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  • December 10, 2019, 01:50:15 PM

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Author Topic: Cannot tune for anything BUT curb idle  (Read 1153 times)

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Offline MIPS

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Cannot tune for anything BUT curb idle
« on: May 19, 2019, 10:01:27 PM »
This weekend was the big event where the Carter 2BBD was stripped down and rebuilt, followed by the timing and all adjustments being reset to spec.
The carb ran perfectly after and drove home last night with minimal adjustment. Today after verifying that the three ignition advance systems were working properly we reset the timing to 15 degrees as per the shop book, then reset the idle. Right now the curb idle is a solid 500rpm and sounds excellent.
The problem comes up when you try to step on the gas at ALL. The engine bogs down, stalls or backfires badly. Vacuum advance reads great at idle, until you step on the gas, then it falls off and then, same as above. No oscillating though, so it's not a really really bad blow-by issue.
Ultimately right now the distributor had to be bumped to 20 degrees before it would both idle and still be driveable but it misses and sounds like crap.

Best I can think of is the CTO is stuck. Basically everything else I can think of testing has been done and either been replaced or tested.
« Last Edit: May 20, 2019, 03:42:11 PM by MIPS »

Offline DAVE

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Re: Cannot tune for anything BUT curb idle
« Reply #1 on: May 20, 2019, 09:27:43 AM »
maybe the harmonic balancer has shifted or slipped causing timing to be different than what the timing light reads
I have heard that this is common

Offline MIPS

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Re: Cannot tune for anything BUT curb idle
« Reply #2 on: May 20, 2019, 12:40:17 PM »
That would be miserable. How do you even do it remotely accurately when your reference point is off an unknown amount? Replace the entire pulley?

This morning I checked the CTO and found it configured as seen below but can someone explain what the delay does in the cold position?



The theory of operation is that the EGR remains off when the engine is cold and the distributor runs from manifold vacuum, once the engine warms up however the EGR gets vacuum and the distributor advance switches to ported vacuum. The functional testing in the manual uses port lettering and numbering but depicts switches different from the installed one above, so I don't know how to reliably test it and do not have a replacement immediately available.

Edited: Verifying if the balancer has slipped should be easy though. The manual says that once the engine is warm the CTO switches from manifold to ported vacuum for distributor advance, so get 'er warm, bypass the CTO and go straight to ported and if it still misbehaves then the balancer is bad, right?
« Last Edit: May 20, 2019, 02:33:17 PM by MIPS »

Offline MIPS

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Re: Cannot tune for anything BUT curb idle
« Reply #3 on: May 21, 2019, 11:38:27 PM »
Unless someone says otherwise, it might not be a plugged CTO so much as a leaking CTO.
As a test I plugged all but the manifold vacuum port and with a hand pump could not hold it for any reasonable amount of time above 5"hg. Plugging that and testing from the ported connection was no better. It got worse if I tried a stronger vacuum. I ended up driving home with the distributor hooked into the manifold directly and while I lacked power it seemed like it would behave well enough to hold me over until a new CTO arrives.

Offline derf

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Re: Cannot tune for anything BUT curb idle
« Reply #4 on: May 22, 2019, 10:45:22 AM »
I'd just run the vacuum straight to the manifold and skip the CTO altogether.
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Offline MIPS

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Re: Cannot tune for anything BUT curb idle
« Reply #5 on: May 23, 2019, 01:19:07 AM »
But then the engine always runs with a skewed vacuum advance, which throws off the computer.

Offline vangremlin

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Re: Cannot tune for anything BUT curb idle
« Reply #6 on: May 23, 2019, 06:26:47 PM »
Thought this link might be helpful if you are looking for a replacement CTO

http://www.drbob.tqhosting.com/tech/cto.html
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Offline MIPS

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Re: Cannot tune for anything BUT curb idle
« Reply #7 on: May 24, 2019, 03:21:13 PM »
Thanks for the link as it's an excellent cross-reference.
It does however seem to confirm that my orange 5-port unit which I am struggling to find in stock anywhere, or cheap online, is somehow different than the black 5-port model that CAN still be found somewhat easily still and much cheaper. It doesn't give exact details though, so I'm going to take a gamble and see if the Duralast E960 (BLACK) is compatible with the E956 (ORANGE) and if not, what makes it incompatible.

Edited: Ah, here we go. Straight from Mopar.



