OK, I know there are alot of these on this newsgroup but I have not been able to find the answer thus far. I am going to post as much detail as possiable so bear with the long winded start.

I have a 97 Chev Blazer, with the 4.3 Vortec engine and 206000 Klms

Problem is like this.
As soon as I start the truck its has what is best described as a miss fire and a major hesitation on acceleration. After 60 sec of the engine running the check engine lite will start to flash. Approx once per sec. This will happen exactly the same everytime I start the truck. Computer would display no codes.

I did notice a very slight perf degradation the week leading upto the problem. Not even really noticeable untill I though about it after the problem got really bad.

the problem has been occuring for approx 1 week at this point in time. I waitied for approx 5 days before the check engine lite finally came on after starting it. I then checked the codes and it displayed an "P0134 - Low voltage Upstream O2 sensor". Thought finally I get to get rid of this problem. I replaced the O2 Sensor just before the Cat, cleared the code and tried a run test. Turns out still have the exact same problem.

Drove it for another day and got another code "P0137 - no activity on Downstream O2 sensor". umm this one had me puzzled, I took the O2 sensor I removed from the front of the cat and swapped it with the O2 behind the Cat. Cleared the code and still no Diff.

Thought it may be the Cat itself being plugged so I disconnected it and ran around the block. Still same problem.

About a month before the problem started did a complete tune up. Cap, Wires, Rotor, plugs. Now if I disconnect the plug wires one at a time with the engine running I get a slight change in the running of the engine with I disconnect cylinder 1,3 and 5.(left bank) But I get a huge difference to where it will almost stall if I unplug 2,4 and 6. (right bank)The old plugs I took out were at .050 gap when removed. (I am using Boche Platinum Plugs)When the new ones were put in they were at .045 gap, Now I checked the new plugs about a month old are already at .057 gap.
I am going to be putting new plugs again in it tomorrow but I want to do a sanity check. Am I going down the wrong path here? or is there something I missed.

common problem on these vehicles is the fuel injector. might want to look into that

is there anyway to test the injector or is it one of those replace and pray items?

Mack

Maybe a simple problem. Really sounds like a vacuum leak. Check the basics first. Might also take off the EGR valve and check the pintle/seat for a chunk of carbon, common on high mileage S10s.

OK here goes

Last night I did the following, Changed all 6 spark plugs, Took out the Boche and replaced with AC/Delco Platinum gapped to .060. Which is what it says on the Sticker under the hood. Also removed the EGR valve and cleaned with TBI cleaner, the pintle seems very easy to move and does not appear to be binding. Moves to the full extent in and out with no problem.
Guess what, same problem, Guess its back to square 1.
Next things to try are the following, Fuel pressure regulator. Any other suggestions are more than welcome.

Just a quick test, Somewhere in the forum I saw a note of to give a quick idea where the problem might be take off the vacume host to the brake booster and stick your nose to it. Well Just did and got an awful smell of raw fuel. Looks more and more like the Fuel reg. again, will keep you posted.

Update
This morning I stripped off the intake Plenum. Found Fuel Wash in cylinders 1,3,5 and 6
5 and 6 are the rear most below the fuel reg and 1 and 3 are the 2 front drivers side cylinders. I am assuming at this point its the fuel reg. Is it common to have fuel wash as far forward as 1 and 3 cylinders if the reg is bad?
Can anyone comment on this one?

at the risk of becomming repetitive,.... update :-)

Yesterday I had the Fuel reg come in from the dealership and installed it last night. A note to anyone doing this around the top of the CPI injection unit there is a sillicone O-ring gasket. The dealer says it a non-serviceable item. they want you to buy the CPI unit. its rediculus, they want you to buy a $186.00 (CDN) cpi unit to replace a $0.50 gasket. (I am mad, but I digress) Let me give you a helping hint, Pickup an assortment of Rubber O-rings before you start the job. Cost me about 11.50 taxes in.

Anyway to make a long story I still have the same problem. Nothing has changed. Now I have to say I am really scratching my head over this one.

Finally - Problem resolved
I was gently told by a friend of mine to "go back to basics" Fuel, Compression, Spark

- Well After checking the pressure on the fuel lines with it now sitting at 64psi I figured I was good there.
- Pulled out the Plugs and all cylinders were within 3 psi weakest to strongest.
- then decided to check for spark, I figured it would be ok because I just did a complete tune up only a month ago.

I look an old Plug I had removed form the old tuneup and started pulling off wires 1 by 1 and cranking it over. Well to my chagrin...... Cylinders 2 and 4 had a very stong spark but cylinders 1,3,5 and 6 had a very weak spark. (remember earlier in the thread I had noticed something with these 4 cylinders on 2 occasions) Now I am really smacking myself for that one.

Took the 4 old old wires from before my "tuneup" and swapped them out. Well the truck fired right up and never had another rough idle since.
Needless to say brought the wires back and had them replaced under warrently and managed to create a few new words to add to the english language on my way there. Actually I think I came up with a few french ones too.

Anyway the moral of the story is; No matter if that computer is telling you something is wrong always start with the basics first before you make the mistake I did and start assuming the worst. For me it was a little costly but I have learned my lesson.

Also for the makers of this site, Thanks for helping all of us backyard machanics. I just want to say, You rock!!

Is it not madening how these trucks both make you hooked and crazy. Just like a woman!