Gti6 Stalling When Coming To A Stop (Still!)

[petert 600]

That's because an alternator doesn't do anything much until it's rotating at approx 1400 rpm ( alternator shaft). You probably have a pulley step up ratio of approx. 2.3:1, which means your alternator isn't doing anything meaningful until approx. 600 rpm (crankshaft). Turning off circuits is just removing current loads from your battery. Below is typical RPM (shaft) vrs Amps diagram.

 

I don't think that's your problem.

 

Did you try disconnecting the vacuum from the FPR like I said?

Edited May 15, 2016 by petert

[2052006 10]

That's because an alternator doesn't do anything much until it's rotating at approx 1400 rpm ( alternator shaft). You probably have a pulley step up ratio of approx. 2.3:1, which means your alternator isn't doing anything meaningful until approx. 600 rpm (crankshaft). Turning off circuits is just removing current loads from your battery. Below is typical RPM (shaft) vrs Amps diagram.

 

I don't think that's your problem.

 

Did you try disconnecting the vacuum from the FPR like I said?

 

So I tried disconnecting the vacuum from the FPR as Peter suggested and then went for a test drive. I used the same roads/hills as I did last weekend to test it, and with lots of electrics on to replicate the same conditions, and I COULD NOT get it to stall. So, new FPR?? Could someone please explain how exactly an FPR works and why it's needed?

[allye 530 3 Cars]

Well, a fuel pressure regulator, regulates the pressure of the fuel!

 

Quite possible yours is failing internally or the o ring is damaged? Have you ever removed it from the rail?

 

All this trouble and it's the bloody FPR! Fuel pump?

[petert 600]

The FPR maintains 3 bar relative to atmosphere. Thus if there is 0.6 of vacuum at idle, fuel pressure would be 2.4 Bar. At wide open throttle, when vacuum is zero, the fuel pressure will be 3 bar. Disconnecting the vacuum signal gives you 3 bar at idle, slightly richening the idle mixture. Your problem may well be dirty injectors. You really need to hook up a fuel pressure gauge to make sure you have 3 Bar. If so, then dirty injectors. If not, then faulty fuel pump.

[2052006 10]

So Peter, are you saying it can't be the FPR that's at fault, or is that still a possibility? I've taken the FPR off. It is a Weber one and says the following on the side: RPM 40; 300 KPA; 3037/01. Whatever that all means, I presume it is the correct one for a gti6 engine? I certainly have never changed it, but doesn't mean previous owners didn't.

[2052006 10]

Can someone point me in the right direction of the correct type of pressure gauge I'll need? How would it connect etc?

[petert 600]

http://www.ebay.co.uk/itm/Fuel-Pressure-Gauge-Kit-With-Inline-Adaptor-8mm-Hose-Tail-Connection-Pump-Rail-/191877985154?hash=item2cacd1b382:g:TOoAAOSwp5JWVF~4

 

You should also test the flow rate. This will reveal a dud pump or a broken internal hose in the tank. Take a hose off the FPR outlet and feed into a bucket etc. You should get >500mL in 15 sec.

[2052006 10]

Cheers. Cheap enough, I will order one and see what's what. Thanks for the help.

[2052006 10]

Right, with a pressure gauge attached I get the following:

 

1. Ignition to ON (fuel pump primes, but engine not started) - 3 bar, dropping to 2.8 once relay clicks off and stops priming. However, on a few occasions, once the fuel pump stopped priming, the pressure completely dropped away to 1 bar or even nothing - ??? I couldn't get it to repeat this after the first few times it did this though...

 

2. Engine running at idle, FPR vacuum connected - 2.4 bar

 

3. Engine running at idle, FPR disconnected - 3 bar

 

4. Engine running, FPR vacuum connected and increasing throttle - initially rise to 3 bar, or almost 3 bar, then would drop to 2.2, before stabilising at 2.4. Every time I gave it some throttle, it would rise to 3ish, but then drop back down (even with constant throttle applied)

 

5. As per number 4 (throttle applied), but with FPR disconnected - constant 3 bar

 

Thoughts?!

[petert 600]

It means the FPR is working perfectly. Clean the injectors next.

[2052006 10]

OK, will send injectors off. But what about the pressure bleeding away, as described in point 1, it was rather strange? I'm not sure, but I think I've read that the fuel pump has some sort of non-return valve? I was wondering if this pointed towards a duff valve and somehow this was, on occasion, creating a loss of pressure, leading to my problem? (P.s. Not had a chance to test flow rate of pump yet, ran out of time)

[petert 600]

If it's holding 2.4-3 Bar while it's running, then all is fine. I wouldn't worry about bleed off when you turn it off, if volume and pressure is correct. If the non-return valve is perfect, it will hold 3 Bar for ever, once turned off. It just makes it easier/quicker to start.

