JasonAndreas

You could do it with a light but you don't need to, you can hear (the engine is not running for this test) the injectors buzz when they pulse on/off. But you must run the test via the scantool software or a Bosch Hammer from the ECU and not just look while the engine is running. If those are fine, then you have to work your way backwards from cylinders 1, 2 and #4, starting with the individual ignition wires (be VERY careful, there is a ton of voltage).

You would think that because everything was fine BEFORE you dropped the engine to fix the gearbox, that it has to be something that you touched, i.e. a ground, but there is nothing that is common to only those cylinders. How was it determined the cylinders 1, 2 and #4 are not firing?

Alex Sol

hall sensor is one of my problems. mine is more likely broken wires crossing and most likely the engine harness which is mainly on the only bit that was touched when i did recent engine drop, fixed the broken bit in the transmission and then re installed.

When i fired it up... it ran like hell. prior to this it was pretty smooth and firing on all cylinders....

Alex Sol

cylinders 1,2,4 not firing:

run the motor at idle

remove each injector and look for change ie: stall, sputter, extra roughness (already running rough).

when removing the 'good' cylinders, there is significant change on 3,5,6 but no change at all on the cyl 1,2,4

pretty crude method...

all the injectors were flowed before latest rebuild...

as far as injectors working , we pulled the rail with injectors still plugged in. ran the motor and fuel squirted out in a nice, large spray pattern....

made a bit of a mess.

Goughary

For what it's worth, my engine wiring harness was absolute toast when I did my top end rebuild few years ago. Cracked brittle and parts of the casing were melted. I came to find out that our engine wiring harness is way too expensive, as are most things on my car... But, I found this guy, and for a reasonable price he tested and rebuilt mine and sent it back in good shape....it's been perfect ever since... https://bowlsby.net/914/WiringHarnesses/ No affiliation, am just happy that guys like him are out there.

Alex Sol

nice tip goughary. new engine harness is about $1500.00 very close to pulling the trigger.

i've found some used for around $500.00 but am worried it will have its own set of issues!!

Alex Sol

Okay, finally the weather is decent again and have the motivation and time and shop to hoist up the 964 and do some testing...

When mine had issues with the Hall sensor the symptoms were cutting out and down on power at the top end. The symptoms where the same when I ran with it unplugged (I just unplugged it at the distributor). However, I wouldn't say it ran rough or misfired because of the hall sensor problem. Try unplugging it and see how it runs?

Motor runs the same with or without the hall sensor plugged in

will resolder the brown, white and shield for the hall sensor

checked almost all the 55 pin for electrical disconnect.

keeping in mind the motor ran flawlessly on start up and then settling into idle only weeks prior to my troubles starting after a recent engine drop / transmission split in the late fall of 2013 - like it did prior to my engine teardown / rebuild

Alex Sol

can anyone suggest how to check:

pin # 1 and 2 - ingnition pulse to output stage and #2 ground?

#5 tank venting valve

#13 lead L from diagnostic plug - shouldn't make a difference on how my car runs..

#23 resonance plate

#39 version coding - again shouldn't affect how the motor runs

#44 intake air temp ntc I

#45 engine temp ntc II

#46 altitude potentiometer - where is this?

#54 coding plug

#55 diagnostic plug, lead K - where you plug in the hammer? again, not that important here as i'm trying to get the motor running smooth and powerfully - plus we were able to scan using hammer and showed absolutely no issues and injectors were cycling correctly

Alex Sol

clue: i am running super super rich and getting about 5kms per litre of 91 octane gas. usually get about 10 kms per litre of gasoline.....

should i be looking back at vacuum and vent intake etc???

I had the intake off and replaced and had all 5 clamps on pretty stiff: 1 for each of the three intakes and 2 on the top side (one in front and one in the rear)

J richard

Have you checked the distributor belt?

Alex Sol

thanks for suggesiton. yes, distributor belt is fine and notches lined up with the rotors.

Alex Sol

question may be, what causes the afm to slap around? at idle and while driving at various rpms.

J richard

The full rich mode is typical of the motor going into limp mode but that should be getting you a check engine light, is it working? Some immediate places to look: Burned and or plugged cat, bad o2 sensor or wire, split or leaking oil tank vent line from the back of the intake to the oil console, oil filler cap leaking, small one way vent on the top of the oil tank missing or damaged, gummed up or sticking afm flapper door...

Alex Sol

great stuff J...

no check engine light and no codes from the hammer

plugged cat... possible, mine is original, if i straight pipe, the issues would go away?

o2 sensor - no code and may also be original... but would it cause all the mis fire?

split or leaking oil tank vent line - now that could be... will check for vacuum - any suggestions on how to do this?

oil filler cap leaking? not likely but will check...

one way vent on top of the tank - will check but all my hoses (that i don't know what they all do) are intact and will double check they are not leaking

sticking afm flapper door - replaced with rebuilt last year and worked fine though i have hear the door slap prior to the engine rebuild

could be from wires crossing in the engine harness? ie: fuel injector wires or others that have burned inside and now crossing??

my harness is pretty old and brittle.

$1,600 for a new one. $500 for used... yikes!! And still not sure that's the issue though my local Porsche specialist suggests it's wiring. checked out a lot of stuff.

we pulled the ecu and have been testing continuity and grounds on about 30 or the 51 pins. some are blank and some i don't where to test.

ie: pins 1&2 which seem important - ignition pulse to output stage

Alex Sol

found the air flow meter slap is caused by back fire through the intake...

due to?

improper timing?
heads not properly rebuilt?
compression issues?

distributor off by 360 deg?

will check...

Mark Brook

Any news on this???