lean

**illy** · 09-29-2012

I kno this has been addressed and I have read all the other lean posts. Here's my situation

I have a slight exhaust leak somewhere that I can not find because I can smell the exhaust strong with the hood open but I don't see it escaping anywhere. (I have sd headers)

I think the maf might be bad. I disconnected it and the stft and ltft both locked into 0 is that a sign of a bad maf?

Fixed the vacuum leak I think. Its fluctuating between -16 and -19 in-hg. This seem right?

Only hittin about 8 lbs of boost tho with a 3.6 pulley, I thought it'd be more. With it boosting I was also hitting 16 degree of spark advance. Normally around 27 at idle.

It's idlin smooth and runs strong but the fuel economy is terrible.

Also shot a u1153 code today.That only showed up on my aero force and not my handheld scanner which I think is very strange.

Any input would be great. And much appreciated. I'd like it to run as good as it looks!

**dsmuts** · 09-30-2012

To find your exhaust leak run some seafoam through a vacuum line and see where it's leaking.

8#'s of boost seems about right on a 3.6 w headers.

**Tony Mendez** · 09-30-2012

You should see a steady vac reading of about 17 inches. If you have a fluctuation in vacuum, you may have other problems.

Hook up a scan tool with the ability to monitor sensor valves (PIDS) and pull up the mass air flow sensor. Record your MAF sensor reading at idle, and again at various RPM ranges. Compare the values against specifications. Next, start from idle and increase throttle opening while watching MAF reading. Increase should be steadily proportional to RPM change. Perform the same checks while lightly tapping on the sensor, or heating the sensor with a blow dryer. Any fluctuation, or out of specification reading indicates a mass air flow sensor, or related wiring concern. Repair and retest. I would also recommend monitoring MAF values while driving the vehicle and checking readings while the concern is present. Have an assistant drive while checking these readings. If the mass air flow reading is within specification while a concern comes and goes then it is not likely the problem. Be sure to check all air intake connections and gaskets, as well as the air filter before faulting the sensor, as these types of concerns can affect readings.

Another thing I do is measure VE(volumetric efficiency). get your engine up to operating temp and go out and do some WOT pulls. 5000 rpm in second gear. Record the data and plug it into the VE calculator( Volumetric Efficiency Calculator). You want to see a VE of no less than 75%

**Fivefingerdeathpunch** · 09-30-2012

Originally Posted by Tony Mendez

You should see a steady vac reading of about 17 inches. If you have a fluctuation in vacuum, you may have other problems.

Atleast 19-20, 17 is too low really, unless your running a cam with alot of lope.

**Tony Mendez** · 09-30-2012

17 is the low end of the spectrum. I rarely get concerned with a steady engine vac unless its below 17 in. Even then, a properly running engine can produce as little as 15 in of vacuum at idle. I have only seen this during a driveability course i attended at the Ford Regional Training Center, but have yet to see it in a real world setting. I prefer to see a vac reading near 20 in. A cam with alot of lope will produce a gauge fluctuation due to valve over-lap and should be taken into consideration when using a vac gauge to diag a engines health.

**matt5112** · 09-30-2012

A 3800 with a vac leak will still produce 19-21 in Hg of vacuum.

**illy** · 10-01-2012

It will go to 19-21 but not constant and doesn't usually go as high 21 often

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**Tony Mendez** · 10-01-2012

I have yet to see a intake leak produce anywhere near 19-21 in of vacuum. Thats 20+ years in the automotive repair industry. Not to say its not possible. Just saying I have yet to encounter it.

**matt5112** · 10-01-2012

A big one sure. But little ones can easily go unnoticed. Like a torn egr tube for example.

**illy** · 10-01-2012

i have the egr deleted. i have a custom block off on the headers and a penny and rtv on the other side. im wondering if somehow thats where its leaking, it looks sealed very well tho

**BillBoost37** · 10-02-2012

spray and find out.

**BillBoost37** · 10-02-2012

Originally Posted by Tony Mendez

I have yet to see a intake leak produce anywhere near 19-21 in of vacuum. Thats 20+ years in the automotive repair industry. Not to say its not possible. Just saying I have yet to encounter it.

Tony.. I hear ya. These 3800's though are pretty good at maintaining good vacuum with a decent amount of leaks. Even then..I've found battery cable corrosion causing an issue with lean bank 1. So hey..in that case..it wasn't even a leak.

**sseilmnop** · 10-02-2012

How much vacuum would you expect with a VS Cam? I'm getting 17 inches but I think this is normal.

All vacuum numbers in park, correct?

When we spray are we using carb cleaner and what will we get a dip in the idle?

**BillBoost37** · 10-02-2012

17 is normal. Like mentioned..you may not see a change in vacuum.

A change in idle..repeatable when you spray in the area where you first hear it change. Up/Down.. whatever..you are listening for a change. Then can make it repeat.

**sseilmnop** · 10-02-2012

Thanks Bill, I've never seen a vacuum number on a VS cam.

**BillBoost37** · 10-02-2012

Me either. But if the bigger XP and S1X are running about the same..then it's a good general number. Thing is..often with these motors you can't base the vacuum on the lean etc. Because the iac would try and counter act any vacuum leak.

**Erik Adam Rodriguez** · 10-18-2012

my vacuum reading is 10 to 13 inches

**illy** · 10-18-2012

i was getting an exhaust leak from the headers which is fixed, but i think my 17 in is too low there has to be a small vaccuum leak that the carb cleaner cant find, i tried to do a smoke test but i dont think i did it right, i didn't see any smoke