Jer82Z28

well I'm back up to stock jetting with my edelbrock
took it for a drive this afternoon and it ran strong
but that miss was still there, I thought it was a lean miss, but my a/f guage was showing normal to rich the whole time

if i rev it up in neutral and keep it at a certain rpm, the car misses badly. it's not a consistant miss, more of a slight stumbling
it does this to a lesser effect cruising with very light throttle (high vaccum)
give it any kinda gas and it goes away and feels strong.

I'm thinkin of a stronger step up spring.

tonight i went for a drive again, the stumbling seemed worse and the guage was way over on the lean again (probably 60-65F out)
it didn't feel as powerful at night either...

F-BIRD'88

It's not the carb...

Jer82Z28

valvetrain/valve timing then?
ignition?

onebad82z

iTrader: (7)

Ignition problem...how old/new is everything on yours?

F-BIRD'88

Yes..... Remove the valve covers and watch the valves.

What was the last component you replaced in the ignition system before this came up?

Fuel Pump?

Jer82Z28

spark plugs were the last ignition change
i gapped them pretty small though .035

the rest of the ignition is about a year old. I just had the distributor cap off and serviced it. the distributor itself is still factory.

RB83L69

vacuum leak

F-BIRD'88

Either a faulty spark plug. It does happen.
or a bad plug wire.

I would try and track down which cylinder is causing the problem.
First get a vacuum guage and watch the needle as you
disable one plug wire at a time.
If one cylinder drops very little compared to the others, this is the bad one.
You can get a simple spark gap tester from Princess auto
and find the weak plug wire or plug.
It will be the one that won't jump the gap on the tester when all the other cylinders will.

F-BIRD'88

Pull out a few plugs and inspect the gap.
If the ground electrode ends past the center electrode
you can get a an eratic spark.

This is caused from closing the gap on a plug that was factory gaped to .045 or more.

Carefully cut the ground electrode back a little and regap them.

F-BIRD'88

Much better like this. Try it.

Jer82Z28

hehe well the plug wire test didn't really pan out, kept getting zapped!

I took a pyrometer to it though all the header primaries were close to the same temp..

I'll check my plugs for what you showed me, they came gapped at .035 which is why i left them like that.
maybe I'll try the spark indicator one at a time?

I hosed down the whole engine with carb cleaner looking for vaccum leaks, I couldn't find any leaks.

my vaccum guage twitches with the 'miss' vaccum drops when the cylinder(s) missfire.
very noticable in neutral
it gets less as i go up in gear, overdrive the miss is virtually non existant.

330hp_91RS

Is the motor backfiring through the intake, can you see a flame come out of the carb when it backfires???? Look at it at night with the hood up, if there is a flame,

YOU HAVE A BENT VALVE, I had the same problem, stop screwing with the carb, I even tried THREE DIFFERENT CARBS, THE MOTOR STILL BACKFIRED

ronterry

Hey Jeremy,

:sillylol: :sillylol: :sillylol: If I would of got on here earlier, I would of warned you about pulling live plugs wires.
My neck still hurt from getting zapped in 1989!!!

I would just drop in a new set, in fact I usually buy a couple of sets of plugs trying out gaps, and of course smudging them to **** from being to rich Which BTW reduces the performance & idle pretty quick.

If you have an old set of wires to rule out your current ones would help also.

My misses a little at speed, but I need to mess with vacuum advance a little?

In fact I was about to go out and pop another set on & gap to .050...
I like the RC12YC's from champion, cause there usually stocked, and cost maybe 10 bucks for 8.

I like the idea about the erratic spark from 'F-BIRD'88', cause I had a set of rapid fires with a super coil run like crap.
I wasn't till I put the stock coil back in that it ran good???

...again my needle bounces around a little at idle, but this cam is a little loopy. Does yours smoothen out at 1000rpms???


Ron

F-BIRD'88

From what you said, you can rule out the carb.
It is either ignition or internal (valves) or vac leak.

Because it gets worse as you rev it up, I would look for a bad valve spring.

Track down which cylinder is missing with a vac guage
Disable one cylinder at a time. The one that has no effect
is the bad one. Do the spark gap test on that cylinder and two others to rule out an ignition problem.

