VR6 Cutting Out

[Dicky 0]

Hi folks,

 

my (’93) VR6 often cuts out when rolling to a halt at junctions (it starts and idles perfectly every time – including after cutting out). The garage’s diagnostics test indicated an air leak (a high Lambda value indicating the engine is running lean). The MPG are down to about 21 on my run to work where I would normally see around 31 MPG. Oil and water temperatures are ‘normal’ at ~ 110° and 90° respectively. There is often a fruity smell outside the car – possibly unburned fuel??

 

I’ve searched the Forum and found several references to cutting out at junctions but with no definitive cause being identified so I thought I’d post this with all the details I can remember. (In fact, I have already applied many of the posted solutions.)

 

I've cleaned (twice) and subsequently changed the Idle Stabilisation Valve (ISV). The inlet and exhaust manifold gaskets have been changed. The exhaust down-pipe had a crack in it and has also been replaced. According to the garage’s workshop manual this sequence of repairs should have solved the problem.

 

In addition, I’ve had a new ignition switch, 2 new Lambda probes, new ignition leads, new ECU and fuel pump relays. (On the subject of Lambda probes – how many wires should it have and what should they all do? There seem to be 4 wires on the connector but 2 have been cut.)

 

I still have the cutting out problem and have now noticed a loud hissing noise from the damper (connected to the ISV). What does this part do and should it make a loud hissing noise? I'm fairly sure it was never this loud but I can't be 100% certain. I've cupped my hand around the damper and this reduces the severity of the hissing but I cannot feel any sucking or blowing from the part! I can’t see any obvious splits in any hoses. I went to look at a (’94) Golf VR6 with the intention of listening to the damper but it didn’t have one, or an ISV. Are they not fitted to later engines or was it removed by the previous owner (the guy who owns it now bought it as is).

 

Since everything downstream of the MFA has been replaced I’m not sure where to look now. Could a faulty MFA manifest itself as an air leak?

 

Now I’m running out of ideas - any help would be appreciated as I’m rapidly running out of money!

 

Thanks.

[dr_mat 0]

You mean MAF not MFA?

The ISV wasn't fitted on OBD2 VR6 engines, it was all done in the fly-by-wire throttle housing.

The damper makes a loud sucking noise, that's normal.

You've reset the faults on the ECU? It may be that your faults *have* now been cleared but you need to reset the ECU to get it to re-adapt to the fixed sensors.

Do you still get sucky MPG after changing the lambda (again)?

[double-6s 0]

Yeah, maybe the split in the downpipe was causing the lambda to freak out? Reset the ecu and see what happens mate.

[tonytiger 0]

On the subject of Lambda probes – how many wires should it have and what should they all do? There seem to be 4 wires on the connector but 2 have been cut

 

I think 2 of the wires are for the lambda heater, another one is a positive feed, the other is the signal back. I think the lambda main earth is just from the lambda body itself.

 

Have you confirmed that the lambda is working since replacement. My VR suffered from stalling (never cured) and intermittent heavy fuel consumption - pretty much the same as yours. The heavy fuel consumption still suggests that the lambda isn't working, or at least the ecu isn't seeing appropriate values. Is the wiring for it sorted now? If you're still getting poor economy you could try unplugging the lambda and see if it improves.

 

Best way to see what the lambda is doing is to fit an AFR meter - you can see what's happening while you're driving then.

 

And as dr_mat and double-6s have said, reset the ecu again.

[Dicky 0]

Thanks for the replies.

 

I did mean MAF :roll:

 

The fuel consumption was normal when I had the Lambda probe replaced and the car was fine for a while - it has since reverted to the same symptoms.

 

I'll get the diagnostics checked on Monday and let you know what it says. I'll also ask the garage to reset the ECU for me too. I assume disconnecting the battery overnight is not sufficient to reset the ECU?

 

I wouldn't have thought so but could the leaking downpipe have damaged the new Lambda probe? Why would the garage have cut 2 of the wires off?

 

What is an AFR meter? :oops:

 

Cheers guys.

[Supercharged 2]

I assume disconnecting the battery overnight is not sufficient to reset the ECU?

 

Yep that's fine or just unplug the ECU itself...

[Dicky 0]

I did that and it made no difference - that's why I assumed an ECU reset wasn't as simple as disconnecting the battery. So it looks like I've still got a problem! I'll get the diagnostics looked at on Monday and post the results - hopefully they'll shed some more light on the problem.

 

What about the MAF? Could a fault with the MAF look like an air leak?

[tonytiger 0]

What is an AFR meter?

 

Air Fuel Ratio meter - see this thread

[Dicky 0]

OK Guys,

 

I've just got back from having the diagnostics checked and there were 2 fault codes:

 

00537 008 – Lambda Control Regulation Limit Exceeded

00525 029 – Lambda Probe G39 Short Circuit To Earth

 

I’m on my 2nd new Lambda probe after the first new probe failed. Could the new probe have been damaged by the leaky exhaust downpipe (which was replaced a couple of weeks ago)? The fault wasn’t cured by replacing the pipe – even though it did have a crack in it!

