New fuel pump, filter, in-tank sock- No start.

1987 740 GLE

OK, picking up where I left off:

1. Pulled the in-tank sending unit out to see why car stalls under 1/4
tank gas in turns. I broke wiring inside the sending unit.
2. I got a replacement sending unit and pump. BUT, they didn't have a
1987 model, so I bought a re-designed 1988 model and hard wired it.
3. Car ran like crap, then died. D-e-a-d.
4. I checked a bad ground wire off the in-tank sending unit. Car ran
great. 4 blocks and then D-E-A-D again.

Question was then, even with possible bad in-tank pump, why NO start?

5. Today I bought a new main fuel pump, new main filter, new sock for
in-tank sender unit. I re-assembled everything. Car didn't start.
6. Swapped out fuel pump relay. Nothing.
7. Swapped #1 fuse. Nothing.

I will go back and double check the wiring to the main fuel pump. I
could have made a bad connection with those butt-connectors. After
turning over the ignition, there is a buzz for a couple seconds. Isn't
that the main pump working?

I am stumped!!!!

 

Do the following test. You will need to listen to or feel the system/fuel
relay.

Turn key to ON, system relay portion should click. When you crank the
engine in an attempt to start, the relay should click a second time. This
is the fuel portion of the relay.

If no first click, system fuse or wiring. No second click a bit more
complicated. Second click depends upon a signal that the engine is
rotating. No engine rotation, no fuel pumps. I think in 87's signal for
engine rotation is from distributor Hall sensor. A test for spark while
cranking engine will verify.

There is also a radio supression relay somewhere under the hood that will
stop a 700 dead. I do not know where it is since I'm most familiar with the
200 series. Engines and controls swap between, not all wiring.

Duane

 

The buzz is the main pump running, so it sounds like that part is fine.
Where did you get the new pump? They're a lot cheaper online than at the
dealer. It's time to narrow things down a bit. Pull the low pressure
hose off the main pump and turn the key, verify fuel squirts out of this
hose. If it doesn't, then the problem is somewhere between that and the
sock in the tank. If it does, pull the return hose off the fuel pressure
regulator at the engine, turn the key, fuel should squirt out the
regulator, if it doesn't, then look at the main pump and hose. You can
also check for voltage at the connectors of the pumps to see if they're
receiving power when the engine cranks. There's just not many components
in this area, it should be pretty easy to diagnose.

 

Autozone happened to have the pump, and I usually don't like to buy
these type things from them - I had exposed gas tanks and fumes I
wanted to hurry up and seal.

Today I will do a complete check. A few things coming to mind are:
1- recheck the wiring to the pump.
2- I never checked to see of the line was clear from where the in-tank
pump connects, through the sender. When I pulled this sender out of
the parts car, it had no sock. I could easily blow through the pump -
but never checked to see of the lines through the sender were clear.
Maybe fuel is not getting through the sender.
3- I want to check the line from the tank to the main pump. When I
disconnected the fuel lines to the main filter and pump - fuel poured
out of the engine side under pressure, but only trickled a bit from
the tank.

If I redo the wiring and still get no start, I am thinking definite
fuel starvation. Remember - this car ran perfectly before I swapped
sending units. The only problem it had was sputtering and stalling on
turns with less than 1/4 tank.

Something changed when I added the 1988 model, used sending unit.
Possibly some obstruction, otherwise there is something funny about a
1988 model that makes it NOT like a 1987 car that it wasn't designed
for.

 

OK:

I rewired the fuel pump. Purple wire to positive, black to negative.
Nothing.
I pulled the fuel line from the tank off the pump - no gas. I blew
hard into the line, then I got some return fuel at a good pour. I
reconnected -- nothing.

I disconnected the in-tank electrical wires, except the ground.
Nothing.

Car turns over, but no firing.

Swapped fuel pump relays with some spares - nothing.

jamie

 

Do you have voltage at the pre-pump? It sounds like that pump is either
dead or not getting power. You can check at the connector. It may be
helpful to make a jumper out of a couple of male spade connectors and a
short piece of wire to fit in the relay socket and bypass the pumps on
for testing. Also make sure you didn't wire the pre-pump backwards, you
could be sucking fuel back into the tank.

