Hesitation and Generally Running Rough 77 911S CIS

[Moozak]

77 911s 2.7, hesitates upon acceleration and generally is running a little rough. Just replaced fuel pump as it was really noisy. Idles nicely, CO mixture is at around 2.4. Checked fuel pressures today:

Temp. 23C
Cold: 1.9 bar
System: 4.9
Warm got to 2.8 after a couple min.
Residual 1.5 @ 10 min
1.2 @ 20 min
WUR is 033

I've been researching other posts...
I'm stuck... any ideas?

Jon

[47silver]

1.. had an issue with my coil to distributor wire arcing to one of the wires on the coil, idled perfectly but did not accelerate at all. found it at night in a dark area,, lift the engine cover it will look like a light show.
2. years ago had the black points wire shorting to the cam lobe intermittently but this was not a consistent as the coil wire arcing.

[Moozak]

Thanks, I'll check into that. How did you fix the issue? Replace the coil wire?

[47silver]

i bought 2 from pelican so i had a spare.

[Moozak]

Just had a look in the dark... no light show. Too bad that would have been mildly entertaining

[Moozak]

I just did some exhaust work recently and had it checked by a muffler shop, but it still feels like there is an exhaust issue. Pops here and there... Could be something else too. I've done some extensive air leak chasing in the recent past and highly doubt it's an air leak. Also, the idle is pretty solid where as when I was chasing leaks the idle was high. Ever since I came back from a road trip (about 3 hours each way) it's not been running right. It was beautiful on the way there and back, but when I got home and started it the next day it was off. I found the exhaust crack in the thermal delete pipe that connects the header to the heat exchanger (replacing the thermal reactors). I've replaced them recently with the Bursch units. It's close, but not quite right...

[Moozak]

I've noticed, every now and then that on a hot day when I've had the targa top off and it's been parked in the sun, when I first start the car sometimes the tach doesn't work. It comes back to life after a few minutes of driving. Not sure if it is somehow connected, or a separate issue.

[T77911S]

you have a vacuum controlled WUR. warm CP is 3.5 WITH vacuum to the WUR, 2.8 is the CP WITHOUT vacuum to the WUR.

if you still have the thermo time valve, it may be bad, you have have the WUR connected to the wrong port or the diaphragm in the WUR is bad

[FrankBlack]

I had a very similar problem. Turned out that point gap closed up too much. Not sure how this happened. I replaced the points, set the gap and dwell.
Now it's back to as good as its ever been.

[Moozak]

I'll check warm pressure with vacuum. I guess testing warm pressure with the car running is a good idea to see if the TTS is activating.

I'll double check points gap too, although my timing didn't change.

[T77911S]

its nice to have a hand vacuum pump.
thought you checked pressure with it running.
check timing and make sure advance is working

[BK911]

Originally Posted by Moozak

I've noticed, every now and then that on a hot day when I've had the targa top off and it's been parked in the sun, when I first start the car sometimes the tach doesn't work. It comes back to life after a few minutes of driving. Not sure if it is somehow connected, or a separate issue.

My '78 does the same thing. Anybody know why?

[Paulporsche]

Moozak,

Have you checked your points/dwell?

[Moozak]

Checked the timing advance and it is working... Today I will double check points gap/dwell, fuel pressure with vacuum and double check CO mixture... I'll post any updates,

Jon

[Moozak]

Checked and reset the points gap... it was too tight. After I reset the points, I took the car for a spin, warmed it up and reset timing and CO. This helped a lot, but I still have hesitation when I really step on it. 3rd gear at about 4500 RPM is most noticeable.
I didn't have time to check fuel pressures with vacuum (car running), but will do that tomorrow. Feels closer, but not quite there yet...

Jon

[Festive_Zombie]

Whats your dwell at?

[Moozak]

Need batteries for my dwell meter... will check tomorrow and report back.

[Festive_Zombie]

Once you have it fixed you should come up to Whistler on Saturday, you guys should come meet us for a drink

[Moozak]

Checked Dwell and it was high at about 45. Adjusted it until it was bang on 38 and that made a HUGE difference. No more hesitation! Thanks guys!

Alex, can't make it to Whistler today, but enjoy your weekend and the Porsche show!

Jon

[T77911S]

i never set the dwell/points on my 77. eyeballed them everytime, never made a difference. i even tried wide settings and narrow settings, not a change.

glad you fixed it.