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Fuel pressure

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Ynysmon View Drop Down
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    Posted: 02 Jan 20 at 11:04
Hi, I’m new to the group and I’m
Hopeful someone can help me with a problem that’s beaten two mechanics so far!

I purchased a 2012 t28 102TDi swb van back in June. It had just under 100000 miles on the clock. The van soon went into limp mode and gave a fault code of low fuel pressure. I changed the filter etc but still the same. The van starts first time but doesn’t sound great with a hunting noise present and as soon as it hits around 30,000 revs it goes into limp again, we noticed that once the van had started if I unplugged the ecu connection off the fuel rail the engine tone changed and the engine sounded better. Soon as you try to move with it unplugged it went straight into limp mode again. 
Since then I’ve had the high pressure fuel pump checked ok, the ecu checked ok, two injectors changed, wiring harness checked fuel regulator changed and still have this fault. If anyone could
Help in anyway it would be more than appreciated as I’m really at my wits end
Thank you in advance

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Charlie Dog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jan 20 at 11:35
Has anyone measured 
the pressure in the fuel rail yet?

Plenty of kits on eBay
if you wish to measure
the actual fuel pressure
in your injector rail.

Fuel Rail Pressure Test with VCDS by Ross-Tech

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Ynysmon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ynysmon Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 20 at 23:21
Hi Charlie,

    I asked the mechanic had he checked this and he has. It’s showing fine on the manual gauge. He took the fuel rail off over the weekend and cleaned it and flushed it through. The engine does seem to tick over a little better without hunting not as evident but soon as you drive off and the revs increase it’s back into limp modeAngry
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Charlie Dog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 20 at 08:27
I think you need to find a way
to measure fuel pressure
in the rail while you are driving.

It's possible your pump
can't keep up 
with higher fuel needs
at higher loads.

It's possible your filter
can't keep up 
with higher fuel needs
at higher loads.

It's possible your fuel line
can't keep up 
with higher fuel needs
at higher loads.

I daresay there are other options too.
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Ynysmon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ynysmon Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 20 at 08:40
Thanks for your reply. I’ve had the hp pump tested and the in tank pump it’s come back fine, I’ve also replaced the following
Fuel regulator 
2 injectors
Fuel filter
A regulator on the hp pump

Had the ecu checked, all ok

I’ve thrown a lot of money at it now so I’m at the stage of no return 🤦🏻‍♂️ So have to keep ploughing money into it and get it sorted.

I’m getting another auto elec to look at it next week as I fb the pressure isn’t fluctuating we’re thinking it’s maybe a wiring issue??
Have heard that a bad earth under the seat can cause all sorts of problems but not sure it would cause this.

Thanks again for taking time to reply and I’m hoping someone will see this that can point me in a new direction  to get it sorted
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Charlie Dog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jan 20 at 09:19
Were the pressure tests
done under load?

You go into limp mode under load
so it's likely the load causes the problem.

An ammeter in your pump circuit
that you can read in the cab
would indicate an electrical problem
is one exists in that circuit.

You can get easy access 
to the fuel pump circuit
at the fuel pump fuse / relay.

Aimless poking about with electrics
can cause more problems than it solves.

You may be able to find a faulty connection
with a sensitive infra red thermometer.



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Ynysmon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ynysmon Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 20 at 17:44
had the van back today and drove it fine until the revs picked up again. After what you’ve advised I checked and the van won’t rev pasT3,000 when stationary and out of gear. 
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Charlie Dog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 20 at 18:15
If you wish to get any further yourself Ynysmon
I think you need to invest in some software
that will find out what you ECUs have got to say.

And 

Seem to be popular.
As far as I know the software is free.
You have to buy the kit to run it though.

There are rip-off kits,
which may or may not do the business.

Gossip and rumour reckon rip offs 
can damage your van's health.

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Ynysmon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ynysmon Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 20 at 18:43
I’ve had the ecu etc checked too🤦🏻‍♂️ The only fault we get is the low fuel pressure. Both mechanics have had it on their software and it tells them the same. It’s got everyone stumped at the moment 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 20 at 19:02
Some software, records what's happening as you drive.

I expect both of those do.
Probably best to ask first.

Perhaps someone on this forum
has the software 
and is prepared to help
if you travel to them.

You could also have you ECU 
examined and repaired is necessary.

If you contact Honest John 
He may recommend someone VAG specific
honestadvice@telegraph.co.uk

He recommends a few ECU specialists here: -

There no guarantee 
that it's the right place to look I'm afraid :-(
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Ynysmon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ynysmon Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 20 at 19:05
thanks for the assistance Charlie. I’ll give him a try
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 20 at 19:16
Good luck :o)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 20 at 09:59
Any joy yet Ynysmon?
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Ynysmon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ynysmon Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 20 at 11:57
noAngry it’s now with another auto electrician, who thinks it’s a ‘ghost Code and it might not be a fuel pressure issue?
I drove it the other day a fair distance but kept it under 30,000 revs and it was drivable. I did notice on some occasions whilst stationary it wouldn’t rev pasT3,000 revs out of gear!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 20 at 12:30
"Ghost code" is that a variation on "GOK?"


Must be costing you a fortune :-(

How about asking this fella?
honestadvice@telegraph.co.uk
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Ynysmon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ynysmon Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 20 at 12:45
I hope not🤞 Its a ******* nightmare though. It’s nearly beaten us at the moment. Not sure where to go if this ends up at a dead end again
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Charlie Dog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 20 at 12:59
How about asking this fella?
honestadvice@telegraph.co.uk

I've had a few chats with him,
I reckon he knows his stuff
despite that we don't always agree.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 20 at 13:38
I don't really know a lot about the common rail T5's but the exact code you got for 'Low Fuel Pressure' might give some better clues.  Have you checked the low pressure pump in the tank?  The high pressure pump expects fuel to be supplied at the correct pressure.  If you can, try and find out what the exact code was and have a read of this in the mean time. http://wiki.ross-tech.com/wiki/index.php/16471/P0087/000135

Edit- 'Ghost code'  I really doubt if it some kind of spurious code if it won't clear given your symptoms.  


Edited by T5 TDI - 20 Jan 20 at 13:52
2004 2.5 174
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 20 at 09:55
Originally posted by Ynysmon Ynysmon wrote:

noAngry it’s now with another auto electrician, who thinks it’s a ‘ghost Code and it might not be a fuel pressure issue?
I drove it the other day a fair distance but kept it under 3,000 revs and it was drivable. I did notice on some occasions whilst stationary it wouldn’t rev past 3,000 revs out of gear!

From my end of the scope,
if it both
revs to 3k under load
and then cops out
and
revs to 3k not load
and then cops out
then it's more likely
to be summat limiting revs.

Anyone know what could limit revs please?
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fenwick458 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fenwick458 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 20 at 23:07
I have just had what sounds like the same problem. was driving it for a year with it going into limp mode above 3000rpm, I was convinced it just needed calibrated after I had changed the pressure reg
turns out the pressure reg was faulty. it cured the initial problem (rough idle) but would not rev above 3000rpm.
I got the 1st one from ebay for £92, it said it was a bosch and it looked real and came i a bosch box...but who knows??
the second one was £310 plus VAT I think from TPS
My advice would be take it to a VW specialist who has pressure regs to use for testing in the workshop, get them to try it with a new one and see if the fault remains.
I have also heard other reports of these cheap ones being no good, not just mine

also, when I was faultfinding on mine, I seem to remember trying to rev it up to 3000rpm whilst stationary to see if it went into limp mode, and mine didn't rev that high in neutral, it hit a limiter that was way lower. could be a software limiter, it knows the van isn't moving so limits the revs...?

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