low compression

[Guled22]

I have cylinder #4 misfiring and i took it for diagnostic and found out that it has low compression. I've been told by the dealership that they cant give me an estimate untill they at least take apart the engine, and when i took it to some shop near my house the guy just said he has to rebulild the whole engine and it would cost me $1500. what do you guys think the problem is and do you think that sounds like a resonable price to get it fixed? its a 97 by the way, no major mods just a k&n filter and flow's.

oh yea and if anyone has any recommendations on where to take my car in the phoenix area let me know

 

[Mike97gt]

ok be carefull with this diag..

many times a serious misfire can cause unburned fuel to wash the rings down. this will give you a low compression reading on the misfiring cylinder.

I highly suggest you pull the plug on that cylinder and drop a tiny amount of oil down there.. then crank the engine over and do a compression test. You may find that you have your compression back and the only thing wrong with your car is a bad coil/plug

I have seen this a million times, I have rediaged cars other techs said needed a motor or head and it was this.

 

[Guled22]

should i take it back to a shop and ask someone to do that because i have no access to a machine to test compression.

 

[BlackenedSVT]

ok be carefull with this diag..

many times a serious misfire can cause unburned fuel to wash the rings down. this will give you a low compression reading on the misfiring cylinder.

I highly suggest you pull the plug on that cylinder and drop a tiny amount of oil down there.. then crank the engine over and do a compression test. You may find that you have your compression back and the only thing wrong with your car is a bad coil/plug

I have seen this a million times, I have rediaged cars other techs said needed a motor or head and it was this.

Not to doubt what you're saying. But i thought that oil in the compression test ("wet compression testing") determines that the PISTON RINGS are not sealing properly, and its the piston rings that need replacing. How does this test tell u the coil is bad??

 

[Mike97gt]

Not to doubt what you're saying. But i thought that oil in the compression test ("wet compression testing") determines that the PISTON RINGS are not sealing properly, and its the piston rings that need replacing. How does this test tell u the coil is bad??

yeah thats exactly what I am testing for this way the piston rings....the coil and plug you test for in other ways. a serious misfire can wash the oil coating off the rings and cause a compression drop. when you drop abit of oil down there this will reseal the rings, if you then swap the coila nd plug on that cylinder you will find the ring will stay sealed because it is no longer "washed down" reread my first post and you will see this is what I am talking about.. a ring washed down.

So to sum it up.. this is what happens

1. coil/plug goes bad and eninge misfires

2. as you drive around like this unburned fuel leaks past the rings into the oil pan and causes the rings to loose it's oil coating. the rings without the oil coat do not seal as well

3. tech goes in even if he fixes the ignition problem the cylinder will still misfire because of the low compression caused by poor ring seal

4. tech does not understand the concept of unburned fuel washing the rings down and runs a compression test and sees a 20-40 percent drop in compression on that cylinder.. so he assumes it needs a motor..

All it really needed was a little bit of oil to reseal the rings and the ignition problem fixed and oil changed. after this it would run properly and the rings will stay sealed.

The rings were never damaged, they just can not seal properly when this happens, as soon as the misfire is fixed and oil gets on the rings the compression will come back.

sometimes a simple problem can cause another simple problem, and this can confuse the tech if he has not seen it before. in this case a ignition failure causes a low compression condition.

many techs make this mistake.. I learned this myself years ago when I got burned on a crown vic 4.6.. I sent a perfectly good motor back to ford

 

[Guled22]

so do you suggest i replace the plug at home i already replaced the wires yesterday it was bad, and put say a couple of drops in the cylinder and take it somewere to get it tested again?

 

[Guled22]

oh and ive been driving it like this for the last 3 days do you think the ring could have been totally screwed by now.

 

[Mike97gt]

drop a little bit of oil in, replace the plug and see if it runs better. I doubt you did any damage in three days. I am not saying this is 100 percent what is wrong, but it's worth a shot before you spend 1500 bucks without knowing if it's just somthing this simple.

