Cylinder 3 Misfire.

[Chris88CL]

Some of you know my project, others dont.  Im going to be brief in the description.  Its a 3400/3500 Hybrid with forged pistons, custom cam, etc that has been fitted with a T3/T04E turbocharger w/3" exhaust all the way back.

My issue is Im having a fairly severe cylinder #3 misfire.  All other cylinders are ok but experience misfires once in a while (likely from the old gas).  If the gas were to blame, then cylinder 3 would be the same as the others.

I've pulled/cleaned the plug.  Made quadruple sure the plug wire is seated properly.  I've swapped out the coil.  Still I have the same misfire on cylinder #3.

The wires are BRAND NEW magnecor 8mm's.  Plugs are AC Delco 42LT's gapped at .045

Im going to try swapping the #3 wire to #1 or 5 and see if the misfire follows the brand new wire.  Perhaps there's a manufacturers defect in the wires.  Other than that, Im pretty stumped.

If it were a coil it should affect 2 cylinders.  Ignition module should affect atleast 2 cylinders if not all of them.  Crank sensors should screw with all of them.  Im running out of ideas.

Anyone have any?

[1988GTU]

What is the combination of your valve train?  I know there were a few people running certain seats that would walk with the spring bending the stem.  Eventually it would drop a valve and cause for some deeper problems.

Do a leak down test?

How about injectors?  Bolt up a fuel pressure gauge and see if the rail loses pressure quickly.

[Chris88CL]

Injectors are brand new 42.5lb units.

Valvetrain is tried and true.  3500 heads, Comp Cams springs, stock seats(new), stock (new) guides, stock valves, 3500 roller rockers with custom length pushrods.

My compression tester went missing so Im unable to do a leakdown test at the moment.

I'll test the fuel pressure this weekend when I get back to working on it.

Any other ideas?

[wicked-irocz]

Hey chris.  

A brand new injector can be bad or the injector driver circuit can be bad (test with noid light).

A leakdown test and a compression test are different and I would do a leakdown if you can.

Does it happen under load or not?  What is your actual compression ratio?  When do I get a video?

[Chris88CL]

My compression tester did both I do believe.

The injector wont be bad.  It was both ohm and flow tested prior to delivery.

I dont notice the misfire under load but the exhaust and turbo are so damn loud its tough to tell.  It does it ALOT at idle though.

I have no idea what my actual compression ratio is these days.  If I had to guess I'd say close to 8.4-8.5:1.

The first video I post will be at the same time I post my 12 second time slip......




















Next Year.

[yellow3800]

I didn't see where you tested a plug externally and visibly looked at the spark quality.  Hey, its simple and obvious.

Use a different plug.
use a different wire.
ground it [I like using jumper cables on plug, other to gnd]

now you said "misfire" I sorta assumed spark.

Andy