knock & stupid high AFR - Team Camaro Tech
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post #1 of 43 (permalink) Old Oct 12th, 11, 12:36 PM Thread Starter
r_w
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Robert
 
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knock & stupid high AFR

Just put on a new intake, I went from a high rise single plane to an Edelbrock performer dual plane. The good news is the oil and water leaks are gone. The bad news is there is WAY too much knock, and the AFR is not close, it runs above 20 at idle, WOT tends to get down around 12 so not too bad. Those numbers are just from glancing at the readout, haven't looked at the log. Car is real rough off idle, smooths out at WOT.

I have some ideas, but the forum is much wiser than I, so I thought I would get some input before I started wrenching tonight.

Here are the specs:

327 (didn't change)
291 double hump heads, in pretty sad shape (didn't change)
Edelbrock performer intake (did change)
Holley 4160 750 cfm carb (didn't change) - floats set ok, screws 1 1/2 turns open
HEI distributor (didn't change)
New distributor cap
New plugs, gapped .038
Old plug wires

Timing without VA is 14* at idle, going to 34* at 3K. VA adds about 8*. This didn't change.

Do I have a vac leak?
Intake leak?
Carb idle too lean?
Too far advanced in timing?
Bad plug wire? (they are old and unknown condition)

Be gentle, I'm just learning here

Robert

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post #2 of 43 (permalink) Old Oct 12th, 11, 02:29 PM
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Re: knock & stupid high AFR

Quote:
and the AFR is not close, it runs above 20 at idle
An enine will not run above about 17 on petrol at all
The air u breath is 20.9 ....
High AFR reading is a general indiaction that there is misfire....the O2 not being burnt.

Quote:
haven't looked at the log.
Well that can tell u a lot to.

Quote:
WOT tends to get down around 12 so not too bad
Thats good.

Quote:
Timing without VA is 14* at idle, going to 34* at 3K. VA adds about 8*. This didn't change.
Thats ball park

Quote:
291 double hump heads, in pretty sad shape
In what way...bad heads dont run an engine well.

Quote:
Old plug wires
u mean the old orginal for the HEI?
They would have sucked a kumura well before now....
Quote:
so I thought I would get some input before I started wrenching tonight.
Checked vac leaks? floats? accel pump gap? fireing order? correct timing tab for that harmonic balancer?
Quote:
WAY too much knock
From what? detonation? [istomn? tappet?..checked located with a stethoscope?

My Spelling is not incorrect...it is creative

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post #3 of 43 (permalink) Old Oct 12th, 11, 02:50 PM Thread Starter
r_w
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Re: knock & stupid high AFR

Quote:
Originally Posted by Steptoe View Post
High AFR reading is a general indiaction that there is misfire....the O2 not being burnt.
Sure acts like misfire. The engine was fouling plugs, and it felt a lot the same. So I changed out the plugs and it didn't get better. I wondered with all the pulling on and off of the plug wires one might be damaged. I don't know how old they are, but they aren't clean...

Other possibility I read is that I have an exhaust leak. I'm sniffing it from the Innovate tail pipe mount (no cats of course). But that wouldn't explain it running so bad.

Quote:
In what way...bad heads dont run an engine well.
Leaky valve seats at least...



Quote:
From what? detonation? [istomn? tappet?..checked located with a stethoscope?
Sounds like detonation. Tappets are okay, I adjusted them a few weeks back.

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post #4 of 43 (permalink) Old Oct 12th, 11, 04:11 PM
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Re: knock & stupid high AFR

If you have true dual exhaust put the sensor on the opposite side to see if there is a difference. If you have a vacuum gauge take a reading at idle and see what it is doing.
If this behavior just started after the intake change, suspect plug wire damage, vac leak or idle mix screws too lean. Exhaust leak will just make noise, not make it run badly or foul plugs.

'67 rs - ordered new by my Grandfather
327 L30, K-K, Deluxe int, tach & gauges, 12 bolt posi, 4 speed.

