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Old 11-19-2012, 10:19 AM   #1
aaron1
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Engine miss

When my engine is cold it has a slight engine miss according to a friend of mine. Since I do not know about engines this miss is very slight to me.

However after driving my vette for an hour the engine is now jumping around because the miss is now more noticeable.

I think that the cause is most likely ignition oriented.
I had put new wires and new ac delco plugs in before starting engine for first time. There is also a new cap and rotor.

I think that as the engine becomes hotter the resistance in the ignition becomes greater thus limiting voltage to a cylinder.

Other than removing plugs and checking wires what els would I look at?

How would I check the primary ignition?


Thanks for everyones help.
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Old 11-19-2012, 10:42 AM   #2
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post very clear pictures of your spark plugs, label the cylinder # they came from, and measure the fuel pressure you can tell a good deal if you know those factors and how to read plugs.
most engine misses are related to either fuel/air ratio changes or ignition, so the first step is isolate the problem, or the cause, it could be the timing, advance curve, fuel pressure , a vacuum leak,or a defective ignition etc, you need to do a few tests

http://forum.grumpysperformance.com/...php?f=70&t=202

http://forum.grumpysperformance.com/...g+right#p16459

http://forum.grumpysperformance.com/...ng+right#p2762
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" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"
Old 11-19-2012, 12:02 PM   #3
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Thanks Grumpy! will do.

Here is something else I noticed, after I had driven vette for an hour I was looking under hood to look for the cause of it running rough when I discovered that the efe valve was opening and closing every 10 seconds. Is this the normal function?

A friend said that the efe is only supposed to be used when engine is cold and untill engine warms up then valve stays open to fully allow exhaust gasses to flow out.
He said that the blue colored vacuum valve is bad.

I turned the black and white vacuum one way valve around so that there would be no vacuum to the efe valve and drove the car another hour and the engine still had the miss.

Thanks for your help.
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Old 11-19-2012, 12:13 PM   #4
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doing a compression test, and verifying your ignition timing and testing with a vacume gauge,adjusting the valves, sure would not hurt here either

http://forum.grumpysperformance.com/...hp?f=70&t=4683

http://forum.grumpysperformance.com/...php?f=70&t=875

http://forum.grumpysperformance.com/...eakdown#p14266

http://forum.grumpysperformance.com/...php?f=52&t=196

http://forum.grumpysperformance.com/...me+gauge#p5410
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" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"
Old 11-19-2012, 05:52 PM   #5
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Not wanting to sound simplistic but...If you replaced the wires,plugs,cap and rotor is it possible you do not have the firing order correct?
All of Grumpys suggestions are good ones but sometimes we tend to overlook the obvious. I know I have from time to time.
Good Luck!
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Old 11-20-2012, 06:11 AM   #6
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Did you have the miss before you changed plugs, wires, cap, and rotor?

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Old 11-20-2012, 06:20 AM   #7
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Quote:
Originally Posted by Sly Vette View Post
Not wanting to sound simplistic but...If you replaced the wires,plugs,cap and rotor is it possible you do not have the firing order correct?
That's what came to my mind first as well. Good to make sure that all of the simple stuff has been re-checked first before getting into the deep stuff.
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Old 11-23-2012, 11:26 AM   #8
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Wow! Grumpy has me overwhelmed with things to check out.

Everyone who replied has valid points to look at.

I have made sure that each ign wire is in the proper location.

A user on another forum suggested that I look and see if there is any lightning happening under the hood when its dark outside.

After my eyes became acclimated to the dark I could see all 8 cylinders arcing. The NAPA blue max wires were arcing at the rear of the engine. The plugs were arcing across the porcelain from the boot to the metal on the plug.

So I replaced the plugs and upgraded the wires to MSD ign wires.

I drove it again to my friends house an hour away and noticed the engine was still jumping around. After letting engine cool down rechecked that ign wires were firmly seated. They were.

My friend said that I should replace the coil next. So I just ordered a AC Delco coil.

While I am waiting on coil I will check out some of those items Grumpy posted.

Thanks for every ones reply!

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Old 12-05-2012, 10:11 AM   #9
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I ended up replacing the distributor, new AC Delco ignition modual ,AC Delco coil, cap rotor and wires.

The miss is still there.

So I put on a vacuum gauge and have steady 18'' of vacuum when engine is cold and after driving car for two hours.

I already had a new timing set installed so that is not an issue.