Quote
13   
SWITCH, Dual Function CTO
J3238932 (E960, the BLACK one)
1981 (Intake Manifold Coolant Passage)
1982: EXPORT, Australian Design Rules, Economic Commission of Europe, Non-Regulated Markets (Intake Manifold Coolant Passage)
1982: US-49 States, CANADA (Intake Manifold Coolant Passage)
1983: With Automatic Transmission, without High Altitude Operation (Intake Manifold Coolant Passage)
1984: US-California, EXPORT, without Non-Regulated Markets (Intake Manifold Coolant Passage)
1985-86: US-50 States, EXPORT, without Non-Regulated Markets (Intake Manifold Coolant Passage)
Quote
13   
SWITCH, Dual Function CTO
J3241784 (E956, The ORANGE one)
1982: Japan (Intake Manifold Coolant Passage)
1982: US-California (Intake Manifold Coolant Passage)
-source

The E960 operates at 155 degrees (F), whereas the one currently in the car should operate at 115 according to AMC's wording. All cross-referenced substitutes for the E960 list their operating temperature anywhere between those numbers, so that's close enough.
So technically it should be functionally identical, just one is rated for California Emission Standards.
« Last Edit: May 24, 2019, 08:20:12 PM by MIPS »

Offline AMC1

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Re: Cannot tune for anything BUT curb idle
« Reply #8 on: June 09, 2019, 01:30:29 PM »
I'm going through the similar problem after reaching normal operating temp. I've replaced almost everything & the last thing is the MCU. A rebuilder is working on that as I write this. If that doesn't do it I'll have to do a bypass. One thing however is to take a look at the ignition coil. Mine turned out to be OK but they frequently enough go bad after getting hot.
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Offline MIPS

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Re: Cannot tune for anything BUT curb idle
« Reply #9 on: June 10, 2019, 12:32:53 AM »
I have the replacement CTO switch here now and am able to verify that indeed the one currently installed is leaking however it will still be another week before the correct wrench (1 1/4") arrives to replace it. The switch sits nested between the carb and the casting for the coolant jacket so you cannot get at it with adjustable pliers.

Offline TheBirdman

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Re: Cannot tune for anything BUT curb idle
« Reply #10 on: June 14, 2019, 12:40:27 PM »
Stuff like this is why tearing out the cec was thefirst thing i did.

But hey, good on you for going all in on keeping it original.
83 eagle wagon 4.0

Offline MIPS

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Re: Cannot tune for anything BUT curb idle
« Reply #11 on: June 16, 2019, 02:31:49 PM »
New one is installed. For the love of god, for anyone who has to do this have both an open ended 1 1/4" wrench and a pair of adjustable pliers and remove the carburetor and relocate any lines routed over it temporarily because it's in a REALLY tight spot.



With the old unit removed (orange body, stamped EF3241784) it was found to hold vacuum cold however leaked on the distributor side once warm. Should be good to tune next weekend once the heater core is reinstalled.

Offline AMC of Houston

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Re: Cannot tune for anything BUT curb idle
« Reply #12 on: June 16, 2019, 05:13:44 PM »
I use a really big crow-foot wrench on things like this.   Those things have come in handy on lots of things (like torqueing the big-nut driveshaft nut on my '64 American to 350 lbs!).
George G.
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1960 1902 Rambler Replica
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'78 Pacer Coupe, '78 Pacer Wagon
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'09 Nissan Titan
'10 Nissan Maxima

Offline MIPS

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Re: Cannot tune for anything BUT curb idle
« Reply #13 on: June 25, 2019, 10:55:25 PM »
Okay, I got the timing set back in spec and it's got power but I had to omit a line from the procedure.

To the book, you disconnect and plug the vacuum advance, unplug and jumper the CeC retard connection at the SSI, start the engine, set the idle to 1600rpm and for an automatic transmission put it in Drive, then set the timing. The result each time was the above crap engine. I just left the transmission in Park and set the timing and everything was fine. What exactly is the purpose to loading the engine with it in park?

Offline AMC of Houston

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Re: Cannot tune for anything BUT curb idle
« Reply #14 on: June 26, 2019, 06:58:53 PM »
Have you seen the AMC IS-12e Service Letter??  Final iteration was Nov. 1987.  It was AMC's revised timing & carb tuning procedure for the 6-banger CEC Eagles.  I can email you a copy if you'd like.
George G.
'81 Eagle Sundancer
'85 Eagle Waggie
1960 1902 Rambler Replica
'64 American
'70 AMX (Big Bad Blue), '70 AMX (White)
'77 Gremlin
'78 Pacer Coupe, '78 Pacer Wagon
'79 Pacer Wagon
'73 Jensen Interceptor
'86 Audi 5000 Turbo
'98 Aston Martin DB7
'09 Nissan Titan
'10 Nissan Maxima

 

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