Best tool to check the Fuel Pressure on ZT 1.8Ts. - Page 2

Lovel · 10th September 2017, 20:12

Quote:

Originally Posted by SD1too

Gary; excellent research and evidence, thank you.

I did not expect 'regulated' fuel pressure to vary with engine speed. Why should it?

But then, does it? 4.5 at full revs then 4.3 at idle? It would seem that pressure readings at the schrader valve are anything but reliable data for fault diagnosis.

Simon

There is a regulator on the end of the inlet manifold which receives vacuum from the inlet manifold, hence as throttle opened or closed the fuel pressure is regulated to an extent in addition to the 4.5 Bar regulator built into the fuel pump itself.

Perhaps a simple fuel pressure reading static is not that accurate, and you really have to run the vehicle a decent distance to obtain a reliable reading however if you have low fuel pressure such as FOC, blocked filter or inferior pump, or leak in high pressure fuel line inside tank it should manifest itself with a particular low reading perhaps in realms of 1 to 2 Bar or less?

Lovel · 10th September 2017, 20:15

The fuel pump priming and cutting out after a few seconds is not because there is pressure present in the fuel line. The ECU sends voltage for that few seconds or so to fill/pressure up the system, however if you have a crappy pump or blocked filter or FOC it could be 1 Bar or 10 Bar and the pump will still receive a voltage to pump until the ECU switches it of again.

Lovel · 10th September 2017, 20:47

I spent a long time trying to track down similar circumstances on a horrid little 205gti, it turned out that there was a hairline split in the flexible pipe on the upstream side of the fuel pump within the fuel tank and all it would do was to recirculate back into the tank. I could get the car started but it would just cut out, we may have had about 0.5 Bar pressure at the manifold end or so with the split pipe but it was not enough to get the engine going.

Perhaps someone had been in the tank area before you, knowing that the pipework on these saddle tanks are not that simple, the pipework shrink and harden over time especially since they are located inside the tank, and couple this with a pair of heavy hands and little patience can often be the undoing of things.

SD1too · 10th September 2017, 21:56

Quote:

Originally Posted by Lovel

There is a regulator on the end of the inlet manifold which receives vacuum from the inlet manifold ...

Ah yes, the device which you correctly referred to as the damper!

From all that you've found out Gary, what is your conclusion about pressure readings at the schrader valve? Does less than 4.45 bar (1.8T) at idle definitely mean there's a fault?

Simon

Lovel · 14th September 2017, 11:04

Quote:

Originally Posted by SD1too

Ah yes, the device which you correctly referred to as the damper!

From all that you've found out Gary, what is your conclusion about pressure readings at the schrader valve? Does less than 4.45 bar (1.8T) at idle definitely mean there's a fault?

Simon

Well what can I deduce from the testing carried out?

-Perhaps @<3 Bar the owner would experience running problems.

-It would also appear that the pressure readings improve over time, ie take the car for a drive first then take the readings.

-For a better understanding of pressure readings hook up the pressure gauge for a dynamic reading while test driving if safe to do so.

-Would be interesting to obtain owners pressure readings from vehicles that have had the filter housing backing off and after they have twisted it back on with the dry and tiny cross section o-ring potentially extruding from the housing due to lack-of lubricant upon assembly, but then again my thread from October 2013 investigating fuel pump alternatives showed pressure readings of 2.8 Bar with a partially backed off filter housing.

Looks like the pump itself also fits the complete 75/ZT petrol range. It is perhaps the 4.55 Bar pressure regulator (1.8T) on the filter housing that is changed dependant upon the type of engine installed. Note the same VDO pump number is also used in Mini models R50 & R53 so perhaps another good source from the scrapyard that we could use.

https://www.merlinmotorsport.co.uk/s...pumps/rover/75

http://www.ebay.co.uk/itm/Fuel-Pump-...QAAOSwInVXHL4n

https://the75andztclub.co.uk/forum/s...+pump+pressure

10th September 2017, 20:15	#12
Lovel I really should get out more....... P6B, L550, Imp, F56, Commando Join Date: Nov 2006 Location: Aberdeenshire Posts: 2,886 Thanks: 352 Thanked 677 Times in 440 Posts	The fuel pump priming and cutting out after a few seconds is not because there is pressure present in the fuel line. The ECU sends voltage for that few seconds or so to fill/pressure up the system, however if you have a crappy pump or blocked filter or FOC it could be 1 Bar or 10 Bar and the pump will still receive a voltage to pump until the ECU switches it of again. Last edited by Lovel; 10th September 2017 at 20:35..

10th September 2017, 20:47	#13
Lovel I really should get out more....... P6B, L550, Imp, F56, Commando Join Date: Nov 2006 Location: Aberdeenshire Posts: 2,886 Thanks: 352 Thanked 677 Times in 440 Posts	I spent a long time trying to track down similar circumstances on a horrid little 205gti, it turned out that there was a hairline split in the flexible pipe on the upstream side of the fuel pump within the fuel tank and all it would do was to recirculate back into the tank. I could get the car started but it would just cut out, we may have had about 0.5 Bar pressure at the manifold end or so with the split pipe but it was not enough to get the engine going. Perhaps someone had been in the tank area before you, knowing that the pipework on these saddle tanks are not that simple, the pipework shrink and harden over time especially since they are located inside the tank, and couple this with a pair of heavy hands and little patience can often be the undoing of things. Last edited by Lovel; 10th September 2017 at 20:51..