HiWind

^ if it is a leak as Indy says check the throttle body sleeves - rubber ones - on the 'feet' of the intake are easy to see/feel/hear a leak but the two smaller of the 4 on the TB ie the ones further back can get loose if a clamp fails or pinched and not be so easy to see. I found a problem/pinch with one of those that was causing a stall.

Here's the airflow meter in action

Alex Sol

good tip. i'm sure the six rubber boots that connect the throttle body to the fuel injector boots are firmly connected.

i have had an incidence where we 'blew' the throttle body apart due to unburnt fuel and no spark and finally one big spark caused the blow out...

i'll check all four of the clamps... two large in front and two smaller in behind...

hope that is it.

i did open up the DME ECU and found the resistor number 751/752 had some corrosion and that happens to correspond to pin numbers 51 and 52??? could that be possible coincidence only or the way it's set up.

If so, i will look for a spare dme to test and see if the issues are resolved. i will tighten up all clamps.

took the 964 for a long drive tonight and with the heater tubes connected (between header and hot air box - Not sure of the exact names) i was getting fumes coming into the car. my original header had this issue and now the spare that i purchased seems to also have the same issue.

also found some oil leaking (lots) so will have to take a closer look for the source.

engine is making lots of power with the cold air and fresh re seal / rebuild... but still far from correct.

Alex Sol

indy i'll continue to check for leaks in intake and thanks for the engine braking info.

rob interesting video of the afm...

Indycam

Sparks are hidden from the intake by closed valves , the intake and exhaust valves should be sealed when the spark happens . An intake backfire can point to an intake valve that is not sealed shut when it should be . If the cam timing is off , if the valve is leaking when seated , if a valve spring is broken , etc etc . A leaking intake valve can act as an intake system leak . An intake system leak that keeps the engine from braking .

Indycam

This also points to an intake leak . It sounds like the engine was running on air leaking in not via the throttle butterfly .

Alex Sol

Indy,

"Sparks are hidden from the intake by closed valves , the intake and exhaust valves should be sealed when the spark happens . An intake backfire can point to an intake valve that is not sealed shut when it should be . If the cam timing is off , if the valve is leaking when seated , if a valve spring is broken , etc etc . A leaking intake valve can act as an intake system leak . An intake system leak that keeps the engine from braking ."

wow, i had suspected a leaky valves from the my rebuild heads from a very decent porsche shop whos owner is a machinist of 30 years... i brought them back to have them inspected and had them inspected by another shop using the vacuum test..

tests showed the heads were not leaking and were properly sealed...

but still does not explain why i could hear (and feel) air coming out of intake and exhaust ports when leak testing...

Indycam

Tell me more about this ? What test ? How was it done ?

Alex Sol

with the motor still on the stand, and one spark plug out, we installed an air hose into the other spark plug hole, and put compressed air in at 100psi. leak down numbers on brand new rebuild showed figures of between 90 and 92 psi... and we could hear and feel a light breeze coming out:

1. intake
2. exhaust and intake
3. none
4. exhaust
5. exhaust
6. intake and exhaust

Alex Sol

we could also hear air coming out the piston/cylinders... on all six

Indycam

Did you rotate the crank between each test to close the valves for each cylinder before you tested that cylinder ?

Indycam

So whats going on with this ?
Any news ?

HiWind

let's hope no news is good news!

Alex Sol

sorry disappeared this weekend.

i was responding to a idle air control valve question and think i have my upside down....

would that cause a bunch of stuff to not work???

please confirm: arrow points to front or rear? metal clip is on top or bottom?

talk about dum!!!!

the leak down test was done rotating the 60 deg each time round.. and i think it was the sequence same as the firing order. so it could be an issue of the valves not correctly gapped... will be doing this once i put about 1,500 kms on it.. but that may be a little tough with a couple inches of snow on the ground this morning.

i finally broke down and dropped the 964 to local porsche specialist after trying the theo jenniskens tool over the weekend. didn't give much info and maybe because i was not using properly...

hope to find a simple fix...

Indycam

Please don't wait 1500 kms . The valves need to seal . Bad things happen when they don't .

Alex Sol

brought my 964 into local specialist who has worked on my car for last few years... checked:

compression - ok
valve gaps - right on
injectors - left side not running
spark plugs - left side wet from fuel
distributor - ok
idle air control valve - correct direction
air - even opened the throttle body looking for rag (left inadvertantly) found nothing
swapped in dme ecu no difference
we have fuel on both rails but it seems the fuel spray pattern is more liquid than mist and does not explain why the plugs are wet and at idle, pulling the injector connectors make no difference on left side bank of cylinders...
no fault codes
thought it might be - throttle switch but jumped the switch to bypass and makes not difference
have spark on both primary and secondary
wires are new
plugs are new (were new now fouled!!)
rotors new
caps are new
distributor belt is fine though secondary is off by about 5mm or perhaps one belt tooth??? otherwise acceptable according to my local porsche specialst

my only thought now... timing, ignition, computer not sending pulse to injector at the same time as spark is coming around... or there is one broken wire in the harness causing havoc or one ground that is not quite grounded.... my main harness is so old and stiff - $1600 for a new one...

also after more than 5 hours of diagnosis @ $100 / hr to confirm everything i've already done... banging head against the wall and... prior to motor drop 3 weeks ago... motor was not misfiring and seems to be purring like a kitten at idle... only thing i did was drop the motor/trans to repair the break in the housing by using aluminum weld to the cross shaft holder (i had forgot to replace the needle bearing and seals...)


somebody please... throw me a bone here!!!!!!