 

The probe (as I have previously mentioned) only has 2 wires coming out of it (the other 2 being cut off). The mechanic who fitted it wasn’t there but another said that the other 2 wires are for probe heating. Are these not needed? Can you just disconnect them without any effect on the system? Why would they be there at all if they are not necessary – or is this a generic probe that fits lots of cars? (It is supposedly a genuine VAG item by the way.)

 

Anyway, does it look like I need yet another new Lambda probe?

 

Cheers,

 

Richard.

[dr_mat 0]

OK Guys,

 

I've just got back from having the diagnostics checked and there were 2 fault codes:

 

00537 008 – Lambda Control Regulation Limit Exceeded

00525 029 – Lambda Probe G39 Short Circuit To Earth

 

 

Are you certain that these errors were generated *since* swapping your Lambda? They will stay in the ECU until they are cleared, so even swapping the lambda itself won't make the car run right till you clear the codes.

 

As far as number of wires goes, I think that there's a different number required for early vs late cars. Have a dig around the search, I don't remember the details. It's quite possible that someone messing around with the downpipe might have damaged the lambda at the same time, yes, but it's unlikely.

[Dicky 0]

Thanks for the reply dr_mat,

 

The Lambda probe was replaced some time ago - I can't remember when off the top of my head. Even so, the ECU has been reset by the garage several times.

 

When the garage replaced the downpipe they told me they hadn't reset the ECU. When the fault recurred I assumed the new downpipe hadn't fixed the problem I disconnected the battery overnight believing the ECU fault codes would be reset. (This was a couple of weekends ago.) If this action does indeed reset these codes then the two codes I have posted are new.

[dr_mat 0]

Ok, yes, then the codes must have been generated SINCE you last reset the ECU. Therefore this does indeed mean the current lambda probe is not correctly connected or faulty.

[Dicky 0]

The good news is that this probe is in warranty. However, I don't think the garage will believe it could be faulty again!

 

What could kill a Lambda probe?

[dr_mat 0]

"Lambda Probe G39 Short Circuit To Earth"

 

This looks like a wiring glitch to me. Follow the wires up from the lambda, see if they're unbroken. Check for continuity (if you have a multimeter) along the wiring loom. Look for a bust up bit of wiring somewhere, perhaps some wire has been clamped hard against the car's metalwork - this can cause a short to earth.

[tonytiger 0]

Dicky, depending how much the garage charge you for diagnostics and how long you intend keeping the car, it could be worth investing in vagcom. Even if you don't already have a laptop you could probaby pick one up fairly cheaply secondhand.

 

It's quite possible that some wiring was damaged when the downpipe was replaced (though you'd probably struggle to prove that -though it may help if you've got diagnostic results for just before and after the downpipe work).

 

Not that it helps, but you're not alone in having problems like this with no obvious solution - I've sufferred the same sort of thing (see here). If you resolve all the problems listed in the diagnostics, but it's still no better then I would suggest you do try a replacement MAF then (preferably a known good one from somewhere).

 

Does the car smoke at all? The only other thought I had for mine, was that because the head needed rebuilding and it was burning oil sometimes then perhaps that affected the lambda reading. So I basically gave up trying to fix mine until I had the head sorted (though it's now way beyond that. :( )

[Dicky 0]

tonytiger,

 

the garage aren't charging me for diagnostics - they're a good bunch of guys.

 

The car doesn't generally smoke. It has done it 2 or 3 times when coming on the throttle after a long period on the over-run (probably worn valve oil seals?) - even then it was only a brief puff of smoke. I think (hope) the head is in good shape.

 

I've kind of got stuck on the thought that maybe there is a wiring issue or that the overfuelling caused by the cracked exhaust downpipe has somehow damaged the lambda probe.

 

When I had this problem before and the probe was replaced the car was running like a dream.

[martyjmcfly 0]

Replace the ISV - if your car has the original one in its goning to be dog tired and won't cathch the revs in time. I had this problem, particulary this summer whilst on long dual carridge way stretches, coming up to roundabouts and dipping the clutch and it stalls witht the red lights flashing.

 

A new ISV and all is fine. Oh and i removed the sound damper as suggested by Mr haywire and The Phirm which may have also helped.

[Dicky 0]

Hi Folks,

 

I thought I'd post an update. I had a new Lambda probe fitted yesterday and all seems well so far: no cutting out; no fruity smells and mpg up from 18 to 32 on a steady run. 8)

 

Fingers crossed she's sorted now.

 

In summary (and in order of completion):

1. fitted new Lambda probe. [faulty]

2. cleaned ISV.

3. replaced inlet and exhaust manifold gaskets. [probably not necessary]

4. replaced ISV. [probably not necessary]

5. replaced cracked exhaust downpipe. [definitely needed]

6. replaced Lambda probe (s/c to earth). [possibly killed by overfuelling as a result of the cracked downpipe]

 

I think all the problems I had were a direct result of the cracked downpipe - just goes to show that you shouldn't get too hung up on blaming an obvious component.

 

Yesterday was the first time in 6 months she was a pleasure to drive - reminded me of the good old days! :luvlove:

 

I'll report back in a week or so.