I absolutely flat out give up.

[JackT]

I have a 1982 911SC. Sounds like the same problem I had. Replaced many things trying to fix. I was close to selling the car I was so frustrated. Ended up being that my warm up regulator was acting up. Replaced it and the car redlines with no hesitation. I love my car again.

[john walker's workshop]

the pressures were supposedly checked. that should have shown if the WUR was in spec.

[thrown_hammer]

I did pull the WUR off and clean it out with carb cleaner including the little screen in there with no improvement. Maybe I will replace it. Just tired at throwing money at the car with no improvement.
Maybe I will just stop in at Autozone and get some chrome plated pedal covers and bask in my coolness.

P.S. John, any updates on the bugster/speedster thingy?

[stormcrow]

Shawn,

If you can redline the car by feathering the throttle, then you may have a fuel flow problem. Check your air sensor plate and make sure it is set where the specs call it to be. If it is set wrong, (too high) your fuel distributor plunger may be on the high side of the slits and may be reducing fuel flow when you mash down on the throttle.

On the other hand, the return line going back to the fuel tank may be clogged causing a higher than normal pressure on the fuel distributor causing it to run a little lean.

Mine was plugged and I had a similar problem - no power at higher rpms. Remove the line from the fuel tank and see if fuel comes out of the tank. If it doesn't it's blocked.

Make sure when you start adjusting your fuel distributor (if you decide to) you keep track of your starting point so you can use that as a reference in case the car doesn't want to run properly.
after you make some adjustments.
Steve

78 911 SC Targa

[Superman]

Darnit. In one post you said you don't want to keep replacing expensive parts with no improvement, and you are thinking you'll just replace the WUR. Which is it?

I suggest you uncover what is wrong first, before you go replacing the WUR. I know it can be frustrating. Ignition is first, and generally easy to check. Put a timing light on it and rev to 5000 rpm. If it advances about 25-30 degrees beyond idle, then your advance is working. Check to see if the spark is blue and makes a nice snapping noise. See if it will jump an inch or two. If so, your ignition is fine.

Unless you are JW, and perhaps even if you are, follow the fuel system troubleshooting procedures. They will have you checking the fuel pressure, warm and cold, which will tell you if your pump and WUR are behaving properly. Check for voltages at the various components. Adjust the sensor plate if it's not right. Those procedures eliminate, one by one, the various things that might be wrong. Measuring the fuel flow at various sensor plate positions is a good idea, like JW suggested. Quit guessing and spending money. It does sound like a fuel volume problem.

[thrown_hammer]

When my wrench had the car he had it for about two weeks. He tested and checked the entire fuel system. He said all the pressures and the mixture was in spec. He also set the timing. He said try a tankful of Techron fuel treatment. When I got it back I drove it for about a week with the techron. I took it back to him to have it rechecked because it ran the same. It checked out okay from a fuel standpoint. He has been a certified Porsche mech. since 1978. The only thing left is the CD unit on the spark side. To me it acts like it is not completely burning the fuel mixture at high RPM's. But I am here because I can't do this alone!
I am going to follow all the leads I haven't already tried on this thread as I get time. Thanks for everyones input.

Superman, I said I don't want to. I never said I wouldn't.

[bell]

this is a shot in the dark but i had a problem a while back with my turbo dodge, it did simalar things yours is doing (i know it's not a porsche).
the main fuel line had been crushed (most likely by something in the road), once fixed she ran like a banshee.
if the fuel line is damaged it will severely restrict high volume flow.
just a thought.

[dean]

I am going with the WUR. That is sort of what was happening with my 930. The pressures were ok in N/A mode, but in boost I think they were all fuched up. Stephen at Imagine Auto gave me a used one to test out and bingo it ran great. So I boought it.

See if there is one you can borrow. I have one for a 81SC but it might not be the same.

[s2per]

I had a similar problem on my SC recently. It turned out to be a broken valve spring; intake side, outer spring. Changed springs on that valve, set all the valves, and no more high speed stumbling.

[RoninLB]

this "subject" turned into a great one...everyone had something to offer...anyway, what bugs me with CIS is that I can't quickly determine if the problem is ignition or fuel related..w/carbs I can play with a standing car's throttle, or drive it if I have to, and get a quick drift on which direction to take.and trying to offer a helpful reply without being in front of the engine may make me feel stupid.I'm not a pro so I don't see 911 engine problems routinely, which might help in following the "drift" w/CIS..but that's my problem................Ron

[RazorRacer]

If it sputters above 4000 rpm in all gears, then it's probably not a fuel problem. If it sputters above 4000 rpm when hot or cold it's probably not a WUR problem. My guess is that it's a timing problem. As the engine rev's higher under load, the fuel is not properly igniting.

Do like superman suggested and check the timing above 5000 rpm. Get a timing light and play around with the setting. Try driving 5 degrees BTDC, then 10 degress BTDC. At least that's what a 78SC can tolerate. Check your car's specs to be sure.

Does your car have a vacuum advance? Once you have narrowed down where the problem is, then have your wrench fine tuen it.

