Alfa Giulietta 1.4 MA vacuum test

[jamesw68101]

Hi,

First post here so hello!

I need to conduct a Vac test on a Giulietta 1.4 Multiair, the only accesible Vac Line I can see from the manifold goes to the fuel pressure regulator.

Is this a suitable line to T into to test vacuum? Any issue into FPR...

Obviously car to temp befor vacuum test

Thanks in advance

[E-bmw]

Yes, no problem at all.

[jamesw68101]

Thanks, won’t cause any idle issues with the T piece restricting any vacuum to FPR giving any false readings or crappy idle

Says on the Draper gauge something about not connecting to fuel related lines, but not specifically FPR

Thrown instructions now so can’t replicate 🙄

[E-bmw]

The "pressure" in the line is just used as a reference to the FPR to ensure the fuel pressure remains the same pressure above the manifold pressure for consistent running.

Don't worry all you are doing is increasing the volume of the line very slightly, for what you are doing there will be no problem.

[jamesw68101]

Ok so heres a results update, things dont look too good!


At idle

8-10 Hg fluttering between the 2

At 1500 rpm

Drops to 3 Hg, increases to 17Hg drops to 5 Hg then settles back to 8-10 Hg

At 2500 Rpm

Drops to 3 Hg, increases to 18 Hg, drops to 5 Hg then back to 8-10 when idling

3000 rpm is the same

Any ideas on this one, assuming vacuum source is correct from being T into FPR

Thanks again

[E-bmw]

A couple of questions/assumptions first.

By Hg do you mean "Hg, as in inches of Mercury?

I also take it you are talking vacuum not positive pressure?

[jamesw68101]

Hopefully image has attached, this is what it looks like at idle, needle does fluctuate between 8-10

When revved it drops into the 3-4 hg mark (should do i think), then increases to around 18 (in the green), then decreases to 5, then back to 8-10 - thats the same at 1500, 2500 and 3000 rpm

Yes Hg as in inches of Mercury, had a look at some google images of vac readings but it seems like my exact symptom may not be covered.

Thanks for your help

Edited by jamesw68101 on Monday 2nd July 12:46

Edited by jamesw68101 on Monday 2nd July 12:47

[jamesw68101]

It might help to state why im doing this vacuum test in the first place.

- Lumpy idle, car vibrates through steering wheel and seat at idle, smooths out when revs increased or Air con on
- Poor fuel consumption, MPG calculator on dash reads ok but fuel gauge is dropping like a stone!
- Fuel trims checked (hopefully ill attach photos) - Very lean at idle, but equals out when revs applied

Air filter is good, spark plugs are good, MAP sensor is good and oil levels and condition are good (Full Alfa history)

Idle raises by itself to around 1200 rpm periodically then decreases back to 750 ish rpm. Doesnt do this all of the time and hasnt today

[E-bmw]

Sounds more like pre-cat lambda sensor to me, I take it if you have an OBD reader you have checked that the MAF/MAP (delete as appropriate) are giving "live" data?

[jamesw68101]

Some more snippets of that data you mentioned and important to mention, no OBD codes at all.

Only thing that looks out of whack is the LTFT, i would assume caused by a large enough Vacuum leak, hence the vac pressure test, which has also shown extremely low at idle.

Wondering if its an Inlet manifold gasket/crack causing this. Cant easily access the manifold to do a basic spray test at idle, i have done this at the top i can access but not underneath.







Again, thanks!

[E-bmw]

OK, I fully understand why you have thought of a vac leak but with an 02 reading like that surely that would rule out a vac leak?

[jamesw68101]

May be way off, but if the LTFT are high then that means the mixture is Lean as in too much air or unmetered air vs fuel - if the adjustment is made in the fuel trim by the ecu would that still make the o2 read correct? Or is the o2 sensor feeding the info to make these adjustments.. "Shrugs shoulders"

As the LTFT decreases on rev increase and since the amount of air flowing through the vacuum leak doesn’t increase, the leak has less affect on air/fuel ratio at higher speeds and loads, so LTFT will come down as engine speed goes up, which it does..

Thats why the Vac leak thought process and the use of the gauge, what i need to know basically with the fuel trim info and the gauge info, what is this likely telling me as trim is high and Vacuum is low both at idle

Tis a pain

[E-bmw]

OK, I am the first to admit if I am wrong but this is my (possibly flawed) understanding.

AFR is going up & down around the 14.7 mark, which is as it should be.

That would imply to me that there is unlikely to be an unmetered air leak.

Not sure about what to expect EXACTLY from your vac readings but they don't seem too alarming from my limited understanding.

What is the car like performance wise?

[jamesw68101]

Hesitant on low revs when going through the gears

High fuel consumption

Pulls ok on open throttle at high revs

Stuttery on idle and vibrations in cabin.

Doesn’t feel right at all. I took the car back to the dealer I purchased from and they did diagnostics (based mainly on what I told them) and diagnosed a “potential” faulty throttle position sensor.

Not sure how they came to that conclusion after 1 hour but I’m doing all this to ensure I’m armed with enough information to keep them from re booking the car in every week

Regarding the vacuum pressure, it should be somewhere between 15-19 at idle so I’m told and based on the gauge markings that would ring true, it’s miles off that as you can see from the photo

Thanks

[E-bmw]

Can you read the TPS on live data?

Should be in there somewhere.

[jamesw68101]

Can see throttle position & absolute pedal position I think it is

No idea what the % values mean or should be.

[E-bmw]

What are your engine temperatures like?

Is the one in the cabin reading right as often that is a take off from the IAT?

[jamesw68101]

Yeah 90 flat in the middle on dash guage

Upto 96 degrees on idle in accordance to OBD

[E-bmw]

Does the On Board Computer have a displayable for external temp as this is frequently derived from IAT?

[jamesw68101]

It does, showing correct temp