10 mpg 3.2 - can’t find where the fuel is going

[mysocal911]

Originally Posted by Discseven

Tested:

Speed sensor - static resistance = OK
Dynamic AC voltage = OK

Reference sensor - static resistance = OK
Dynamic AC voltage = OK

Test procedure is per Specialized ECU Repair:

Disconnect harness plug from ECU. Multimeter, set on ohms, connects the following pins:

Speed sensor: connect pins 8 and 27. Ohms to be between 600 - 1600.
Reference sensor: connect pins 25 and 26. Ohms to be between 600 - 1600.




Speed


Reference


For dynamic testing: Check car’s battery has 12+ volts = OK (12.6 v)
Gearbox in neutral, parking brake ON.
Multimeter set to AC voltage.

Speed sensor: connect pins 8 and 27 with multimeter. Crank engine. Voltage should be greater than 1.0 v = OK (is 2.6 v)

Reference sensor: connect pins 25 and 26 with multimeter. Crank engine. Voltage should be less than 1.0 v = OK (is 0 v)

.

Typo right? AC voltage ~ 200-500 mv

[Discseven]

Originally Posted by mysocal911

Typo right? AC voltage ~ 200-500 mv

Dave... I did not take pics of the dynamic tests. Multimeter was set on 200 ac v.

Reference used: https://www.youtube.com/watch?v=zeFOOcLSk60
.

[Discseven]

Just pulled.
.

[Mr. Merk]

Originally Posted by Discseven

Odo test

Was done with Google maps. Stride app was not run.
Route followed had 2 legs.

Combined route total per Google = 12.3 miles.
Trip odo reading = 12.4 miles.

Question:

Are these 12.4 miles from cold? Or has the car already been fully warmed up to operating temp before conducting this test and calculating MPG?

[scarceller]

What's the spark gap set at? Needs to be 0.7 to 0.8mm
But the color of all 6 plugs looks decent, those plugs do not look like they are running RICH.
The 10MPG is likely not result of rich mixture, I suspect some sort of friction drag. Could be a sticking brake caliper or parking brake? Have you tests temps of rotors after a city drive?

Originally Posted by Discseven

Just pulled.
.

[scarceller]

Testing speed and ref sensors is best done with a scope. But honestly I don't think you have issues with crank sensors.
I really suspect some sort of mechanical drag in the drive train
Your plug colors are not indicating overly rich mixture and all 6 are also showing that all cyls are firing.

[mysocal911]

Originally Posted by Discseven

Dave... I did not take pics of the dynamic tests. Multimeter was set on 200 ac v.

Reference used: https://www.youtube.com/watch?v=zeFOOcLSk60
.

Better references exist here on Pelican Parts!

Why did you write this;

Voltage should be less than 1.0 v = OK (is 0 v)

A reference sensor voltage of 0V is NOT OK for starting. After starting, yes the reference voltage can be 0V.

[scarceller]

Also, I think you mentioned you have a Wide Band O2 gauge installed? If it shows reading in the 14s around town it confirms you are not burning extra fuel. Meaning the fuel is properly matched to the air intake. But you could still be taking in more air than normal because of mechanical friction?

Another worthy test is a 5 gas analyzer, this will also show hydro carbon, an indication of raw fuel in the exhaust. It could be helpful to get data from gas analyzer.

[scarceller]

If the ref sensor was not working the engine would not start. Testing the ref/speed sensors is fine but likely not your issue. And you really need a scope to see the wave forms, and since engine runs I'd scope the sensors with engine running.

[rsscotty]

Make sure your distributor is phased correctly...shown is where it needs to be at TDC #1

[scarceller]

I went through all the posts in this thread again today. The AFR city graphs clearly show you are in the correct target 1.0 lambda and you do not have black plugs nor black tailpipe. These 3 things tell us you are not running rich.

I'm not sure what the issue is here but it's most likely something mechanical. Double check all ignition components and firing order.

Also 27-28MPG highway is on target and as expected.

