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If the V6 engine on this car has a cylinder that has low compression and is triggering a misfire, shouldn't that in turn trigger the CEL?
 

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With the OBD-I systems, I'm not sure exactly what conditions triggerthe SES light for a misfire.

What you can do, however, is run the OBD self diagnostic and cylinder balance tests. That will tell you which cylinders, if any, aren't firing normally. In short, you ground the small single gray plug near the test port by the air cleaner, start the car and wait for the check engine light to flash at you. At that point, it wants you to jerk the steering wheel 1/2 turn, then do a quick WOT snap on throttle. It'll do some more tests, then start flashing codes at you. After the last code flashes, you can tap the throttle lightly and it will then do the cylinder balance tests.

http://oldfuelinjection.com/?p=13

http://oldfuelinjection.com/?p=94
 

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If the V6 engine on this car has a cylinder that has low compression and is triggering a misfire, shouldn't that in turn trigger the CEL?
Not on a 92! I think that only happens with newer OBD-II systems & coil-on-plug ignition that a misfire is sensed by the computer.
 

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Discussion Starter #5
Thanks everyone. I'm just trying to figure this car out and make sure the other systems were working. Didn't know Ford's OBD 1 didn't detect misfires.

One of the cylinders is down to something like 60 psi. Probably not a good thing. Don't know what to do about that right this second.
 

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Thanks everyone. I'm just trying to figure this car out and make sure the other systems were working. Didn't know Ford's OBD 1 didn't detect misfires.

One of the cylinders is down to something like 60 psi. Probably not a good thing. Don't know what to do about that right this second.
do you know if the head gaskets have ever been changed on it?
 

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do you know if the head gaskets have ever been changed on it?
I don't have a clue. I've had the car for 5 years now. This car is the most temperamental and confusing car I've ever owned. It did this before about 3 years ago, but the problem just "magic'd" itself away. Tried shops, they couldn't find anything wrong with it.

Now it's doing it again. I don't know if it'll move another 3000 miles or stop moving tomorrow.
 

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Thanks everyone. I'm just trying to figure this car out and make sure the other systems were working. Didn't know Ford's OBD 1 didn't detect misfires.

One of the cylinders is down to something like 60 psi. Probably not a good thing. Don't know what to do about that right this second.
No, a cylinder with only 60psi is not a good thing. Yes, it could be a blown head gasket. And/or cracks in head and/or block. Signs of which are coolant in the oil. Oil in the coolant, and steam out the exahust. Bubbles blowing up in the puke tank. Hard starting.

Something else to consider:

I take it you did perform a compression test to determine this low compression reading. Did you perform a "wet" compression test? This would be to squirt a couple of shots of motor oil into the cylinder, and perform the compression test. If the psi's go up it means the piston compression rings are not sealing properly. The oil acts to seal worn rings better.

Next I would do a cylinder leakdown test on that bad cylinder. Basically, you bring that cylinder's piston up to TDC, both valves MUST be in their closed positions, and pump about 30psi of air into the cylinder via the spark plug hole. No more than about 30psi, otherwise, the compressed air will push the piston down.

While the air is being pumped into the clyinder listen for a hiss of air from the throttle body throat, exahust pipe, and crankcase, where you put oil into the engine.

If you hear a hiss from the intake an intake valve is not seating well or not at all.

If you hear a hiss from the exhuast an exhaust valve is not seating well or not at all.

If you hear a hiss from the crankcase then it is in the bottom-end.

Since you wrote the problem came and went, and is now back again there is a possibility there is a suck valve that is not seating well or at all.

A bad lifter could be the cause. Do you hear a top-end tick while the engine is running bad, and no tick when the engine has run good.

Lee.
 

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Well I changed the oil a few days ago and nothing out of the ordinary came out, no foam or coolant or anything. The car will idle rough/really misfire when it's cold now. As it warms up it calms down. Above 40 MPH and below 25 mph you can't tell anything is amiss with the car. It seems to be at its worst in between that range.

Out of curiosity's sake and from a mechanical standpoint, does continuing to drive it affect the rest of the cylinders? Will the engine implode in the near future?

Only did basic compression test as of now. Haven't done leakdown/wet yet.
 

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Well I changed the oil a few days ago and nothing out of the ordinary came out, no foam or coolant or anything. The car will idle rough/really misfire when it's cold now. As it warms up it calms down. Above 40 MPH and below 25 mph you can't tell anything is amiss with the car. It seems to be at its worst in between that range.

Out of curiosity's sake and from a mechanical standpoint, does continuing to drive it affect the rest of the cylinders? Will the engine implode in the near future?

Only did basic compression test as of now. Haven't done leakdown/wet yet.
I drove my bird about 50 miles on 5 cylinders. Same problem as yours, higher rpms were smooth, but it got to a range where it felt like the wheels were gonna fall off. If the motor is that bad, I can't see what more damage can be done. But I'm no expert.
 

