Auto trans rambling question

mondshine · Post by **mondshine** » Wed Aug 15, 2007 3:02 pm

I'm about to put my '71 square on the road. My major dislike about this car is the fact that it has an auto trans. I've replaced all of the trans seals and the modulator valve; which adjusted exactly as it should. I'm still looking for an inch/pound torque wrench to adjust the bands, and I hope this trans will be OK. My major auto trans beef is the idle speed required to keep the engine at about 850-900 RPM while in gear. When the trans is in N or P, the idle speed is way too high for me.
So the question is: has anybody come up with an idle control to keep the idle constant regardless of load? I've thought about the digital idle stabilizer like the water cooled cars used in the 70's -80's but I'd have to adapt the hall sender ignition from a water cooled distributor to my T3 FI distributor. What about additional vacuum advance when in gear with the brakes on? This could be done with a couple relays and a solenoid valve. It seems to me somebody else has already dealt with this; any ideas?

raygreenwood · Post by **raygreenwood** » Thu Aug 16, 2007 7:12 am

If the idle is excessivley high when in neutral...something is not quite right. It should drop some under load but not a huge amount. What i your idle while in neutral? Ray

mondshine · Post by **mondshine** » Thu Aug 16, 2007 7:53 am

The engine must idle at 1200 - 1250 in neutural in order to maintain 850 -900 in gear. The transmission functions normally in every other way.
Thanks Ray.

raygreenwood · Post by **raygreenwood** » Fri Aug 17, 2007 8:46 am

That is about 200 rpm too high when in neutral or park. Mine...wether 411/412's or type 3...all idled at roughly 1000 to maintain 850+ in gear.

By what method did you adjust the modulator valve? Is this D-jet injected? If so...the adjustment of the injection can have a bit to do with it. Also...an idle stabilizer valve will defeat the MPS if this is D-jet..causing stalling and flat spots. Let me think about this. Ray

mondshine · Post by **mondshine** » Fri Aug 17, 2007 3:39 pm

Ray-
I used my K-Jet fuel pressure gauge (and some fittings to adapt to the 10mm thread on the trans. Once at operating temp., the engine idle is very stable, as are the pressure readings on the gauge. The modulator valve was purchased from Long Enterprises; it uses a small flat blade screw driver to adjust (instead of an allen wrench) but I have no reason to believe that it's the wrong valve. When the vacuum hose is connected, the pressure drops down to exactly where it should be.
I'm still sorting out a funky aux air regulator, but it is off the engine now, and the hose plugged for this purpose. I'm 99.9% sure of no vacuum leaks, and the valves were adjusted very carefully when cold. (I'm aware that tighter tuning is possible by adjusting the valves hot, but the standard method should put me in the ball park.)
This is a stock D-Jet system with the end cap still intact on the MPS.
What is the best device to use to adjust CO (within the purchasing power of an average hobbyist) ? I was considering the Gunson Gastester...about $200. What do you use?

raygreenwood · Post by **raygreenwood** » Fri Aug 17, 2007 4:05 pm

You do realize that setting the modulator valve is done only during driving...not at rest?
There are some variations in modulator valves. Long enterprises is a pretty good source.
It is also possible that your vaccuum signature is off.
I myself...do not have a CO tester. A wideband must be used. I borrow the shop of a friend of mine when I need to tune. I am shopping for one also and am looking on with interest in some of the threads in the fuel injected forum.

I need to sit down with my brown book and go over this in my head. I have not had to adjust one in years.....but there is a specific sequence.

The valve adjustment is correct. Timing has to be spot on also. I will be back with more. Ray

mondshine · Post by **mondshine** » Fri Aug 17, 2007 11:47 pm

Ray- It seems to me that the Bentley manual calls for adjusting the modulator valve at a "fast" idle, and the main pressure is to be checked while driving. I dont have the book with me; (I'm working out of town) but I'll check it again when I get home.
Thanks again for your insight.

raygreenwood · Post by **raygreenwood** » Sun Aug 19, 2007 9:06 am

Yeah...you may be spot on. I am away from my book as well. Did you by chance check the main pressure? The thing I am concerned with is that if there is a large variation in the main oil pressure it may be causing the modulator pressure to need to be changed.

One other thing to look into. Since at idle the load is increased ,it changes teh vacuum signature and load on the MPS as well. It could simply need an adjustment. What is your fuel pressure by the way? Ray

mondshine · Post by **mondshine** » Sun Aug 19, 2007 8:14 pm

My fuel pressure is right at 2 bars; very steady. I might have some fuel pump check valve issues because the fuel pressure drops 10 psi in about 15 - 20 minutes after shut down, and the engine is difficult to start after sitting overnight. Is there any reason an in-line check valve couldn't be installed between the pump and the ring main?
I have not checked the transmission main pressure yet because 1) I don't own a guage that goes that high. 2) The transmission functioned normally before it was removed. 3) I didn't think there was anything I could do about it if the main pressure was out of spec.
On mixture adjustment, I've ordered that Gunson gastester CO meter because I didn't want to spend the money for an LM1 and I didn't feel like drilling a hole in my brand new German T3 muffler for the O sensor. I've read more good than bad about it, so I hope I can make it work at idle and 2500 rpm. I'm looking forward to getting home and spending time in the garage-mahal.
Thanks again for your help with this, Mondshine