Cold Start/Running Issue - Lack Of Power/Surging in 81 SC

[UrQuattro]

Hey all,

I have an 81 SC, and when it is warm, it runs great - consistent power, pulls strongly especially above about 3800rpm, and has great throttle response (even with cis..heh)

Anyway, when i start it in the morning (i dont drive it every day, maybe between 2-4 days per week) it starts up just fine, and gives the standard cough of smoke for a few seconds and then that goes away, but when i start driving, it is as though there is no power. If i exceed, maybe, 1/3 throttle, it is as though i just hit a wall with the acceleration. On two occasions, just to test, i tried flooring it, and seeing what would happen. In 1st gear, it wouldn't even get to redline, it would accelerate to about 2k, then start surging, and anytime it's above 4k, it just has NO power. BUT, if i back off the throttle, i feel some of the power coming back...

After about 5 minutes of driving, this pretty much goes away, every single time, but it's something that i thought would be worthy of querying the list about.

One tidbit is that when i had the car tuned in late july (that is when i resurrected the car after inheriting it from my father and not being able to use it for about 4 years - so it did not run for 4 years - and i had an excellent local porsche specialist do the work to get it up and running correctly again). It ran just fine, but a couple times, while warm, it would stall when coming to a stoplight - especially if i was hard on the throttle, then let off, and put in the clutch. And then it would be difficult to start back up. If i revved the engine, the rpm's would drop to almost stall speed, and then catch at about 300rpm and then idle at about 800... I took it back to the shop and told the mechanic about this, and he immediately adjusted the mixture (im guessing richer, since it started idling higher on its own), and then adjusted the idle speed down to compensate. Is it possible that it is set TOO rich? My fuel mileage isnt that great - im having problems getting more than about 17mpg combined (though im not really a lightfoot, but other people seem to be able to get much better highway mileage than me.) The stalling issue went away, but now i have the cold start problem...

Im wondering if maybe it is either one or the other, either deal with crappy power/running when cold, or have the engine stall occasionally... ugh..

One other datapoint that may be important is that I live in the bay area, and in CA, wee are renowned for our gas quality..hehe...

Thanks for any feedback!

michael

[James Brown]

do you have a pressure gauge set? what is the cold pressure? how is the timing? any vacuum leaks? is the AAR working? there are a ton of troubleshooting steps to take with this. and most of them you can do when the engine is cold. Lots of info if you search for it. And if you want to do it yourself. Otherwise, a trip to the shop is in order. (sounds like it's lean when cold or a big air leak).

[don gilbert]

+1 on what james said, with out the gauges it hard to diagnose, just guessing, control press. could be to high when it cold. You could try to richen it up with the 3mm screw when it cold just to see it that helps, will give you an idea if its to lean.

[Paulporsche]

Sounds like your control pressures are off, especially the cold cp. Could be your cold cp is too high and someone has richened the mix to compensate. Your mech probably leaned the mix to stop the surging so it's now too lean @ startup.

As the others said, get a CIS fuel pressure gauge and test the WUR (warmup regulator). The Bentley manual has lots of info on this, but probably all of it is available here.

If you search you will find this is very common for these cars. Ricks911S has posted some videos on the test procedure.

Always make sure your ignition components are operating correctly.

[ossiblue]

+1 on all the comments above--check the fuel pressures first.

As far as the stalling when coming off of hard throttle, that may be the decel valve (or lack of it.) The decel valve holds the revs up for a few seconds when the throttle is released. Many times the valve is disconnected/removed from the throttle circuit by PO's. What you describe does match a car with the decel valve plugged so the engine rpm's will drop immediately. If the fuel/idle mixtures are not in spec, the result can be stalling as you describe. Just something to check out, along with the other advice already given.

[fireant911]

I took a special interest in this thread because my car, also an 81 SC, abruptly started performed the same way Michael described. Last week while driving to work in the morning, all was well with nothing out of the ordinary. About at the half way point I noticed that my car did not feel right upon accelerating. The other thing I noticed was that my Air/fuel meter was reading nothing (before the strange behavior began it was reading a fluctuating 14.7 as normal).

On Friday I fired it up for a drive an it started fine but upon depressing the gas pedal, some major belching immediately started occurring. The pop-off valve was clearly popping and the engine was really surging and simply not taking the gas. I immediately returned home as I am stumped as to what may have caused this sudden misbehavior. I am lead to believe that it is more pronounced when the engine is cold. Cold control pressures cannot suddenly change from one moment to the next… can it? I went over the engine thoroughly on Saturday and no apparent vacuum leaks were found. Why the sudden night and day different?

[James Brown]

This is the easy answer: something broke, now, to find out what, do the above troubleshooting procedures. Unfortunately, if you have any problems with the CIS, you must systematically check every part to find what happened. All the components work together at the same time and any one will effect the rest. nothing you can do but check them all. Once you do this several times, it only takes about a hour to diagnose the system. And, you get pretty good at it!

[UrQuattro]

Thanks for the info guys. I think I have a cis pressure tester kit somewhere that I bought to work with my urquattro. I haven't seen it for a while though.

Do you think there is danger to the engine with this? If I take it gently in the morning, let it idle for a bit before taking off, and rev it a few times a bit, it seems to be ok within a few minutes.

I just need to save up so that I can have someone who knows these cars better than me check it all out.

I'm totally comfortable with my urquattro but I'm intimidated by the p-car. Not having a bentley isn't helping. I'd give anything to find an affordable version of the factory repair manuals foe this bad boy.

Thanks
michael

[UrQuattro]

I'll expand a little. My car doesn't backfire or anything like that (though I do have the popoff valve installed).

This morning it happened again. When accelerating, it started surging so strongly that it was like I was literally flooring it, getting off the throttle, and then flooring it again.

It's consistent and always transient.

Michael

[James Brown]

yeah it sounds like the cold condition is lean and the engine has to "catch-up" (in a lean condition) when you accelerate. when the rpm's increase to the position you called for in the throttle position, then the mixture "richens" some and everything is fine as rpm's are constant.
you can try to richen it up some with the 3mm allen just note how many degrees you tune the screw (cw) not more than 1-2 degrees at a time.
In any event, that needs to be looked at.

[fireant911]

UrQuattro,
I do not know if your issue has been rectified but if it has not you might want to read the following thread (especially what Pete Zimmerman stated). My issue has certainly been put to bed!

81 SC Oxygen Sensor Relay