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Old 11-07-2009, 10:14 PM   #1
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Low Compression Cylinder #4

I hope someone else may have had this problem. I just had the timing belt changed on my 01 ZX3 Zetec. I had a idle problem when I stopped at a light and the idle would become a little rough when I would take my foot off the brake. I was hoping the new timing belt would take care of this problem but it seems like it is a little worse.

I just replaced the air intake tube since the old was falling apart. The airbox had some fabric in it like a mouse may have been trying to make a nest, but the filter was clean. Iwas hoping this was the idle issue.

The mechanic that replaced the timing belt is telling me the #4 cylinder compression is low and it could be a bad valve or maybe the rings on the piston. There is 132K miles on it and I already had a motor mount replaced, so I don't think that is causing it.

I've seen some threads that the IAC may be bad or dirty, but I haven't seen anything about low compression. It seems like all these Foci have common issues as you read through this forum and I am hoping the compression isn't the real reason for the rough idle while at a stop. Anyone able to confirm compression issues and rough idles? I just did a lot of repairs close to $2K in a $3500 vehicle and I don't want to spend much more especially on major engine work.

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Old 11-07-2009, 10:16 PM   #2
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Valve!! Good Luck. pull the head yourself
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Old 11-07-2009, 10:32 PM   #3
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Sorry to hear that you are having this problem, but I am here to tell you man, if you have a "dead" cylinder then you are going to have idleing problems and drivability issues as well.

Run a compression test and post the results. You should have even numbers across the cylinders such as this: 1) 130, 2) 131, 3) 128, 4) 135. You don't want those numbers to be far from each other at all. The rule is 10% difference between cylinders. Anymore and you are possibly going to have a problem. Low compression on all cylinders is actually better than having one dead cylinder.

After the compression test, if you see that you have a dead cylinder, or one that is partiularly lower than the others, then I would recommend doing a cylinder leakdown test. This will require a fancy little tool that you will only use once. lol Try the loan a tool program at Autozone or Advance for this. What this test does is to tell you where the cylinder is leaking and at what percent. Very handy little outfit to have but if you are a weekend mech, then I doubt that you will want to pony up the cash to keep something like this on hand for such rare uses.

This may help a little:


COSDEVSVT Harness bar for ZX5, (1) Schroth 6 point harness, (2) Schroth 4 point harnesses $300 OBO for all. Eibach Pro full suspension- trade for SVT suspension. PM for details...
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Old 11-08-2009, 01:10 PM   #4
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I have the same engine and the compression was 180.
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Old 11-08-2009, 01:31 PM   #5
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I'm betting you'll be doing rings soon.
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Old 11-19-2009, 01:34 PM   #6
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Well I got the car back and the mechanic said that cylinder 4 may have been washed due to a bad coil wire not firing the plug. He said it could heal itself and he also found the bad PCV hose and replaced it. He didn't like the way the coil wires were not seating themselves in the coil, so I replaced the coil wires and coil pack so that I could ensure a good spark on #4. It runs great on the highway, no issues doing 70mph, but as soon as I stop at a light, I get the initial idle okay and then it starts to want to stall. I have to keep it rolling or put it in neutral to keep it running.

I probably had the low compression before he did the timing belt but it never wanted to stall like it is doing now. He double and triple checked that the timing belt is on correctly but something has definitely changed. I cleaned the MAF and the only things left are the IAC and TPS but I don't have a CEL. I cannot figure out how to get the IAC of since I can't see the top screw from the bottom nor the top.Is there a link as how to get the IAC off without removing the intake and throttle body???

I think I'll check the TPS next since that is all that is left except for the IAC.

I was told by the service manger that the Zetec for the ZX3 is NOT an interference engine. Is that correct? I suggested that maybe a cam lobe was off, but he said that would be only apply if it was an interference engine.

Thanks for the feedback so far and any additional would be great.
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Old 11-19-2009, 04:09 PM   #7
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the low compression is not going to heal itself...do a compression test on all cylinders..if number 4 comes up very low again...the manual states to pour a tablespoon of oil down the cylinder and compete another compression test on that cylinder..if the compression goes up then you have worn rings..if it does not go up you have bent/leaking or burnt valves...

if compression is unusually high the combustion chamber are probably coated with carbon

if 2 adjacent cylinders are low that would suggest a head gasket..
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Old 11-02-2011, 05:42 PM   #8
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Leojake09, hi.
I have just the same issue as your focus (mine is a 2001 SE zetec 2.0 DOH).
Today the mechanic told me it was a burnt valve; but he was not so good explaining why he thinks so.
I have changed all pulleys and water pump and timing belt, 3 eng.mounts, DPFE, PCV (twice, cause I saw oil in it after 2 week of change), thermostat and housing broken, colapsed pcv hose, spark plugs motorcraft, put air filter 1000,000 miles warranty.....

It runns in the I-10 with no issues more than 60 mph.

I'm unsure if opening engine or not.......(well by a mechanic)
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Old 11-02-2011, 07:58 PM   #9
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I would just do a leak down test on #4. You really don't even need to buy the "Special Tool." Use your compression tester hose and hook air to the back of it after running the hose to the spark plug hole on #4. Before this ensure the piston is at TDC. Once you get the air on it listen for air leaking through either your exhaust, intake, or oil dipstick. Also see if you have bubbles in your coolant overflow for a possible HG issue. If the exhaust is leaking then bad Exhaust Valve. Intake... intake valve. Oil dipstick... possible ring failure or something worse. This will pinpoint your problem before making a decision that may not be needed.
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Old 11-02-2011, 08:59 PM   #10
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I'm sorry you're having this issue, BUT IT "PISSES ME OFF" that you have to deal with mechanics that are just GUESSING instead of doing the BASIC appropriate tests that others have mentioned already....

Compression check, followed by a leakdown test if anything is NOT "up to spec" is the FIRST thing ANY competent mechanic would do BEFORE making comments like you've quoted here....

PLEASE find another shop, or follow the advice given here & learn how to fix it yourself...

(that's how I ended up being a mechanic, it was CHEAPER to do it myself , than PAY idiots that were "clueless")

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