Unsure if the surging is MFI or Distributor related
 

ang,

More stuff with my car.

I had alot of work done on straightening out the car last year. Now it is a real dream to drive. Only issue now is the stumbling, starting about 1500 rpm. Much of the time the motor stumbles to 3000 or 3500, sometimes it stumbles to 2000 or 2500 rpm and rarely, it runs like a r.... ape from 1500 to 7000.

It sounds like a fuel cross over problem with the upper fuel rack not quite delivering sufficient fuel. All of the electrical bits have been changed.

Could it be a distributor problem as the car has the original distributor. Don't know if it has an advance or not.

The fuel system should be set. The distributor has all new stuff in it. A mate said the distributor needed some work, but will a distributor that is off cause shuttering?

Ideas?

dom
_________________
domtoni
1969 911E

I'll assume you have points/condenser (in your distributor) Are the points new? are they properly gapped? Have you used a dwell meter to check the point dwell while the engine is running?

This is a good place to start. Anytime there is a persistant performance or tuning problem always start with the primary ignition first. Think of this system as the foundation of your tuning.........because it is like the foundation of a building

Using a dwell meter will tell you if there is a problem with the primary ignition. If the point gap is off or the condenser is bad or the distibutor shaft is worn it will show up as you increase rpm

Thanks Asphaltgambler,

The car was set up by a good local shop last year. All of the parts were new, and the car has done 500 miles since then.

The timing was set to the book. one of my friends got the car running after its 15 year storage experience said the timing may need to be moved (can't remember if he said more or less advance) from the stock setting. My friend also said that the distributor was not right. I think the springs / weights were not in good order after the car came out of storage.

I paid the second guy to do the job. The distributor did not have a rebuild. Just unsure if the surging is fuel or electrical related.

I appreciate your response and will use it when I chase him down.

Best
Dom

Check out this thread about distributor maintenance. These dizzys are 30 years and older so I bet only a handfull have had this done.

I would start with this and if it made no difference you would have a "known baseline" for future reference.

http://forums.pelicanparts.com/showthread.php?s=&threadid=5432&highlight=distribu tor+lube

Don,

Just put some Remmington gun oil in the center of the shaft and the car started immediatly with a vengance. Too wet today to drive, but maybe I will take it out later once it dries a bit.

Best
Dom

Just got back from a 40 mile drive. Car is much better. The oil did not not totally eliminate the shuddering, but that is probably down to timing (old car may not need to be at book specs) or the need for a distributor rebuild.

Thanks all for your kind assistance.

Best
Dom

Dom,

“Britts and Yanks are separated by a common language.” HeHe. :D

Lets define some terms:

Surging typically occurs at constant throttle position and road speed. It isn’t unusual for MFI to surge in 2nd gear holding speed with light throttle at 2500 to 4000 rpm. The surge feels as if the engine is “hunting power” where the power is changing (surging up and down) without any input from you. This is commonly a (lean) mixture problem but not necessarily from pump adjustment. It can be from worn throttle bodies, incorrect correlation, defective MFI injection nozzles, leaking cold start and many more.

Stumbling usually refers to the situation where you increase throttle position and the engine doesn’t respond with increased power. In severe cases the engine will reduce power as you increase throttle position. This is usually transitional and after a stumble or two the power picks up. Again this can be a mixture issue as above. It can also be an ignition arcing problem or other.


Please stay on the conservative side of the ignition timing. With a two-liter engine and today’s petrol, damaging detonation can occur if the timing is advanced above spec. A ’69 911E is specified to be 30° total advance at 6000 rpm. The permitted adjustment range is 29° - 31°. With pump petrol, I would stay to the low side.

The best way to service your distributor is to run it off the engine on a distributor machine. Find an “auto electric” shop with one of these machines. This will allow you to have an accurate chart of the actual advance curve and compare it to the factory curve. You will know the relationship between static timing and the advance at 3000 distributor rpm (distributors turn half engine speed).

You also want to see if the advance mechanism “hangs up” in more advance as you slowly reduce the rpm. There are several other common faults that can show up. Most are covered in other Pelican threads. For example a Bosch distributor is specified as 38° ± 3° dwell. If the dwell varies during a run by anywhere close to that much, the distributor shaft bearings (bushings) are probably worn.