Good luck.

[CamB]

If you are truely frustrated and desparately want to know, it might help to have the car run on a rolling road and run through the problem zone with an air/fuel check and timing/ignition check.

Not so cheap though.

[Kevin Stewart]

Seems as though you have tried everything, been there i chased a problem for a year and know how it feels, but heres a couple suggestions, bad distributor caps (cracks etc) will cause a high rev miss and also the rotor button also will cause this, i think i would start checking connections for corrosion, my problem was a corroded cdi plug, yep took a year to find, I replaced almost all the fuel injection parts looking, when i took it to the shop the mechanic would say well the warm reg is bad then this etc, replaced everything he said a year later took it back to the same guy just searching for anything, guess what he wants me to replace all the same parts again, well it was a grand the first time, he was wrong, i got peeved went out and was gonna spend the whole day till i found it, the first thing I grabbed and shook was it, other people on the board have found corroded wires leading to the cdi and had to replace like 6 plus inches, and this caused low readings on fuel injection parts when a ohm meter checked them, so you may try reving by hand and just lightly tapping things does wonders for finding problems, i hope you find it soon, i almost sold my car because of it, but truely love it again, please post when you find it, Kevin

[thrown_hammer]

This board is mind boggling. Now I have every weekend from now until spring planned out. Some of the stuff brought up I have tried, some stuff I haven't. I will trudge along until I find this "ghost". I am going to rule out the fuel system (for now). If all the pressures were good and the mixture is right I feel that says no restrictions in the system. I will concentrate my efforts on the spark side. First I will trade out the CD unit. Then check all my connections. Sound like a plan?

[A Quiet Boom]

Ignition first then fuel! Check timing both with and without the vac attached 30-36 total is a good range but no higher. Definately check connections on the ignition system, under light load (such as feathering the throttle) the ignition is not stressed as much. Only after you've eliminated the ignition should you check the fuel system (besides it can hurt to give it an ignition tune up) You said the fuel system was pressure tested? What about flow tested? Things like a partially clogged filter of crush fuel line etc. won't show up in a pressure test. My gut feeling from this side of the computer screen it fuel starvation at higher rpm and that can kill an engine due to detonation. I'd still check the igntion first though. I had an MSD CDI unit go bad on me in my dragcar with the same conditions you decribed, it would start and drive fine but the spark was to weak to fire under heavy load in the upper rpm range, a "plug cut" run showed black plugs so I swapped in my spare carb and recheck fuel pressure with a different guage but the problem still existed. A quick call to MSD tech suggested that this is the way CDI units and coils usually fail, swapping the box solved the problem.

[A Quiet Boom]

LOL we posted at the same time, sounds like a good plan to me.

[avendlerdp]

My old '73.5T did this. I traced it down to a bad fuel distributer. I replaced everything then figured this out. If you can find out what cylinder(s) are dropping out at high rpm you can switch around the fuel lines on the F.D. and find the clogged cell. The F.D. has VERY small slits and passages that once clogged can cause BIG issues.

Alex

[Superman]

The official troubleshooting procedures for CIS fuel systems end with the FD. That is, if everything else checks out and it still is not behaving properly, 'the book' says to replace the fuel distributor. But DO NOT do that yet. They are spendy.

Your attitude is good. I'll reiterate my suggestion to check advance with a timing light. It does not have to be perfect, but total advance needs to be in the 25-35 degree range. If ignition timing is not doing that, then this is your problem. I'll admit that a bad coil or CD box may be the culprit, but I have my doubts and suggest you find out before you replace those spendy parts.

My main suspicion (not trying to insult the mechanic) is that the fuel system is the problem and that the problem is volume. Crushed fuel line, line packed with rust, tired fuel pump, all will prevent the engine from getting a sufficient volume of fuel under load and at high RPMs. The volume test is one of the tests I have suggested. Get the Bosch CIS FI troubleshooting book. Or look in your little spec book, find out how much fuel the pump is supposed to deliver in a given time. Detach the fuel supply line at the fuel distributor, stick it in a bottle and run the FP (turn on the key and life the sensor plate). If you're not getting the specified volume, then this is your problem.

So:

1. total advance
2. fuel volume

[RoninLB]

I would not be suprised if the fuel tank filter is dirty....Ron

[thrown_hammer]

Heres an update.
Joeaksa sent me a spare CDunit he had. I plugged it in last night and drove the car to work this morning. Seems to have the same problem. And as a bonus when I was coming down the home stretch my accelerator pedal dropped to the floor and car falls to idle. So now I have a linkage problem as well.

Now more than ever I feel like a sparrow headed for a plate glass window...REPEATEDLY

Some things I thought of that I don't think I said before. When I replaced the coil with a Pertronix flamethrower the car ran great for about a week, then it slowly headed back to sputterville. I have also recently pulled the plugs and they look textbook. When it is cool out(like in the morning) it sputters less. When it is hot out it almost dies when I floor it above 4000.

Now if you will excuse me I am going to nail one foot to the floor and run in circles.