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I'm in the process of purchasing a 91 740. It doesnt start. The owner thinks it's a fuel pump relay but hes unsure. It will start sometimes but only for a few seconds. Any idea what could cause this and how to go about fixing it.
Thanks in advance
Update: Okay so fuel pump is in and it will start and run but it only runs for a minute or so then cuts out. Fuel pressure is good. Any ideas? It has a code for low/high battery voltage and idle control valve or something like that. It will just turn off like someone turned the key off.
Last edited by Syndave; Aug 30, 2019 at 03:16 PM.
Reason: Updatw
never buy a car that doesn't run, as you have no way to verify that the suspension, brakes, steering, etc are all functional, and it could quickly become a huge money pit.
Invest into a relay, see what happens. It's probably something else but who knows? Sellers usually choose the easiest thing they can think of... Generally if it's a nice car I'd look at it as these cars are robust mechanically, the visual cosmetics are the parts that are hard to get and or falling apart but yeah, usually not advisable to buy a non runner...
When you start the car, put your left hand on the fuelrelay. Does it click? Then thats not your problem. Now check the crank position sensor behind the distributor cap. You can easily see and feel it with your left hand following the cable. Is the cable shielding worn away, groudnig out on chassis? Give the cable a good tug and see if it fires right up. New one can be ordered if thats your problem. Next you can see if you get spark from your Regina coil. Its squarish in shape. I had same problem and for me it turned out to be the coil. Was a Regina coil on the 91 model. They get bad easily.
a 91 could be either Regina or Bosch ignition and injection. if its a turbo, or if its a California model, its for sure Bosch. the original poster really didn't give us anything to go on.
hey grab a can of starter fluid or brake cleaner and go look at it. shoot it in the intake if it fires and runs on the spray you know its probably gonna be fuel related.
hey grab a can of starter fluid or brake cleaner and go look at it. shoot it in the intake if it fires and runs on the spray you know its probably gonna be fuel related.
a 91 could be either Regina or Bosch ignition and injection. if its a turbo, or if its a California model, its for sure Bosch. the original poster really didn't give us anything to go on.
hey grab a can of starter fluid or brake cleaner and go look at it. shoot it in the intake if it fires and runs on the spray you know its probably gonna be fuel related.
Thank you. When I see it tomorrow I'm gonna try this
When you start the car, put your left hand on the fuelrelay. Does it click? Then thats not your problem. Now check the crank position sensor behind the distributor cap. You can easily see and feel it with your left hand following the cable. Is the cable shielding worn away, groudnig out on chassis? Give the cable a good tug and see if it fires right up. New one can be ordered if thats your problem. Next you can see if you get spark from your Regina coil. Its squarish in shape. I had same problem and for me it turned out to be the coil. Was a Regina coil on the 91 model. They get bad easily.
There are any number of things that could cause it not to start, so you've got to be prepared to do some troubleshooting. To determine if it is the relay, look for a thread on this site describing how to locate the relay, remove it, and jump the two terminals that will bypass the relay and cause the pump to run constantly. If it still doesn't crank, you know it isn't the relay. With this bypass jumper in place, you should be able to hear the pump running. If your car has a Bosch system (2 pumps, one in-tank, one under the car), the pump you're listening for will be under the car, approximately just behind the driver's seat, toward the middle of the vehicle. If it is a Regina system, the only pump will be in the tank, and you will probably need to put your hand on the gas tank to feel for vibration, or if you have a stethoscope, that would help. This would be a place to start. Be aware that as long as this jumper bypass is in placed, the fuel pump will run constantly, even with the key off and out of the ignition, so don't leave it there.
There are any number of things that could cause it not to start, so you've got to be prepared to do some troubleshooting. To determine if it is the relay, look for a thread on this site describing how to locate the relay, remove it, and jump the two terminals that will bypass the relay and cause the pump to run constantly. If it still doesn't crank, you know it isn't the relay. With this bypass jumper in place, you should be able to hear the pump running. If your car has a Bosch system (2 pumps, one in-tank, one under the car), the pump you're listening for will be under the car, approximately just behind the driver's seat, toward the middle of the vehicle. If it is a Regina system, the only pump will be in the tank, and you will probably need to put your hand on the gas tank to feel for vibration, or if you have a stethoscope, that would help. This would be a place to start. Be aware that as long as this jumper bypass is in placed, the fuel pump will run constantly, even with the key off and out of the ignition, so don't leave it there.
The car cranks and I guess you can say coughs. It tries to start but just cant that get push to do it. Does this rule out fuel pump since it does start occasionally but just cuts out at 15 seconds?
note that you need TWO jumpers on the fuel pump relay, one for the ECU power and the other for the fuel pump. and its not easy to reach the socket on a 740 as its in the center console between a bunch of other relays.
note that you need TWO jumpers on the fuel pump relay, one for the ECU power and the other for the fuel pump. and its not easy to reach the socket on a 740 as its in the center console between a bunch of other relays.
What kind of jumpers do i need and whats the best way to get to the relays
on a 740/940, most all the relays are behind the ashtray. remove the ashtray, remove the bezel around the cigarette lighter, remove the 1 or 2 screws visible behind that bezel, and remove the lighter socket and tray next to it, now you should see the relays and fuse panel.
you need a 3-pin jumper, pin 30 needs to be jumpered to both 87/1 and 87/2 to power both the ECU and fuel pumps before the car can start. This drawing below only shows the fuel pump jumper, which will let you test the pumps, but not let the car start until 87/1 is also connected.
on a 740/940, most all the relays are behind the ashtray. remove the ashtray, remove the bezel around the cigarette lighter, remove the 1 or 2 screws visible behind that bezel, and remove the lighter socket and tray next to it, now you should see the relays and fuse panel.
you need a 3-pin jumper, pin 30 needs to be jumpered to both 87/1 and 87/2 to power both the ECU and fuel pumps before the car can start. This drawing below only shows the fuel pump jumper, which will let you test the pumps, but not let the car start until 87/1 is also connected.
Is there somewhere cheap to get a jumper? The Kits on amazon are all $50
740 no start UPDATE
