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Question help about power loss on a 81 SC

Hi folks, I've got a strange issue with my car.

Out of the blue, I started to have issues with the idle and the power loss.

The car starts fine; but when I accelerate; say to 2000 rpm, I can see the needle going down, like if I am loosing power somehow. This is more evident if I am driving in traffic, since when I stop, I can see the rpm go down to almost stalling the car, and then it goes up again. No misfire or smoke, not more than usual I would say (I notice blue smoke sometimes when the car sit long time or is cold; but I am aware that the engine will need some work at one point to replace at least the seal).

The pressure in the engine is not dropping, so I would exclude a problem with the cylinder seal (I should see the needle dropping pressure otherwise, as suggested by other SC owners).

When I accelerate, feels like driving a 1980 ford truck; until you hit 5000 the car drive like a truck with a bad engine. The issue seems to not go away either if the car is warm or hot.

I started checking the electric part, to be sure that no wires or rotor were damaged; but so far everything seems fine, including the CD box.

So I decided to give a try and replaced the spark plugs wires, just to be safe, but the issue is still there.

So I moved on the fuel, and replaced injectors, fuel distributor, fuel filter and the lines, since probably they were about 35 years old anyway. But even in this way, I still see the issue. Checked the cold start valve, but the car starts fine and hold the minimum, the problem is just when I accelerate..then it seems like everything goes off. The fuel seems to run fine when I pull out the injectors, I see the spray that is uniform from the injector nozzle.

At this point I am clueless at what could it be, and I would like to avoid to continue to replace parts at random, until I find the one that cause the issue...can anyone suggest some reliable test that I can try, to see if I can nail down the issue?

I went trough the 911 manual, and the CSI manual from Bosch, but I am no mechanic, so I am not sure if I overlooked anything. Thanks!
Old 04-16-2014, 02:55 PM
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The Mighty Pieholio
 
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Air, fuel spark.

Once you nail the problem, your car will run like a million dollars!

Let's think...... It is an O2 sensor car?

Have you popped the distributor cap off and taken a look at the condition of the contact points?

Plugs were not mentioned.

What if your mechanical advance has frozen in the distributor?

Do you have a timing light? Where are you located?
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Old 04-16-2014, 03:06 PM
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Hey Bob

I am sure; the car has been running wonderfully with minimal maintenance

It has the sensor; which was replaced few years back.

I did popped the distributor cap and checked the contacts on the rotor and inside the cap; I even used a clean cloth to polish them a bit, in case some condense was in it.

The spark plugs were not replaced yet, since I didn't consider that they could cause such behavior, but I will change them too...it is almost time after all.

Not sure what do you mean by "your mechanical advance has frozen in the distributor"
Old 04-16-2014, 04:21 PM
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Basic fuel injection test.........

Shinyknight,

You had replaced a lot of CIS components but I don't find any information about your fuel pressures and vacuum test. Who made the decision to replace the fuel injectors and FD? You or your mechanic? Do you have the old CIS parts that were removed from the car?

Bob's suggestion to test your ignition timing with an inductive timing light is a good one. But don't look for any contact/breaker point inside the distributor. There will be none.

Do you have access to a fuel pressure gauge kit? You need one to make a meaningful investigation. Otherwise, you'll be hoping everything is OK which could not be the case. Keep us posted.

Tony
Old 04-16-2014, 04:36 PM
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Good point; I didn't check the pressure since the injectors were spraying consistently, I will have to buy a pressure gauge and check that.

I made the decision, based on what I read here and on other forums; the car is old and may parts were still original, so I had to change them anyway sooner or later, or at least verify and clean them.

I have avoided mechanics for now; the last few experiences were not that great, so I try to do on my own, what I can; I like to learn too.

I will check also ignition timing; I didn't check the values point to point; just checked overall the connections with the multimeter, and so far no luck.

Will let you know once I get a pressure kit; I think I know someone that has one, he has a CIS car too, altho is not a 911, but in the end I need a pressure gauge with a T connector and pipes...can't be that hard to find

Thanks for the suggestions!
Old 04-16-2014, 05:18 PM
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Quote:
Originally Posted by shinyknight View Post
Not sure what do you mean by "your mechanical advance has frozen in the distributor"
Inside the distributor there are weights and springs. As the RPM's increase the spark has to fire earlier as the explosion pretty much expands at the same rate regardless of engine speed.

The explosion has no idea how fast your engine is spinning.

So the weights and springs expand away from the center shaft as more centrifugal force is applied by a faster turning distributor. As they expand, the weights apply a little cam action on the top part of the distributor, can't exactly describe what parts are involved, but the bottom line is your signal to the CD box will occur several degrees sooner and your rotor will align with the contact points several degrees sooner. "Several" degrees is about 25 for the SC depending on RPM.

Pull your cap. Pull the orange hose off the distributor vacuum unit, put another hose on it and pucker up and suck on that hose and the rotor should move some. That's your vacuum advance. Advise on what you see. Then reach in and twist the rotor counter clockwise. It should move a little then stop. There should be spring tension that takes it back to where it was. That is your mechanical advance. If no movement is noticed. You have some work to do.

