Inline spark testing

Joe,

I am checking apart using a lisle inline spark tester. Plugs in between plug and coil wire. It has red light light that flashes. I will try to attach video of cylinder one. May need to blow it up or zoom in to see light.

Ground wire? Is this the main wire from battery negative terminal? It goes to front drivers side bottom of engine. There is a smaller cable coming off of it near battery that goes under the radiator.

I traced main ground wire to bottom of engine block. On same connector is. Smaller wire that travels into a larger cable harness. That harness goes to top of manifold and combines with main cable harness that runs over the bank 1 coil packs. The bank 1 coil pack cable and bank 1 injector cables combine into this same main harness.

The ground connections at block are snug and in good shape.

Thanks Joe. On the ground I am going to be certain and loosen the bolt tomorrow because the small cable going into wiring harness is behind the large cable on the bolt and I cannot see it. The bolt is tight, the cables seem attached well when I try to move them, but they are covered with cable panduit.

I am only getting P0300 code and none of the 301-308 codes. My cheap Ancel AD310 plug in is limited. However, today I purchased Torque Pro application and it does more. It shows me the cylinder current and history misfire data. I am not a mechanic and not sure what is normal but I am now aware 1 and 8 seem to be the culprits.

I am attaching my dashboard I built. It is a video of me accelerating hard, then slowing down. Left side is all bank 1, right side bank 2. Graphs are LTFT and STFT, small icons are O2 and Trim sensors, and bottom are cylinders left to right as 1, 3, 5, 7 then 2, 4, 6, 8 showing the current misfires on top row and history on bottom row.

Plugs are new, plug cables are new, coils original but have been swapped around with no change. Intake gaskets replaced with Fel-Pro metal frame type and torqued to spec (89 in pounds). Injectors are new ($120.00 set off Amazon), CAM sensor new, MAP new, Purge Solenoid new, Throttle body new, Fuel Regulator new, fuel filter new (Fuel pressure 42 psi per spec for 2004 Tahoe 5. Z Flex), all hoses and lines on intake new except the fuel purge tube is original. Original MAF but I did clean it.

I built a smoker can that connects to bicycle pump and smoke test passed with flying colors. No smoke from intake anywhere, but after pumping for a couple minutes I do see smoke from oil dip stick tube.

Compression testing on cylinders 2-8 is 179-186 psi (4% variance), cylinder one dry test is 160 psi, wet test 160 psi, but it can reach 180 psi if I double the start cycles from 5 to 10 count. It reached 151 psi after only to cycles and have read that 80% of pressure should occur in first two cycles.

Leak down on number one was 85/80 (5% leakage) with leak detected mostly at throttle body and some from oil inlet. I forgot to listen to exhaust. I want to think pressure measurements are okay for combustion to occur? Tomorrow or Sunday I will leak down test #8.

I am not rich but car is paid off so I have thrown parts and new tools at it just to learn how to do it. If I can fix it myself I basically get experience and tools for free I can use in future.

I have also pulled the valve covers off and connected coils so I could watch valves. All sixteen valves are moving /rockers/springs clicking so I understand this means lifters are working and thus camshaft loves are okay? I replaced valve cover gaskets also.

Hi Joe,

I have changed the regulator.

I forgot to share that the pressure was 50 psi key on/engine off. The 42 psi I mentioned above is with engine running.

On YouTube or somewhere there was mention that when running the psi should drop about 8 psi which matched my numbers.

Joe

If there were a MAF sensor issue where ECU was measuring incorrect air flow and causing a lean/rich fuel supply would that not spread misfires more evenly across all cylinders? Not just focused on #1 and 8?

Joe I may be reaching but I found that the firing order is 1-8-7-2-6-5-4-3. Is it coincidental that my problem misfires are on cylinders 1-8, the first 2 in the order? Is there anything else common to these cylinders such as ECU wiring, common return wire, etc?

I am trying to think beyond the obvious items since I have addressed the common issues like fuel, air, plugs, coils, vacuum. I have check the ground today and it’s good.

My gut tells me it is something less obvious but lack of mechanical experience has me handicapped.

Yes. When I was replacing the intake gaskets I decided to replace the cam position sensor because of its location is very difficult to reach. If there is a relearn procedure or something I should have performed I was not aware.

Joe

If the compression values of a cylinder are 160+ and leak down loss is only 5% can we fully eliminate cylinder pressure as a cause for misfire?

