still can't solve my fuel issue on Diesel ZT

Rick-sta · 19th July 2017, 13:35

Hi all,

Some of you may have seen or remember my posts earlier in the year regarding starting and cutting out issues I've had with the ZT since April. It all started at the beginning of April where 1 day the car took longer than usual to start. Then the next day it turned over for even longer before starting, until eventually on the third day it wouldn't start at all.

After having the car on a bit of diagnostics kit we checked the fuel pressures and the low fuel pressure was only 1 bar, whereas it should have been around 3.6 bar, and due to this the high pressure was 0 bar. Strange, as the first thing I checked was both fuel pumps to ensure they were running, and I could hear the in tank pump running fine and the under bonnet pump was running too.

Well in the end it turned out the in tank pump was causing the issue as it started up after that pump was replaced, which was odd as the in tank pump was working and running with the same humming noise it always had (I even checked it with the fuel access panel off), so no idea why it wasn't sending across enough fuel. Anyways, so I thought great, it's all fixed... turned out this wasn't the case.

Whenever I run down to about a little below the 1/4 of a tank of fuel level, the starting issue comes back. The car starts taking longer to start, and at times will take 3 or 4 attempts to start after turning over for some time. Also, once it's finally fired up I can't rev the engine properly, for a while the revs go as far as around 2k with my foot hard down on the accelerator, and then eventually runs as normal.

I've also had the car cut out on me whilst driving at that fuel level, and then take a while to restart, again not reving very high after restarting for the first 3 - 8 seconds. The first couple attempts at starting the car just turns over like there's no fuel at all, then after that it starts coughing up a bit trying to start before it finally fires up. But once started and running it runs fine again, so it's almost like maybe there's air getting into there. I have a feeling I lose a bit of power as well once I'm below 1/4 tank of fuel, as I'm sure it feels slower when I have my foot down from 40-70mph.

Now the problem is clearly a low fuel pressure issue but I'm just totally lost at what could be causing it. The in tank pump is brand new, I've replaced the underbonnet pump by swapping it with the one from our 75 just to eliminate that, and my underbonnet pump works fine on the 75, so it's not that. My high pressure pump is a refurbished unit fitted just over a year ago. I've replaced the fuel rail sensor, fuel regulator on the HP pump, cam sensor and crank sensor, so it's none of those (all of these sensors were swapped with those on our 75, with my old ones being fitted to the 75 and that still runs fine). My injectors are also new. Fuel filter has been replaced.

The only thing I thought that it could be is a blockage in the fuel line between the in tank pump and the underbonnet pump. Reason is that when I pulled out my old in tank pump to replace it, I found that the filter that's mean't to be on the pump had come off and was sitting in the bottom of my tank, so I'm not sure if that may have allowed dirt to be sucked into the pump and into the fuel line. Which may be the reason why my in tank pump wasn't working properly as that hadn't failed when I changed it, so it may have been clocked up with dirt.

But from what I've read in other posts, apparently the pump can't suck up the dirt that's sitting at the bottom of my fuel tank, even when I run the car at a low fuel level. My tank has got quite a fair bit of dirt in the bottom of it and I remember that I had been running the car on very low fuel just before the original starting issue in April began.

One thing I have noticed though is that the under bonnet fuel pump on our 75 makes a constant low pitched sound whilst running, however my ZT's underbonnet pump is constantly fluctuating between low pitched and high pinched every 2 seconds. It kind of sounds like there may be air getting into there, but it does this no matter what my fuel level is. I've tried 2 underbonnet pumps on my ZT and they both make the same noise, and yet when they're fitted to the 75 they don't make that noise.

I'd kind of just left the issue over the last few months as this low pressure problem wasted 5 days of my time the first time round back in April, so just been running the car with more than a 1/4 tank of fuel at all time since, but I would like to try and fix it as otherwise it's quite annoying as it knocks off around 100 miles off my range before I have to refuel. As long as I'm not below 1/4 of fuel the car runs perfectly fine.

Does anyone have a diagram of the fuel system showing where exactly it picks up the fuel from the tank? does it pick it up from the same side as the in tank pump or from the nearside? Is it possible that wherever the fuel is picked up from could have moved up higher, making me run out of fuel earlier?

I think my fuel level sensor is working ok, because when i refuel at the point of when I start having the issues at 1/4 of fuel, it only takes me about £50 to refuel, whereas a full take up from near empty would take me near £70. so there's definitely fuel there in the tank.

Any help would be much appreciated as I'm pretty stuck with this issue at the moment, as anything that would usually be causing this kind of issue has already been changed on my ZT.

