Charcoal Canister Drawing Vacuum?

[BobBarry]

My '88 GW has a persistent run-on problem. I suspected the NLRV was feeding too much vacuum to the distributor advance, bumping up the idle and making it want to keep running.

So I took the NLRV out of the lines, and with the engine warmed up at idle, was *still* seeing a vacuum signal at the distributor advance.

I traced it back to the purge signal port on the charcoal canister. It's supposed to be activated by ported vacuum, letting the engine draw in the fuel vapors above idle. Instead, this port is producing about 10" of vacuum while the engine is at idle, which was bumping up the spark advance when it shouldn't.

Anybody familiar enough with the inner-workings of these charcoal canisters to say what is causing this? I can only imagine that there is a leak inside, creating an opening between the purge port (which goes to the PCV valve) and the vacuum signal port. Any ideas?

------------------
Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[christopher]

there is a cap on top of the canister. remove the cap, there is a black diaphram valve. replace this valve. I found one in the bone yard from a 90s toyota pickup. bring the valve to the bone yard for comparison

[Va-Rob]

I'll be watching this thread with interest. I have a similar problem with my 90 Wag. I have occasional run-on and rough idle. The mechanic needs me to leave it with him for a couple day's so he can test the systems. He thinks it could be any of a number of things but most likely a bad CTO valve. The only question is which one. He thinks it might also be a sticking EGR valve. At 65.00$ an hour for test I might just change out a few parts to see if it fixes it myself. If not it goes to the shop.

Rob

[andy d]

my interest is piqued. 88gwag occasionally runs on. usually, its in warm wet conditions. its more of a curiosity than a problem. prolly due to the high idle (35mph) http://www.ifsja.org/ubb/biggrin.gif

------------------
'88 gwag,pure stock

[nograin]

Will try here. Your theory of a damaged valve sounds real good.
The new mighty vac book shows the purge sig as a vac diaphram/motor that lets the vapors get drawn into the F/A mixture through the PCV port. Since the charcoal is open to fresh air(?maybe not directly on later cars) a reading of 10" could easily represent a bled down manifold vac signal.

Can you pinch or better remove & plug the can purge line from the can and remeasure the purge sig port?

Mighty vac book also implies there should be no communication from the purge sig motor. Says it should hold 2 - 5" Hg for at least 15 sec. without leaking down.

Hope that helps some.


------------------
360 auto select
body by beer (PO)
carries wood inside
no "wood" outside

[wagdriver]

Dr. Bob have you checked your CTO for proper operation. I believe the purge control signal is tied to the operation of one if not two of them if you have the heavy duty cooling system. It is my understanding that the purge canister is not activated until the engine has warmed to normal operating temperature. If the CTOs were not funtioning properly, leaking because they are not seated that may provide the vacumm signal at the wrong time causeing your problem. Or maybe I have got it all wrong, anyway just a thought.
wagdriver




------------------
wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[nograin]

ooooo, I'm a grease monkey! for trying to help Dr. Bob. http://www.ifsja.org/ubb/smile.gif

WagD: Going off the 84 & 85 vac diagrams, the purge control is direct T into the ported vac source from the carb. Does yours show different?

AndyD: Are you serious? Ever consider one them idle stop soleenoids? http://www.ifsja.org/ubb/smile.gif

Va: I'll take up ClarkGriswold's banner..my Mighty Vac Silverline (all metal) kit cost about $50 from a not so local parts store. With it and another gage, you diagnose most of the stuff yerself. I see it as a savings in both direct cost and time. Something to consider anyway.

[wagdriver]

nograin and company OK guys I goofed again The signal for the canister is directly teed of the ported vac. The point I was trying to make is that if you trace back from the distributer vac advance you go through one or 2(if you have the heavy duty cooling option)CTO to get back to the ported source. http://www.ifsja.org/ubb/wink.gif

Va-Rob If I were you I would replace one or all of the CTOs I replaced all of mine at around 100k as preemptive strike, I figured sooner or later one of them was going to die and cause me a bunch of grief. If I remember right they were less than $10 a piece, and still available at the dealer. You may find them at the auto parts stores, however I did not have any luck there when I was looking for mine. http://www.ifsja.org/ubb/frown.gif

------------------
wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[BobBarry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by wagdriver:
Va-Rob If I were you I would replace one or all of the CTOs I replaced all of mine at around 100k as preemptive strike, I figured sooner or later one of them was going to die and cause me a bunch of grief. If I remember right they were less than $10 a piece, and still available at the dealer. You may find them at the auto parts stores, however I did not have any luck there when I was looking for mine. http://www.ifsja.org/ubb/frown.gif
<HR></BLOCKQUOTE>

I've got all-new CTO's on my '88, so a leaky one isn't the problem (that was my first suspect). My search for non-factory CTO's to solve the problem was the origins of the CTO interchange page at:

http://home.off-road.com/~wagoneer/tech/cto.html

Running true ported vacuum while idling at temp didn't solve the run-on problem... http://www.ifsja.org/ubb/frown.gif

I'll be trying another anti-diesel solenoid; the problem seems to be worse with winter-formulated fuel, leading me to believe that it may just be a problem with the volatility of the fuel we have available right now.

I'm even more concerned that the engine-rebuilders didn't put this thing back together properly. I have a multi-keyway timing set, and I have no idea if they were careful in lining up the marks. Plus, the truck fails the "dollar-bill test", and gets poor fuel economy. I may redo a set of heads from the motor I'm pulling out of my Cherokee, and strip the motor down to the block to properly degree the cam. That way I'll at least know the motor is basically sound.

------------------
Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[nograin]

Dr Bob,
Did the PCV / purge port check out?

Sorry to hear about the possibble bum engine rebuild. I assume what your saying is they may not have timed the cam right? Can you get your hands on a solid lifter - that way you could check the cam timing without tearing everything down.

Hate to say it, I had to yank the heads on my long block 340 from RHS about a year after getting it. Valve work was very poor - had them redone at a shop with a good rep.

-Matt

[BobBarry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by nograin:
Dr Bob,
Did the PCV / purge port check out?<HR></BLOCKQUOTE>

I haven't checked it out yet; too dang cold up here! (it's supposed to get above freezing this week, finally)

<BLOCKQUOTE>quote:</font><HR>Sorry to hear about the possibble bum engine rebuild. I assume what your saying is they may not have timed the cam right? Can you get your hands on a solid lifter - that way you could check the cam timing without tearing everything down.

Hate to say it, I had to yank the heads on my long block 340 from RHS about a year after getting it. Valve work was very poor - had them redone at a shop with a good rep.<HR></BLOCKQUOTE>

I wish I had the time to build it myself when it needed it. Pulling the heads is no big deal; it will give me a chance to do some minor porting and polish the chambers (to reduce detonation). Plus I'll add some performance valvesprings (though I did have them install new stock replacement springs at rebuild time). I just don't like the idea of having to tear down a motor just 12,000 miles after it's been rebuilt... &gt; http://www.ifsja.org/ubb/frown.gif

------------------
Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[wagdriver]

Its my understanding that the diesleing solonoid allows the throtle plate to close more to cut of the flow of air and stop the engine from getting air, forcing it to shut down for lack of air. you might want to check the clearance on the throutle plate it should be closed off completely when you turn off the key, I think.
wagdriver

------------------
wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[Va-Rob]

Thanks for the info on the CTO's.

Rob