The Stovebolt Site Forums The Shop Area Engine Shop 250ci misfiring on cyl #1

Hi guys, I have a 1966 Chevrolet c-10 with a 250ci in it. it has been misfiring on cylinder #1 for the past few months. I cleaned the spark plugs one time and got it to fire on all 6 then it went back to running on five over the next couple of days, I pulled the plugs again and they were fine. I then purchased a Reman Distributor from autozone thinking that the problem was in the distributor, it wasnt, put the new one in and still misfiring on cylinder #1. So today I went and purchased a distributor cap and wires for the truck and it ran great after that until I went to turn down the idle. Its back to running on five cylinders again. I have tried to adjust the points on it, but when I try to adjust the points, the whole points plate moves, what am I doing wrong guys?? please help its beginning to get very annoying!

Thanks

Jordan

Hy JDF 1986, have you checked the intake manifold for a vacuum leak at #1 cylinder? It sounds like it might be too lean to fire, also a compression test might reveal something, hope that helps.

how did you determine that it wasn't firing on number 1 ?

here is a video that might help, although it is a different engine then yours adjusting the points are done the same way, just a different gap..

the adjustment is at the end of the video
click here

or read these instructions.

Loosen the screw that holds the stationary point bracket to the base plate. Not completely, just enough so that you can move the bracket by inserting a screwdriver tip and twisting it Adjustment is a matter of trial and error. Move the stationary point out a bit if it was too close, tighten the holding screw (not too tight), and measure the gap. If it still isn't right, try again. The feeler gauge should have a light drag when the points are properly adjusted. This is where practice and patience comes in handy.


good luck

I determined that it was misfiring on CYL #1 by while it is running, pull off the s/plug wire and it didnt change the idle speed, it would however change if I held it close to the plug to make it fire. When adjusting the points by loosing up the screw on the bracket and inserting a screw driver to adjust the points, the whole points assy moves not just the part that contacts the cam on the distributor. I did check for vacuum leaks around the intake manifold by using WD-40 while it was running and it didnt change the idle one bit. the distributor in it is only two months old but dad and I think that it is no good and also he thinks the acclerator pump in the carb is bad also.

I'd have to be conviced by argument that the points maladjustment or a bad remanufactured distributor would cause the # 1 plug only to misfire. The accelerator pump may well be bad, but isn't causing the # 1 plug to not fire.

Some where between the # 1 cylinder and the distributor cap is your problem, as you describe it. If you have a new plug, wire & distributor cap and the problem still exists, then its not the electrical side of the engine. I assume you have determined that the # 1 plug is not being fouled by oil, that there is not a compression problem in the # 1 cylinder and that the # 1 cylinder valves are functioning.

A 66 C-10 is well worth restoring. Sweet truck. Mines a 65 C-30. Dave.

Are the autozone plug wires copper core? If not try to find 440 packard sparkplug wire.I bought mind off of ebay.Points system needs copper core wires.

Use a dwell meter to set the points betweem 30 and 36 degrees.


Use spakplugs with the heat range equal to the oringal sparkplug R46T.I use R45T or R45TS sparkplugs.

I have had new points that were bad,the points would cause the
engine to miss.

I have had a bad carburator that would make the engine feel like it was missing.

You might need to adjust the valves,could be a bad lifter.

A loose intake would give the engine a bad ideal.

I have owned a 66 Chevy C10 with a 250 engine with point system more than 10 years.

Jimmy

I just had the same problem on a 235 that someone gave Me I wanted to run the engine before I put it in storage to rebuild later it turns out that the PO had adjusted the lifters and the intake on # 2 was to tight and was staying open no compression adjusted the valves and engine runs great , so I would do a compression check , it does not sound like a elect. problem .



Pete

What is the color of #1 plug? oily, white, grey, brown.....

Does the engine make any kind of noisy, lifters ticking?

Does it miss under a load or only at idle?

Can you hear the miss in the exhaust pipe or just feel it?

Is the engine using coolant? Are you loosing coolant out of the radiator?
#1 cylinder is weak around the front of the block where the water pump bolts on, if the head bolt is over tightened, you can crack the block causing coolant leaks.

As for the carburetor, anything wrong with it and all six cylinders will be affected, plus a leaking intake port will affect two cylinders since its a siamese head design. (two cylinder ports for one intake port)

This engine has a hydraulic lifter and cam set up. They don't need any adjustment of the valves. If the cam is going bad, you should hear the loose rocker making noisy. You might pull the valve cover and watch the rockers on #1 just to verify they are lifting as much as the others. With the engine off, grab the valve spring and see if you can move it sideways, pry and push, this will tell you if the valve guide is loose, causing oil usage and fouling the plug.

