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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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"Hunting" in Volvo 740 GLTViews : 2656 Replies : 33Users Viewing This Thread : |
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Jan 28th, 2018, 01:28 | #11 |
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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. |
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Jan 28th, 2018, 11:34 | #12 |
Go redblock or go home
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Jan 28th, 2018, 12:29 | #13 |
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No worries, easily done!
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Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........ |
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Jan 31st, 2018, 18:52 | #14 |
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Thanks all, we're running a series of tests this week, let you know the outcome.
Yours Peter |
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Apr 4th, 2018, 13:16 | #15 |
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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 |
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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,
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Apr 4th, 2018, 14:28 | #17 |
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Has anyone mentioned the crank position sensor?
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Apr 4th, 2018, 14:37 | #18 |
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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.
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Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........ |
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Apr 4th, 2018, 20:49 | #19 |
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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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Apr 17th, 2018, 18:32 | #20 |
Rogerthechorister
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Ask a silly question
Have you read the codes from the flash box in the left hand inner front wing?
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