TomRS · 19th July 2017, 14:17

Interesting read...

My immediate take on this would be if you have sucked in dirt and that by the sounds of it could be the case, then anything you have replaced is now under suspicion as dirt could be caught in any of the fuel lines from the tank to the UB pump to the HP pump, if lots of sand and debris have worked through your HP pump the innards could be worn and it could be struggling to make pressure.
Sand and dirt is by far THE WORST for damaging any metal moving parts it really doesnt take much to do some serious damage.
The low fuel pressure certainly sounds like its struggling to suck enough fuel.... can you bypass the fuel line int othe underbonnet pump with that of a jerry can when the car is really low and try it? i know that sounds silly but i was having a similar issue.
I later traced it to a kinked fuel line from a bad repair on the fuel pump, car would run fine but under 1/4 would not start i assumed pump, replaced that and still the same low pressure unless tank was full.

So for whatever reason when the fuel is low the pumps are working overtime to suck the fuel and if there is any blockage or slight impass it just destroys all fuel rail pressure.
Poor design really but it is what it is.... the later single pump setup is much stronger and more reliable as im sure your aware of.

But yeah try that... if it starts fine on the jerry can then you've got line problems or pump issues.
im gonna assume it will be fine on the can as you say its fine when above 1/4 but its worth a test to rule it out.

Santara man · 19th July 2017, 14:58

I'm thinking like Tom ....A new pump so I wouldn't imagine it's faulty , so I'm thinking fuel pickup pipe maybe a blockage or a small fracture (doesn't need to be much) down near the quarter full mark.

Mickyboy · 19th July 2017, 15:25

Hi Rick,

On T4 or another diagnostic that I won't name but you probably know, you can measure the fuel pressure with the engine running and if you Rev it up you can see how low the fuel pressure drops, it would be interesting to see how low the fuel pressure drops at 3000 rpm,
I have recently found a vehicle that had a faulty Pierburg valve, (pressure limiting valve)its located underneath the pump near to the battery box, that caused a low fuel pressure issue with starting, got me wondering if this could be causing a problem for you.
I do also agree with the kink in the fuel line theory as I have found kinks in the cross pipe in the tank before.
Mick

Nobby · 21st July 2017, 15:52

Quote:

Originally Posted by Rick-sta

Hi all,

Now the problem is clearly a low fuel pressure issue but I'm just totally lost at what could be causing it. The in tank pump is brand new, I've replaced the underbonnet pump by swapping it with the one from our 75 just to eliminate that, and my underbonnet pump works fine on the 75, so it's not that. My high pressure pump is a refurbished unit fitted just over a year ago. I've replaced the fuel rail sensor, fuel regulator on the HP pump, cam sensor and crank sensor, so it's none of those (all of these sensors were swapped with those on our 75, with my old ones being fitted to the 75 and that still runs fine). My injectors are also new. Fuel filter has been replaced.

Any help would be much appreciated as I'm pretty stuck with this issue at the moment, as anything that would usually be causing this kind of issue has already been changed on my ZT.

Rick, I know you've got new injectors but a faulty one can cause these exact symptoms. I had a similar problem with one of my cars after an in-tank pump failure. There's no connection other than possibly dirt in the lines but after sending my newish (under 1500 miles) injectors to Lynx Diesels one was found to be faulty. Refurbished and all was well. Just a thought

Mike Noc · 21st July 2017, 22:25

Quote:

Originally Posted by Rick-sta

The only thing I thought that it could be is a blockage in the fuel line between the in tank pump and the underbonnet pump.

You can do a quick visual check Rick - unplug and disconnect the supply pipe to the UBP, and remove the outlet pipe from the nearside tank module, switch the key to position II and you'll see the flow from the outlet connection on the tank top. Connect the pipe back up there and then do the same test looking at the inlet to the UBP. You should see more or less the same flow through the pipe if there isn't a blockage - it will be a little less as some fuel will return to the tank via the bleed off in the five way connection. Common partial blockage is from the protective cap on the inlet pipe of the UBP being left on when fitting from new. You should see it in the pipe, or feel it with a cable tie put down the pipe.

Quote:

Originally Posted by Rick-sta

But from what I've read in other posts, apparently the pump can't suck up the dirt that's sitting at the bottom of my fuel tank, even when I run the car at a low fuel level. My tank has got quite a fair bit of dirt in the bottom of it........

If you have dirt in the tank then it can get stirred up every time you fill up with fuel and get into the LP system but should be picked up by the filter. Worth cleaning it all out.

