Slow Starting 91 S2
#16
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This could be a design fault. Maybe the starter motor is underpowered as Porsche may have used the starter from the 2.5 engine. The starter is not rotating the engine fast enough. This can cause the start fuel/air mixture not to be perfect for a quick start. I remember reading that people have experience quicker starts if the car is jump started. Jump starting with a good battery can add about 2V to the battery voltage, which can be almost 20% extra power added to the starter. The extra voltage could also increase the power of the fuel pump, spark voltage and also alter some of the sensors output. All these could contribute to a quicker start.
But as the car starts predictably every time, it took me not more then 1 week to get used to the way it starts. View this as a S2 trademark and start enjoy the real S2 assets.
But as the car starts predictably every time, it took me not more then 1 week to get used to the way it starts. View this as a S2 trademark and start enjoy the real S2 assets.
#17
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My above post failed to mention that I have a 2.5 NA, and my starting is just as slow as everyone elses. There have been about three times where it started almost instantly, but that was just weird. I think this is just what any 944 does.
#18
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"This could be a design fault. Maybe the starter motor is underpowered as Porsche may have used the starter from the 2.5 engine. The starter is not rotating the engine fast enough." ![grr](https://rennlist.com/forums/graemlins/cussing.gif)
You own a Porsche and you basically insult them? How could you?
![grr](https://rennlist.com/forums/graemlins/cussing.gif)
You own a Porsche and you basically insult them? How could you?
![popcorn](https://rennlist.com/forums/images/smilies/popcorn.gif)
#19
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The fuel pump is turned on and off by the second DME relay. As soon as starter voltage is applied to the starter, pin 4 of the DME gets that voltage and causes pin 20 is driven to ground and the second DME relay is turned on. Inside the DME, either a bit from the computer " OR " 12 V applied to pin 4 will cause pin 20 to go to ground and turn on the second DME relay.
So as soon as the starter sees voltage, the fuel pumps starts working. After it is started, the DME holds the fuel pump ON. I do think it is true that if the RPM drop below some very low number and the ignition is on, the DME releases the second DME relay and the fuel pumps turns off.
I still like the finding the right relationship of cam vs crank timing before it can start. Crank turns 2x the cam after all.
So as soon as the starter sees voltage, the fuel pumps starts working. After it is started, the DME holds the fuel pump ON. I do think it is true that if the RPM drop below some very low number and the ignition is on, the DME releases the second DME relay and the fuel pumps turns off.
I still like the finding the right relationship of cam vs crank timing before it can start. Crank turns 2x the cam after all.
#20
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Checked the PET and it looks like the starter on S2 is likely to be the same as the one on the 2.5 (1.4KW) model. However they seem to have a more powerful starter (1.7KW) (20% more !!!) if you have option M198. I wonder if that option is common?
#21
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My S cranked longer than I thought it should (few seconds), especially when it was warmed up. New FPR fixed that 100% - now starts instantly every single time no exceptions. FPR was leaking down fuel pressure so it took a bit to rebuild pressure. Other symptoms for me were groaning fuel pump and fuel pressure >100psi. Any source of fuel pressure leak down might cause the leakdown I suppose.
I'd measure fuel pressure and leakdown to rule this out.
I'd measure fuel pressure and leakdown to rule this out.
#22
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I agree with Tom, Joe and the other S2 owners...My '91 is a 4 to 5 cranks-to-start car.
It's normal. When you have to worry is when it turns over so slow that it won't start....then it's time to (in the words of Sid V ) check your f-ing grounds, battery cables and if all else fails...replace the starter.
It's normal. When you have to worry is when it turns over so slow that it won't start....then it's time to (in the words of Sid V ) check your f-ing grounds, battery cables and if all else fails...replace the starter.
#23
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Same here 944T. I haven't heard any 944 start right up, they all crank a bit then fire up.
#25
Not the sharpest tool in the shed
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This is all very interesting. I think 'gtroth' may be on to something here regarding the FPR leaking down. It makes sense and perhaps there is somewhat of a design error that has been interpreted as a design feature ![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
It is impossible to think an erroneous benefit of faster starting is related to replacing the FPR. Nothing works better on a Porsche when there is an error involved.
I also like the line of thought regarding higher compression requires stronger starter.
There is just no example anywhere in the modern fuel injected automovtive universe where an engine turns over more than a couple of times before firing. Either something is not strong enough (starter), or holds/builds pressure fast enough (FPR/fuel pump) or there is a lack of juice (battery, poor ground/contacts). On other cars I have had this condition was related to the cold start sensor or something similar.
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
It is impossible to think an erroneous benefit of faster starting is related to replacing the FPR. Nothing works better on a Porsche when there is an error involved.
I also like the line of thought regarding higher compression requires stronger starter.
There is just no example anywhere in the modern fuel injected automovtive universe where an engine turns over more than a couple of times before firing. Either something is not strong enough (starter), or holds/builds pressure fast enough (FPR/fuel pump) or there is a lack of juice (battery, poor ground/contacts). On other cars I have had this condition was related to the cold start sensor or something similar.
#26
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I've had mine seven years and it's always taken 2-3 seconds to start. Very rarely it'll start very quickly (like this morning when it was 10 degrees outside) but the long start is a Porsche trait that you learn to love.
#27
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I was tuning a new MAF and had replaced the FPR with a new 3 bar and was monitoring the pressure so I could see the leak down rate which was quite slow. Still started after second or so. I also do believe the valve that stops fuel preasure leak down is valve next to the fuel pump.
#30
Racer