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Engine compression

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Hello all,

 

I've done a compression test on my 95 2.5L and I found these numbers:

 

1 cylinder has 100 psi

5 cyliners have 115 psi

 

I feel that those numbers are low and making numbers, the compression would be 7:1 and 8:1 for my engine.

 

Any of you have at hand the right compression in "psi" for this engine?

 

Thank you

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I don't know what the correct number should be.

 

But - when all the numbers are so close that is a good sign, so I'd think that you are OK.  Do you have any other evidence of low compression?

 

Best Regards,

 

Al Seim

SVT Contour 2000

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I notice very low acceleration and very low milleage, it has new head gaskets, plugs and plug wires.

 

On the other hand, in the engine specifications I found that the engine provides a compression of 9.7:1, if my maths are rigth this equals to 181.3 psi, at least I would belive this will be at sea level, it should be less at 1.4 miles over sea level but I don't think that justifies 65 psi less.

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Normally all cylinders are supposed to be within 10% of eachother. Sounds like you have a burned valve or internal issue. Most cylinders should be 120+ PSI.

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Somehow I misread 100 as 110, so yes there is some difference there.

 

BUT - I'm not convinced that the other numbers are low.  Since the intake valve stays open during the first part of the compression stroke, you will never see as much pressure during slow speed cranking as you'd expect from the compression ratio.  Taking Buckeye's number of 120+ at lowish altitude, 115 at your altitude sounds very reasonable.  Altitude calculator online says that your air density is only 77% of sea level which should cause a 23% reduction in the compression reading vs sea level.

 

If you can find a "leakdown tester" that may give some indication, in addition to numeric values it is helpful to just listen to where the air is going on TDC of the low cylinder vs TDC of a good one.  Crankcase (oil filler cap) = rings, exhaust pipe = exhaust valve, throttle body = intake valve.

 

If the engine has not been run recently, all these things are iffy as a tiny bit of carbon or corrosion can cause a biggish leak.

Quote

 

 

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Hello,

 

Thank you for your information, I see that the issue is not as big as I initially thought.

 

The engine runs "good" in load, but sometimes is a little rough when in idle and around 550-600 rpms, after a few seconds it changes and stabilizes around 750 rpm.

 

The cylinders were machined about three years ago, the cylinders were adjusted to 0.20, I see then that I need to check with the guy that did the job to check the failing one.

 

In the time this happens, does this justifies lack of power when cold and bad milleage?

 

By now, the car is used about 7 to 10 days a month.

 

 

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My guess is a bad sensor, vacuum leak, or other fuel injection system problem rather than low compression causing most of your problems.  Have you looked at OBD codes if any?  Does anyone have a diagnostic scanner that is compatible with your car?

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Hello,

 

No, I hadn't scanned it yet, I will take it to the service next month for emission testing, I'll ask them to scan it, anyway, the Check Engine light is off.

 

Vacum leak, I doubt it since it hasn't been run much since the engine was resurfaced, but still a possibility.

 

What kind of problems can the injection system could present?

 

 

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While we're on the subject, the early 2.5L's had some issues with carbon tracking the plugs. This led to them stuttering and running poorly cold or hot. You said it runs fine when hot, but gets poor mileage? Intake gaskets leak, fuel pressure regulators fail... It could be a lot of things causing those issues. 

 

-Dominic

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Yes, it runs good when hot but with poor milleage, it used to provide 300kms per 3/4 tank, today, they are 220kms per the same 3/4 of tank, both measured in city trafic.

 

The plugs and cables are new, they have at most 1000kms, the previous ones that were older provided me a little less milleage and less power at runing.

 

I will have to talk, with the guy in the service... as I see it, in the mid to long term, it could be cheaper to replace the engine with a used (with warranty) but newer Mondeo engine.

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The numbers given if real are lousy, need at least 150 psi with that engine, but always suspect the gauge as they give countless problems.

 

100 psi if real is a virtually dead cylinder, it WILL try to miss at that low, the number is low enough the heat drops off that cylinder and then the plug will not burn off to stay clean to fire right.

Edited by amc49

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Today I pulled codes from the ECU (I got an scanner), I got the next codes:

 

Code 111, KOEO ==> System Pass

Code 10 ==> This is not in the manual

code 176, Continuous ==> Failrue into the HEGO (HO2S) sensor fault / allways lean.

 

I didn't executed the KOER test since the user's maual says to not execute it until all previous codes are repaired.

 

What is the HO2S sensor? the Oxigen sensor?

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I found this post

 

Dom states that the proper compression should be around 160 psi, with this, it is real that I have a compression problem, since it has new gaskets, it leads me to think that it may have an internal problem, the rings may be?

 

I will need to evaluate this, it could be cheaper to replace the engine instead of repair it..

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I would make sure engine timing (timing chains) is correct since it's been apart before for the head gasket replacement. The early model 2.5L's had false flags on the cams that people would line up and the engine would run poorly and could have poor compression as the valve timing would be out of sync from the crank timing.

 

-Dom

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Hello Dom,

 

That's the most direct answer that could explain all this...

 

Is information available about this? I mean, is it documented somewhere? how about the correct way to synchronize it?

 

Regards

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It'll require pulling the intake manifold and both valve covers to check properly. Bring the crankshaft around to TDC (mark on pulley lines up with line on front cover). Then check both sets of camshafts to see where the marks are. I can help you once you get to that point.

 

-Dom

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Hello Dom,

 

I really appreciate your offer, but I'm not skilled enough to do that kind of job, no space and tools to do it, but I need more info in order to talk about it with the guy of the service.

 

How far are the false flags against the real ones?

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Update on this issue, the timing is fine, it has no issues, they double checked, one against timing marks and other time against the timing method.

 

In the same session they also repaired a leak on the ATX, when doing this, they found that the wheel that the starter moves to start the engine was damaged, they replaced it while the ATX was out; I don't know how it is related but it now behaives a lot better when cold; it doesn't seem to suffer while accelerating and when I take it out from the basement.

 

There is still some way to go; it still has bad milleage and since I have a code 176 related with a lean condition, I think that the next step is to check and/or replace the O2 sensors, since they were replaced 130,000 kms ago, new ones won't hurt.

 

Update in a few weeks...

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