'83 911SC cold start prob

WB3 · 02-11-2004, 08:27 AM

Hi all, I hope someone can lend a hand. This problem started right after the rectifier on my alternator went south. Wheather it has any connection with the current problem I don't know. It takes about three tries to get her started. Anyway, when it starts it will idle roughly and @ 400rpm. If any attempt is made to give throttle it will backfire through the pop valve. I can smell fuel too. Once the engine warms up to about the halfway mark on the temp gauge she starts acting more civil and like her old self again. The rpm's gradually rise to about 800. At this point it is drivable but I still get some bucking if the air temp is low (35-45 degrees). I also notice a slight poping in the exhaust note when I let off the throttle. I know now that the first step should have been a pressure check. But knowing little about the CIS system I went ahead and changed the WUR. No fix. I also changed out the AAV with a working used one but that didn't do the trick. The AAV is not stuck closed and it opens almost all the way when I put it in the freezer for 15min. I've checked the vacume lines and airbox for leaks too. I think the 02 sensor is disconnected though. There's a single black wire that comes up through the sheet metal on the left side but it's not connected. Where does the 02 sensor connect to? I've also read in other postings about three switches in the CIS system...15 degree switch etc. Where are these switches? Could it be a bad frequency valve? Any help you can send my way would be greatly appreciated!

Graham Archer · 02-11-2004, 08:53 AM

If it will run when warm, then your frequency valve is functioning. Also, the fact that it starts at all, indicates that your thermo-time switch (and extra injector) is working.

Since you have checked for a vacuum leak (my first suspect), then I would look at the fuel mixture.

WB3 · 02-11-2004, 09:05 AM

Thanks for the input Graham, Is it possable that the fuel mixture would go so out-of-wack as to cause this problem? Getting at all the vacume lines for inspection seems nearly impossible without dropping the engine. I've wacked my head more then a few times way in the back of the engine compartment. Do you know where the 02 sensor connects to? The mixture control is ontop of the fuel dist where all the fuel lines connect to correct? I've never messed with the mixture since I've owned the car...about three years. Thanks for your help.

Graham Archer · 02-11-2004, 09:23 AM

I would doubt that the fuel mixture would suddenly go off. It is more likely that a vacuum leak formed. You might want to look very closely at your pop-off valve. Sometimes that can leak or even work themselves loose. Other vacuum leaks can be found by using an unlit propane torch. When the propane is introduced close to the leak, the rpm's increase.

konish · 02-11-2004, 09:27 AM

Vacum leak is a likely culprit especially at the temps you are talking about when it finally starts to run a bit better. However, check your temp sensor mounted on the right hand cam chain housing. I forgot the temp this thing is supposed to open, but when it is cold, it should be closed and show resistance...I'll have to check my book when I get home. When cold, the temp switch sends a cold signl to the lambda control box indicating it to run a slightly rich duty cycle...I think the number is 60%. When it finally warms, the switch opens, and the Lambda moves into warm open loop, which is 50% duty cycle. If your O2 sensor was hooked up (and the location is left side engine bay...little black wire), the Lambda brain would move into warm closed loop when the O2 sensor reaches the proper temp. The other temp switch is mounted on the breather tube assembly (again, from memory), and it helps with cold enrichment as well but again I can't for the life of me remember the temp. My O2 sensor is still in the exhaust with the pigtail, but the engine compartment plug has been disconnected..not sure where it went originally but the end of it looks like a spark plug boot, and the wire is pretty short so I would guess that it plugged into the Lambda harness at the left side, lower firewall or wire harness.
Also, don't assume that just because you bought a new WUR, that the pressure is correct...I've heard from others that out of the box they can be very lean. You still need to check the cold control pressure to eliminate that as a contributor.
Finally have your CO adjusted when the car is at operating temp. The mixture control is accessed through a small hole on top of the sensor plate housing, just to the right (opposite of the fuel dist)..you may have to use a mirror to get a good look, but it is on top of the housing, and easy to get to. However, I would not think that the mixture could get knocked far enough out of whack to cause that level of rough running unless it was intentiaonlly moved to the leanest position possible. If you want, richen the mixture up a bit and see if it helps...but I would do this in very small increments.

R/
Dustin

WB3 · 02-11-2004, 10:08 AM

Thanks Dustin, I just looked at the RH cam cover and found three switches. One looks like it's the oil pressure sending unit? It's about two inches in dia. Then there is one directly beside it (left) underneith the fan housing. Then there is another at the very right side of the chain housing. I'm lost about the switch that you say is mounted on the breather tube assembly. Which breather tube are we talking about? I see the spark plug boot looking thing you're talking about where the 02 wire hooks up and I thought that's what it was. Seems there's some plastic in there that has gotten brittle from heat. Almost like a shift coupler bushing that is crumbling. But the wire is barely sticking out of the boot...no insulation at all.

konish · 02-11-2004, 03:52 PM

>Then there is another at the very right side of the chain housing.
On the upper RH "corner" of the cam chain cover. That is the 15 degree switch. Also, I remembered its function backward...open when cold, and closed when switched at temp...sends ground signal to the Lambda brain to enter into warm, open loop.
>I'm lost about the switch that you say is mounted on the breather tube assembly. Which breather tube are we talking about?
The breather tube housing on the rear center of the engine...the 35 degree swtich is located there and provides off idle, acceleration enrichment...only at 2-3 degress of throttle angle, and then again at partial throttle (15 degrees throttle angle). The switch reaches its temp, the contact opens and stops providing the enrichment.
>I see the spark plug boot looking thing you're talking about where the 02 wire hooks up and I thought that's what it was. Seems there's some plastic in there that has gotten brittle from heat. Almost like a shift coupler bushing that is crumbling. But the wire is barely sticking out of the boot...no insulation at all.
Mine looked similar...

