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Matt
Matt, Engineer
Category: Volvo
Satisfied Customers: 21126
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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My 2004 Volvo xc90t6 was running fine, then all at once it

Customer Question

my 2004 Volvo xc90t6 was running fine, then all at once it would not go over 5 mph and the information screen said something like "engine not running at optimal performance". after about ten minutes started up and read fine. took to mechanic and no codes found.
Submitted: 1 year ago.
Category: Volvo
Expert:  Matt replied 1 year ago.

Hello

to get this error and not generate any codes I'd say its possibly a mechanical issue

like low fuel pressure or a vacuum leak?

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine