I am trying to start a 1991 740 SE that has been sitting for several years, we tried starting it and have checked for spark, got a new battery, the spark plugs were dry and clean, changed the filters (oil and fuel) checked if it was getting fuel, main fuel pump was working, tank is clean, but its still sputtering, not starting. The main fuel pump is kinda loud when trying to start tho, and it doesn't stop priming, that's probably because its still got air in it from not being started for about 8 years. I decided to check the relay, and found a melted circuit #4, I checked a couple sites and one is saying that circuit is for p shift lock. Does anyone have experience with this circuit or know why it would have melted the fuse block?
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Trying to get my dad's 740 up and on the road again
- Thread starter alekz
- Start date
2 old for this
Well-known member
- Joined
- Mar 12, 2018
Are you checking the white relay?
DET17
Reformed SAABaholic
- Joined
- Nov 1, 2009
- Location
- NW GA / East TN
Melted connections are caused by (1) very high resistance which generates heat, and (2) excessive current (likely dead short to ground without fuse protection).
Once you repair that circuit, when you key up the car put an ear at the fuel cap pipe.... you should clearly hear the PRE pump run for about 3 seconds when keyed up ON. The fuel relay in the 7/9 is a notorious failure point..... find a EURO made used one on eBay and change it out.
A whining chassis pump can indicate there is NO pre-pump function. What is the age of the chassis and tank pumps?
Once you repair that circuit, when you key up the car put an ear at the fuel cap pipe.... you should clearly hear the PRE pump run for about 3 seconds when keyed up ON. The fuel relay in the 7/9 is a notorious failure point..... find a EURO made used one on eBay and change it out.
A whining chassis pump can indicate there is NO pre-pump function. What is the age of the chassis and tank pumps?
- Joined
- Mar 8, 2003
- Location
- Monroe, OR USA
There is simply a timer built into the ECU to prime the fuel system. IOW, there is no pressure sensor. The fact the pumps keep running mean either someone has hot wired the system, or, the ECU itself has a problem. If the car has been sitting more than 5 years it may have stuck injectors. You need to bite the bullet and pull the injectors out while they are still attached to the fuel rail and do a spray test to see if they are working.
Unless he means it runs the pump all the time while key is in cranking position, which I think is what it's supposed to do.
I'm pretty sure LH2.2 doesn't even pre-prime with key on at all, but don't remember if a 91 would be 2.2 or 2.4. 2.4 does run the pump for a few seconds.
I revived a 740T years ago that wouldn't run and finally figured out the fuel injector nozzles were plugged from sitting, exactly. Had to swap in a set of known good injectors and it fired right up on some fresh gas. Agree with the above, need to get a visual on injector functionality.
I'm pretty sure LH2.2 doesn't even pre-prime with key on at all, but don't remember if a 91 would be 2.2 or 2.4. 2.4 does run the pump for a few seconds.
I revived a 740T years ago that wouldn't run and finally figured out the fuel injector nozzles were plugged from sitting, exactly. Had to swap in a set of known good injectors and it fired right up on some fresh gas. Agree with the above, need to get a visual on injector functionality.
I did check the fuel relay it seems to be working, I definitely felt it click. My dad also had to hook a couple of the wires back up when we pulled the main fuel pump out, so I'm hoping that these two wires maybe got switched around? The fuel pump runs the entire time that the key is in the priming position. Also, had my dad check the tank while I turned the pump on, and he said he heard bubbling. I'm pretty sure its the original in-tank pump and main fuel pump, if that helps anything. I thought of pulling the injectors when I first started, but I have been trying to find other problems that could have been keeping it from starting.
- Joined
- Mar 8, 2003
- Location
- Monroe, OR USA
Check whether you have power at the injectors with the key in the run position. There’s actually two relays in one in that fuel relay. One relay runs several other components in the fuel injection system. As I said above, the fuel pump should not run with the key in the run position unless the car itself is running. You have a problem with the fuel pump circuit.