Hello,

Was planning to attack a rough idle/hesitation when cold problem in 2002 Blazer 4.3 (130,000mi.) tomorrow. (It's raining pretty heavy in NY right now...)

Drove the vehicle 150mi. yesterday. Ran OK but felt funny, almost like timing was retarded. Went out for a bit today, still felt funny, the SES light blinked and it threw the dreaded P0300 code. SES light went out after short time. Ran better after it reached operating temp (usually stays around 210F).

I hear a lot of talk about worn distributor gears and plan to check that.

I remember feeling a bit of rotational (10 degrees maybe...) and vertical play (around 1/4" IIRC) when I changed the distributor cap a few months ago. Couldn't find much info online about these tolerances.

How much play is considered normal?

thanks

 

Both values you have listed are WAY too high. Axial play (up/down) should be kept to between 0.010" and 0.020". Shims are available to properly set the axial play, but rotational play is set by the gear on the bottom of the distributor shaft and how it meshes into the gear on the back of the cam. It is not all that uncommon for the distributor gear to get chewed up.

From the sounds of it, your distributor is toast.

 

Thanks for your help.

Checked it out yesterday and the slop wasn't as bad as I thought, but it still seemed excessive. Went for a new aftermarket distributor from a local parts house. Came with cap, rotor & CMP.

The cap & rotor that came with it looked like junk, so I used my existing Delco ones which were in good shape.

The truck runs great! Hasn't been this snappy in ages. I do have a problem though with hard starting. Previously, the truck would pretty much start when I looked at the key... now I have to crank it for a while, and it feels like it is kicking back. Once it catches, it's fine though.

I was very careful to get the new dist. in on the right tooth. Marked it and it lined up perfectly. Runs too well to be off anyway... Should I try the old CMP? I was thinking that the computer might have remembered the old timing on the sloppy dist. even though I disconnected the battery while doing the job. Make sense at all?

Any insight would be appreciated.

 

OK, I just went outside and replaced the Delco cap & rotor with the aftermarket unit which came with the distributor.

The truck fired up like it was new...

On closer observation, it seems like the OEM cap didn't "sit" properly on the aftermarket distributor. I could see how the spark was hitting at the bottom edge of the poles. It previously hit around 1/8 in up on the metal. I'm sure this will be fun when it's time for a new cap & rotor, but it's working for now.

Gonna take it out for a drive...

peace

 

That's odd. Let us know how it goes long term.

 

If its off 1 tooth advanced it will run and start great cold. But have a tough time starting warm. Check this article EDI Ignition timing swartlkk posted it and it is the only way to check and be sure your on time.It has to point dead at the 6 to run right and its pretty easy to do.

 

Wanted to follow up on this... The truck has been running great. Right after my previous post, I messed around with the distributor cap a bit more and realized that I probably didn't have it pushed down tight at first. Might have been on crooked too...

The aftermarket dist. has a metal bottom plate with a fairly thick coat of black paint on it. The cap just needs to be pushed down tight. It kind of sat on top of the old dist., but a slight bit of force is needed here to seat it properly before tightening the screws.

I also found that the secondary winding of the coil showed an open-circuit reading on the ohm meter when cold. Readings were normal when warmed up, but I could hear the spark jumping inside the coil when it was cold.

Between the new distributor, cap, wires and coil, the truck runs like new. Just passed the NYS emissions inspection too. Thanks for all the help and info here.

P.S. Robert, thanks for pointing out the timing info. I simply marked the position of the old dist. before taking it out, and put the new one in the same way. I did bring up the marks on the harmonic balancer and checked the rotor position after I read the article. Was right on the money.

peace

 

I have the same blazer as you, same miles and everything when the PO300 code showed up, exact same thing was wrong with mine. Getting it fixed right now, and hopefully this takes care of the problem. Did you have any other issues with misfires or problems starting after the fix? i know you posted this a year ago...so i figured i might as well see if anythign else happened.

 

The Blazer has been running fine. Note that I also replaced the coil and wires. A new sensor came with the aftermarket distributor, which overall seemed to be much better made than the OEM part.

Last fall, I also replaced the intake manifold gaskets. If they haven't been done before, you may encounter that issue soon. It was not too difficult. Plan to put in a full day if you do it yourself.

Good luck!
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