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Low Vacuum pressure on -13 in Hg

  • hudarsono
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11 Feb 2019 19:00 #26980 by hudarsono
Low Vacuum pressure on -13 in Hg was created by hudarsono
Hi,

Saw your youtube on backpressure test. I have a question, my car Ford Ecosport Petrol 2014 have issue of low vacuum pressure at idle. Its only around -13 in Hg.

When I rev it to 2500 rpm, vacuum will goes to -9 in Hg for a very short, then hovering around - 13 in Hg again. When I let go the rev, I will increase to -14 in Hg for a while.

May i know what is the issue? Apart from that I seems to have rich condition, with LTFT on +10%.

Many Thanks!

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11 Feb 2019 21:04 #26984 by juergen.scholl
Replied by juergen.scholl on topic Low Vacuum pressure on -13 in Hg
What is the altitude your at? As air pressure decreases with altitude so does the vacuum reading in the intake manifold . This is because the intake vacuum - better low pressure - is referenced to atmosferic pressure...

If your not at 8000 feet above sea level then or so then you might have some kind of an air leak. On a MAF system this could also cause your positive fuel trim. It may well be a fuel delivery problem as well, pump, filter, injectors......you'll have to provide more data to get into the right "funnel".

How is the fue trim at higher rpm and under high load?

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11 Feb 2019 21:21 #26987 by hudarsono
Replied by hudarsono on topic Low Vacuum pressure on -13 in Hg
I am at sea level (1 atm). As a note, my car barely has 56000 km.

As regards to fuel trim, it will decrease to < 5% when I press the pedal at idle. So yes I suspect a leak there, but maybe small leak?

Could small air leak(vacuum leak) also cause low vacuum pressure?

I asked the repair shop to replace the fuel filter during routine service few weeks ago (hopefully they didnt forget to do it), however all the issues remain.

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12 Feb 2019 08:39 #26994 by Tyler
Replied by Tyler on topic Low Vacuum pressure on -13 in Hg
How are you measuring the manifold vacuum, exactly? Is this with Global OBD data, or with an actual gauge?

If it's Global data, then usually some math is involved to get the real value. Usually, you have to take the BARO value and subtract the MAP value to get what an actual gauge would show. As an example, if your MAP shows 10 inHg and the BARO is 29 inHg, then your true vacuum level is 19 inHg.

Since you're at sea level, 29.9 inHg, subtracting 13 gets you 16 inHg. That's not great, but it's not horrible, either. :silly: 16 inHg might be reasonable depending on when the measurement was taken. During a cold idle, for example. Or if this engine has VVT, and is programmed to change the valve timing at idle for emissions purposes.

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12 Feb 2019 09:03 - 12 Feb 2019 09:15 #26999 by juergen.scholl
Replied by juergen.scholl on topic Low Vacuum pressure on -13 in Hg

Tyler wrote:
If it's Global data, then usually some math is involved to get the real value. Usually, you have to take the BARO value and subtract the MAP value to get what an actual gauge would show. As an example, if your MAP shows 10 inHg and the BARO is 29 inHg, then your true vacuum level is 19 inHg.


I think his mentioned values are the true pressure values in the intake manifold. Otherwise the quoted data while accelerating and decelerating would not go along with differencial pressure reading with regards to atmospheric pressure.

On the other hand, yes an intake vacuum leak will result in lower than normal MAP values at idle.

An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Last edit: 12 Feb 2019 09:15 by juergen.scholl.

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12 Feb 2019 16:32 #27008 by mcmullan
Replied by mcmullan on topic Low Vacuum pressure on -13 in Hg
you have a lean condition due to those numbers, what does it read with KOEO?

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12 Feb 2019 20:16 #27015 by hudarsono
Replied by hudarsono on topic Low Vacuum pressure on -13 in Hg
Yes, I am using OBD data and Torque APP, it shows as "Turbo boost and Vacuum Gauge" parameter in the app.

Since my car doesnt have turbo, it shows as "Vacuum" and the number is around -13 in/Hg. So I guess there is kind of "vacuum sensor" that send data to OBD.
This car doesnt have MAP sensor, only MAF sensor.

you have a lean condition due to those numbers, what does it read with KOEO?

Yes, sorry for my mistake, its actually lean rather than rich. Regarding KOEO, i will test and update later.

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18 Feb 2019 07:04 #27136 by hudarsono
Replied by hudarsono on topic Low Vacuum pressure on -13 in Hg
It seems I found the cause of vacuum leaks, it was the pipe from maf to throttle body not tightened.

Soon after it was tightened and throttle body cleaned, the LTFT become 0%. However 2 days later, when i leave it at idle long enough, LTFT keep going down becomes -10%, which is the reverse of +10% it was before the vacuum leaks fixed. I am confused. However when moving, its close to 0% though most of the time.

Any advice?

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