964 Keeps Stalling
05-26-2009, 01:17 AM
#1
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964 Keeps Stalling
It's a '91 964 C2 Cabrio. I was having great fun with the top down and enjoying the early summer sunshine, everything was so fine and I parked it away for a week or so ...... then since early this week, after the engine fired up after the first crank but then it suddenly stalled. From then on, it required a few cranks (5-6 times) to get the engine to rev up, and then it stalled again and again and even if I continue to press the gas pedal. 
Would it be simply a spark plug problem or something a lot serious? Any advice would be highly appreciated.
Thanks in advance.
Ken
Would it be simply a spark plug problem or something a lot serious? Any advice would be highly appreciated.
Thanks in advance.
Ken
05-26-2009, 01:26 AM
#2
Instructor
I'm having a bit of a similar problem....but mainly cold morning starts (not sub zero kind of cold.....8-10deg C), used to crank once, fire, idle and go beautifully, for the last 3 weeks - cranks fires stalls, about three times then stalls at the first set of lights as well, after that runs fine. Had a 20000km service about 3000 ago, so figure most stuff should have been done that needed doing, but wonder if it needs to go back for a tweak ?
05-26-2009, 03:56 AM
#4
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Thanks guys ... took it to my mechanic and he said the computer controller need to be replaced, and some of the wiring also .... wow, looks like I am in for a costly repair as will behard to fnd reliable used parts for these ...
05-26-2009, 06:43 AM
#5
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I would ask your mechanic, why he thinks it's the computer that has to be replaced. There are many electrical issues that can cause your problem, that are cheaper to solve. The brain alone runs $400.00-$500.00. He could swap one for a test, before replacing.
05-26-2009, 07:39 AM
#6
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I agree with getting a second opinion. If your mechanic did not check any of these items first, you should look for a new mechanic:
What are the active diagnostic codes?
What were the results of the fuel pressure and fuel leak-down tests?
How many miles since the engine was serviced?
Any contamination in the fuel?
When was cylinder compression last checked?
Compression in particular will point to a far more expensive problem, but at least you get there without spending money on parts you do not need. Hopefully your mechanic is tip-top, and will get you running at the lowest possible cost.
What are the active diagnostic codes?
What were the results of the fuel pressure and fuel leak-down tests?
How many miles since the engine was serviced?
Any contamination in the fuel?
When was cylinder compression last checked?
Compression in particular will point to a far more expensive problem, but at least you get there without spending money on parts you do not need. Hopefully your mechanic is tip-top, and will get you running at the lowest possible cost.
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05-26-2009, 09:50 PM
#9
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mmm I'm with newsboy... if the computer had failed, how could it run initially and then stall?
I had a stalling problem recently, which was caused by the ignition coils, but you haven't mentioned any other of the classic symptoms for ignition coils.
I'm sure the chaps here on the forum will help you track down the fault, they're very helpful, knowledgeable... and persistant.
Hope you sort it soon.
I had a stalling problem recently, which was caused by the ignition coils, but you haven't mentioned any other of the classic symptoms for ignition coils.
I'm sure the chaps here on the forum will help you track down the fault, they're very helpful, knowledgeable... and persistant.
Hope you sort it soon.
05-27-2009, 12:43 AM
#10
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I know mine does this from time to time cold and I assumed it was because of the LWF. It will stall and stall but if i Give it gas for a bit it will catch and if I hold the idle for a bit it will usually stay running. I do notice that once it catches I can start it up repeatedly with no issues afterwards.
05-27-2009, 12:44 AM
#11
The first question is always "What has changed lately". It sounds like there was no work done between the time the car ran well, and not at all.
To confirm, no oil added? No fiddling at all? Is this correct?
Has the shop run the Bosch 301 (Hammer) diagnostic tester on the car to read the codes or to perform any system checks? This is a must before throwing money at the problem; especially DME Control Unit kind of money. You can also do a fair bit of testing without the Hammer, but it's a bit more effort.
