Acceleration...or lack of
09-01-2001, 06:36 PM
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Acceleration...or lack of
My 1990 C4 runs fine except one problem,i get a hesitation before the car picks up and accelerates, it seems to happen at around 3000rpm whilst accelerating . It seems to happen most whilst going from 2nd to 3rd gear and is only for a second or so then all is fine. Does anyone have any idea as to the cause of the problem and where i should start to look??
09-02-2001, 02:05 AM
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Hi Iant,
Boris is right--you should verify your distributor belt is intact, if you haven't already.
See the recent thread "Poor Performance/Good Performance" for more information.
Boris is right--you should verify your distributor belt is intact, if you haven't already.
See the recent thread "Poor Performance/Good Performance" for more information.
09-03-2001, 08:54 AM
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I would love someone to explain to me how a broken secondary distributor belt can damage the engine. If one set of spark plugs is not working, the rotor of the secondary distributor is not turning so no spark is being generated so how can this damage the engine. I have heard it a couple of times now but when I ask for an explanation, nothing is forthcoming.
It will certainly affect performance, burn efficiency is reduced and starting takes longer but how do you damage the engine. For The Record, there are no such warnings or cautions on this subject from Porsche in any of their manuals,
Ciao,
Adrian
911C4
It will certainly affect performance, burn efficiency is reduced and starting takes longer but how do you damage the engine. For The Record, there are no such warnings or cautions on this subject from Porsche in any of their manuals,
Ciao,
Adrian
911C4
09-03-2001, 10:20 AM
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Adrian,
My understanding is that if someone is unlucky, when the secondary distributor rotor comes to a stop, it can stop at a plug contact and continually fire one plug. So in that one cylinder you end up with the worst detonation know to mankind. This in turn can burn a whole in the piston, wreck the valves, etc. One the other hand it is possible for the rotor to come to a stop b/w contacts with no ill effects at all. Hope this nevers happens to anyone.
My understanding is that if someone is unlucky, when the secondary distributor rotor comes to a stop, it can stop at a plug contact and continually fire one plug. So in that one cylinder you end up with the worst detonation know to mankind. This in turn can burn a whole in the piston, wreck the valves, etc. One the other hand it is possible for the rotor to come to a stop b/w contacts with no ill effects at all. Hope this nevers happens to anyone.
09-04-2001, 05:03 AM
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Dear Chris,
This is why two knock sensors are installed. They will detect this change in detonation, advise the DME accordingly which will immediately retard the timing by 6 degrees on the crankshaft and if this doesn´t work and the detonation improve then other protection devices are activated. Drops straight to idle I believe and the
The DME also monitors the ignition system.
There is sufficient protection built into the system design (Porsche would have had to deal with this on the drawing board) to avoid such destruction. The scenario you suggest is actually a fault tree analysis item which is carried out during the design stage. Been there, done that, bought that t-shirt.
Not in a race car. These protections are normally removed.
Ciao,
Adrian
911C4
PS: Nothing is perfect but mass destruction by the failure of a little rubber belt in a road car is not something I would worry about.
This is why two knock sensors are installed. They will detect this change in detonation, advise the DME accordingly which will immediately retard the timing by 6 degrees on the crankshaft and if this doesn´t work and the detonation improve then other protection devices are activated. Drops straight to idle I believe and the
The DME also monitors the ignition system.
There is sufficient protection built into the system design (Porsche would have had to deal with this on the drawing board) to avoid such destruction. The scenario you suggest is actually a fault tree analysis item which is carried out during the design stage. Been there, done that, bought that t-shirt.
Not in a race car. These protections are normally removed.
Ciao,
Adrian
911C4
PS: Nothing is perfect but mass destruction by the failure of a little rubber belt in a road car is not something I would worry about.
09-04-2001, 05:17 PM
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My guess is that with the high compression of these engines, detonation is sure to occur without the second spark.
