I have a 2000 Blazer 4.3 6cyl. It started running extremely rough, with a multiple cylender misfire a few days ago. After doing a tune up (new plugs, wires, distributer cap, and rotor) it ran a slight bit better, but still had a nasty misfire. I did some searching and reading and found that it could be the Spider (oh yay!).

Replaced the spider with the new version (purchased at Advance), and the motor ran much smoother (and yes, the old spider was SHOT!). Also replaced the plenum and throttle body gaskets and cleaned the throttle body.

Here is my dilema though, it backfires when sitting at idol (1000 - 1200rpm), won't drop to 700 rpm (old average idol), but if I bring the tach to about 1600 or higher, no backfire. When the motor first starts, there is no backfire, but after about 2 minutes, it starts.

After doing a little testing, i found that if i remove the #3 plug wire from the mix, no more backfire! Took the plug and wire back and exchanged for another (even though they are new thought it was worth a shot!)...still have the same problem.

I let the motor run for a few minutes until the backfire started again after letting the vehicle set, placed a towell at the muffler, and watched to see if it was sucked back into the exhaust any when the backfire occured...no suction...which means the "poor mans" cataletyc converter test passes.

There is a nasty leak where the cat bolts to the manifold (after replacing it with a direct fit, i was never able to get the bolts to tightnen all the way), but it has had that leak for about 2 years now....ran fine all the way up until last Monday.

Quite honestly, I'm stumped...Don't want to admit to the fact that the valves may be stuck, but it isn't looking good for the home team here. ANY help would be appreciated!

 

I hate to tell you this but....... see my thread.
Sounds like the problems I was having. however I ended up with 0 compression...

https://blazerforum.com/forum/engine...roblems-80276/

 

Thanks for the reply. I tested compression on cyl3 and it was reading good (150 i think)....but i will re-test to be sure after the new changes have been made.

 

I HOPE that it isn't what your post was lol, but i agree with the quote of "My cars sit in the driveway and conspire to see which one will be messing with me this week. On a real quiet night I can hear them talking" for sure!

 

I HOPE that it isn't what your post was lol, but i agree with the quote of "My cars sit in the driveway and conspire to see which one will be messing with me this week. On a real quiet night I can hear them talking" for sure!

On the new spider, is it possible to "unplug" injector 3? if the cylender is dead or acting up, could this be done as a "temp" fix to nurse it from the parkinglot to home?

 

From what I have been told, most of the time with the 4.3 the multiple random misfire is caused by the valves getting pitted and not being able to disperse the heat. They will get hot and start to bind in the valve seats. My solution would be to remove the heads and take them to a machine shop to get them rebuilt before anymore damage can be done. Make sure to have them install spiral valve seats instead of normal ones. The spirals will hold more oil to keep them cool.