Gurus - help me diagnose a no-code miss - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
LinkBack Thread Tools
post #1 of 2 (permalink) Old 10-11-2011, 06:05 PM Thread Starter
Regular Member
Join Date: Oct 2011
Posts: 214
Gurus - help me diagnose a no-code miss

I have an LT1 in a caprice wagon. New optispark, new wires, engine is not throwing ANY codes at all. However, I feel a distinct miss throughout all RPMs. At idle, under load - it doesn't matter. Car starts right up - within 1/2-1 rev of the starter. Idles with just a touch of a miss - every revolution without fail. Engine appears to idle well if you're looking at it, but if you put your hand on it, you can feel it.

I JUST bought the car so I am a little pissed.

Vac reads 18.5 at the manifold. All the plug leads are carrying spark. There were a few vac leaks at the mani that I took care of. Replaced the PCV. Tightened the manifold down - some of the nuts were borderline hand-tight. No ticking or knocking to speak of.

Initially, I thought it was a resonance/harmonics issue with the dual flowmasters not having any sort of h-pipe, coupled with the fact that the dolt who installed them didn't use isolation mounts on the rearmost section. However, at a very low cruise RPM, just strolling along at about 35 and in a high gear, you can feel it "chug, chug, chugging" along.

The miss is dead-on rhythmic. At this point, I am thinking it may be a fueling (injector) issue or bad plugs.

Thoughts? In the past, if I've borked up the firing order, a typical SBC will barf out of the intake or pop though the exhaust, so I don't think that is the problem. I'll be checking anyway when I re-do the plugs.

O' LT1 gurus of the forum, I seek your guidance...

Last edited by AtlantaDan; 10-11-2011 at 06:21 PM.
AtlantaDan is offline  
Sponsored Links
post #2 of 2 (permalink) Old 10-11-2011, 07:07 PM
Regular Member
Join Date: Dec 2009
Location: midland tx
Posts: 86
It sounds like your miss is load related, so I would start with your coil and icm. Have you done the icm cooling mod? Some auto part stores can test your coil and icm. Have you used dielectric grease both ends of the coil spark plug wire? I would start here, then check for codes, then datalog. One other place to check is the wiring harness that goes from the opti to the wiring harness on the passenger side of the intake manifold. Make sure the wires are not frayed, or the connector has corrosion on it.


andy schuck

Last edited by andys94t/a; 10-11-2011 at 07:09 PM. Reason: add more info
andys94t/a is offline  
Sponsored Links


Quick Reply

Register Now

In order to be able to post messages on the LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome