AAR Specs

[Mysterytrain]

I've been going thru the CIS system on my 78 SC. One thing that puzzles me is the operation of AAR over time. The heater on the unit measures 17 ohms..a bit lower then spec which I think is 34. It also does the open and close thing but I think it is closing too soon. I read in one of the CIS books that I have that the AAR valve should be fully closed within 10 mins. Mine will fully close in 2 mins with voltage applied to the heating element. I think {correct me if I'm wrong} that a longer open time should correspond to the time it takes for the engine to reach operating temp. The issue I'm having is that after the intially cold start cycle the engine will idle at 1200 rpm for about two minutes which is when the AAR fully closes. Once the AAR closes I have to feather the throttle to keep the engine from stalling until it fully warms up..then of course all is wonderful. The car is very drivable except for the fact that it will stall when I come to a stop. I have worked around this problem by adjusting the throttle linkage so that the throttle plate is cracked open a c-hair more. This prevents the car from stalling and doesn't seem to effect the idle once the car is warmed up. I have never seen an adjustment procedure for the throttle plate rest position although there is a stop adjustment. So how long should the AAR be open? I assume I need to take it apart and tweek the valve? Also, does the higher resistance heater coil slow down the closing process. Thanks, Ron
PS..I've pressure tested the system and have replaced the decel valve and the WUR.

[MotoSook]

The higher resistance should make it heat up faster, but it shouldn't matter so much as long as it closes. Don't mess the the throttle plate stop. Put the throttle linkage back to normal . There is something else going on.

What else have you done? You could take the AAR out and clean it. The little plate gets sticky some times. Spray some carb cleaner in there and clena it good. Have you checked you idle mixture?

Put everything back to normal and start with the idle settings.

[Mysterytrain]

Souk,
I have had the AAR out and I have cleaned it. It seems to work fine ..fully open when cold and shuts completely in two minutes. I just figured that it should close a bit slower..it is acting like an automatic choke I guess. I haven't opened it up yet but I recall hearing that the moving plate can be adjsted to stay open longer. My CO has been adjusted using the sensor plate lift method not real scientific but I have been lead to believe close enough. Details: Fresh rebuild 3.0 =>3.2 short stroke, all new injectors (except the start valve, brain fart!), new hoses , new intake boots. Idles fine cold or hot except that it needs a bit of throttle to stay running when cold? Some popping from exhaust when coming off throttle with no load..figured that was the SSI's and Dansk 2in/1 out. You think this is mixture related?

[MotoSook]

Maybe your cold start is dribbling fuel into the intake when it shouldn't be, hence the need for more air through the AAR when it's cold. MAYBE!

Get a new cold start valve. It can be replaced with a partial drop...or not, depends on how familiar you are with the back of the CIS.

I would start there and then get everything dialed in as they should be...then see where you are.

Good luck.

[Paulporsche]

I think your mixture is just a little lean. Try richening by 1/16 turn. See what happens. Try another 1/16 turn if reqd. If your popping on decel stops but you do not get idle hunting, then you are probably OK.

[RarlyL8]

I'll put in my $0.02
Before touching anything you need data. WUR pressure when cold/warm, A:F ratio for same.
Off the cuff, sounds like the engine is running to lean when cold.

[Paulporsche]

But not just lean when cold because he is getting the popping off throttle. This is why I'm thinking a little lean in general.

[Mysterytrain]

Cold Pressure {after sitting overnight } 1.3 bar /18psi
System pressure 5 bar/ 72 psi
Warm Pressure {voltage applied to WUR} 2.8 bar /41 psi
Amibent temp during these tests was 21 deg C / 70 deg F
No co meter or AFR meter yet..but remember this is a 78 with no ox sensor.
There is about 1K miles on the rebuild..pulled a plug and saw carbon soot, not white soot. The poping from exhaust is most noticable in the garage when opening the throttle and releasing. (hence, no load) and does not happen all the time. the big issue is that it will stall while trying to warm up..thanks for all the input.

