Compression test question - Results Posted

TwoBallScrewBall · Oct 13, 2004

I'm going to take a baseline compression test on my motor after work today, just for my own information. I will remove all 6 plugs. Do I need to do anything to the ignition to prevent damage while cranking with the plug wires disconnected? Thanks again!

R.Johnson · Oct 13, 2004

Re: Compression test question - Results Posted

You can ground the plug wires to the block, or you can leave the key off, and jump the starter at the solinoid. Don't crank it with the key with the wires ungrounded.

TwoBallScrewBall · Oct 13, 2004

Re: Compression test question - Results Posted

Thank you, I thought I read somewhere that there was a chance of damage if the wires were not grounded. Do you happen to know, looking at the starter, which terminals to jump? Is it the two large ones? If I remember correctly there are two large lugs and a couple smaller ones. Thank you.

Dhadley · Oct 13, 2004

Re: Compression test question - Results Posted

Your remote starter switch goes between the large terminal with the cable from the battery and the small terminal with the yellow wire with a red tracer. The other small terminal goes to ground -- dont hook your switch to that. If you have all the plugs out and your compression tester in one cylinder and the starter wont stay engaged, just remove one plug at a time to check compression.

TwoBallScrewBall · Oct 13, 2004

Re: Compression test question - Results Posted

Why would that happen? What do you mean if the starter won't stay engaged? DHadley, thanks again for all the help the past couple days.

Dave Abrahamson · Oct 13, 2004

Re: Compression test question - Results Posted

I think he means the motor might spin up to fast with no plugs to add compression and thus the starter would disengage, like if the motor had started......I think. Hope I didn't step on any toes. Dave

Dhadley · Oct 13, 2004

Re: Compression test question - Results Posted

Sometimes with no resistance, except in the cylinder the compression gauge is in, the starter disengages from the flwwheel before youre done getting a reading. Makes it difficult to get a reading. Doesnt hurt or change anything -- just aggravating.

TwoBallScrewBall · Oct 13, 2004

Re: Compression test question - Results Posted

OK I see. Thanks!

TwoBallScrewBall · Oct 13, 2004

Re: Compression test question - Results Posted

I did have to do the test with all 5 other plugs in. Otherwise the starter would just kick and spin. Here are my numbers, tell me if they sound a little low for an engine with an indicated 290 hours. I also decarbed last night with OMC tuner but there is still come carbon on the plugs so maybe it needs another dose... Looking at the back of the V6 they read like this, dead cold motor: TOP | 110|stbd |110 |port | 107|stbd |105 |port | 102|stbd |100 |port BOTTOM Whaddya think?

Cricket Too · Oct 13, 2004

Re: Compression test question - Results Posted

Well to me it's not that they are low, I have twin 2000 200hp Johnsons and I read 100 across the board on both. I would be a little concerned with the difference between the 110 and 100, that 10psi difference is indicative of a problem, that may not be too bad yet but could get worse. I would decarb again overnight, then run the heck out of it, and re-test hot.

Dhadley · Oct 13, 2004

Re: Compression test question - Results Posted

Looks good to me. They are well within the 15 lbs the OE gives us. It might not hurt, as suggested, to run the Engine Tuner to decarbon since the motor has been lugged so badly.

Paul Moir · Oct 13, 2004

Re: Compression test question - Results Posted

I certiainly know nothing about your engine Steve, but did you happen to start at the top and work your way to the bottom? If so, I think I can see your battery draining from here!

TwoBallScrewBall · Oct 13, 2004

Re: Compression test question - Results Posted

Thanks guys. Glad to hear the range sounds OK. Paul, very funny,

but no, I did the port side and then the stbd side. So I saw 110, 105, 100, 110, 107, 102. Good observation though! Supposed to be rainy out the next few days here. I am planning on fishing Sunday morning, so I'll run the decarb through Saturday afternoon/evening, let it soak overnight, and then run it hard first thing in the AM. Thanks again.

Dhadley · Oct 13, 2004

Re: Compression test question - Results Posted

Do not let it soak longer than the directions say!!! Follow them closely. Engin Tuner is some very powerful stuff.

TwoBallScrewBall · Oct 13, 2004

Re: Compression test question - Results Posted

OMC can says 3-16 hours. The engine was still pretty warm in the driveway from the run on the bay, so I did a warm compression check. My compression dropped 5psi across all 6 cylinders. Is this normal?

DRIPPING WET · Oct 13, 2004

Re: Compression test question - Results Posted

Hello . I have a question about compression testing. Do you have to have the throtle wide open? Is ENGINE TUNER the same as MARVEL'S MYSTERY OIL?

Solittle · Oct 13, 2004

Re: Compression test question - Results Posted

Welcome Dripping - Marvel Mystery oil is fabulus stuff but it is not for decarbing. Go to the red search at the top of the page and enter decarb and read away.

G DANE · Oct 13, 2004

Re: Compression test question - Results Posted

I found it normal compression drops a bit when motor warms up. A lot of helathy V6'es have compression areound 90. Remember the decarb will only work on a warm motor, only slightly on a cold.

TwoBallScrewBall · Oct 14, 2004

Re: Compression test question - Results Posted

When I decarbed the first time I let the engine warm up on the hose, then ran the decarb through the access port, then let it sit for 3 hours, then ran the crap out of it on the bay. I found a can of valvetech decarb (sprays in through the carbs) that the can says to let sit for only 15 minutes. Why does the OMC stuff need 3-16 hours?

TwoBallScrewBall · Oct 15, 2004

Re: Compression test question - Results Posted

Should the throttle be open when testing as asked above? I did the test with the throttle at idle.

Compression test question - Results Posted

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