Do I really have to do a compression test??

86bayliner · Jul 18, 2005

Do I really have to do a compression test? I have an engine that was doing some popping after we did a tune up. Later, I discovered that by disconnecting #7 spark plug the popping would go away and motor sounded great again. I did a little test, and found the spark is getting to the plug. However, when i removed the plug , it was a bit oily. it does get spark though. Should i just assume a valve job/and or piston rings? and fix that or is there still something like fuel/air mixture, can fuel/ air mixture only cause just one cylinder to make the popping noise.? -------------------------------------------------- thanks 86bayliner

crazy charlie · Jul 18, 2005

Re: Do I really have to do a compression test??

It could be that the wires are crossed.Double check that first.A compression test is always a good indication of the condition of the motor.If the motor was not doing any popping before the tune up then something went wrong with the tuneup.Double check that the correct parts were used and that they were installed properly.Charlie

86bayliner · Jul 18, 2005

Re: Do I really have to do a compression test??

i was just looking back in some previous threads and found where Bondo thought my spark was fine. Well it is, he was right and then he said that he would be looking at fuel delivery, ummh"

Wotknot · Jul 18, 2005

Re: Do I really have to do a compression test??

Bondo knows his stuff.....BUT, you say that by taking the wire off the #7 plug that the popping goes away. That is electrical, I would tend to think.

86bayliner · Jul 18, 2005

Re: Do I really have to do a compression test??

yes, popping goes away

Limited-Time · Jul 18, 2005

Re: Do I really have to do a compression test??

Originally posted by 86bayliner: However, when i removed the plug , it was a bit oily. it does get spark though. Should i just assume a valve job/and or piston rings? and fix that or is there still something like fuel/air mixture, can fuel/ air mixture only cause just one cylinder to make the popping noise.? -------------------------------------------------- thanks 86bayliner

You can dump a bunch of money on head and rebuild work and hope that corrects the problem, or buy a compression tester (way cheaper than any part of your rebuild plans) and verify the problem and correct it accordingly.

Don S · Jul 18, 2005

Re: Do I really have to do a compression test??

When you pull the spark plug wire off #7 and it stops popping, that means you have stopped the ignition going to that cylinder. Now, if that cylinder has a warped or tuleped valve, each time the plug fires, it will blow back through the intake and carb. Do the compression test...... If you can't or don't want to do the diagnostics necessary to find the problem, then you are going to be going in circles changing parts and not getting any results. We can't hear your engine run, and what may sound fine to you may sound like a dead cylinder to someone with a trained ear. I've had too many customers come in with a "It runs fine" comment and when I start it, it's obvious it has a dead cylinder or two.

Wellcraft 89 · Jul 18, 2005

Re: Do I really have to do a compression test??

I'd do a compression test.also chk the wires. A valve could be burned or sticking. Rich

86bayliner · Jul 19, 2005

Re: Do I really have to do a compression test??

Im about to have to have the compression test , and a leak down test, i think thats what they call it. if i end up having to pay a mechanic to fix the valve problem and or rings, maybe even to check everything out when the heads are removed. How much should i expect to pay a mechanic that knows what they're doing? Roughly? And is it soemthing i can do by following the right direction, and research. Expensive tools though i would need huh.? Is it cheaper to try and find another engine to drop in? but then id have to pay someone for that too lol , im screwed for a while. Or, Would it?, do damage to run the engine on 7 cylinders,, you know end up with a have a v7 ?lol thanks guys 86bayliner

Mahoney · Jul 19, 2005

Re: Do I really have to do a compression test??

before you do anything, change the number 6 plug with the number 7 and see if you get the same results.

Don S · Jul 19, 2005

Re: Do I really have to do a compression test??

Don't get all excited and start asking for a leak down test. You aren't in that area yet. Get a compression test done......... Ask them to do one and make suggestions on the next step. Then if they can't answer your questions, ask here. If you have a cylinder with ZERO compression, then you probably have a warped valve. No reason in the world to spend money on a leakdown test, it popping through the intake. Best thing to do, is go to WalMart or tool discount store, and get one of their compression testers cheap and do a compression test. Then post your results, and we can suggest a course of action.

