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Update: I have the newer two wire head temp sensor. We replaced it at the time of the rebuild so its new....My mechanic asked me if knew what 'new' meant...he informed me 'Never Ever Worked'. And so it is. The testing yielded an open circuit and hence a bad sensor. Can't wait to replace this with wire intact so as to preserve it's retainability for refund...
Could it be that the reason it starts cold is that the computer stipulates a rich start but that when (after a couple of minutes) it gets no signal from the head sensor, it shuts down sending signal to the injectors?
Actually, the value of the temp sensor is such that it always indicates a rich mixtures. So when the engine warms up, the mixture based on the temp sensor, is now too rich causing the engine to die.
__________________
Loren
Systems Consulting - Automotive Electronics
Specializing in Porsche cars http://www.systemsc.com/
yup classic CHT issue .. id be finding a new mechanic anyway as thats one of the easiest spots on a 3.2 engine. Runs to rich and chokes.. jumper leans it out. anybody who has a 3.2 should carry a paperclip in their toolkit..
Mine is fixed!! I had 2 problems....One of the wires was pulled out of the temp sensor plug but still inside the shrink wrap from long ago....That seems to have fixed the running lean issue and the stalling/hard start issue. As for my radio cutting out......it was a bad voltage regulator. I went ahead and swap the alternator to as it was a previously rebuilt model. All is well! Engine runs smooth and clean and i now have music!
Mine is fixed!! I had 2 problems....One of the wires was pulled out of the temp sensor plug but still inside the shrink wrap from long ago....That seems to have fixed the running lean issue and the stalling/hard start issue. As for my radio cutting out......it was a bad voltage regulator. I went ahead and swap the alternator to as it was a previously rebuilt model. All is well! Engine runs smooth and clean and i now have music!
actually i think you will find it was a running rich issue , but doesnt matter .. good fix on that regulator too, glad your radio cut out as the only other indication you would have had is the smell of sulpher as your battery boils over into your frunk and goes into the front pan.
actually i think you will find it was a running rich issue , but doesnt matter .. good fix on that regulator too, glad your radio cut out as the only other indication you would have had is the smell of sulpher as your battery boils over into your frunk and goes into the front pan.
You are correct....definitely rich! The radio thing was only every once in a while....some days i would drive 30-40 miles and the radio was fine.....others it would cut out constantly. We have a great sunny 80 degree weekend ahead of us....finally. I can test it all weekend!!
You are correct....definitely rich! The radio thing was only every once in a while....some days i would drive 30-40 miles and the radio was fine.....others it would cut out constantly. We have a great sunny 80 degree weekend ahead of us....finally. I can test it all weekend!!
from what i have read recently over voltage protection on radios has saved a lot of serious rust damage on the front suspension and body pan of 911s ....
those who know ... know ..
from what i have read recently over voltage protection on radios has saved a lot of serious rust damage on the front suspension and body pan of 911s ....
those who know ... know ..
Ok..a couple months later...Loren has had my DME and it's fine. I have removed all my 'new' injectors and had them tested and cleaned by Dr. Injector in Federal Way, WA. If I don't mess with it, I can start it quickly and it seems to run rich (black smoke) and surges at an idle of over 1000. When I test the Idle Switch by removing the connection, it does as prescribed, and slows down so much it stops. I plug the connection back together and it will NOT restart. I wait a few hours (or a day) and I can restart it with the same result.
I would like to try and adjust the idle speed adjustment screw in, as after having cleaned all the injectors and rebuilt the top end I assume that will need to be done. To do so, of course, the engine has to start... I have been told to bridge the test port "B" and "C" before adjusting the idle screw.
Ok..a couple months later...Loren has had my DME and it's fine. I have removed all my 'new' injectors and had them tested and cleaned by Dr. Injector in Federal Way, WA. If I don't mess with it, I can start it quickly and it seems to run rich (black smoke) and surges at an idle of over 1000.
Your problem is the black smoke (a very rich mixture) and unrelated to the idle switch (once it's open/disconnected it has NO effect)!
Originally Posted by vsurg
When I test the Idle Switch by removing the connection, it does as prescribed, and slows down so much it stops.
Then open (CCW) the idle screw on the throttle body. No need to try and get it set precisely at this time. Do the procedure when the engine runs correctly!!!!!
Originally Posted by vsurg
I plug the connection back together and it will NOT restart. I wait a few hours (or a day) and I can restart it with the same result.
It's flooded!
