Hard start and poor performance - comment on my battle plan
 

I've recently bought a '80 911 SC that has turned hard to start (cold and warm) and has poor overall performance. When I bought it, it started right away and pulled fine. When I do get it running it idles with only a slight up and down in revs and is drivable, but feels tired and when engine braking there is a distinct, sort of "bubbling" sound from the exhaust (SSIs).

The past days I have read in the Bentley manual and in lots of various threads on here to try and figure out what could be done. So far I've come up with the following battle plan:

1. Check the sensor plate alignment and movement and clean the whole assembly and air boot.
2. Check spark plugs and sparks.
3. Check ignition timing.
4. Check fuel pressure. I don't have a gauge so I want to rule out as much else as possible before spending money on that (too =).

Are there any other basic things I should check before moving on to specific parts (WUR, AAR, CSV etc)?

I also have two specific questions:
* The manual instructs to relive fuel pressure by loosening the control pressure fitting at the fuel distributor. Does it have to come off fully and how much fuel can I expect to come flowing out of it?

* When I turn the ignition on, there is an electrical whine from one of the components on the left side in the engine bay. Is that normal or could it suggest something is wrong with the ignition (the whine was there when I bought the car)?

Any suggestions and comments are welcome!

Cheers, Björn

CIS troubleshooting............
 

Bjorn,

The whining noise you heard in the engine bay was the CDI. Removing the fitting at the fuel distributor is not as convenient as doing it at the other end (@ WUR). I like to install the fuel pressure gauge at the WUR side instead of the FD side.

BTW, don't forget to add in your list of things to check: vacuum or air leak. Lastly, avoid tinkering the air-mixture screw unless you could verify that your system does not have unmetered air going into the system. Invest in a set of fuel injection pressure gauge kit and probably the best $60 you would spend on your car. Keep us posted.

Tony

Thank you for your input Tony. I've checked the sensor plate and it moves as it should and is in the correct resting position. The only thing that I'm not sure about is this: when I lift the plate there is some resistance which I believe is normal. If I then drop the plate and directly lift it again the resistance does not start until a bit up. Is there supposed to be a delay? I thought the fuel plunger had to be in sync with the sensor plate at all times?

I've now put everything back together after having checked the sensor plate and cleaned everything I could reach. I also cleaned everything inside the distributor cap.

On the first starting attempt it sort of ran, backfired and stopped. Tried again, it started after a few turns and then idled fine. Turned it off, waited maybe 15 min and then tried again. Came to life almost instantly which it has not done in a while. :)

Tomorrow I will try it again and also go for a spin to warm it up and see if the performance has improved. Will check the timing then as well.

Cheers, Björn

I would do a leak down test first to verify the engine is healthy. Then go through the ignition. Then mess with the CIS.

Björn,

I have an 81SC and I walked out to the garage to repeat your air sensor test. I am assuming you had the key on so there was pressure in the system. With the key on and a cold engine, the first lift had little resistance for a couple of centimeters but then I felt the resistance. When I repeated the lifting the resistance was present immediately.

a couple of things bother me. you checked the plugs. if they are old or you have had fuel problems, they could be fouled and need to be replaced.

you said you cleaned the dist cap. replace it if it is old. i have tried the cleaning thing, it does not work except in an emergency.

you may need to check residual fuel pressure.

when you lift the sensor plate with the key on, you should feel resistance right away. if you lift it, drop it and lift it and feel a dead spot, the plunger is sticking. try techron with about a half a tank of gas and run the piss out of it. you may have to go through several bottles.

the idleing up and down is due to too rich of a mixture. get the ignition sorted and then move on to the fuel.

Actually, I haven't checked the plugs yet because I don't have a spark plug tool nor multiple short extenders. But I will get those asap.

I checked the sensor plate with the fuel pressure relived, as described in the Bentley manual. But I will check with pressure and key on today.

Thank you for your input!

/björn

CIS troubleshooting............
 

BK,

If you have an engine with a decent compression, ignition and timing close to spec., good fuel and a working FP, you should be able to start and run the engine with minimal problem. Lean or rich mixture is not a problem for starting unless you have a significant unmetered air going into the system. I'm no expert, but I haven't encountered any problem with CIS engines that could not be diagnosed correctly. Avoid the guess-work in CIS troubleshooting and life will be fun and enjoyable. Every individual CIS components could be bench tested and does not need a running engine to perform such tests.

Tony

If it has an 02 sensor, the control unit may not be working.

i use one short extension on a swivel with a sparkplug socket- craftsman

dont try to adjust or diagnose CIS without first doing a tune up.

tony not an expert??

