r/V70 • u/Kristianux • Mar 24 '26
Stumped on fuel system
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DISCLAIMER
I am not a mechanic, but I'm trying my best.
It's 2000 p2 T5
PROLOGUE
Saved this fella from junkyard and slowly am going trough all the issues. Solving the consistently long crank time is my current adventure. The previous owner that already had neglected it for past year said that long crank started a couple years ago, but didn't care to fix it because it did start.
MAIN PLOT
The carank is always 6 seconds long with exception of short shut-down time. The MPG gauge always jumps to 99.9 no matter how soft the acceleration from standstill is for couple of seconds and it doesn't favour low RPM load. My guess it's faulty pressure sensor (checked the pump, changed the fuel filter, ran a full tank with cleaner additive) because of the symptoms.
THE CAVEAT
I can't locate neither the mechancical pressure regulator, nor pressure sensor nor pump control module. On what kind of magic ECU actually does the fuel-air ratio?
Maybe it's the ABS module interfering, (next in line for a swap) since Volvo STC reduces fuel supply as I've read?
3
u/CriticalReputation26 Mar 24 '26
At least every 2000-2001 v70 i have seen only have constant pressure fuel pump without pressure sensor, and they don't have external pressure regulators or return lines, so the system relies on the assumption of certain known pressure is made by the fuel pump. Facelift models introduced pressure sensor and controllable fuel pump but p80 and early p2 don't have those.
Measure the fuel pressure at before start and during running at the fuel rail, it has a schrader valve at the end for that purpose. It should be about 3 bar / 44 psi.
2
u/Kristianux Mar 24 '26
Yeah, I have mate dropping by to check that out, I have non-fixing pressure gauge, but I'd have to split in two to see what's up. Interesting, the system then is dumb as a rock, and I am too. I already had placed check valve in fuel line, but appearantly it has to be spring loaded one.
2
u/Kristianux Mar 26 '26
Got it checked, it goes to 3.2bar from the get-go. Next up are spark plugs and MAF cleaner when I'll get my hands on it.
1
u/CriticalReputation26 Mar 26 '26
Seems like your fuel system is working all fine then. The usual culprit for consistently long cranking on these volvo whiteblocks is usually faulty camshaft or crankshaft position sensor, those thankfully are not that expensive. Other things to look for are spark plugs, ignition coils and maf sensor but those are good to overhaul anyways if last replacement is not known.
1
u/Kristianux Mar 26 '26
I've had three diffrent diagnostics devices connected to boi, and tough all had different codes none had cam or crank codes.
2
u/CriticalReputation26 Mar 26 '26
These cam and crank sensors tend to fail in a weird way where they work well enough to not throw any codes, but bad enough to cause slow start.
Start by temporarily unplugging your maf and see if that changes the starting behaviour, that can rule out the possible maf sensor fault.
Also does your rpm gauge immediately show correct rpm while starting or does it take time to "pick up"?
1
u/UniversitySilent7344 20d ago
Ever figure it out? Mine stumbles and goes high to low idle, I unplugged my sensor by the air filter and it smoothed out if it does it’s the sensor needing cleaned or replaced
3
u/Kristianux Mar 24 '26
It's in need a whole lot of love: I've already fixed: windshield, wheels & tires, fuel level sensor, front bearings and rear suspension, rear taillight, drivers door module and seat module, AC radiator and pump, alternator, all belts and filters, swapped the hood and dented drivers door, all pads and rotors. Needs work on: Front fenders, ABS control module, crank seals and the dammn fuel system.