Hello, I am still trying to diagnose a cold start problem and now my fuel pump will not come on at all. Maybe related but anyway..... Turn key and no fuel pump pressure and no pump noise. I hooked up my snap on scanner and it shows no voltage at the fuel pump. I can reach the fuel pump relay from the drivers side and when I cycle the key I can fell it "click". If it clicks is it good? What else should I look for?


One other question for the masses... Can you have good fuel pressure but low volume?

89 GTA 350 TPI

 

A click would be a sign that the relay's activating. Most of the GM relays have 5 terminals:

2 for the coil
1 common
1 normally open
1 normally closed

On my TBI engine, one of the two relay terminals is always grounded. The other terminal is connected to the ECM which provides +12VDC to energize the coil.

On the other side of the relay, the common is connected to the fuel pump. The normally open side connects to a +12VDC source. The normally closed is supposed to connect to the ALDL terminal G (I think). This does nothing except allow you to place +12VDC to terminal G and bypass the ECM & most of the relay circuitry.

So basically when you key on, the ECM energizes the coil by sending +12VDC to it which pulls the relay contact from its normally closed to the normally open position. The relay moving is this clicking sound you're hearing.

The next step I'd take would be to:
1.) Probe the relay's normally open side for power. If none, you have a problem between the battery & the relay. If all is good, go to step 2.
2.) Key on and probe the relay's common terminal. If no power, verify that the coil is energized by probing the coil leads. If the coil is energized, but the common has no power, you've got a bad relay. If you have power at the common line, go to step 3.
3.) Unplug the fuel pump harness at the body up underneath the car and probe there for power. If you have power here, it's either a bad fuel pump ground or a bad pump. If no power, then it could simply be a fuseible link is blown. I see a fusible link on my TBI schematic between the hot side of the relay (the common terminal) and the pump. You could temporarily run a length of line from the loose fuel pump harness hot line to the battery and another from the harness to ground to check the pump. It a direct connection to the battery does nothing, you've got a dead pump. Otherwise it's either the relay, wiring or the ECM (which I would very much doubt, but could happen.). If it's the ECM, replace the relay as well because a shorted relay coil is probably what blew the ECM in the first place.

If it is the ECM & you wanted to get it working now the "wrong way", disconnect the relay's hot line from the ECM and run it to some accessory that powers with the key on.

Anyone else have a better TPI troubleshooting procedure or is this good here, too?

Don't know if you already knew any of this -- just passing it along in case not.

 

I've attached a truncated schematic that I found in a post from Vader. I've cut out everything except for what I wrote about above. Note: You've got an oil pressure switch, but I do not know if it would play a part in your system. Need input from a TPI guy on this...and if this does not match your ECM, the terminal designators will not match either, but the schematic should be the same for most everyone, I believe.

 

For the second part, yes, it is possible for the pump to develop adequate pressure and be unable to deliver adequate volume. A clogging filter can also cause the same situation.

 

I bought a new fuel pump relay, did not fix anything. Where exactly is the fuel pump harness at the body located? I want to probe it for power. I hope I have power to the fuel pump and the pump is bad. I have suspected that the pump has been my problem and that it has finally just quit. If that is the case its Walbro time!!!

 

The fuel pump wiring goes down the driver side under the door sill panel. It will be either a tan/white or a pink wire that goes behind the backseat almost in the middle of the hump where the gas tank is.

 

Yep...you should be able to access the harness from either inside the car (if you pull back the carpet) or underneath the car (Look in the area in between the fuel tank retaining bolts -- centered between the two bolts will be a weatherproof connector).

I prefer going underneath the car because I can unplug the harness & access the wires I need directly, but from inside the car it's just the same and probably easier.

 

Will the wire stay hot or will it just be hot for a few seconds after the ignition is turned on?

 

In most cars if the key is in the run posistion the fuel pump will run continuously, and will only shut off when the key is taken out of the run. Also, some cars also have an inertia fuel shut off switch that if it trips no power will go to the fuel pump (safety feature in case of accident).

 

The inertial switch isn't used in the 3rd gens. They are connected through an oil pressure switch and I have yet to see a factory fuel pump that stays on constantly when the car is in run. You turn the key to run, it primes the pump then when the car is started it stays on.

 

So there is nothing under there that will show power...

