Compression test help

ChrisK · May 17, 2017

Hey y'all. So I'm trying to troubleshoot a misfire on my 3.0. Trying to do a compression test just to rule it out, and I'm having some trouble.
I've got the plugs out, fuel pump and coil disconnected. But when I try to crank the engine the starter just spins? It's been turning over fine until now, am I missing something?
It would really suck if the starter failed right now while I have the plugs and everything out, could something else cause the starter to malfunction?

RonD · May 17, 2017

Welcome to TRS

Certainly reads like starter motor issue

You don't need to unplug the coil(no spark plugs), or the fuel pump, just hold gas pedal down all the way while cranking, that shuts of fuel injectors, and gives the engine full air flow for the test

Tap on the starter solenoid, smaller cylinder on top of starter motor, thats what pushes and pulls the starter motor gear in and out to engage ring gear on flywheel/flexplate

heavy breather · May 18, 2017

Are all the plugs out? If so, are you sure it's not turning over the engine? Depending on battery charge, starter condition and eng condition, it can spin quite fast.

Sent from my iPhone using Tapatalk

ChrisK · May 20, 2017

So I finally got some time to mess with it today. It's as heavy breather stated, it actually was spinning the engine. I had all the plugs out, and the tester on cylinder one, which actually has no compression whatsoever. Explains my misfire I guess. I'm thinking it's a stuck valve, because I also have a loud tick on that side of the engine.

So, I guess I need to dig into that side of the engine and inspect everything? Could the valve just be gunked up? Would it be worth doing the old seafoam in the vacuum line trick or should I just focus on getting the valve cover off?

Thanks for the help y'all, this place rules :icon_thumby:

RonD · May 21, 2017

Take valve cover off, see which valve is stuck open.
If its an intake valve you could hydro-lock engine and bend a rod or break a piston if you pour fluid into intake

ChrisK · May 22, 2017

Took the valve cover off yesterday, found a broken spring on cylinder 1 exhaust valve. Pretty surprised honestly, I expected to see a bent valve or something stuck in it. Don't think I've ever heard of a valve spring break... The valve itself seems okay though, I'm gonna replace the spring and do another compression test.

I sure am glad I didn't seafoam and run the piss out of it though, seems like it wouldn't take much force to have completely dropped that valve!

RonD · May 22, 2017

Good work finding that :icon_thumby:

I use a rope down the spark plug hole with piston 1/2 way down, get a coil of it in there then move the crank to get piston and rope to the top to hold valves in place while I remove the spring(s)

Some use air pressure but just never trusted it myself, lol

ChrisK · May 23, 2017

Nice, I've seen the rope trick, I'll probably give that a try since I don't have a compressor on hand. Unfortunately it'll have to wait due to some unforseen medical expenses. Im gonna go ahead and replace all the springs though, since they're cheap and it'll help me sleep better. Gonna do the valve seals too probably while I'm in there, figure I might as well.

RonD · May 23, 2017

Need a smaller spring compressor to get at all the springs

Also pick up some extra sets of keepers, they can go flying when installing or removing them.

And plug/cover all the oil drains, lol, that's where the keepers like to go, down to the oil pan

ChrisK · Jun 10, 2017

Just checking in with the conclusion to this saga. Got all the springs and seals replaced, took all day but the engine purrs now. And I didn't lose a single keeper!

One thing that took some time to figure out; I had to give the old springs a good tap with a hammer prior to compressing them, otherwise the keepers were just wedged in there and wouldn't come out.

Glad it's done though, thanks so much for all of your help!

RonD · Jun 10, 2017

Good Work

Thanks for the update

Compression test help

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