver's side headlight.

The advice given above by Phil & Jazzman are good troubleshooting sequences. Follow them.

Thanx for the replies. I will go run a 'short circuit' check on that fuel pump pin in the ALDL block as I merely checked for voltage at the lighter socket and jumped that to the pin. As a side note, the fan now runs for 2 seconds and shuts off... maybe an exorcism is in the near future?!? Beyond that, its looking like the tank gets dropped tomorrow, only to wait til tuesday for parts.

Thanx again for the help.

Steve

Assuming that you checked the correct pin in the ALDL connector (look at the keying tabs) then yes, you've got a short either in the wiring or the fuel pump itself. If you unplug the fuel pump connector and it is still shorted, unplug the relay. If still shorted then unplug the connector at the oil pressure sender. If still shorted then the wiring is shorted in the harness somewhere.

JazzMan

I'll run those checks tomorrow. Thanx for all your help. I have a car that needs clutch work and I'll drop that tank and just swap tanks for now if it comes to that. If theres a bad harness, I'm sunk.

Steve

OK - I ran that test and it shows continuity to ground at the pump terminal

Now wait a minute. You do know that you can read continuity thru the windings of the pump? A short to ground, is zero resistance and will undoubtedly blow the fusible link. What you are looking for is an open circuit, (max resistance)such as you would get if the connector on the pump had come off, or if the winding on the pump motor had burned in two. The 'hot at all times' wire is fed from a fusible link.

[This message has been edited by maryjane (edited 08-30-2003).]

That is what I was thinking but I'm not going to question the advice given here when I'm not absolutely sure of everything involved. My first thought was I should be checking for an open, not a short. I cant say if it was 0 resistance but the needle did sweep what appeared to be the full face of the meter and it was properly adjusted prior to testing. I will get a more accurate measurement tomorrow.

Thanx,

Steve

If you've got zero ohms through the pump it's a short. If it's low ohms then you're measuring the resistance of the pump windings. The fuse for the pump is 10A, so at 12V the pump will have a resistance as low as 1.2 Ohms before it'll blow the fuse. In reality the pump probably has 2-3 Ohms resistance. Worst case scenario, you can just connect the cigarette lighter power to the ALDL pump terminal and see if the pump runs. If it's shorted all it will do is blow the BAT fuse, you can replace that and start looking for the short in the harness.

JazzMan

[This message has been edited by JazzMan (edited 08-31-2003).]

[This message has been edited by JazzMan (edited 08-31-2003).]

Jazzman- the fuse only protects the circuit that controls the input to the relay. Once the relay 's contacts are closed, or the oil pressure switch closes, the pump is fed directly from the 'hot at all times' fusible link. I've cut the fused circuit out of the posted diagram, to save space, but that's how it works.

I was aware of that. I was referring to using the cigarette lighter power connector as a power source for the pump at the ALDL connector. If his fusible link for the pump is blown and he's not getting power to the pump, then jumping the pump with the cig lighter will work because it's on a separate fusible link. This is safe because the cig lighter power is protected by a separate fuse. My suggestion to do this was based on saving time trying to analyze all the possible circuits in the system, instead just hook it up and see what happens. If the fuel pump works then he doesn't have to drop the tank. If the pump doesn't work and/or the fuse blows, then he needs to drop the tank.

Measuring the Ohms at the connector to check for a complete short would save the time of replacing the fuse, but only if he has a decent Ohmeter.

JazzMan

I gotcha-sometimes hard for my old brain to folow along.

LOL! My brain follows along just fine, only problem being that the last time it followed someone it didn't come back.

JazzMan

Thanx for the clarifications. The meter is accurate enough to measure the drop across the windings vs a dead short. I measured it last night by the dim glow of the interior lights so this time I'll make sure everything is as accurate as I can make it.

I'm assuming the 'hot at all times' pin will be hot with the key off and from that diagram I can determine if it is live or dead at the relay.

I'm trying everything I can to isolate this problem electrically as I was told the pump was recently replaced and I wont be able to drop the tank by myself as its showing half full on the guage. Time to design a hydrolic 'helper'.

Thanx again... this is much appreciated.

