04 XC70 Could it be the fuel pump?

Post by **jimmy57** » 24 Jun 2014, 06:43

Your Volvo has a standard tire valve for fuel pressure port and that is a widely used fitting on fuel pressure gauges.

mikeamondo · Post by **mikeamondo** » 24 Jun 2014, 07:15

Thanks for info guys... much appreciated! I'll have my son pick up a gauge. I see now the lower psi gauges say "not for fuel injected vehicles" on them. That makes sense.

So we are looking for around 55 psi / 3.8 bars / 379.31 kPa at idle dropping no lower than 29 psi / 2 bars /200 kPa 20 minutes after shutdown. I'm mathematically challenged, so those may or may not be accurate.... I actually qualify for certain government math subsidies.

I will post the results when I get them back! Mike

mikeamondo · Post by **mikeamondo** » 26 Jun 2014, 18:00

So... Andy drove the car a time or two more, with no additional problems, but has now also filled the tank. It has no failed to start again. As a reminder, it would fail to start pretty much every other time he drove it, prior to filling the tank.

He bought the pressure gauge and it showed 58 psi at idle... so that's good. He did not check it 20 minutes after shut down, but I've asked him to check that and I should have an update shortly.

Are there other things in the fuel system that could cause the vapor lock issue besides the fuel pump being weak?

Is it possible for the strength of the pump to come and go?

Does this car have the fuel pump module mounted outside the cabin on the tank? If so, what are the symptoms when that part goes?

Thanks for the input!

sergio · Post by **sergio** » 30 Jun 2014, 10:09

May I suggest you check the wiring regarding the pump AND the controls (level sensor etc)

I have a S60 with a different tank-pump-level sensor. The same problem happened to me. After a LOT of time spent searching everything on the car I found out the the point of contact between the wires and the level sensor was burned out. Sometimes there was juice sometimes there wasn't.
I had to replace the level sensor.
It may be worth checking before buying something

This must be your system, I have my level sensor at # 35 on this picture.

.

draser · Post by **draser** » 30 Jun 2014, 11:34

There's a fuel pressure sensor that monitors and controls the fuel pump. I'd think there will be a DTC set for intermittent low fuel pressure...

Post by **hansenjg** » 30 Jun 2014, 15:27

Has anyone changed the fuel filter? Similar to the "weak pump" theory, a clogged filter might work better with a full tank. Most of the time a dirty ff will show up as OK at idle, but trouble at hard acceleration or high speed. It's a cheap way to rule out something that should be changed anyway.

mikeamondo · Post by **mikeamondo** » 03 Jul 2014, 04:38

Fuel filter... probably not changed recently. He filled the tank and it ran well, but had a minor version of the problem... slow to start, but started and then ran ok. But the tank is still mainly full. He still has not done the bleed down test, but we will be visiting this weekend, and I plan to do the test, as well as clean the contacts on the ECM and TCM. We may also pull the back seat, and open up the tank so he knows how to do it, in case the pump turns out to be the culprit. Just makes sense to put a new fuel filter in while we are messing with it.

Where is the fuel filter on the 04 XC70?

Post by **abscate** » 03 Jul 2014, 04:50

I've read the "full fuel tank helps weak fuel pump" idea a few times recently and I don't think physics supports this theory very well by the way. Certainly there isn't enough head to help push the fuel through give these systems run at about 3 ATM fuel pressure.

It's more likely an overheating pump is cooled by a full tank, or the experience of filling he tank allows a warm pump to cool off, than a pressure issue.

draser · Post by **draser** » 03 Jul 2014, 06:59

From your initial description the problem seems related more to the vapor management system than the fuel pump. The fuel tank has a vapor press sensor and solenoid to monitor and control vapor press build up. Also, as suggested, I'd check the fuel pp control module for contact corrosion as well.

Post by **abscate** » 03 Jul 2014, 08:19

I like sergios post on the level sensor. That really makes sense, as that probably inhibits the fuel pump from operating when the tank is dry. If the sensor is iffy, then it it shutting off the fuel pump.

You need to measure the fuel pressure at the rail under 'no start' conditions of course, to diagnose.

04 XC70 Could it be the fuel pump?

Re: 04 XC70 Could it be the fuel pump?