Misfire

Hey again,

I have a 1993 S-10 Blazer I recently replaced a distributor because of excessive play in the shaft to try to fix the incredably erratic idle. I put in the "rebuilt" distributor and hooked it up and the engine wouldn't start. My buddy and I miscommunicated on the firing order. Anyways when we cranked it, it fired early enough on the compression stroke to stop the motor. I took out the number one sparkplug and broke the wire, and dropped the sparkplug closing the gap to .20. The next day it idled great and drove better than years until it warmed up. It developed a misfire. I went ahead and replaced the wireset and the sparkplug that was bad. It ran better but not by anymeans well.

On another vehicle I gapped an ungappable spark plug and got the exact symptom, that machine gun sounding miss under light throttle only difference is that I give it more gas and it goes away the other car did it worse the more i hit the gas. I ran through a checklist chart and am beginning to suspect the distributor itself. Other then the shaft play in the distributor the only other difference between the two that I see is that the two star shaped things under the rotor (I'm assuming the points? Correct me if I'm wrong.) just brush by (touch) each other while the old distrubitor they did not. A few days before I replaced the coil with improvement so I don't suspect the coil. I never had a miss under load or speed just at Idle before I replaced the distributor.

I'm concerned I either got a bum distributor or broke it somehow.

I'm not getting any codes and am not quite sure which cylinder it is as I haven't had time to short out cylinders but it it rythmic so I believe it is a single cylinder.

Also the idle is fairly decent warm and near perfect cold. It also has a small hp fluctuation at wide open although it always has. It was much worse before changeing the distributor so I assume it was another problem exaggerated by the distributor. Varing engine speed the ignition timing is consistant and is correct at idle, although wanders a bit at idle.

If anyone has any insight I greatly appreciate it.

-Mark

Check for good hot blue spark to all plugs.

Pull one wire at a time and watch for rpm drop the same on all cylinders to see if any cylinders are missing.

Post back what you find there.

Ok, I got blue/orange spark on all cylinders. It is a bit weaker on cylinder 6 with distance it will jump, but the same color. Odviously 6 had the lowest RPM drop. I also switched back to the old distributor for a bit and it fired cosistantly although the timing is erratic with that one. So I'm assuming it has to be this new distributor.

I'm wondering if filing down those two star shaped things would help as my old one and the one in the picture in the haynes manual have air gaps there.

-Mark

Ok, I got blue/orange spark on all cylinders. It is a bit weaker on cylinder 6 with distance it will jump, but the same color. Odviously 6 had the lowest RPM drop. I also switched back to the old distributor for a bit and it fired cosistantly although the timing is erratic with that one. So I'm assuming it has to be this new distributor.

I'm wondering if filing down those two star shaped things would help as my old one and the one in the picture in the haynes manual have air gaps there.

-Mark
Make sure plug and coil wires are good.
Swap wires with another cylinder.
Try another dist if dist is losng spark on one cylinder .
Fire should jump well over a 1/4 in.
If fire is weak or real red try another coil.

Ok, I swapped back out to the old coil and it somewhat cured the problem. The new coil was defective. Later on I ran some seafoam through it on a whim and it cured the problem completly.

Must have had a plugged poppet valve that wasn't real apparent with the old distibutor in there. I guess new parts aren't always better too.

Thanks for your help.

-Mark

Ok, I swapped back out to the old coil and it somewhat cured the problem. The new coil was defective. Later on I ran some seafoam through it on a whim and it cured the problem completly.

Must have had a plugged poppet valve that wasn't real apparent with the old distibutor in there. I guess new parts aren't always better too.

Thanks for your help.

-Mark

You are welcome and thanks for posting back how it went.
Glad you found the problem.
If plug wires are old I would consider replacing them an make siure plugs are Good AC delco plugs and cap and rotor good.
Yes sometimes you can get bad new parts.
Always go for a good known brand of parts.
And do proper testing before and after replacing anything.
Good Luck