Talk me into, or out of, it...

[0xDEADBEEF]

Talk me into, or out of, BBQ

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[someotherguy]

So that set of new plugs I never got around to installing? Did it this morning. Had to fight the wires off a little bit, even though I'd used a dab of dielectric grease in the boots when I installed them. Couldn't find my gap gauge anywhere, not that I'd attempt to re-gap platinums with a simple bendy-tool.. but just to check them. They're AC Delco 1's, pre-gapped at .045. Looked fine coming out of the boxes.

Old plugs looked like a bit of a mixed bag, especially #4 and #8, which are a little surprising because the truck was running pretty well. Should be noted these are the same plugs that were in it when I bought it, and it had a really bad set of wires - the #1 wire was actually broken, so when I replaced the wires, I pulled the #1 plug and cleaned it.

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Got through installing them but didn't fire the truck up just yet as I had yard work to do before threat of rain. Finished that up and went back into the garage, started the truck, and it's running like -hot garbage- and I mean terrible. Stinking the garage up, stumbling, etc. I shut it down and checked all the wires, everything's plugged up correctly. Only did 1 at a time and they're still in the looms, no chance at all they got mixed up. Didn't touch anything else doing the plugs, but I looked over the misc. wiring harness and vacuum connections, don't see anything amiss.

Figured well let's hook up the ole Snap-On MT1460 cylinder shorting bad boy and see what we can see? I'll confess I'm no expert with this tool, and I'm used to watching my buddy Dennis use his much older analog version. When you short each cylinder on the digital, you get a sort of random/bouncy display amount of RPM's that it loses due to that cylinder being shorted. A couple on the even side seem weak but the bouncy numbers are a little hard to follow. It also has an "even" and "odd" function where you can short all the cylinders in that group of the firing order. I don't think that's terribly useful on a manifold that isn't divided, but both choices seemed to drag the engine down a similar amount, which is puzzling.

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So now that the engine is hot, garage is hot, I'm worn out from yard work, and annoyed with a truck that ran fine until I changed the plugs.. I've stopped for the day. My guesses so far are: plug wire(s) got damaged removing them from the old plugs, or new plug(s) are defective. Or both.

Richard

 

[95burban]

Why platinum plugs?

 

[0xDEADBEEF]

4 looks like it was firing until it got fouled, 8 looks it hasn't been firing for a while.

Have you done a compression test?

 

[someotherguy]

Why platinum plugs?

No reason other than they should last longer. And according to Rock, these are the correct ones for the TBI 7.4 (if one were to choose platinums, anyway) - and I hadn't heard anything about these engines having problems with them, unlike the gimmicky plugs from the various vendors with the weird ground strap designs, etc. Maybe I shoulda just got more CR43TS's.

4 looks like it was firing until it got fouled, 8 looks it hasn't been firing for a while.

Have you done a compression test?

Nope, but that's next (tomorrow). I actually thought about it this morning while I was changing plugs but didn't wanna wake my wife up; we were up really late last night so she was still asleep. So I changed the plugs, goofed around on the computer for a while, then hit the yard work.

What's crazy is.. again, it was running fairly decent when I pulled it in the day before.

Richard

 

[Caman96]

Platinum I’ve had the same set in for 4 years.

 

[fancyTBI]

First, that Snappy tool is neat. I’m going to have to look up more info.
Second, always something with these project trucks! We just want to drive them!!

Very odd that it was running poorly after the plug change. I hope it’s nothing major.

 

[0xDEADBEEF]

What's crazy is.. again, it was running fairly decent when I pulled it in the day before.

Richard

On the bright side, it'll have 25% more power when you fix it!

 

[Scooterwrench]

#4 oil fouled and #8 fuel glazed. I'm leaning towards plug wires. If you haven't changed the cap and rotor now would be a good time to do it, then you know all your secondary ignition is fresh.
I'm with you on analog meters. You can tell more about what's happening watching a needle twitch that you can with flashing numbers. Digitals have their place too for reading small DC voltages and resistances but an analog is almost as good as an oscilloscope for the AC stuff.

 

[someotherguy]

#4 oil fouled and #8 fuel glazed. I'm leaning towards plug wires. If you haven't changed the cap and rotor now would be a good time to do it, then you know all your secondary ignition is fresh.
I'm with you on analog meters. You can tell more about what's happening watching a needle twitch that you can with flashing numbers. Digitals have their place too for reading small DC voltages and resistances but an analog is almost as good as an oscilloscope for the AC stuff.

Cap and rotor, and plug wires, new when I bought the truck a year ago, because they were very bad. The plugs were new, too but sat on my workbench covered in other parts and I somehow forgot about them.

That tach/dwell tool is nice but when I found it, I was actually looking for an analog one like my buddy has. Both are very "old school" by now but at least still usable on the TBI's ignition setup.

Richard