yet another CIS question

[Kemo]

ive been fighting a CIS issue for a while and I was hoping to get some input on where to look next as I am out of ideas.

so here is the back ground. Its an 81' SC with stock motor and correct for the year WUR. I had resurrected this car from a long sit as the car was off the road for quite a while. During that time, the gas went bad. I ~thought~ i had got all the junk out of the gas tank but i didnt. i ruined a fuel pump and clogged up all my injectors and what not. in any event, the fuel distributor and WUR went to CIS flowtech for a rebuild along with the purchase of 6 new injectors. while waiting, i replaced the gas tank with a new one and cleaned the fuel lines as best i could along with a new fuel filter.

after reinstalling everything, i was able to get the car running without too much issue. Armed with an innovate LM1, CIS pressure gauge and timing light, i got the car where i thought it would run pretty good. and it did. except the fact that I couldnt set the timing with any confidence as the tick mark was bouncing around. So i sent the distributor out to Jerry Woods for a rebuild.

after reinstalling the rebuilt distributor, here is how I have everything setup.

Distributor retard hose removed, port plugged on dizzy, hose plugged as well
Timing set to 5 deg BTDC at 950 RPM
Oxygen sensor unplugged
Air Fuel Ratio is set to ~13:1 with engine fully warm

CIS Pressure tests:
cold start - system pressure - 4.8. engine sputters up to a low 800 rpm and the control pressure starts at 1.9 bar and climbs to 3.3 bar in 1 minute or so. after 3 min the pressure stablizes at 3.4 bar. System pressure stable at 4.9

as the motor warms up the idle slowly climbs over a period of time to about 975 or 1000 rpm as set when hot.

20 minute leak down pressure - start pressure is 2.9 and after 20 im at 2.0 bar.

I have tested the AAV and it closes over a 4 min time frame nice and slow.

I have pulled the 12V to the WUR on cold start test and noticed that the pressure does not rise until plugged in and at that time it rises as mentioned above over a period of a minute or so from 1.9 or 2 bar to 3.4 bar.

Might I say that this car runs very good once it gets started even just a couple of minutes after first start of the day. steady idle, no bouncing, very consistent. Its just this cold start behavior.

I was under the impression that when the car is first started, the control pressure is low which allows the air across the meter plate to pull the plate a little higher which causes more flow to the injectors creating a richer environment for warm up. to accommodate the rich environment, the AAV is open at cold providing more air during warmup and closes over time as the control pressure rises. As the control pressure rises, the pressure lowers the meter plate in the same air flow which lowers the flow to the injectors and leans the air fuel ratio back down to set point value. in my case 13.0:1

so i was at a loss as to what could be the problem as I would expect a higher RPM during warmup as oppossed to starting low and slowly rising to warm set. I would also expect the cold start AFR to be rich and then slowly funnel down to 13.0.1. So i tested this with my innovate LM1

Cold start AFR: 13.2:1 and it slowly richens up to 13.0:1 over 5 minutes bouncing down to the 12.9:1 at most.

so...upon start, my AFR doesnt change a whole lot at all im guessing the AAV is adding some air as its working.

So why doesnt the mixture go rich? could this be a sticky plunger? i would find that hard to believe as I just had everything rebuilt at CIS Flowtech.

Any advice welcome and thanks in advance for any help here.

[mhackney]

So 2 things:

1) how are you using the LM1? With a CAT you need to measure the AFR upstream of the CAT with the O2 sensor mounted in a bung. I've helped someone recently who was sticking the O2 sensor in his tailpipe!

2) in addition to measuring fuel pressures and setting timing the third most important thing you need to test for is air leaks. You can and will get all sorts of weird behavior with air leaks. I have an inexpensive smoke tester and it is worth its weight in gold for finding leaks.

[Bob Kontak]

1.9 BAR is perfect if the ambient temp is 55F.

Where is stoichiometric?

Is this not on the radar screen?

I know you have the O2 sensor unplugged but when do you plug it in?

[gazzerr]

mhackney what smoke tester do you use?

[mhackney]

I got one of these on eBay. I've used it on my car and several Pelicans that live near me.

I'm completely sold that one of these should be in every SC owner's tool cabinet (if they are a DIYer). It will show every leak clearly and you can use a bicycle air pump or just blow into it if you don't have a compressor. Simple to use and effective. Worth every penny.

[gazzerr]

Thank you!

[Kemo]

to answer a few questions...i have not been using the o2 sensor at all. i keep it unplugged all the time and run in open loop. when measuring the o2 level with the LM1, i plug it into the O2 bung on the pre-muffler. as far as leaks, i have not used the smoke test, but I have replaced all of the rubber collars and replaced all of the plastic inserts into the runners along with new rubber o-rings around the injectors. when i pull the oil filler cap, the idle drops.

