Rythmic stumble during idle and acceleration,is that a miss?

[Blaze One]

1995 CPI 4.3

A few days ago : rpm was erractic and jumpy , about 500 rpm when accelerating/driving . Idled fine , but not perfect ( a little rough but drivable )

Today : went to start it and there is now a really rough rythmic idle , and this con't upon acceleration .

I would like to do a tune up anyways , so is there a "how to" on this site ? ( i can't find it )

I feel that it is a missfire because the idle roughness is so rythmic and consistant . The truck starts fine and had good power before the problems began .

The fuel pump makes the familar sounds for a s10 lol

Am I on the right track ? .

[HenryJ]

Basics first. Check the plugs, cap, rotor and air cleaner. Change the fuel filter.
Careful of the plastic distributor housing, Heed the warning on the stock information page.

[Blaze One]

well this morning the truck was running great . no rough idle etc .. drove for about 10 mins and then it ran rough again .

i have not had time to look at the plug/rotor/cap etc . but will tomorrow .

here is a short clip of what my idle is like at the tail pipe .

http://www.youtube.com/watch?v=dJpsCQza ... ata_player

[killian96ss]

Yeah, that doesn't sound good. Are there any codes stored? If there isn't, you're just going to have to check the condition of everything mentioned above and replace stuff as needed. Clean all of the sensors & throttle body. Sometimes it helps alot.

Steve

[ApproachMedium]

well this morning the truck was running great . no rough idle etc .. drove for about 10 mins and then it ran rough again .

i have not had time to look at the plug/rotor/cap etc . but will tomorrow .

here is a short clip of what my idle is like at the tail pipe .

http://www.youtube.com/watch?v=dJpsCQza ... ata_player

My truck did this, get at fixing it quickly before you end up with a dead #3 cyl at idle. Check the condition of #3 spark plug and make sure its not fouled up. Are you getting alot of fuel smell when it idles funny like that? Unburned fuel smell is a sign of misfires, esp the kind where the cyl is not firing at all during idle which is what my #3 does. When it gets up to speed, over 1,000RPM all cyl fire properly.

Mine has a burn/bent valve most likely. Its been this way since 200k, it has 252k now and it still runs, drives, and hauls ass. Ill worry about it when the cops start worrying about my failed inspection.

[Blaze One]

i took it to the mechanics and had it scanned ... there is a misfire on the #1 cylinder . mechanic said my plugs are all in good codition , but the wire to #1 is fried .

So . I relpaced the ignition wires , and the misfire is still there . who knows if the mechanic was B.Sing me or not .

secondly , the mechanics report said my cap and rotor need to be replaced ... I don't know how the mechanic knows this since he didn't remove it to inspect it .

But I will be replacing the cap and rotor tomorrow just to make sure it is in good shape .

[killian96ss]

Make sure all of the spark plug wires are fully seated in the cap and on each plug. They should snap into place and not be easily pulled off. It's also a good idea to make sure the plug wires are routed correctly. The engine will still run if 2 wires are accidentally switched so make sure the firing order is correct. I would also try swapping the #1 plug with another one just to make sure that plug isn't bad.

Don't buy a cheap cap & rotor! Some are made better than others. The Accel cap & rotor is the nicest one available, but also the most expensive. There is a topic around here somewhere that shows the differences between brands. If the misfire does not go away after installing a new cap & rotor, new plug wires, and new spark plugs, then it must a fuel delivery problem to that cylinder, or mechanical damage like burned valves, broken or weak valve springs, etc.

Steve

[roadrunner]

I would be highly suspicious of the cap and rotor. I went through a bad cap situation that was not visible or provable to the eye or the scanner. Ended up being shorted internally between some of the terminals of the cap itself. I even cut it apart trying to find the track unsuccessfully. Replaced with AC Delco for both and no more problems. I now keep a spare for each on hand. Further since the #1 wire was fried that would cause that cap terminal to seek new path to ground most likely shorting to another terminal. They pass pretty close to each other internally in the cap. My .02 worth.

[Blaze One]

well ... no good news .

i replaced the cap and rotor - they were in rough shape





I double checked my wire connections at the plugs and the cap - all good .

But the problem still persists . the engine runs smoother , but the so called "missfire" is still there .

I think it is electrical short some where , maybe a bad ground ?

I touched the boot of the wire(short one going to cap) going to the coil and was shocked by it . And there is a very slight "tick,tick" every time the engine misses . the "tick" sound is just like a the sound you would hear from a spark or arc .


bad coil ??

[HenryJ]

Spray down the ignition system external surfaces with cheap hairspray. Pay attention to areas where you see spark jump after inspecting at night or in a very dark garage.

You may want to research the "nut fix" for CPI engines. Our trucks did not come with this engine.

[roadrunner]

I have an alternate suggestion to HJ's. Take a spray bottle of water and with the engine running spray small areas of the wires and coil till you hit an area that either makes the miss solid or causes the engine to die. I once found a cracked coil tower that was not visible using this method. You don't need to drown it just hit small areas and observe for changes in engine operation. Also I would suggest to you perhaps the coil wire itself is bad even if new. Your experience getting shocked (if the coil wire is good) indicates there is high resistance somewhere in the plug wires/cylinders. Or at least high enough that your hand became the shortest path to ground. Note: this can also be caused by an extremely lean condition in your number one cylinder perhaps caused by a vacuum leak on that cylinder or a faulty/clogged injector.

[Blaze One]

ok thanks .

I am going to wait until it is dark out , then see what I can find in terms of a arc or sparking .

[killian96ss]

Make sure you try another spark plug on #1 so you can be sure its not a faulty plug. This may sound stupid, but make sure all of the spark plugs are properly tightened. I've seen loose plugs cause misfires. A coil that is going bad will have random misfires, not just a specific cylinder, so I don't think it's your coil. If you have a new cap & rotor, new plugs, and new wires, your problem is most likely fuel delivery related or you have some sort of mechanical damage to cyl #1. Like Brule said look at the engine in the dark while its running. Any voltages leaks should be obvious. The garage is a nice dark place at night, just make sure you leave the door open so you dont create another problem.

Steve

[Blaze One]

it probably should not look like this inside the intake ... looks like my problem is a leaky injector