Intermittent miss started about a month ago asthe weather got cooler. It would miss when started from an overnight cool down, and a couple minutes later as it warmed up the miss would go away. As long as I kept the engine hot, the miss would not come back. At 1st I was leaning toward a bad injector for #2, but I replaced the whole spyder/injector/regulator assy last August with a NEW DELPHI Unit.
We had a warm spell a couple weeks ago and I noticed that the engine would not miss when cold started. HMMMM. When it got below 45* outside overnight the miss would return. Then a few days ago I started getting #2 misfire CEL warnings. It was below 45* outside. So I pulled pligs #2 and #4(for comparison) and found #2 gas fouled and black, while #4 was dry and gray colored. Plugs are Autolite AP605's. Wires were Advance Auto Generic 7mm wires. I had bought some 8.2mm Taylor Thundervolt wires and had put them off until after back surgery. So it's now 12 weeks post op and I had a few hours so here's what was done y'day.
1.) I put the new wires on. Fit, Finish, Overall Quality is Fantastic. These are the plug wires GM should have put on all V6 S Series trucks and SUV's.
2.) Cleaned (wire brush onthe grinder) and checked gap on the plugs, and checked firing of the plugs via a Timing light while running. Got constant pulses on the lamp on all cylinders except #2. When #2 & #4 swapped and tested again the #2 wire fired all the time.
3.) Thinking I might have either a bad injector or regulator, I checked the Injector pressures.
3a.) Static pressure 58psi (Engine OFF)
3b.) Running Pressure at idle. 61psi.
3c.) Blip throttle and back to idle. Dropped to approx 45psi and bounced back to 61 psi.
3d.) Hi pressure bleed down 1/2 hour. Started at 58psi. Test ended at 30 minutes with 57psi.
3e.) LO pressure bleed down 30 minutes. Bled pressure down to 10 psi. Test ended at 30 minutes with 10psi.
3d and 3e tend to rule out an injector / regulator problem as does current MPG of 23mpg on Interstate @65mph, 2200rpm and 14" mercury on Vacuum gauge.
Distributor is an ALLIED Electric from Rock Auto (metal housing), about 8 months ago. Rotor and cap are slightly worn with minimal arcing/burning on the contacts. I would consider this normal for 1500 miles on it since installation.
I don't have any spare plugs so I swapped #2 and #4 plugs and took it for a ride around the block. It still missed BUT it now read #4 misfire on the CEL reader. New wire is 40ohms per foot and 115ohms corellates with the just under 3ft wire for #2 and #4 plugs. And I checked in the dark for arcing from wires to engine or chassis. NO ARCING SEEN
We can rule out Fuel Injectors and Regulator
We can rule out Distributor Cap and Rotor
We can rule out Spark Plug Cables
Which leaves Plugs.
So I've ordered 6 NEW Autolite AP605's from Rock Auto and will install at least 5 of them (#3 I have to pull steering shaft) unless it''s really warm out and then I'll pull #3. I had a L5-S1 Vertabrae fusion on 12Sept16 and I feel it when weather gets chilly. Other than that, I'm just limited to weight carrying/bearing.
I'll update when I put in the plugs. Until then, it's not getting used. The Jimmy is running just fine.
2002 S-10 ZR-5 Quad-CAB
1995 GMC Jimmy 4Dr. SLT