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Old 05-26-2022, 11:27 PM   #1
dualcitizen
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Default 92 940 turbo no start, no fuel pressure

Hopefully someone can help me here. I don't understand exactly how the fuel system works on this car. As the title suggests, the car won't start. It won't even hiccup. I've checked for a spark and that seems to be fine so I don't think there's an issue there.

I'm pretty sure the issue is no fuel, but I'd like to understand what to look for. Here are the details and what I know.

Key on, no sounds. Fuel pump does not start. I understand that there are two pumps, one in the tank and one underneath. Should I be hearing both pumps before cranking? (I don't hear either one)
Since I couldn't hear the fuel pump(s), I disconnected the wires and checked the voltage on the pump underneath the car. 0 volts when key turned on. Afterwards, I applied 12 volts directly to the fuel pump terminals and it turned on. While the fuel pump was running, I check the fuel rail at the little twisty nub thing by first injector but no fuel came out, totally dry. Tried starting the car again with the fuel pump wired up but nothing.

Checked the relays behind the fuses (fuse #1 is good) and jumped the relay terminals on the fuel pump relay (87/2 - 30), found a guide here: https://www.240turbo.com/740relaybypass.jpg When I did that the fuel pump kicked on. Pulled the relay out, took it apart, nothing seems to be fried or burned inside. With a power supply I was able to verify that the solenoids were activating and that there was 0 ohms across the switched terminals, therefore relay seems okay.

I'm a bit unsure about what to look for now. Any advice would be greatly appreciated.
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Old 05-27-2022, 05:05 AM   #2
Janspeed
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The injection module and ignition module are interconnected. If there is no ignition happening the injection will not start injecting fuel.
So, maybe check if the engine is getting spark?

Another possibility could be a broken ignition switch.

Last edited by Janspeed; 05-27-2022 at 05:10 AM..
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Old 05-27-2022, 08:16 AM   #3
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I already checked that, at least I checked the spark plugs. Pulled all of the plugs out and checked each one will cranking the engine. All were getting a spark.

I think it's fuel because when I turn the key on I don't hear any fuel pump noises.
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Old 05-27-2022, 09:02 AM   #4
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on some cars there will be valve in the fuel gallery, the valve looks like a tire valve. If you push it in fuel should squirt out because residual pressure. If nothing comes out there is no fuel pressure. the high pressure pump will be suspect. I think that your car has the pump (+ fuel filter) in a small frame hanging from the car floor under the drivers seat.
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Old 05-27-2022, 09:16 AM   #5
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By fuel gallery you mean the fuel rail? There is a cap (like a valve stem cap) on the fuel rail close to the first injector which I undid but it was dry. Is there something inside of there that I need to push in (like a valve stem)?

And I tested the HP fuel pump by bypassing the relay - it turned on.
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Old 05-27-2022, 10:19 AM   #6
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Crank sensor is the most common no start cause on these cars.
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Old 05-27-2022, 10:25 AM   #7
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Quote:
Originally Posted by ZVOLV View Post
Crank sensor is the most common no start cause on these cars.
Would a bad crank sensor prevent the fuel pump from turning on?
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Old 05-27-2022, 01:27 PM   #8
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. During cranking, but not for the prime. EFI/Fuel pump relay turns on the pump.

Get a test lamp. Click my sig for no start thread.


740/940 also like to burn up fuse #1
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Old 05-28-2022, 01:17 AM   #9
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Update:

I bypassed the relay and checked to see if there was fuel pressure at the fuel rail. Undid the cap and poked the bit in inside, fuel came out. Still wouldn't start though.
As I said above, I checked to see if there was a spark on all of the spark plug wires - got a spark on all four.

I don't know if this is worth mentioning, but when I turn the key on, there's a bit of a buzz/click sound coming from the ignition coil. Is this normal?

Fuse #1 is fine
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Old 05-28-2022, 10:34 PM   #10
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I bought some starting fluid, took the intake hose off and sprayed some fluid into the manifold. Opened the throttle and it fired up! (briefly)

Afterwards, I reconnected the hose, bypassed the fuel pump relay and tried again. The car fired up and ran fine! So I'm not positive what the problem is, but I think it might be the relay. I ordered one anyway, so we'll see what happens in a few days when it arrives.

Any other advice?
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Old 05-28-2022, 11:31 PM   #11
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Quote:
Originally Posted by dualcitizen View Post
I bought some starting fluid, took the intake hose off and sprayed some fluid into the manifold. Opened the throttle and it fired up! (briefly)
You are on the right track!

Got that TEST LAMP yet??? Another common issue with these cars is the relay, and the wiring to it, which powers up the injectors (aka radio interference suppression relay). Peel back the boot to the fuel injector connector and confirm power to the injector. GOT INJECTOR POWER????


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Originally Posted by dualcitizen View Post
Any other advice?


Last edited by ZVOLV; 05-28-2022 at 11:46 PM..
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Old 05-29-2022, 09:11 PM   #12
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Quote:
Originally Posted by ZVOLV View Post
You are on the right track!
Got that TEST LAMP yet???
I have a multimeter.

Quote:
Another common issue with these cars is the relay, and the wiring to it, which powers up the injectors (aka radio interference suppression relay). Peel back the boot to the fuel injector connector and confirm power to the injector. GOT INJECTOR POWER????
I'm pretty sure that the injectors are working properly, because after using starting fluid and bypassing the fuel pump relay, the car ran fine.
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Old 05-30-2022, 12:56 PM   #13
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I just replaced a torn hose in the fuel tank on my 1991 744 Turbo. It was having problems starting and I could get it started with brake cleaner and then drive it.
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Old 06-03-2022, 04:00 PM   #14
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I updated my NO START THREAD in my signature with how to use a test lamp.
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Old 06-06-2022, 11:26 PM   #15
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Found the issue. It was the fuel pump relay. I thought the old one was fine when testing it, but I thought I'd order a replacement anyways since they're not too expensive, I guess that's what it was. It starts fine now.
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Old 06-09-2022, 11:20 AM   #16
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You can use a pry to take the cap off the relay. That way you can inspect it and look for cracked soldering points and try resoldering them. There is a good chance that the relay will be totally fine. You can test that obviously. That way you will have a spare that you can keep in the car. Nice to have on a longer road trip.
https://www.youtube.com/watch?v=NR1zkHWEuf8
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