Do you have a rev-limit rotor installed? Try a non-limiting rotor as a test.

Is your distributor clamp in good condition? You should not be able to turn the distributor when the clamp is tight.

Remember to set the engine at TDC #1 cylinder before removing the distributor.


I assume you have the original 3-pin Bosch CD ignition box. That is a good CD but one of its shortcomings is the very short duration spark. Under some conditions (usually lean), the short spark causes surging. A “fatter” (longer duration) spark will cure that. As a test you can change the transformer to a coil and use a points, condenser, ballast resistor, coil Kettering ignition. That has a very “fat” spark but no where near as fast rise-time. Only good for a test.

What do your sparkplugs look like? Do they seem to be the correct heat range for your E and use? Any signs of oil fowling? Does the average mixture seem correct?

You said the ignition parts are new. That means new cap, rotor, wires and plug connectors. Are the wires in their rubber holders? Are the wire connections at the cap and plug connectors proper?

Notice I haven’t said anything about the mixture. Before you touch the MFI, go back through all the CMA steps again. This is best done after some “spirited driving” :cool: with the engine basically running correctly (so it doesn’t injure itself). This will blow out the cobwebs and let you get accurate readings and set the valves properly.

How many miles since you put it back in service?

Best,
Grady SmileWavy

Grady,
My gut feeling is the distributor needs a rebuild. Below are my responses to you.

“Britts and Yanks are separated by a common language.” HeHe.
- Sorry if I break your image, but I am a Yank with an Italian passport. I either have the good or the bad fortune to live in the UK.

Lets define some terms:

Surging typically occurs at constant throttle position and road speed. It isn’t unusual for MFI to surge in 2nd gear holding speed with light throttle at 2500 to 4000 rpm. The surge feels as if the engine is “hunting power” where the power is changing (surging up and down) without any input from you. This is commonly a (lean) mixture problem but not necessarily from pump adjustment. It can be from worn throttle bodies, incorrect correlation, defective MFI injection nozzles, leaking cold start and many more.
- The surging is coming at roughly half throttle accelerating from 1500 to 3000 rpm and sometimes to 3500. As I put some oil into the distributor center shaft, reference in the pelican link shown above, the surging reduced and the car performed much better. A term better is bucking, not surging. After 3000 or so RPM, the power increases much better. With higher octane fuel, ie 99 octane, the car runs better.
The car bucks under acceleration. Constant throttle, the car runs smooth. Idle is dead nuts on 1000 rpm.

Stumbling usually refers to the situation where you increase throttle position and the engine doesn’t respond with increased power. In severe cases the engine will reduce power as you increase throttle position.
- This happened only in 5th gear below 2000 rpm. In 2nd or 3rd, the power picked up but it bucked. Once over 3000, the bucking stopped.

This is usually transitional and after a stumble or two the power picks up. Again this can be a mixture issue as above. It can also be an ignition arcing problem or other.
- I am aware that the cross over takes place in this period (from what I learned last autumn). I think the mixture, as read on the exhaust gas analyzer, is accurate, and within tolerance.

Please stay on the conservative side of the ignition timing. With a two-liter engine and today’s petrol, damaging detonation can occur if the timing is advanced above spec. A ’69 911E is specified to be 30° total advance at 6000 rpm. The permitted adjustment range is 29° - 31°. With pump petrol, I would stay to the low side.
- As noted, I paid a local shop to do this job. He has the records. The guy was one of the race mechanics on the LeMans 934 raced in 1975 as sponsored by Harley Davidson, and Swinford Motors. The car is now for sale by Manfred Freisinger in Germany.

The best way to service your distributor is to run it off the engine on a distributor machine. Find an “auto electric” shop with one of these machines. This will allow you to have an accurate chart of the actual advance curve and compare it to the factory curve. You will know the relationship between static timing and the advance at 3000 distributor rpm (distributors turn half engine speed).
- A good local shop is available. I will give them a call.