[cmonref]

<< The higher resistance should make it heat up faster>>

Isn't this backwards? Power dissipation is voltage-squared over resistance for a DC circuit.

[MotoSook]

I'm not looking at a chart, but the cold and warm pressure seem a bit low. We've posted CIS P-T charts before. Do a search or look in the Bentley or Haynes...

Low control pressure -> rich

[Mysterytrain]

Ok, I got out the guages and the hammer and tweeked my cold pressure on the WUR.
Temp sunday morning was 65 degrees in the garage
Cold Pressure is now 1.9 bar/28psi
Warm Pressure is 2.8 bar/41 psi voltage applied (stayed the same0
Warm Pressure with vacuum applied 3.6 Bar /51 psi
Car starts right up ...one crank, ( still a bit of white smoke -1k on the rebuild). Idles at 1.6k for a minute or so and drops down to 1K. Fairly smooth idle as it warms up to operating temp. I can drive the car..when I come off throttle the revs drop below 1k to about 800 rpm and then stablizes at 1k and hasn't stalled yet. then once its warm its happy. Looks like I still have some issues with CIS leakdown pressures..I'm thinking the cold start valve should be replaced ( kicking myself for not doing it while the engine was out)and I'm looking seroiusly at the the 26 year old accumulator. I guess I still need to get a proper CO reading, I've been adjusting it with the sensor plate lift pull method. Looks like its time to write a ck for the Gunson.

[MotoSook]

Originally posted by Brian K. Haggard
<< The higher resistance should make it heat up faster>>

Isn't this backwards? Power dissipation is voltage-squared over resistance for a DC circuit.

Brian, I'm not an EE, and I hated EE lab as a student. My reasoning is that the heating element being of greater resistance should heat up faster...the resistance generates heat. Oh well...I'll stick to mechanical stuff..electrons and I never liked each other.

As for -train's problem, looks like he's on his way to fixing it. I wouldn't waste money on a Gunson tester. If all else is right, just set the idle mixture midway between rich and lean, richen if you have to. And I could never get a smooth idle at 850 RPM. Hell, even my DME engine doesn't idle as smooth as I like it at the 850-900 RPM range. My CIS engine idles at 1000 or 1100 and it's fine that way...smooth and no dipping toward stalling. Who said it HAS to absolutely be at 850?

[Paulporsche]

Mysterytrain,

I think you are almost there. Try setting the idle to 1050 when warm.

When there is a swing as you describe, where off the throttle the revs dip slightly before they go back up to normal, usually you are too rich. Try leaning 1/16 turn and you just might have it.

Usually if the car starts, the cold start valve is OK. There is a possibility it is a decel valve problem, but I would try leaning slightly for now. Leaning may make your idle revs go up a little.

Let us know.

[Mysterytrain]

Paul,
Thanks..the decel is new and solved the hanging high idle problem. That dip from low to high is only when the car is in warm up mode. The cold start valve replacement is because I'm leaking down to fast...maybe some post nasel drip from the valve..that might also effect my warmups. I'm also suspect of the accumulator..26 years old and I'm sure it has had its share of some bad fuel..the car sat for 2 years before the rebuild. I cried when my mechanic told me he ran the old fuel thru the system!

[Paulporsche]

Did you say you checked your residual perssure? It should be at least 1.3 bar after 10 min, and at least 1.1 bar after being off for 30 min. This will tell you if the accumulator or check valve are OK or not.

It's possible your cold start valve is leaking, and making your warmup mixture rich, although that usually will cause flooding when starting a warm engine.

Have you tried slightly leaning the mixture? You might find you can get it to be a good compromise for warmup and warm running.

[Mysterytrain]

Hey Paul,
I leaned her out a bit and might have gone a snot too far..my idle is slow to come down now and will sometimes hang at 2K. I'll make a small adjustment today and report back.