Got into this fuel puzzle the end of ‘24. Interruptions occurred since then forcing me onto other matters including a few fixes found along this fuel hunt path. Getting back into it now and starting a fresh thread. This has been more twisted a puzzle to solve than any I’ve ever faced.
Background:
Engine - ‘85 3.2 in an ‘80 chassis. City mpg was 18 prior to engine rebuild. After rebuild, it’s now 10. Highway remains a respectable 27. These results have been tested a number of times with the same results. My fault when rebuilding? Everything was done by the book. Rebuilt a 3.3 before this so this 3.2 was done with a measure of prior experience. Odo is good—matches state posted mile markers. Not a leadfoot as is easy to suspect. Have filled tank consistently at the same Shell station’s nozzle until deciding to change the fuel brand to see if gas was the cause. Wasn’t. Engine runs well… Immediate start, idles evenly, no hesitation throughout RPM range with throttle eased on, or hammered WO. Pulls strong.
Mods done with rebuild:
964 cams, 40-40 grind, 1.45mm timing.
SSI exhaust
Danks 2-in-1-out muffler
What critical measures & machining 3.2 rebuild called for was done by Porsche specialists: Total Engine Concepts and Xtreme Cylinder Heads.
Checks & tests done to date. (Not necessarily listed in sequence until after 5.8.25 notes begin):
Fuel leaks - None
Air filter - Clean
Sweeper inside AFM was tested - Consistent across entire sweep.
Adjusted AFM spring tension - Advised not to do this - Returned it to original position.
Set ECU fuel dial from zero to position #3 - Advised not to do this - Returned it to zero.
Tire pressure - OK
Wheel alignment - OK
Slipping clutch - No. Acceleration is too crisp. New clutch & pressure plate was installed.
Vacuum leaks - Brake booster system. Booster rebuilt, new check valve, new hoses front & rear. Still 10 mpg.
ECU chip date checked - Correct
Individual exhaust down pipes temps checked - OK
Free roll of car - OK when I checked it. Then on occasion the parking brake would stick. Reverse gear slightly and they released. Pulled rear disks and found signs of pads dragging against the hub. Thought this was it. Wasn’t. Rebuilt parking brakes and still 10 city.
Dragging caliper pads - No
Compression tested - OK
Hand turn engine with plugs out - OK
Spark plugs checked - cleaned - OK
Spark plugs replaced - W6DPO to Iridiums - slight mpg improvement but negligible.
Fuel pressure - OK
Fuel flow - Not checked correctly but there’s good flow
Exhaust manifold tightness to heads - Tight
Tested fuel injectors. The ones installed (Lucas) and spares (Original Bosch.) Done by Mr. Injector - Both sets "passed."
ECU - tested - “No faults”
Resistance tests:Ignition wires - OK
Cap & rotor - OK
Fuel injection cables - Redone prior to rebuild so proven to get 18 city mpg - OK
Distrib - Well lubricated - OK
Grounds - All tight
Replaced Lucas injectors with original Bosch - Still 10 mpg
"Cylinder balance" - Pulled injector leads one at a time - does affect O2 as it should.
Checks / tests done after 5.8.25 (these are sequential):
964 cams continue being questioned - specs on stock 3.2 and 964 cams as provided by Webcam are compared. Post #32
Fuel pressure regulator and dampener vacuum hoses checked after engine run - both dry
Analyzing exhaust gas composition recommended - Checked around and shops don't do this any longer (in FL.) Tool, new condition = too costly to invest in. Used = unappealing as gear needs to be well cared for to operate accurately, and all the parts need to be included.
Rear end lifted to check rear hubs for any rock (bearings) and spin - No rock either side. Both sides spin equally in neutral and in gear.
Removed brake pads on RR and repeated spin test in neutral and in gear. Slightly more resistance---attribute to smaller OD of hub compared to tire OD.
Gear box oil - full. Looks good.