Steve

I created some confusion it seems. The 'hot at all times' wire is not at the aldl. It is only at the fp relay. The G terminal you are measuring from is a direct test wire from aldl to the fp, & normally does not carry any voltage at all, key on or off, except for the 2 secs when key is firs turned on.

[This message has been edited by maryjane (edited 08-31-2003).]

I understand. I'm checking the hot wire at the relay plug, not the G terminal on the ALDL. I'll be checking for Ohms at that terminal. As long as theres no surprises like resistance wire in that path, I should determine, via Ohms read, whether there is a short or not.

Did you try just hooking up 12v to the ALDL terminal to see if the pump runs yet? If it does and generates pressure at the fuel rail then you're done testing the pump and won't have to drop the tank. Then you can move on to finding out the problem with the harness. This is such an easy test to do and it quickly eliminates half of the things you have to check.

JazzMan

With the key off, there should be one hot wire at the relay, fed from a fusible link. When the key is first turned to on, there will still be that one hot wire, plus another that should be hot for 2 seconds. During those 2 secs, the output from the relay to the pump should also show 12v. sent you a pm.
edit:
Jazzman-that's what I asked him in the pm.

[This message has been edited by maryjane (edited 08-31-2003).]

I've done that without success. I just used the big meter on the Ohm check and I read just over 3 Ohms. I checked and doublechecked that reading against a known 0 Ohm load [short] to verify the meter is zero'd out and the reading at the terminal remains constant. I measured voltage at the lighter and got 12v so I know that is working. Jumpering that to the terminal yields nothing.

After looking at that diagram, it appears I should get a voltage at the G terminal when the ECM performs the initialization function. That also turned up negative. I tried cranking the motor and, after oil pressure built up, I got a reading of about 1.25v at the terminal. The meter is set to 3v for accuracy as it barely moved at 30v. If I'm chasing shadows here, let me know.

steve

Ok, that doesn't sound good. One, it indicates the pump is no good, or the circuit to the pump is open.
It also says the relay probably isn't energizing, because you should have read 12v for a couple of seconds when the key was turned on.

There is another place you can check operation of the fuel pump, but itt isn't as easy, & I'm not sure where it is on your car. It is a connector, that plugs the fp wire into the harness on the firewall. On my 84, it is behind the firewall heat shield, and has the wires for the gas gage sending unit, and the FP wire on it. Find it, unplug it, find the correct wire, & apply 12 volts to it. You should hear the pump run. If not, prepare to drop the tank.

Well the car is in the garage. Now I need to find out how to jack these things up 2 feet off the floor and where the best support points are. I'm assuming somewhere near [not on] the suspension on each corner.

This is the first Fiero I've ever worked on. Once past the idiosyncrasies I'll be able to handle it. If anyone has any ideas, please pass them on.

Thanx,
Steve

For some real good jacking tips go to the ogres cave at the top of any page and look under safe jacking. He shows a diagram of jacking points. Very nice!

I did a search in Tech and found his site and the area that showed the jack points. One problem... my floor jack wont fit with clearance to pump the handle. I tried Fiero jacks on each side and I couldnt get it high enough before the car became unstable. I need an air over hydraulic floor jack http://www.jackxchange.com/products/71245.cfm and even then I'm not going to get the clearance I need to crawl under and work.

Looks like the '35 Ford Stake Rack moves outside so I can use the pit. Too bad its raining... Anyone wanna buy a truck??

Its goin cheap... I need my garage back!

(edited for url)

[This message has been edited by FieroMojo (edited 08-31-2003).]

[This message has been edited by FieroMojo (edited 08-31-2003).]

I just removed mine a few days ago to change the fuel pump strainer. All I did was jack up the back and used 2 jack stands. You really only need enough room so the tank will slide out the back. The fun part is disconnecting the hoses

I was concidering that but I dont think my arms are quite that long. I'm hoping I can do it solo in the pit with about 5 gallons in it.

I jacked mine up and put it on 4 jackstands at their lowest height. Had plenty of room. The hoses are a beech. Before you can lower the tank, you will have to unplug the wire going to the pump. May as well do that first, apply 12v to the pump side of the wire, & see if the pump runs, just for sheets & giggles. The connector should be in the firewall aarea somewhere. It was right in the center on mine, right behind a heat sheild.