Some sort of extra mechanical drag is what I suspect, but not sure what that is. Could be collapsed brake hoses? Are these new? Test is easy to do, car on jack stand. Engine at idle in neutral. Have someone apply the brakes and attempt to turn a wheel by hand. Then have them remove foot from brake pedal. The MOMENT they lift off pedal the wheel MUST spin easily. If you find a delay between time they took foot off brake and wheel spins you have a bad hose.

[Discseven]

Originally Posted by Mr. Merk

Question:

Are these 12.4 miles from cold? Or has the car already been fully warmed up to operating temp before conducting this test and calculating MPG?

Merk... Those mile numbers are not mpg. They were to check the accuracy of the trip and main odometers against a route laid out on Google maps. Most recent city mpg result has engine at 11.55 mpg. City mpg is always calculated after having run the fuel tank down 1/2 to 4/4. Takes me any number of weeks to accomplish this.

Originally Posted by scarceller

What's the spark gap set at? Needs to be 0.7 to 0.8mm
But the color of all 6 plugs looks decent, those plugs do not look like they are running RICH.
The 10MPG is likely not result of rich mixture, I suspect some sort of friction drag. Could be a sticking brake caliper or parking brake? Have you tests temps of rotors after a city drive?

Sal... gap is 0.8mm.

Friction. Parking brakes were found months ago to have signs of dragging. Rebuilt both sides back then. Then checked mpg and wasn't the parking brakes. Calipers dragging - all wheels rotate freely. Wheel bearings - no rock of any wheel on its spindle. CV joints - no noticeable binding when rotating either rear wheel. And no crunching sound. Rears turn easily in or out of gear (rear end in the air.)

Rotors - these were temp checked a few times over the months of this journey. Most recently a number of days ago. Last results are in post #56.

Other friction checks & notes...

Gearbox - fresh oil installed with rebuild and just checked level a few days ago - it's full & clean. Crank rotation - was checked months ago by tensioning belt, no spark plugs in, and turning crank by turning the fan. Not a problem turning the crank this way. During rebuild, galleys were all flushed. Bearings installed correctly. Engine temp operates at 210 with Mocal cooler in front fender, dual fans. When case was first closed, crank was turned to feel rotation - silky smooth. Journals were all polished. All were in spec for std. bearings. Rod large ends were rounded and bored to spec and new bushings went in on small ends, machining done by Total Engine Concepts up by Xtreme. Xtreme did heads. Pistons and cylinders were within spec. New Goetz rings were correctly installed. ARP rod bolts torqued to their spec. With each added section that was installed, the crank was turned over to feel for any anomaly. I'd have u-turned had any oddity in the least been sensed when doing these turns. Nothing was rushed. Break in was with a 20 minute run of engine at 2000 rpm. Engine oil & filter changed. Inspected oil and it looked good. Magnet too.



I too am concluding it is as if the car is now moving an extra load, and the air & fuel are dialed into this "need." But, why only for city miles? Is momentum on the highway overcoming the friction if indeed friction is what it is?

There is no question that what is in the car now in terms of weight is what was in the car when it was doing 18 city. Exception being the wideband system but that's negligible. So carrying actual added weight cannot be a factor. In the absence of actual added weight, it must be drag. More to the point, drag that only exists to get the car in motion. Not to keep it there.

If I have missed a drag factor in the recent checks for it, what did I miss?
__
Sal... conversation is appreciated. Looking again at the brakes
.

[zuch]

Tire air pressure?

[3rd_gear_Ted]

Gosh, you might drive it around in spirited manner and take an IR gun to the mechanicals, see what they tell you.
You would think all that fuel gets turned into Btu's some how and would leave a heat signature.

[rokemester]

This thread reads like a mystery novel for Porsche nerds! I don’t understand many of the expert commentary, but sure looking for the exciting conclusion. Kudos to the original posters follow-up for each thought and comment. Extraordinary.