AFM - inside disk turned & set at 3 notches clockwise / increasing tension on "barn door" to lean fuel - wideband confirms leaning. Engine not running well now. Returned to original position. Post #69
Ohm test throttle position switches - Idle and WOT both OK.
Throttle butterfly position when gas pedal is floored = fully open. No slack in throttle cable - post #72
Idle & full throttle position switches ohms tested - OK - post #72
WOT signal checked - points close at 69-70% throttle - post #78
Odometers, trip & main tested for accuracy - OK - post # 93
AFM intake air temp sensor - OK - post #96
Cylinder head #3 temp sensor - QUESTIONABLE - Not related to fuel per Sal in post #98
Speed & reference sensors resistance and dynamic - OK - post #100 - Done per Specialized ECU procedure
Spark plugs pulled again to look at color - OK - post #103
Looking for friction... soapbox brake release test - OK - post # 130
Looking for friction... brake release test on each individual wheel - OK - post
Looking for friction... each wheel corner inspected with a checklist - chafing of a-arms against rotor shields found. Not calling this friction related to mpg puzzle - post #162
Looking for friction... individual brake release test - all corners OK - post # 168
Timing check - timing advances as rpm increases - looks OK to me but I don't know timing - post # 168
Suspected worn tie rod found - passenger side - "suspected" as it has yet to be removed and proven - play is 3.75 mm - not severe enough to cause handling issue. Not calliong this the cause of mpg puzzle - post # 169
Because of suspected tie rod... toe is checked - post # 169
ECU - although previously tested by ProGrama with "No faults" found, ECU remained suspect as it was NOT with car prior to engine rebuild. A loaner ECU known to be good was borrowed from "Inaminit" / Dean and swapped in for my wonky "10 mpg" ECU. City miles were driven. Result: 17.64 city mpg - post #173
PROBLEM SOLVED:
By Systems Consulting, 310-545-3716. They replace my wonky ECU with a restored unit of theirs. Result:
City = 19.001 mpg
Highway = 28.18 mpg
Post #270
Wideband
SSIs came with single bung on 1-2-3 side. I added second bung on 4-5-6 side. 2nd bung is positioned so both are symmetrical from collective and angles match. Bosch 4.9 sensors are connected to Innovate LC-2 controllers. Running LogWorks for charting O2 streaming data. Interesting way to “see” into the engine… but no smoking gun… yet.
EDIT: After dealing with Innovate's LC-2 system including their 4.9 O2 sensor hardware over a number of months, I found the system problematic from the get go. But issues were corrected by investing a great deal of time debugging. Finally, it became so glitchy that it was not worth dealing with---last issue seemed internal to the controllers. Innovate tech support offered no assistance each time I called them. My take is the hardware is made cheaply and tech support knows little about the workings of their product. LogWorks software worked flawlessly. It's a free download, installs in seconds, is quick & easy to configure, and simple to operate. Unfortunately LogWorks appears to be dedicated to Innovate's systems exclusively---don't quote me on this.
ECU
ECU now in the car is NOT the ECU that was in the car when getting 18 city mpg. Why this new ECU is installed is a long story and not relative. Getting the prior ECU is now not possible. I did send the currently installed ECU out for inspection. “No faults” were found.
EDIT: Turns out it was a bad ECU. To their credit, my bad ECU came from Vertex.
O2 Logs
Red dot-dash line is 1.0 Lambda = 14.7 AFR. Blue and green trace lines represent each side of the engine.
Above, city drive. Not hard on the throttle here. According to log data, engine is running lean yet this does not match fuel consumption. Because of this, wideband system accuracy is questioned. System is checked / tested including:
Controllers - swapped side to side
O2 sensors - swapped side to side
O2 sensors replaced with new sensors, calibrated per Innovate specs
Sensor cables replaced with new cables
Reloaded LogWorks software
With each change of gear and software, car was city-driven and new logs recorded. Log data did not change.
Conclusion: wideband system works as it should.
Steady cruise reading. 3,000 rpm in 4th gear.
WOT.
.