Quote:

Originally Posted by Rick-sta

Does anyone have a diagram of the fuel system showing where exactly it picks up the fuel from the tank? does it pick it up from the same side as the in tank pump or from the nearside? Is it possible that wherever the fuel is picked up from could have moved up higher, making me run out of fuel earlier?

Fuel is picked up from the offside at the base of the tank module. As mentioned, a split pipe or leaking connection in the tank can give you problems when the level drops low enough. Again, stripping it out and checking all the pipework should sort it.

rustymotor · 22nd July 2017, 05:39

You probably have already but is the diesel filter under bonnet OK?

Lotaskin · 22nd July 2017, 11:45

Rick
Do you get a rush of air into the tank when you remove the fuel cap?
When you next have trouble starting remove the fuel cap and if it then starts you know where to look.

Rick-sta · 26th July 2017, 23:21

Quote:

Originally Posted by Nobby

Rick, I know you've got new injectors but a faulty one can cause these exact symptoms. I had a similar problem with one of my cars after an in-tank pump failure. There's no connection other than possibly dirt in the lines but after sending my newish (under 1500 miles) injectors to Lynx Diesels one was found to be faulty. Refurbished and all was well. Just a thought

I don't think it's an injector issue on mine in my case, as my injectors were brand new 2 years ago. I'd already tried swapping the injectors back in April when all these problems started and it didn't help at all. And the issue only happens when I'm low on fuel, and my original issue back in April was found to be fuel pressure related and I think it still is fuel pressure related.

Quote:

You can do a quick visual check Rick - unplug and disconnect the supply pipe to the UBP, and remove the outlet pipe from the nearside tank module, switch the key to position II and you'll see the flow from the outlet connection on the tank top. Connect the pipe back up there and then do the same test looking at the inlet to the UBP. You should see more or less the same flow through the pipe if there isn't a blockage - it will be a little less as some fuel will return to the tank via the bleed off in the five way connection. Common partial blockage is from the protective cap on the inlet pipe of the UBP being left on when fitting from new. You should see it in the pipe, or feel it with a cable tie put down the pipe.

Nice one cheers mate I will give that a go

Is there a diagram of the fuel lines anywhere as I was wondering if it would be possible to run a new fuel line from the in tank pump to the underbonnet pump outside the car just to see if that solves the issue, if it does that would mean there's a blockage in the line somewhere.

Quote:

If you have dirt in the tank then it can get stirred up every time you fill up with fuel and get into the LP system but should be picked up by the filter. Worth cleaning it all out.

Quote:

You probably have already but is the diesel filter under bonnet OK?

The fuel filter is new so that's not blocked up.

Quote:

Fuel is picked up from the offside at the base of the tank module. As mentioned, a split pipe or leaking connection in the tank can give you problems when the level drops low enough. Again, stripping it out and checking all the pipework should sort it.

I'll have to check all the pipe work, maybe it is a split somewhere at the back inside the tank causing the issues. Don't think the fuel lines are leaking anywhere else, there's no smell of diesel and my car is parked in the same place every night and there's no diesel on the floor.

Quote:

Rick
Do you get a rush of air into the tank when you remove the fuel cap?
When you next have trouble starting remove the fuel cap and if it then starts you know where to look.

Ermm I'm not sure. I will have to try that. If I do get a rush of air into the tank, what would that mean?

Lotaskin · 27th July 2017, 08:49

Good morning Rick
If you were to get a rush of air as you remove the fuel cap this could indicate a vacuum within the tank that the fuel pump might not be able to overcome. This could be caused by a blocked breather pipe to the tank. This could explain why it happens when your down to 1/4 of a tank as the more fuel used the greater the vacuum. I can't find my RAVE cd at the moment so I would have a better idea of our fuel system.