 

Not sure if I have voltage at the pre pump. Wiring - there are 3
wires, plus a ground. The pump is wired using only the purple wire
from the car, it grounds through the black wire. The brown and grey/
white wires run the gauge. I disconnected the pre-pump to see if I
could start the car. No start.

I want to re-check the Fuel Pump relay. I swapped 3 used ones, but
never checked for clicking (1st and 2nd).

So let's think - I do nothing but replace the sender unit and the car
runs crappy. I drive to the gas station and add just under 1/2 tank of
gas. The car is now barely running, so I limp home.

I undo and redo the ground wire for the sender unit, and the car
starts right up and idles great. I take the car for a test drive, get
4 blocks and it is dead. No start.

I replace the fuel pump, main fuel filter, and sock on the sender. No
change.

What could a replacement sender from the parts yard have done to cause
such a failure? Now, even with the replacement sender disconnected -
no start.

 

OK, still no change other than I need to charge my battery from
cranking.

Today , here was what I did:

1- Pulled main fuel line off fuel rail. No fuel there.
2- Pulled return line off valve and blew - air got to tank.
3- Cranked engine - no fuel from main fuel line coming out.
4- Removed entire fuel pump rack and disassembled. Nothing clogged.
5- Tested fuel pump - it works, even sputtered out a bit of gas.
6- Checked fuel pump relay -- two clicks.
7- Disconnected lines from in-tank sender. I can easily blow air
through main fuel line to pump. (No obstruction)
8- I can blow air from return line at tank to engine. (No obstruction)
9- I can blow into both metal tubes for sending unit - fuel returns
from both tubes. No obstructions
10- I can blow through fuel filter - (No obstructions)
11- All fuel filter/pump connections had no obstructions.

So, as far as I can tell, the relay works. The pump is getting power.
I have just under 1/2 tank of gas. No lines seemed clogged or pinched.

Why would you think no fuel is making it to the engine? The pump
operates and the lines are clear.

Thanks,
Jamie

 

After much thought, I am convinced that the only thing different that
caused problems was the new sending unit. I am wondering, could there
be cracks or something allowing AIR into the system, so when the pump
runs, it sucks air and not fuel?????

 

My bet right now is that the pre-pump is wired backward and is blowing
fuel back into the tank against the suction of the main pump or the
pre-pump is bad. Without fuel in the line already the main pump is
probably not able to prime the system in a reasonable amount of time.
You still haven't said whether you pulled the hose off the input of the
main pump to see if you have fuel flow there.

 

Yes, I have fuel flow all the way to the main pump. From there I can't
get it to the rail. Now, when I disconnect the line at the pump, no
gas comes out. So I blow into the return line at the rail to force gas
to the pump. From there, I can't get it to the rail. I get air
pressure when I release the inlet line at the rail.

I'm trying to see how I could reverse wire the pre-pump. I ran purple
to the pump line, then gray/white to gray/white and brown to brown for
the gauge. Is this wrong?

 

Yes, I have fuel flow all the way to the main pump. From there I can't
get it to the rail. Now, when I disconnect the line at the pump, no
gas comes out. So I blow into the return line at the rail to force gas
to the pump. From there, I can't get it to the rail. I get air
pressure when I release the inlet line at the rail.

I'm trying to see how I could reverse wire the pre-pump. I ran purple
to the pump line, then gray/white to gray/white and brown to brown for
the gauge. Is this wrong?

 

Yes, I have fuel flow all the way to the main pump. From there I can't
get it to the rail. Now, when I disconnect the line at the pump, no
gas comes out. So I blow into the return line at the rail to force gas
to the pump. From there, I can't get it to the rail. I get air
pressure when I release the inlet line at the rail.

I'm trying to see how I could reverse wire the pre-pump. I ran purple
to the pump line, then gray/white to gray/white and brown to brown for
the gauge. Is this wrong?

 

Well if you have fuel flow to the main pump but no fuel at the rail then
the pre pump is operating and either the main pump is defective, not
receiving power, or there's a kink or clog in the line. Loosen the banjo
bolt at the filter output and see if fuel sprays. I know it's a new pump
but it could be defective.