86' 740 Fuel Delivery Problem

waynegarbo · Post by **waynegarbo** » 27 Feb 2016, 18:10

I have a fuel delivery problem. I have spark, changed the fuel pressure regulator, both fuel pumps and filters, have voltage at my main fuel pump, jumped the relay junction box at terminal 30 to 87/2 and hear both fuel pumps; then I pulled my fuel pressure regulator, draped off the motor, and the car started and ran smooth while it spewed nice pressure onto the drap which I immediately then shut off the motor. So now I am stumped and don't know what to do.

waynegarbo · Post by **waynegarbo** » 27 Feb 2016, 18:17

I have a fuel delivery problem. I have spark, changed the fuel pressure regulator, both fuel pumps and filters, have voltage at my main fuel pump, jumped the relay junction box at terminal 30 to 87/2 and hear both fuel pumps; My main fuel pump was only three years old and the back up I had was used out of a 93 940. then I pulled my fuel pressure regulator, draped off the motor, and the car started and ran smooth while it spewed nice pressure out the fuel rail onto the drap which I immediately then shut off the motor. When I put the fuel pressure regulator back on there is no start and no fuel pressure return. I have three fuel pressure regulator's and none of them have fuel coming out of the vaccum port. This points to low fuel pressure but now I am at a standstill and need help from the forum. Thank You.

lummert · Post by **lummert** » 27 Feb 2016, 18:27

Did the vacuum hose to the fuel pressure regulator have gas in it? Or the smell of gas.

93Regina · Post by **93Regina** » 27 Feb 2016, 19:44

waynegarbo wrote:no fuel pressure return

Either your main pump or tank pump has an issue...or the line is clogged.

waynegarbo · Post by **waynegarbo** » 29 Feb 2016, 18:23

No gas in any of my fp regulators. since my post I have done a fuel pressure test. there is no fuel pressure reading through the ignition start. but there is normal pressure reading from the jump at relay terminals 30-87/2. all three of the fp relays have good ohm readings around 80 and the soder
joints SEEM to look good(how can I have three bad relays). And I tried all of them. Now I am pointing at my ECU. How do I check from the
junction relay terminals to the ECU? Please provide specific instructions with my volt meter as I get really confused on how to check continuity. Thanks.

93Regina · Post by **93Regina** » 29 Feb 2016, 19:34

Download and save this: TP31058_1

See page 20 (PDF's page 20), and look for terminal #17 on LH control unit (217).

From terminal 17, there is a colored wire that goes to the relay, so find it at the relay. Remove relay, and hook one side of your volt-meter to a positive voltage, and the other side to terminal's #17 clip at relay. Crank engine...is there voltage? If not reverse voltmeter leads...???

Download the enclosed document, and notice terminal #9, check it too. It appears to be a positive voltage.

I think on LH 2.0 thru 2.2, the engine must be cranking before relay circuit is energized.

Not related: Repairing Your Own LH 2.2 ECU

lummert · Post by **lummert** » 29 Feb 2016, 19:42

On thing you haven't mentioned is the Radio Noise Suppression Relay.

https://www.matthewsvolvosite.com/forums ... hp?t=49080

On LH2.2 the fuel pump relay triggers the fuel pumps and the radio noise suppression relay for a few seconds when returning the key from start to run, not while cranking the engine. This is why fuel pressure rest pressure testing is so important. If the engine doesn't start the first try, the pumps won't run.

93Regina · Post by **93Regina** » 29 Feb 2016, 21:04

lummert wrote:while cranking the engine

LH 2.4 - When key is switched to on position, fuel pump circuit will energize for a few seconds.

LH 2.0 - Engine must be cranking before fuel pumps circuit is energized. Distributor's signal is the trigger.

1981 VW Rabbit - CIS Bosch setup....Same as LH 2.0...RPM signal is used to trigger fuel pump

LH 2.2 - I don't own one, but RPM signal would allow relay circuit to work.

In case vehicle's fuel line was severed in a crash, Bosch used RPM signal as a safety to shut down fuel pump(s).

waynegarbo · Post by **waynegarbo** » 03 Mar 2016, 19:27

lummert wrote:On thing you haven't mentioned is the Radio Noise Suppression Relay.

https://www.matthewsvolvosite.com/forums ... hp?t=49080

On LH2.2 the fuel pump relay triggers the fuel pumps and the radio noise suppression relay for a few seconds when returning the key from start to run, not while cranking the engine. This is why fuel pressure rest pressure testing is so important. If the engine doesn't start the first try, the pumps won't run.

I don't have a radio suppression relay

waynegarbo · Post by **waynegarbo** » 03 Mar 2016, 19:35

93Regina wrote:
lummert wrote:while cranking the engine
LH 2.4 - When key is switched to on position, fuel pump circuit will energize for a few seconds.

LH 2.0 - Engine must be cranking before fuel pumps circuit is energized. Distributor's signal is the trigger.

1981 VW Rabbit - CIS Bosch setup....Same as LH 2.0...RPM signal is used to trigger fuel pump

LH 2.2 - I don't own one, but RPM signal would allow relay circuit to work.

In case vehicle's fuel line was severed in a crash, Bosch used RPM signal as a safety to shut down fuel pump(s).

Mine does not have the RPM. Yes I depend on the the Distributor for the signal. I do have spark, and have tested the dist ground and the other two power leads for continuity and all check out. I also checked the dist power wires at the harness and they do have the required 11v and 5v. And
I notice on crank my tach needle jumps slightly, so that tell's me that the hall sensor is working.