19th July 2017, 13:35	#1
Rick-sta This is my second home MG ZT 2.0 CDTI+ in Typhoon, MG TF 135 in Typhoon & Rover 75 Connoisseur CDTI SE in Pearl Black Join Date: Oct 2012 Location: Norfolk Posts: 7,534 Thanks: 2,718 Thanked 2,827 Times in 1,462 Posts	still can't solve my fuel issue on Diesel ZT Hi all, Some of you may have seen or remember my posts earlier in the year regarding starting and cutting out issues I've had with the ZT since April. It all started at the beginning of April where 1 day the car took longer than usual to start. Then the next day it turned over for even longer before starting, until eventually on the third day it wouldn't start at all. After having the car on a bit of diagnostics kit we checked the fuel pressures and the low fuel pressure was only 1 bar, whereas it should have been around 3.6 bar, and due to this the high pressure was 0 bar. Strange, as the first thing I checked was both fuel pumps to ensure they were running, and I could hear the in tank pump running fine and the under bonnet pump was running too. Well in the end it turned out the in tank pump was causing the issue as it started up after that pump was replaced, which was odd as the in tank pump was working and running with the same humming noise it always had (I even checked it with the fuel access panel off), so no idea why it wasn't sending across enough fuel. Anyways, so I thought great, it's all fixed... turned out this wasn't the case. Whenever I run down to about a little below the 1/4 of a tank of fuel level, the starting issue comes back. The car starts taking longer to start, and at times will take 3 or 4 attempts to start after turning over for some time. Also, once it's finally fired up I can't rev the engine properly, for a while the revs go as far as around 2k with my foot hard down on the accelerator, and then eventually runs as normal. I've also had the car cut out on me whilst driving at that fuel level, and then take a while to restart, again not reving very high after restarting for the first 3 - 8 seconds. The first couple attempts at starting the car just turns over like there's no fuel at all, then after that it starts coughing up a bit trying to start before it finally fires up. But once started and running it runs fine again, so it's almost like maybe there's air getting into there. I have a feeling I lose a bit of power as well once I'm below 1/4 tank of fuel, as I'm sure it feels slower when I have my foot down from 40-70mph. Now the problem is clearly a low fuel pressure issue but I'm just totally lost at what could be causing it. The in tank pump is brand new, I've replaced the underbonnet pump by swapping it with the one from our 75 just to eliminate that, and my underbonnet pump works fine on the 75, so it's not that. My high pressure pump is a refurbished unit fitted just over a year ago. I've replaced the fuel rail sensor, fuel regulator on the HP pump, cam sensor and crank sensor, so it's none of those (all of these sensors were swapped with those on our 75, with my old ones being fitted to the 75 and that still runs fine). My injectors are also new. Fuel filter has been replaced. The only thing I thought that it could be is a blockage in the fuel line between the in tank pump and the underbonnet pump. Reason is that when I pulled out my old in tank pump to replace it, I found that the filter that's mean't to be on the pump had come off and was sitting in the bottom of my tank, so I'm not sure if that may have allowed dirt to be sucked into the pump and into the fuel line. Which may be the reason why my in tank pump wasn't working properly as that hadn't failed when I changed it, so it may have been clocked up with dirt. But from what I've read in other posts, apparently the pump can't suck up the dirt that's sitting at the bottom of my fuel tank, even when I run the car at a low fuel level. My tank has got quite a fair bit of dirt in the bottom of it and I remember that I had been running the car on very low fuel just before the original starting issue in April began. One thing I have noticed though is that the under bonnet fuel pump on our 75 makes a constant low pitched sound whilst running, however my ZT's underbonnet pump is constantly fluctuating between low pitched and high pinched every 2 seconds. It kind of sounds like there may be air getting into there, but it does this no matter what my fuel level is. I've tried 2 underbonnet pumps on my ZT and they both make the same noise, and yet when they're fitted to the 75 they don't make that noise. I'd kind of just left the issue over the last few months as this low pressure problem wasted 5 days of my time the first time round back in April, so just been running the car with more than a 1/4 tank of fuel at all time since, but I would like to try and fix it as otherwise it's quite annoying as it knocks off around 100 miles off my range before I have to refuel. As long as I'm not below 1/4 of fuel the car runs perfectly fine. Does anyone have a diagram of the fuel system showing where exactly it picks up the fuel from the tank? does it pick it up from the same side as the in tank pump or from the nearside? Is it possible that wherever the fuel is picked up from could have moved up higher, making me run out of fuel earlier? I think my fuel level sensor is working ok, because when i refuel at the point of when I start having the issues at 1/4 of fuel, it only takes me about £50 to refuel, whereas a full take up from near empty would take me near £70. so there's definitely fuel there in the tank. Any help would be much appreciated as I'm pretty stuck with this issue at the moment, as anything that would usually be causing this kind of issue has already been changed on my ZT. __________________ How to retrofit Cruise Control on a diesel with no OEM wiring in place: Link How to retrofit heated electric memory seats with no OEM wiring in place: Link How to operate FBH and ATC via text Link How to restore cloudy projector headlights Link Last edited by Rick-sta; 19th July 2017 at 13:46..

