"...burst into flames." Funny to a degree. There's no cabin smell of fuel. Nor is there when walking around the car immediately after a drive. Bearings... I have lifted the car and spun the wheels. All smooth. Roll of the car when coming to a stop... with brakes off just before a complete stop, car will creep along very slowly to a gentle stop. Slightest of inclines... brakes off in neutral... car rolls easily.

Am thinking the same as you ErrorM about the mixture and so 10 mpg not being engine related. With all that has been checked, obviously there's still a piece of the puzzle hidden. ...The answer is out there.

Assuming a bit more performance is gained with 964 cams, 1.45 overlap, SSIs and Dansk muffler over the engine's prior stock config (pre-rebuild) there must be more air flowing through the engine. And so more fuel to reach stoich. Must question if these relatively simple mods translate into a drop from 18 mpg city to 10? I can't get there. A 911 at 10 mpg is 1 mpg better than a 930.

With the same engine getting 27 highway, this is Twilight Zone-ish. Would make sense if the highway mpg was 17ish! To be sure, the odo is correct (provided the State's mile markers are.)

Will keep at it until the answer is found. Appreciate the thinking ErrorM.


Showdown... I've run through a number of O2 sensors now. Always calibrating per Innovate's specs. Swapping them side to side to compare. Swapping controllers side to side. Substituting sensors and controllers, always recalibrating when needed. Would have been easy were that gear at fault. It's not. If LogWorks software is accurate or not, that I do not know. Will dump the software currently installed and reload it. See what comes of it. Thank you for this instigation.

Not quite sure what you're thinking of relative to low milage & driving---the two are inseparable here. Low mpg was discovered immediately after the rebuilt engine went back on the road. At half a tank, I used to see 180 miles in the city. Quarter tank, 90 miles etc. No longer. Since the "discovery," formal mpg tests have been in progress.
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Plugs pulled 2.24.24 for a look at color. Slight bias of llight coming in from left side to consider. That said, the differences seen represent the plugs very closely.

http://forums.pelicanparts.com/uploa...1735151050.jpg

http://forums.pelicanparts.com/uploa...1735151050.jpg

Over the years looking at plugs, #6 has always been the dark one and continues that way post engine rebuild. Assuming the Bosch fuel injector's flow tests are accurate, color differences must be the result of cylinder temp and that in turn the result of cooling air flow bias. Am speculating here.

Driving around yesterday before pulling plugs, my brakes felt very hard. Harder than the previous drive. Brake hardness has been dancing back & fourth in my head since having the car back on the road (after the rebuild.) Is it harder or is it me is the dance. I replaced the racing brake pads that were in with Mintex about 2 months ago thinking the race pads were unpleasant Seemed to be better afterwards. ...Seemed. Yesterday there was a distinct change. Add the test done a few days ago with attempting to hold 3,000 rpm while applying the brakes... brakes had no bite. Tried a few versions of the test and eventually decided to stop. Put the pieces together and am thinking there's something possibly awry with the booster hose or with the master cylinder and/or booster. I believe these parts are original to the car. 44-45 years in service.

Disconnected booster hose by the engine. Idle dropped but not by much. Finger-plugged hose on the manifold side and idle went back as it was with the hose attached. Then listened by the master/booster but couldn't hear a leak. Might be there but noise from the engine is drowning it. Reservoir fluid level was topped off once a few weeks ago. Brake system was flushed during the engine rebuild, bled and reservoir topped off. So recent top off might be something. Level has been stable since recent top off. Felt mc and booster for leaks. None found but didn't go at this tooth & nail---superficial check at best. Will disconnect suction hose at booster in the next day or so. No matter what is found, time to renew these parts.

If a leak is found anywhere along the hose or at the booster/mc, I don't know if this would result in 10 city mpg or not. Don't know this air-fuel business well enough (yet.)
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I recently replaced the brake booster hose on my car:https://forums.pelicanparts.com/porsche-911-technical-forum/1153485-pulled-engine-my-84-targa-now-fun-begins-3.html#post12366945

John Walker's thread here has some good info on it: https://forums.pelicanparts.com/porsche-911-technical-forum/435952-vacuum-leak-you-probably-didnt-ever-think.html

The hose runs from the engine up to the back of the tunnel. I had the engine and the foam blocks out of my car so it was easy to replace.

Here is the correct hose: https://belmetric.com/cohline-series-2633-high-pressure-hose/?sku=RH12X19HP

Unplugging the brake booster vacuum hose should have made a substantial impact on the running engine or caused it to stall completely.

Are you sure the hoses are connected to the right places? Have you sucked on the hose that goes to the brake booster to see if it holds vacuum?

Very on-target links ErrorM... Thank you.


Pete... substantal impact not happening. Minor difference only. Add very hard braking to this info and booster system is instantly high on the attention list.

I'd like to think all the hoses are where they should be but now it's open for confirmation.

Fine idea to suck on that hose. Have not done but will do it now. Thank you.
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Tight engine at fault for mpg? - To confirm status, pulled plugs, turned crank with fan/fan-wrench with belt tensioned. (I did check rotation of crank and cams during build. All turns were silky.)


http://forums.pelicanparts.com/uploa...1735248565.jpg

Check booster line from engine running forward - Added piece of hose onto existing nipple. Made sure add-on was clamped tight to nipple. Sucked and... there’s resistance but clearly not a seal. What vacuum is created doesn’t last. Will get car in air to check the booster hose before it enters tunnel. Also foot well. Then in frunk.

Thanks for the suggestions & intel here guys. Sal, ErrorM, Pete... Much appreciated.

Sal, you suggested logging city miles. Planned that for today but got side tracked. Is on tomorrow's menu.

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Tested brake booster line from engine bay to frunk. Leaks.
Tested booster. Leaks.

Did not do city drive to log wideband. Back to that after sorting booster stuff.
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Plug the brake booster lines at the air box. It should run better. Take it for a test drive. Caution, the brakes will be stiff.

Fine idea Pete. (I have 3.2.) Will log wideband to see if there's a difference with the "plug" compared to recent city drives.
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Leaking vs. plugged brake booster system

Plug is in after the “Y.” (Hose leading to booster and booster are now offline.) Didn’t get into WOT today. Not being used brakes as hard as they are, expired insurance (effective today), and it raining… WOT can wait. Braking = much harder without the booster connected so while the boost system leaks, it still works to a significant degree that’s better than zero boost.

Did same tests today as done 12.14.24. Comparing prior cold and warm idle logs revealed only subtle differences---not worth looking at. There is a difference under load…

Bosch 158 injectors in all cylinders.
Green = 1-2-3
Blue = 4-5-6
Red dot-dash = 1.0 lambda / 14.7:1 afr

3,000 rpm in 4th gear, level pavement
Logged 12.14.24:

http://forums.pelicanparts.com/uploa...1735505022.jpg


3,000 rpm in 4th gear, level pavement
Plugged booster system
Logged today 12.29.24:

http://forums.pelicanparts.com/uploa...1735505022.jpg

Leaner when leaking brake booster is plugged? I have yet to wrap my head around Motronic air-fuel metering.

That's odd, especially the split between the left and right cylinder banks. I'm no 3.2 expert, but the Motronic uses O2 sensors to keep the AFR in a narrow range. Possibly an O2 sensor is bad?

Split is more prevalent at idle and at high rpm with no load. Is possible this separation between sides stemming from the throttle body's bias to the 1-2-3 side. Why the sides come close to balancing out under load... not a clue.

My ECU is operating blind as far as O2 is concerned. (Doesn't matter for 3.2 if O2 sensors are connected or not.)
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