A simple compression check will tell you a lot about the cylinder as well.
How much blow-by comes out the breathers?
Loose or broken rings will effect how they run.

Joe

Had same problem. It was I think #4 intake valve guide,I pulled the valve cover and ran it,pushed sideway's on each valve till miss went away.Turned out the guide was bad.Tom

Run a comp. test if you havn't already. If that is o.k. pull the valve cover. Check for a broken valve spring. Look at the valves, when closed they should all be about the same heigth. If one is up higher then the rest it can indicate a recessed valve seat, which often doesnt show up on a comp. test. To set the points, turn the engine to get the rubbing block on the high point on the cam on the dist. shaft. Put a .019 feeler gauge between them & adjust the points to get a drag on the gauge. It is correct for the point to move as you make the adjustment. Tighten the retaining screw down when you get the adjustment. Unless the shaft is bent or the bushings worn the dist would not cause this problem.

I should have said adjust the rocker arms.


Start with the simple things.Set the points with a dwell meter,reset the timing to where the engine takes the gas without hasatation.Set the ideal speed with the dwell meter to 600 rpms for manual,little lower for automatic trans.

Good Luck, Jimmy

your stated that it was running fine until you tried to adjust the idle.........I cant think of any reason why adjusting the idle would make it misfire...might make it run bad if you adjusted in down to much..

are you also adjusting the carb ??

if it was running good till this point I dont know of anything that would change it..

how high was the idle when you try to adjust it.. I always ran mine a little on the high side..

let us know when you find the problem,
and if you get it running good again, dont mess with the idle.......lol

the spark plug color is usually oily/black.

the valve train makes no noise on the motor.

It did at one time misfire while idleing and got worse when put under load, now it doesnt. it misfires constantly. at one time I took the #1 plug wire off and just sit it on the plug to make it fire until the motor got up to operating temp and then I put the wire back onto the plug and it would fire on it after that, but it only lasted a couple of days. When it does run on all six it is very responsive to the throttle. I got a lifetime warranty on the distributor and I will get another distributor this week and a new set of plugs. I'm fairly sure that there is nothing wrong with the valves on the motor.

Sounds like you are pumping oil onto the plug. When you run with the wire off a little ways that clears it out. What type plug are you useing? An extended tip plug will work better then the old style that had the tip back in the shell. R45s or r46s AC plugs. You may be needing valve seals or a ring job.

I run ac R45 xls spark plugs in it. Do you think the R46 will work better? isnt that a hotter plug? I will have my ATV and computer paid off by June of next year then I can dig into the motor, are there any temp fixes until then? I will just be moving it around the yard and hauling fire wood out of the woods with it this winter until I can get it repaired right.

Did You do a compression check , do that frist it will take alot of things off the table or it will tell You what is wrong.



Pete

You wouldn't gain much going to R46S plugs & I'm not sure they are available any more. We used to use a plug called Aldors that fired in oil. The last I knew J. C. Whitney had them. There are extensions you can get that gets the plug away from the oil but thats pretty temporary because it causes the plug to run hot & burns them out.

I will get around to doing a comp test this week sometime, I will also take off the valve cover to check the valves to make sure they are working properly and that nothing is broke. I will look in J C Whitney for the plugs this week also. I will post an update probably early next week as I am going to missouri this weekend to visit my mother and I need to get my 1980 Honda ATC 110 out of the shop.

Jordan

Any local auto store will have new plugs. They also have the anti-foul adapters. Its just a extension you screw on to your plug. Holds heat in the plug tip to keep oil burnt off better. Same idea as putting a hotter heat range of plug in the one hole. Be sure to get a new valve cover gasket if yours is very old.

Joe

I got two new valve cover gaskets (fel-pro) from autozone in 2004 when I was planning on putting new gaskets on the engine and wound up with two valve cover gaskets, not sure how I did that. I might get a set of anti-foul adapters, not sure. Next year I plan on starting on the bed of the truck (the worst part of it) and work from there to the front on repairing/cleaning and painting the truck. I will then pull the motor out and probably rebuild it as I would like to keep the truck original looking.

You will only need one anti-foul adaptor if its just one cylinder fouling the plug. Don't install any more then that.

Have you done a compression test yet? Joe

you already changed your handle since the start of th is post..
hard to keep up with folks with that going on..

at any rate, have you found the problem yet?

Try swaping the #1 plug with another to see if the miss moves. A bad plug can drive you nuts.
Jim

Ok what farmer51 just said,and much earlier in the post:grub
1:swap plug 1 with plug 2,does the trouble follow?
2:swap 1 plug wire with whichever wire will reach does the trouble follow
3:like grub said,I also had an intermittant miss on a motor,turn out to be a bad exhaust valve guide
I hope this will help, Boyd