[mhackney]

Thanks Kemo, I still suspect and recommend checking for air leaks. On my 83 Cab I KNOW I have a split seam in the airbox and it leaks. But I also get a drop in RPM when I open the oil cap. In my case, I plan to replace the airbox and all the other culprits after the driving season. It runs reasonably well but on occasion I have a cold run situation where the car starts, idles at 950 for a split second and then drops to 800 or so and then rises back to 1000 or a little higher as it warms up. This is, I am sure, completely related the air leak I have. In my case, the leak appears to be due to failed adhesive between the lower vacuum side and the larger upper unmetered air box. I suspect that vacuum can pull the parts together and actually help seal the unit. But sometimes if the seam is open a little more when I park, that extra air leads to the issue described. I now pop my hood and press down on the top of the airbox before starting. Sometimes I'll actually feel a little movement. Since I've been doing this the last month or so I've not had the described cold run issue but I'm also not idling at 1150 or so and then coming down to 950. I'm typically idling at 1000 during warm up. Most of the above is speculation based on very careful observation and testing with the smoke tester.

[rwest]

Originally Posted by mhackney

Thanks Kemo, I still suspect and recommend checking for air leaks. On my 83 Cab I KNOW I have a split seam in the airbox and it leaks. But I also get a drop in RPM when I open the oil cap. In my case, I plan to replace the airbox and all the other culprits after the driving season. It runs reasonably well but on occasion I have a cold run situation where the car starts, idles at 950 for a split second and then drops to 800 or so and then rises back to 1000 or a little higher as it warms up. This is, I am sure, completely related the air leak I have. In my case, the leak appears to be due to failed adhesive between the lower vacuum side and the larger upper unmetered air box. I suspect that vacuum can pull the parts together and actually help seal the unit. But sometimes if the seam is open a little more when I park, that extra air leads to the issue described. I now pop my hood and press down on the top of the airbox before starting. Sometimes I'll actually feel a little movement. Since I've been doing this the last month or so I've not had the described cold run issue but I'm also not idling at 1150 or so and then coming down to 950. I'm typically idling at 1000 during warm up. Most of the above is speculation based on very careful observation and testing with the smoke tester.

I bought a similar smoke machine and was wondering where you were injecting the smoke and what you plug?

Thanks

[mhackney]

So far I've removed the brake booster vacuum line from the driver side of the air box and inject the smoke into the box. Cork the hose. It can be a pain to remove that hose though so I just 3D printed a tailpipe adapter and I'll injection the smoke in that way. I've read about others who have done this. Then, if your air box cover seals well all you need to do is put a glove (latex, nitrile) over the air box snorkel.

[Walt Fricke]

Mh - that smoke machine looks like some parts of it would be easy to fabricate. A paint can, and a pressure regulator (the one there looks like a refugee from a propane grill or the like). But I see wiring - does it go to a heating element, and what do you put in to make the smoke?

[mhackney]

Sorry to hijack this thread. If there are other questions, please start a new post.

Yes, it would be easy to fabricate if you have the materials and knowledge. I priced out purchasing the needed items and because one can't just buy "X feet of nichrome wire" or 6" of the wicking material or 2 of the insulated connectors, and depending on what you have already or can buy locally the shipping and other parts quickly went over the $100 mark and I'd still have to build the thing and probably buy the plans that are out there to know exactly how and what to make the heating coil with. Even running out to my local HD to buy the regulator would be an hour round trip and they want $29.95 for it. This particular project fell into the "it is a better investment of my time and money just to buy a known good unit with a a fair price and good reputation"!

The heating element is nichrome wire. So one would either have to 1) buy plans that are available to learn what nichrome to purchase 2) take a swag at some calculations, purchase some wire and then test and iterate until you got it right or 3) measure the wire and resistance of a working unit. The nichrome needs to be insulated from the can so the connectors you see are designed to insulate on the through hole, not your average HD connector. A piece of woven fiberglass forms a wick. The smoke material is simply mineral oil. It produces a dense white smoke, not at all greasy. It is what the $1000 commercial units use.

[javadog]

Specifying the control pressure readings without mentioning the temperatures they were measured at is meaningless. Make sure your initial control pressure reading is correct for the ambient temperature when the motor is dead cold.

Set the CO using a gas analyzer to what Porsche specified for your motor. Setting it to some random fuel/air ratio isn't the right approach.

Plug the O2 sensor in and use it. It's there for a reason. If you want to run an additional sensor, add another bung.

Checking for intkae leaks is always a good idea.

JR