The Shop Manuals provide some diagnostic trouble shooting information for No Start, Hard Start and Erratic Idling. Your problem sounds like a Hard Start condition, as you've indicated that it did start, but won't hold an idle and then dies, even if you try to apply throttle.
The list of possible checks is long, but the Engine Temperature Sensor sounds like a likely thing to check (see below). Without this input the engine will be running lean or rich at cold start and will be difficult to keep running.
The DME relay can be flaky. It is fairly easy to remove and jumper the pins to test. I don't have the pin-outs handy, but will fetch them if no one chimes in.
The coils have also been failing on these (nearly) 20 year old cars of late. They are about $50 US each and are probably worth changing if you want to start throwing money at the problem rather than time and effort.
There is also a TSB (Tech Service Bulletin) regarding the AFM (Air flow meter) wire connector on the back of the AFM. The connector wire can receive interference from piping behind the air box. The solution is to tie back the wiring harness (see below).
There are checks, values and instructions in the Shop Manuals for each of the items listed below. If you want help with any particular one, or all of them, just ask.
Shop Manual Diagnositcs:
Good luck getting it sorted.
Cheers,
Dave
To confirm, no oil added? No fiddling at all? Is this correct?
Has the shop run the Bosch 301 (Hammer) diagnostic tester on the car to read the codes or to perform any system checks? This is a must before throwing money at the problem; especially DME Control Unit kind of money. You can also do a fair bit of testing without the Hammer, but it's a bit more effort.
The Shop Manuals provide some diagnostic trouble shooting information for No Start, Hard Start and Erratic Idling. Your problem sounds like a Hard Start condition, as you've indicated that it did start, but won't hold an idle and then dies, even if you try to apply throttle.
The list of possible checks is long, but the Engine Temperature Sensor sounds like a likely thing to check (see below). Without this input the engine will be running lean or rich at cold start and will be difficult to keep running.
The DME relay can be flaky. It is fairly easy to remove and jumper the pins to test. I don't have the pin-outs handy, but will fetch them if no one chimes in.
The coils have also been failing on these (nearly) 20 year old cars of late. They are about $50 US each and are probably worth changing if you want to start throwing money at the problem rather than time and effort.
There is also a TSB (Tech Service Bulletin) regarding the AFM (Air flow meter) wire connector on the back of the AFM. The connector wire can receive interference from piping behind the air box. The solution is to tie back the wiring harness (see below).
There are checks, values and instructions in the Shop Manuals for each of the items listed below. If you want help with any particular one, or all of them, just ask.
Shop Manual Diagnositcs:
Code:
Engine Will Not Start
supply voltage - turns over and did start so not likely
engine temp sensor - seems like a strong possible
dme plug test
connect ohmmeter test leads between terminals 45 and 30
0*C = 4.4 - 6.8 kOhm
15-30*C = 1.4 - 3.6 kOhm
40*C = 1.0 - 1.3 kOhm
80*C = 250 - 390 kOhm
100*C = 160 - 210 kOhm
break (infinit Ohm)
In the event of a break the system uses a fixed (warm) setting
which means there is no cold start enrichment and, therefore, cold
starting problems.
Short-circuit (0 Ohm)
In cold state, no engine pick-up, too lean, and engine stops.
No effect if engine is at operating temp.
test sensor plug
similar values as above
idle stability valve (ISV) - added any oil lately?
control unit faulty - turns over and did start so not likely
dme relay - try jumping this relay out
injectors - can be tested with hammer
fuel pressure - could be a fuel pump failure; does it start at all any more?