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post #5 of 43 (permalink) Old Oct 12th, 11, 05:18 PM Thread Starter
r_w
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Quote:
Originally Posted by Melrose RS View Post
If you have true dual exhaust put the sensor on the opposite side to see if there is a difference. If you have a vacuum gauge take a reading at idle and see what it is doing.
If this behavior just started after the intake change, suspect plug wire damage, vac leak or idle mix screws too lean. Exhaust leak will just make noise, not make it run badly or foul plugs.
I knew someone would suggest swapping sides...since the wire reach will be hard! That makes sense, will try it.

Just put new plug wires on it because I was going to anyway, but no better.

Vacuum kind of acts the same at idle as before, it bounces around 15" hg.

It really acts like a misfire, but she has new plugs, new cap, new wires. Could be the coil got damaged when I swapped it to the new cap.

I don't think I drank enough beer that day to cross the plug wires, but I better check...


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post #6 of 43 (permalink) Old Oct 12th, 11, 05:37 PM
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Re: knock & stupid high AFR

Quote:
Vacuum kind of acts the same at idle as before, it bounces around 15" hg.
your answer
Quote:
Leaky valve seats at least...
And also high O2
And
Quote:
It really acts like a misfire
,

Quote:
I knew someone would suggest swapping sides...since the wire reach will be hard! That makes sense, will try it.
I have never been a fan of tail pipe clamps...doesnt take much to blow a hole in the top side (10 oclock to 2 0clock ) of the ehaust pipe with the acetylene torch, weld the O2 adapter(s) in ...ans when not in use blank off with the bungs.
And in a 69, run the cables into the car by removing the plates around the steering column, and can replaceover the cables if need be.

My Spelling is not incorrect...it is creative

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post #7 of 43 (permalink) Old Oct 12th, 11, 06:07 PM Thread Starter
r_w
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Are you saying it's the heads?

I'm no fan of the tail pipe clip. No torch, and the welder requires pulling put the stove and using a home made 240V extension cord snaked to the garage, so wifey prefers I plan that one out!

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post #8 of 43 (permalink) Old Oct 12th, 11, 06:26 PM
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Re: knock & stupid high AFR

I put my 02 bung into the collector with a step drill, some filing and the mig welder.

It sounds like a vacuum leak. Does this manifold have an EGR block off and is it leaking? How about PCV valve- stuck open?

What is the idle RPM you are able to get it down to?
I have the same heads, intake and timing as you, my cam is 218 duration and I'm able to pull 20" of vac at idles with the carb tuned right so I think unless you have a more radical cam you should also.

You could also try a compression test with a loaner tester from Autozone.

'67 rs - ordered new by my Grandfather
327 L30, K-K, Deluxe int, tach & gauges, 12 bolt posi, 4 speed.

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post #9 of 43 (permalink) Old Oct 12th, 11, 06:41 PM Thread Starter
r_w
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Robert
 
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Quote:
Originally Posted by Melrose RS View Post
I put my 02 bung into the collector with a step drill, some filing and the mig welder.

It sounds like a vacuum leak. Does this manifold have an EGR block off and is it leaking? How about PCV valve- stuck open?

What is the idle RPM you are able to get it down to?
I have the same heads, intake and timing as you, my cam is 218 duration and I'm able to pull 20" of vac at idles with the carb tuned right so I think unless you have a more radical cam you should also.

You could also try a compression test with a loaner tester from Autozone.
It has a block off plate I generously sealed down, but it could still be it.

EGR rattles a lot, if I grab the EGR hose I feel it.

Compression is low in two cylinders, but that was the same before.

I have never had it above 15" hg, even with the old manifold...but I suspect the engine is pretty tired. Just trying to learn on it and get it running while my pit crew gets old enough to help me build a new one.


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post #10 of 43 (permalink) Old Oct 12th, 11, 06:45 PM
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Re: knock & stupid high AFR

Quote:
Originally Posted by r_w View Post
It has a block off plate I generously sealed down, but it could still be it.

EGR rattles a lot, if I grab the EGR hose I feel it.

Compression is low in two cylinders, but that was the same before.

I have never had it above 15" hg, even with the old manifold...but I suspect the engine is pretty tired. Just trying to learn on it and get it running while my pit crew gets old enough to help me build a new one.