Maybe JD or BG should have have something at the top of the 964 discussion page that sez "it's probably your distributor belt"
You guys have me all stressed about the condition of my drive belt, and I haven't even driven mine yet
http://www.vintagebus.com/3.6
Maybe JD or BG should have have something at the top of the 964 discussion page that sez "it's probably your distributor belt"
You guys have me all stressed about the condition of my drive belt, and I haven't even driven mine yet
http://www.vintagebus.com/3.6
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09-05-2001, 03:49 AM
#8
Adrian:
You're putting WAY TOO MUCH FAITH in the DME programmers. The DME program did not account for the busted distributor belt, hence the problem. HAD they accounted for this, the engine would (smartly) shut itself off or shut off signals going to the secondary distributor, but it doesn't. For those of us with the "check engine" lights, it apparently doesn't even send up a warning that something is wrong.
The problem with holes being blown in pistons occurs when a distributor belt breaks and the rotor stops close enough to one of the contacts in the distributor cap that only a single spark plug gets all the sparks that were intended to be distributed to all six spark plugs. This means that a single spark plug will be firing at the start of the intake stroke, during the compression stroke, firing when it's supposed to (which at this point is meaningless),during the exhaust stroke, and various points in between. The DME just gets confused and attempts to continually adjust everything, but if a computer program was never designed to handle an unexpected problem, it isn't going to fix it. Had the DME accounted for this problem in it's design stage it would have either put a warning light up and shut down all activity to the secondary distributor or just shut the engine down....it does neither....it's oblivious to the problem...it sees this as a fuel/air ratio problem and continually (and incorrectly) attempts to adjust it.
The typical scenario for holes being blown in pistons occurs under RACING conditions when the belt fails and the rotor settles on top of a contact. The typical, non-racing symptoms are a slight loss of power (which occurs when the rotor settles far enough away from any of the rotor contacts that no spark is ever generated on any of the secondary plugs) to the worst case, which I just described. If the typical non-racing driver encounters a worst case scenario, he usually gets a significant loss of power accompanied by backfiring and knocking. Most people have enough common sense to realize this is a problem and take the car to a shop before the problems get worse...but I suppose there are some out there who just blow it off...how I don't know!
As someone who programs DME-like equipment, I can SAFELY tell you that we can't account for problems that we aren't told about. If Bosch engineers were never told to account for a distributor malfunction from a broken belt, there will be no code in place to handle it. The CPU integrated with the DME is fairly simple by todays standards...keep in mind memory was a high priced item in 1991 and typical CPU speeds were on the order of MHz, NOT 100's of MHz. As such the DME can only function in what I refer to as a "linear" mode....it checks it's sensors, it compares the readings to the fuel maps, and then it makes adustments. It's simple and straight forward, and that was pretty much the norm for that time....no multi-cpu systems, no multi-tasking embedded OSes, no busses...just a simple "aim and shoot" program.
I'd be willing to bet 993 owners have a CPU that will cut the secondary off if a busted belt occurs. It takes time to realize problems exist, and in the case of the 964 this was likely years.
Bill Wagner
You're putting WAY TOO MUCH FAITH in the DME programmers. The DME program did not account for the busted distributor belt, hence the problem. HAD they accounted for this, the engine would (smartly) shut itself off or shut off signals going to the secondary distributor, but it doesn't. For those of us with the "check engine" lights, it apparently doesn't even send up a warning that something is wrong.
The problem with holes being blown in pistons occurs when a distributor belt breaks and the rotor stops close enough to one of the contacts in the distributor cap that only a single spark plug gets all the sparks that were intended to be distributed to all six spark plugs. This means that a single spark plug will be firing at the start of the intake stroke, during the compression stroke, firing when it's supposed to (which at this point is meaningless),during the exhaust stroke, and various points in between. The DME just gets confused and attempts to continually adjust everything, but if a computer program was never designed to handle an unexpected problem, it isn't going to fix it. Had the DME accounted for this problem in it's design stage it would have either put a warning light up and shut down all activity to the secondary distributor or just shut the engine down....it does neither....it's oblivious to the problem...it sees this as a fuel/air ratio problem and continually (and incorrectly) attempts to adjust it.
