Random Misfire finally fixed!

Random Misfire finally fixed!

Postby OnSafari [OP] » February 19th 2009, 10:36pm

I've been dealing with a random misfire in my 96 Safari for a Loooooooog time. I changed plugs,wires,cap,rotor,coil with non AC Delco parts. Eventually all of those were replaced again with AC Delco parts. Still misfiring. Checked fuel pressure etc, all ok. I thought about doing the injector upgrade but couldn't get myself to spend the $ plus I was fairly sure it was ignition related.

Finally, my fix. I noticed that, with the distributor cap off, I could twist the rotor counterclockwise nearly 1/2 inch. I checked my 2000 Astro and it would turn less than 1/8 inch. So, I pulled the distributor out and found that the drive gear was noticeably worn. I replaced that gear and reinstalled the distributor and, with less than 1/8" play, she runs like new.

I read posts a lot and don't post often but I had to share this one with you all. I hope it helps someone else out with the p0300 random misfire code.
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Re: Random Misfire finally fixed!

Postby astro355 » February 20th 2009, 1:15am

Yeah, that's definitely a good find there.
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Re: Random Misfire finally fixed!

Postby Matrixx » February 20th 2009, 7:14am

Amen to that. Great work OnSafari, that is definitely out of the norm for random misfires .:)

Thanks for the update.:)
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Re: Random Misfire finally fixed!

Postby rev_les » February 28th 2009, 8:14pm

I wish I'd have seen this ages ago, lol.... I've had the same problem, DID the injector upgrade (which really wasn't that hard), replaced cap, rotor etc., and the problem kept getting worse all the time, and I finally suspected the same thing, and found the excessive slop in the distributor.New distributor should be here soon, and out of curiosity,was yours worse until it warmed up?Mine bucks like a wild bull till I've driven it like 15 miles, then it eases up somewhat
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Re: Random Misfire finally fixed!

Postby OnSafari [OP] » March 1st 2009, 12:23am

Mine bucks like a wild bull till I've driven it like 15 miles, then it eases up somewhat

Sounds about like mine. It does ease up a little but it is still very noticeable.

It's been running bad for so long that I still can't get used to how smooth it's running now.
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Re: Random Misfire finally fixed!

Postby seahunt56 » March 2nd 2009, 12:56am

I have been haveing the same problem and code for some time. I talked to the parts buy at the local chevy dealer about maybe a seal or o ring between the distributor cap and base. (The pins inside the cap were turning green.)He said it did not have one but what parblem was I having. It seems like i was getting moisture in side the cap. He said on some Astros there is an AC line going right over the distributor the could sweat and drop beads of water on to the cap. I checked mine and sure enough, I have that AC line right where he said. I took a piece or 1/2 in plexiglass and some alluminum flat stock and made up a little cover to keep the cap out of harms way. Put a couple hunderd miles on it and all is well. No Check Engine light and smooth running. Knock On Wood. No I am going back in and see how much play the rotor has.
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Re: Random Misfire finally fixed!

Postby thyubernoob » March 2nd 2009, 3:08am

Thanks for the info, that's a good one to remember! :ty:
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Re: Random Misfire finally fixed!

Postby rev_les » March 3rd 2009, 2:15am

hey all.. Put the new distributor in today.. BAM code 1345.... after putting the original cam pos. sensor back in... same thing, found another string on here for PROPER dist indexing (Haynes is about useless) i came to the conclusion that the gear wasn't indexed EXACTLY like the original, ( I tried moving it over a tooth, it would be too far one way or the other) anyhoo.... after reading somewhere that the "zero" might have to be reset via Tech II , I decided to elongate the hole in the dist. clamp, to index it myself... VIOLA!! once I got the rotor to align with the arrow in the dist base... no more code. *just a thought if anyone else ever has this problem* btw........ the original gear with 185K on it was SERIOUSLY worn, lol..
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Re: Random Misfire finally fixed!

Postby Buzzterbrown » August 27th 2009, 11:46pm

Man! I have been dealing with the very same misfire on a 2000 GMC Savanna van 1 ton with a 5.7 liter for some time now. I pulled the distributor and sure enough, the gear teeth were eaten up! Popped in a new distributor and problem solved! Finally the internet pays off. Thanks a lot bro!
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Re: Random Misfire finally fixed!

Postby Big_kid » August 28th 2009, 12:23am

Glad it helped you too! Next time I'm in mine I'll have to check it.
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Re: Random Misfire finally fixed!

Postby OnSafari [OP] » August 30th 2009, 8:34am

Wow! I'm glad this post helped you all. I ended up having to change the gear in my Astro too. Fixed it first try this time :dance:
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Re: Random Misfire finally fixed!

Postby fozzy19 » October 6th 2009, 12:15am

I am having the same problem. Multiple cyclinder misfire. I replace the dist. cap, the wires, plugs and still having a misfire. I took out the ditributor and gear looks fine, some wear, but not missing any teath, and rotor rotates minimally with the cap off(see pictures). I am at a loss and losing hope here. I have consistant vacumn and fuel pressure. The coil is firing and rotor shows no signs of wear. The only thing I have not done is a compression test. I just seafoamed it, hoping that it would do something and nothing changed.

