"Hunting" in Volvo 740 GLT - Page 2

aardvarkash10 · Jan 28th, 2018, 01:28

If its hunting that badly, I'd look at fuel supply. If there is insufficient pressure (or flow) the engine will idle ok, but die with the throttle. A very low mileage car like this will likely have a history of gummy fuel etc - filters, pumps etc slowly get a build up of gunk Also a possibility that rust from the tank is doing the same thing.

If the vacuum leak tests don't turn up a result, get a fuel pressure gauge and look into supply side.

360beast · Jan 28th, 2018, 11:34

Quote:

Originally Posted by Laird Scooby

Thanks for adding the WD40 in - i forgot!

I somehow missed your original post haha.

Laird Scooby · Jan 28th, 2018, 12:29

Quote:

Originally Posted by 360beast

I somehow missed your original post haha.

No worries, easily done!

Peterquest · Jan 31st, 2018, 18:52

Thanks all, we're running a series of tests this week, let you know the outcome.
Yours Peter

Peterquest · Apr 4th, 2018, 13:16

Still no luck on this problem!
The fuel pressure is good and holds even when the accelerator is pressed, the MAF and throttle position sensors have been changed.
No leak can be detected on the intake, all hoses are in good condition and I would expect this to effect the idle as well as when the accelerator is pressed.
This problem occurred between use ie. one day it ran fine the next time it was started there was this issue and the issue has not changed or got worse when being run for testing and it always starts well.
Any further ideas would be welcome
Thanks

827Roverman · Apr 4th, 2018, 13:34

All of the help/advice you have been given is good, but just a thought, is it worth checking all spark plugs & leads, dizzy cap etc, also worth checking the timing,

Rumbo · Apr 4th, 2018, 14:28

Has anyone mentioned the crank position sensor?

Laird Scooby · Apr 4th, 2018, 14:37

Something i've just thought of that i had once and took ages to find is a faulty non-return valve on the brake servo vacuum line. At idle (because the vacuum was higher) it was held closed but once the throttle was opened and the vacuum slightly depleted, it didn't hold shut so well so allowed air to return to the manifold upsetting the mixture and causing hunting. Clamping the hose off between the non-return valve and the inlet manifold will prove this one way or the other.

aardvarkash10 · Apr 4th, 2018, 20:49

get it on an exhaust gas analyser and a scope and determine if its fuel or spark.

All else is a guess.

rogerthechorister · Apr 17th, 2018, 18:32

Have you read the codes from the flash box in the left hand inner front wing?

Apr 4th, 2018, 14:37	#18
Laird Scooby Premier Member Last Online: Today 12:22 Join Date: May 2012 Location: Lakenheath	Something i've just thought of that i had once and took ages to find is a faulty non-return valve on the brake servo vacuum line. At idle (because the vacuum was higher) it was held closed but once the throttle was opened and the vacuum slightly depleted, it didn't hold shut so well so allowed air to return to the manifold upsetting the mixture and causing hunting. Clamping the hose off between the non-return valve and the inlet manifold will prove this one way or the other. __________________ Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........

Apr 17th, 2018, 18:32	#20
rogerthechorister Rogerthechorister Last Online: Dec 16th, 2023 02:15 Join Date: May 2006 Location: Rochester	Ask a silly question Have you read the codes from the flash box in the left hand inner front wing? __________________ B234F estate, H reg 100k miles. RIP melted B280E. 760T estate, F reg 133k miles. 940 Sport M90 estate, N reg 170k miles. 940 Sport M90 estate, N reg 100k miles, ex Lovejoy. 960 Estate, N reg, 56k miles, blown up and sold.

Jan 28th, 2018, 01:28	#11
aardvarkash10 Master Member Last Online: Oct 8th, 2022 22:22 Join Date: Sep 2016 Location: Auckland	If its hunting that badly, I'd look at fuel supply. If there is insufficient pressure (or flow) the engine will idle ok, but die with the throttle. A very low mileage car like this will likely have a history of gummy fuel etc - filters, pumps etc slowly get a build up of gunk Also a possibility that rust from the tank is doing the same thing. If the vacuum leak tests don't turn up a result, get a fuel pressure gauge and look into supply side.

Jan 31st, 2018, 18:52	#14
Peterquest New Member Last Online: Jun 22nd, 2022 16:39 Join Date: Nov 2017 Location: St Ives	Thanks all, we're running a series of tests this week, let you know the outcome. Yours Peter

Apr 4th, 2018, 13:16	#15
Peterquest New Member Last Online: Jun 22nd, 2022 16:39 Join Date: Nov 2017 Location: St Ives	Still no luck on this problem! The fuel pressure is good and holds even when the accelerator is pressed, the MAF and throttle position sensors have been changed. No leak can be detected on the intake, all hoses are in good condition and I would expect this to effect the idle as well as when the accelerator is pressed. This problem occurred between use ie. one day it ran fine the next time it was started there was this issue and the issue has not changed or got worse when being run for testing and it always starts well. Any further ideas would be welcome Thanks

Apr 4th, 2018, 13:34	#16
827Roverman VOC Member Last Online: Oct 4th, 2022 16:02 Join Date: Jan 2016 Location: UK	All of the help/advice you have been given is good, but just a thought, is it worth checking all spark plugs & leads, dizzy cap etc, also worth checking the timing,

Apr 4th, 2018, 14:28	#17
Rumbo Time Traveller Last Online: Oct 12th, 2023 00:08 Join Date: May 2016 Location: Cornwall	Has anyone mentioned the crank position sensor?

Apr 4th, 2018, 20:49	#19
aardvarkash10 Master Member Last Online: Oct 8th, 2022 22:22 Join Date: Sep 2016 Location: Auckland	get it on an exhaust gas analyser and a scope and determine if its fuel or spark. All else is a guess.

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