993, stall on overrun
07-01-2004, 01:08 PM
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993, stall on overrun
First.. Yes I have checked the archives, and I am a bit of a loss.. here is the story.. I should also appologise for cross posting this in the 911 section, but it is a 993 issue as well as a 911SC one.
I have just brought a 911SC, which had a 993 engine fitted by JMAuto's in London a couple of years ago.
In short, its sending me nuts... it starts runs and idles just fine... but each time I come to a stop, especially after a hard long run, like the end of or leaving a motorway (interstate to our american brothers) the engine dies, unless I do a real balancing act with the throttle, clutch and brake (a bit like left foot braking, but more comical and more dangerous)
it always starts up again fine, without touching the throttle.
But even if I dip the clutch when driving in 5th gear (or most gears) I see the rev counter dip down to almost a stall, then the engine (normally but not always) recovers back to idle speed, sometimes it stalls, but if I rev the engine, it does the same thing again... re engage the clutch and off I go.
I have no other problems with the car or engine, but this small issue.
My local Porsche mechanic, Jon Mitchell, has seen the car, and has another car in, also an SC, also with a 993 engine conversion from JMAuto's with exactly the same problem (he says that all the conversions from them seem to be problem children!)... it seems on both of our cars, the idiots at JMAutos didnt wire in the diagnostic connectors and cut them out of the loom, even though both cars have engines and ECU's which support them... the other car is having the loom modified to sort this out, as Jon said its a lot easier to diagnose the problem and see if its something simple with the connectors wired in, and it would allow him to hook the car up to the computer and check everything out, and could save me money in the future.. Do I need this doing? I trust Jon 100%, but just wanted to check that he isnt being over the top.
Jon also said that it could be that I have a light weight flywheel and the engine isnt catching the more rapid drop in rpm soon enough.. whats the members thoughts on this? (I have read some posts which indicate it) He also mentioned that there are aftermarket chips to sort this out.
Anyone?!!! Please help before I rear end someone!!!
Is there anything that crops to mind which may cause this? I am panicing that its something serious or expensive! lol
I have just brought a 911SC, which had a 993 engine fitted by JMAuto's in London a couple of years ago.
In short, its sending me nuts... it starts runs and idles just fine... but each time I come to a stop, especially after a hard long run, like the end of or leaving a motorway (interstate to our american brothers) the engine dies, unless I do a real balancing act with the throttle, clutch and brake (a bit like left foot braking, but more comical and more dangerous)
it always starts up again fine, without touching the throttle.
But even if I dip the clutch when driving in 5th gear (or most gears) I see the rev counter dip down to almost a stall, then the engine (normally but not always) recovers back to idle speed, sometimes it stalls, but if I rev the engine, it does the same thing again... re engage the clutch and off I go.
I have no other problems with the car or engine, but this small issue.
My local Porsche mechanic, Jon Mitchell, has seen the car, and has another car in, also an SC, also with a 993 engine conversion from JMAuto's with exactly the same problem (he says that all the conversions from them seem to be problem children!)... it seems on both of our cars, the idiots at JMAutos didnt wire in the diagnostic connectors and cut them out of the loom, even though both cars have engines and ECU's which support them... the other car is having the loom modified to sort this out, as Jon said its a lot easier to diagnose the problem and see if its something simple with the connectors wired in, and it would allow him to hook the car up to the computer and check everything out, and could save me money in the future.. Do I need this doing? I trust Jon 100%, but just wanted to check that he isnt being over the top.
Jon also said that it could be that I have a light weight flywheel and the engine isnt catching the more rapid drop in rpm soon enough.. whats the members thoughts on this? (I have read some posts which indicate it) He also mentioned that there are aftermarket chips to sort this out.
Anyone?!!! Please help before I rear end someone!!!
Is there anything that crops to mind which may cause this? I am panicing that its something serious or expensive! lol
07-01-2004, 01:17 PM
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Its a 97 993 engine, with varioram.
I believe its a lightened flywheel (how do I check?) and it IS using the standard 915 gearbox (which I have a hunch means it must be using a light flywheel as I am not sure if there is a non light version for doing the conversion.