This happened out of the blue, the van was running fine and then one day I went to drive it (about a week ago) and it just chugs and chugs, you can tell one or more cyclinders are not firing. I really would like to get this fixed so I don't have to junk the van, but I'm running out of hope, patience and most importantly $$$.

If anyone has any suggestions, I would greatly appreciate any further input.

Thanks!
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Re: Random Misfire finally fixed!

Postby astro355 » October 6th 2009, 1:04am

So how much play is there in the distributor when its installed? 1/16"? 1/8"? 1/4"? 1/2"?

That gear doesn't look in the best of condition.
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Re: Random Misfire finally fixed!

Postby astroturf » October 6th 2009, 1:11am

astro355 wrote:So how much play is there in the distributor when its installed? 1/16"? 1/8"? 1/4"? 1/2"?

That gear doesn't look in the best of condition.


astro355, Quick question. How much play is acceptable? Thanks, Jim
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Re: Random Misfire finally fixed!

Postby Jasen » October 6th 2009, 4:16am

That's one of those ones you really don't think about.

Years ago after doing a tune up on a 65 Belvedere I just bought, it was nearly undrivable. Me, nore none of my buddy'd could figure it out. Took it to the mech and it turned out to be a bent dist. shaft.
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Re: Random Misfire finally fixed!

Postby fozzy19 » October 6th 2009, 12:29pm

I replaced the distributor and it's still misfiring. I would say the original distributor had the same amount play in rotor as the new distributor, it's a $90 part so I think that I will return it.

I have not tested the coil, I am not an expert and was wondering if anyone could point me in the right direction as far as a procedure to test the coil. I have also read that the coolant temp sensor and intake temp sensor can go and can cause a misfire.

Any other suggestions?
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Re: Random Misfire finally fixed!

Postby astro355 » October 6th 2009, 3:50pm

fozzy19 wrote:I replaced the distributor and it's still misfiring. I would say the original distributor had the same amount play in rotor as the new distributor, it's a $90 part so I think that I will return it.

I have not tested the coil, I am not an expert and was wondering if anyone could point me in the right direction as far as a procedure to test the coil. I have also read that the coolant temp sensor and intake temp sensor can go and can cause a misfire.

Any other suggestions?


Can you measure the amount of play in the distributor, please?
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Re: Random Misfire finally fixed!

Postby fozzy19 » October 6th 2009, 4:05pm

astro355 wrote:
fozzy19 wrote:I replaced the distributor and it's still misfiring. I would say the original distributor had the same amount play in rotor as the new distributor, it's a $90 part so I think that I will return it.

I have not tested the coil, I am not an expert and was wondering if anyone could point me in the right direction as far as a procedure to test the coil. I have also read that the coolant temp sensor and intake temp sensor can go and can cause a misfire.

Any other suggestions?


Can you measure the amount of play in the distributor, please?


I sure can, what's the best way to measure it? Just a tape measure, or is there some other method? I want to be as accurate as possible so I can get solid feedback, and when you're getting down to 1/16" it's easy to miss the true measurement.

I won't be able to get to it until later this afternoon because I am at work, but I'll get it done as soon as I get home.

Can anyone let me know how to test the coil?
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Re: Random Misfire finally fixed!

Postby astro355 » October 6th 2009, 4:14pm

A tape measure will be fine, just use a point of reference.

The easiest way to test the coil would be to get a spark tester. Unplug whichever spark plug wire from a spark plug, plug in the spark tester and crank the engine. Really, that will test every component in the ignition system. Using a spark plug in this fashion is not ideal. It will let you know if it is firing at all but since the spark plug fires differently at atmospheric pressure compared to the compression chamber, its not a good gauge of how well its firing.
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Re: Random Misfire finally fixed!

Postby fozzy19 » October 8th 2009, 1:06pm

Ok, so I measured the distributor rotor movement it and it's moving about a 1/16", no more. So I would think that was within tolerance, but then again I don't know.

I borrowed a OBD II tester from a friend and now it's kicking out a P0305 code, meaning a cyclinder 5 misfire, before it was kicking out a P0300, multiple cyclinder misfire. I have replaced all ignition system components and am still experiencing the same issues.

As I mentioned before I have done a vacumn and fuel pressure test and it seems to be within the acceptable range. I need to do a compression test to see if the cyclinder is not firing, or weaker than the others, I might be able to do this tonight or tomorrow. The other thing that came to mind was a possible fuel injector failure on cyclinder 5. I looked up the removal instructions for the fuel injectors to discover that it is a huge pain in the rear end or a job to remove them. I removed the upper intake manifold last night, besides being very dirty on the inside, nothing looked out of place, granted I have never taken anything like this apart before. I am wondering if there is a way to test the fuel injector now that I have the upper intake manifold off? Or if there is anything else I should check while I have this disassembled that might help resolve my issue?

Any other suggestions?

Thanks!
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