Go Back   The 75 and ZT Owners Club Forums > The 75 and ZT Owners Club Forums > Technical Help Forum
Register FAQ Image Gallery Members List Calendar Mark Forums Read
Notices

Reply
 
Thread Tools Display Modes
Old 21st March 2012, 11:57   #11
HarryM1BYT
This is my second home
 
HarryM1BYT's Avatar
 
75 Contemporary SE Mk II 2004 Man. Sal. CDTi 135ps, FBH on red diesel, WinCE6 DD

Join Date: May 2010
Location: Leeds
Posts: 17,273
Thanks: 2,160
Thanked 2,061 Times in 1,586 Posts
Default

I had always thought that the 1/4 tank failures were due to the high point of the saddle being at, or a little above the 1/4 tank level, but that drawing seems to show the saddle as being very much higher than the 1/4 tank level.

I think I might just start carrying a spare UBP in the boot - good for replacing either a failed UBP and possibly a failed ITP.
__________________
Harry

How To's and items I offer for free, or just to cover the cost of my expenses...

http://www.the75andztclub.co.uk/foru...40#post1764540

Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing.

I've taken a vow of poverty. To annoy me, send money.
HarryM1BYT is offline   Reply With Quote
Old 21st March 2012, 12:14   #12
Mike Noc
This is my second home
 
Mike Noc's Avatar
 
Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4.

Join Date: Jul 2009
Location: Hampshire
Posts: 11,531
Thanks: 3,470
Thanked 3,119 Times in 2,247 Posts
Default

Quote:
Originally Posted by HarryM1BYT View Post
I don't think the ITP pump type would generate anything like 52PSI, so why a pressure regulator there and are you suggesting that the regulator is actually in the tank? If it is indeed there, between ITP and UBP - why there, surely it would have been more sensible to have a regulator after the UBP?
Harry there is another pressure relief valve fitted after the UBP which will bypass fuel back to the inlet side of the UBP in the event of any over pressure between the UBP and HP pump.

Interestingly the ITP has its own pressure relief valve, a ball and spring valve built into its casing. So It is a mystery that the pressure relief valve in the tank is set at 52 psi. I can only think it may be there to vent any excess pressure if there is a fault in the HP pump and the return side.

That doesn't make sense looking at the drawing, but as I mentioned earlier when the fuel is cold and the thermostatic valve is closed it looks like the returning fuel circulates straight back to the UBP not to the tank with the ITP topping up what is lost to the HP pump. So that is effectively a closed circuit with only a restrictor going back to the tank, and it would need a pressure relief valve fitted.

Good idea to carry a spare UBP - I keep my old good one in the boot just in case. No need to worry about the ITP - if it fails just keep the tank over a quarter full and it will run fine.

Mike

Last edited by Mike Noc; 21st March 2012 at 12:35..
Mike Noc is offline   Reply With Quote
Old 21st March 2012, 12:31   #13
T-Cut
This is my second home
 
Rover75 and Mreg Corsa.

Join Date: Nov 2006
Location: Sumweer onat mote o'dust (Sagin)
Posts: 21,751
Thanks: 341
Thanked 3,660 Times in 2,924 Posts
Default

Quote:
Originally Posted by HarryM1BYT View Post
I had always thought that the 1/4 tank failures were due to the high point of the saddle being at, or a little above the 1/4 tank level, but that drawing seems to show the saddle as being very much higher than the 1/4 tank level.
Yes the crest of central divider is more like the 75% full mark.

I think this sheds a little light on the myths about pumps and levels.

TC
T-Cut is offline   Reply With Quote
Old 21st March 2012, 12:38   #14
HarryM1BYT
This is my second home
 
HarryM1BYT's Avatar
 
75 Contemporary SE Mk II 2004 Man. Sal. CDTi 135ps, FBH on red diesel, WinCE6 DD

Join Date: May 2010
Location: Leeds
Posts: 17,273
Thanks: 2,160
Thanked 2,061 Times in 1,586 Posts
Default

Quote:
Originally Posted by T-Cut View Post
Yes the crest of central divider is more like the 75% full mark.

I think this sheds a little light on the myths about pumps and levels.

TC
Myths are understandable with such a complex plumbing system.

Has anyone actually conducted any experiments to see what happens when the power is deliberately removed from the ITP at various tank level?
__________________
Harry

How To's and items I offer for free, or just to cover the cost of my expenses...

http://www.the75andztclub.co.uk/foru...40#post1764540

Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing.

I've taken a vow of poverty. To annoy me, send money.

Last edited by HarryM1BYT; 21st March 2012 at 13:29..
HarryM1BYT is offline   Reply With Quote
Old 21st March 2012, 12:45   #15
Mike Noc
This is my second home
 
Mike Noc's Avatar
 
Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4.

Join Date: Jul 2009
Location: Hampshire
Posts: 11,531
Thanks: 3,470
Thanked 3,119 Times in 2,247 Posts
Default

Quote:
Originally Posted by HarryM1BYT View Post
yths are understandable with such a complex plumbing system.