The typical scenario for holes being blown in pistons occurs under RACING conditions when the belt fails and the rotor settles on top of a contact. The typical, non-racing symptoms are a slight loss of power (which occurs when the rotor settles far enough away from any of the rotor contacts that no spark is ever generated on any of the secondary plugs) to the worst case, which I just described. If the typical non-racing driver encounters a worst case scenario, he usually gets a significant loss of power accompanied by backfiring and knocking. Most people have enough common sense to realize this is a problem and take the car to a shop before the problems get worse...but I suppose there are some out there who just blow it off...how I don't know!
As someone who programs DME-like equipment, I can SAFELY tell you that we can't account for problems that we aren't told about. If Bosch engineers were never told to account for a distributor malfunction from a broken belt, there will be no code in place to handle it. The CPU integrated with the DME is fairly simple by todays standards...keep in mind memory was a high priced item in 1991 and typical CPU speeds were on the order of MHz, NOT 100's of MHz. As such the DME can only function in what I refer to as a "linear" mode....it checks it's sensors, it compares the readings to the fuel maps, and then it makes adustments. It's simple and straight forward, and that was pretty much the norm for that time....no multi-cpu systems, no multi-tasking embedded OSes, no busses...just a simple "aim and shoot" program.
I'd be willing to bet 993 owners have a CPU that will cut the secondary off if a busted belt occurs. It takes time to realize problems exist, and in the case of the 964 this was likely years.
Bill Wagner
09-05-2001, 04:15 AM
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Dear Bill,
This is the type of conversation that I am not entering into.
My original statement stands. Show me the evidence please.
By the way. I happen to have a lot of faith in these people. I have worked with them,
Ciao,
Adrian
This is the type of conversation that I am not entering into.
My original statement stands. Show me the evidence please.
By the way. I happen to have a lot of faith in these people. I have worked with them,
Ciao,
Adrian
09-05-2001, 09:07 AM
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Okay Guys, now I know how the system works I am very confident in saying, the myth about a broken secondary distributor belt destroying your engine if the secondary rotor stops at a specific contact, 1 thru 6 is "Not True".
The spark plug according to the documentation I have just found and read, can basically fire at any time. In some autos they have the spark plugs firing in the exhaust stroke as well. It is a waste of energy that is all. If the affected secondary spark plug is actually sparking in the ignition stoke before the primary one, that is, too early, the knock sensor will pick this up and retard the timing of the spark to that cylinder.
The purpose of the knock sensors is to protect the engine against pre-ignition if it occurs.
The Hall Effect Sensor is monitoring piston position so the DME knows where each piston is, all the time and only if the spark plug which is constantly firing causes pre-ignition will any timing retard action take place. Sparking during the other three stroke action does nothing which causes any problems. The second spark plug is supposed to fire slightly behind the first to aid in combustion. The worst problem this can cause is pre-ignition on the one cylinder affected. This will not cause the destruction of the engine. It is obviously not good in the long term but not a threat. In my research in the past few hours I have found that a slipping belt is more of a potential cause of problems than a broken one.
The literature on this subject is found on the web. I just used the search words "Bosch Dual Ignition",
Ciao,
Adrian.
911C4
The spark plug according to the documentation I have just found and read, can basically fire at any time. In some autos they have the spark plugs firing in the exhaust stroke as well. It is a waste of energy that is all. If the affected secondary spark plug is actually sparking in the ignition stoke before the primary one, that is, too early, the knock sensor will pick this up and retard the timing of the spark to that cylinder.
The purpose of the knock sensors is to protect the engine against pre-ignition if it occurs.
The Hall Effect Sensor is monitoring piston position so the DME knows where each piston is, all the time and only if the spark plug which is constantly firing causes pre-ignition will any timing retard action take place. Sparking during the other three stroke action does nothing which causes any problems. The second spark plug is supposed to fire slightly behind the first to aid in combustion. The worst problem this can cause is pre-ignition on the one cylinder affected. This will not cause the destruction of the engine. It is obviously not good in the long term but not a threat. In my research in the past few hours I have found that a slipping belt is more of a potential cause of problems than a broken one.
