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240 Diagnosing intermittent rhythmic power cut

Wren said:
Your issues sound exactly like a car I worked on a couple of years ago. Turned out to be a bad fuel filter. How old is yours?
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Had the fuel pressure guage hooked up when it ****ed up today. Dropped to below twenty. Now monitoring output from main relay. Bought a new fuel filter, I'll replace that also.
 
Volts on fuse #6 doesn’t drop when the issue occurs. So I’ll change out the fuel filter and the only other possible culprits would be the main pump or wiring to it.
 
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Not necessarily. How old is the fuel pressure regulator?

I had one fail similarly on a customers car but the opposite way. The fuel pressure would be fine for quite a while, then jump up to 80 psi suddenly and engine ran like crap. Shut off the engine and restart and it would run normally. The check valve in the regulator was sticking sporadically and sending full pump pressure to the injectors. Perhaps yours is sticking in the open position and returning most of the fuel to the tank.
 
hiperfauto said:
Not necessarily. How old is the fuel pressure regulator?

I had one fail similarly on a customers car but the opposite way. The fuel pressure would be fine for quite a while, then jump up to 80 psi suddenly and engine ran like crap. Shut off the engine and restart and it would run normally. The check valve in the regulator was sticking sporadically and sending full pump pressure to the injectors. Perhaps yours is sticking in the open position and returning most of the fuel to the tank.
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It has about 2 hours on it. I had to buy a new one to fit the late style fuel rail with the schrader valve on it. I got a genuine Volvo one from tasca.

I guess it could be pluggage in the in tank pump also, but I'm feeling a lot better have narrowed it down to a few components.
 
That pretty much rules out the regulator.

The in tank pump is a good place to look. It seems like they have 2 failure modes as some say they've found dead pumps but the car runs fine and others have problems with fuel delivery. It's like the pump can stop where it will block the flow of fuel or it might not, if that makes sense.
 
hiperfauto said:
That pretty much rules out the regulator.

The in tank pump is a good place to look. It seems like they have 2 failure modes as some say they've found dead pumps but the car runs fine and others have problems with fuel delivery. It's like the pump can stop where it will block the flow of fuel or it might not, if that makes sense.
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Just took it for a spin with the chassis-ear clipped to the main pump, no change in operating noise when the issue occurs. I'll change the fuel filter and if I have another occurance, I'll buy an in-tank pump and sock.
 
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Overall, I'm a little disappointed in my use of the parts cannon but I don't think it was money wasted. I now have a nice set of NLA spares in a pelican case so I can easily troubleshoot and repair any issues on the road.
 
This is what came out of the inlet of the fuel filter:



The main fuel pump is running much quieter. In my experience a fuel filter should last much longer than three years and 35k miles. I must have got some bad gas. Come to think of it, this issue resurfaced shortly after refilling.

I am still baffled by the symptoms. In my experience a plugged filter just makes the car stumble worse and worse until it dies. The intermittentness, temperature dependence and consistent rhythmic power loss threw me for a loop.
 
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I think we can close the file on this one. Fuel pressure rock solid at 45psi at 4K Rpms on the freeway, was ~35 and jumped around +-5psi before tanking when the car began to stumble.
 
Wow, that's a lot of crud. Are you going to pull the tank and clean it out? The in tank filter must be plugged up too, no?
 
hiperfauto said:
Wow, that's a lot of crud. Are you going to pull the tank and clean it out? The in tank filter must be plugged up too, no?
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I am planning on running the fuel level down and dredging the bottom of the tank, flushing It out and cleaning everything in the sender pump assembly. I'll probably get to that in a couple weeks.
 
Fuel pressure began dropping into the low thirties today. Pulled the filter again, and dumped out more of the same crud. Looks like I’m going to have pull that tank sooner than later.
 
Well thanks for nothing! :-P

<iframe width="560" height="315" src="https://www.youtube.com/embed/L1BDM1oBRJ8" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
 
Here's the fuel that was in the tank:


Here's what it looked like inside the tank:


Used a mason jar lid to seal up the sending unit hole:

Duct tape for the filler hole:


Phosphoric acid is soaking in there right now. We'll see how clean I can get it.
 
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Have you figured out what the gack is in your fuel?

That's a little more than a crappy load of fuel!

Or are you de-hibernating?
 
Dirty Rick said:
Have you figured out what the gack is in your fuel?

That's a little more than a crappy load of fuel!

Or are you de-hibernating?
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I think some of that discoloration is the under coating dissolving as the fuel rolls down the bottom of the tank while draining out of the pet cock. It had about 2" of rust piled up at the bottom. I am not dehibernating, I've been driving this car for the last 6 years.
 
Got the tank cleaned, new in-tank pump, new seals, replace the fuel filter again.

My process for cleaning the tank went like this:

1. Empty and remove gas tank, remove sender/pump assembly.
2. Pour in 1 gal of biodegradable degreaser
3. Shake thoroughly, let stand for 15 mins, shake and rotate throughout, drain into bucket for disposal.
4. Pour 1 gal of muriatic acid, add 4 gal of water.
5. Add a couple of handfuls of random nuts and bolts.
6. Close off the bung hole with a mason jar cap, the old o ring and the gland nut.
7. Duct tape over the hole for the filler.
8. Shake vigorously and repeatedly for about two hours.
9. Drain and neutralize the acid solution with baking soda
10. Repeat steps 4-9 with phosphoric acid, except for only 30 mins.
11. Rinse thoroughly with garden hose, once it starts coming out clear, keep flushing it for another ten minutes.
12. Add 2 quarts of denatured alcohol to dry it out. Shake vigorously, dump into bucket.
13. Empty a can of WD40 into the tank, shake and coat the entire inside with it. Drain into a bucket, remove the bolts and nuts.
14. Reinstall and fill promptly.

Got mine looking like this:
 
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