Joe

Also should I remove valve covers one more time and reconfirm valves are working? I did that prior and all were rocking/moving. I thought I wiggled them all to see if any were loose but I cannot remember if I “pulled up” on the arm (valve side) to see if it raised or dropped on rod side.

If all valves are rocking does that fully eliminate a lifter and valve open/close concern?

I have read that to set the valve lash on a hydraulic system is to turn set screw until tap is heard then back off 3/4 a turn.

NOTE: I have never heard tapping or lifter noise on my vehicle, so could a valve not be opening enough for proper intake?

Joe,

I swapped the 7&8 coil and plug wire and drove this morning. No change and misfires remained on 8. I had already swapped 1&3 prior and misfires remained on 1. Thus I am 100% convinced it’s not coils or plug wires. I am 99% sure it is not plugs unless I got some bad ones from AutoZone. It could still be a coil harness but unless 1&8 are together and both have similar continuity issue odds are the wiring is okay.

New information:

Maybe this information helps but I noticed 2 main things when driving today. As I monitored my Torque Pro dashboard the misfires only occurs below 20 mph. I set cruise at 70 mph for five miles with no misfire counts. So either the sensors cannot detect them at high rpm or they stopped occurring at higher rpm? I can only feel them and see them at less than 20 mph.

Second is that FTs seemed to work normally in that LT would stabilize at a certain speed and not move, and ST would bounce +|- 5%. However, LT1 and LT2 seemed to act differently. At low speeds 0-20 LT1 would be low (ex 8.0) while LT2 would be high (ex 18), but when I accelerated and set cruise on 70 mph they came towards each other. LT1 rose up to around 12, and LT2 dropped to around 12 and stabilized. As I lowered speed the went separate ways again. I would think they both would do the same thing, not opposite?

Joe

I just swapped the injectors around. They were new but not OEM.

I swapped injectors as follows:

Before swapping cylinders 2-7 running good with no misfires. 1 & 8 misfiring.

1&3 swapped
2&4 swapped
5&7 swapped
6&8 swapped

After swapping injectors no change. Cylinders 1&8 still the problem. The others also look good. So I am convinced the problem is not fuel pressure or injector related. Also per prior email it’s not coil, plug, or plug cable related. I had swapped quad coil mount bracket from bank 1 to bank 2 which moveed position 1 to 8. I guess it’s possible both 1-8 have bad wiring from coil to primary mount connector but odds of that are very low?

MAP is new, CAM sensor new, gaskets new, hoses new, vacuum is steady needle @ 19 inhg, MAF cleaned but original.

My next item I will check leak down on cylinder 8. It measured 182 psi on a prior compression test, so I never did a leak down.

Joe

I found an article about restricted exhaust (cats) below. This seems what is happening to my FTs. Thoughts?

“Restricted exhaust. (Although no two converters fail exactly the same, if fuel trim goes high under acceleration on only 1 bank, suspect a restriction on the other. The MAF reads complete air intake, and then ECM initially distributes fuel evenly to both sides. If much less air is going through one side, there will be more than enough fuel for that restricted side and not enough fuel for the unrestricted side.)”

Ken, I am new to this. What am I looking for when I take off the valve covers? Do I remove rocker or anything? Where do I look with flashlight?

I have checked the injector outputs with a NOID tester. But have not measure pin to pin on connector. On the coil connector I did measure pin to pin and all of the signal or igniter violates on bank 1 are the same. I think they all were around 3 volts. I will find my information and share.

Ken,

I saw a article on cylinders pressure and spent all day today doing testing. Below is information and I hope you can see the table below. What a job. I am sore from climbing under truck to turn crankshaft.

NOTES for TABLE:
1) Leak down input was 80 psi.
2) Wet and Dry were 5 starter cycles.
3) Snap was gas pedal 2500 rpm hit, but not consistent.

Cyl Dry Wet Idle Snap Leakdwn % Loss
1 160 160 85 110 75 6%
2 179 Skip. 85. 130 78 3%
3 185 Skip. 85 115 77 4%
4 179 Skip. 82 130 78 3%
5 179 Skip. 80 110 79 2%
6 186 Skip. 80 110 78 3%
7 186 Skip. 85 100 79 2%
8 182 Skip. 85 120 80 0%

I will look at CAM per request, but need to know more about how I do it and what I am looking for.