MG ZT Diesel Fuel pressure issue

mostin6556 · 3rd May 2015, 13:18

Hi Everyone.

I have a MG ZT with a possible fuelling issue. The main symptoms are it will not rev passed 2000 rpm and thats a struggle. it has no power whatsover and takes an age to get to 30mph and if it uphill you have no chance.

Now i have read a few threads around about smiler problems and checking the fuel pressure sensor voltage output came up. This is fine reading at 1.3 on idle and 1.2 on crank it gets to 1.8 on reving the info says it should be 2v at 3000rpm but i cant get it that high to check. I have changed the seal on the high pressure regulator which made no difference.

it will rev up to redline if you start it with foot on throttle but will drop right down to 2000rpm again. i have noticed a wooshing sound from the HP pump when the car is on stage 2 priming. it also is continuously priming ( used to petrol which primes for a few seconds up to pressure and stops so not sure if this is normal).

Both low pressure pumps make noise (not that that means they are pumping enough) i will change these but i wanted an opinion on whether theses cars should prime continuously or not and if the wooshing noise in the hp pump when priming is normal. Don't want to replace both low pressures to find its the HP pump.

FrenchMike · 3rd May 2015, 13:34

Quote:

Originally Posted by mostin6556

Hi Everyone.

I have a MG ZT with a possible fuelling issue. The main symptoms are it will not rev passed 2000 rpm and thats a struggle. it has no power whatsover and takes an age to get to 30mph and if it uphill you have no chance.

Now i have read a few threads around about smiler problems and checking the fuel pressure sensor voltage output came up. This is fine reading at 1.3 on idle and 1.2 on crank it gets to 1.8 on reving the info says it should be 2v at 3000rpm but i cant get it that high to check. I have changed the seal on the high pressure regulator which made no difference.

it will rev up to redline if you start it with foot on throttle but will drop right down to 2000rpm again. i have noticed a wooshing sound from the HP pump when the car is on stage 2 priming. it also is continuously priming ( used to petrol which primes for a few seconds up to pressure and stops so not sure if this is normal).

Both low pressure pumps make noise (not that that means they are pumping enough) i will change these but i wanted an opinion on whether theses cars should prime continuously or not and if the wooshing noise in the hp pump when priming is normal. Don't want to replace both low pressures to find its the HP pump.

Hi,be welcome

Your HP measurements looks correct (at low rev)But i guess you next enter in emergency mode .
Have a look at the LP sensor value ;it must stay stable for any throttle position.
(around 4 volts so 2.5 bars)

Have you tried MAF disconnected ?how are the intercooler O rings ?

BTW ,both LP pumps must purring softly ...

Mike

mostin6556 · 3rd May 2015, 13:39

Hi,

thanks for the welcome. I have disconnected the maf it made no difference Also disconnected the battery over night. I haven't checked the LP sensor will do that this afternoon. Not looked at the O rings as didn't suspect a turbo issue as thought sat on a drive way reving a turbo leakage wouldn't restrict rev range so heavily.

Do these prime for a set time or just keep going?

FrenchMike · 3rd May 2015, 13:44

Quote:

Originally Posted by mostin6556

Hi,

thanks for the welcome. I have disconnected the maf it made no difference Also disconnected the battery over night. I haven't checked the LP sensor will do that this afternoon. Not looked at the O rings as didn't suspect a turbo issue as thought sat on a drive way reving a turbo leakage wouldn't restrict rev range so heavily.

Do these prime for a set time or just keep going?

Self priming !,
turn your contact pos 2,you'll hear both LP pumps for about one minute and
Watch if you get 4 volts on the sensor .

mostin6556 · 3rd May 2015, 13:57

sorry think i haven't explained it very well

I turn the ignition to stage 2 and the pumps run.............and keep running for a long time and i can here a wooshing noise from the HP pump whilst it does it. My petrol primes for a few seconds and is done.

So if these should cut out after a min then its not geting priming pressure which i would then supect LP pumps.

Excellent I will check the votlage on LP sensor when i get back from work this afternoon.

Coups · 3rd May 2015, 15:26

Try just unplugging the sensor from the top of the fuel filter. See if it makes a difference. Having very similar issues and by unplugging the sensor full power is returned. Indicates a low fuel pressure but I wouldn't recommend running for any great time with it this way.

I've a new ubp arriving early next week. Hoping that cures it. Thinking it's either that or the sensor. Will keep you updated!

Mike Noc · 3rd May 2015, 16:19

Quote:

Originally Posted by mostin6556

sorry think i haven't explained it very well

I turn the ignition to stage 2 and the pumps run.............and keep running for a long time and i can here a wooshing noise from the HP pump whilst it does it. My petrol primes for a few seconds and is done.

So if these should cut out after a min then its not geting priming pressure which i would then supect LP pumps.

The diesels LP pumps don't work like that - they are just timed and don't cut off at a set pressure. With the engine running they run continuously. If they are doing this before you start the engine then check the relay and wiring.

Both pumps are fed from the same relay, and a previous owner may have modified (read bodged) the wiring if they had a problem with the ECM.

As FrenchMike and Coups have mentioned - sounds like the engine is in limp mode due to lack of LP fuel pressure.

mostin6556 · 3rd May 2015, 17:05

hi everyone,

when these go into limp mode do they take themselves back out of limp when the problem is solved or do they need T4 to clear it?

having read other peoples problems with gunk in the tank i pulled the in tank pump to check and its all clean in there however the pipe from the pump attaches to a white plastic square with a metal hook on it randomly just floating around in the tank.

will check fuel pressure on LP side when i get my meter back after tea. As for unplugging the LP sensor would that not stop the car from starting. is the LP sensor not there to prevent the HP pump from running with no diesel in it coups? I unplugged the high pressure one made no difference.