Let us know. Also check side to side movement of the shaft for excessive play.
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Old 04-17-2014, 10:41 AM
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I see, thanks Bob! I had no clue about the whole thing here. I follow what the Bentley manual says, which of course can't substitute with experienced users.

So, that may explain why the car is sluggish while at low RPM?

BTW checked the pressure and it is fine; the friend came by and checked with me, so we had 4 eyes instead of 2. I have values in the range. Replaced also the spark plugs, and got no improvement.

Last thing to check is what Bob suggested; checking the distributor, then I need to find one of these lights to check the timing...I wish I had more time to work on the car; I am on the road 6 days a week (delivery boy ), instead the only time that I can drive the car, I spend it fixing it :P

Thanks a lot for your suggestions!
Old 04-21-2014, 02:19 PM
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Quote:
Originally Posted by shinyknight View Post
the only time that I can drive the car, I spend it fixing it :P
Budget a couple of years to fix the bugs if you are doing it yourself.

Live with some imperfections - except maybe oil pressure.

Don't buy parts until you bounce your thoughts off the forum.
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Old 04-21-2014, 02:31 PM
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Quote:
Originally Posted by Bob Kontak View Post
Budget a couple of years to fix the bugs if you are doing it yourself.

Live with some imperfections - except maybe oil pressure.

Don't buy parts until you bounce your thoughts off the forum.
Good advice; I had the weird idea that since the car is "simpler", was also easier to fix

So far the car gave me a lot of joy; but now it seems like all the issues are starting to pop out...I just expect to start to see leaks under the engine at this point -_-

The idea is to fix anything major; then if it does not rain inside and is running decently, I can live with it

So far I have tried the timing and it is OK; to save time I took it to a mechanic last wednesday and he checked valve, cams and timing, and told me that all was fine. 200 bucks lighter, probably I could have purchase on my own the equipment :P

The distributor is also OK, took it out and followed another guide on the forum to take it apart, and few videos on youtube, that show how it works, so I tested it and it seems fine.

While searching for similar issues on the forum, I found a thread about issues with the O2 sensor, the box under the passenger seat and a relay (also under the seat); which I will have to check this weekend. Will try to disconnect the O2 sensor, replace it and check the voltage at the box and relay contacts, under the seat.

Another thread was talking about the cold start sensor (which I have not a clear idea about why should bother once the car is not cold anymore), at this point I am looking at anything that could fix my power issue.

Was also following the CIS troubleshooting guide from this site; to have even more options.

Is quite annoying to drive a car that feels like if is towing an RV, when accelerating
Old 04-25-2014, 02:10 PM
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U can check the voltage output on your o2 sensor or a quick check is when the car is at idle unplug the relay and you should hear a difference in idle that will tell if if the relay works etc
Also check where the o2 sensor plugs into its conector in the left engine bay I just replaced mine and that connection is not very snug I just taped it and tried to snug it good into its conector
Old 04-25-2014, 04:08 PM
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Clogged catalytic converter? Or neighbor kids jam debris into tailpipe? (The old potatoe in the tail pipe trick comes to mind)

I experienced this on an old Chevy. The car wouldn't accelerate over 30mph the back pressure was so bad. It was like you hit a crazy head wind, or were towing around an RV....

Just a thought.
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Old 04-25-2014, 09:39 PM
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Did you check & confirm cold & hot control pressures as well as system pressure?

Check CO at idle?
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Old 04-25-2014, 11:21 PM
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This weekend I will check the O2 sensor voltage, and try to replace it. I am just worried to touch the connector, since I heard that with time it crack and break easily...

I've check the tailpipe and it is clear; can't say about inside the cat thou. Would a clogged cat cause loss of power, especially in the range 1000-2500? If I accelerate more it seems that the issue is less prominent.

I have on my list also the cold and hot control pressures; the system pressure was fine, when a friend did the check with me.

Should I test also the cold start sensor? Not sure how many valve and sensor are on the cold start circuit, the Bentley is not really clear on that; just list what is on that specific system.
Old 04-30-2014, 05:50 PM
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Basic fuel injection troubleshooting........

Quote:
Originally Posted by shinyknight View Post
This weekend I will check the O2 sensor voltage, and try to replace it. I am just worried to touch the connector, since I heard that with time it crack and break easily...

I've check the tailpipe and it is clear; can't say about inside the cat thou. Would a clogged cat cause loss of power, especially in the range 1000-2500? If I accelerate more it seems that the issue is less prominent.

I have on my list also the cold and hot control pressures; the system pressure was fine, when a friend did the check with me.

Should I test also the cold start sensor? Not sure how many valve and sensor are on the cold start circuit, the Bentley is not really clear on that; just list what is on that specific system.


Start the basic test for fuel injection. You need to use a fuel pressure gauge and if you don't have one, stop diagnosing your problem because you are wasting your time and effort. It is not how hard you work but how smart you do it.