The literature on this subject is found on the web. I just used the search words "Bosch Dual Ignition",
Ciao,
Adrian.
911C4
09-05-2001, 05:49 PM
#11
Adrian:
It took me about 3 minutes to find the following link:
http://www.titanic.co.uk/FAQs/FAQ02_...DriveBelt.html
Here's another link from a current discussion. Please note what Roland Kunz says about the failures:
http://www.pelicanparts.com/ultimate...ML/000006.html
I think you're incorrect. Bruce Anderson and another writer for Panorama have both seen the "hole in the piston". One of the mechanics in our local area warns us about "knocking, backfiring, and severe loss of power" being symptoms of a busted belt. You can only retard timing so far. If the DME sees the position of the pistons as being in a location that doesn't make sense to it, it probably doesn't analyze it. If it did, these problems would not happen AT ALL! If the cylinder is on the intake stroke and its sucking in fuel and air and a spark fires, what happens? If things worked as you say they did, then when the belt broke, the DME would "magically" adjust things so there was no engine knock, and yet many have reported severe engine knock and loss of power when this occurs. It is IMPOSSIBLE for the DME to do this without completely shutting the spark off to the secondary distributor, which it DOES NOT DO!!
All you need to do is search any of the many Porsche sites available to find this out. I'm not wasting any more time on it.
Bill Wagner
It took me about 3 minutes to find the following link:
http://www.titanic.co.uk/FAQs/FAQ02_...DriveBelt.html
Here's another link from a current discussion. Please note what Roland Kunz says about the failures:
http://www.pelicanparts.com/ultimate...ML/000006.html
I think you're incorrect. Bruce Anderson and another writer for Panorama have both seen the "hole in the piston". One of the mechanics in our local area warns us about "knocking, backfiring, and severe loss of power" being symptoms of a busted belt. You can only retard timing so far. If the DME sees the position of the pistons as being in a location that doesn't make sense to it, it probably doesn't analyze it. If it did, these problems would not happen AT ALL! If the cylinder is on the intake stroke and its sucking in fuel and air and a spark fires, what happens? If things worked as you say they did, then when the belt broke, the DME would "magically" adjust things so there was no engine knock, and yet many have reported severe engine knock and loss of power when this occurs. It is IMPOSSIBLE for the DME to do this without completely shutting the spark off to the secondary distributor, which it DOES NOT DO!!
All you need to do is search any of the many Porsche sites available to find this out. I'm not wasting any more time on it.
Bill Wagner
09-06-2001, 05:00 AM
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Dear Bill,
Too many probables, to many assumptions and not one word of fact. Just your opinions on how something might work. Second hand stories. Not one spec of evidence. Just words. People creating stories making the 964 look fragile and weak and subject to blowing up. Another myth to add to the endless created ones against the 964 by people in these forums. One rubber belt breaks in a secondary system and now we have holes in pistons.
I deal with the facts. If the facts prove that this rubber belt can cause the destruction of an engine then so be it but nobody has proven anything. Just written thousands of unsupported words.
I will continue to research the rather elusive internal workings of the 2.1 DME and see what it does.
I have read all the Porsche data (written by Porsche) and there are no cautions, warnings or any other form of indication that this rubber belt can destroy the engine. Unless of course this is an X-files conspiracy.
This subject is closed for now. When I have the full operation of the system down on paper I will reopen the debate. In the mean time I would be interested to know how many people across the world have blown holes in their pistons, left their engines across the road etc, caused by this rubber belt breaking.
Also all the 964 owners who had broken belts and never felt any problems.
One last point. I found some data on power losses. It is "claimed" in dyno tests that up to 10% loss of HP is caused by the secondary system going off line.
Ciao,
Adrian
911C4
Too many probables, to many assumptions and not one word of fact. Just your opinions on how something might work. Second hand stories. Not one spec of evidence. Just words. People creating stories making the 964 look fragile and weak and subject to blowing up. Another myth to add to the endless created ones against the 964 by people in these forums. One rubber belt breaks in a secondary system and now we have holes in pistons.
