Crank sensor symptoms

Matt82 · 17 May 2013 at 21:30

Ive got a bit of a puzzler going on with the Golf (1.8t)

Some morning (particularly when cold) when you start and drive away it will have a pronounced stutter when you might light throttle inputs, it feels like the car has plain stalled for a second.

The other day i could feel it doing it in the evening (rare, normally only when cold)

No fault codes, ive monitored ignition timing, afr, throttle position, everything, no obvious signs

For it to cut so abruptly im thinking crank sensor, but the tacho doesnt show any signs

If voltage dropped at the fuel pump, do you think it could cause such an abrupt stutter?

There are similar posts on mk4 boards but no one ever seems to cure it

Fuzz · 17 May 2013 at 23:18

If it's cutting out then you haven't been watching AFR closely enough as you would have seen moohasive lean spikes as it spat fresh air down the exhaust.

Got access to a scope?

Matt82 · 17 May 2013 at 23:22

unfortunately no, never used one

im only able to watch afr etc by obd and i dont think its fast enough tbh.

thinking about it, is fuel pump voltage or the fuel pump itself something that could be intermitent only when cold and only on light throttle applications?

crank sensors normally only go duff when hot (in my experience)_

rodenal · 17 May 2013 at 23:23

Similar thing happened with my 1.8t A3 when I had it. Turned out a coilpack and cam sensor had gone at the same time, no idea why the coil didn't affect it all the time - could run fine 4 starts out of 5 then splutter about when it decided not to play ball.

The cam sensor threw a code though

Fuzz · 18 May 2013 at 00:09

A dying fuel pump will give you stuttering at full throttle / long period acceleration / high revs, not something that would make it stutter on light load.
Fuel pressure to the fual rail is controlled by the Fuel Pressure Regulator, not the pump.
Check the vacuum hose from inlet manifold to FPR is intact / not perished.
Sounds more MAF / Lambda related to me. lambda is easy to diagnose but MAF a pain in the ass.

Any crank sensor issues and you'd not only have rev counter going offline but also spark and injector traces would vanish to and that would almost definitely throw up a fault code.

Wild out there thoughts on cam timing (sloppy cambelt) may cause a ref / sync error with the cam sensor but again, likely to throw up cam sensor fault.

For reference, I have Mk4 golf Gti and it does the same thing, only occasionally and I've never looked into it.

Matt82 · 20 May 2013 at 08:34

Well, I had a look under the bonnet on Saturday, first targets were air leaks between maf and turbo and the pcv. That was all fine. Checked vac hoses for FPR and DV, everything intact. The vac hose at the secondary air intake valve wasn’t the best, so changed that. I have disabled the N249 on mine but the pipework was still in place, so I junked that because it just confuses everything.

I went to reassemble everything but decided to put a drop of oil IN the FPR as ive come across these being sticky (on NA cars, not turbo one) though.

The car drives really nice again now. Transitioning between off to light throttle is smooth as a babys bum. The car is smoother/nicer to drive and ive not had to compensate for any poor running since.