Well, I've now made another go at getting to grips with the engine gremlins but sadly only made things worse...

Getting it to run was pretty easy from cold but a drive reveled that it did not run any better than before. Coming back with a warm engine I proceeded to check the ignition timing. At idle it seemed quite right but from what I could tell it did not move to 21 degrees when revving to 6000 RPM (both cases with both vacuum hoses off). So I decided to try and make a small adjustment, turning the distributor a tad clockwise. This seemed to make the idle a bit better at first but then when I put the hoses back the car would not idle and died several times. Turning the distributor back CCW made no difference. The engine also got really hard to coax to life, the only way to get it going was to run the pump and injectors for a few seconds by lifting the sensor plate and then crank it as usual.

I feel as I should not have messed with the ignition timing without thinking a bit more about what affects what but I figured it would be easy to revert any changes, guess not.

I tried also tried to look get a spark plug out by using a swivel but my extension was too long to fit so I need to get a shorter one. I'm also gonna get some carb cleaner and start to look for any leaks. I've had some nasty backfires so even with a pop-off valve the airbox might be cracked. I'll also go through the Bentley manual trouble shooting instructions step by step to rule out as much as possible.

Good news is that the fuel plunge seems to be working ok, I have instant and uniform resistance when lifting the plate with pressure.

Feel a bit gutted at the mo' but no way back now...Thank you everyone for helping out!

/björn

Spent yesterday reading even more and building some new enthusiasm. Now I've put together a new list of things to do based on how easy it is to do (for me), how likely it is to sort the problem and how expensive it might get (new tools, parts etc).

1. Measure ignition wires (280-7)
2. Clean distributor cap, make sure everything is to spec (280-8)
3. Check for air leaks, I will use carb cleaner for that.
4. Check fuel pressures, this includes checking regulator and accumulator.
5. Check fuel injectors (240-16)
6. Check spark plugs (030-8)
7. Measure throttle position switch (240-28)
8. Cold start valve and thermo start switch (240-22).
9. Look for faults in the distributor cap and possibly get a new or renovate.

Will post back when I've made progress.

Cheers, Björn

The burbling you described on deceleration sounds like backfiring. It can be caused by unburnt fuel in the exhaust, resulting from a mis adjusted ignition timing. You need 5 deg BTDC at idle, and 28 deg or so at 6000 rpms. From your descriptions, it seems like your ignition advance mechanism may be stuck and your distributor may need to be cleaned.

In any case, if you just bought the car, you should just give it a basic tune-up: oil, filter, new spark plugs, cap and rotor.

Today I did nr 1 on my list and found the following :

Cylinder 1: 1.5kΩ
Cylinder 2: 1.5kΩ
Cylinder 3: infinity
Cylinder 4: 2kΩ
Cylinder 5: 2kΩ
Cylinder 6: 5kΩ

So, pretty much everyone are off (not sure if to low resistance is a deal breaker- should be 3kΩ) but obviously the nr 3 is really bad. I'm guessing something happed when I took it off but something was wrong before as it looked like this on the inside

http://forums.pelicanparts.com/uploa...1281468088.jpg
http://forums.pelicanparts.com/uploa...1281468110.jpg

I tried to clean it to see if I could create a connection but with no result. Obviously need to get new wires and probably a cap (and rotor?) before I can resume "engine on" work. Might give the distributor renovation a go instead.

Replace cap and rotor. You can try to dip the end of the wire in ammonia to clean it, but I would order a new set.

Yes, I will order new ones. Will go for Clewett but can't decide on red or black :rolleyes:

Not really sure which plugs to go for, are the Bosch WR-5-DC+ the correct ones for my car? Another site here in Sweden suggests I should by the WR3CC but I can't find them on here and I don't have my manual with me (@ work =).

/Björn

the wr3 is too cold. wr3 would be used in something like a turbo, or something that has very hi compression. you might get away with a wr4, but just stick with the 5's. once you have it all sorted out, you may need to change the plugs again. then, if the plugs are not clean or are too black, you may want to try a wr6, one step hotter. but start with the 5 and see how it does. always start with a cold plug and work up to a hotter one. check a few plugs every 2-300 miles. plugs with a gazilion miles dont tell you much, you need to keep an eye on the plugs while they are fairly new. i usually pull 1 and 4 or 2 and 5.

Thank you for clarifying, I'll go for the WR-5-DC+ then.

Cheers, Björn