I deal with the facts. If the facts prove that this rubber belt can cause the destruction of an engine then so be it but nobody has proven anything. Just written thousands of unsupported words.
I will continue to research the rather elusive internal workings of the 2.1 DME and see what it does.
I have read all the Porsche data (written by Porsche) and there are no cautions, warnings or any other form of indication that this rubber belt can destroy the engine. Unless of course this is an X-files conspiracy.
This subject is closed for now. When I have the full operation of the system down on paper I will reopen the debate. In the mean time I would be interested to know how many people across the world have blown holes in their pistons, left their engines across the road etc, caused by this rubber belt breaking.
Also all the 964 owners who had broken belts and never felt any problems.
One last point. I found some data on power losses. It is "claimed" in dyno tests that up to 10% loss of HP is caused by the secondary system going off line.
Ciao,
Adrian
911C4
09-07-2001, 04:30 AM
#13
Adrian:
I stand by my original statements.
I found out about the "holes being blown in the pistons" almost two years ago when I first started looking into buy a Porsche. Through some research, I ran into an individual who was at a DE event in California. If I recall correctly, Bruce Anderson was also at that event. It's been a while, but if I recall this story, the driver was pushing the car to about 130MPH+ when all of a sudden he heard one bang followed by a severe lack of power, smoke, and then even more noise. Needless to say, he took the car off the track. A detailed evaluation of the engine revealed that a hole was indeed blown in one piston. Further checks indicated that the distributor belt broke, and not only did it break but it apparently wrapped itself around the secondary shaft in such a way that it locked the rotor ON TOP of a single contact in the distributor. This was apparently the basis for Bruce Anderson's comments about holes being blown in pistons. I remember this VERY CLEARLY for one reason and one reason only: I made the comment to the owner of the car that he was indirectly "famous...but not for a very good reason". Bruce Anderson apparently followed up on this event and this is the basis for his claim.
Is his claim a "freak" occurance? Probably. But the potential exists. In this country, if you published a book on a car and openly stated that "this type of problem can't happen", some people will take it to mean "it won't happen". If you tell people it won't happen, then when their car starts exhibiting problems that are related to a BAD case of secondary distributor lock up (moderate to severe knocking), they may very well just ignore them. When things get worse as time passes, I can just see these people contacting lawyers and pointing at your book and saying "he wrote that this wouldn't happen". Do you have legal insurance, or is your potential publisher prepared to pay for a lot of major engine overhauls?
I have no data on failure rates and associated symptoms (and I'm not going to obtain any), I only rely on my memory. Most people report either no obvious symptoms (and are often surprised to find their belt has broken) or report anything from mild to severe knocking, at which point they take the car in for repair. Never the less, if the possibility exists, it shouldn't be dismissed.
I recommend that you contact the person I identified in my previous post. I would hardly consider what he's posting as being, as you put it, "Second hand stories. Not one spec of evidence". Perhaps you can tell him that what happened to him really didn't happen.
Remember the old saying "If a tree falls in the forest and no one is there to hear it does it make a sound"? In your case, this statement should be modified to be "If a tree falls in the forest and I wasn't there to see it, then the tree never fell down".
Might I add, I found the response you just offered to my post to be EXTREMELY insulting, in case you can't figure that out!!!!!!!!!!!!!
I stand by my original statements.
I found out about the "holes being blown in the pistons" almost two years ago when I first started looking into buy a Porsche. Through some research, I ran into an individual who was at a DE event in California. If I recall correctly, Bruce Anderson was also at that event. It's been a while, but if I recall this story, the driver was pushing the car to about 130MPH+ when all of a sudden he heard one bang followed by a severe lack of power, smoke, and then even more noise. Needless to say, he took the car off the track. A detailed evaluation of the engine revealed that a hole was indeed blown in one piston. Further checks indicated that the distributor belt broke, and not only did it break but it apparently wrapped itself around the secondary shaft in such a way that it locked the rotor ON TOP of a single contact in the distributor. This was apparently the basis for Bruce Anderson's comments about holes being blown in pistons. I remember this VERY CLEARLY for one reason and one reason only: I made the comment to the owner of the car that he was indirectly "famous...but not for a very good reason". Bruce Anderson apparently followed up on this event and this is the basis for his claim.
