Knock and Idle issues

[MIPS]

Over the summer I pulled the head and most of the front off my engine and replaced the timing chain and sprockets, oil seal, water pump, thermostat, lifters, plugs and swapped out the '82 head which turned out to be warped with a shop rebuilt head from an '84. No performance parts were added and both timing and idle adjustments were set to spec.

I've always had knock issues that developed when I dropped 2000 feet to visit people on the coast but that was otherwise it and completely understandable. Now the engine starts to knock really badly as soon as the computer satisfies its temperature sensors and the choke is completely open. Accelerate from a light? knock. Accelerate to pass on the highway? Knock. To me that sounds like it's running lean. The CeC tester doesn't find any faults and the choke adjustment is correct. I retarded my timing an additional three degrees to cut back on just how badly it was knocking when passing on the highway. Still does it but at least I can more gently accelerate without sounding like I'm nuking the cylinders.
Two new faults however have now developed. One is that once warm (CTO opens, coolant and air temp switches satisfy) the engine will occasionally develop a miss. Other times the curb idle drops WAY too low to the point the engine will throw the alternator light or just completely stall. What throws me completely off is that you can't reproduce it. Sometimes I can pull into a parking spot, put it into park and turn the lights off and it will do the above, other times it's a smooth idle. I checked to verify the EGR was working and not sticking open and it seemed fine. I'd buy another because those backpressure ones are a pain to test but someone just bought the last cheap Delco one off RockAuto.

The only really suspect things I can find is the two arms on the throttle are loose and a solenoid kick can get cancelled out by the play. The other is the throttle shaft is loose in the throttle body, so it probably needs to be sleeved.....but it's not loose enough that if I spray starter fluid on it the engine doesn't rev from a vacuum leak.....but it really feels like there's a massive vacuum leak somewhere because even putting your hand over the air horn doesn't stall the engine easily. Manifold vacuum is reading about 19 InHg. Carb was rebuilt about a year ago.

[amcfool1]

check your power brake booster. could be a leak there. happened to me once. took forever to diagnose. good luck, gz

[MIPS]

It's not a leak in the hose or grommet, at least. You pull that sucker off with the engine running and the catastrophic loss of vacuum stalls the car instantly.

I'm going to pull the carb tomorrow and verify I don't have either a plugged jet or a broken gasket somehow. I already have my other two spares out to make a few comparison checks.

[AMC of Houston]

Did whoever rebuilt the carb perform the AMC idle bleed service letter??   Is to drill out the bottom of the idle bleed tubes to 0.032 (I always drill to 0.030 with no problems).  Makes a world of difference on the BBD idle issues.

Do that, and adjust everything to the AMC IS-12e service letter; and see how it does.

[MIPS]

Me and the mechanic did not because we did not have the tools or resources to widen the orifice. Everything else however was cleaned and overhauled.

[Taylor]

I think I used a small hand drill, like a old school yankee screwdriver when I drilled mine out about 10-11 years ago. Highly recommend doing it. I have since performed the ECM Test bypass and a gronk 2150. Lucky for me the chinese made carb hasn’t been too bad. I am considering a replacement carb, with this https://www.edelbrock.com/avs2-500-cfm-carburetor-with-electric-choke-in-satin-non-egr-1901.html
Installed a HEI last winter. Does excellent burnouts now...

[vangremlin]

Installed a HEI last winter. Does excellent burnouts now...

Can you please share a video of the burnouts?   

[MIPS]

Pulled the carb apart. Washed and blew out the circuits. The gasket surfaces are clean and square and everything looked fine aside from the plastic insulator was upside down, so vacuum on the choke pull-off and the air horn doors hadn't been working for months....

Unfortunately I found no signs of any leaks or plugged tubes. Now that it's back together and on the car it still knocks.

[Taylor]

Could it be running lean? or is it possible the distributor might have worked loose and advanced the timing a bit?
Have you checked this as a possible source?
http://amceaglesden.com/~iowaeagl/guide/?title=Diagnostic_ECM_Test

[MIPS]

I verified I was still at 12 degrees BTDC (15 degrees base and three degrees of retard due to knock) before I reset the idle screws (it's part of the TSM). Computer checks out fine using the ET-501 tester so it isn't a computer or sensor problem.
It could really just be that it is running lean. After the rebuild last year we drilled the plugs out and adjusted the mixture screws but I've never gone back and adjusted them again just in case it was something else. At this point there isn't really anything else left I have not double checked, cleaned or replaced.

