07 XC70 fuel pump or …

[erikv11]

Car starts then dies, won’t idle for more than about 5 seconds.
Starts over and over again - will always start.
As it starts, fuel pressure jumps up to like 45 using cheap tire gauge, then drops until the engine dies at like 15 psi. If you try to rev it, it just dies sooner.
Fuel tank is almost full. Mileage 180k.
Replaced fuel pressure sensor on rail with known good one (Bosch) no change.

Codes present
ECM-280C fuel pressure sensor, signal to high
ECM-291D fuel pump, control module, signal to low
CEM-3F90 fuel pump, relay, open circuit or shorted to ground

A good shop said the problem is the fuel pump but I won’t be able to talk to them until like 10 days, they are closed for a vacation. Would like to fix before then eg buy parts now while Labor Day sales still going.

I’m thinking fuel pump trust the shop, or check the fuel module (PEM ?). Any way to differential diagnose?

I’ll scour the internet on this one later tonight but any suggestions/ideas welcome!

[abscate]

Get your fellow Doctor Potato Head to scour his spares for his spare Pem and send it over for a parts cannnon diagnosis.

[jonesg]

with battery disconnected, if you backprobe the pump connector and supply a constant 12v you should get 80 psi constant at the rail,
does it have a PEM?

if you can communicate with the pump via vida then PEM is good.
without VIDA you're playing parts cannon, although I would favor the mechanics diagnosis unless you have VIDA to verify.

[erikv11]

Hey, no making fun of my (preferred) parts cannon approach! Hold that (good) thought, I actually may be able to do a swap here see below.

The dead car has a PEM yes, located in the spare tire well so not exposed to the elements. I do have VIDA, I'll fire it up and see if II can find where to check if it can talk to the fuel pump.

Technically have a "spare" PEM is in the other XC70 (also '07) parked next to it now. Same plastic fuel tank, same PEM location inside the spare tire well. But in case there is some small risk (?) of killing a good PEM by swapping it into the dead car, instead I'll swap the potentially bad PEM into the good car, minimal risk there correct? And if the working car still runs with either PEM then I know they are both good.

Assuming no tricks to swapping a PEM, just disconnect the battery first.

[jonesg]

try the parts swap, wont hurt anything.

[BlackBart]

Hey, no making fun of my (preferred) parts cannon approach!

I have sometimes employed the parts cannon in the past, to sadly find it runs the same.

[erikv11]

Both PEMs seems to be good, based on swapping. So parts cannon test eliminates fuel press sensor, PEM.

In VIDA, I don't see any place to specifically activate the fuel pump. Checked all the modules. Under CEM I can see that the fuel pump relay activates when the key is turned, can read the fuel levels L and R tanks, and can read live fuel pressure. With key in pos II, car off, fuel pressure reads like 460 kPA, then when I start it up the pressure rapidly drops to like 200 as the engine dies, then pops back up to 450+ with the engine not running with key still in position II.

So I interpret that the PEM works, the fuel pressure sensor works, but something, presumably the fuel pump, does not maintain sufficient fuel pressure. There are no fuel leaks evident anywhere, no smell of gas. And yes, I do have that second-hand, "almost for sure it's a bad fuel pump" diagnosis from the shop I mentioned in OP.

Maybe inside the tank a pump hose is off or kinked, or maybe the pump motor is in fact bad, but regardless it seems the next step is to open it up expecting to pull and replace the pump, so I'll order a fuel pump soon here. If when I get in there I find something easier like a frayed wire then I can just return the pump.

I haven't checked for a clogged fuel filter, and it actually looks like the current one was installed at 101k (!). I'll buy a new fuel filter too, install it first before replacing the pump.

[Krons]

I haven't checked for a clogged fuel filter, and it actually looks like the current one was installed at 101k (!). I'll buy a new fuel filter too, install it first before replacing the pump.

On my P2s I suspect every one had original fuel filters when bought at 150k, 138k and 190k respectively. The 2002 had what felt like a decent horsepower gain with a new filter so a possibility that could be it.

[abscate]

Skip that fuel filter change , that’s a long shot. There is a Schrader valve up stream of the filter where you can measure unregulated fuel pump pressure, but a clogged filter isn’t going cause a pump to operate then die. That would be like bacteria causing ulcers.

Read up on that XC70 fuel pump change. You need a messenger line to route the saddle tank pickup assembly, and kinking it is a real nightmare. See shockwave thread in XC90 forum

[erikv11]

Thanks for the tips. I have watched a few good videos including Peppermint’s and saw the kinked-pickup-after-install nightmare thread. Not sure I saw shockwave’s thread I’ll check that out.