1980 911SC Suddenly running Rough...Any Ideas?

[Bob Kontak]

Originally Posted by BOJAN

also when you pulled the relay i thought i noticed a difference in your idle...mine,there is no difference when i pulled the relay.

Thought for sure that was your problem. I even had a few gin and tonics while writing these posts up in early celebration for fixing your problem. :-)

My 81 has a brass tube that hooks into the back of the throttle body. It angles up from the drivers side of the engine. Pretty easy to see if you have one. Mine can fall out of the hole where it enters the throttle body and cause crappy idle and drivability (spelling?) issues.

This and other vacuum leaks can be found with the the pressure check mentioned.

However, I am still a little stumped as to why a vacuum leak would cause intermittent operation unless you are saying the car runs ok for the first 15 seconds - and that is it. Was under the impression it can run good then bad then could bounce back to good.

[john walker's workshop]

unplug the O2 sensor and see if that helps.

[Vereeken]

Is this not the time when we ask to see WUR control pressures measured from cold to warm over a duration of 4-5 minutes? The engine does not need to run in order to do this
Or did I miss them.

Also how is the screen on top of the WUR looking? See the photo attached. This mesh can get clogged. If you start at cold with Low bar the CSV injects extra fuel and the WUR leaves more fuel through, after the WUR heats up it reduces the amount of fuel and if that screen is clogged it could just as well be reaching a point of not enough fuel anymore.

[BOJAN]

Bob, i really have a feeling is fuel related.....yes sometimes it would run ok for 10-15 sec from start....but this would be one of manny tries i start the car...most times would be running rough from get go....Also i notices a white gas smelling smoke now about 10 sec from starting...(could this indicate one of the injectors cloged or leaking)...yes i thought about WUR as well....fuel distributor?

O2 sensor has always been disconnected. My city mpg always been high, and yes smell of fuel always been there(little more than typical classic car)...could something that was going from all along reached its point...?

Its ok..i always try to figure this myself before handing the car to the pros....i am greatfull with the help that i received from all of you guys, that i have troubleshoot things i did not know before...now i know where the fv valve and o2 relay is haha....

My first 911, and aside from alternator rebuild really never had issues with it in 8-9 months of ownership...was getting a little bored...one should be carefull of own wishes

will try to update once figured out

[BOJAN]

Not ready to throw in towel just yet....

Went for a drive today.....whatever it is it could be temp related...
Car started rough...for first few min i was not able to even get the rpm past 1k rpm,throtlle would go nowhere,complete clog,backfire from air box every time...but as the car warmed up it started run better and better....i went on the freeway..took it 90 MPH+(fuel inj cleaner intank)...not the best accel but drove non the less....at idle however the rpm woul stay at 5k(not a smooth idle)....also there was an arching/missing of some type.....

Busy with kids b day this week....but will check the WUR after weekend/plugs

[boyt911sc]

Originally Posted by BOJAN

Bob, i really have a feeling is fuel related.....yes sometimes it would run ok for 10-15 sec from start....but this would be one of manny tries i start the car...most times would be running rough from get go....Also i notices a white gas smelling smoke now about 10 sec from starting...(could this indicate one of the injectors cloged or leaking)...yes i thought about WUR as well....fuel distributor?

O2 sensor has always been disconnected. My city mpg always been high, and yes smell of fuel always been there(little more than typical classic car)...could something that was going from all along reached its point...?

Its ok..i always try to figure this myself before handing the car to the pros....i am greatfull with the help that i received from all of you guys, that i have troubleshoot things i did not know before...now i know where the fv valve and o2 relay is haha....

My first 911, and aside from alternator rebuild really never had issues with it in 8-9 months of ownership...was getting a little bored...one should be carefull of own wishes

will try to update once figured out

BOJAN,

How many times have you mentioned that you felt it was fuel related. But you never once attempted to check it. If you don't have a fuel gauge to check for the fuel pressure, you could do the volumetric or flow rate check. Test the FP and measure the amount of fuel coming out before the FA (fuel accumulator). Do multiple measurements. If the flow rate is 1 liter+ per 30 sec., consider the FP out of the equation.

An out of spec WUR will also give you starting problem too. So you need to know the control fuel pressures. Last but not the least, you have unmetered air going into the system. You may not know it but it's there. Unless you test and confirm the absence of a significant source of air leak, you are simply relying on quess-work troubleshooting. Stop quessing and you'll know and find out what's causing about this non-start scenario. You also could do visual inspection of all injectors including the CSV. Keep us posted.

