Went to start and move my 88 4cyl and could not get fuel to the TBI. I have the manufacturers manual but do not understand what I need to do to test whether or not the fuel pump is bad. I know the fuel pump test circuit is under the front left headlight, but am not sure how to "apply a voltage" to it to test it? Can anyone explain in more layman's term, step by step how to test the fuel pump? It doesn't seem to be coming on when I first turn on the ignition (don't hear anything). I also noticed that my fuel gauge is pointing all the way to the right and does not respond to the ignition being turned on. The oil pressure sensor is supposed to be able to regulate fuel if the fuel pump is not functional according to the manual, but this too does not seem to be working and it is brand new. I need to get the car running and just don't seem to be able to understand where all I need to check and how and with what tools are necessary. I have a multimeter, but am unsure how it needs to be set up (configured) to test once I get to the right places. Sorry, electrics are not my cup of tea. Any and all help with this would be greatly appreciated!

Not sure about the under the headlight thing, but you should have a test terminal underneath the cigarette lighter cover panel.

This is called the ALDL connector, I believe Jetman is the uploader of this picture:


When you first turn the key to the "Run" position, you should be able to hear a click in the engine bay as the ECM triggers the fuel pump relay. If you don't, it is possible the relay has failed or an ECM issue. When you turn the key, does the "Service Engine Soon" light turn on like normal?

[This message has been edited by Xanth (edited 01-22-2011).]

I do hear the "click" and have the service engine light on. I tested the ALDL last night and only got the code 12 over and over...no codes. It seems to be the fuel pump, but I'm unable to figure out how to test it. In the 88, the test link is under the front left headlight. All other years it is behind the drivers side seat in the engine bay close to the relay. How do I apply voltage to it to test it?

[This message has been edited by zefferk (edited 01-22-2011).]

That picture I linked above, one of the terminals is labeled Fuel Pump Terminal. You just need to run a wire from a 12 volt source in the car to that terminal. Just make sure you get the right one and don't accidentally send it through the data terminals.

Your manual is wrong. There is NO test port at the left headlight.

quote Originally posted by Xanth: One other thing If I remember correct, if the sending unit/fuel pump harness were to come unplugged somehow your pump would not work and the gauge would read pegged past full.

Where is this located? That could be the issue, but I'm unclear where this is. Under the car by the pump or where? Thanks!

Yellow plug, on the firewall, inside the ENGINE compartment, behind the passengers left elbow. It is the only yellow connector in the engine compartment. I highly doubt that the connector came unplugged but check it anyways. Three wires on it.

quote Originally posted by phonedawgz: Your manual is wrong. There is NO test port at the left headlight.

No, actually there is a connection there and the leads match that which is shown and described in the official Pontiac service manual. I believe the trouble chart A-3 describes it in the fuel emissions and driveability section...don't have it in front of me currently. It clearly states to apply a voltage to this port to test the fuel pump function. I tried to connect the fuel port to the ground on the ALDL to get the pump to cycle, but nothing...

Test your fuel pump....

ECM or ignition could be bad...
Injector will not fire if ECM can't see reference signal because ignition is bad, or ECM is bad.
Get a noid light... see cave, more scanner tools in ECM section

------------------
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The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

idk - re headlight. If it's there it's news to me.

There are two relays behind the drivers seat, but in the engine compartment. One is a fuel pump relay, the other an AC relay. The fuel pump relay should be clicking on when you turn the key to just ON, then off about two seconds later. Try swapping the two relays and see if that clears up the problem. Both are the same type. If that solves your problem then you will need to replace the one since that will either make your AC fail, or your fuel pump not run, depending on which connector the relay is in. Note - The fuel pump relay might be either of these two relays since they can be unhooked from the firewall and put on the other way.

I'm not sure on the 2.5 but on the 2.8 the air filter housing is in the way and needs to be removed to gain access.

quote Originally posted by phonedawgz: Yellow plug, on the firewall, inside the ENGINE compartment, behind the passengers left elbow. It is the only yellow connector in the engine compartment. I highly doubt that the connector came unplugged but check it anyways. Three wires on it.

Thanks, I'll check this too!

On the fuel test pin on the ALDL you apply +12v to get the pump to run, not ground.

Btw - there is +12v on the connector that connects to the cig lighter.

So to apply +12 to pin G, take out the two screws for the cig lighter, unplug the connector from it, stick a short wire into the connector and stick the other end into pin G. Make sure you don't let the wire touch ground or it will blow the fuse for that circuit (BATT fuse) in the fusebox

Since you jumpered A-B on the ALDL you should know which those two are. Sometimes the ALDL is mounted upside down. G is away from where you jumpered A-B. Since you could read the 12 code fine, you jumpered A-B exactly how it should have been done.

