Well guys I bought this 2001 Blazer a couple years ago and have worked through several issues. The issue I'm having now is a random miss fire issue on cylinders 1, 2, 3, 4, 6, none on 5. Most of the miss fires are on cyl #2. I've had a miss fire issue with it most of the time that I've had it. The first thing I did to it was replace the lower intake gasket because it was leaking and while I was in it I replaced the spider injection with the newer style. It was still miss firing so I smoked the intake and found the air intake hat on top of the throttle body was leaking. Fixed the hat and the miss fire almost went away so I left it at that. Now the miss fire is starting to get worse so this is what I have looked at so far. The LTFT is around -11% on B2 and 0% on B1 at idle, at cruise speeds LTFT is around -4.5% on B2 and 0% on B1. If I remove a vacuum line and cause a large vacuum leak at idle the miss fire goes away and the fuel trims go positive as expected but are still about 10% apart. I have no miss fires at cruise or under hard acceleration just at idle. I have checked both grounds on the back of the heads and they look good. Did a pin out check on the wires from the injectors to the computer and 12v supply and computer grounds. Did a leak down on the fuel system, it dropped 10lbs in thirty minutes. Did a compression test that showed no issue with compression. The plugs, wires, cap and rotor only have about 20,000 miles on them. I'm thinking the spider injectors are not working right on the passenger side. What do you guys think.

Ken

 

Also wanted to add that I tried swapping the O2 sensor from one side to the other. The rich condition stayed on B2.

 

I'd also say the injectors are leaking. But then again, why on B2 only...? I doubt it's a mechanical problem with them. Maybe they share a common signal inside the spider assembly...?
Just to make sure: take the readings on idle and on 2,5k rpm. Do You see any change if You're running a cold engine?

 

On a cold a engine the LTFT is still richer on B2 but the miss fires go away. The miss fires are only at idle with operating temp at 195deg. The LTFT difference is greatest at idle (about 11%) and decreases to around 4.5% everywhere else. Another thing I just remember was I had a few times with a hard start after setting for 30min or so. It usually starts immediately. This is another reason I think it could be the injectors.

 

Well I changed the Spider injection last night and the LTFT's are now zero on both sides and the miss fires have cleared. Pulled the cap and rotor. They looked good so I just cleaned the rotor and cap contacts and reinstall them. Thanks everyone for the help.

 

What was the original 'spider injection' brand you used ? When you changed it out, did you use the same or a different brand ? What brand did you use the second time ?

 

The first one was a second design with actual injectors not the popit type from Advance Auto, carquest line. The one I just installed was a AC Delco from Rockauto. It also is a second design.