[Mr. Merk]

Originally Posted by Discseven

Merk... Those mile numbers are not mpg. They were to check the accuracy of the trip and main odometers against a route laid out on Google maps. Most recent city mpg result has engine at 11.55 mpg. City mpg is always calculated after having run the fuel tank down 1/2 to 4/4. Takes me any number of weeks to accomplish this.

I guess a better asked question is how many miles do you normally drive in "city" situations? How much of your driving is short miles or warm up miles? How much is done at operating temperture?

We had a client one time complain about their fuel economy being much lower than advertised. It turned out their commute was only three miles each way.

[scarceller]

The OP already found brake drag on the e-brake, once that was fixed MPG went from 10 to 12.
I suspect we still have some sort of brake drag occurring more often during city driving.

I also assume he is comparing same city driving pattern and style from before rebuild to after?

[Discseven]

Originally Posted by zuch

Tire air pressure?

Zuch... all good.

Originally Posted by 3rd_gear_Ted

Gosh, you might drive it around in spirited manner and take an IR gun to the mechanicals, see what they tell you.
You would think all that fuel gets turned into Btu's some how and would leave a heat signature.

Ted... Down pipe temps were checked early on in this "mystery novel." Numbers below are after a city drive and car is obviously parked. At the time these temps were taken, the fuel injectors and spark plugs were being questioned. Temps below are notably with Lucas and W6DPO spark plugs installed. There are now Bosch 158 injectors and Iridium plugs installed. Temps seen here were shot on the SSI down pipes just below the heads and just before the pipes enter the heat exchangers. I post these temps not because they apply now, but for anyone wanting to make a general comparison. At this moment, we're beyond thinking there's something wrong with the engine.

Originally Posted by rokemester

This thread reads like a mystery novel for Porsche nerds! I don’t understand many of the expert commentary, but sure looking for the exciting conclusion. Kudos to the original posters follow-up for each thought and comment. Extraordinary.

Roke... we're getting there. Inch by inch. TY ~~~

Originally Posted by Mr. Merk

I guess a better asked question is how many miles do you normally drive in "city" situations? How much of your driving is short miles or warm up miles? How much is done at operating temperture?

We had a client one time complain about their fuel economy being much lower than advertised. It turned out their commute was only three miles each way.

Merk... Interesting detail. Most of my city driving is beyond 6 miles. Anything less and I bike it. Am not sure at what city milage the engine has warmed to op temp---I call op temp 210 as read on the dash gauge. I do know for certain that at 3 miles... the engine's temp is NOT 210. Is something I'll check.

At a standing idle, it takes this engine, as it is now, 20 minutes to reach 210. Have timed this. I also know this engine can sit, running, in dead-stopped traffic indefinitely. Dirty engine with trombones... traffic can be a problem. I mention this for anyone overheating in traffic. Clean case and heads + fender Mocal with fans is a thermal solution. I went though this puzzle a few years ago.

Originally Posted by scarceller

The OP already found brake drag on the e-brake, once that was fixed MPG went from 10 to 12.
I suspect we still have some sort of brake drag occurring more often during city driving.

I also assume he is comparing same city driving pattern and style from before rebuild to after?

Sal... Correct on e-brake. Also correct on city driving pattern being same now, after the rebuild, to city drive pattern before. "Pattern" being where I drive city-wise. How I drive is different. Am much more tuned to driving fuel efficiently, ie, looking far ahead at traffic lights. Looking for holes in traffic so coasting can be extended. More coasting rather than harder braking. Etc. MPG numbers don't show much if any gains from doing this. To project forward, when the guilty party is revealed & corrected, perhaps then, applying "how" to drive more fuel-thoughtful will see better city mpg than 18. We'll see.



Focus now is off the engine's running. All evidence combined at this moment suggests engine's doing what it should do... Wideband readings + plug color + engine's performance taken into combined account.

I missed something in the hunt for friction. That hunt is now back on.
.

[mikedsilva]

Maybe you've been driving into headwinds recently???

[ant7]

What octane fuel are you using ?
Ant.