BTW take a good look at your oil too. see if it looks/smells fuel diluted

 

[Guled22]

ok ill try that in the morning, when you say a little bit of oil your talking about a few drops of motor oil rite? and after i put the oil in should i just start it like normal? if that ends up not being the problem you think 1500 sounds like a resonable price?

 

[Mike97gt]

ok ill try that in the morning, when you say a little bit of oil your talking about a few drops of motor oil rite? and after i put the oil in should i just start it like normal? if that ends up not being the problem you think 1500 sounds like a resonable price?

1500 is a very good price for a eninge overhaul.. in fact almost to good to be true, thats one reason I am highly suspect of this diag.

keep us posted..


all you got to do is.

1. pull plug
2. drop a small amount of clean oil in ( several drops should do the job)
3. install new plug
4. start engine.

if it still misfires, make sure the coil pack is good. you can do this by taking the plug wire off and place the plug wire close to a metal part of the engine ( so it can ground) but not touching then watch and see if you have spark ( carefull that spark can give you a nice little shock.. it won't kill you or hurt you but it will feel unpleasant).. this is a way you can do it without the right tools.

 

[Torinalth]

curiously... would it be in good practice to put a few drops in each cylinder when you change your plugs for preventative maintanence?

Torinalth

 

[Mike97gt]

curiously... would it be in good practice to put a few drops in each cylinder when you change your plugs for preventative maintanence?

Torinalth

no you don't need to do that. The reason you do it on the car we are talking about here is to reseal the rings so that cylinder can start firing again. once the wash down condition has passed it will be fine on it's own.. IF thats what the problem is here.

 

[Pearl02]

Very interesting thread. This could save others time and money. Thanks for the explaination Mike. Pearl02.

 

[Guled22]

ok heres the update guys i just replaced all the plugs, and changed the battery while i was at it. i put the oil into the cylinder and put everything back together and started the car and let it idle for 5 mins. the car is running noticibley smoother, and the check engine light hasnt come on yet. but then again it could still start misfiring later on. im gonna drive it around later on tonite and let you guys know what happens

 

[Mike97gt]

ok heres the update guys i just replaced all the plugs, and changed the battery while i was at it. i put the oil into the cylinder and put everything back together and started the car and let it idle for 5 mins. the car is running noticibley smoother, and the check engine light hasnt come on yet. but then again it could still start misfiring later on. im gonna drive it around later on tonite and let you guys know what happens

hopefully it stays running good.. Did you notice if the oil smelled of fuel.. I highly recomend you change the oil, even cheap oil for now

 

[Guled22]

i didnt notice the smell but i did notice that when i took the dipstick out the oil was at a higher level than last week. do you think the fuel leaked into the oil?

 

[Mike97gt]

i didnt notice the smell but i did notice that when i took the dipstick out the oil was at a higher level than last week. do you think the fuel leaked into the oil?

yeah and a lot of it too juding by that... Do not run the car untill you cfhange the oil... you will refoul the plugs rewash the rings down and possibly spin a bearing in the engine.

 

[Guled22]

damn i wish i would of read that last nite. the check engine light came back on and the code i pulled was still cylinder 4 misfire. you think the rings washed out again? and just out of curiousity why is it only that certain cylinder that is having its rings washed out. if the fuel was in the oil tank couldnt it possibly have done it to another cylinder?

well heres some more info that may or may not be helpful:
1.The car still is running fine besides the fact that its throwing the code i cant really feel the misfire like before.
2.The check engine light flashs half of the time.
3.Since the problem started earlier this week the exuasht sounds a little diffrence, nothing bad or really noticible but just a little bit of diffrence in the tone.
4.When I drove the car yesterday and parked in the garage, the car had a light scent of burning oil that cold only be smelled because it was trapped inside the closed garage.


Just pulled the plug in that cylinder and its covered in oil or fuel or a mix of em. i wiped it off and i think it should be good, should i drop another couple drops of oil in the cylinder again and change the oil?

 

[Guled22]

bump

 

[Guled22]

anyone have any ideas?