I removed A/C and Cat. How do i trick ECU and plug feedback system back in?

[freeman]

My 85KC 720 5 spd 250k. Las Vegas, Nv.

 

Hey Yall.

I removed my ac(thru away) and cat(kept)  and now it wont idle.  i have to unplug the yellow feedback connection so it idles.. and runs ok. except the performance has diminished and am getting 30+ less miles per tankfull.

 

I believe its the Ac info thats missing for the ecu to work properly.

Where will i find the ac wire and make the ecu think the ac is there and working properly?

 

Im sure everything all other parts are good and sending info for ecu.  id like to start with the ac ecu pin trick...then test all the other feedback parts last. i may have to buy and learn to use a multimeter is ok except what dial location should it be set to? and where is that ac wire for the ecu.

 

BTW>  Also been curious Where is the FIDC located(Fast idle control devise)..and what does it look like? is it the fast idle cam? i dont think so and it has no wire going to it.

 

Thank you very much.  -Wayne Freeman

[captain720]

Anyone on here will buy your AC.

[Charlie69]

Datzenmike most likely has the information and pictures you need he will probably be on here later.  He is a great source of information.

[datzenmike]

AFAIK there is just an idle up solenoid (FIDC) to compensate for the added load on the engine. I/m not aware the ECU has any interest in the a/c and if on or not.

 

Two things... do you have one or two wing nuts holding the air filter on? If one, do you have an O₂ sensor in the exhaust?

[freeman]

Its the single nut with o2 at the exhaust manifold area..  fairly new o2 sensor.  

Nevada has smog testing and i want to get the regular Nevada license n tag..and get back performance and mileage.

 

I got some info at High impact Motorsports here in Vegas..He mentioned the fidc location and ac probably not involved with ecu also. i fixed a cracked vac line at fidc and cleaned connections.

 

I plugged the yellow wire back and  dies at idle immediately or eventually and ecu light didnt come on when i helped it idle. no ecu light is new.

When yellow is disconnected and i pull on the ac fan lever..it will idle a bit high and return to normal back n forth like its ready for a compressor to come on.

 

so ill say i guess its time to check the sensors?

neutal switch/  vacuum switch/ water temp/..o2/  ecu ground/..ign coil trigger/..mix sol/ anti diesel/ battery volt.

What would you do?  Thank you for some directions ..i have to lay down.. before riding the electrical. depression bike..

[datzenmike]

What's this Yellow wire you mention???

 

Single wing nut and O₂ is an electronic feedback (ECC) carb. Keep in mind that the main jet is a solenoid that opens and closes many times a second to vary the mixture. This is all governed by feedback from the O₂ sensor. If there is a failure in the ECC it defaults to a 'limp home' mode of extra rich so the engine cannot accidentally go over lean and be damaged.

 

On start up the system operates in open loop because the choke is on and the engine warming up. If the water temp sensor has failed (NOT the water temp sensor for the gauge in the dash) the ECC may be fooled into thinking the engine is in warm up mode. Once warmed up the O₂ sensor takes over and adjusts the fuel mixture for best economy

 

There is a vacuum switch that senses heavy lkoad full throttle and this over rides the ECC to run richer for full performance. If the switch has failed the ECC may be fooled into thinking the throttle is floored all the time.

 

 

That's just a couple of things that might be wrong. The 720 6 wire plug behind the carb is also known to be problematic. Here are the wires to and from the carb itself...

 

[freeman]

You know..the feedback system disconnect wire is yellow..  you know.  at pass firewall.. back left of carb

the water temp sensor and vac sensor sounds like it.    esp since i forgot to be careful not to damage something else.. as usual. always happens.

So old anyways ill replace them.    see if any local store has in stock....maybe test but i only have a test light for power to it

ok ill find out where there located...just follow the 6 wire connector to them  or pics online.

 

Thanks man def a good place to start. i appreciate it. 

 

ecu ground an easy fix while out there too.

 

my af sol does the clicking 

anti diesel sol works

battery groung good as i have it grounded to starter..firewall and the power steering resevoir bracket. haha  (learned importance from a 72 caprice when it would backfire returning from a long trip. started at 75 mph then on down to 70 65 60 55 50 45 40 35. a mechanic hooked up another ground and fixed. amazing.cost me $20)