Hissing EGR valve and related TPS / fuel pump question
Posted: Tue Feb 16, 2010 8:29 pm
I finally traced down an annoying hissing noise on startup with my L400.
It only occurred when the beast was starting from dead cold (and disappeared after a few seconds), and intermittently under load. The latter accompanied a bit of a lack-of-power at speed and a recent fuel economy drop from 12.5L/100k to around 15L/100k.
I had previously cleaned out the over-pressure poppet valve on the rear of my intake manifold (see earlier post) and my boost gauge is showing 11 psi, so not the culprit.
So I removed my EGR valve, and lo and behold it was nicely coked up and failing to seal properly. Exhaust gas was leaking by the valve and around the shaft of the valve itself (the outside of the valve shaft was getting black from sooty blow-by).
So one fabricated blanking plate on the intake manifold later, and although the hiss remains, she pulls stronger, and is less rattly on cold startup.
One other thing I discovered on my research on the UK website is that the ECU uses the throttle position sensor (TPS) readback to determine when to close the EGR valve. Having earlier adjusted my TPS to make the tranny shift earlier and smoother, I find out that this same operation causes the EGR to close at much higher RPMs, robbing power at moderate engine speed.
So if anyone out there has recently adjusted their TPS down to around 0.8V like I did, the UK site seems to recommend blanking off the EGR valve too.
Finally, the last thing to fiddle with for me is the fuel pump. I understand that the delivery setting is a relatively simple mechanical system with two adjustment screws; one to set max fuel flow, and the other to adjust the offset based on turbo outlet pressure.
I have no idea how to properly calibrate these settings. Having found out that my TPS adjustment has messed up my EGR, now I want to make sure that my fuel pump is set correctly.
Anybody calibrated one of these before with sage advice to give? Thanks.
It only occurred when the beast was starting from dead cold (and disappeared after a few seconds), and intermittently under load. The latter accompanied a bit of a lack-of-power at speed and a recent fuel economy drop from 12.5L/100k to around 15L/100k.
I had previously cleaned out the over-pressure poppet valve on the rear of my intake manifold (see earlier post) and my boost gauge is showing 11 psi, so not the culprit.
So I removed my EGR valve, and lo and behold it was nicely coked up and failing to seal properly. Exhaust gas was leaking by the valve and around the shaft of the valve itself (the outside of the valve shaft was getting black from sooty blow-by).
So one fabricated blanking plate on the intake manifold later, and although the hiss remains, she pulls stronger, and is less rattly on cold startup.
One other thing I discovered on my research on the UK website is that the ECU uses the throttle position sensor (TPS) readback to determine when to close the EGR valve. Having earlier adjusted my TPS to make the tranny shift earlier and smoother, I find out that this same operation causes the EGR to close at much higher RPMs, robbing power at moderate engine speed.
So if anyone out there has recently adjusted their TPS down to around 0.8V like I did, the UK site seems to recommend blanking off the EGR valve too.
Finally, the last thing to fiddle with for me is the fuel pump. I understand that the delivery setting is a relatively simple mechanical system with two adjustment screws; one to set max fuel flow, and the other to adjust the offset based on turbo outlet pressure.
I have no idea how to properly calibrate these settings. Having found out that my TPS adjustment has messed up my EGR, now I want to make sure that my fuel pump is set correctly.
Anybody calibrated one of these before with sage advice to give? Thanks.