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Do you mean the PCV rattles? Block it off completely for a test.
How low is the compression. They will likely NOT be all the same. But within 10%, if I remember correctly, is OK.
What is the idle rpm?

'67 rs - ordered new by my Grandfather
327 L30, K-K, Deluxe int, tach & gauges, 12 bolt posi, 4 speed.

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post #11 of 43 (permalink) Old Oct 12th, 11, 07:26 PM Thread Starter
r_w
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Re: knock & stupid high AFR

Quote:
Originally Posted by Melrose RS View Post
Do you mean the PCV rattles? Block it off completely for a test.
How low is the compression. They will likely NOT be all the same. But within 10%, if I remember correctly, is OK.
What is the idle rpm?
Yes, PCV rattles. While running, I pulled it out and kinked the hose. Here is what happened:

PCV in: Idle 800 rpm, AFR 16 to 18
PCV hose kinked: Idle up to 1000 rpm, AFR up to 18 to 20
PCV in: Idle 800 rpm, AFR 16 to 18

Then I pulled the vacuum hose from the brake booster. I just don't understand...

Brake booster vacuum in: Idle 800 rpm, AFR 16 to 18
Brake booster line plugged: Idle rpm down to 600, AFR 21 to 22, engine real rough
Brake booster vacuum in: Idle 800 rpm, AFR 16 to 18

If I block off the brake booster, shouldn't the car not care? Not all cars have vacuum brakes...And if the brake booster were leaking, and I plugged the hose off, wouldn't the AFR go down???

I have the Brake booster plumbed to the base of the carb, I have the PCV plumbed to the hole in the intake behind the carb.

Compression is: 160, 130, 160, 145, 155, 145, 160, 170. More like a 20% range.

The car did run okay before the intake change, it wasn't great, but it was ok. I've changed something...

I've tried the propane around the leak points and didn't see any change in idle, though I may not have done this right.

I checked the O2 sensor in free air and it is right at 20.9%...

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post #12 of 43 (permalink) Old Oct 13th, 11, 08:26 AM
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Re: knock & stupid high AFR

Don't know if it makes a difference but, both my SBCs with vacuum brakes have the PCV to the base of carb and the brake booster to the intake manifold behind the carb.

In case I missed it, do you know what camshaft is in there.

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post #13 of 43 (permalink) Old Oct 13th, 11, 08:48 AM Thread Starter
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Re: knock & stupid high AFR

Quote:
Originally Posted by Luwi67 View Post
Don't know if it makes a difference but, both my SBCs with vacuum brakes have the PCV to the base of carb and the brake booster to the intake manifold behind the carb.

In case I missed it, do you know what camshaft is in there.
Now that you mention it, looking back at the pics I took, that was how it was originally setup. I assumed that it didn't matter, since both are vacuum sources with the same size ports, but I could be very wrong about that.

I don't know the cam in it, but it sounds good . Now if I can only get it to run as good as it sounds.

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post #14 of 43 (permalink) Old Oct 13th, 11, 01:29 PM
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Re: knock & stupid high AFR

Quote:
Are you saying it's the heads?
Trouble shooting at 5000 +miles is not the best..
The stuff Melrose and Rw are saying could just as equally on the mark
Known bad seat is one of several things those symtoms indicates.
With those compressions, even 20% u will get the engine to run ok....at that level it indicates the engine is well used/worn, whatever and expect to do something about it in the near future.
The PVC and brake booster can go to the same piont on the manifold T. may crabs have a manifold port alsao....some setups cant use the valley cover port ...room whatever, other dont have a port.

A dirty or incorrect PVC valve in effect gives a vaccuum leak.

My Spelling is not incorrect...it is creative

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post #15 of 43 (permalink) Old Oct 13th, 11, 01:56 PM
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Re: knock & stupid high AFR

Quote:
Originally Posted by r_w View Post
I've tried the propane around the leak points and didn't see any change in idle, though I may not have done this right.

...
Force the situation by creating a vac leak, put the propane on it and observe. That way you know what to expect.

'67 rs - ordered new by my Grandfather
327 L30, K-K, Deluxe int, tach & gauges, 12 bolt posi, 4 speed.

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