You also want to see if the advance mechanism “hangs up” in more advance as you slowly reduce the rpm. There are several other common faults that can show up. Most are covered in other Pelican threads. For example a Bosch distributor is specified as 38° ± 3° dwell. If the dwell varies during a run by anywhere close to that much, the distributor shaft bearings (bushings) are probably worn.
- Not sure if the bushings are worn, but after 38 years, I would not be surprised.

Do you have a rev-limit rotor installed? Try a non-limiting rotor as a test.
- Yes, rev limiter is installed.

Is your distributor clamp in good condition? You should not be able to turn the distributor when the clamp is tight.
- Don't know, but I think so.

Remember to set the engine at TDC #1 cylinder before removing the distributor.
- Thanks

I assume you have the original 3-pin Bosch CD ignition box. That is a good CD but one of its shortcomings is the very short duration spark. Under some conditions (usually lean), the short spark causes surging. A “fatter” (longer duration) spark will cure that. As a test you can change the transformer to a coil and use a points, condenser, ballast resistor, coil Kettering ignition. That has a very “fat” spark but no where near as fast rise-time. Only good for a test.
- CD unit was replaced in 1975 and has 15000 miles on it. It still sings, so it should be good.

What do your sparkplugs look like?
- Plugs were replaced last autumn with 500 miles.
Do they seem to be the correct heat range for your E and use?
- Should be correct and are platnium.
Any signs of oil fowling?
- I have not seen the plugs, but I don't think so.
Does the average mixture seem correct? Yes

You said the ignition parts are new. That means new cap, rotor, wires and plug connectors. Are the wires in their rubber holders? Are the wire connections at the cap and plug connectors proper?
- should be correct, and all are new.

Notice I haven’t said anything about the mixture. Before you touch the MFI, go back through all the CMA steps again. This is best done after some “spirited driving” with the engine basically running correctly (so it doesn’t injure itself). This will blow out the cobwebs and let you get accurate readings and set the valves properly.
- As noted, the mixture should be within tolerance.

How many miles since you put it back in service?
- 500 to 1000 since the first work was done.

Any further comments please ?

Thanks Again !!

Best,
Dom

Dom,

I’m concerned that you can notice that the car runs better
with 99 octane petrol. The only reason you could notice a
difference is if there is detonation with the lower octane.
Detonation doesn’t have to be an audible “knock” to
reduce power and do damage. Insidious inaudible
detonation can damage the pistons, top rings, and rod
bearings. Check the ignition timing and set to 29°.
Compare 99 octane again and see if there is still a
difference. If so, you should use the higher octane all
the time.

I'm begenning to think the bucking is a combination of
detonation, too low octane, too low rpm, too much
throttle (for the rpm) and possibly too much ignition
advance in the 2000 - 3500 rpm range.

Don’t let this happen to you:
http://forums.pelicanparts.com/uploa...1148951185.jpg


This is a 2.0T piston with detonation having knocked a
hole in it. It has lower compression ratio than your 2.0E
pistons.

You should get the distributor squared away, put in all
99 octane and drive a full tank or two of fuel with “spirited”
driving. Include extended highway driving. Keep track of
your fuel and oil consumption as accurately as you can.

You should consider 3000 rpm as a minimum rpm in all
gears except 1st. The “bucking” you feel may be
detonation. This is where you need to know the actual
advance at every 500 rpm. You need to know what the
distributor has been doing before you rebuild it.

Your 2.0E will like running between 3500 and 5000 all the
time. Yes it sounds busy but it will run best there. Part
of the problem is the 911E cams are pretty wild for 2000
rpm. This isn’t like a CIS 911. I wouldn’t give it 25%
throttle until 3500 and full throttle only above 4000 rpm.
Squeeze it on.

You may find you want to use inexpensive sparkplugs during
this testing, tuning and break-in period. NGK BP7ES (hotter),
BP8ES (cooler) or BP9ES (usually too cold for the street) are
suitable for 15% cost of Bosch Platinum. You can put the
good platinum back in later. 911s are particular about
sparkplugs. Porsche’s recommendations are a “cover all
bases” average. You may find a Champion, Autolite, NGK
or other that works best.

