Replacement Fuel pump.

[Steve Webb]

Just double checking, but is the Walbro GSS342 the drop in replacement for the Q4 fuel pump?

Seems to be from some of the old posts on here.

2815

Cheers

[AlfaJack]

It is according to Juan:

http://forum.berlinasportivo.com/archive/index.php/t-1172.html

[Steve Webb]

Cheers Jack,

Just double checking myself.

Steve

[jNk]

It seems to be I've got some issue on high rpm (4.5k+) where the engine starts to stutter so good to know the GSS342 is a straight upgrade.

[Steve Webb]

I'd take a check of your spark plugs\leads as well for a problem like that.

[jNk]

I've bought NGK BPR6EIX (https://www.ngk.com/product.aspx?zpid=9476) spark plugs couple of years ago so I doubt they are causing this issue but my car mechanic friend will check some things on it at the weekend for sure.

His first idea was too lean mixture, hence my thinking of upgrading to Walbro (and maybe some 440-500cc injectors)

[Steve Webb]

Take a check of your plugs, see what colour they are, should give you an idea if you are running lean. I was worried about fuel pressure a while back so fitted a fuel pressure sender and gauge.
How much power roughly is your engine making? I posted up a couple of fuel related calculators recently, looking at the standard Q4 injectors, even at 3 bar, once you start making more than 250 bhp you are going to be running the injectors at very high duty cycles.

Keeps us posted as to what you find out.

[jNk]

My engine is stock so I assume its making the stock-ish power, havent dynoed it yet.

We went out today to check some things and it seems its not a fuel pump or spark plugs or lead issue but a turbo one. Its making the normal boost (0.6-0.7bar) on normal acceleration but when he floored it the boost went up to 1.2+bar and the stutter was ignition/fuel cut, aka overboost protection, until he decreased the acceleration.
Normally the ECU/Turbo allows the overboost until 1.1bar for a short time but mine for some reason does not limit it at the moment.

[Steve Webb]

Sounds like your wastegate might be stuck or the pierburg valve is keeping it closed and allowing too much boost to build up. Should be a (relatively) easy fix though.

Disconnect the electrical connection from the Pierburg valve and you should only see the 0.7 bar boost of the wastegate.

[jNk]

I've tested the turbo with the disconnected pierburg valve and its worked as you said, the boost maxed at ~0.6bar with normal acceleration and even when I floored it.

Btw the disconnected PV hose to the inlet pipe has any other effect than the typical sound during acceleration pedal release ?

[Steve Webb]

Sounds like your Pierburg valve might be faulty, its purpose is to present some of the boost pressure to the rear side of the wastegate, keeping it closed for longer, and letting the engine make the 1.1 overboost pressure.
If the PV lets too much pressure through to the rear of the wastegate then the engine makes too much boost and the ECU steps in to cut ignition to stop damage to the engine.

The valve might just be sticking so you could try cleaning it, not sure if replacements are available, I'd imagine they should be, but you might have to hunt for one. Failing that you could go down the aftermarket boost controller route.

[jNk]

Thank you for the detailed working description, it was more usefull than the q4fuel.pdf's engineer/technical version :thumb::biggrin:

Can I take apart the PV (do I want it?) or just unplug the hoses, remove it from the car and try to clean it with brush and/or high pressure air ?

ps.: This seems to be a off-topic issue now, can we split and make a new one or stay here ?

[Steve Webb]

jNk I've just created a new forum for ECU and electrical issues, when I was moving threads i did notice a couple were pierburg valve related. You might want to check in there first.

Steve