intake system leak - overnight? not likely unless wrenching done
ground and plug connections - could be
speed/reference mark sensor
ignition system and output stage - coils
Engine Hard to Start
idle speed contact (idle micro switch) - ground short or break
dme plug test
connect ohmmeter test leads between terminal 52 and 24
bridge ground to terminal 30
throttle closed <10 ohms
throttle open (> 1 degree) infinit ohms
throttle switch plug
connect ohmmetter test leads between terminals 1 and 2
throttle closed <10 ohms
throttle open (> 1 degree) infinit ohms
engine temp sensor
idle stability valve (ISV)
control unit faulty
dme relay
tank venting valve
injectors
fuel pressure
intake system leak
ground and plug connections
speed/reference mark sensor
ignition system and output stage
Erratic Idling
idle speed contact (idle micro switch) - ground short or break
engine temp sensor - seems like a possible
air flow meter (AFM) - TSB on AFM wire connector
TSB 9005 Engine, Inconsistent Performance
http://www.pcarworkshop.com/images/b/ba/24_x_1990_620590geolab.pdf
need wire tie on AFM wire connector to prevent contacting vent pipes
idle stability valve (ISV)
oxygen regulation stop
oxygen sensor signal
intake air temp sensor
control unit faulty - turns over and did start so not likely
dme relay - try jumping this relay out
tank venting valve
fuel pressure
intake system leak
ground and plug connections
ignition system and output stage - coils
Cheers,
Dave
05-27-2009, 01:00 AM
#12
My version of Adrian Streather's Enthusiasts Companion, pg 387 indicates that the DME jumper should connect relay sockets 3, 5 and 7, which corresponds to relay pins 30, 87 and 87b.
Although, I recall there was an errata on this pin-out and I'm not sure if my version of the text was before or after the update.
If someone could please chime in the with definitive pin-out I'd appreciate it.
Cheers
Although, I recall there was an errata on this pin-out and I'm not sure if my version of the text was before or after the update.
If someone could please chime in the with definitive pin-out I'd appreciate it.
Cheers
05-27-2009, 02:04 AM
#13
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I failed the dme /fuel pump relay and the emergency fix is simple. Your jumper connections are correct. Connect a jumper across 30, 87 and 87b together to bypass the relay.
I made a simple jumper wire with three correctly sized blade terminals and keep it in the glove box just in case I or someone else fails a relay on club runs or at the track.
I agree that it sounds like more troubleshooting is in order before repalcing an ECU and assorted wiring. Sounds like an expensive, shot int he dark, shotgun approach to me. Good luck.
I made a simple jumper wire with three correctly sized blade terminals and keep it in the glove box just in case I or someone else fails a relay on club runs or at the track.
I agree that it sounds like more troubleshooting is in order before repalcing an ECU and assorted wiring. Sounds like an expensive, shot int he dark, shotgun approach to me. Good luck.
06-01-2009, 08:30 PM
#14
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I am deeply impressed by this forum with so much valuable inputs from you folks. Thanks so much! 
My mechanic told me he made a quick swap with another car's ECU and the engine fired right away. So looks like he has correctly identified the cause is due to a faulty ECU. So far so good until he quoted me a rebuilt unit for $1800 and threw me off my chair. I called the official Porsche dealer and they quoted me the same also. I then searched the web and found a ECU specialist who can supply a rebuilt unit for $600 wih 5 yr warranty. Great! After couple of days waiting, the rebuilt unit arrived and when put into the car, it did not work as intended. It cranked and stalled repeatedly. So, I am in the process of getting yet another rebuilt unit from the same supplier and waiting ......
Regards,
Ken
My mechanic told me he made a quick swap with another car's ECU and the engine fired right away. So looks like he has correctly identified the cause is due to a faulty ECU. So far so good until he quoted me a rebuilt unit for $1800 and threw me off my chair. I called the official Porsche dealer and they quoted me the same also. I then searched the web and found a ECU specialist who can supply a rebuilt unit for $600 wih 5 yr warranty. Great! After couple of days waiting, the rebuilt unit arrived and when put into the car, it did not work as intended.
It cranked and stalled repeatedly. So, I am in the process of getting yet another rebuilt unit from the same supplier and waiting ......Regards,
Ken
06-02-2009, 01:45 PM
#15
OK - so with the rebuilt unit you just paid $600 for, your car had EXACTLY the same problem that it had with your original ECU?
That wouldn't convince me I needed another rebuilt unit - it would convince me that the ECU wasn't the problem and your mechanic has reached the wrong conclusion.
That wouldn't convince me I needed another rebuilt unit - it would convince me that the ECU wasn't the problem and your mechanic has reached the wrong conclusion.