Tony

[Bob Kontak]

You are a long, long way from throwing in the towel if you can hang in there. FYI - For one hours labor at a pro you can almost buy a set of pressure gauges. Those will be available point forward for additional issues you will have.

If you want to do it without gauges, let Tony know you want to check the fuel rate and he can help you with specifics (which fitting, how to make the fuel pump run and so on). I have never done this as I have gauges so I will chill on advice here given my batting average in this thread.

Also a mirror on a stick and a good flashlight can be your friend for finding fuel leaks - especially the cold start valve. It will leak after then engine is off so you don't have to stick yourself in there with the engine running.

Have a good weekend.

[BOJAN]

I did not have much time to work on the car...but this is where i am at

I believe i was completly wrong in thinking this is a fuel problem. Now when i purchased the car,it was set up rich with advanced timing. I could not pass the smog with timing out of spec so i had the timing set properly and i passed. I felt the performance was lost a bit,but ran good non the less. Few months later i had the fuel mix leaned (prob to the limit), and car still ran good, untill my troubles started. Now the other day i had my mech test the injectors and richen the mix and the car came back to life. I can start it cold and drive away,some hesitation and slugishness while cold but nothing like before, where i needed 10 min just to move the car. I think that cause of my problem is an an vacuum leak somewhere,and since i was running very lean the car completely stumbled. Now..At idle, when i unsrew the oil cap nothing happens,absolutely nothing. Prior to my troubles,when i unsrewed the oil cap there was definitive change in idle speed.

Now i have tried spraying some carb cleaner around intake,but without any results. I also tried the propane method,and nothing. Visually i can't see any cracks or anything like that. I will keep at it,and see if i cand find this leak(s)..

[area man]

I've been reading through this thread and thinking vacuum leaks too.

The propane/carb cleaner method is not conclusive - it can easily miss significant leaks. You'll need to use pressurized air and soapy water to be sure.

[BOJAN]

Area man, i just read your post too and that preaty much sums up my situation too.

When car was with advanced timing/rich it was noticably faster. As things slowly get back too spec there something new always arises..something gets better and something gets worse. I have not dumped any money in this yet, and have also thought about just getting by as is and save for PMO's. With CSI there is a lot to go wrong,so manny hoses connctions in a tiny space thats designed to run hot,well..O how do i miss my tiny BMW 02's, nicely slanted 4 where a blind man can do work. With this fancy "flat six" i am thinking of ingesting two tylenols each time i open the engine lid and hope my headache goes away.

Now with the soapy water method...can this be done with engine in the car(hope it can)...can you pls explain a bit more .. I do not have the air compressor but do have the vacumm that can blow air...

Thanks.

[area man]

pressurized air test can definitely be done with engine in the car. Do a search for it on this forum - I believe its explained somewhere. I suppose you can do it with the shop vac and the air intake. With a compressor, use the brake booster port on the left side of the airbox. very little pressure is needed - just enough to make positive pressure inside the CIS system. I'd check the seal around the pop-off valve, if you have one, and the seam in the air box that connects the lower section with the upper. The airbox seam can blow on the right side, where it's very hard to see from above with the engine in the car.

[porwolf]

How about changing the tank ful filter? If dirt in the tank is an issue that should help. It unscrews from the bottom of the tank.

[Porsche987]

Check #18 Fuse. It is probably blown. Check to see if your dome light (NOT dash lights) comes on, as it is controlled by the same fuse.

[keithbkeller]

IF you unplug the WUR on a cold running, stumbling motor and nothing changes, as in the case of Bojan's car. And the engine continues to exhibit the same symptoms, then how can you exclude the WUR as the problem??

[everforward]

Have you tried replacing your oxygen sensor relay ($15.00) under your passenger seat yet? It is a cheap 1st check and it worked for me....

[Guardsred911]

+1 on Bob's comments about the under seat relay....I do have an 80 SC, had the same issues, per his instructions, I changes it out, instant fix..... After chasing a lot of other ghosts.... But, up to you...

[Mike Kast]

have you done the propane around the intake manifold while running test yet? They caused me more crazy ghost chasing hours than I can say. Those things might last a couple of years or so but they always seem to fail slowly, minor adjustments resolve issue and then majorly, nothing resolves issue. Much head scratching and denial ensues...
while running, send some propane around the intakes and the airbox, if the idle goes up you have a vacuum problem. Partial engine drop required and while your in there...

[ClickClickBoom]

Based on the sudden onset, his mechanic retarding the timing and leaning the fuel. I also read backfires, any thought to a cracked air box?

[Mike Kast]

I bet it is the intake sleeves

[Mike Kast]

or wait, this thread is old news and has no resolution from BOJAN. It is from July