[This message has been edited by phonedawgz (edited 01-22-2011).]

This is the fuel pump connector, looking down by the right decklid hinge:



In the service manual, Page 6E2-A-22 references terminal G of the ALDL as a the Fuel Pump Test Terminal. The next page shows the test I was describing.

Ya, I knew the relay was there, but there is a test port in front (don't know why they moved it there?). Anyways, how do I jump the +12V from the cig lighter to the ALDL?

I did find that my O2 sensor was not connected, but nothing changed once connected....dag nabit!!!

The ignition is completely new...new tps, new control module, new coils (MSD), and new wires and plugs. It will start with gas placed into the TBI unit. Just no fuel getting in...

Well I described it above but here is a way to do it.

First check that the cig ligher does work.

Again take out the cig lighter housing (2 screws) and unplug the POWER wire from the CENTER back it. The one to the shell of the housing is ground. Take a straighened paperclip and put it in pin G. Connect the cig lighter POWER wire connector to the other end of the paperclip. The cig lighter wire has +12v on it at all times.

Radio off, semi quiet location, you should hear the fuel pump run.

[This message has been edited by phonedawgz (edited 01-22-2011).]

Yes

The fuel pump and the gas gauge use the same ground for a return. The black wire is the ground wire. It connects from the pump/fuel sender to the Yellow Connector (C502) and then to a large splice S213 by the console. There is about zero chance the slice went bad. There is about a 95% chance the ground came off at the fuel sender/pump. 5% is the wiring in between the two.

So I am also guessing putting voltage to pin G did nothing.

The picture is looking down by the passenger side decklid hinge.

Okay, that is what I thought it was. Mine is not yellow and has purple and grey wires coming out of it. The connection is tight and was connected well. I've disconnected it and have sprayed some electrical connection cleaner on both ends. I'm waiting to let dry and then I'll re-connect and try again. If this doesn't work, do you think the connector is bad? Why would the pump run for a few seconds when I first hot wired it to the cig lighter and now I can't get it to cycle now? Even more baffling is the fact that the fuel gauge doesn't respond either. I think it points to the connection , but how do I check it? Like I said before, I am no wiring expert.

The connector is just one link in the chain that makes the fuel pump and fuel gauge work. You can only fix the problem by finding the broken link and fixing it.

One way to think of it is of a game of higher or lower. There are places you can check to see where the problem is and they will point you in the right direction (higher or lower) but they won't tell you exactly where the problem is. One thing that can go wrong is when you "pre-decide" where the problem is and then you try to prove the problem is there.

I am making an assumption that the fuel gauge problem and the pump problem are related. What I would like you to do is to measure the resistance of the fuel gauge sender in the tank. What this will do is tell you if at the connector the fuel gauge sender is looking like it is working. Of course if you measure at the connector and find that the fuel gauge sender isn't working, then it really looks like the trouble is inside the tank, or at least on the wires on top of the tank.

You said there were two wires at the connector but there should be three. A Tan a Pink and a Black. What I want you to do is measure the resistance between the pink wire and the black wire on the connector of the wire that goes to the tank. To do this you need to have your meter on, set to OHMS and black lead in COMMON and the red lead in OHMS (and a whole bunch more). You will know you have the leads in and the meter set right if when you connect the two probes together the meter changes to a zero reading. It might beep also. With the leads not connected you should get something that represents infinity. Different meters use different symbols so it's hard to say what yours will say. But the meter has to change from that symbol to 0 when you connect the leads together.

Then go to the car and read the resistance between the pink and the black wires. Again make sure its on the wires that go to the tank. You should get some reading. NOTE - your meter can read the number of ohms in K ohms or M ohms. K means x 1000. M means x 1,000,000. So be careful when you read the meter that you are reading the real number of actual ohms and not getting fooled if the meter is saying K or M.

The reading you get should indicate the amount of gas in the tank. The sender WILL read about 90 ohms with the tank full. It WILL read 0 ohms with the tank empty. If the reading is way above 90 ohms (like 1.03 K ohms) then there is a problem in the sender/tank/ground. If the sender reads something like 45 and you had a half tank, well then the wiring to the sender is good and we should look back towards the car itself.

I think what you will find is the sender is going to read way high indicating a problem in the tank.

Note - you can also try to see what you get between the pink and the tan wires. This is reading both the resistance of the sender PLUS the resistance of the fuel pump. That number SHOULD be higher than the Pink to Black reading. If the PINK to TAN reading is lower than the Pink to Black, that would for sure say you have a ground problem at the tank.

Three wires...my bad. They are purple, tan, and black as you say. I will follow your suggestion above and report back as to what I find. Thanks so much. I hope you'll continue to follow my progress until I have this resolved. I really appreciate it!

Coolz