[2052006 10]

And so it continues:

 

Fitted my newly serviced/cleaned injectors, went for a test drive with high hopes, nope, exactly the same as before

 

Remembered I never got round to testing the flow rate of the fuel, as suggested by petert earlier, so returned home and tested that. Now, if as he suggests it should be more than 500ml per 15 secs, I'm getting nowhere near that.

 

The first 500ml gets close to that amount/time (i.e. when engine is first switched on), but then it slows considerably - takes 2 or even 3 times the time for the next 500ml and so on.

 

So - duff pump? Is it meant to be >500ml every 15 seconds, no matter what?

Edited June 2, 2016 by 2052006

[petert 600]

Here's the test info, from the Mi16 manual. I would have thought that poor flow would mean leaning out under load, not at idle. It is worth checking the small hose on the pump is in tact and not leaking internally however. Otherwise I'm stumped.

[2052006 10]

Latest:

 

I changed the fuel pump, but no dice. Still exactly the same symptoms. I was pretty fed up!

 

Today, I changed the FPR, having initially thought it was functioning ok as per previously in this thread. Bingo! No more stalling.

 

However - it would seem I inadvertently ordered a 3.5 rated FPR, instead of the OE 3 bar. A bit of internet research suggests this may be for later Xsaras? Though I'm not sure if this is correct. (Mine is a phase one Xsara engine). I thought I'd give it a go anyway, and it appears to have done the job.

 

But it does beg a couple of questions:

 

1. Is it solving my problem simply because it is a higher pressure rated one. Does this mean it will operate at a higher pressure all of the time i.e. at idle too?

 

2. Is it safe to use a higher rated FPR? Will it have any negative effects?

[Anthony 1,003]

That's a Ph2 Xsara one. Ph1 one should be 3 bar, same as a GTi6.

 

It'll likely overfuel a little when lambda isn't trimming fuel with the higher pressure. That overfuelling will be similar at idle to having the vacuum hose disconnected on your old FPR, which presumably is masking the underlying issue.

[2052006 10]

That's what I feared. I'll have to order the correct one.

 

Any idea why the Phase 2 Xsara used a higher pressure FPR? Did they use different injectors as well or something, I wonder what the reasoning was behind changing things?

[Anthony 1,003]

Yes, different injectors amongst various other changes.

[welshpug 1,666]

different ecu, different injectors, twin lambda sensors, better fuel economy!

[petert 600]

Glad to hear you solved it. My next suggestion was to leave the compensation hose disconnected, which you effectively did by fitting a 3.5Bar reg.!

Edited June 20, 2016 by petert

[2052006 10]

As expected, fitting the correct (brand new) 3 bar FPR, causes the symptoms to return

 

I could of course just drive round with the vacuum disconnected, or with the 3.5 bar one fitted. But as Anthony says - this is just masking the underlying issue. I'm determined to get to the bottom of this.

 

I tested the flow-rate of my new fuel pump today, and it's clearly a lot better than the old pump, and flowing what it should now. But that doesn't appear to have been the problem anyway.

 

Next, I disconnected the lambda - this seemed to help - I couldn't get it to stall, though didn't drive it for very long. But, is disconnecting the lambda, just causing it to run rich, much like disconnecting the FPR vacuum??

[dobboy 231 2 Cars]

Have you checked you don't have any links or bashes to fuel lines? Fairly new filter?

 

Just a thought.

[petert 600]

What cam(s) are in it?

[2052006 10]

Dobboy - All fuel lines (including the hard line underneath) were replaced less than 2 years ago, filter's about 18 months old (Bosch 106 filter). Anyway - there appears to be no problem with fuel flow - it's flowing what Petert posted it should now.

 

Petert - cams are standard (at least I've never changed them). I took the engine out of the Xsara myself, the rest of the car was in a pretty sorry state and completely standard, I doubt it had been fiddled with! The only non-standard parts, engine-wise are lightened flywheel and crank pulley.

 

I ran through (again) unplugging other sensors as well as lambda - TPS (relatively new), VSS (relatively new), carbon canister valve - each in turn. Still stalled with the VSS unplugged. With the others, it was just like disconnecting the lambda - revs seemed to drop a lot slower and never stalled. I'm just presuming this is because it's overfueling with these disconnected, reverting to a "safe" map or something?

 

I do wonder about the alternator or something related to it (like wiring) though. It does only seem to do this when I'm running lots of electrics (nothing out of the ordinary - lights/wipers/stereo/phone plugged in to 12v socket). Next thing, when I get a chance is to get the manifold off, again, and go over wiring/earths. Yet battery is charging fine and I get approx 14.1v at battery when running, and 14.3v at alternator. Don't think there's anything wrong there?