[[email protected]]

I have a miss fire on #1 cylinder that has been kicking my butt. I have swapped plugs, swapped wires, cap and rotor look good. It has the newer style spider injectors that I installed a few years ago. I did an injector balance test and only have 1lb of pressure drop difference between the highest to lowest injector. Fuel pressure is 55psi and holds the pressure at 55psi for over 30min. I did a smoke test to check for leaks and I don't see any leak near the #1 port. Anyone have anything suggestions that might help?

 

[oldeerslayer]

If you are know how to do a injector balance test, you know as much or more than most of us. About the only thing you didn't mention was a compression test. Since you have proper fuel and spark it's about all that's left. Could be a worn or nicked valve. Maye a small leak in the head gasket? Especially since it's limited to one cylinder.
Have you graphed the misfire? When does it misfire?

 

[crazy_ate]

I have a miss fire on #1 cylinder that has been kicking my butt. I have swapped plugs, swapped wires, cap and rotor look good. It has the newer style spider injectors that I installed a few years ago. I did an injector balance test and only have 1lb of pressure drop difference between the highest to lowest injector. Fuel pressure is 55psi and holds the pressure at 55psi for over 30min. I did a smoke test to check for leaks and I don't see any leak near the #1 port. Anyone have anything suggestions that might help?

collapsed or collapsing lifter?

 

[[email protected]]

I did do the Compression test and that was 160psi and a leak down which came out to 2%. I don't think it is a lifter issue because the valve train is not noisy. Thanks for throwing some different ideas out there. I'm thinking that I may have something like a failing MAF sensor, a MAP sensor or noisy throttle sensor that is only causing an issue with #1 now but may be more random as it fails further. I didn't mention it but it is also intermittently being sluggish on take off. So more to come. I'll post any further info. If anyone has anything else please post.

 

[oldeerslayer]

Maf, Map, and Tps tend to be more of a P0300 random thing. Those can be a PITA to find. If it's running on 7 it should be a bit of a dog.

 

[chevymec]

You said cap and rotor looked good. Were their any signs of hot spots in the cap? I would change the cap out before I went any further to eliminate that.

 

[PeteD]

I did do the Compression test and that was 160psi and a leak down which came out to 2%. I don't think it is a lifter issue because the valve train is not noisy. Thanks for throwing some different ideas out there. I'm thinking that I may have something like a failing MAF sensor, a MAP sensor or noisy throttle sensor that is only causing an issue with #1 now but may be more random as it fails further. I didn't mention it but it is also intermittently being sluggish on take off. So more to come. I'll post any further info. If anyone has anything else please post.

If cranking (both wet snd dry) compression cks sre within 20psi across all cylinders and also all close (10% of) to incredible 2% Leak Down you state , block and heads not the issue. Air , fuel and ignition delivery need closer scrutiny

 

[[email protected]]

Not sure why I didn't do it earlier but I ran the Blazer today with the scanner hooked up and checked fuel trims. Driving down flat road at 60mph the trims were near zero % on bank #2 and around +1% on bank #1. At idle the fuel trims went to around +16% on bank #1 and +13% on bank #2. The misfire is only happening at idle and light acceleration. No miss fires under hard acceleration or holding steady speed at 60mph. So with that said it looks like I have air in leakage. Since there was no visible smoke leaking around the upper or lower intake seals I think I have a bad EVAP purge Solenoid. I know it does discharge near the #1 inlet inside the upper intake. Thanks again for the continued thoughts on what might be going on. More to come.

 

[[email protected]]

Well I got it fixed. The high positive fuel trims turned out being a MAF tune issue. When I got that corrected, the fuel trim on bank one was around +2-3 percent and Bank two was 0. So with everything else eliminated, the injector was changed even though it passed the injector balance test. I had a spare spider injection setup out of an old motor so I removed #1 injector, ultrasonic cleaned and swapped it with the one that was in it. Miss fire gone. What I hate about this is the injectors that are in the blazer are Deiphi's with only about 20,000 miles on them. I'm not sure what it is but in the last 5 or 6 years I have had several new parts back right away or go bad way before they should. Thanks everyone for your input and help.

 

[svsqopiwhjwdb]

Fuel pressure is 55psi and holds the pressure at 55psi for over 30min. I did a smoke test to check for leaks and I don't see any leak near the #1 port. Anyone have anything suggestions that might help?

 

[[email protected]]

Mine turned out to be a defective injector. But you need to look at the ignition system first and remember the number one inlet in the intake is on the passenger side under the throttle linkage when looking for leaks.