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?
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.
nordmaschine
forced instruction
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- Feb 12, 2012
- Location
- The Balkans, BiH
LH2.2 doesn't prime. But his car, being 1991, has to have LH2.4.
Maybe the car has 561 ECU? They sometimes have fuel pump circuit failure, some people get around it by hooking it up so fuel pumps run all the time with key on.
Maybe the car has 561 ECU? They sometimes have fuel pump circuit failure, some people get around it by hooking it up so fuel pumps run all the time with key on.
Sorry for no update in about a month, so I believe the first thing that I did after reading all of your responses was pull the injectors, those were difficult to get out as they had likely never been pulled before, but the injector needles were clean and they were all in usable condition, so I put those back in. I had a friend suggest getting a new main fuel pump and fuel filter, so I did, and the car started easy from there, but the main fuel pump still runs the entire time the car is running, while there is still bubbles heard from the tank when pressing an ear against the cap. We tried to see if we could hear the in-tank pump, but if it was doing anything we couldn't hear over the sound of the main pump working as hard as it could to pull fuel. I'm trying to figure out how to test the in-tank pump next, anyone got advice?
Last edited:
Rushin
Member
- Joined
- Jan 20, 2022
The main pump and the lifter pump are supposed to run the entire time the car is running. I'm not 100% on how the 740 pump is mounted in the car, but the 240 has some rubber cone-shaped grommets that hold the pump to the main bracket. When those go, the pump can get loud.
For the in-tank pump, an easy way is to get a stethoscope on top of the lifter pump plate. You should also be able to give the pump voltage through the plug and hear it. Otherwise, you can pull the pump and apply voltage to it directly. This is a pain in the ass.
The non-OE lifter pumps are also sometimes labeled backward from the factory, so the motor will spin the opposite direction it's supposed to.
ortho stice
Active member
- Joined
- Feb 9, 2015
- Location
- Braddock, PA
Unplug it at the connection under the driver's side storage compartment in the trunk (the trapdoor thing, there's one on each side of the trunk area) and apply 12 volts to the hot wire and ground the negative. I think power to the pump is pink but double check that because the wiring for the level sender is there, too.
Temporary wire your IN tank pump .... disconnect the delivery line to your chassis pump. With a helper, run the lift pump for a few seconds and inspect to see if fuel is being delivered. Keep a fire extinguisher OR a garden hose/sprayer right next to you..... gasoline is VERY dangerous and will injure/kill you.
Alternately, just go ahead and change the lift pump (in tank).... a good stage ZERO step for a car coming out of hibernation.
Alternately, just go ahead and change the lift pump (in tank).... a good stage ZERO step for a car coming out of hibernation.
- Joined
- Mar 8, 2003
- Location
- Monroe, OR USA
Just slide under the car and disconnect either wire from the main pump, crack loose the fuel line going to the fuel rail and put the end in a jar/milk jug and cycle the key to run the prime feature, or crank the engine to get the pumps to run. Obviously, only the in tank pump will run unless it is dead. They are low pressure pumps and will be pushing fuel through the main pump which isn't running, therefore, don't expect a major stream of fuel like you would see if both pumps were running. All you need to see is that it is pushing fuel through the system.
Again sorry for no update in awhile, I didn't think I would be held up on this for this long as the YouTube vids make it seem easy to do, buuuut I checked the in-tank pump with a stethoscope and it was doing absolutely nothing, so I went ahead and pulled it out, I pulled the pump off the apparatus and wired it to a battery(just in case the contacts were bad) and it still did nothing, so my in-tank is dead, but that's not my problem as I can buy a new one of them, I can't buy the whole fuel sending apparatus which is what I need because mine is rusted real bad. I've been looking on marketplace and around my area to see if there's anyone with a 700 series Volvo they're trying to part out or sell cheap, but what I'm probably going to have to do is remove the rusted line from the cap and replace it somehow, but that's just me guessing.
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I might end up doing that if I can't get one that's in good condition for a decent price, I'd have to get creative for the holes in the lines tho, I was thinking that I could get a slightly bigger line that I could flange on the end, and cut the old line back to where it's good, and then sliding the flanged end over the old line and sealing it somehow, but idk how well that will work/seal.
If Im understanding right, you just want to extend the flexible hose from the fuel pump to meet a better point on the metal tube connection since theres a hole? I think that should be fine if it's clamped properly, no need to overthink it.
- Joined
- Mar 8, 2003
- Location
- Monroe, OR USA
Does the sending unit still send the signal to the fuel gage? The hole in that line makes no difference at all. That is the return line.
MasterBlaster
Well-known member
- Joined
- Feb 16, 2009
- Location
- Port Coquitlam
That's what I thought too, but then I looked closer. Feed line also looks bad.
Pic 4 - The squared-off pipe is the return, clipped to the plastic. Feed has the rubber hose.
Pic 3 - (brightened a bunch) shows a long rusted hole in the return.
Pic 1 - The rusty return after being snapped of into a hypodermic needle shape.
Pic 2 - The back side of the feed pipe, possibly with a hole of its own.
Pic 1 - Zoomed and brighter, shows that possible hole again, and maybe another near the clamp.
