I made the little chart in Microsoft Word using the "Tab" key to make columns. When I pasted it here, it omitted the tabs and ran everything together. Then when I tried to correct things, I messed up the two red entries. The new numbers are shown in Black.


[email protected]
STFT B1+1.2 (+.4 +2.7)
STFT B2 -2 (-3.5 +1.2)
HO2S B1S1 +.84 (+.83 +.86) HO2S B1S1 .5 (+.03 +.87)
HO2S B1S2 +.84 (+.83 +.86) HO2S B1S2 +.73 (+.71 +.75)
HO2S B2S1 +.42 (+.05 +.85)
MAF +6.3 (+6.26 +6.46)


I watched them in graph mode and you are right about the rapid shift.


As to the Misfires, they start over approx. 18 seconds.
#3 93 74 76 80 @620rpm
#4 78 72 79 81 @620rpm


#3 59 48 39 @1200rpm
#4 48 43 61 @1200rpm


Both #3 & #4 misfires disappear @ 2000rpm

 

That is a significant number of misfires.

 

The misfires can be felt but not really pronounced in my opinion. Always at idle. Never on the road except when stopped to turn etc.

 

Sorry I was pulled away from the computer in mid sentence by my wife for some time....

MAF may be a little high, but the O2 sensor and FT readings seem pretty normal to me.

If it was a vacuum leak or IAC or EGR stuck or fuel system problem I would expect those FT and O2 sensor readings to be goofed up (which they are not)

Maybe we should get down to basics. I think that pull all plugs and compression test might be in order. Would have to be pretty low compression to not fire at idle, but who knows. At this point we're just trying to cover all our bases. But first you might want to finish up the ignition system with a new Delco cap and rotor, after inspecting inside both boots of each plug wire for carbon tracking and testing all the plug wires with an ohm meter for under 2000 ohms. Your choice. I say that because the spark plugs and compression test is much more difficult to do than replacing cap/rotor and checking wires and who knows exactly what might fix it.

I would take the steering column loose from the steering box to get at #3 plug. If you pull the plugs, keep them in order so we can evaluate them. Know that regular AC/Delco spark plugs work as well or better than platinum ones (my opinion) - just don't last as long.

 

Not to put words in Joe's mouth, but it sounds like he did the compression test which led to the new right side head gasket (previous thread info)... So, start with cap & rotor? Then check wires and plugs? I'm on the edge of my seat waiting and cheering!!

 

Sounds like Joe put the head gasket on to fix 80psi compression on #4 (which in itself would not cause a miss), yet the miss as originally described (goes away above 2000) is apparently still there as evidenced using the scanner misfire counter. I'd like to see compression test done again.

Joe, let's finish up the ignition system by installing a new Delco Cap and Rotor - and inspect/test all wires. If problem persists, pull all plugs and verify compression again (all plugs pulled and freshly charged battery is important) - then lets inspect the plugs for anything abnormal and throw in a new set. If you have an air compressor, we can do some leak down testing when the plugs are out - but you may not have one. If you do let me know.

If we don't find anything ignition or compression-wise, then we can do the fuel system tests to eliminate fuel system problems. Joe, your 2002 or may not have the upgrade MPFI injector spider from the factory (was mid-year change), or someone may have upgraded it to MPFI. Do you know which one it has? MPFI has a wire connector attached to the injector at the end of each spider leg. But if it has the older design, know they are more prone to issues because they have to have a minimum pressure to "pop off" the injector nozzle against spring pressure. The MPFI is 100% electronically actuated, so are less sensitive to fuel pressure probelms. I could see a remote possibility where the fuel pump pressure happens to be marginal (especially during low alternator output at idle) and one or two injectors don't deliver. It's a bit of a stretch, and I would expect fuel trims/O2 sensors to be off at idle - but I think that doing fuel pump testing (per the sticky at the top of the 2nd gen forum) would be the next logical step afer completing the ignition system for this problem, based on what we are seeing.