19th July 2017, 14:17	#2
TomRS Posted a thing or two Mk1 ZT 190 - Mk2 ZS 180 - Mercedes E63 AMG S - Ford Ranger Hawk Join Date: Mar 2016 Location: Middlesbrough Posts: 1,456 Thanks: 123 Thanked 409 Times in 281 Posts	Interesting read... My immediate take on this would be if you have sucked in dirt and that by the sounds of it could be the case, then anything you have replaced is now under suspicion as dirt could be caught in any of the fuel lines from the tank to the UB pump to the HP pump, if lots of sand and debris have worked through your HP pump the innards could be worn and it could be struggling to make pressure. Sand and dirt is by far THE WORST for damaging any metal moving parts it really doesnt take much to do some serious damage. The low fuel pressure certainly sounds like its struggling to suck enough fuel.... can you bypass the fuel line int othe underbonnet pump with that of a jerry can when the car is really low and try it? i know that sounds silly but i was having a similar issue. I later traced it to a kinked fuel line from a bad repair on the fuel pump, car would run fine but under 1/4 would not start i assumed pump, replaced that and still the same low pressure unless tank was full. So for whatever reason when the fuel is low the pumps are working overtime to suck the fuel and if there is any blockage or slight impass it just destroys all fuel rail pressure. Poor design really but it is what it is.... the later single pump setup is much stronger and more reliable as im sure your aware of. But yeah try that... if it starts fine on the jerry can then you've got line problems or pump issues. im gonna assume it will be fine on the can as you say its fine when above 1/4 but its worth a test to rule it out. __________________ http://i66.tinypic.com/5cd6xj.jpg

19th July 2017, 14:58	#3
Santara man Avid contributor 2004 Rover75 Tourer Join Date: Dec 2014 Location: Winsford Cheshire Posts: 147 Thanks: 41 Thanked 43 Times in 32 Posts	I'm thinking like Tom ....A new pump so I wouldn't imagine it's faulty , so I'm thinking fuel pickup pipe maybe a blockage or a small fracture (doesn't need to be much) down near the quarter full mark. __________________ Growing old gracefully in a 75...Real nameTony

19th July 2017, 15:25	#4
Mickyboy SERVICING AND DEALER DIAGNOSTICS MG ZT CDTI 135 + & MGZT CDTI AUTO 160 & ROVER 75 TOURER CDTI 160 TROPHY YELLOW Join Date: Aug 2013 Location: Hernebay Posts: 4,331 Thanks: 818 Thanked 2,414 Times in 1,141 Posts	Hi Rick, On T4 or another diagnostic that I won't name but you probably know, you can measure the fuel pressure with the engine running and if you Rev it up you can see how low the fuel pressure drops, it would be interesting to see how low the fuel pressure drops at 3000 rpm, I have recently found a vehicle that had a faulty Pierburg valve, (pressure limiting valve)its located underneath the pump near to the battery box, that caused a low fuel pressure issue with starting, got me wondering if this could be causing a problem for you. I do also agree with the kink in the fuel line theory as I have found kinks in the cross pipe in the tank before. Mick __________________ [SIGPIC][/SIGPIC] T4 Owner Jobs done : new UBP, Spy hole mod, Rear hub(wheel bearing),plenum cleaned and emptied, Inline thermostat fitted,Full service, In car Digital tv/DVD Bluetooth Satnav etc, Replaced UBP, Restored headlights,Fixed airbag connection.replaced HP pump,replaced rear light seals,changed intercooler O rings. Jobs to do: ,replace drivers lock,.[/SIZE] Last edited by Mickyboy; 19th July 2017 at 15:37..

22nd July 2017, 11:45	#8
Lotaskin Avid contributor MG ZTT CDTI Join Date: Dec 2011 Location: Basildon Posts: 172 Thanks: 100 Thanked 31 Times in 30 Posts	Vacuum Rick Do you get a rush of air into the tank when you remove the fuel cap? When you next have trouble starting remove the fuel cap and if it then starts you know where to look.

22nd July 2017, 05:39	#7
rustymotor Posted a thing or two Rover 75 Tourer Join Date: May 2017 Location: Hull Posts: 1,848 Thanks: 216 Thanked 432 Times in 340 Posts	You probably have already but is the diesel filter under bonnet OK?

27th July 2017, 08:49	#10
Lotaskin Avid contributor MG ZTT CDTI Join Date: Dec 2011 Location: Basildon Posts: 172 Thanks: 100 Thanked 31 Times in 30 Posts	Good morning Rick If you were to get a rush of air as you remove the fuel cap this could indicate a vacuum within the tank that the fuel pump might not be able to overcome. This could be caused by a blocked breather pipe to the tank. This could explain why it happens when your down to 1/4 of a tank as the more fuel used the greater the vacuum. I can't find my RAVE cd at the moment so I would have a better idea of our fuel system.