• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

740 740 no start

N

nickvolvo746

Member
Joined
Nov 13, 2017
Location
New Jersey
1991 745 turbo
Sorry idk why it posted twice and i cant delete it somehow

Hey all, just threw a new starter in the 740 and it now turns over but im not getting fuel. Took the hose off that goes to the fuel rail and not a drip when i turn the key. Definitely gettin spark. hear the relay clicking so believe it works. Also pretty sure the pump did work so how can i check for sure?
 
You could apply 12v to the pump as a test.

Your fuel pump relay on a 7/9 also sends a 12v signal to the radio suppression relay, which powers injectors. Have a spare fuel pump relay to test?
 
Before you get fuel. You have to have spark. I would make sure you have a good strong spark. If that is good then the computer will turn on the fuel. Put a test light on the coil 1 terminal and see if you have switching. If that looks good then I would proceed to fuel testing.
 
dl242gt said:
Before you get fuel. You have to have spark. I would make sure you have a good strong spark. If that is good then the computer will turn on the fuel. Put a test light on the coil 1 terminal and see if you have switching. If that looks good then I would proceed to fuel testing.
Click to expand...

How so? Plenty of instances where you can lack fuel fuel but still have spark, lack spark but have fuel, lack both, etc.

OP try spraying an alternative fuel source into the intake manifold (ether or brake clean) and see if it sputters to life for a few seconds. This completely narrows your issue down to being only fuel related.
 
dl242gt said:
Before you get fuel. You have to have spark. I would make sure you have a good strong spark. If that is good then the computer will turn on the fuel. Put a test light on the coil 1 terminal and see if you have switching. If that looks good then I would proceed to fuel testing.
Click to expand...

Yeah it has good spark, got it goin on brake cleaner before realizing it wasnt gettin fuel.
 
iHateVolvoPeople said:
How so? Plenty of instances where you can lack fuel fuel but still have spark, lack spark but have fuel, lack both, etc.

OP try spraying an alternative fuel source into the intake manifold (ether or brake clean) and see if it sputters to life for a few seconds. This completely narrows your issue down to being only fuel related.
Click to expand...

Thanks mate, actually tried that, shoulve mentioned it in the post. Im thinking ill check the radio supression thing
 
iHateVolvoPeople said:
How so? Plenty of instances where you can lack fuel fuel but still have spark, lack spark but have fuel, lack both, etc.

OP try spraying an alternative fuel source into the intake manifold (ether or brake clean) and see if it sputters to life for a few seconds. This completely narrows your issue down to being only fuel related.
Click to expand...

Only if the secondary part of the ignition is failing. If there is no switching. Then there is no fuel. The fuel ecu must see the switching signal from the ignition computer before it will turn on the fuel pump relay. So if switching is there. You most likely have spark. Unless of course the secondary part of the ignition isn't working.

This is why you start with spark. Ideally making sure it is good all the way to the plugs. Then move to the fuel system from there.

BTW your spray is doing the same thing. I'm just doing the tech boi method and the spray is the less technical method. Both versions make sure there is spark before fuel.
 
From there I move to the fuel pump relay and check that the output is turned on.

Always good to check the wiring under the car by the pump. It can decay and corrode losing the connection to the pump.
 
nickvolvo746 said:
Thanks mate, actually tried that, shoulve mentioned it in the post. Im thinking ill check the radio supression thing
Click to expand...
What was the outcome? Did the vehicle start with the starting fluid? If so, that drastically cuts down on potential issues.
dl242gt said:
Only if the secondary part of the ignition is failing. If there is no switching. Then there is no fuel. The fuel ecu must see the switching signal from the ignition computer before it will turn on the fuel pump relay. So if switching is there. You most likely have spark. Unless of course the secondary part of the ignition isn't working.

This is why you start with spark. Ideally making sure it is good all the way to the plugs. Then move to the fuel system from there.

BTW your spray is doing the same thing. I'm just doing the tech boi method and the spray is the less technical method. Both versions make sure there is spark before fuel.
Click to expand...
Ah okay that makes sense!
 
iHateVolvoPeople said:
What was the outcome? Did the vehicle start with the starting fluid? If so, that drastically cuts down on potential issues.

It did in fact start. I have twelve volts at the pump relay and i also tried jumping it. The in tank pump seems to be working just fine. The one under the drivers seat is probably the culprit. Will be checking the wiring asap
Click to expand...
 
iHateVolvoPeople said:
You could apply 12v to the pump as a test.
Click to expand...

I've had pumps run on the bench when directly juiced up with battery, but not run in the car.


Original poster, click my sig for no start diag.

A crank sensor is also suspect on these cars. Wiggle the wiring and inspect.
 
nickvolvo746 said:
It did in fact start. I have twelve volts at the pump relay and i also tried jumping it. The in tank pump seems to be working just fine. The one under the drivers seat is probably the culprit. Will be checking the wiring asap
Click to expand...
Sounds like you’re off to a good start.
ZVOLV said:
I've had pumps run on the bench when directly juiced up with battery, but not run in the car
Click to expand...

Me too. My in tank pump 'failed' and left me stranded in the mountains due to fuel vaporization. Turned out to be failed wiring at the sending unit. It was receiving 12v, but no where near enough current to power the pump. I would’ve been A-OKAY if I’d applied 12v directly from a car battery or something. Oh well, live and learn.

If he applies 12v to the pump and it works, he’ll need to verify he’s getting a proper 12v to the pump from the relay. If he is and it still doesn’t work, he’s likely got some voltage drop or grounding issues.

Also, a note on the crank sensors...they do weird stuff. They can fail all together, or intermittently, and they can make you think you have fuel/spark when you don’t. Only way to really test them is with a scope or by swapping with a known good one. I have had a $13 amazon crank sensor for over a year now without issues. But I’d still probably recommend a Bosch OE part if you care. Or buy 2 from amazon, test both, keep 1 as a spare.
 
iHateVolvoPeople said:
Sounds like you?re off to a good start.


Me too. My in tank pump 'failed' and left me stranded in the mountains due to fuel vaporization. Turned out to be failed wiring at the sending unit. It was receiving 12v, but no where near enough current to power the pump. I would?ve been A-OKAY if I?d applied 12v directly from a car battery or something. Oh well, live and learn.

If he applies 12v to the pump and it works, he?ll need to verify he?s getting a proper 12v to the pump from the relay. If he is and it still doesn?t work, he?s likely got some voltage drop or grounding issues.

Also, a note on the crank sensors...they do weird stuff. They can fail all together, or intermittently, and they can make you think you have fuel/spark when you don?t. Only way to really test them is with a scope or by swapping with a known good one. I have had a $13 amazon crank sensor for over a year now without issues. But I?d still probably recommend a Bosch OE part if you care. Or buy 2 from amazon, test both, keep 1 as a spare.
Click to expand...

thanks for this, I will be checking all the grounds tomorrow.
 
You must log in or register to reply here.
Back
Top