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Well, your motor mounts will hate you for sure...
 

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Alright, just trying to get an idea of the repercussions. Thanks.

I'm no moron, I can't imagine driving on 5 cylinders is IDEAL nor advisable, I was just trying to figure out if continuing to drive it will start causing other cylinders to shut down and eventually brick the car and leave me stranded in a field. If I am right, to fix the problem properly the engine will most likely have to come out, correct? If that is the case then I would just find another engine to plop in there, no point in putting this old thing back in. This one has at least 300,000 miles on it.
 

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Alright, just trying to get an idea of the repercussions. Thanks.

I'm no moron, I can't imagine driving on 5 cylinders is IDEAL nor advisable, I was just trying to figure out if continuing to drive it will start causing other cylinders to shut down and eventually brick the car and leave me stranded in a field. If I am right, to fix the problem properly the engine will most likely have to come out, correct? If that is the case then I would just find another engine to plop in there, no point in putting this old thing back in. This one has at least 300,000 miles on it.
Exactly, bear in mind, mine was a 4.6 running on 5 cylinders :D But yes in my opinion it's about that time for the engine to be retired and a new (upgraded?) one to be installed.
 

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Exactly, bear in mind, mine was a 4.6 running on 5 cylinders :D But yes in my opinion it's about that time for the engine to be retired and a new (upgraded?) one to be installed.
Hah, so are we talking catastrophic failure at one single point or slow deterioration/worsening of the engine? Like I said, I think it's very weird that the faster I go in the car, the smoother everything runs.

Highway speeds are great, it's the around town thing that has the car crying and moaning. :tongue:
 

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Hah, so are we talking catastrophic failure at one single point or slow deterioration/worsening of the engine? Like I said, I think it's very weird that the faster I go in the car, the smoother everything runs.

Highway speeds are great, it's the around town thing that has the car crying and moaning. :tongue:
Mine was the same. But I bought the car thinking it was just an ignition or fuel problem (I didn't know much at the time). Turns out I was really just handed off someone else's pile of crap. But I made the best of a bad situation and learned a lot. I did all the work myself and I'm proud to say that I was the only wrench turner on the whole project. I love the car now, and it's only getting better. As far as your question goes (blame the ADD here) I don't know if it was a slow deterioration, or an all at once thing. I do know the car sat for quite some time though. The only thing I can think is causing it to be smoother at higher rpms is that you are getting better (not good) compression when the engine goes faster. There is less time for the air to seep through a seal than at lower rpm.
 

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Mine was the same. But I bought the car thinking it was just an ignition or fuel problem (I didn't know much at the time). Turns out I was really just handed off someone else's pile of crap. But I made the best of a bad situation and learned a lot. I did all the work myself and I'm proud to say that I was the only wrench turner on the whole project. I love the car now, and it's only getting better. As far as your question goes (blame the ADD here) I don't know if it was a slow deterioration, or an all at once thing. I do know the car sat for quite some time though. The only thing I can think is causing it to be smoother at higher rpms is that you are getting better (not good) compression when the engine goes faster. There is less time for the air to seep through a seal than at lower rpm.
Well here's a short story about this car a few years ago:

I said at the beginning of this thread that my car did this exact same thing a few years ago. Being the genius that I am, I decided that the car was about to be toast and figured what better way to just burn the thing out and have it go out with a bang than to drive 1500 miles to visit some family?

Start it up, misfiring/low compression just like it is now, and went off on my journey across the USA. About 400 miles in I stop for some food. Park it, go in and eat, come out, and start her up.

Problem....solved? The misfiring, engine shaking, rough idle, everything was just gone. Drove the rest of the way, drove BACK, problem never came back. Until now. Years later.

Bizarre car I tell you. That's why I'm asking what SHOULD be happening, because this car is a funny little animal. :D
 

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Just my 0.02 here, but with what you just posted, I would point to sticking valve (badly sticking in some instances) Highway driving will help an engine run better, whereas city or stop and go driving, if there is a problem with the engine already will probably make it more pronounced. But with 300k on it, baby it, then when you have the money and time to replace/upgrade it. Send it off with a bang - Rev limiter until boom imo. Then you replace your mounts and drop in the new power plant. All is well again in your world :D
 

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Just my 0.02 here, but with what you just posted, I would point to sticking valve (badly sticking in some instances) Highway driving will help an engine run better, whereas city or stop and go driving, if there is a problem with the engine already will probably make it more pronounced. But with 300k on it, baby it, then when you have the money and time to replace/upgrade it. Send it off with a bang - Rev limiter until boom imo. Then you replace your mounts and drop in the new power plant. All is well again in your world :D
Sounds like a good theory on what the problem is. Guess the old 25th Anniversary edition emblems makes my car feel too special to break down like normal! :rolleyes:
 
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