Misfire Cylinder 1, running lean, low compression. PLEASE HELP!

[Frdtuff]

Sorry this is long but I want to explain everything to help give you a better idea.

I bought my son his first car about nine months ago. 96 Ford Explorer XLT. The exterior and interior is in great condition and it ran pretty good when I bought it. The guy I bought it from said it needed new O2 sensors and had a vacuum leak but that the engine had about 60K miles on a rebuilt. We changed the O2 sensors shortly after we brought it home but stripped the threads on the pipe for the downstream sensor. Bought a thread tool, rethreaded it, put a new sensor in it, but it didn't seem to want to go all the way in so we got it tight and left it at that thinking we would deal with it later. A few months ago it started running rough and it was guzzling gas from the day we brought it home. So we took it to a mechanic who said it needed the lower intake gasket replaced. My son picked it up from the mechanic and it was running really bad now. Shaky at Idle and sounds like crap. We took a chance and replaced the upper intake gasket which seemed to help some but not much.

After driving it a few more weeks, we took it to another mechanic who said its misfiring in cylinder 1 and running lean, he said he checked the compression in cylinder 1 and it only has 40psi and that it needs a valve job and to throw the car away. I'm frustrated. I could be wrong but I really have a feeling it's not a valve job that's needed but maybe just a combination of a leaking gasket and the O2 sensor? I'm not a mechanic but I've read it can be a number of things and not sure why he jumped to "throw the car away". Any ideas or advise???

 

[imp]

Sorry this is long but I want to explain everything to help give you a better idea.

I bought my son his first car about nine months ago. 96 Ford Explorer XLT. The exterior and interior is in great condition and it ran pretty good when I bought it. The guy I bought it from said it needed new O2 sensors and had a vacuum leak but that the engine had about 60K miles on a rebuilt. We changed the O2 sensors shortly after we brought it home but stripped the threads on the pipe for the downstream sensor. Bought a thread tool, rethreaded it, put a new sensor in it, but it didn't seem to want to go all the way in so we got it tight and left it at that thinking we would deal with it later. A few months ago it started running rough and it was guzzling gas from the day we brought it home. So we took it to a mechanic who said it needed the lower intake gasket replaced. My son picked it up from the mechanic and it was running really bad now. Shaky at Idle and sounds like crap. We took a chance and replaced the upper intake gasket which seemed to help some but not much.

After driving it a few more weeks, we took it to another mechanic who said its misfiring in cylinder 1 and running lean, he said he checked the compression in cylinder 1 and it only has 40psi and that it needs a valve job and to throw the car away. I'm frustrated. I could be wrong but I really have a feeling it's not a valve job that's needed but maybe just a combination of a leaking gasket and the O2 sensor? I'm not a mechanic but I've read it can be a number of things and not sure why he jumped to "throw the car away". Any ideas or advise???

@Frdtuff

Yes. He sensed you would hesitate to spend the kind of money he would ask for, to effect a repair. Misfiring in one cylinder will cause just the opposite of what he told you: it will run RICH, not lean. Simple logic. Keep dumping fuel in which does not get fully consumed, it runs rich, and the unburned fuel comes out the tailpipe. The O2 sensors detect the rich condition, trying to reduce the fuel injected, and hence the engine runs overall crappy. These types of problems are far more completely diagnosed automatically in the next Gen of Explorers, unfortunately.

If the "mechanic" only checked the compression in one cylinder, regardless of code(s) indicated, he is remiss in his work. In any event, leaking intake gaskets CAN cause a lean condition. He knows that.

Other cause for low compression: a broken piston ring or rings. Less likely than a burnt valve, but more costly to remedy. The right bank cylinder head really needs to be removed, and the valves examined. Not an easy job, as the timing chain driving the right bank valves is located in the BACK of the engine, necessitating removal of the transmission, at least, or removal of the engine, bigger job yet, IF it's the V-6 Overhead Cam engine. I am not certain when that engine came into use; I owned a '96, and it had the Overhead Valve engine, far and away easier to do valve work on. So, I think most likely it is the OHV engine. I wish I still had one.

Regarding the O2 sensor not tightened in place, the only result would be noise from the exhaust gas leaking around the threads. imp

 

[96eb96]

Sorry this is long but I want to explain everything to help give you a better idea.

I bought my son his first car about nine months ago. 96 Ford Explorer XLT. The exterior and interior is in great condition and it ran pretty good when I bought it. The guy I bought it from said it needed new O2 sensors and had a vacuum leak but that the engine had about 60K miles on a rebuilt. We changed the O2 sensors shortly after we brought it home but stripped the threads on the pipe for the downstream sensor. Bought a thread tool, rethreaded it, put a new sensor in it, but it didn't seem to want to go all the way in so we got it tight and left it at that thinking we would deal with it later. A few months ago it started running rough and it was guzzling gas from the day we brought it home. So we took it to a mechanic who said it needed the lower intake gasket replaced. My son picked it up from the mechanic and it was running really bad now. Shaky at Idle and sounds like crap. We took a chance and replaced the upper intake gasket which seemed to help some but not much.


After driving it a few more weeks, we took it to another mechanic who said its misfiring in cylinder 1 and running lean, he said he checked the compression in cylinder 1 and it only has 40psi and that it needs a valve job and to throw the car away. I'm frustrated. I could be wrong but I really have a feeling it's not a valve job that's needed but maybe just a combination of a leaking gasket and the O2 sensor? I'm not a mechanic but I've read it can be a number of things and not sure why he jumped to "throw the car away". Any ideas or advise???

I have this truck.
These engines do have some(rare) issues with cracks in the head. The bottom end is extremely sold. They are very good engines though.

That being said, a bad 02 sensor and a vac leak COULD ruin an engine. It may even run great, but it is because of compensation and additional fuel(which isn't great either). Once you get a P0171/4 the system can't really compensate and you are suffering the effects of extra air. Who knows how long it was going on with the prior owner?? Running lean makes the engine combustion chamber run very hot. Lots of oxygen is pretty much what you have with cutting torch that cuts metal. Eventually the valves could get burnt. Also, If the 02 sensor didn't seal perfectly fuel trims may be skewed and who knows what happens. The sensor is precise and needs the full exhaust stream to give a correct reading. Likely running lean. Can you supply us with some fuel trim readings? What side was the badly threaded sensor on? Bank 1/Cyl 1 is passenger.

I've heard of cases with carbon buildup, so pull the lower intake and have a look. Lean could cause that as well. You may get lucky. sometimes it can hold a valve open. Maybe seafoam the engine and change plugs.

As for the mechanics advice, considering what these things are worth and what the labor would be on such a job he may be right. Also, you don't know how far behind a transmission or transfer case is. If you can do the work yourself it may be worth it. This engine is designed for the average Joe to work on.

If it was an SOHC 97+ with issues you should probably be calling the scrap yard.