Techical Discussions => General Tech => Topic started by: Mike on October 23, 2008, 04:45:02 PM

Title: Curb Idle Solenoid
Post by: Mike on October 23, 2008, 04:45:02 PM
How can you tell is the curb idle solenoid on a AVS carb is bad?

Title: Curb Idle Solenoid
Post by: Johnny D. on October 23, 2008, 04:51:06 PM
doing a little diggin for geno eh P?

this is on a 1970 spread bore carb, from a '70 340 cuda with a 4 spd  manual...

their is continuity on the circuts from the alt, and if you hook the solenoid to a battery it will pop until too much pressure is exerted on it to do so...

Title: Curb Idle Solenoid
Post by: Steve on October 23, 2008, 06:03:15 PM
Quote from: MobStaffCar72
Title: Curb Idle Solenoid
Post by: Johnny D. on October 24, 2008, 07:00:28 AM
the wires are giving juice and the unit works if you test it... if you hook it up though, all together it does squat.

Title: Curb Idle Solenoid
Post by: Butch Houghton on October 24, 2008, 07:57:49 AM

Uh yeah...HUH?

You just turn the ignition key on & go out & crack the throttle open to see if the solenoid kicks out.   If not make sure there's voltage at the solenoid connector first.   If there is then either the solenoid is bad or there's a ground problem with the solenoid.

If there's no voltage there then chase it back.

You can check solenoids off the car with a 12v source & a couple of clip leads.

If you got a 70 model car with  a T-quad then somebody put it there....they didn't exist in70.

Just read the last one......if it has voltage but won't hold open then the coil is too weak's bad.   You could check it's get ground that way.   Take it off & clean the surface good.   Might make sure the throttle return sprin isn't too strong.   with enough force you can push the Idle solenoids closed, they aren't super strong.


HemiFury2008-10-24 13:02:51
Title: Curb Idle Solenoid
Post by: Mike on October 24, 2008, 03:25:01 PM
Thanks Butch I'll be sure to give all that a try, I'll also try to get some pictures to you fellas as well.

Title: Curb Idle Solenoid
Post by: Mike on October 28, 2008, 06:28:08 PM
   Butch the carb is an AVS not a Thermoquad, we have continuity from soleniod to alternator. Soleniod checks ok off the car with a 12 volt source, alternator shows 8 volts off the contact to soleniod. Not sure if it is horizontal or vertical pole , could the alternator be bad , or balast resistor be bad? Also were else could I look to run the ground issue down. Any help would be appreciated as always.
Title: Curb Idle Solenoid
Post by: Butch Houghton on October 29, 2008, 07:28:45 AM
Lesse here....I'd say 8 volts is too low to kick it.     My test to see would be a wire straight from the battery ( provided it's charged good )  to the connection at the solenoid & see if it kicks.   If it does then you have a voltage drop in the harness somewhere.   Was this voltage check done with the car running?   If the battery is a bit low then start the car & check it again.

This is why I've made up clip lead sets of varying lengths to test stuff.    Makes trouble shooting easier.    A simple piece of wire will do though. 

A quick check of the charging system is to just measure across the battery with the car running,  should be 13.8 - 14.2 volts if the charging system is working.  If not then it's Alternator/regulator/wiring issues.  If it's good the first place to check stuff is the Bulkhead ( as usual ) .   A quick check of the underhood  voltages would be the input side of the Ballast resistor,  it should have 12V since it gets voltage straight from the Ign switch (through the bulkheadof course ) .  if it's low there then it's time to definitely check the bulkhead.  If it reads the same at the bulkhead then go inside & see what it is off the Ignition switch at the base of the column connection.   If it'slow there might be a bad ignition switch.   If it's good at the base of the column then the issue is between there & the bulkhead.   I don't think that run branches off anywhere from the switch but would have to check a schematic to be sure.    Most likely in this case it would be the bulkhead cause this is where most of our wiring problems come from with age.