Originally Posted by vsurg
I would like to try and adjust the idle speed adjustment screw in, as after having cleaned all the injectors and rebuilt the top end I assume that will need to be done. To do so, of course, the engine has to start... I have been told to bridge the test port "B" and "C" before adjusting the idle screw.
Again, that comes later.
You checked the flow rate of your "new injectors" and compared them to original 911 3.2 injectors from another car, right?
Again, FP is 30 - 35 PSI, right? The temp sensor measures less than 200 ohms on pin 13 of the ECM at hot engine, right?
The spring tension on the AFM flap is correct, right?
1. I have the flow sheet from the injector diagnostic and clean out. Flow rate prior 57-63 cc . post: 64-64.5cc.
2. Fuel Pressure is between 30-35lbs
3. I need to check the temp sensor again but I can't get a hot engine until I can start it again. If the idle switch had nothing to do with this, then why won't it restart after removing it and replacing it. Just won't start...until probably tomorrow.
4. The flap on the AFM seems to have normal spring tension and we checked the resistance when opening which was within range.
5. I can open (counter clockwise) the idle screw but that seems counterintuitive as the idle is already over 1000 and running rich.
1. I have the flow sheet from the injector diagnostic and clean out. Flow rate prior 57-63 cc . post: 64-64.5cc.
2. Fuel Pressure is between 30-35lbs
3. I need to check the temp sensor again but I can't get a hot engine until I can start it again. If the idle switch had nothing to do with this, then why won't it restart after removing it and replacing it. Just won't start...until probably tomorrow.
4. The flap on the AFM seems to have normal spring tension and we checked the resistance when opening which was within range.
5. I can open (counter clockwise) the idle screw but that seems counterintuitive as the idle is already over 1000 and running rich.
Thanks for your patience on this.
SPM
Where's the flow number for an original 911 3.2 injector? Check for fuel leaks in the vacuum lines for the fuel pressure regulator & fuel damper.
Again, it's too rich!!!!
Then, if the idle is too high, turn the throttle body air screw CW. Again, don't use the idle adjustment procedure in the manual until the problems are solved.
1. We have discussed the mistake made in discarding the original injectors. They were not tested prior to that. Life tuition...Can't get 'em back.
2. I was able to get it to start this AM after 20-30secs of ignition on (engine usually starts right away). When it warmed up, it was surging between 700-1400 about. The smoke was white, not black. I messed with the throttle body air screw and it made not difference. After a few minutes, I pushed on the throttle mechanism and the engine died, not to restart.
3. I rechecked all the vacuum lines and they are as intact and normal as I can tell without a smoke test.
1. We have discussed the mistake made in discarding the original injectors. They were not tested prior to that. Life tuition...Can't get 'em back.
1. You need to eliminate the "new" injectors as the problem source. Find/borrow at least one known original injector you can compare with a flow test.
2. Open the AFM and tighten the spring.
3. Check ignition timing.
Time to find another 911 3.2 to switch parts with!
we did a oscilloscope assessment of all the major areas (AFM, Injectors, speed and position sensors) and found nothing out of spec. The injectors have been certified to be the original Bosch low resistance injectors and all are to spec. The fuel pressure is 30-35lbs (3 bar). I have inspected all the vacuum lines on the back of the engine and all are intact without apparent leaks (no smoke test yet).
It starts and surges with idle. When the throttle is manually depressed it runs, rough, but runs until you let it go back to idle and then it dies. I have fiddled with the throttle body screw without effect. The timing is in spec.
To reiterate: the whole top end was rebuilt with pistons cleaned, rings replaced, valve seats reground, spark plugs and wires new, injectors rebuilt and tested certified, Cylinder head temp sensor replaced (twice), speed and position sensors new). The car ran great before I rebuilt it (to deal with an oil burning problem at 175K).
Who does this?? When I find them... (resistor in Head Temp Sensor line)
After months of checking every knowing circuit, Fuel, Spark, Mass Airflow, Oscilloscope to it all and nothing, we went back to the most likely source, the Head Temp Sensor (symptoms: starts fine but within a minute is surging and then floods and can't restart for a couple hours). From terminal 13 at the DME to ground it was an open circuit. testing only beyond the connection in the engine compartment the resistance was in spec. We peeled back the rubber cover to the white clip and see a broken wire with a resistor attached to one wire! The hardest problems to fix are those created by someone else. Jumped the wire and it purrs like a tiger. Will replace the connector and wire tomorrow!!!!
03-31-2022, 11:54 PM