86bayliner · Jul 19, 2005

Re: Do I really have to do a compression test??

ok Don , you win! I have the compression tester in hand. just havent opend it yet. I will get it done . Am i gonna have to test all cylinders, or just the the problem cylinder , think i can get away with it. Because its gonna be a real pain, to get to the #4 and 6 cylinders. I know, i can pretty much do the rest of them , arggggghh. ???oh i believe its mainly the riser on that side that gets in the way. The other side is awkward enough. thanks again Mr Don ------------------------------------- 86bayliner over and out

Don S · Jul 19, 2005

Re: Do I really have to do a compression test??

Yes, you need to do them all, and yes they can be a PITA to do. Don't forget, I work on boats for a living, and I am not asking you to do anything I haven't done a hundred times. Follow the service bulletin I gave you a link to in the other post. Keep the battery charged up, and the throttle wide open, or all your work will be worthless.

86bayliner · Jul 19, 2005

Re: Do I really have to do a compression test??

ok , and one more thing? I know I see many instances where you say you dont like Clymers manual, I have a Seloc, but i think it is weak too. Is there a paticular manual, that you would suggest or like. Or are we stuck with these. Do I have to sleep with mrs. Volvo herself to get a better manual? like maybe something they made at the factory for the people at the factory?? umm ok well goodnight then , just curious anyway how do you find the time? Not timing, Time, between your work and helping us Newbtards out. My friend who reffered me to you guys, told me youve been on for a couple of years? Alot of reading and writing thats for sure...) Bondo to I hear, what dedication people have for some things 86bayliner

bamadave · Jul 20, 2005

Re: Do I really have to do a compression test??

There are alot of great guys here that give their time unselfishly and with little thanks to help the unlearned boat owners out there. I'll buy any of you a drink if y'all ever come near Logan Martin Lake (near Talladega race track) to show my appreciation. Alot of hours a day goes in this forum. Thanks to all that make this happen!

DHPMARINE · Jul 20, 2005

Re: Do I really have to do a compression test??

86bayliner Was the engine popping before the tuneup? If not you probably crossed 2 wires,and don't have a problem on just one wire. I'm not a fan of either after market manuals mentioned,but they should list an accurate firing order.Check it out. I support the above posts,because when the problem is not a simple fix,I gather all the info I can,and then diagnose.This is why compression reading are needed. But if the popping started RIGHT after the tuneup ...reheck your steps. DHP

86bayliner · Jul 20, 2005

Re: Do I really have to do a compression test??

yeah uh, I have gone through everything this week, and as far as I know. Firing order seems to be perfect. After short deliberation because i have work in the morning, I decided to go ahead and take boat and drop it off at a shop to get the compression test and any other further diagnosis done, hopefully i'll luck out with someone who will do me justice. I'll let you guys know what happens. they said it could be a week or two before they can (get off their a$$)...get to it so they said. i bet they call me sooner. ----------------------------------------------- p.s are they're any questions , i should ask them. 86bayliner Norcross, Ga

Bondo · Jul 21, 2005

Re: Do I really have to do a compression test??

Good Luck,.......... After catching up on this thread,......... I think you exhausted the Fuel,+ Igntion issues.......... You still haven't mentioned Exactly When it started Popping......... Before,..... Or After the Tune-Up,......???.... If it's Before,...... I'm betting on a Bad Valve............ If it's After,......... Crossed Wires.........

86bayliner · Jul 21, 2005

Re: Do I really have to do a compression test??

started after, but I really think i was right on the wires. Believe me, Im hoping Im wrong about the wires, but i think im right. Id love for the problem only to be a wire. Im not a total nube, but theres a lot of stuff for left to to learn. ok droped boat off today, we'll see how things go. thanks guys 86bayliner

Do I really have to do a compression test??

Petty Officer 2nd Class

Vice Admiral

Petty Officer 2nd Class

Petty Officer 1st Class

Petty Officer 2nd Class

Vice Admiral

Honorary Moderator Emeritus

Petty Officer 2nd Class

Petty Officer 2nd Class

Chief Petty Officer

Honorary Moderator Emeritus

Petty Officer 2nd Class

Honorary Moderator Emeritus

Petty Officer 2nd Class

Petty Officer 1st Class

Captain

Petty Officer 2nd Class

Moderator

Petty Officer 2nd Class