Cold start issues - fuel rail pressure too low p0087-002

[iremk5gti]

Hey all - Having a difficult to solve issue with my "08 mk5 GTi. Intermittently, when the car is left for a day or two, it's excessively cranking and hard starting. It's then going into limp mode and throwing: 000135 - Fuel Rail/System Pressure P0087 - 002 - Too Low - Intermittent

If I leave it running a few seconds, turn it off then restart it, it'll generally start right back up perfectly. No limp mode. Sometimes it takes a few restarts. It always goes away, and has never remained in limp mode after one or multiple restarts in succession.

CEL is on after this happens, even though car runs great and pulls as normal. No hesitations, nothing unusual. After a brief drive the CEL turns off.

For the remainder of the day it'll start and run great. It only happens after long periods of time sitting. However, to throw a curveball, it's not consistent:
- Left it sitting for 8 days recently whilst away, started perfectly upon return
- Left it sitting for 2 days last week, hard start and limp mode
- Has happened 5 times in the last 2 months.

The car at idle has a slight vibration that is more pronounced on an incline and non-existent on a decline. And by vibration, I mean a slight shimmy that your average person wouldn't notice unless pointed out. Feels like unwanted combustion. However no misfires are being recorded (checked with VCDS). Also read this may be normal with our cars, lots of similar reports.

With VCDS and when running normally all the values for blocks 103, 106 and 230 are normal. Requested and actual fuel pressures at 50psi. Nothing is out of spec.



When the cold start issues occur I'm hearing a faint electronic whine from the LPFP area under the rear seats. It's a distinctive electrical noise, like a low-key siren almost! Then it goes away after a few moments.

Before throwing parts at it I thought I'd post here. Research leads me to believe it could be G410 fuel pressure regulator, in-tank LPFP or LPFP module. The randomness of this makes me believe it could be something electrical.

Recently bits maintenance bits done, to rule them out:
- Cam follower regularly been checked and replaced, most recently last month.
- Cam lobe is in perfect condition
- Has had 4x new fuel injectors and walnut blasting to clean out carbon buildup
- Fuel filter replaced as first attempt to fix this issue

Wondering if anyone has similar issues or advice 
 

[Octoparrot]

It sounds like fuel pressure is bleeding off over time which is normal I think but then the in tank pump isn't supplying enough pressure on the first start up. After a pressure has built back up it will start fine again as the pressure hasn't had long enough to bleed off. I'd be looking at the LPFP and module first.

[ROH ECHT]

Use VCDS to watch MB 231 when it initially primes. Watch the pressure without starting the engine. The low pressure may drop after it initially primes.
 
The whole MB 230 and 231 being within spec at idle doesn't mean it will not suffer while running. Mine appeared to be "within spec" at idle, both LPFP and HPFP, and when I logged the data for those two...the LPFP pressure dropped to near 1 bar causing the high pressure to be near 30 bar below its target/spec.

Yes, a sensor reporting inaccurately can cause it to run poorly. But you will see a poor report in the data. Typically, it's the G410 failing more than the G247. I recommend you replace it with a genuine sensor if you choose to swap it for new. Seems to be hit-or-miss with aftermarket sensors. This will lead you to continue the search when all along it was a "new" aftermarket G410 that doesn't work properly.

[iremk5gti]

Sorry to resurrect an old thread but I’m still getting this issue. Intermittent cold start it’s going into limp mode, then a few minutes later it’s perfect and drives perfectly thereafter.

Totally dumbfounded here. Since my original post I’ve replaced:

- LPFP
- LPFP module
- Fuel filter
- G410 low pressure side fuel sensor

The G410 sensor was weeping fuel, and had saturated the connector. I’ve cleaned it all up, but since gotten the same issue with the new sensor. How would one go about checking it hasn’t done damage to the connector?

This doesn’t feel like it’s the HPFP at fault as it’s running beautifully otherwise. But I could be wrong.

Has anyone else any ideas and where to look or what to do? Driving me nuts.
-

[GreigC]

This sounds like Clogged/leaking fuel injector.

[iremk5gti]

This sounds like Clogged/leaking fuel injector.

I thought potentially but I checked for misfires and am not having any. It doesn't have any problems starting hot either. Car runs great beyond the bizarre cold start issue.

[GreigC]

With what I said is very common on our engines. If your injector is partially clogged or even leaking it causes poor start up. Once started then restarted immediately afterwards it can run perfect with no misfires on idle or driving. Although on WOT you can “sometimes” feel a shudder at 2.5k RPM this can be very intermittent though.

Before spending more money/time on the issue. Getting a VW specialist would be my next step. Thanks