VR6 ABV crank position sensor question - now fuel pressure issue

[fendervg 29]

Would be great if you could check your pressure to have something to compare against. Hmmm - I'll check the wiring to the relays as well to be on the safe side - although both my alarm and immobiliser were installed very neatly the last time I looked. And when it cuts out, neither are engaged. But it's worth a try - cheers.

[fendervg 29]

Bumping this up in case there are new eyes looking at it - and if anyone has a VR6 and a fuel pressure gauge to hand it would be real favour if they could test their pressure with the engine running and let me know the results. Many thanks.

 

I even asked Pierburg in German about this and they say all their pumps for the VR6 are 3 bar, that's all they ever sold and in 10 years they haven't had any negative feedback on them! Why then a 4 bar fuel pressure regulator?

[fendervg 29]

Just had a really interesting quick chat with Vince at Stealth about this. According to him, 3.5 bar at idle and 4 bar with the vac hose off is perfectly normal, so it looks like there is absolutely nothing wrong with my pump. He suggested I monitor the ECU voltage in VCDS over time when the car is idling to see if there is any variation - could be pointing at our old friend relay 109 again, or the wiring to it. Will work on this tonight or over the weekend and report back.

[Jon_vr6 1]

Vince is the man when it comes to the vr6. Good suggestions hope you get to the bottom of it.

[GreenRado 10]

Sorry it's taken me so long to get back, the weather's been crap here for the past few days. Anyway looks like my results confirm what Vince had told you. I'm getting 3.6 bar at idle, 4.1 with FPR hose off and plugged. Residual pressure stays above 3 bar after engine is turned back off.

[fendervg 29]

@greenrado - thanks for checking, so that's in line with what I'm seeing. Great.

[fla 9]

to rule out relay 109 completely, bridge the connections with two spades and see how you get on. Make sure you remove the bridge afterwards though!

 

Wiring is something I always assume (to my cost!)is ok, so as you say, its worth checking.

[fendervg 29]

I've replaced relay 109 with a spare I had and will test more tomorrow. I was seeing 13.8-14.2 volts in VCDS at the ECU, with no large variations. One strange thing I saw was that the coolant temperature reading is -49C with the engine turned off? If this is not right it could be our old friend the blue ECU coolant temp sensor again. Will swap in another and work on it further over the weekend. Didn't stop it starting though - same overall symptoms - engine runs for about 10-20 mins and then cuts out and won't start for another 10 mins.

 

The first image are the VCDS readings with the engine running and up to temp - the second one is with it off, but ignition on. One thing I'm not sure is the EGR temp at the bottom right - this always reads 217C. Still learning this stuff.

[Dox 22]

When the engine cuts and wont start what's missing, spark, fuel or both?

[fendervg 29]

Good point Dox - back to basics. I'll pull the no. 1 plug when it happens again during testing.

[fendervg 29]

Here's a picture of the no 1 plug:[ATTACH]82156[/ATTACH]

 

Any comments on the condition - they've been in for about 5000 miles?

[fendervg 29]

Also - pulled a spark plug and checked for spark and got a nice shock off it so it looks like it's getting current! Then disconnected the central lead from the distributor and ran the starter and there was a good smell of petrol from the plug hole, so it seems to be getting fuel. Tested all the temp senders - fine - and even swapped the ECU coolant temp plug onto the other sender in the thermostat housing for the radiator fan - car started, but cut out again on idle after 5-10 minutes. To me this leaves:

- dodgy Hall sender on the distributor ( a pain to test as access is not very good for getting a multimeter on it)

- crank position sensor (although would have thought engine would not start at all if this was dead)

- leaking injectors flooding the engine

- Lambda probe (it only happens when the car is on the full fuelling cycle, i.e. Lambda signal on)

 

Any ideas here? I have a new crank position sensor on the way (even though I have a spare, but it's second hand as well) and am looking into a distributor replacement - they can be got, but are pricey. The hall sender is built into the distributor casing itself and there doesn't seem to be a rebuild kit available.

[Dox 22]

So you had a spark from number one and smelt fuel too but the car wouldn't start on the 5 cylinders left untouched?

[fendervg 29]

No, it did start on 5 after a while left to cool down.

[Dox 22]

No, it did start on 5 after a while left to cool down.

 

But you had a spark and fuel when the car wouldn't start?

 

I use a jump lead to check for a spark, one clip on a good engine earth point the other on the plug, no shocks.

 

[fendervg 29]

Doh! Your way makes more sense. Will do that in future. Yes, spark and fuel were present. I wonder is there anything that would stop the ECU firing the injectors?

 

As I understand it - I could be wrong - the distributor is purely mechanical apart from the hall sensor, which sends a pulse back to the ECU with the number of camshaft rotations. This is then used for the injector timings. Hmmm

Edited August 16, 2015 by fendervg

[fendervg 29]

Took the distributor off and found this. Will try a bit of super glue first. [ATTACH]82168[/ATTACH]

Looks as if the hall sender plug connector has broken off due to age and brittleness.