I know very little, please bear with me
)
I believe its a lightened flywheel (how do I check?) and it IS using the standard 915 gearbox (which I have a hunch means it must be using a light flywheel as I am not sure if there is a non light version for doing the conversion.
I know very little, please bear with me
)
07-04-2004, 02:45 PM
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Some more digging today. It turns out that my engine is a 1996, which I think is designed to have the varioram (m64/22) but the ecu I have is a pre-varioram ecu!
Steve at Rennsport systems (http://www.rennsportsystems.com) is being a real help... it seems whoever did the conversion on my car (JMAutos) made a real mess of it, even to the point of not fitting the correct ECU!! I just hope they got the loom right (the next thing I am going to check)
Steve seems quite convinced that its the wrong ECU which is causing the stalling.
I also seem to remember, that my car seemed to hessitate a little at some point above 4500 when at full throttle. I am begining to wonder if this was the variorams opening up (or not) and the ECU not doing its "special thing" because it was an ECU not designed for the car.... hmm... millions of theories are going through my head of the ramifications of the wrong ecu being in there and why that may cause the big problem of my stalling situation.
One of my theories (and give me all your ideas of my theory) is that the at high rpm (my problem was always at the end of a hard run especially), and full throttle, the variorams are opening, the fueling is messed up, knock sensors and lambda sensors are sending the ecu and running of the car into a tail spin, which means that when the car returns to idle it just does not know what the hell to do and ends up stalling. (just a theory)
The other theory is that after a run, the varioram having been open, the ecu fueling what a non varioram would be taking (which I guess is less fuel for less power and air breathed.), the valves are getting damned hot (lean condition) and thats causing the fuel on the return to idle to vapourise before it gets to the cylinders causing a lean idle and a stall.... (just another idea)
One things for sure.. it looks like I will be needing a new ECU and the old one will be up for sale to help cover the cost once its been tested as not halmed by the whole episode...
I just hope a replacement ECU will solve all this and bring me a car that runs... if its going to be still more problems, I can see the wife nailing my wallet to the wall where she can see it!
I had to tell her our 944 was a present for her when I brought it, just so she didnt complain about me buying yet more toys (but I tell ya what, it worked!! so far...)
Steve at Rennsport systems (http://www.rennsportsystems.com) is being a real help... it seems whoever did the conversion on my car (JMAutos) made a real mess of it, even to the point of not fitting the correct ECU!! I just hope they got the loom right (the next thing I am going to check)
Steve seems quite convinced that its the wrong ECU which is causing the stalling.
I also seem to remember, that my car seemed to hessitate a little at some point above 4500 when at full throttle. I am begining to wonder if this was the variorams opening up (or not) and the ECU not doing its "special thing" because it was an ECU not designed for the car.... hmm... millions of theories are going through my head of the ramifications of the wrong ecu being in there and why that may cause the big problem of my stalling situation.
One of my theories (and give me all your ideas of my theory) is that the at high rpm (my problem was always at the end of a hard run especially), and full throttle, the variorams are opening, the fueling is messed up, knock sensors and lambda sensors are sending the ecu and running of the car into a tail spin, which means that when the car returns to idle it just does not know what the hell to do and ends up stalling. (just a theory)
The other theory is that after a run, the varioram having been open, the ecu fueling what a non varioram would be taking (which I guess is less fuel for less power and air breathed.), the valves are getting damned hot (lean condition) and thats causing the fuel on the return to idle to vapourise before it gets to the cylinders causing a lean idle and a stall.... (just another idea)
One things for sure.. it looks like I will be needing a new ECU and the old one will be up for sale to help cover the cost once its been tested as not halmed by the whole episode...
I just hope a replacement ECU will solve all this and bring me a car that runs... if its going to be still more problems, I can see the wife nailing my wallet to the wall where she can see it!
I had to tell her our 944 was a present for her when I brought it, just so she didnt complain about me buying yet more toys (but I tell ya what, it worked!! so far...)