I sent you a PM and your reply to me was: "Are you having the same problem?" I had a grin on face and thought, new kid on the block. Do some search and reading. Everything you need to know are well covered and discussed in the technical forum.

Tony
Old 04-30-2014, 06:23 PM
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Quote:
Originally Posted by shinyknight View Post
I've check the tailpipe and it is clear; can't say about inside the cat thou. Would a clogged cat cause loss of power, especially in the range 1000-2500? If I accelerate more it seems that the issue is less prominent.
Bend over and put your hand over the exhaust pipe. Rev the engine using the mechanical throttle mechanism.

It should blow your hand back plenty.

If it feels whimpy at higher RPM's, yes the cat can be clogged and this will kill performance. It will kill it dead. You won't be able to climb a hill.

FWIW, one of my many, many wives had an 85 Chevette. No power. The thing was mint. 35k miles. I replaced everything, tune up wise. Then checked the exhaust flow. It was pathetic. It was new enough that GM replaced the cat.

Ran like a scalded dog afterwards.

I don't read of cats clogging on the 911's, but if it is clogged, you are dead in the water.
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Old 04-30-2014, 06:26 PM
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Start the basic test for fuel injection. You need to use a fuel pressure gauge and if you don't have one, stop diagnosing your problem because you are wasting your time and effort. It is not how hard you work but how smart you do it.

I sent you a PM and your reply to me was: "Are you having the same problem?" I had a grin on face and thought, new kid on the block. Do some search and reading. Everything you need to know are well covered and discussed in the technical forum.

Tony
Indeed I am the new kid on the block

I did some research; in fact you can read my previous posts, I've mentioned that; I've also mentioned that I did a pressure test on the fuel line and it came out clear, the fuel values are in range with the manual, so the pressure shouldn't be an issue (checked the pipes and tubes, the fuel injector was replaced not too long ago with a rebuilt one, the pump is buzzing and pushing as expected, the injectors has been replaced too less than 3 months ago).

The issue is that every person has the same problem, or so does it seems; but then it is resolved in a different way; so I am going by exclusion, I am no mechanic so I rely on what I read

I have the CIS troubleshooting guide and the original repair manual for the CIS system (from internet), trying to do what I can to get to the bottom of it, with the limited time and resources that I have, so possibly I may (and I will ) make mistakes.
Old 04-30-2014, 08:32 PM
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Quote:
Originally Posted by Bob Kontak View Post
Bend over and put your hand over the exhaust pipe. Rev the engine using the mechanical throttle mechanism.

It should blow your hand back plenty.

If it feels whimpy at higher RPM's, yes the cat can be clogged and this will kill performance. It will kill it dead. You won't be able to climb a hill.

FWIW, one of my many, many wives had an 85 Chevette. No power. The thing was mint. 35k miles. I replaced everything, tune up wise. Then checked the exhaust flow. It was pathetic. It was new enough that GM replaced the cat.

Ran like a scalded dog afterwards.

I don't read of cats clogging on the 911's, but if it is clogged, you are dead in the water.
Now that's something new to me; I thought that you never clog the cat unless you damage it. Thanks for pointing it out. After all is a 35 years old car, I can expect that the cat may require some love.

So far it moves air, it flaps my pants when i have my leg close by, but won't really blow away my hand, the flow seems quite regular; can't really describe.

The car feels like a 35 year old car, not like a 35 year old 911....was running fine until a couple of weeks ago; then one day, I started it and it began to give me low power issues, misfire at low rpm and in general, feel very sluggish. I want my car back as it was before

Should I take it to a cat specialist and have it checked? BTW the car pass every year the smog check with flying colors; last time was 4 months ago (got the history of the past 6 years, never failed, which is impressive for such an old car). Not sure if this may be relevant or not.
Old 04-30-2014, 08:42 PM
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Ok, so the issue was the O2 sensor.

I've tried to unplug it, and the connector just crumbled in my hand, breaking the wire. I had to replace the whole connector with a new one.

When I tried to remove the sensor from the CAT, it was barely screwed in the slot; put in a new one and now the car seems back in shape (still struggling to set it up again with the idle and such, but at least is working).

Thanks for all the suggestions and help!
Old 05-05-2014, 01:00 PM
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Hmmm... that sounds a little strange. If the O2 sensor were disconnected, it should not cause the car to run poorly. I suppose that if the crumbled wire or bad O2 sensor resulted in the ECU falsely thinking the mix was too rich and it was trying to lean it out, that would cause the symptoms you had. Anyway, glad you got it resolved.
Old 05-05-2014, 02:31 PM
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Tirwin, not sure if it was disconnected, but is possible that there was a poor connection? The connector literally crumbled when I pulled the sensor plug; no idea what was the state of the wire inside at this point.

I will drive few days and see how it goes; so far this morning started like a champ and was delivering all the power that it used to; almost felt like a new car

Thanks!
Old 05-05-2014, 03:16 PM
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