SC starts and pops, then runs rich - AAR?

Won · 05-10-2006, 05:32 PM

Here's what's happening:
I walk over to the car, open the door, get inside, put the key in, start. Virtually no cranking, then with the "whoosh" sound (from CSV?) engine starts. Now, during the winter months, the idle will climb right up to and stay around 1200 for the first few minutes with a cold engine. Right now, after the whoosh, RPM immediately drops to about 200, then it pops through the toilet flapper a couple times.

I understand that to be lean running condition, so I pushed in the plug of WUR a little. That made the car run richer during warm-up, as there is way more backfire through exhaust on off-throttle and the lean surge when shifting is gone. That's nice, right? But it still pops upon start.

For the first minute or so, anything other than the smoothest throttle pedal movement will make the car pop. But after that time, idle RPM drops to around 500 and runs rich until it's fully warmed up and idles at 900. I know the warming up part is not working properly, but I want to fix the popping first.

The thick tubing with an inch of black soft line that connects to AAR was loose because the soft line has shrunk and the hose clamp wasn't tight around it anymore. I put some tape around the soft line to bring back the diameter and that was done in the winter, and had no popping problem.

What happens when that tubing is left open, or has a leak? I'm guessing, because of the fairly consistent time delay between popping and running rich, it's one of the components with heating elements on it. I haven't taken off the AAR to see how much it opens. Which one do you think I should check first, AAR or WUR? Could the problem be related to the ambient temperature?

It pops too when the car's warm, but not fully warmed up, but the lean stage lasts much shorter.

86 911 · 86 911's Garage

Bump - I'm having the same popping effect, but only when I apply gas during the first 15 seconds of start up.

Al S · 05-15-2006, 09:03 PM

Won,

Before you do anything else, you need to know if the WUR is doing its job, with the use of a fuel pressure tester. The pressure should be around 25 psi cold (temp dependent) then slowly increases to 55- 60 psi after about 5 minutes (the heater in the WUR gradually changes the pressure). I recommend making the WUR adjustable (lots of threads on this), you'll thank yourself later. I have the tester if you want to visit Maple Ridge again..

If the WUR checks out, then the AAR is next. It has to close completely, after about 5 minutes (once again, via internal heater). It also has to open the right amount when cold (hit and miss method). This thing comes apart and is easy to adjust (lot's of threads on this too). The AAR is definately "seasonal", and rather fickle. I installed a flow control valve next to my AAR to make the seasonal adjustment easy.

If the AAR checks out, then adjust the idle mixture - lots of threads on that.

If all the above check out, then start looking for vacuum leaks....

Good luck!

Won · 05-16-2006, 01:36 AM

Yes Matt, same thing here, even before my car started to pop regularly upon startup. Are CIS just not meant to be driven for the first minute or two? I can still drive but like I said, I have to be really really smooth with the gas pedal otherwise it will pop like crazy.

Hi Al, thanks for helping me out with the "pinging" before and now "popping"

I might just drive to Maple Ridge... I haven't taken the AAR off to check yet, can I disconnect the "output" tubing without forcing it too much? Do I need to bend or fully disconnect both ends of the tubing to clear the "nozzle" on the AAR body? How likely do you think is it to have a bad AAR that opens too much when cold and closes too quickly? Or WUR that sets the mixture too lean when cold and within a couple minutes turns it too rich? By the way, the warmer the engine, the less tendency it has to pop upon startup. Does that sound familiar? I read a thread on making AAR adjustable, but I should look at the flow control valve on yours next time.

Thanks!

Paulporsche · 04:38 AM

Won,

I think Al is right on the money. Both have an effect over your situation, and they both vary w/ the time and temp, but it would be best to establish whether the WUR is correctly set first, then tackle the AAR. You may have to lean your mixture now, if you are getting popping on overrun.

Matt,

The above applies to you, too. It's most likely just an out of spec WUR, but as you can see the AAR comes into play too.

Al,

Tell us about your adsjustable AAR mod.

Mysterytrain · 05:16 AM

I'm by no means an authority on CIS but I have had a similar issue with my system. My car would start within seconds of cranking and then stumble and cough for 20 secs before sorting itself out. This problem also seemed to get worse as the weather got warmer. Another odd thing it did was during start up in sub freezing temps. The engine would fire right up and then wildly hunt from 600 to 1.8k rpm for a couple of minutes until it warmed up. The stumbling issue reminded me of a overly choked lawn mower engine where it fires up, runs like crap until you lean the mixture.
I finally got off my butt last week and examined the system and control pressures. At 19 degrees C, I had a cold pressure of 2 bar and system pressure of 4.8 bar. These measurements were on the rich side of the spec for a 78SC so i decided to lean it some. I removed the WUR, opened it up and raised the plug using a C -clamp until it was flush with the top of the WUR housing. I then re-installed it and reset the cold pressure to 2.3 bar, the system pressure remained the same. Amazingly, the car starts right up, the stumbling is gone as is the annoying surging when trying to drive 25 mph. I still need to see how the system behaves when summer arrives but so far so good.
I was curious as to how this adjustment would effect my mixture at idle so I re-checked it using the push /pull method on the air sensor plate and found that it had not changed!

hbkramer · 05-16-2006, 05:16 AM

Do a search for souk and his threads on CIS . extensive stuff and you will thank him. also buy Probst's Bosch Fuel inj and Bently manual.
record what you do stepwise to get it right or so you can un-do it in the event ...someone else has to dig in and help. I only know enough to be dangerous ,so wont offer anything other than this.