[ringlert]

I have an '03 with a 'tec engine. It has ~115000 miles on it. It has been missing for awhile so when I took it in for the yearly inspection, I asked them to look at the misfire problem. I have received the engine trouble light twice in the past 2 or so months but the light cleared on it's own. It misses at idle and does a pretty good buck if I'm cruising around 30 to 40 MPH and slowly push down on the accelerator. I can pretty much make it buck at will. Does not appear to miss at cruising speeds, at least it's not noticeable. Fuel filter changed at 80,000 miles.
It was put on the computer at the shop.
No codes were present.
diagnostics said the problem was a #6 misfire, seen on the computer.

Plug was replaced - no change
wire was replaced - no change
coil replaced - no change
injector replaced - no change
Compression was checked and showed OK though I don't have the number.
The mechanic said the injector was getting a signal to pulse and it looked good.
They are at a loss and of course I am. A bit of help would be appreciated. Their suggestion was to take it to ford.

 

[jw89sho]

Re-do compression test and also do leakdown test. Post results.

 

[bossvt]

This sounds very similar to the problem I was having. The ultimate fix for my problem was replacing the gaskets on the upper and lower intake manifold. This seems to be a typical problem with the Duratec when it gets up in mileage.

You'll find many other posts about it in this forum. Best to search on "duratec rough idle".

 

[ringlert]

I did do some searching, but not that particular string. I'll try it, thanks. The leakdown test will be a little tougher, I'll need to get with the mechanic. I don't have the instrumentation.

 

[ringlert]

I took my car to a Ford dealership and let them put it on the diagnostic machine. They came up with an occasional misfire on #3 and a misfire on #6. A relative compression test showed for the firing order of 1,4,2,5,3,6, a differnce of 0%,0%,1%,1%,0%,15% respectively. I'm assuming that means that all cylinders are basically balanced except for #6, the known problem child. The mechanic said that I have a burnt valve. He said, if a 'tec engine is going to burn a valve it will most likely be #3 or #6.
I took the car to my local mechanic for a recheck of #6 compression and a leakdown check on #6. I also asked him to do compression checks on 4 & 5.
He said the leakdown check failed, don't have actual numbers but he said air was blowing out the exhaust. Compression readings on #4, #5, and #6 were 80,80, and 40 respectively.
I tried to redo the compression checks at home but the flex hose did not seem to have enough threads for engagement in the plug hole and the solid extension would not slide down into plug hole, end too big. Has this been a problem and is there a brand of compression gauge that fits with no problem, or is this a problem with my abilities?
Is the relative compression test accurate enough for me to say; if the 80# readings on #4 & #5 are correct and the relative test indicates that 1 thru 5 are basically equal, then 1 thru 3 are around 80# and my engine is worn out?

 

[thecurrent]

Ford does not list a "specific" cylinder compression reading.
The indicated compression pressures are considered within specification if the lowest reading cylinder is at least 75 percent of the highest reading.
In your case since 40 is only 50% of your highest reading (80) then you have a problem. Seems that even 80 is pretty low. These #'s 40, 80, 80 are in PSI correct?

What were the compression #'s for cylinders 1,2,3?

 

[wjc]

I guess by relative compression test, the dealer means he ran a scantool-commanded RPM drop test run by the engine computer. Anyway, I agree with the current, something is very strange with those compression numbers. 80 PSI is low, I wonder if he did the test right.

At any rate, the Duratec is known as a disposable engine due to the cost of rebuilding it, so if it needs work a junkyard motor will make more sense. Before going that route though pull the valve cover and check out the valvetrain. You might get lucky and the cam caps are loose or something.

 

[thecurrent]

I guess by relative compression test, the dealer means he ran a scantool-commanded RPM drop test run by the engine computer. Anyway, I agree with the current, something is very strange with those compression numbers. 80 PSI is low, I wonder if he did the test right.

At any rate, the Duratec is known as a disposable engine due to the cost of rebuilding it, so if it needs work a junkyard motor will make more sense. Before going that route though pull the valve cover and check out the valvetrain. You might get lucky and the cam caps are loose or something.

Ahhh yes... Forgot the Relative Compression comment from OP.
The Relative Compression test we run on the IDS gives us a general idea of any base engine concerns. If we see any abnormalities, we do a full engine compression test and investigate further. Its more of a "quick check" on the IDS to assist in any further diagnostics.

 

[ringlert]

To WJC:
The relative compression test is performed by a RPM change performed by the Ford dealership's diagnostic computer I believe. The actual pressures were obtained from a different shop using a compression gauge.
To thecurrent:
I did not have the shop perform compression tests on 1,2, or 3.

I don't believe the cylinder pressures are as low as 80# or 40#. My compression gauge will not fit down in the valve cover hole. What brand of compression gauge is used to perform testing on a 'tec Ford? I would like to verify the compressions on 4,5, and 6. This is for my own information before I decide what to do with the car. Why do I need to pull all spark plugs if I only want to perform compression tests on 3 cylinders? Does it cause bad readings or is it just to keep the load off the battery?

 

[JW657]

I think you should first verify the compression on all 6 cylinders. That would make a lot of sense, you need to have an idea of what the engine is like in general. You should have had the mechanic do a full test.

If that compression test is valid, the engine would be running very badly at those numbers.