Best,
Grady

Dom,

Grady, Just went out for a 25 mile blast up the same shake down road that I used last night, but cut the trip a bit short due to traffic. Couple of points:
- IPreviously, I drove the car as if it was a modern vehicle, and it is not.
- I remember from my youth that 911s should be driven over 2000 rpm. Never thought that power should be squeezed on to 3000 rpm before giving it the full throttle.
- see further comments below
- I learned alot by this post !!!

Thanks

I’m concerned that you can notice that the car runs better
with 99 octane petrol. The only reason you could notice a
difference is if there is detonation with the lower octane.
Detonation doesn’t have to be an audible “knock” to
reduce power and do damage. Insidious inaudible
detonation can damage the pistons, top rings, and rod
bearings. Check the ignition timing and set to 29°.
Compare 99 octane again and see if there is still a
difference. If so, you should use the higher octane all
the time.
- The car ran noticably smoother with the 99 octane fuel. I also bought some octane boost made by a local shop. The brand is said to be the best in the UK, and used by everyone in the racing world, including F1 people.
One 911 driver suggested that the stuff is great, and he would not drive his car without it. Just mixes it with normal 92 octane unleaded fuel. Will let you know how it performs after the next tank.


I'm begenning to think the bucking is a combination of
detonation, too low octane, too low rpm, too much
throttle (for the rpm) and possibly too much ignition
advance in the 2000 - 3500 rpm range.
- interesting you should note this. To cause the bucking, I gave a lot of pedal at low rpms. That may have been causing some of the problem. I will have Chris check the advance (if he has the equipiment) next time the car goes in for service.


Don’t let this happen to you:

This is a 2.0T piston with detonation having knocked a
hole in it. It has lower compression ratio than your 2.0E
pistons.

- You should get the distributor squared away,- will do
put in all 99 octane and drive a full tank or two of fuel with “spirited”
driving. Include extended highway driving. Keep track of
your fuel and oil consumption as accurately as you can.
- only problem with oil consumption is the oil leakage from one cylinder head gasket.

You should consider 3000 rpm as a minimum rpm in all
gears except 1st. The “bucking” you feel may be
detonation. This is where you need to know the actual
advance at every 500 rpm. You need to know what the
distributor has been doing before you rebuild it.
- driving above 3000 rpm made the car feel happy. I did notice that on a hill with 25% throttle and under 3000 rpm, the car did buck a bit. Bucking ran up to something like 3200 rpm, and then stopped.
Your 2.0E will like running between 3500 and 5000 all the
time. Yes it sounds busy but it will run best there. Part
of the problem is the 911E cams are pretty wild for 2000
rpm. This isn’t like a CIS 911. I wouldn’t give it 25%
throttle until 3500 and full throttle only above 4000 rpm.
Squeeze it on.
- the car has always seemed happy at 3500 to 5000 rpm, but I did not realize that I should drive it at this range all of the time. No reason why I cannot do so.
I will take your advise.

You may find you want to use inexpensive sparkplugs during
this testing, tuning and break-in period. NGK BP7ES (hotter),
BP8ES (cooler) or BP9ES (usually too cold for the street) are
suitable for 15% cost of Bosch Platinum. You can put the
good platinum back in later. 911s are particular about
sparkplugs. Porsche’s recommendations are a “cover all
bases” average. You may find a Champion, Autolite, NGK
or other that works best.
- I will take a look at this !!

Ciao
Dom

Dom,

Grady, Just went out for a 25 mile blast up the same shake down road that I used last night, but cut the trip a bit short due to traffic. Couple of points:
- IPreviously, I drove the car as if it was a modern vehicle, and it is not.
- I remember from my youth that 911s should be driven over 2000 rpm. Never thought that power should be squeezed on to 3000 rpm before giving it the full throttle.
- see further comments below
- I learned alot by this post !!!