Has anyone actually conducted any experiments to see what happens when the power is deliberately removed from the ITP at various tank level?
I haven't but I did connect the two pumps on the bench to see if the UBP could suck through a failed ITP and as mentioned found that it will draw fuel until the fuel level drops below the top of the ITP then it just sucks air as the priming valve is open.

Mike
Mike Noc is offline   Reply With Quote
Old 21st March 2012, 12:50   #16
T-Cut
This is my second home
 
Rover75 and Mreg Corsa.

Join Date: Nov 2006
Location: Sumweer onat mote o'dust (Sagin)
Posts: 21,751
Thanks: 341
Thanked 3,660 Times in 2,924 Posts
Default

Quote:
Originally Posted by Mike Noc View Post
I haven't but I did connect the two pumps on the bench to see if the UBP could suck through a failed ITP and as mentioned found that it will draw fuel until the fuel level drops below the top of the ITP then it just sucks air as the priming valve is open.
If it was repeated with the tank, it should work providing the scavenger system (HP backflow) works. This ensures the ITP inlet is always flooded.

TC
T-Cut is offline   Reply With Quote
Old 21st March 2012, 12:57   #17
Mike Noc
This is my second home
 
Mike Noc's Avatar
 
Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4.

Join Date: Jul 2009
Location: Hampshire
Posts: 11,531
Thanks: 3,470
Thanked 3,119 Times in 2,247 Posts
Default

Quote:
Originally Posted by T-Cut View Post
If it was repeated with the tank, it should work providing the scavenger system (HP backflow) works. This ensures the ITP inlet is always flooded.

TC
Yes TC but with a failed ITP the priming valve is open and this sits at the highest point on top of the pump when it is fitted in the tank, so as soon as that level is reached the UBP starts sucking air.

This is what happened when I bench tested it as I only had the inlet to the ITP immersed in the diesel and it wouldn't work until I immersed the whole ITP.

Mike
Mike Noc is offline   Reply With Quote
Old 21st March 2012, 13:09   #18
DerekS
Posted a thing or two
 
Rover 75 Tourer

Join Date: Nov 2006
Location: Malpas
Posts: 1,526
Thanks: 34
Thanked 118 Times in 89 Posts
Default

What a *&&^% complicated system. I suppose thats progress. Oh for those days where you had a rubber diaphragm or bulb to squash to prime the system, as in the 218 with xud peugeot engine !
It looks as though the design was given to a student with orders make it as complex and to use as many funny bits as possible.
Why the need for a saddle tank anyway ? For the V8 propshaft ? If so why not make a special tank for that , instead of a special for everything else ?

And how about a small pipe from one side to the other , outside at a low level ?


But also , full marks to you guys trying to understand how it all works . Thanks.
DerekS is offline   Reply With Quote
Old 21st March 2012, 13:32   #19
HarryM1BYT
This is my second home
 
HarryM1BYT's Avatar
 
75 Contemporary SE Mk II 2004 Man. Sal. CDTi 135ps, FBH on red diesel, WinCE6 DD

Join Date: May 2010
Location: Leeds
Posts: 17,273
Thanks: 2,160
Thanked 2,061 Times in 1,586 Posts
Default

Quote:
Originally Posted by Mike Noc View Post
Yes TC but with a failed ITP the priming valve is open and this sits at the highest point on top of the pump when it is fitted in the tank, so as soon as that level is reached the UBP starts sucking air.

This is what happened when I bench tested it as I only had the inlet to the ITP immersed in the diesel and it wouldn't work until I immersed the whole ITP.

Mike
So it that where the 1/4 tank level problem perhaps starts?
__________________
Harry

How To's and items I offer for free, or just to cover the cost of my expenses...

http://www.the75andztclub.co.uk/foru...40#post1764540

Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing.

I've taken a vow of poverty. To annoy me, send money.
HarryM1BYT is offline   Reply With Quote
Old 21st March 2012, 13:42   #20
Mike Noc
This is my second home
 
Mike Noc's Avatar
 
Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4.

Join Date: Jul 2009
Location: Hampshire
Posts: 11,531
Thanks: 3,470
Thanked 3,119 Times in 2,247 Posts
Default

It could well be. What I couldn't understand when my car stopped with a dead ITP was that putting 5 litres of fuel in didn't get it going but 15 litres did. Adding 5 litres would easily immerse the inlet to the ITP, so it had to be something else.

I remember having some lively discussions with TC over on the dark side when we were trying to get to the bottom of what was happening.

Thought at the time that the fuel was drawn from the other side of the saddle, so needed to put in more fuel to get it over the saddle, but now I think that when the tank level gets down to the priming valve then adding 5 litres may not be enough to cover it again as the cross section area of the tank at that height is quite large. Only guessing but it could make sense.

Mike

Last edited by Mike Noc; 21st March 2012 at 13:48..
Mike Noc is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 01:04.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright © 2006-2023, The Rover 75 & MG ZT Owners Club Ltd