04 XC70 Could it be the fuel pump?

[mikeamondo]

Ah... so many things to check! abscate - I too was dubious about the weight of the fuel helping out a weak pump... the cooling issue on a full verses empty tank does make some sense EXCEPT..... for the fact that opening the tank momentarily and closing it allowed the car to start instantly. There would not have been sufficient cooling down in those few seconds, I think. Of course, that was just 1 occurrence, after which he filled the tank, at which time all problems stopped.

Let's add this to the mix. After he filled the tank, it did have one VERY MINOR starting issue... just a hesitation to fire.... but then it started. That's when the Brake Failure warning came on... the one that says slow to a safe stop. Of course, he wasn't moving and the brakes were fine. That msg went away and the problem did not yet reoccur.

So what would turn on that brake warning, AND cause vapor lock like symptoms in low fuel situation, and other assorted lights/warnings when the start issue is more severe?

Getting ready to leave WV for the 11 hour haul to NH now. Will be looking at the car, hopefully running a scan with VIDA on my old laptop, and pulling the TCU/ECM boxes to make sure the contacts are clean. I will post more when I have it.

Also... some info on where the various mentioned parts live on the car would be helpful. I understand the fuel pp control module is exterior of the cabin, mounted on the corner of the tank, if it hasn't been retro fit to inside.... Is that correct? Ad is the level sensor on the sending unit portion, inside the tank on the driver's side port, connected with wires through the tank? How about the vapor pressure sensor and solenoid.

Thanks, guys! All your help and ideas are much appreciated!

[draser]

Not sure why we got stuck on this fuel pp issue, because the various dash warnings point rather to a more generic problem with the electrical system maybe... do you get the 14.4 volts on the batt w/engine running and are the batt posts clean and tight? Also if you're able to start the car after loosening the gas cap as a rule - or most often than not - then your vapor control system does not work.
The fuel pp theory is that if you run very low on fuel - to the point where the pp would be dry at times - you'd ruin the pp because of lack of cooling and over rotation (due to no fluid at impeller). And that is possible when the fuel float is off located (or bad sender) - where it would show quarter tank but you're actually close to empty.

[abscate]

I'm not weighting the one time a full fuel tank ' solved the problem' too heavily yet. Too many other variables to make that call.

[mikeamondo]

Well... we're half way to New Hampshire and I get more confused the closer I get. I think the plan will be:

Pull and clean the ECM and TCU from the engine compartment (bought the special puller tool from ARD), adding some dilectric grease when reinstalling,
check and clean the battery terminals.
Pick up a cheap multimeter and check the voltage at the battery while running
Attempt to install the VIDA on my laptop and check for stored codes.
Conduct the engine off bleed down pressure check, 20 min after shutdown.
Remove the rear seat backs and open the tank access panels (mostly to show my son how to get in there in case he needs to later).
Check the fuel pump control module for corrosion - Question: is this located on the corner of the tank, under the car? Anyone got a pic of what I'm looking for?

I like the logic behind the failed level sensor - that's in the side of the tank opposite the pump, right? And doesn't a new level sensor come with the pump, or no?

The opening of the tank issue would logically seem to show a failure in a vapor control system, however, why again would that only have happened when the fuel was low, and not repeat itself now that the tank is full? It's like it controls the vapor issues when full, but not when empty. He's driven for several days now, making several trips about town, without the problem reoccurring, when before, it happened every day or two at the very least.

Thanks!

[draser]

Lot more vapors when tank empty... One way to check is to measure fuel press full vs empty. If you get a lower reading empty the pump is fighting vapors.

[abscate]

Lots more vapor in volume, but identical vapor pressure regardless of tank fill level

All the symptoms here point to an intermittent electrical problem of some kind, not a fuel Delivery problem.

[mikeamondo]

I would think electrical as well... but electrical that is effected in some way by the fuel level. Does that make sense? If it's a vapor control issue.... lower tank level = more vapor... so vapor control might be indicated?

What are the components of the vapor control system that you mentioned and where are they?
And.. where is that fuel pump control module on this car? It's external of the cabin, correct? On the corner of the fuel tank. I want to clean up those contacts if possible while I'm here. Starting to mess with the car this afternoon....

[abscate]

Take a look at very ground you can see, and there a lot of them, before you start messing with that fuel pump. If the fuel pressure at the rail is good, you have ruled out the vapor lock theory and have to start troubleshooting from the beginning, with compression.

[mikeamondo]

ok... that was particularly unproductive work session. We did the following:
1 - We used the ARD tool to pull the ecm or tcu.. not sure which. The other one would not come out... seemed like the tool was not fitting all the way in. The pins were bright and clean on the one we got out... so we put it back.

2 - we did a test of the fuel pressure again, with the tank now half full, and the bleed down test. At idle, she's showing 60psi. 20 minutes after shutdown, she was still showing 39psi.... so that should be good. Does that add anything to the problem solving?

3 - I can verify that this car has a plastic, not steel gas tank, but I was not able to find the PEM (pump electronic module) mounted on or near the tank. Should it be there? I did see one obvious module back there, but it seemed to be attached, at a 45 degree angle to the ground, at the point where the driveshaft comes into the rear end housing.... so close to, but not on, the fuel tank. That's not it, is it?

In terms of running, the car is a beast. This is the first time I've see one up close, or driven one, and now I can't wait to get my hands on the S60 manual I've been dreaming about. Think I may be infected with Vovo Fever...

[abscate]

I think you can move off fuel system.

Check all the coil connectors under the cover of the cylinder head and make sure all the could are firmly mounted down with the single screw tightly. They ground through those screws.

The next time you get a no start, you need to duplicate that fuel pressure to rule out fuel pump problems.

ECU problems are 1 in 10,000 and usually because someone messed with it. Let's leave that alone too.