So, I have an annoying misfire on #8. It started as an occasional slight miss during acceleration, and now it results in major roughness and flashing SES. There is no coolant loss, overheating or tail smoke.

I hooked up an inline spark light this morning and let it idle for a couple mins. No codes and light seemed to flash ok. Revved it a few times at 1500-2000rpm for about 5 sec each. No lights and it had a minor vibration, but nothing too bad. Tried to go for a short drive, but the stumbling and flashing SES started right away so I went back and parked it.

A few hours later, I put some Redline SL-1 in just to see if it might be injector related and went for a drive. Did fine until I got to temp (190ish). Started flashing the SES and running really rough. Used some welding gloves to hook the test light up and took a vid.

Is this a normal fire frequency?

Note: dark garage so it looks like a blank screen. Watch for the little orange flash in the middle.

 

Here is a vid taken about 20 seconds later.

Much more consistent. Is this a bad wire? CPS?

 

It takes less then 20 volts to make those things flash, while it takes 35,000 to 50,000 to properly fire a plug in a engine.
Might want to PM me your number and I'll call you.

 

That makes it even more strange that it would only blink once every couple seconds

 

It has been suggested I do a compression test.

Online opinions say that the Craftsman tester is a good unit and as cheap as one should go. At $65 it isnt too bad a hit, but I would rather avoid buying something that may get used a handful of times tops.

Does anyone have opinions on the quality of a loner unit from the auto parts stores?

 

Ok for a start, but a leak down test will give you better/more accurate information and if you have low compression you'll want to do one anyway to know what's causing the low compression.
Have you verified your plug, wire and coil pack are good?

 

Damn, they dont even have loaners of those! At $75 bucks for a leakdown tester I would definitely just get that rather than both.

The previous owner had misfires on 8 and 5, and the mechanic she took it to eventually replaced the wires and the coil pack. The new coil pack was verified when I did my head gaskets...I think its generic, but definitely new.

Did you check out the first video I posted of the spark light?

 

If you have to a leak down tester I'd just do a compression test using a tester from the auto parts store rental. If it looks good then don't worry about the leak-down.
If you have bad compression in one or more then do a leak-down to verify what's leaking.

 

Ok, Ill go rent one and see what happens.

Any opinions on that spark test?

 

I already answered that question for you.
Do you know the proper way to do a compression test?