Alex Sol

okay... deep breath.

02 sensor but wouldn't make that much difference
vacuum leak.. somewhere but also wouldn't cause left side cylinders to not fire

crank position sensor , checked gap and is new

dme relays.. tried lots of em

feels like i'm in limp mode...

but mainly the spark is not lighting the fuel at the right time and therefore idle is all over the place and while driving there is all kinds of hesitation, misfiring even above 3,000 rpms

one thing i did do on this rebuild / reseal was... i am using pre 1991 non seal ring piston/cylinders.

fuel is fresh 91 octane, shell mixed with very very little old fuel as i have burned through about 300 kms and filled 30 litres twice... talk about rich!!! or about 1/2 the mileage i am used to... on mostly highway, i get about 550-600 kms on 65 litres.


.

robt964

You say the left bank is not fueling / makes no difference when you disconnect the injectors?
Do you get continuity between each plug and its cooresponding pin on the end of the wiring harness? Then from the engine bay fuse box to the ECU?
I'd get the wiring diagrams out and go through everything on the engine harness back to the ECU.

Alex Sol

thanks for tip robt

yes sir the left bank of injectors have fuel and are sending but when engine is idling, there is no difference between injectors plugged in nor injectors not plugged in...

could it be i have the right side bank of injectors wired to the left side??

i have the wiring diagrams (which i don't understand how to read)

there is definitely continuity to each injector and i'm using an injector pulse light that shows it flashing and therefore communicating with the injectors

we pulled the right side off and saw the spray pattern seemed a little 'wet' vs more of a vapor but i have frame of reference here...

robt964

>could it be i have the right side bank of injectors wired to the left side??

It is possible but I doubt it would make *as* much of a difference as what you are seeing. The timing of when the injector fires is far less critical when compared to ignition. It's the duration the injector is fired for that's important.

Background question for the motronic bods: Does the DME support sequential or batch or both?

Does each bank have its own ground? I would certainly perform a resistance check and compare against the 'good' bank. A poor ground will limit the current which theoretically could effect the speed at which the injector is capable of switching. If it does, the fueling will be effected far greater at these lower duty cycles than it would at higher RPMs.

At idle, your injectors will spend 99% of their time off. As the engine speed increases, so does the duty cycle.
If a poor ground intoduces a degree of latency in opening the injector, you can see how this will have a markedly greater effect on the injectors duration at low speed than it would at high speed.

I'll dig out the wiring diagrams this evening and take a look

Lorenfb

"Background question for the motronic bods: Does the DME support sequential or batch or both?"

Both, batch is used when the Hall sensor is disconnected and sequential with
the Hall sensor connected. So the 964/993 will run without the Hall sensor.

robt964

Thanks Lorenfb

Thats perfect! I don't recall if its actually possible to wire the banks the wrong way round? - will the leads actually reach? If they do, to confirm its an electric issue with that banks loom/drivers, you could swap the banks (loom) over and then disconnect the dizzy hall sensor. If the left/right behavior is now reversed, then we've made a further step forward in the elimination.

Vandit

You'd have to be pretty asleep, yet very determined, to mix up the injector wiring harness banks. They break out from the main harness a good 6" apart from each other and break out in different directions (1-3 point to the rear fusebox, 4-6 point toward the firewall).

Alex Sol

Vandit,

correct on the injector wire swap - almost impossible and we confirmed that they are in correct position...

RobT / Loren, i request the grounds be checked if in fact they are separate.

I have ground in about 4 positions and they seem to be fine.

1. alternator to top of motor - brown wires
2. main harness to top of motor - brown wires
3. coils - brown wire
4. starter - red wire
5. motor to body - thick black wire
6. battery to body

Not sure what other grounds to check. an obvious good start

Indycam

You put early pistons / cylinders together with late heads ?

Alex Sol

yes..

Alex Sol

okay, i have been in a deep dark 964 depression due to my issues...

bit the bullet and brought into the local porsche specialist.

he went through all the usual tests:

compression - fine
crank position sensor - slight adjustment
engine timing - fine
spark plugs - correct order? yes
distributor - set up correctly
pulled the valve covers - check gaps and they were all fine
pulled the right hand side intake to check to see if i left a cloth in the intake (really!) and found nothing but that is how the car feels...
ran diagnostic - he has the hammer and other tools - nothing
pulled my ecu and put into another 964 - ran flawlessly

findings: cylinder 1,2 and 4 not firing

90% it is related to a bad engine harness - mine is very brittle

what i've done since he told me the news:
nothing for 3 weeks while waiting for the ice storm to pass through and heavy snow to melt
took into friend's warm garage with hoist last night

on the hunt for electrical gremlin

pulled the ecu
grounded a wire connected to a paper clip

started checking the obvious for continuity:

injectors 1,2,3,4,5,6
crank position sensor
idle air valve
knock sensor
hall sensor
grounds


then checked #30 hall sensor/knock sensor 1&2 shield / ground

knock sensor 1 & 2 shield - no problems, got continuity
hall sensor shield on the same #30 circuit - no continuity
pulled back the wire and found the white and brown wire broken but not touching and not completely snapped either

ran out of time and have to ask the question: would this hall effect sensor shieldground cause the mis timing and therefore misfire of cylinders 1,2, and 4 and all my other rough running issues????

next i will be checking: injector wires and look for shorts, cut wires crossing etc.... more likely the culprit from my limited knowledge of electrical issues -

JasonAndreas

Did he/you use the Bosch Hammer to manually cycle each injector and confirm that the DME control unit was actually turning on/off those (#1,2, and 4) injectors when it thought it was?

Alex Sol

i'll check...

Alex Sol

Did he/you use the Bosch Hammer to manually cycle each injector and confirm that the DME control unit the simple check is that the injectors plug is pulsing using the test light plug. is this adequate?

boxsey911

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?