Is his claim a "freak" occurance? Probably. But the potential exists. In this country, if you published a book on a car and openly stated that "this type of problem can't happen", some people will take it to mean "it won't happen". If you tell people it won't happen, then when their car starts exhibiting problems that are related to a BAD case of secondary distributor lock up (moderate to severe knocking), they may very well just ignore them. When things get worse as time passes, I can just see these people contacting lawyers and pointing at your book and saying "he wrote that this wouldn't happen". Do you have legal insurance, or is your potential publisher prepared to pay for a lot of major engine overhauls?
I have no data on failure rates and associated symptoms (and I'm not going to obtain any), I only rely on my memory. Most people report either no obvious symptoms (and are often surprised to find their belt has broken) or report anything from mild to severe knocking, at which point they take the car in for repair. Never the less, if the possibility exists, it shouldn't be dismissed.
I recommend that you contact the person I identified in my previous post. I would hardly consider what he's posting as being, as you put it, "Second hand stories. Not one spec of evidence". Perhaps you can tell him that what happened to him really didn't happen.
Remember the old saying "If a tree falls in the forest and no one is there to hear it does it make a sound"? In your case, this statement should be modified to be "If a tree falls in the forest and I wasn't there to see it, then the tree never fell down".
Might I add, I found the response you just offered to my post to be EXTREMELY insulting, in case you can't figure that out!!!!!!!!!!!!!
09-07-2001, 05:04 AM
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Dear Bill,
I will find the data. I am in contact with people who know about such things, here in Europe and in the USA.
When I have a true and complete story for the average 964 road going users I will certainly post it all, warts and all. I have no intention of looking at racing events. I am only interested in the affects of this problem and how to deal with it on road going 964s. The people who use these lists for advice are generally ordinary people and not race goers.
I am sorry that you feel insulted. I call it spirited argument which seeks to find the truth among the opinions. These discussions arguments often lead to the truth or as close as one can get. Every day I get into my 964 I have the potential to die. I like to separate potential from likely and certain.
Your laws do not apply to me. I am protected by Swiss law. It will be my intention to tell the truth and what we discuss on these forums helps me to get to that truth. Certainly motivates me to find the truth.
Ciao and have a great weekend,
Adrian.
911C4
I will find the data. I am in contact with people who know about such things, here in Europe and in the USA.
When I have a true and complete story for the average 964 road going users I will certainly post it all, warts and all. I have no intention of looking at racing events. I am only interested in the affects of this problem and how to deal with it on road going 964s. The people who use these lists for advice are generally ordinary people and not race goers.
I am sorry that you feel insulted. I call it spirited argument which seeks to find the truth among the opinions. These discussions arguments often lead to the truth or as close as one can get. Every day I get into my 964 I have the potential to die. I like to separate potential from likely and certain.
Your laws do not apply to me. I am protected by Swiss law. It will be my intention to tell the truth and what we discuss on these forums helps me to get to that truth. Certainly motivates me to find the truth.
Ciao and have a great weekend,
Adrian.
911C4
11-05-2001, 11:09 PM
#15
I recently pruchased a 1992 c2. according to the maintenance records this car had the distributor belt changed about 8000 miles ago. Since aquiring the car I have read many stories about what can happen it the belt breaks and how to identify it if it does indeed break. I don't know anything about the laws in Switzerland as compared to the liabitlity laws in the States. I for one put this into the realm of routine maintenance. For the price of the ventilation mod. around $15.00 American if self installed..which is less than the cost of an oil change..I'll install it..as part of my routine maintenance program. After all is preventative maintenance just that?...preventative? I do belive the vent mod has a Porsche part number?