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Subject Topic: 2.0 JTS Fuel Problem Post ReplyPost New Topic
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Chris155
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Posted: 06 November 2008 at 12:57 | IP Logged Quote Chris155

2.0 JTS. Mk 2 facelift on a 53 plate, the odo says its done 53k miles but the management thinks its done 80k….Bought from an auction as a runner.

Unfortunately, it isn’t. It’ll start, idle and even rev cleanly, but not for long. It’ll suddenly loose all will to run and splutter to a stop. From cold, best case scenario for this to happen is around 5 minutes.

A friend, Mark, has been given the task of finding the problem.

Mark’s diagnostic kit has identified the problem as low fuel pressure. JTS’s are direct injection. Fuel is pumped from the fuel tank by an Electric Pump at 5.5bar to a high pressure pump that’s driven off the exhaust camshaft. The high pressure (HP) pump then ups the pressure to between 50 and 120 bar depending on engine load and speed.

The pressure isn’t controlled by the pump. There is a pressure sensor and a solenoid that opens and closes a regulator in the HP fuel rail. Excess pressure/fuel is dumped back into the low pressure feed from the electric pump in the tank.

Essentially, the electric pump provides a large volume of fuel under modest pressure. The HP pump is like a pressure washer. It doesn’t increase the volume of fuel going in, in fact the small bore pipes on the HP side limit volume, it just ups the pressure. Its like the difference between running a pressure washer with the end of the lance on (high velocity, will strip paint) and with it off (limp wristed, nothing for the pressure to act against….)

The engine management has set values for pressure that it aims to meet by opening and closeing the fuel pressure regulator. We know this because the diag kit mark has shows the pressure the management is trying to achieve and also has a realtime readout of the actual pressure.

So if you start the engine, everything is fine. Good fuel pressure for a minute or two - At idle it should be around 50bar.

Then over the space of 10seconds or so the pressure drops sharply to 5.5bar and the engine dies.

So far, this is what has been replaced:

Fuel pressure regulator on the HP side
Fuel pressure sender
Electric pump in the fuel tank (LP side)

That lot, by all accounts wasn’t cheap and in the face of mounting costs – parts as well as labour, the car’s owner will not spend any more money on it without knowing it will cure it. Mark is already out of pocket because he’s has to pay for the regulator and he’s spent hours, unpaid, trying to find the problem. I think because its become a challenge, he refuses to give up.

The regulator solenoid acts like a switch, its either open or shut with no leeway in between. Last night we hooked up a switchable 12v feed to it and stated the engine. As you’d expect when it was shut, FP would climb and when it was open FP would drop.

But here’s the weird thing. Even with the regulator wide open and FP down to an indicated 5.5bar, the engine would still idle perfectly normally apparently running on pressure provided solely by the electric pump in tank.

And when it did decide to play games, we tried holding the regulator shut but FP still dropped and the engine died.

So where the hell is the fuel pressure going?!!! There are no obvious leaks on the HP side. It happens more readily when the engine is warm. The plugs are black as the ace of spades but that could be attributed to the engine only being able to run when its cold so it will be being over fueled.

Grasping at straws, on the basis there could be crud in the system between the HP pump and the regulator, I suggested that we take the regulator out and turn it over.

Turning the engine over resulted in fuel going everywhere, obviously, the in tank pump saw to that. But the hole in which the regulator sits had air bubbling out of it for 10minutes or so after we had turned the engine off…. Is this a red herring or is there an air leak?


Any Ideas?
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TazzyK
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Posted: 06 November 2008 at 14:32 | IP Logged Quote TazzyK

No idea's on any of that apart from the odo - they were replaced under warranty as they stopped reading. Same on my bro's car (it's documented) - AlfaDiag reads it in KM and that is close to the Miles equivalent I think

Edited by TazzyK on 06 November 2008 at 14:34


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tomand
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Posted: 06 November 2008 at 14:47 | IP Logged Quote tomand

Do you check a fuel filter

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Chris155
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Posted: 06 November 2008 at 14:49 | IP Logged Quote Chris155

TazzyK wrote:
No idea's on any of that apart from the odo - they were replaced under warranty as they stopped reading. Same on my bro's car (it's documented) - AlfaDiag reads it in KM and that is close to the Miles equivalent I think


80k miles - converted that.

Interesting info about the speedo though.
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Chris155
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Posted: 06 November 2008 at 14:50 | IP Logged Quote Chris155

tomand wrote:
Do you check a fuel filter


No, not yet. Can't see it being the problem as it will hold 5.5bar.
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michaeld
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Posted: 06 November 2008 at 15:01 | IP Logged Quote michaeld

50 bar for fuel pressure seems high but not for a JTS.

If you are forcing the regulator to stay shut but the pressure is dropping then that would sound like a problem with the regulator. Or there's a restriction on the feed side so that when the engine draws fuel the pressure drops (fuel filter or fuel lines or pump blocked)........sounds like you are getting the pressure ok but not the flow.


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Black Beauty
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Posted: 06 November 2008 at 15:08 | IP Logged Quote Black Beauty

maybe an injector stuck open & therefore thats why it losses pressure?
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Posted: 06 November 2008 at 15:39 | IP Logged Quote Black Beauty

obivious question:

has this car been on a diagnostic machine yet?
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Alfatifosi
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Posted: 06 November 2008 at 16:16 | IP Logged Quote Alfatifosi

Chris155 wrote:

Mark’s diagnostic kit has identified the problem as low fuel pressure.


I'm guessing so BB
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Chris155
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Posted: 06 November 2008 at 16:40 | IP Logged Quote Chris155

Black Beauty wrote:
maybe an injector stuck open & therefore thats why it losses pressure?


If that was the case I'd expect it to idle unevenly.... and it doesan't.
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Black Beauty
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Posted: 06 November 2008 at 16:46 | IP Logged Quote Black Beauty

tiz very confusing indeed.
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selespeedy
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Posted: 06 November 2008 at 17:29 | IP Logged Quote selespeedy

I might be talking out of my arse here, but i guess it sounds a lot like perished/split in tank fuel hoses...
Worth checking.
Check the voltage at the in-tank fuel pump wires while you're at it...

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