Did the engine overheat recently? What lead to the issue in the first place? There's generally some sort of failure that leads to an issue like this. I'm really interested in knowing what the other head is like for compression. At the mileage you have, it sounds like you've destroyed a head or did some big damage to the valve-train.

Take it to a reputable shop and ask for a full compression test, once you get that done with the issue will likely be more apparent.

With numbers that low, why is the engine still going almost 4 months later?

 

[ringlert]

A Ford dealership performed a relative compression test. It indicated that 5 cylinders were pretty much equal and #6 was down 15%. A leak down test was performed on #6 and indicated a problem on the exhaust side, burnt valve. That's why I didn't bother with compression testing on 1,3,or 3. My thought was to recheck the compressions on 4,5,&6, I don't believe the 80# and 40# either. If 4 & 5 compressions were ~equal then that would validate the relative compression test. This was really just for data gathering.
To the real point. I thought that I was at the point where I was either going to put a reman. engine in the car or see what I could get trying to sell it as is and say goodby to it. I thought that I had enough information to say any work required would be costly and still leave me with a >100,000 mile engine. I will not be doing the work myself.

 

[JW657]

A Ford dealership performed a relative compression test. It indicated that 5 cylinders were pretty much equal and #6 was down 15%. A leak down test was performed on #6 and indicated a problem on the exhaust side, burnt valve. That's why I didn't bother with compression testing on 1,3,or 3. My thought was to recheck the compressions on 4,5,&6, I don't believe the 80# and 40# either. If 4 & 5 compressions were ~equal then that would validate the relative compression test. This was really just for data gathering.
To the real point. I thought that I was at the point where I was either going to put a reman. engine in the car or see what I could get trying to sell it as is and say goodby to it. I thought that I had enough information to say any work required would be costly and still leave me with a >100,000 mile engine. I will not be doing the work myself.

I think all the info floating around this thread is confusing.

I think to correctly diagnose the issue, we need to look at one, full compression reading from the cylinders. I don't think the previous ones have told us much, due to their possible inaccuracy. We have contradicting compression tests, until we know for sure what the readings are, we can't really tell what it would be. We don't even know for sure what cylinders are consistently missing. There's no other symptoms to explain the compression issue, like a cracked head or head gasket. I can't really believe that it's running compression that low, but who knows. My guess is that you did cook some of your valves, but there's no way to tell for sure until it's tested and accurate, detailed info is posted about it.

I would advise that you go to a reputable shop and ask for an hours worth of diagnostics:

I have a bad miss over several cylinders, I had some compression readings done but they've been iffy, so I need a full compression test, leak down, pull the codes and have the mechanic inspect for any obvious signs of issue. I just want you to record the engine stats, it won't be repaired here.

Then you'd have all the info needed to diagnose the issue.

Or, you could look into buying a hose that will fit into the spark plug hole, I'm sure if you go to your local auto parts store, they should be able to help you find the right tool.

As for selling it, make sure you disclose the issues with the car. (just a little bitter over being sold something with a blown engine recently, it's a good idea until someone does it to you.)

edit:

Came off sounding fairly condescending, so I cleaned it up. I didn't mean to be offensive.

 

[ringlert]

Very Valid. Obviously I've throw in a bunch of stuff that's understandable to the person intimately involved, me. Sorry, I will be more precise with asked for information.

 

[ringlert]

Compressions
1 - 255
2 - 230
3 - 250
4 - 250
5 - 230
6 - 140
Mechanic said his leak down rig was not working properly. He said air was coming out of the #5 plug hole.
Said nothing coming out of exhaust, which is different from the previous mech.
Has not overheated.
P0306 - random
P0303 - very random

 

[ringlert]

I can't get any more short and precise than my previous entry. I kinda figured somebody would ask me, "why can't I find a technician that can do accurate diagnostics", based on the compression numbers. They seem a bit high to me. Along with the problem with the #6 cylinder, if these compression numbers are too high for normal, then the cams are worn, the engine is shot.

 

[wjc]

Yeah, I'm lost. 255 PSI is nuts, I don't know what to tell you.

 

[ringlert]

What do you think about the camshafts being worn, assuming these compression numbers being right?
If I go to another shop, who knows what kind of data scatter will pop up.

 

[JW657]

Compressions
1 - 255
2 - 230
3 - 250
4 - 250
5 - 230
6 - 140
Mechanic said his leak down rig was not working properly. He said air was coming out of the #5 plug hole.
Said nothing coming out of exhaust, which is different from the previous mech.
Has not overheated.
P0306 - random
P0303 - very random

Well, I really don't think he did it right. Even if he did, you have 25PSI less on 2 and 5, compared to 1,3,4 and then cylinder 6 is just over 100PSI less than other cylinders. Even if the compression test is wrong, it looks like you can see an issue there anyway.

Compression readings on #4, #5, and #6 were 80,80, and 40 respectively.

Even on the other tests, 6 is always lower than the other cylinders. There's obviously a compression issue with that cylinder. I would guess that it's to do with the valve-train, if it was a bad head gasket or a cracked whatever, you would know by now. I'm thinking that the Ford mechanics guess of a burnt valve is correct. The next step is to either take it somewhere that can tell you exactly, or start tearing into the engine so you can inspect it.

 

[ringlert]

Not a question I have asked. What should the compression range run? My book only says a minimum of 100PSI.

 

[ringlert]

So I guess nobody really knows what my compression should run on a healthy 'tec?