Lastly I would like to compliment Joe for his persistence and ability to comprehend/conduct misfire diagnosis without getting off track. Not many people have what it takes. It's a pleasure to work with you sir! I try to improve my diagnostic skills through other people's problems while communicating on a computer. It's a learning experience for me as well. If someone jumps around and refuses to follow instructions (I have even seen newbies make things up because they don't want to do a test and think they know best) it can be pretty frustrating.

 

I do have an air compressor.
But the elementary question (a senior moment which I should know the answer). Here are the resistance tests on plug wires. I did these tests on the 20K range with a pretty good Sperry meter . Am I interpreting them correctly?


#1 = 7.14 (20,000 divided by 7.14 = 2703)
#2 = 6.28 3185
#3 = 6.08 3289
#4 = 5.83 3430
#5 = 5.40 3703
#6 = 5.76 3472
Coil wire = 6.41 3120


Thanks for the compliment but...Persistence is sometimes described as "bull headedness".


If this the case, I need a new set? Going to lunch, be back in a while.

 

I have a hard time believing all the plug wires are high resistance unless that is normal for them. Let me check about spark plug wire resistances some more.

#1 = 7.14
#2 = 6.28
#3 = 6.08
#4 = 5.83
#5 = 5.40
#6 = 5.76
Coil wire = 6.41

These readings should be directly in thousands of ohms with a maximum of 20,000 on that scale.

After checking.................

Looks like that is a normal reading for old fashioned carbon core wires (3000 ohms - 12,000 ohms). I haven't personally seen any for quite some time. They seem to be acceptable for their type but I worry about the extra resistance causing more voltage buildup inside distributor - it just might more easily cause misfires inside the goofy cross-terminal Vortec distributor cap. Must be a really cheap replacement wire set.

The 2000 ohm max range I gave was for spiral wound metal core (which is somewhere around 300-500 ohms/foot). Current A/C Delco OEM replacement wires are spiral wound metal core.

I say ditch the carbon core wires and replace the cap/rotor with new AC/Delco before pulling any plugs (because of difficulty in pulling spark plugs). Might just fix it! If not, pull the plugs and do the rest. Don't forget to twist the rotor back and forth (while holding it down) to check for distributor gear wear when you are changing the cap/rotor.

The Captain knows the best quality plug wires for the money. Much better price then AC Delco. Chuck, what were they again?

I found it https://blazerforum.com/forum/2nd-ge...-mp7673-90491/
see post#4
"With certain parts, you're far better off using AC Delco or Delphi, plug wires is not one of them. Autolite Professional Series 35-6324 have better specs than the AC Delco wires, and they are less than half the price. Both have a lifetime warranty. You can pay more for less, or you can pay less for more, your choice"

Looks like 35-6324 set has been replaced by 35-6327 and is available at Advance Auto Parts for $40 (check local stock and order online - then pick up locally for additional 10% discount - sometimes discount is as high as 20%)

 

I was at town and read your last entry, but on my smart phone I didn't see the last comment about plug wire number change. I had bought the 35-6324 wire set from O'Reillys along with a Delco Cap and Rotor. At start up I thought this was the cure, but after warm up, the misfires occurred, though not as frequent. The Service Engine light came on again, but when I increased the rpm's to 1200, the light went out and left no error code. I checked for rotor gear slop and got approx. 1/16" which by my calcs is 2.2 degrees. The resistance on the new wires varies from 1.97 to 2.91 on the 20k scale. I dropped my torx and 1/4 extension behind the distributor. Searched for quite awhile and gave up. When I started the engine, it fell out the bottom. Maybe the misfire saved them for me.


Next plan, maybe tomorrow, is to pull the plugs and check compression. I dread #3, but I think I will split the steering shaft, at the box, in order to insert my gauge.

 

Great work! You do know about going through the wheel wells with a long extension and swivel socket for the plugs (in addition to taking the shaft off the steering box)?