I'm sure that this topic has gone around more than once, but I had trouble finding a post on point in the archives so thought I had better check. The car is an 83 240 turbo, that started showing some symptoms of fuel check valve failure on cold starts, but not consistent at first. Some mornings it would do it and some it wouldn't. Over the last month or so, the initial priming of the main fuel pump also started getting sporadic; i.e., no buzzing from the pump. And it stalled once at a traffic light. I checked the fuel pump fuse (#7) (it was OK) and replaced the fuel pump relay. The new fuel pump relay seemed to improve things a little when first replaced. Now, there is no response from the fuel pump when the key is turned to the aux position, and it takes 3 cranks to get the engine going without stalling. Voltage at the fuel pump: about 10.9 V. I'm wondering if fuel pump problems might cause a partial relay failure. Whether I need to replace the pump, not just the check valve.

I had another reply almost done, then lost it to a keying error. But here are some quick thoughts:

1- What type Fuel Injection? If it's LH 2.0, Fuse # 7 is NOT in the fuel pump circuit, which is: 25 AMP fuse to Relay 30, Relay 87 to Fuse #5 "hot side" (left) to Main Pump.

Jumping any fuse (6—10) hot side to Fuse #5 hot side will bypass every thing and put full voltage on both pumps, injectors and Idle Control Motor, just as though it came from the relay. But don't do it for long, as the jumper is carrying the whole load. Just do it to see if you get better voltage at the Main pump.

2- The "initial prime" (quick fuel pump buzz") is an Urban Legend. It will happen on some older cars, but is not an intentional part of the FI operation. So I wouldn't consider it when shooting a starting problem (even though it has been implemented on later cars, as my '93 940).
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Now gone)
'83 Turbo 245
'73 142 (98K)
'71 144 (track modified--and still here)
New 144 from '67 to '78
Used '62 122 from '63 to '67

... so my comments about LH 2.0 are all wet. With K-jet, I'd go back to fuse #7 and clean the contacts really well, then pinch then together so they grip the fuse tighter.

Also, feel the fuse after running for a few minutes. If it's warm or hot, there is resistance and a voltage drop there.
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Now gone)
'83 Turbo 245
'73 142 (98K)
'71 144 (track modified--and still here)
New 144 from '67 to '78
Used '62 122 from '63 to '67

The check valves main function is to keep pressure in the system to prevent vapour lock on hot engine starts, it doesn`t hold pressure indefinitely.
If it starts OK when hot there is probably nothing wrong with your check valve.

Colin.

If you jump the pre pump (in tank) and the main pump at the fuse panel (4 & 6 on mine) the pumps will start running without the key turned on to start the motor. Now start the engine, if it fires right up you likely have a bad check valve.

"...and the main pump at the fuse panel (4 & 6 on mine) the pumps will start..."

5 and 7 on the pre-B230 cars.
--
Don Foster (near Cape Cod, MA)

Thanks for the replies. The fuses on this car are 5 & 7. I will try getting the pumps started before turning on the car. But, I am still unclear why I lost that initial priming of the main pump. Any suggestions for a nonexpert. Otherwise, the fuel supply seems to run fine. Well, except my mpg is higher than I like.

That "initial prime" is not really an intentional prime, so to speak. It occurs (randomly) as a result of an initial ignition pulse when the ignition system is first energized.

The fuel pump relay requires a series of pulses from the ignition primary in order for it to engage and power the pumps. This is a safety feature.

These pulses occur when the engine is running and also when you crank it.

When you turn on the key and power the system, the electronic ignition sometimes produces a single spark -- it probably depends on the relationship of the reluctor to the sensor inside the distributor. Or maybe it results from charging a power supply capacitor in the ign module. Whatever, the ignition sometimes, but not always, produces a spark when first powered.

This pulse will trigger the fuel pump relay for about 1/2 second.

Sometimes it happens, sometimes it doesn't.
--
Don Foster (near Cape Cod, MA)

Another myth dispelled in my mind. In the 740/940 FAQ there is a diagnostic test in the Fuel System section that includes listening for a whirring sound with the ignition on without turning the engine on. Does something need to be corrected here?