Bill, just some friendly advice...you really need to buy yourself a Bentley Manual and maybe Charles Probsts book on Bosch EFI...I found both manuals invalueable when diagnosing probs w/CIS

R/
Dustin

DavidI · 02-11-2004, 04:09 PM

This might be a silly question, but do you have an old fuel filter that may be clogged?

WB3 · 02-11-2004, 05:21 PM

Thanks again for the input Dustin. Ok, I see the 15 degree switch that you're talking about. I would assume the switch can be tested to see if it's bad or not? If so, could you explain how I go about doing that? And if I need a new switch, is that what it's known as? The 15 degree switch? I did a search in Pelican for a 15 degree switch and couldn't come up with anything. Do you think in anyway that the rectifier going bad on the alternator had anything to do with this? Because the cold start problem started the next morning. It's just so odd. If the 15 degree switch were bad, would it cause a lean mixture resulting in the backfiring through the pop valve? Is that why it's backfiring through the pop valve...because it's to lean? Also, on the decell valve...If I'm not mistaken, It's the round valve with two large lines and one small seperate line...located on the right side behind the fuel dist? Someone told me the small line hooks up to the cruise control servo? If not, I've got a vacume port open back there somewhere. Is the large line on the CC servo just a "dump" line and not hooked up to anything? I agree with you on the purchase of those manuals 100%...and a decent sized mirror to look behind where all the hoses hook up. Thanks for your time Dustin...really.

Thanks for your input as well DavidI....This problem is really thermal...one that basically goes away when the engine warms up. So I wouldn't think the fuel filter is the culprit. Once the engine is warm, it starts with one crank and I'm only getting the "bucking" I talked about when it's really cold outside. But Thanks! And I do need to change that filter anyway.

konish · 02-11-2004, 05:48 PM

Bill,
Just get an ohmmeter and test the resistance with one lead on the pst on the other to a ground source...take a hair dryer and aim it at the swtich. When it hits the switch temp, you should see resistance on your ohmmeter. You can also remove the switch and test it in a water bath gently heating it and testing the resistance again. The swtich is called the temperature switch. If the switch was bad it could contribute to a cold running issue because your lambda box wouldn't send the signal to the lambda valve to operate at a higher (therfore richer) duty cycle...as the frequency valve (lambda valve..same thing) controls the enrichment by altering the pressure in the pressure bowls in each cylinder of the fuel dist. Not sure about the decel valve and the CC servo...I think most folks just eliminate the decel valve anyway which supoosedly helps on controlling downshift backfires, although mine is still installed. Of course this is all speculation until you test your control / system pressure with a gauge..bottomline is you have to bite the $60 bullet for the gauge if you really want to be able to test and set your pressures. As important as the lamda valve is, it only controls enrichment via the differential in pressure of the pressure bowls, which in turn rely on proper system pressure....

R/
Dustin

WB3 · 02-11-2004, 08:02 PM

Ahhhh, my '67 Baja Bug is lookin better every min. Let's see...there's the carb, the alternator, the hole I put oil in,...you get the Idea. But with over 240K on the SC, it's bound to have a glitch once in awhile. I'll get it fixed. Giddy up!

P.S. Anybody got a 15 degree switch they want to sell?

WB3 · 02-24-2004, 01:25 PM

Thank you Superman for your reply and advice. John, you nailed it. Mookster, you were right on as well. Eureka!!! Problem solved!!! I would never have guessed that such a vital circuit would be wired into the interior lights...glovebox, dome, hoodlight, etc. Man, I am so happy now I can't tell you!!! All this over a 5 amp fuse. I started to think back...when the rectifier on the alternator went south that's when I was opening the hood alot and the interior fuse blew. Turns out, the switch that turns the hood light on and off was shorting out and blowing the fuse. The 02 relay wasn't bad it just wasn't getting any power. Man!!!!

Anyway, I robbed the 5 amp license plate light fuse and plugged her in. In ONE crank the engine fired and the difference was noticeable right away. No more backfiring through the pop valve and it sounded right on! Idle is rock steady @ 1000 rpm. Throttle response is smooth and beautiful once again. I am overjoyed!

I would like to THANK each and everyone of you that responded to my thread...all three of them. Even if your advice did not help me solve this problem, I still thank you very much for your time, effort, and advice. This is a really, really, great forum to have! If I could take you all out to dinner I would! Thank you again everyone, and special thanks to John Walker, Mookster, Konish, Doug Zielke, Gram Archer, and Sammyg2. You guys are great!

HORRAAAYY!!! THREAD(S) ARE CLOSED AND HOPEFULLY THE HISTORY CAN HELP SOMEONE ELSE!

Thanks again!
Bill

ruf-porsche · ruf-porsche's Garage

Must be one last surge when an alternator voltage regulator goes south. When my alternator stop alternating I notice that the a/c also stop working after I had the alternator rebuilt and reinstalled. I thought that the a/c relay that I replace at the beinning of the year had gone south again (Porsche Part order thru PP but it was made in CHINA).

Check the realy and it was fine but wasn't getting any power to the relay. Track it down to the fuse. Kinda strange since the a/c wasn't on when the alternator quit working?