Hi all,

Today I just noticed an issue where my '85 240 DL is mildly bucking as if it were idling rough when driving and accelerating. I had the fuel pumps, fuel filter, and fuel relay replaced in December of 2018 along with the Air Mass Meter.

I'm wondering if there's an issue in the fuel line, however, because a week ago, the car died in traffic on the highway. At that point, the fuel tank was getting low - just above the red zone - and the car had been sitting in the shop for four days without being driven. After dying, the enginge would crank without starting. After about five minutes, however, the engine turned over and started; the car ran for a few minutes before dying again. And again, after about a minute or two wait, the engine started. I ended up having it towed home, added fuel and then drove to a gas station and filled the tank. It seemed to have been running smoothely the past week until today, when the problem described above started.

I live in southeastern Louisiana, which is very hot and humid, so I originally theorized that condensation on the inside of the tank caused the issue a week ago when it died on the highway. I also chalked it up to the car having not been driven for a few days. Now, I am wondering if maybe there is a different issue - perhaps electrical, perhaps in the fuel line? Any help is much appreciated.

 

verify the in-tank pump is working.

have the wiring harnesses been replaced? 1985 is a 'biodegradable wiring' year (83-87 inclusive). www.davebarton.com has harnesses for these cars, there's two, ignition and main engine harness.

 

Thanks for your reply.

I ordered the Bentley manual - will it have a walk-thru for checking in-tank pump?

I have never replaced the wiring harnesses. I will look at them but I imagine they need replacing after 34 yrs....

 

In the Tank - 240 Volvo Tank Pump and Sender

 

after driving more, I think the problem may simply be a suspension issue. For one, the car idles smoothely, and I also put the car neutral and accelerated without any bucking. I also haven't experienced any paused or 'terracing' in acceleration nor crusing, all of which indicate that my original diagnosis may be misplaed.


I also confirmed the fuse for the fuel pump is working.

 

a suspension problem didn't cause the car to die or fail to start afterwards.

 

Of course that would be illogical.

I am chalking that issue on 8/30 to low fuel level, condensation inside the gas tank and that the car had been sitting for 5 days prior. Since then, the car has run fine.

I am saying that rough riding I described prior seems to be a result of a suspension issue and NOT the fuel line, as the car idles normally and has no pauses or bucks while accelerating.

 

Vibration when decelerating can be caused by a bad rear u-joint in your driveshaft. You can easily unbolt the rear driveshaft from the differential (4 bolts) and check the rear u-joint for binding. If it doesn't flex easily then it needs replacement. I have had to do this repair on two of my 240s.

 

if that caused the issue, then your car has a problem. sitting for 5 days doesn't cause that. there seems to be a lot of misunderstanding about fuel pumps, and how they keep cool. it isn't by being fully submerged; they are cooled by the passage of fuel being pumped through them. thus, the myth about low fuel levels in the tank causing fuel pump failures by overheating. i nearly always run the tank to near empty on all of my vehicles every time, and have been doing so for decades and nearly 1 million miles.

 

I read in the Bentley manual that vapor lock can cause the problem I described on hot days. Living in Louisiana, where we get lots of hot and humid weather, does that not seem plausible?

I am still noticing a bit of roughness while driving. It does not seem correlated to acceleration, deceleration and the car idles normally when stopped and parked. Could this problem be caused by one of the fuel filters or the fuel relay?

 

fuel injection is immune to vapor lock. thats something that affected carburetor systems with low pressure fuel delivery.

 

Ok, that's confusing then; why would the Bentley manual mention it in the fuel injection section of the manual?

I did take the fuel filler cap off and could not hear the described whirring of the in-tank fuel pump. I don't have a DMM yet to test the wiring and voltage but will get one this weekend and test to confirm if it is a faulty pump.

If it is the in-tank fuel pump that is faulty, does anyone have any thoughts on this IPD in-tank 'upgrade'? https://www.ipdusa.com/products/5799...ermarket-7845k

 

but did you do the specific test that isolates only the in-tank pump? ie, only the in-tank pump operates, not the main pump, without the engine running (indeed, without the key in the switch, too)?

 

also note, when you turn on the ignition, the pumps only run for about 1 second, then shut off until the engine is cranked over. on older LH2.2 cars, I'm not even sure if it runs for 1 second.

the test described on cleanflametrap that I linked in post #4 using a paperclip on the fuses lets you directly power the pumps individually without the ignition key.

 

So for the cleanflametrap test, I use a paper clip to connect the LEFT side of the in-tank pump's fuse mount to the RIGHT side of the main fuel pump's fuse mount WITHOUT putting the key in the ignition at all?

Thanks for all y'all's help here, I am very new to this.

 

the left side of fuses 6-7-8-9-10 are always powered. if you remove fuse 4, and jumper any one of those to the left side of fuse 4, you will power the main pump. if you jumper any one of those to the right side of fuse 4, you will power the tank pump

 

So I drive around with each side of fuse four jumped and see if the driveability is changed?

 

no, you power the pumps and confirm they are running by listening to them. remove the gas cap and listen at the filler pipe to hear the in-tank pump, its pretty quiet.

 

I did the test and perhaps I did it wrong, but the car appeared to idle normally with fuse #4 in place, with it's right side jumped and it's left side jumped from the left side of fuse #6. I did notice that I could hear a whirring sound seemingly coming from the gas filler pipe when the in tank was supposed to be running - meaning with fuse #4 in place and it's left side jumped.

I do have a multimeter is there's more testing I ought to so to confirm the pump works.

 

with the tank pump fuse in place, it doesn't matter which side you jump, the fuse is connecting them, so both pumps would run in either case.

to test the tank pump in isolation, you REMOVE the fuse and jumper the right side to power just the tank pump.

again, see In the Tank - 240 Volvo Tank Pump and Sender