Mike Noc · 3rd May 2015, 17:12

Once pressure is restored the car returns to normal operation.

Unplugging the LP pressure sensor will also overcome the limp mode but the MIL will light up because the sensor is unplugged.

The HP pump is protected by the HP pressure sensor on the end of the fuel rail, and if HP pressure drops too low the ECM will shut the engine down.

FrenchMike · 3rd May 2015, 17:16

Quote:

Originally Posted by mostin6556

hi everyone,

when these go into limp mode do they take themselves back out of limp when the problem is solved or do they need T4 to clear it?

will check fuel pressure on LP side when i get my meter back after tea. As for unplugging the LP sensor would that not stop the car from starting. is the LP sensor not there to prevent the HP pump from running with no diesel in it coups? I unplugged the high pressure one made no difference.

I think,with sensor removed,a defaut value is given by the ECU but no more security ..

BUT with sensor connected and faulty (or lack of pressure)it enters emergency
mode (less than 1.7 bar or 2.6 volts).

I don't think that T4 is needed to clear the fault ...happily ...

3rd May 2015, 13:18	#1
mostin6556 Newbie MG ZT-T Join Date: Mar 2013 Location: Stafford Posts: 19 Thanks: 0 Thanked 0 Times in 0 Posts	MG ZT Diesel Fuel pressure issue Hi Everyone. I have a MG ZT with a possible fuelling issue. The main symptoms are it will not rev passed 2000 rpm and thats a struggle. it has no power whatsover and takes an age to get to 30mph and if it uphill you have no chance. Now i have read a few threads around about smiler problems and checking the fuel pressure sensor voltage output came up. This is fine reading at 1.3 on idle and 1.2 on crank it gets to 1.8 on reving the info says it should be 2v at 3000rpm but i cant get it that high to check. I have changed the seal on the high pressure regulator which made no difference. it will rev up to redline if you start it with foot on throttle but will drop right down to 2000rpm again. i have noticed a wooshing sound from the HP pump when the car is on stage 2 priming. it also is continuously priming ( used to petrol which primes for a few seconds up to pressure and stops so not sure if this is normal). Both low pressure pumps make noise (not that that means they are pumping enough) i will change these but i wanted an opinion on whether theses cars should prime continuously or not and if the wooshing noise in the hp pump when priming is normal. Don't want to replace both low pressures to find its the HP pump.

3rd May 2015, 13:39	#3
mostin6556 Newbie MG ZT-T Join Date: Mar 2013 Location: Stafford Posts: 19 Thanks: 0 Thanked 0 Times in 0 Posts	Hi, thanks for the welcome. I have disconnected the maf it made no difference Also disconnected the battery over night. I haven't checked the LP sensor will do that this afternoon. Not looked at the O rings as didn't suspect a turbo issue as thought sat on a drive way reving a turbo leakage wouldn't restrict rev range so heavily. Do these prime for a set time or just keep going?

3rd May 2015, 13:57	#5
mostin6556 Newbie MG ZT-T Join Date: Mar 2013 Location: Stafford Posts: 19 Thanks: 0 Thanked 0 Times in 0 Posts	sorry think i haven't explained it very well I turn the ignition to stage 2 and the pumps run.............and keep running for a long time and i can here a wooshing noise from the HP pump whilst it does it. My petrol primes for a few seconds and is done. So if these should cut out after a min then its not geting priming pressure which i would then supect LP pumps. Excellent I will check the votlage on LP sensor when i get back from work this afternoon.

3rd May 2015, 15:26	#6
Coups Posted a thing or two Rover 75 Contemporary SE Join Date: Apr 2014 Location: Dundee Posts: 1,941 Thanks: 545 Thanked 520 Times in 402 Posts	Try just unplugging the sensor from the top of the fuel filter. See if it makes a difference. Having very similar issues and by unplugging the sensor full power is returned. Indicates a low fuel pressure but I wouldn't recommend running for any great time with it this way. I've a new ubp arriving early next week. Hoping that cures it. Thinking it's either that or the sensor. Will keep you updated!

3rd May 2015, 17:05	#8
mostin6556 Newbie MG ZT-T Join Date: Mar 2013 Location: Stafford Posts: 19 Thanks: 0 Thanked 0 Times in 0 Posts	hi everyone, when these go into limp mode do they take themselves back out of limp when the problem is solved or do they need T4 to clear it? having read other peoples problems with gunk in the tank i pulled the in tank pump to check and its all clean in there however the pipe from the pump attaches to a white plastic square with a metal hook on it randomly just floating around in the tank. will check fuel pressure on LP side when i get my meter back after tea. As for unplugging the LP sensor would that not stop the car from starting. is the LP sensor not there to prevent the HP pump from running with no diesel in it coups? I unplugged the high pressure one made no difference.

3rd May 2015, 17:12	#9
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,586 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Once pressure is restored the car returns to normal operation. Unplugging the LP pressure sensor will also overcome the limp mode but the MIL will light up because the sensor is unplugged. The HP pump is protected by the HP pressure sensor on the end of the fuel rail, and if HP pressure drops too low the ECM will shut the engine down.