[86Woodgrain]

When you check the timing are you doing so at 1,600 rpm with the 4 & 10 vacuum electrical plug disconnected and distributor vacuum line plugged? Just making sure...

I just reset the timing on my 86 last week here in Canada too after a carb rebuild...

The sticker on the firewall called for 9 degrees @ 1600 rpm on mine. I put the fast idle cam on to hold RPM and used a digital tach to get as close as possible. Don't waste your time adjusting the curb idle timing (no pun intended LOL). My car was set at 7 degrees and I corrected it.

The idle tubes being plugged would not cause knocking, just poor idle. Also, have you verified your knock sensor is working?

I would recommend you disconnect & plug the EGR valve for a little while too. It was giving me some grief after the carb rebuild. When I plug it the car runs better. Just keep it out of the loop for now during diagnosis.

Also have you tried changing all the vacuum lines you possibly can? I recently went through all the hoses and replaced them and found two sources of leaks, one was the sol-vac but that's irrelevant for you. Oh and there was another line disconnected at the tee at the back of the manifold but I could hear it hissing.

[MIPS]

When you check the timing are you doing so at 1,600 rpm with the 4 & 10 vacuum electrical plug disconnected and distributor vacuum line plugged? Just making sure...

Yes. I have followed the procedure as per the bulletin and NOT what is specified in the '82 TSM. For some reason that one gave me a totally anemic engine that would stall all the time and a wildly different timing.

Also, have you verified your knock sensor is working?

'82 CeC's don't have a knock sensor. I'm planning on installing a Carter Engine Knock Eliminator once I can pick it up in Seattle but was hoping to iron any other issues that might be causing knock first.

Also have you tried changing all the vacuum lines you possibly can? I recently went through all the hoses and replaced them and found two sources of leaks, one was the sol-vac but that's irrelevant for you. Oh and there was another line disconnected at the tee at the back of the manifold but I could hear it hissing.

Every vacuum line in the car (and every other rubber line in the car for that matter) was replaced last spring. I wanted to nail that biggie down before it drove me crazy diagnosing the rest of the engine. Had to custom order in several different sizes of line to make everything fit happily. We should not have any issues with cracked or dry rotted hoses. Anything that interfaces with the vacuum was also tested and replaced. There was a bad sol-vac and choke pull-off.

[86Woodgrain]

Are you buying gas at the same station all the time?

Have you tried running some higher octane gas to see if it helps?

What weight of oil do you run?

Do you know the sound difference between spark knock (detonation) and lower end rod knock (bearings)?

Just trying to cover some basics here...

I wonder if you have a vacuum check valve in backwards somewhere between the carb & the distributor... have you tried running with the 4&10 vacuum electrical unplugged and distributor vacuum line plugged and go for a drive to see if it stops the knocking?

[MIPS]

Are you buying gas at the same station all the time?

Normally and when travelling to the coast, yes.

Have you tried running some higher octane gas to see if it helps?

I considered it was ping, so I put 91 in and no it remained the same. My wallet begs me to not try 94.

What weight of oil do you run?

10W30. Penzoil High Mileage blend.

Do you know the sound difference between spark knock (detonation) and lower end rod knock (bearings)?

No. My assumption is that knock was typically more pronounced under acceleration and goes away while rod knock persists it above-idle RPM's. Regardless, the total lack of knock when cold and while warming up doesn't sound like it could be rod knock. When I hit the highway onramp every morning gunning it won't make it knock but without fail will knock while taking off at the first set of lights about 10 clicks down the highway.

I wonder if you have a vacuum check valve in backwards somewhere between the carb & the distributor... have you tried running with the 4&10 vacuum electrical unplugged and distributor vacuum line plugged and go for a drive to see if it stops the knocking?

For unplugging the vacuum switches no but I do know that if you try to test the computer with them unplugged it will catch it and tell you to check them, so they are working. As for disconnecting and driving without the vacuum advance I have not done that. Initially there was a leak in the CTO that caused the advance to fail and leak over to the EGR circuit but that was fixed by replacing the CTO.
Probably worth adding that when the engine runs cold the vacuum advance bypasses a green/white delay pod. when hot advance runs through it. Now that it's mentioned though I can't recall if it's marked which way around it needs to be installed.

[MIPS]

Okay the car was cold so I took your advice, disconnected and plugged the distributor advance and took it for a drive into town.
The engine was retarded as all heck but the knock went away, even once warmed up.
Pulled over once I was in town and reconnected the advance and drove home. Knock came back.

I ran a leak test on the advance actuator and it passed so.....my vacuum advance adjustment screw is incorrectly set and I'm running too advanced?