Basic troubleshooting,  start at the problem & work back until you find it.    No fun but the best way to isolate the issue.    As these car get older the wiring becomes more of an issue. 

FWIW that supply wire to the solenoid most likely taps into the same run going to the Ballast,  they called that the #2 splice in the books.   Soldered factory splice inside the wiring harness underhood wrapped with cloth tape & then the outside wrap of the whole harness.  They split off most all 12V ignition sources this way under the hood & I've found up to 4 sliced together like this in harnesess.   At least up to 1970 anyway.

AVS makes more sense!    got one here like that too.    70 GTX,  440 -AVS car with the solenoid & it's dead too.    We just set the curb idle & ignore it unless they want to spend the money for a replacement ( pricey ).   All the solenoid does is hold the idle open until the key is off & lets it close to stop run-on ( dieseling ) due to the higher idle speeds usually for the Hi-po cars with a bit more cam in them.  


Title: Curb Idle Solenoid
Post by: Mike on November 02, 2008, 09:01:52 PM
  Hey Butch!

  Thank you for your help!, We followed your instructions and
tonight, we tested the alternator and battery and then the solenoid
again and it kicked so we hooked it up and it worker perfectly!

  My next question is, should the idle of the engine be set to 700
or 800 RPM? The inner fender sticker says 900 RPM at idle so figured
7-800 would do the trick, thats with the engine timed at 5 degress TDC
assuming it is correct.



Title: Curb Idle Solenoid
Post by: Butch Houghton on November 03, 2008, 06:12:16 AM
The 900 is the Idle speed in Neutral gear it'll most likely drop to at least 800.

This is why the Idle Solenoid's came into being,  the higher 900 Idle of say a Magnum 4BBl motor as opposed to the say 2-BBl Idle speed of 650-700 .    It's all about the Compression/Cam profile  for the Hi-po motors.

How far it drops depends also on the Converter,  a tight (Low-Stall) will "pull down"  the Idle more than a factory High-stall ( 2200-2600 depending on the engine ).   How well-tuned the carb is will affect it too as well as the timing.  5 degrees maybe what the sticker says but I never go by that.   By around 70 the Timing specs had to take into account emmissions to an extent so they kept them low.    I usually start with 10 Degrees Initial & see if the Engine "Likes" it.  that means setting Intial there,  taking a look at the total to make sure it's not way high & then driving the car to listen for any "Pinging"  ( detonation).    A dial-back light is really the way to check total but a timing tape on the damper & a regular light will do the job ( the Dial-bacl was one of the best investments I ever made,  can't ever own enough of em'  if you're gonna fool with cars )

Here's what I'd do......Leave it set at 5 degrees ,  set the curb Idle at 900 & then put it in gear & see what it drops to.    Actually sit in the car see what it feels like at that Idle speed.    Does it pull against the brakes too much?  does it feel just right?   Feel just a bit low in gear?    Bottom line is how it  "Feels" to ya,   50 RPM either way can make a big difference in how it feels.     When you got it where youlike it turn the headlights on High-beam & see if it changes much....alternator load can drop them some,   just something to double-check.   

Now go out & drive the car!    take note of how it feels at light throttle & then get on it some & see how it performs.    If you can get climbing a hill in High-gear  even at say 35-40 MPH & just roll into the trottle short of Kickdown you'll have it under a good load to listen for any detonation,  that condition & at wide-open throttle is where you'd hear any detonation.

If all is good.....try bumping the intial timing to 10 degrees & repeat all the driving tests,  remember you'll have to drop the curb idle back because when you rasie the timing the RPM will pick up too.    At least you'll have a good feel for where to re-set it by then.  If it feels even better then leave it there.   If at that timing setting you notice any detonation then it'll be time to recurve the distributor & that's a whole nother' discussion.  

Holler back with results!   Bottom line is any time you change things you gotta go drive the car & see how it responded to them.     That's what "tuning" is all about.