I replaced the lower intake gasket 2 months ago. Since then my 3rd cylinder is misfiring only when I'm going up a hill on the highway. I get the same point of the hill every time and the light starts flashing and turns off 1/4 - 1/2 mile later. It doesn't feel like I'm loosing any power either while I'm driving. I replace the spider injector, wires, spark plugs and distributor cap back in July 2014. I've tried to swap 1 and 3 spark plugs and 3 and 5 wires to see if the code changes to another cylinder and nothing changed. Should my next step be just replace the 3rd cylinder injector?

 

Have you done a compression or leak down test on the cylinders?

 

I did a compression test when when I changed everything last year but not recently.

 

Might be worth redoing the compression test just to compare the outcomes. You can also remove the throttle body to see if it looks like the injector for # 3 is leaking. The intake would appear shiny if it is leaking. I would doubt that it's leaking though...

 

The reason I don't think it's a compression issue is bc it doesn't misfire all the time. I can go days with out a problem.

 

At this point, I would suggest tracking down one of the recent misfire threads and checking things off as you go. They seem to always start with checking the fuel pump...

 

Did you have coolant in the oil? Why did you replace lower intake gasket? Any audible lifter ticking at idle or bearings knocking under load when fully warmed up? Oil pressure at idle hot? What weight of oil? Oil pressure at 65mph hot? I ask because bearings can cause a false misfire code in addition to lifter ticks, bearing noise, and low oil pressure. I had this in mine at 76K miles.

Otherwise, to start chasing a real misfire - check cam sensor retard - should be 0° ± 2° and fuel pump pressures/leakdown (yes, all 4 tests per sticky) and report. Also keep in mind that just because you replaced parts in 2014, doesn't mean the stuff is still good.

 

Haven't changed my oil yet since the lower intake gasket went bad and was spitting out antifreeze. As far as sounds go everything sounds the way it has always sounded. I had my bearings checked not that long ago and they were fine. Since I had my tires off today b/c I was changing them out for snow tires I went ahead and checked the compression. All 6 cylinders were 180-185. However, since I had to pull all 6 spark plugs I did notice some had a lot more wear then others. 2 months ago I swapped around the plugs so I don't remember is #5 used to be in #3 or if #5 if just that worn. Either way #5 should have been the one misfiring not #3 if it was plugs were the problem. They are all basically close to the proper specs except #5.

 

Do you have a question? Doesn't seem so. Sounds like you've got it covered all on your own.

One thing I just gotta know.... how were your bearings checked and determined to be fine?

One thing I just gotta say..... change that oil.

 

Use Ac delco plugs 41 993, should come pre gapped at 60 thousandths

Ac delco rotor D465

AC delco cap D328A

Can use auto lite wires 35-6151

I'd like to know what damaged the #5 plug in less than 18 months...

Were you having this problem prior to the work you did in July 2014?

Did you use Ac Delco cap & rotor?