I need to verify engine timing next. Will keep posted of what I find.

I donot know if this means anything, however the other day when driving I was doing about 35 and let up off the gas and then reaplied the gas and I heard squeling tires and then I looked up into rearview mirror and saw two identical black tire strips on the pavement.

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Old 12-05-2012, 10:48 AM   #10
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Cool

You seem to be replacing parts before you have determined the issue. Have you checked your plugs as Grumpy suggested? This easy task would tell you if one cylinder is not firing as it should. Also a compression test would tell you if the cylinders are in good working order. And if your engine is missing and you are still able to do a good burnout then maybe your miss is not a miss at all but something else. Just my .02
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Old 12-05-2012, 07:46 PM   #11
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Just because its new doesn't mean it's good. Check the mechanicals. What's the oil pressure? The reason I ask is because I've seen a 2.5l ford engine have over a 100psi of oil pressure and it'll miss cause it pumps the lifters up so hard that the camshaft can barely open the valve.
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Old 12-09-2012, 08:40 AM   #12
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I wonder if your chasing a miss at all , if you are the options to cause are very limited and can not be coil related.

Why did you replace the timing set ?

Why did you replace any of the items you have listed ?

If it is not distributor related as it appears not to be it has to be timing , fire order wrong ( 1 8 4 3 6 5 7 2 ) or cam worn or a valve issue which a vac gauge would detect if you know how to read it to trouble shoot.
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Old 12-09-2012, 11:39 AM   #13
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Until you check the plugs it is hard to say if in fact you have a miss at all. If you were to pull them and lay them out in order and take a pic we could read them and tell you if you have a cylinder that is not working as it should.
Just throwing new parts at the problem is an expensive way to go at this.
Good Luck!
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Old 12-13-2012, 05:21 PM   #14
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I agree with everyone about replacing parts and not knowing what is causing the miss, or as someone mentioned maybe its not a miss but perhaps a rough idle!

First of all let me start at the beginning before I thought I had an miss.

I have had my vette now for 11 years. It had not run in 10 years.
It has a little over a 100k miles and I did not know condition of engine.

Since I have planed to drive it a lot I needed to make sure that I had a reliable engine.
I knew that the rear main and front timing cover seals would needed to be replaced.

I already had the water pump off to be replaced. It was leaking out the weep hole and the part that fan bolts to was loose and wobbly.

While replacing the rear main seal I replaced the oil pump with a new stock pump. I also replaced the oil pressure sending unit, as when I bought the car it had very low pressure like about 10 max.

The original timing chain had so much slop in it I was amazed as to why it hadnt jumped. This is why I replaced timing set with a cloyes all metal set. Before removing original set I rotated engine around till the dots lined up.

I then put new ac delco plugs and napa blue max wires on.
New cap and rotor.

I had Lars rebuild my qjet. Replaced the fuel hoses at the fuel tank and at the fuel pump with correct fuel hoses and new spring clamps.

Installed new correct radiator, upper and lower hoses. Purchased off of Flowkooler dot com a balanced Robert Shaw thermastat that stays open when it gets hot, so it will never over heat. A new fan clutch.

Replaced exhaust from front crossover all the way back to mufflers.

Replaced automatic trans cooler hard lines, as the originals were rusted through.

So this is when I started engine for first time in 10 years. My freind said that there was a slight miss.

Now, where I am now.

I was looking through my files on timing and I came upon a paper written by Lars as that some times people chase a miss when it is a rough idle caused by the gasket that the q jet sits on is not positioned correctly causing a vacuum leak.

I do not have this issue, I sprayed ether around carb base and the idle did not change.

I rechecked timing and the timing was off. So I rotated ditributor clockwise until the light flashed on 0 at idle. This is not what some others rec amend however this will do for now.

I put a vaccum gauge on manifold vaccum and at all temps the reading is 16".

The first set of plugs looked uniform as all eight were firing alike. I think that the reason I saw arcing across the porcelain was that there was an accumulation of dirt on the plugs making another path to ground.

I am waiting on a friend to lend me his compression tester.

I will keep you guys up to date. Thanks everyone for there help!

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Old 12-13-2012, 06:24 PM   #15
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Set your timing according to GM specs for your year model Corvette. Get a dial back timing light as you can better set base and total timing. I have one and will never go back to a base timing light. Mine is an Actron brand from Advance Auto...name brand isn't all that crucial as long as you get a decent one.
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As FPSRussia says "As always.... Have nice day"
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