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View Full Version : Kodiac v6 43 Chevy vortec engine miss at 3200rpms



silver_streak
12-11-2006, 08:50 PM
"I have a '01 Chevy vortec 4.3 engine that is carburated( with 102 hrs) that is in my '01 Jetcraft that has a American Turbine jet pump (SD209). The problem that I'm having is under load/accelerating, the engine misses/stumbles at 3200 rpms. I cannot even get the boat on plane. It doesn't matter if the engine is warmed up or not. After pulling the plugs, I noticed black soot on them. Compression test was normal, and leakdown test was also normal. Here is a list of other things that I've checked out or replaced:fuel/water sep-new, gas tank drained, put in fresh fuel with a run of Sea Foam stabilizer/cleaner, checked for air leaks in fuel lines, new anti siphon valve, changed cap and rotor, plugs and wires, new coil and ignition module(EST), checked timing-was to specs, new fuel pump, and out of desperation put a new Edelbrock carb on it(1409)-this replaced the Holley 4160.After pulling the carb, I also noticed black soot on the bottom side/intake side of the primary throttle plate. The only thing in the ignition that I didn't change was the pick-up coil. I've been trying to figure this problem out for a few months. You can tell that I'm desperate to find the problem and correct it. Help! Any advice or pointers would be appreciated"

fastjeff
12-12-2006, 06:38 AM
"..." After pulling the plugs, I noticed black soot on them"

That's a dead giveaway that the plugs are not firing, or the carb is leaking big time. Since you already eliminated the latter....

Some types of "new" wires can be ruined by improper installation. Others can be used as a tow line without damage--the spiral wound type. If you have the graphite core-type "automotive" wires, that might be your problem.

I'm look at the ignition module first, though. I had one that did that on my old race car. Drove me bananas!

Jeff"

silver_streak
12-12-2006, 10:25 AM
"The ignition module was already replaced. All of the parts that have been replaced so far have been GM factory parts. The wires are new (silicone supression 8mm) and resistance has been tested. The one thing in the distributor that hasn't been replaced as of yet is the pick-up coil.

So, the sooty condition of the plugs indicate a possible electrical/ignition problem? Let me give a few more details/symtoms. The engine NEVER misses at idle. But, during acceleration at 3200rpm's the engine starts to stumble/miss. This happens EVERY time. It's so bad that I cannot get the boat up on plane. The engine will not pass through the miss either. While its missing, it surges/stumbles. You can see this on the tach (it goes back and forth from aprox 3000-3600rpm's). From idle up to the engine miss, the engine has plenty of power and feels normal.

How can I test this situation out further? Any more things I should be considering/looking at? Thank you for any help or advice in advance."

bondo
12-12-2006, 07:21 PM
"Just Throwing Ideas out here,........

Is there Anyway in your set up that there could be an Exhaust Restriction,..??..??...
With an I/O, the Exhaust Flappers can fall into the lower Pipe,+ Seriously Restrict it.....

Idea #2,.....
Is your Cam going Flat on a lobe or two,..??..??..."

silver_streak
12-12-2006, 07:37 PM
"Bondo, could you describe in more detail about what you are referring too. I have exhaust flappers right at the end of the exhaust(towards the water end). Are there also a set of flappers that are internal, more towards the exhaust manifold?

What do you mean by the cam going flat on a lobe? A worn down lobe? I only have 102 hours on the engine. Thanks for your input."

bondo
12-13-2006, 08:01 AM
"If the Only Flappers you have are Outboard,... At the Back of the boat,...
That's Not your Problem,....
On an I/O, they are mounted right at the end of the Risers,+ IF they fail, they'll fall into the downpipe,+ restrict the flow,.....
You've got a Jet,+ I can't see How your system is Set Up........

The Direction I'm headed is that the Symptoms you're describing is a Serious Blockage,......

If it's Not a Flapper blocking the Exhaust Flow,.......
The Next logical step is a Flat Cam Lobe........
Cam's can Go Flat within the 1st 1/2hr of running,... Or at Any time.......

You're in a Pickle,+ I'm trying to give you some Ideas of Where to Look.......

You Say you've replaced Most All of the Ign.,+ the Induction,........
That leaves the Mechanical side of the Motor,.......

If you can get a Vacuum Gauge hooked up to the Intake Manifold,.......
There's a Good Chance that It Might be able to tell you WHERE the Problem lies........

A Motor is nothing more than a Big, Self-Powered Air Pump,.......
Your's Sounds like it's Sucking,......
But Can't Blow........."

silver_streak
12-13-2006, 10:26 AM
"Thanks Bondo for some other things to look into. Let me ask a stupid question. Where are the risers on the exhaust system? Coming off the exhaust manifolds are the rubber exhaust hoses that exit the transom (one on either side of the engine). These exit the transom and have a rubber flapper on the outside of the boat. Could there also be a flapper at the start of the rubber exhaust hose/manifold connection?

If it was possibly a bad cam lobe, how could I verify this without an engine teardown? If I pull the valve covers could I tell from looking at anything, ie lifters moving....? Wouldn't this show up on a leakdown test?

One last question: Where can I hook up a vacume guage to the manifold? I have no vacume hose connections on the carb or engine that I'm aware of... What kind of things can the vacume guage tell me about what's going on...? Thanks for your help."

bondo
12-13-2006, 11:46 AM
"The Risers are the part of the Exhaust Manifolds that Rise Up from the main body of the Manifolds........
Older 1s had it at the Back of the Manifolds....
Newer 1s are called Center Risers because the Risers bolt to the Manifolds about in the Center.........

If you lost a Cam Lobe,....
Pulling the Valve Covers,+ Checking the Rise,+ Fall of the Rockers with a Dial-Indicator will give you a general Idea of What's Doing What.......

Hooking a Vacuum Gauge to a boat motor can be abit of a Problem,.....
It depends on Your Motor,.....And I can't See what you've Got.......

Do a Google Search on Vacuum Gauge Diagnosis,........
You should come up with some Good Info....."

silver_streak
12-15-2006, 06:35 PM
"Someone mentioned to me that I might want to check out the oil pressure safety switch. I thought that when these switches go out, they completely go out. They seemed to think that this could be causing the fuel pump to go on and off while the engine is at the higher rpms (3000-3500). Does this seem like a possibility? Can these swithces work normally at idle and low rpms, and then start messing up at higher rpms?? Anyone..? Anymore things that I should be looking at that could be causing my problems...?"

bondo
12-15-2006, 06:45 PM
"Anything thing is Possible,.......

A 3" Jump Wire will by-pass the Switch,.......

I Doubt it's the Problem though....."

1993_yamaha_stern_130
12-17-2006, 09:33 PM
"Just for the fun of it, replace the spark plug wires and distributer cap - also replace the coil to distr cap wire.

Just becuase the wires are new does not mean the wires are not at fault.

I had a missing/hesitation problem in my Grand Prix with the 4.3. New wires did the trick."

jacobnorthwest
04-10-2007, 02:12 AM
dont know if you have fixed the prob yet but is your reverse gate moving completely out of the way when in fwrd ?