Thanks

I’m concerned that you can notice that the car runs better
with 99 octane petrol. The only reason you could notice a
difference is if there is detonation with the lower octane.
Detonation doesn’t have to be an audible “knock” to
reduce power and do damage. Insidious inaudible
detonation can damage the pistons, top rings, and rod
bearings. Check the ignition timing and set to 29°.
Compare 99 octane again and see if there is still a
difference. If so, you should use the higher octane all
the time.
- The car ran noticably smoother with the 99 octane fuel. I also bought some octane boost made by a local shop. The brand is said to be the best in the UK, and used by everyone in the racing world, including F1 people.
One 911 driver suggested that the stuff is great, and he would not drive his car without it. Just mixes it with normal 92 octane unleaded fuel. Will let you know how it performs after the next tank.


I'm begenning to think the bucking is a combination of
detonation, too low octane, too low rpm, too much
throttle (for the rpm) and possibly too much ignition
advance in the 2000 - 3500 rpm range.
- interesting you should note this. To cause the bucking, I gave a lot of pedal at low rpms. That may have been causing some of the problem. I will have Chris check the advance (if he has the equipiment) next time the car goes in for service.


Don’t let this happen to you:

This is a 2.0T piston with detonation having knocked a
hole in it. It has lower compression ratio than your 2.0E
pistons.

- You should get the distributor squared away,- will do
put in all 99 octane and drive a full tank or two of fuel with “spirited”
driving. Include extended highway driving. Keep track of
your fuel and oil consumption as accurately as you can.
- only problem with oil consumption is the oil leakage from one cylinder head gasket.

You should consider 3000 rpm as a minimum rpm in all
gears except 1st. The “bucking” you feel may be
detonation. This is where you need to know the actual
advance at every 500 rpm. You need to know what the
distributor has been doing before you rebuild it.
- driving above 3000 rpm made the car feel happy. I did notice that on a hill with 25% throttle and under 3000 rpm, the car did buck a bit. Bucking ran up to something like 3200 rpm, and then stopped.
Your 2.0E will like running between 3500 and 5000 all the
time. Yes it sounds busy but it will run best there. Part
of the problem is the 911E cams are pretty wild for 2000
rpm. This isn’t like a CIS 911. I wouldn’t give it 25%
throttle until 3500 and full throttle only above 4000 rpm.
Squeeze it on.
- the car has always seemed happy at 3500 to 5000 rpm, but I did not realize that I should drive it at this range all of the time. No reason why I cannot do so.
I will take your advise.

You may find you want to use inexpensive sparkplugs during
this testing, tuning and break-in period. NGK BP7ES (hotter),
BP8ES (cooler) or BP9ES (usually too cold for the street) are
suitable for 15% cost of Bosch Platinum. You can put the
good platinum back in later. 911s are particular about
sparkplugs. Porsche’s recommendations are a “cover all
bases” average. You may find a Champion, Autolite, NGK
or other that works best.
- I will take a look at this !!

Ciao
Dom

Grady,

Hope I don't disturbe you with this question. I brought the car to Chris, the engineer, to check the emissions. The car, when all of the above posts was happening, was running rich.

Chirs re-adjusted the mixture to the factory recommended specs. He originally set the mixture and in the last 1000 miles, I believe that the detergent fuel cleaned the lines etc and the car ran rich.

With the lean mixture, the car now bucks more than it did with the rich mixture.

A local machinist has a Sun machine and can make the bronze bushings. When I brought the car to the UK from Chicago after its 15 year exile in various garages, I think the distributor had either a broken spring or a broken weight and was repaired without too much notice to it being perfect. The guy doing the job is not a Porsche specialist, but a good mechanic.

Could the bucking come from an imbalanced distributor or could it be the beginning of a holed piston?

The motor runs so well above 3500 rpm that I am astounded.

Thanks
Dom

Posted: Sat Jun 10, 2006 2:34 pm Post subject:

--------------------------------------------------------------------------------

Latest update.

Viva Forte fuel line treatment.

After one week sitting in the garage, the car is 95% better than the last post.

After a 30 mile drive yesterday, the following happened:
- exhaust emissions were from 3.5 to 7.5%
- the car pulled from under 2000 rpm up to 7000
- a point of hesitation and some insignificant bucking happened between 3100 and 3500 rpm

The problem seems to be pretty much solved.

Points learned:
- make sure the fuel system is clean
- make sure the carbon is burned out of the engine
- make sure both of the above points are followed before undertaking anything major

Best
Dom
____________