Looking For Help Diagnosing Engine Miss

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Apr 30, 2006 | 10:51 AM

75SHARK

Thread Starter

Racer

Joined: Sep 2001

Posts: 407

Likes: 10

From: Maryville Tennessee

Looking For Help Diagnosing Engine Miss

Hello,

I have a '75 with the L82 engine. My engine has developed a miss, which I can only feel from idle to about 2,000 rpm. When I punch the gas, it goes without missing at all, so I don't think its a fuel problem. I don't feel the miss going down the interstate (at steady higher rpm's) I have a newer Edelbrock quadrajet carburetor and the plugs, wires, cap and rotor are about a year old. I have the timing set and idle mixture set correctly (as far as I know). All of my vacuum hoses and headlight system is new, so I don't think there's a vacuum leak. I don't detect any vacuum leaks around the carburetor as well. I took out a couple of the plugs and they look fine. I'm not sure where else to go other than just trying a new set of plugs and wires and seeing what happens. Or I may just take it to a shop and have it hooked up to a diagnostic machine. Is there anything I'm missing? Thanks!

Robert

May 1, 2006 | 12:57 AM

Thmprr

Racer

Joined: Dec 2005

Posts: 368

Likes: 4

From: . New Zealand

My '76 behaves like this, and it's a wiped cam exhaust cam lobe on #8, it misses until about 2000 rpm then it's hard to tell it's missing. Checked this out by comparing the lift on the valve spring retainers with the valve cover off.
There's a lot of cam wear happening at present due to the oil companies removing zinc as an additive.

May 1, 2006 | 01:29 AM

wombvette

Le Mans Master

Joined: Jan 2000

Posts: 8,918

Likes: 27

From: New Hill NC

Usually a vacuum leak on the 5/8 runner. There is a vacuum fitting there that supplies the headlights, wipers, brake booster etc. a leak in any one of these systems makes 5 and 8 lean. At normal speeds or full throttle it is not apparent, but will miss at idle.

Jun 14, 2006 | 09:12 AM

77 zz4

Instructor

Joined: May 2006

Posts: 122

Likes: 1

From: hazlet township nj

I had the same problem. For me, I believe it is a brake booster vacuum leak. When I plug it with my finger the car runs fine. I'm going to replace them this week.

Jun 14, 2006 | 09:18 AM

PhotoVette1

Safety Car

Joined: Mar 2005

Posts: 3,503

Likes: 2

From: Raleigh NC

You could also have a stuck/sticking mechanical advance. I had the same problem on my '77 and that is what it was. Pull the distributor cap and lubricate it and make sure its free.

Last edited by PhotoVette1; Jun 14, 2006 at 09:22 AM.

Jun 14, 2006 | 03:27 PM

BLUSHRK

Racer

Joined: Apr 2006

Posts: 417

Likes: 0

From: Tacoma Washington

Not to sound like Captain Obvious, and not to insult your intelligence, but did you inspect each plug wire? If they get too close to headers they can get burnt. Happened to me. Caused missing. I didn't notice by looking at them since the burnt part was on the bottom of the wire. I had to physically inspect 100% of the wires to find it. Just a thought...

Jun 14, 2006 | 03:43 PM

Ed Blue 03

Racer

Joined: Apr 2005

Posts: 494

Likes: 0

From: Virginia

Yep, look at your engine in the dark while it's running. You may have a spark plug wire arcing. Once had this problem, took me forever to figure it out. Good luck.

Last edited by Ed Blue 03; Jun 14, 2006 at 03:50 PM.

Jun 14, 2006 | 06:15 PM

75SHARK

Thread Starter

Racer

Joined: Sep 2001

Posts: 407

Likes: 10

From: Maryville Tennessee

I've inspected the wires as best I could, but I do need to pull them out individually and look at them. I had the car running in my garage in the dark, but no sparks seen. That was one of the first things I checked because I my '73 was doing it.