You have to set the gap as wide as possible ( on the tester) Till it just missfires then back in a bit, on a good cylinder then try it on the suspected bad one.

To trace a vac leak, get a propane torch and spray propane down the carb, when it is missing. If it improves with the additional fuel (propane) you have a leak some where.

330hp_91RS

Do what F-bird said,

I will almost gurantee that it's not a vacuum leak though, just find that dead cylinder- If it's a spring, you got lucky cause if it's a bent valve, you'll need to rip the head off, lots of fun!!!

Jer82Z28

It doesn't sound like just one cylinder though, it sounds like several missing.

and I couldnt find any dead cylinders with the pyrometer..
they are all firing... most of the time..

If I had bad springs, wouldnt that only show up when I wind it out?
If it/they were so bad that it misses at idle, racing it would be outa the question dont ya think?

I'll pick up another set on plugs on my way home from work and try those.

I'm also starting to think that perhaps the rotor is broken or something

Keep the ideas comin guys
i gotta have her ready this weekend for a trash talkin capri owner

F-BIRD'88

The pyro meter will only show you a dead cylinder
not one with a random miss. The plug gap tester and vacuun guage will.

I'd stop theorizing on the finer points of inter combustion and start inspecting the parts.
Pop the valve covers off and look for a bad spring or low valve lift on one cylinder. then check out the spark plug wire and plugs
and fine the bad cylinder. then inspect the rotor and cap and coil and pickup coil and module.

Jer82Z28

It's my vacuum advance!

Something told me to play around with the timing before I started ripping stuff out
I advanced it and it got waaay worse
so I retarded it down to about 5* advanced, car idled great, but when i rev it up the flutter is still there
so i disconnected the vac advance and the car ran perfect
reconnected the vac advance and the missfire came back.

is there anyway to adjust the vac advance? or perhaps it's getting worn out?

Sitting Bull

Man, a lot of misery and worry just to track down a vacuum advance canister, eh? Sheesh!

Go grab a Crane vacuum advance kit (about $15) and install it the way Damon Nickle instructs in his Tech Article on HEI ignitions. You'll find a little extra "oomph" with it, too

ronterry

Heyyyy, do I get any credit?
-----
It depend on if it's adjustable, if it is you need a little hex tool to stick in the hole the hose goes on.
I can't remember which way to turn it though, but you can mess with it.
You can disconnect it for now, it won't damage anything, but you fuel consumption will go up a little. I know I have an adjustable vac adv made by crane cams, but you should be able to get them at any parts store, it you DON"T already have one.

BTW:
I also wanted to show you the loop/vacuum mine is putting out...
http://www.ronterry.com/firebird/videos/Loop.mpg

...and if your bored...
http://www.ronterry.com/firebird/videos/Run001.mpg

Ron

F-BIRD'88

It's not the vacuum advance ...It is the pick up coil
or the small wires leading from it to the module.
When the vacuum advance moves, it turns the pick up coil
assembly to cause more advance. When it moves the wires are
going open. this is a common problem.

Replace the Pick up coil.

ronterry

Good point...however remember the vac. adv. can throw in 10° - 20° @ 10"

BTW: counter clockwise to retard(acualy it limits the amount adv.), and **** my MSD doesn't have an adjustable one & is a different size than a regular HEI vac adv.

There should be a way to test the pickup with an ohms meter, and a vacuum pump or you can try retarding 10° with the vac adv hooked up & see what happens...


Ron

Jer82Z28

ronterrry, FBIRD, sitting bull
thanks for the help guys!!

I know what the prob is at least, now it's just a matter of fixing it

:rockon:

ronterry

:rockon:

I'm glad you brought up the original problem, cause I would have never thought the cam would have been my problem...(thanks to Fbird)...I was at .100/.095 jets
I'm now at .110/.104, and is a little rich for 6300 feet, but she likes it
I learned how to degree a cam I've got serpentine pulleys
So thank you Jeremy!!!

BTW, FBird my Victor Jr. will be here on Wednesday I'll sacrifice a little torque below 3500rpms for a good gain of HP on the top end...

Ron