1.9 JTDm GT - Delayed Power Delivery (and High Pressure Fuel System Issues) - Alfa Romeo Forum
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(Post Link) post #1 of 7 Old 19-08-15 Thread Starter
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1.9 JTDm GT - Delayed Power Delivery (and High Pressure Fuel System Issues)

Hi all

I'll apologise in advance for the long post...but really hoping someone can shed some light or make some suggestions here...it's driving me insane

I've been having an issue lately with delayed/hesitant power delivery. I was going to post about it but then I had a fuel leak on my high pressure fuel pipe (pump to rail), which is now sorted.

I'm not sure if the two are linked, and was wondering if anyone has experienced any similar symptoms.

Sequence of events:

- Started developing a noticeable delay in power delivery when flooring accelerator; previously pick up was nice and responsive, even below turbo rev range, then when turbo kicked in it was like a rocket

- Also a bit hesitant when accelerating moderately through the revs; noticed between 2,000 and 3,000 I'd say

- Before I could get across to see the Autolusso lads I broke down with the high pressure fuel pipe leak (http://www.alfaowner.com/Forum/alfa-...esel-pipe.html (Leaking High Pressure Diesel Pipe)) this turned out to be exactly as R.T. suggested, and was a cracked pipe at the very end of the pipe (fuel pump end)

- Replaced the pipe, changed the fuel filter, and flushed out the rail and injector pipes with diesel to get any crap out the system; there were some little particles, hard to say what it was; I didn't fancy removing the fuel pump and checking it/flushing it out, beyond my capabilities; R.T. did suggest it could be due to the fuel pump valve being clogged up and not operating correctly (I still don't know if this is the case or not) sounds plausible

So that's where I am at the moment, and I'm still having exactly the same symptoms of delayed acceleration. So for the time being I'm pretty reluctant to accelerate beyond 2,000rpm as I'm concerned I might cause another high pressure spike and burst another high pressure fuel pipe, so driving ridiculously cautiously

I spoke to Dan at Autolusso (I'm going to see him on Saturday...if I make it over there!) and he was saying that there was someone had recently went through 3 or 4 of the high pressure fuel pipes that had failed on mine, but I'm not sure what the cause of that has been. Maybe it was someone off the forum? Pipe up if it was you (excuse the pun)

So two issues, but maybe linked?

I don't know how the high pressure fuel pump works. I understand there's a valve to regulate the pressure which I guess is based on the pressure measured in the common rail as that's where the pressure sensor is? If anyone can go into detail that would be great.

Could my symptoms be due to a dodgy high pressure fuel pump? Floor it, sticky valve, not enough pressure in the rail so poor injection, poor acceleration, valve starts to operate, pressure builds, good injection, acceleration picks up and gets going. But now and again the ECU overcompensates for the low pressure, then BANG massive spike of high pressure, high pressure fuel pipe cracks and leaks...OR, is that not possible?

If anyone has any thoughts or any experience of the same problems, any help would be much appreciated
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its good logic, but I don't think the ecu would allow the fuel pump to compensate to the level required to banjax a healthy fuel line..the lack of acceleration sounds like a turbo issue to me, one of the usual suspects, vacuum hose being the no1 suspect.

any smoke on acceleration? does the acceleration kick in at about 2500 instead of 1800-2000ish

be better and cheaper for you if it is the vacuum hose or solenoid isnt actuating fully or early enough.
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Yea I guess it's more clever than I'm giving it credit for, the two issues probably aren't related but I don't usually believe in coincidences

Both hoses have already been replaced with the thick silicone type, and after turbo failure in the last couple of months I've got a hybrid in there now (old casing, hybrid internals), so I have got a bit of smoke due to the recent turbo failure but nothing drastic at all and that hasn't changed or got any worse since I've been having the issues...the acceleration point in terms of revs isn't any different, just time delayed, so floor it, picks up very, very slowly...a second or so later, it picks up as it used to and goes, definitely pre 2,500

I guess the reason I link the two is that when the fuel pipe cracked it was just as the delayed acceleration kicked in and started to go.

Which solenoid would that be? Sorry, bit of a novice here, learning as things break...
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The solenoid on the vac line from the turbo, its a little bit switch unit that attaches to the back of the airbox on the GT.. Bit of a PITA to get to as well as the car needs jacking up, undertray removing, and lower boost hose has to come off..

Considering its a 5 min job to inspect/clean/replace, taking 20 mins at each end to get to it makes it a faff!
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Ahh ok, thanks for that

I'll reluctantly keep driving it, like an OAP, and hope it's something(s) that's an easy fix on Saturday.

The driving equivalent of walking on egg shells...it's a horrible feeling
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Originally Posted by DJDan1986 View Post
I understand there's a valve to regulate the pressure which I guess is based on the pressure measured in the common rail as that's where the pressure sensor is? If anyone can go into detail that would be great.
If you have the same pump as my 2004 SW (Bosch CP 1), the pump is a three cylinder piston pump which delivers fuel at a rate proportional to engine speed. Excess fuel is spilled back to the return line by the pressure regulator. Just from studying drawings of it: fuel flows down a small channel, a ball is forced onto the end of the channel firstly by a spring, and also by an electromagnet, controlled by the ecu, which uses the pressure sensor for its feedback signal, as you say. It's easy to imagine the channel getting clogged with dirt particles, as the opening of the ball valve must be tiny, given the pressure it works at. (In the later CP3 pump, the regulator controls the flow INTO the pump, but it's probably susceptible to contamination too.)

The late acceleration does sound like turbo problems, but the hesitation could be due to fuel pressure fluctuations. Perhaps you have both?

If you are handy with a multimeter you could have a go at checking for pressure fluctuations by monitoring the sensor output voltage as shown below. Some meters have 'peak hold' settings which would catch any nasty pressure excursions. I don't know the sensor calibration, but mine gives the following voltages:
Ignition on: 0.5V
Cold idle: 1.5V
2000rpm, no load: 1.95V.
These voltages were nice and steady, so long as the revs were held steady (the pressure is adjusted for every operating condition).

The centre pin is the signal, you can use the engine as the 0V connection (but turn heavy electrical loads off), so you only need one thin wire. This should be pushed into the receptacle before mating the connector. Take care to avoid shorting the pins together. (I'm assuming you don't have MES, which would probably monitor the pressure more easily!)
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That lad that was having the same problem with the pump to rail pipe, yeah that was me

My GT is not modified in any way apart from a Cloverleaf turbo which i had done over Christmas as the original seized. What I believe to be the original pump to rail pipe was on for 8 years or so and around 120k miles. Bought a replacement from the dealer (£56!) and that lasted about 6wk/1000 miles. The end completely sheared off on the pump side. Took it back, got a replacement and that lasted about 600 miles/4 weeks - Hairline crack again on the pump side of the pipe. Got a brand new one special order direct from the factory, that's been on for around 2 months now and probably covered 1200 miles or so. Touch wood, this one has been fine up to now but I have not exactly been testing the high pressure capability.

I initially thought it could have been a problem with the pump/pressure regulator or something. As the original had been on for so long, both time wise and mileage, then maybe something mechanical was failing as well. However, as the current pipe is working alright I'm more inclined to put it down to a dodgy batch of pipes that ARUK had in stock. Touch wood as i said

One other problem i had develop this morning, the 4 individual front pipes from rail to injectors are playing up now so I'm taking the hit on those (£170) and replacing them all at once as chances are if one has failed, the others surely won't be too far behind

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