I still dont think I can fit under there and have room to work. Im not exactly 'thin'. I have no clue as to which one of the 3 connections would be the pump send in that connector and I can just reach it as it is. I'll just drop it the best I can and test the pump outside of the tank and if its opperational, I have a big job ahead of me.

Thanx all for your help.

I've pulled the fuel tank with minimal jacking of the rear end, and it's no fun. This morning I put this '88 Formula up on the homemade ramps you see here. The bottom of the wheels are 9" above pavement. This gave me comfortable room to turn wrenches underneath, and insures clearance for the fuel tank.

Everything that needs to be disconnected or removed is accessable from below, now. I used the MityVac to start a siphon, and removed @6 gallons old fuel thru a long "fishtank" plastic hose, into buckets.

Once the tank was empty, I held the front end up with my knees, undid the two retaining straps, and easily lowered the tank.

Start to finish, jacking up to cleanup, took less than 3 hours, and I work slow. Best thing was not to worry about the car being unsteady.

Notice he didn't mention uncoupling the hoses before lowering the tank? I found it easier to partially lower the tank a little, then undo the hoses. Guess it depends how small & flexible your hands are tho. It can be done before unbolting the straps, but not by me. It's not a really tough job Mojo-jacking the car up securely & safely is half of it. good luck. Good pictures opm2000.

While you have the tank out, it wouldn't hurt to check the hose barbs on the tank that the rubber hoses clamp to. I noticed that one of mine was suspiciously clean and it obviously had a slight leak at the tank. If you can get the hoses, I'd replace them if they are stiff. Mine were flexible enough to reuse.
I don't know if it hurt, but I rubbed a slight coat of petroleum jelly on the hose barbs to make it easier to slide em on.
It's still a pain.

Does anyone know what would happen if the small pump lines were reversed? Would it cause problems like he's having?

TG

[This message has been edited by TennT (edited 09-01-2003).]

This just gave me an idea. I know in my case, being the Fiero newbie that I am, I'd love to be able to go to one place to see common jobs like this in this kind of detail. opm2000...Thanx a ton for the pix and info. I wasnt aware that the MitiVac would withstand gasoline and that makes things look even better for pulling the tank in the pit. Maryjane... thanx for the tip on lowering the tank first before removing the hoses. Its those little things that go a long way in making a task go smoothly.

I bought four 2-ton stands specifically for this job but getting the car up in the air seems to be a chore. Last night the car became unstable on its own scizzor jacks as I was attempting to lift the front end far enough to fit the floor jack underneath and have room to pump the handle. All I was able to do was lift the rearend from the jack points. I must be missing something here but I assume theres only one place per side for those jacks and the rear tires lifted great but all I was able to do was unload the springs in front. Once the car came toward me on those jacks, I became apprehensive about doing the job on the floor and decided to wait til I can get the truck off the grease pit. Right now my only problem is to get the front of the car lifted. Like I stated previously, once I get beyond Fiero's ideosyncracies, I'll be in good shape.

It amazes me how, after nearly 40 years of 'grease to the elbows' working on everything from my own cars [all full size GM] to dads restorations to 15 yard tri-axle dump trucks, I cant seem to tackle this simple task. This should be a walk in the park after doing things like rebuilding motors and repairing truck trannies/differentials. Why cant I get that flipping frontend up in the air? I hope I never have a flat up front!

Confoundedly,
Steve

Yeah, I did disconnect everything before removing the straps. The two big hoses can make you hate living. I used pump-pliers to rotate the hose and break the "age-seal" to the tank outlets...and then a big screwdriver as a lever, with lots of hose wiggling at the hose-elbow. sliping the electrical connector thru the firewall hole is almost as challenging.

BTW, I am a small guy. If you happen to be a "large" person, you might do well to get a teenager to do it for a $10 spot. Or try the hoses after lowering the aft end of the tank a bit. Just watch your fuel weight-shifting on you.

With the MightyVac, either use a real long tube or use the break bleeder cup. I didn't say it would withstand the gas. I just used it to fill the tube and get the siphon started. Gas never touched the MVac.

This '88 has been setting for years and the innards of the tank are really gooked up. I thought I'd try an initial rinse of 50/50 gas/Marvel Mystery Oil....then rinses with hot water...and final rinsing with gas. What would you guys do?