My 99 Blazer seems to run fine at lower speeds, but when I'm on the highway going 50-60 mph's it seems to occassionally misfire. There's a very noticable momentary loss of power. When I'm on the gas pedal, I have good accelleration. Took it to Autozone to get it scanned, came back with an EVAP Emissions minor vacuum leak (0440 if I recall correctly). I have new plugs, wires, cap and rotor. All O2 sensors replaced within the las 1.5 years. What am i missing?

 

Depending on the severity of the hiccup, this could be something that many experience, but few actually track down. I had a very minor hiccup in my '00 Bravada that I never did track down. Turning off the A/C would dramatically diminish the hiccup, but not completely get rid of it.

Now, if it is pretty bad, it could be a bad plug wire that randomly grounds out...

 

was your timing jumping around when you had the scan tool hooked up? could be a bad distributor or the lower gear...

 

The scan tool only picked up a minor vacuum leak. The hiccup is very noticable and random. Could it be the distributor cap? One of the screws is a little stripped, so there a little "play" in the cap since it can't be fully tightened down, but it's not that much. Thisweekend I'm pulling the engine to replace the oilpan gasket and other surrounding engine gaskets, so I'll ensure that everything else is tight. BUT, I'm still at a loss on the hiccup.

 

hey stevo,
it could be a lot of things. you have to cover all your basics first. so make sure all your tune up parts are in working order. and make sure they are all AC Delco brand too otherwise after market parts will cause a misfire in these 4.3 engines. for example, i had bosch spark plugs in my truck and i had a misfire. so i changed them for delco's and the misfire was gone....also have you checked your fuel pressure with a gauge at the back of the intake? check it with the engine on and off. and then while off watch the gaugue for 30-60 minutes to see if it bleeds down. then also go back to autozone and hook up the scanner and go into the live data where it shows your timing. and see where its at and if its steady or jumpy. also, whats the condition of your lower intake gaskets?

 

actually have some what the same problem.. mines a 93 s10 with 166k.. hesitates a lot on higher speeds...but at lower speeds its pretty quick.. just got new wires plugs distributor cap and rotor.. and now my head gasket it probably blown so may have a lot to do with the misfiring engine

 

you can buy a decent no name scanner off ebay for like 60 bucks, even less if you don't want one that is live data capable...like the cheapo ones they use at autozone sometimes.....i bought mine through bestoffer thru a seller named mattandleah .... geez this sounds like an ad, but i know it can be bothersome to have to drive to autozone, and there's been times on my car where I've hooked my scanner up while driving just to see what exactly was going on.

 

so your saying that my 8.5mm plug wires and NKG iridium plugs could be causing my misfire? then i need to replace with AC Delco? As for the fuel preesure, wouldn't low pressure be a constant and not just at high speed? I'm asking cause i don't know. I replaced the fuel pump a few weeks ago, as some of you may recall. I would like to have all issues with my truck worked out, no matter how small, cause i'll soon be driving it a lot more when i move to California. Yeah.

 

NGK makes a good plug. I'd mist down the wires and make sure they aren't loosing the spark before it gets to the plug.

 

Mist down, as in spray with water? What am i goingt o be looking for when i do? They are brand new wires, so if there's a problem with them, i'm going to be mad. Like i said before, the engine is coming out this weekend so i'll have more room to ensure that everything is on nice and tight. Any suggestions on what i might also want to do while i have the motor out?