M25 Breakdown

[oneohtwo]

Had a bit of an odd moment on the M25 last Friday. Was in slow moving traffic when all of a sudden throttle became unresponsive and started stuttering. Pulled over to the left and it seemed to settle down and was ok just at a steady speed or slow revving. The traffic came to a stop and seemed likely to sit there a while so I switched off, but then it wouldn't restart. Kept turning over but not firing.

Pushed it over to the hard shoulder and was waiting for 2 hours for assistance and on the off-chance tried again and the engine fired up and I got to the next services with the engine apparently running fine. Didn't want to risk the same again so got towed.

Could this be fuel pump related or something else? (Didn't want to hijack the fuel pump thread down there!) That's my initial thought... temperature all seemed fine and normal, low 90s. Oil all fine. And how can I diagnose it as fuel pump definitively short of swapping it over and seeing if it happens again?

[a_riot]

Could be a fuel pump or a crank sensor issue from your description of it. The crank sensor can get moody when hot, and without it working correctly the car will crank but won't start. But then a few minutes later it will run just fine. It's typically an inexpensive part and easy to replace.

It could also be a failing fuel pump, bad fuel pump relay or fuel delivery issue. I had an issue with the wiring from the fuel pump to the pump connector and had to resolder those connections due to a bad solder joint. Pierburg pumps, which I assume your is, usually don't have intermittent problems though, they either work or they don't from my experience.

Some diagnostics you can do is listen to the pump and make sure its always running at the same speed, not cutting out at times or slowing down, check the fuel screen at the bottom of the pump and the fuel filter to see if you have some kind of gunk in there blocking things up. If you have a Power Probe, you can send 12v directly to the pump connector and listen to the pump run to see how it sounds. Some say you can check the resistance across the +/- and see what you get, although I'm not totally confident that is always that useful. Normally resistance is low, under 10 ohms iirc, but I've seen different values on pumps that work fine.

I'm currently pulling my pumps to swap the old rubber hoses to new nylon hoses from the pump to the top hat. Many Corrados have the factory hoses replaced with standard fuel hose, which is not rated for submersion in fuel, and so deteriorate and leak over time. Here's what mine looked like.


End of hose delaminating...


Rubber hose turning into black goop...


Imprint of clamp on hose...


Completed with nylon hoses...

[oneohtwo]

Some good info there thanks. Will try and do some investigations this weekend.

That pipe looks nasty, don't particularly want that getting in your fuel!

[1200 bandit]

Got 2.0 16 v had some thing similar,replace the battery,Also found wiring to the throttle body snapped
Removed the fuel pump from inside the tank ,found bits of foam inside the fuel tank,(replace the the 2 fuel pumps)
Once the repairs was carried out running ok
Has not broken down for 12 mouths which is quite amazing

[a_riot]

No worries, hope it helps. The last time I changed the fuel filter, I was surprised at how black the crap that came out of it was. I can't be sure but I suspect its from the black goop that eventually melts off the hoses that was the culprit. I'm going to do the same thing to my other Corrado this weekend so both will get clean gas.

[oneohtwo]

I've not had a chance to poke about just yet, but have ordered a new fuel filter anyway as god knows if that's ever been changed and it's been on my mind anyway.

The crankshaft sensor did sound a likely culprit, so I was going to swap that over anyway on the off chance, but it's no longer available from VW. (Just as well as they were charging over £100 for it!) I've found a few here:

https://www.autodoc.co.uk/car-parts/...i/1755-2-9-vr6

But somewhat unsure what to go for. don't really want to be paying £160 for the top end Hella effort, but nor do I want some cheap junk that's worthless. Was thinking the Valeo might be ok, as I believe they provided some OEM parts, but was wondering if there were any recommendations from that list, or recognised sensors? Cheers.

[oneohtwo]

Went for the Valeo but still waiting for it to arrive, so haven't yet fully got to the bottom of things. In the meantime I've had a listen to the fuel pump and nothing sounded odd about it, and I have changed the fuel filter on the off chance using the wiki guide.

Couple of things I found different to the wiki guide was that the bolts are17mm not 16mm, and it doesn't mention the metal clips holding the cage onto the bolts which were quite fiddly. Also the minimum size of fuel line clips is 14mm. I couldn't find 12-15mm, so ended up with a variety, 12-13, 13-14 and 15-17mm. The 15-17mm are too big and won't tighten, and the 12-13 won't go on.

[oneohtwo]

I finally got a chance to swap out the crank sensor at the weekend, only to find the new part (Not a Valeo one, they sent a Delphi thing) doesn't fit as below:



Word of warning if anyone else is looking to buy one. The original part is the metal one below, new one is the cheap looking plastic one above. You can see at the base of the plastic one it widens and has an O-ring fitted - this won't fit in the hole in the crank case. The O-ring is located in hole and the sensor should be the same diameter all the way along. Very frustrating. Looking on the website quite a few of these sensors have the widened base, including the Hella one for £170! Something to look out for.

Anyway, cleaned up the old one and put it back in, then drove around locally trying to replicate the fault. Engine got up to temp just going along below 30 mph for a good hour but no issue, ran fine... so not sure what to do now! Leave it and hope it was an odd one off?

[a_riot]

Odd. I've replaced both mine and never had an issue with fitment on a 2.8 engine. Don't recall what brand but it wasn't a VW part. I would imagine the sensor itself doesn't fail, its likely just the wiring that fails so you might be able to fix the old one if there is a break in the wiring but at the age it likely is, I'd try and find a replacement if you can. Are you certain the old O-ring came out with the sensor? Just wondering if it got stuck preventing the new one from seating.

[fla]

as A_riot says, sometimes the o-ring remains in the block as well as the retaining collar. Best to clean the block face before refitting to ensure a good contact. Finally chekc your relay 109. This is for the ecu and will shut off the injectors and coilpack. Test by applying power to it and amke sure it doesn't 'buzz'. Best to replace just to rule it out.