 

You should have a constant 12v source going to the relay, then a 12v source that will come on when you turn the key on to prime the pump which you can see on the fuel pump side of the relay until you start the car, then you will read 12v there until you shut the car off.

 

Checked the tan and white wire, 12 volt on that wire until prime is over. Must be bad fuel pump. (Kinda thought there was something wrong with it anyway). Ordered gss340m today.

 

Have you tried jumping power to the G terminal of the diagnostics link? It should give a constant 12v to fuel pump. Try it, try any thing you can... trust me it is not fun in any way to change a fuel pump in these cars....

 

So you are saying stick a 12v wire into G terminal? Will that then power up the tan and white wire all the time. (looking at the diagnostic schematic.

 

Yes, a 12v wire jumped to the G terminal will power up the tan/white wire ...mostly what i am saying is try everything before you go changing the fuel pump...

i thought my fuel pump was gone too... after changing the relay the power jump to G did not work on mine so i went ahead and changed the fuel pump and sending unit. well 6 hours and $250(CND) later the fuel pump still did not come on from the key or the terminal. i hooked the old one to power and i whirrrred away beautifully.
I noticed that the wiring on the relay was for some reason or another stripped back about an inch from the connector. I fixed the wiring and it started!... allbeit very roughly idling (which i have now found out is the MAF relays) the car sat for 6 months before i could do anything with it after the pump cut out.

well i am rambling, the moral is... check all the wiring, the connectors, the connections, everything...

a couple things i would check looking at the relay wiring diagram:

-First of all check the fuse, there is an inline Fuse near the battery (about 6 inches down the wires a 20A ATO in a black rubber holder), it has a red and orange wire coming out of the rubber holder i believe.

- do you have 12v at the E terminal on the Relay? if you are, is there 12v coming out the A terminal with the key on?

- are you getting a 12v signal at the C terminal on the relay (key on)?

- do you get ground from the B terminal at the relay?

- check at the ECM if you are getting any power from B2

- a wire may have rubbed on the chassis somewhere and is grounding out!?

i may be VERY wrong here cause i am not 100% sure Exactly how the circut works but:

i would imagine it is in the "fuel pump relay drive" part of the circut. it looks to me as if the "prime" signal comes from the B2 pin at the ECM, and the power sent through the relay runs the fuel pump when the car is running.

Well that gives you a checklist to start with, (Vets please correct me if i am wrong) if these things all check out, i think i have read in these forums that a faulty Oil pressure switch can cause the fuel pump to not fire up!?...

Good Luck!

 

Looks like the Skunk covered about the entire circuit. Just don't overlook the grounds for the pump motor itself.

If you are measuing 12V to the pump during the 2-second prime cycle, the ECM and relays are probably working correctly. The pump will not get power again until the ECM reads distributor reference pulses (distributor and engine turning) or you shut off the ignition for 20 seconds then turn it back on to initiate another prime cycle.

 

Vader,

The connector under the vehicle that the fuel pump plugs into..... Being under the vehicle looking forward at the connector....On the left side I'm getting 12v, middle I am getting a very low voltage reading, the test light barely lights and right side I think is ground. Are these readings correct? Thanks

 

I cannot really tell by connector position or orientation, but wire colors would help. Chances are you are reading 12V at the pump line, some unknown voltage from the fuel guage, and 0V on the ground terminal. Make sure the ground is indeed a good ground.

 

I cant see the wires, its the connector that comes through the body of the car behind the back seat. When I was trying to diagnose this problem I checked some wires that were mentioned in a earlier response up above. They run along the drivers side under the carpet retaining panel. It was a tan/white wire which was 12v during the ignition prime. There was a pink wire that gave me the low voltage (dim test light) like in the connector that I mentioned before (fuel pump body connector).

 

The pink wire is for the fuel gauge. The tan/white is the fuel pump feed and the black (or black/white) will be the ground.

 

This just happend to my fuel pump but might not have anything to do with yours. I thought my fuel pump was gone bad so I spent 5 hours replacing it and put a new one in. It ran fine for a time or too then quit. It did the same thing. It ended up being the distributer(sp?) coil. I replaced it and everything is fine.

A good way to check if your fuel pump is working is to disconnect the fuel line thats hooked into the fuel filter. Then turn the car in the run position and see if its pumping out. Its gonna be leaking some out to begin with, but if the pump is working it'll be a whole lot faster.