Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak?

Honest John Back Room » Technical matters
View Threaded
Wed 24 Feb 2021 16:05
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Joe tuzzer

Hello, sometimes when I start my car, the revs shoot up too around 2000rpm and then come back down after a second or two. This happens intermittently.

Another thing too point out is when I accelerate in any gear and get too around 2000rpm,there is a hissing/metalic grind noise. Sounds like a tsssssssssss noise. As soon as the revs go about 2000 rpm the noise isn't there.

Any ideas, could it be a vacuum leak? I have had a look at rubber hoses and pipes and can't see anything out of the ordinary.

Cheers

Reply | Report as offensive | Link
Wed 24 Feb 2021 19:05
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - elekie&a/c doctor
Check the vacuum breather hoses and pcv valve under the inlet manifold.
Reply | Report as offensive | Link
Wed 24 Feb 2021 19:37
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Joe tuzzer

I have had a look and can't see any splits or anything. Whe you rev the engine while stationary you can't hear that hissing noise. It's only when the engine is under load. It's not a pulley or anything because I have replaced all of the pulleys including the cambelt and the noise hasn't changed at all.

Reply | Report as offensive | Link
Wed 24 Feb 2021 20:28
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - elekie&a/c doctor
A vacuum leak would be most noticeable at idle . There would also be unstable and erratic idle .
Reply | Report as offensive | Link
Wed 24 Feb 2021 20:33
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Joe tuzzer

The idle goes up and down very slightly. Maybe 50 or 100 rpms. I wouldn't say the idle is erratic. Maybe it's a small leak so it's not affecting the idle much?

Reply | Report as offensive | Link
Wed 24 Feb 2021 22:50
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - bathtub tom

We know about the boy racer backbox, but are there any other changes you've made?

Reply | Report as offensive | Link
Wed 24 Feb 2021 23:03
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Joe tuzzer

Nope :)

Edited by Joe tuzzer on 24/02/2021 at 23:03

Reply | Report as offensive | Link
Wed 24 Feb 2021 23:04
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Joe tuzzer

This was happening before I put my boy racer backbox on

Reply | Report as offensive | Link
Thu 25 Feb 2021 18:51
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Railroad.

The idle goes up and down very slightly. Maybe 50 or 100 rpms. I wouldn't say the idle is erratic. Maybe it's a small leak so it's not affecting the idle much?

Manifold vacuum is at its highest when the throttle is closed. If a vacuum leak is not noticeable at engine idle then it definitely won't be when the throttle is open.

Reply | Report as offensive | Link
Thu 25 Feb 2021 19:08
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - bathtub tom

Spray some carb cleaner or something like WD40 around the vacuum hoses at tickover. If the revs change then it's being sucked in.

Reply | Report as offensive | Link
Thu 25 Feb 2021 22:35
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Joe tuzzer

Good idea, I will try that tomorrow and see how I get on. Cheers for the reply

Reply | Report as offensive | Link
Thu 25 Feb 2021 22:35
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - Joe tuzzer

So does that mean I probably don't have a vacuum leak? Cheers for the reply

Reply | Report as offensive | Link
Fri 26 Feb 2021 10:56
Ford fiesta 1.6 petrol zetec s 2007 - Possible vacuum leak? - edlithgow

I had similar symptoms. Car would idle OK but become intermittantly undrivable when hot. My best guess was that something (perhaps the intake manifold) was opening a gap due to thermal expansion.

Blowing butane over all the plumbing and manifold didn't find anything.

I'd already blanked off or disconnected all the 80's carb rats nest of vacuum hoses (which I didn't understand), leaving only distributor vacuum advance, to address previous issues, which it did.

Over a couple of weeks I painted sunflower oil over the carb, hoses and manifold, and it stopped doing it, touch wood and so far.

My guess is the oil crept into a gap and polymerised, sealing it.

Sunflower oil un-mixed with anything else seems to de-polymerise long term (say a couple of years) and even longer term re-polymerise, so this probably isn't stable. Used in combination with aluminium as an abrasive (for rust treatment on bodywork, for example) it seems stable long term.

Not sure about commercial alternatives, but you can get "creeping" leak stoppers, or maybe try PVA, or varnish.

Edited by edlithgow on 26/02/2021 at 10:59

Reply | Report as offensive | Link