2004 XC70 no start - faulty fuel pump and/or electrical connections? Topic is solved

[abscate]

FWIW the no-start condition is exactly mimicked by pulling the starter relay under the driver-side dash.

Wait, are we fighting a cranks well, doesn’t start condition or a no-crank condition?

[enotslim]

FWIW the no-start condition is exactly mimicked by pulling the starter relay under the driver-side dash.

Wait, are we fighting a cranks well, doesn’t start condition or a no-crank condition?

Sorry. My mistake. The mimic is pulling the fuel pump relay, not the starter relay. The car cranks forever when it won't start. Both the spontaneous failure to start as well pulling the FUEL PUMP relay result in three cranking/attempts to start with fewer ignition cycles on each successive try until there is no ignition on attempts four and beyond. Just as if a decreasing amount or residual fuel at the rail, in the absence of resupply by the fuel pump, is consumed on each attempt until no fuel remains.

[lrock]

I had a fuel pump issue which only happened when the tank was 1/4 or 3/8 full. It turned out that it was the fuel pickup assembly that was faulty. Replacing the whole fuel pump and fuel pickup assembly resolved the problem. Like OP my 2004 has no sensor on the fuel rack and not module on/near the fuel tank.

had this too on '01 v70 xc. The guy i bought it from told me to keep it topped over ~1/4 and it would be fine. Get near that though and it would cut out, car would shutoff completely like an EMP hit it then nothing. shut it off, crank no start. But it was also affected by
-time of day (more likely at night)
-ambient air pressure (more likely with higher air pressure)
-temperature (more likely to happen on a "fuller tank" at low temperatures)
-altitude (more likely at higher altitude, related to air pressure/temp i would think)

interesting data trend...

[enotslim]

I had a fuel pump issue which only happened when the tank was 1/4 or 3/8 full. It turned out that it was the fuel pickup assembly that was faulty. Replacing the whole fuel pump and fuel pickup assembly resolved the problem. Like OP my 2004 has no sensor on the fuel rack and not module on/near the fuel tank.

had this too on '01 v70 xc. The guy i bought it from told me to keep it topped over ~1/4 and it would be fine. Get near that though and it would cut out, car would shutoff completely like an EMP hit it then nothing. shut it off, crank no start. But it was also affected by
-time of day (more likely at night)
-ambient air pressure (more likely with higher air pressure)
-temperature (more likely to happen on a "fuller tank" at low temperatures)
-altitude (more likely at higher altitude, related to air pressure/temp i would think)

interesting data trend...

Did you discover an intervention that would start this car after such an event? I currently must simply wait until it starts. It could be a few hours to several days later. This is the biggest obstacle to my using this car. I wouldn't mind (much) if I could restart it predictably.

[enotslim]

I had a fuel pump issue which only happened when the tank was 1/4 or 3/8 full. It turned out that it was the fuel pickup assembly that was faulty. Replacing the whole fuel pump and fuel pickup assembly resolved the problem. Like OP my 2004 has no sensor on the fuel rack and not module on/near the fuel tank.

And what do you mean by "the fuel pickup assembly that was faulty"? Could this have been failure of the spring-loaded system that pushes the siphon to the bottom of the tank to ensure that fuel is brought to the pump until the tank is entirely empty? That could explain variability over time as well as volume-dependence and position-dependence. (Altitude and atmospheric pressure as relevant variables sound odd to me.)

The spring-loaded fuel pickup mechanism is illustrated beginning at ~3 minutes in the video at the link below. Failure of this mechanism could be the problem. Debris in the tank (see 5:50 in the video but don't submerge your exposed bare skin in the fuel) that works its way under the siphon could also prevent the siphon from bottoming out and emptying the tank even if the mechanism itself is intact. This would essentially mimic an empty fuel tank and would not be corrected by replacing the pump and assembly unless the debri was also removed during the procedure. I guess I should tear apart the fuel pump and associated structures to eliminate this as a cause of my no-start condition. Or maybe I only need to examine the left side with the siphon and can leave the pump (right) side intact - at least to start. Luckily the tank is almost empty (even though I cannot get it to fail to start now).

Not sure what effect the above might have on fuel level sensors or whether this can explain the two DTC below that I've observed on and off during this ordeal. So far they have always appeared/disappeared together suggesting they are both secondary to some other single cause.
* REM-4A37 Fuel Level Sensor. Signal Too High Or Signal Missing (right side)
* REM-4A33 Fuel Level Sensor. Signal Too High Or Signal Missing (left side)

A major flaw in proposing this as the source of my problem is that it should also, at least occasionally, cause the car to falter while driving (after starting and getting on the road). This has never happened.

[lrock]

Did you discover an intervention that would start this car after such an event? I currently must simply wait until it starts. It could be a few hours to several days later. This is the biggest obstacle to my using this car. I wouldn't mind (much) if I could restart it predictably.

yeah.. i put gas in it.

i had forgotten what the previous owner had said about letting the tank get below a 1/4 tank. happened to me on a highway around midnight, had to get towed to a nearby hotel, it thankfully started in the morning and i went straight to the gas station and filled it up, never let it get below 1/2 tank again.

[goldxc70]

I had a fuel pump issue which only happened when the tank was 1/4 or 3/8 full. It turned out that it was the fuel pickup assembly that was faulty. Replacing the whole fuel pump and fuel pickup assembly resolved the problem. Like OP my 2004 has no sensor on the fuel rack and not module on/near the fuel tank.

And what do you mean by "the fuel pickup assembly that was faulty"? Could this have been failure of the spring-loaded system that pushes the siphon to the bottom of the tank to ensure that fuel is brought to the pump until the tank is entirely empty? That could explain variability over time as well as volume-dependence and position-dependence. (Altitude and atmospheric pressure as relevant variables sound odd to me.)
....

The arrangement in the XC70 is that the gas tank is shaped like a saddle bag straddling the drive shaft/tunnel. So the fuel pump assembly includes a pickup that sits under the driver side gas tank port. That pickup brings the gas from the driver side of the tank over the hump and into the pump. If the pickup is faulty, the car acts like it's running out of gas. To make it more confusing, when exactly this happens depends if you're on a hill or not. And, of course, the gauge is showing 3/8 full so you think, well, it can't be the gas!

If you watch that YouTube the guy explains the arrangement starting around 2:15. He mentions a siphon but it isn't. The plastic pickup has an impeller in it and, in my case, that was faulty.

Replacing the pump is an easy job and I posted about my job including making a tool to remove the locking rings viewtopic.php?p=437010#p437010 . Just be sure to attach a fish wire (as suggested in that YouTube) to the driver side assembly before removing it.

[abscate]

We had a user on the XC90 forum thst had his fuel pump replaced at a dealer, and they kinked the crossover line on install. After several months of SWMBO getting tired of a car that would pseudo random;y die 15 minutes from home on the 5 Freeway, he finally tracked it down.

[goldxc70]

We had a user on the XC90 forum thst had his fuel pump replaced at a dealer, and they kinked the crossover line on install. After several months of SWMBO getting tired of a car that would pseudo random;y die 15 minutes from home on the 5 Freeway, he finally tracked it down.

I can see that happen quite easily. The baffle between the two sides of the tank is finicky to get past even with a fish wire in place. I layed mine out and used a helper to hold it as I gently pulled making sure nothing got twisted. Guess you could do it solo by laying it out near the passenger side port and carefully feeding it across while pulling on fish wire,.

[enotslim]

To make it more confusing, when exactly this happens depends if you're on a hill or not. And, of course, the gauge is showing 3/8 full so you think, well, it can't be the gas!

If you watch that YouTube the guy explains the arrangement starting around 2:15. He mentions a siphon but it isn't. The plastic pickup has an impeller in it and, in my case, that was faulty.

Replacing the pump is an easy job...

(OP here) Regarding "hills" the last three failed starts ocurred after driving (down) into an underground parking lot (twice) or driving the front wheels (up) onto ramps. Hmmm ...

The car has been tested many times and has not failed to start since I last posted in May (2023). This included multiple times on ramps and short drives (up to 3 miles) starting and stopping only in my driveway. Tank below 1/4 full the entire time. I did not stop anywhere else for fear of becoming stranded. The only “intervention” was to disconnect the battery except when starting and driving. I finally gave up, drove to and from Firestone for alignment I then drove 70 miles to/from a conference with almost no issues. (The tank was nearly empty after the alignment - warning light was on - and still started fine. ) However, after 6 hours in an exposed parking lot with the battery connected (in order to lock the car) a test start was very difficult with signs of low fuel delivery - balky, hesitant. After ~ 5 seconds the engine started. Ran 30 seconds. Turned off. An immediate restart was fine. Disconnected the battery and left the car urlocked until I left four days later when the car started fine and I drove home.
- The battery has been connected for ten days and the car is starting fine.
- I guess I'll just drive till it fails and hope to diagnose then, but any suggestions are very welcome in the meantime. Or I could replace the entire fuel pump assembly without knowing it is bad. Tried to avoid that. And towing from an underground garage with low clearance is a pain.
- Can the fuel pickup/impeller/(not a siphon) be serviced? Blocked by "stones" that presumably precipitate from contaminants in the tank?