 

Tested voltage at the hall sender plug coming from the loom - I have a good earth, 5V in the centre pin and 12V on the outside pin, so that looks fine and rules out voltage and wiring going back to the ECU. Going to put the distributor back in after glueing the sender socket back on and will put a test LED across it. It should flicker.

 

Removing the distributor on the VR6 and putting it back on turned out to be an easy job - there are red marks showing the correct alignment and it's held on by two 5mm allen bolts - you need to clear away some of the cabling to get good access and of course and remove the spark leads and distributor cap as well as the plastic engine cover on the right. It then simply pops off and back on. I'd advise not turning the engine over though with it off, just in case.

Edited August 16, 2015 by fendervg

[fendervg 29]

Right - more news. Wiring to the hall sensor was fine, but it proved impossible to test the sensor itself with a diode, as you need to supply 12V reference to it and the connector is too small to get three crocodile clips into. It's also in the worst possible place, on the far side of the distributor as you are facing it. It turns out VW have a special test harness that they use for this. I'm definitely going to replace the distributor as a precaution, and a new one comes complete with rotor arm and cap. The Bosch part# for the distributor complete unit is 0986237642, if anyone is looking and can be had for anywhere between €280-420 on an exchange basis with your old one. It's also very straightforward to take out and put back in.

 

I also disconnected all the sensor wiring and reconnected it - MAF, idle stabilisation valve, temp sensors etc. during testing.

 

I then put in my old crank position sensor, which was the original VW one that came with the car instead of the spurious replacement part encased in black plastic that I had bought second hand. I did some testing on these - the official tolerances are: 480-1000 ohms between pins 1 and 2. The VW one measured 590 and the other one 900, so both within limits, although in theory the second one should have been better. i have a new VW one coming anyway.

 

After putting it all back together, it ran on idle for an hour without cutting out, and I also did a 30 minute test drive when warm, and no problems! So either I had a loose connector or the crank sensor was at fault. More driving will prove the point I suppose. I think the broken hall sensor casing will cause problems eventually and may be malfunctioning when the engine temperature rises. It's easy to forget how really hot the VR engine bay gets. Good info on hall senders in general can be found here:

http://www.wellsve.com/sft503/Counterpoint3_1.pdf

Apparently the magnets used in them will lose their effectiveness over time, and I didn't realise that the crank position sensor is really a hall sender as well.

 

I'll let you know how I get on - I'll also set up a thread collecting all the info I have dug up on VR6 2.9 ABV fuel pressure and pumps and the replacement options, as it's really confusing.

[Will.I.Dub 11]

Good to see you're getting sorted, did anyone check their fuel pressure for reference? Can't easily get hold of a gauge myself

[fendervg 29]

Checked with Vince at Stealth and a few other sources - 2.9 ABV engined cars run 4 bar pumps and will run at 3.5 bar with engine running, and 4 bar with the FPR hose disconnected. 2.8 AAA engines and the other Corrado's run on 3 bar pumps and FPRs. More on this later.

[Jim Bowen 1]

Great news, hope its fixed.

 

Interesting re: the pumps, i've gone to a 2.8 block instead of a 2.9, but left original pump in, can't see that being an issue, or rather hoping that's not an issue

[fendervg 29]

Should be fine as long as you run the matching fuel pressure regulator for the pump. I'd say you can even run the 2.9 on a 3 bar pump if you have 3 bar FPR - it's not that much of a difference in displacement after all.

[Mawrick 0]

Haven't read the whole thread - but personally had hot start problems with mine, without ever getting it sorted (changed cam position sensor etc) - until I did the things described in this thread:

 

http://the-corrado.net/showthread.php?82988-VR6-hot-start-problem-seem-to-have-been-resolved-just-thought-I-d-post-experience

 

I'v never had a hot-start problem again,I suspect it can cause other problems then the hot-start problems, and as you will see in the thread VW did a "fix" for bad pumps........but fix is discontinued.....:)

[Roger Chatfield 0]

Great news, hope its fixed.

 

Interesting re: the pumps, i've gone to a 2.8 block instead of a 2.9, but left original pump in, can't see that being an issue, or rather hoping that's not an issue

 

Won't be a problem, FPR controls the pressure and not the pump, also the Corrado is closed loop ODB1 so will 'tune' the injectors to deliver the correct amount via data from the O2 sensor.

 

Rog.

[fendervg 29]

Another update after two weeks of driving the car to and from work daily.

 

The car now drives relatively well, not cut-outs at idle or when going off-throttle, and pulls better than before. I would put this down to the new distributor with a working hall sender.

 

However, I still have low residual pressure - this manifests itself on cold starting in the morning or when going home, where it splutters on the first turn of the key and will always catch on a second try. This is the pressure building up.

 

I now suspect either the valve in the pump (possibly leaking back into the tank through the feed line) or worn injector seals. I've ordered a non-return valve that I am going to fit on the fuel feed from the pump (hopefully this will keep more pressure at the rail when left standing over long periods) and I have sent off a set of injectors to be tested and refurbished by Mr. Injector and will fit these when they come back.

 

Fingers crossed - as always (or so it seems with this car), there was more than one problem causing the issue!