97 2.0 SOHC Lost compression on cylinder 4

[bronzeback5]

Car started throwing PO304 and checked coil, plugs, wires and injectors before finally checking compression. Checked #4 and it was 70. Checked #3 and it was 150 something. Got mad and quit


3 weeks ago the CEL started coming on only when i was low in a gear. Like rolling to a stop sign and taking off in 2nd instead of 1st. Dogging the car to avoid downshifting i guess i would say. Car would jerk like crazy and throw a code but would drive out of the jerking and run fine.


There are no loud noises coming from the valves. Engine runs a lil rough at idle but you would not notice it after you get going. Spark plug #4 had some oil on the threads, others did not. No antifreeze in oil, looks good. Throws PO304 constantly now..


Buddy came over and said he would first check the timing belt to see if it had slipped before digging into the head. To tell the truth, i probably will not be digging into the head anyway's. I probably could not find the problem anyways.

Just wondering what could be some realistic explanations for losing most compression on one cylinder. Could the valve seat be getting ready to go or is that a all or none type of deal?? Could the timing belt be the cause of this? Any help and direction of things to narrow this down will be appreciated.

This is a 97 wagon with 314,000 miles. I am getting 37 MPG and it drives straight as an arrow. Just replaced all tie rods and brakes and had her front end aligned and this is how she treats me. Would like to save this car as i really like it for my 700 miles a week commute to work. Judging the price of used cars nowdays, i have thought about replacing the engine with a used one if it comes to that but we will have to see.

[tempfixit]

Originally Posted by bronzeback5

Car started throwing PO304 and checked coil, plugs, wires and injectors before finally checking compression. Checked #4 and it was 70. Checked #3 and it was 150 something. Got mad and quit


3 weeks ago the CEL started coming on only when i was low in a gear. Like rolling to a stop sign and taking off in 2nd instead of 1st. Dogging the car to avoid downshifting i guess i would say. Car would jerk like crazy and throw a code but would drive out of the jerking and run fine.


There are no loud noises coming from the valves. Engine runs a lil rough at idle but you would not notice it after you get going. Spark plug #4 had some oil on the threads, others did not. No antifreeze in oil, looks good. Throws PO304 constantly now..


Buddy came over and said he would first check the timing belt to see if it had slipped before digging into the head. To tell the truth, i probably will not be digging into the head anyway's. I probably could not find the problem anyways.

Just wondering what could be some realistic explanations for losing most compression on one cylinder. Could the valve seat be getting ready to go or is that a all or none type of deal?? Could the timing belt be the cause of this? Any help and direction of things to narrow this down will be appreciated.

This is a 97 wagon with 314,000 miles. I am getting 37 MPG and it drives straight as an arrow. Just replaced all tie rods and brakes and had her front end aligned and this is how she treats me. Would like to save this car as i really like it for my 700 miles a week commute to work. Judging the price of used cars nowdays, i have thought about replacing the engine with a used one if it comes to that but we will have to see.

When you did the compression test did you do a dry and wet test (wet test is squirting some oil in the clyinder on top of the piston and testing again)??? If the compression increases the piston rings aree bad oor sticky, if no increase in cimpression it is a valve issue.

Do you use regular oil or synthetic oil and how often do you change???

[GTP Dad]

It isn't necessarily a valve issue as you may have a blown head gasket on #4. The gasket on my Escort blew and it displayed the same symptoms that you indicate your car is having. Mine went between 2 & 3. The result will be the same even if it is a valve issue you will still need to pull the head to see what is going on.

[tempfixit]

Originally Posted by GTP Dad

It isn't necessarily a valve issue as you may have a blown head gasket on #4. The gasket on my Escort blew and it displayed the same symptoms that you indicate your car is having. Mine went between 2 & 3. The result will be the same even if it is a valve issue you will still need to pull the head to see what is going on.

Correct, I should have stated that if the compression increases with adding oil to cover and seal the clyinder piston rings the problem lies from the head gasket to a valve issue.

[bronzeback5]

I was thinking i would have some more signs of blown head gasket if that was the case. Oil looks clean, no overheating, etc... I will do a complete compression test like i should have done

[zzyzzx2]

I also think that you did not drop a valve seat, but when you fix it, make sure that you repair it so that won't happen. If you had dropped a valve seat there would be a lot of noise, plus I have never heard of anyone getting CEL's because of it either.