Frequency Valve/Computer Qu My jmoestion

[Superman]

Here's one for the Swami's of CIS:

I've got an '83 motor I want to use in a '78 car. '83 motors have narrower intake runners, which draw air at a higher velocity than the earlier, fatter intake runners. My motor has 20/21 cams, which work very well with the narrower intake runners. Unfortunately, the intake system on the '83 motor requires some circuitry including a computer box thingie that goes under the passenger seat. The '78 tub lacks the proper bracket, and I don't want to undertake the welding that would be required to retain a computer that I'd rather ditch anyway.

So.......how can I use my '83 CIS intake system without using the computer? My O2 sensor is unplugged anyway, so the system is always in "open loop," or whatever you call it. The frequency valve has to BUZZZZZZ in order for the system to work. Is there a way I can make the frequency valve BUZZZZ without the computer?

[euro911sc]

My guess would be pin it to a switched power source in the engine bay if open loop = powered buzzing freq valve. Otherwise pin it to a ground. Simple voltage measurement at the valve while running open loop would tell you which way to go. I do not have my wiring diagrams here at work...

-Michael

[john walker's workshop]

it always has power. the ground is pulsated by the computer.

[T77911S]

one option would be to change the FD to either a 78 or 79 that does not use the FV, just one more electrical component to go bad, especially if you REALLY are not using it. i have also heard that the 77 FD was a good replacement because it flows more fuel than the 80's FD. you would also need the 033 or 045 WUR with vac control.
another option would be to plug the 2 lines the FV is connected to. you may have to adjust WCP to make it work, but if gets rid of the FV it may be worth it.
one question for you or someone else out there. the 83 CIS has a throttle switch for enrichment, correct? if you remove the computer, would you be better off with the 78-9 FD and WUR anyway? the FD/WUR combo of the 77-79 provided a lot of fuel at WOT.

[Superman]

Hmmmmm....... I don't understand these things. I've got two complete CIS systems, and I'm going to use the '83 motor (smaller intake ports than early SC's). It sounds like I'll either have to mount and use the computer.........or take parts off the '78 CIS system to reconfigure the '83 system, so it can work (with the smaller intake runners). Sounds like a PITA either way.

Anybody got a decent pair of Webers or PMO's?

[john walker's workshop]

early FD and WUR on late engine, along with their fuel lines.

[T77911S]

no its not.
if you are not useing the 78 CIS, take the FD with all the lines and bolt it to the 83 AFM, about a 5 minute job if on the bench. then swap the 78 WUR over to the 83. this gets rid of the electrical crap. i would also swap the TB too. it will have the proper port for the WUR, it should be in the rear (he,he, i said in the rear) at the bottom. the 83 may or may not have the proper port the the vac control on the WUR. the TB i took off the 80 CIS had the port, not sure if the 83 has it. you can swap all this in a 1/2 hour unless you decide to clean it all up.

JW, since i you are here, i put the larger 3.0 TB on my 2.7, nice improvement. i have not heard of others doing this, so i thought i would get your input or at least pass the idea on.

[don gilbert]

superman, why dont you go ahead and fix the 02 system, makes for a more powerful car in stock configuration, and get 25+ mpg, plus, you can make all kinds of afr adjustments during open loop, (past the 35 degree switch) and still run stoiche at cruise and part throttle. dont be scared of the 02 system, it is your friend. if you go non 02 rt, will need to get f/dist, and a vacuum controlled wur,( the vacuum wur are getting very hard to find)

[Superman]

O2 systems don't do much and what they do......is they lean the mixture. I'm running maximum distributor advance, so I cannot afford a lean mixture. I'm not the slightest bit concerned about gas mileage. Not even a little. What I'd really like..........is a 3.8 MFI engine.

Thanks, guys. It looks like I can retain my CIS, save money and have a good-running car. Sht! I want carbs.

[JFairman]

The pulse/frequency valve bleeds off fuel pressure from the lower side of the 6 differential valves and returns it to fuel tank.

If there are 6 little button head allen screws next to the banjo bolt injector line ports on the top of the fuel head you are using, you can unscrew them and there is a little 3mm allen head screw under each one.

Those 3mm screws are holding spring tension on the top side of the differential valves.
Adjusting these correctly will help even out the volume of fuel delivery to the 6 injectors, and can also compensate for removing the frequency valve which would always be buzzing and returning some fuel to the tank.

930 fuel heads have these adjustors but I don't know if the one you are using has them. Would have to see a picture.

[MatthewBrum]

Originally Posted by john walker's workshop

early FD and WUR on late engine, along with their fuel lines.

Why couldn't you just use the early WUR and be done with it, is there a difference between the early and later FD's, and why do you sugest using the early fuel lines?

thanks-Matt

[don gilbert]

all things being eqaul, an 02 car will out perform and get way better gas milage than a non 02 car, it does not lean the mixture, it keeps the mixture at stoiche during idle and part throttle, past the 35 degree throttle switch, the frequency valve goes to a 90 percent duty cycle and richen the mix up. as I said in my prev, post, the beauty of an 02 car is the ability to make afr adjustment (richen it up) and still get the great milage when just cruising.