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Low Pressure in Cylinder 1: Skoda Octavia 2001 1.4 16V, Engine Uneven, Replaced Rings, Error 16490

mimokd 50554 25
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Why does cylinder 1 still have low compression on a 2001 Skoda Octavia 1.4 16V after the rings were replaced?

Persistent low compression in cylinder 1 is most likely caused by leaking valves/valve seats or a cracked cylinder head near cylinder 1, not by the rings, because the oil test did not raise the pressure enough [#10686054][#10686286][#10686291] Valve stem seals are not the cause of compression loss; they only seal oil [#10686286] Another suggestion was to inspect the valve hydraulics/tappets, since that is a common fault in these engines [#10688081] If repairing it, the advice was to remove the head, check the valves for tightness, lap or replace the valves, fit new seals and springs, and test the head for leakage with kerosene [#10686336] The 16490 manifold/barometric pressure sensor fault was noted as unrelated to the compression problem [#10689137]
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  • #1 10686034
    mimokd
    Level 10  
    Posts: 41
    Rate: 45
    Skoda Octavia 2001 1.4 16V
    The engine runs unevenly, has no power, dims.
    Vag shows error:
    16490 - Manifold / Barometric Pressure Sensor (G71) / (F96): Implausible Signal
    The pressure measurement showed:
    cylinder 1 - 8.5
    cylinder 2 - 14
    cylinder 3 - 14
    cylinder 4 - 14
    after oil test:
    cylinder 1 - 9.5
    cylinder 2 - 15
    cylinder 3 - 15
    cylinder - 15
    I changed the rings and after replacing it still the same:
    cylinder 1 - 8.5
    cylinder 2 - 16
    cylinder 3 - 16
    cylinder 4 - 16

    Can anyone tell me what could be causing the low pressure in the first cylinder...?
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    #2 10686054
    Ture11
    Level 39  
    Posts: 5406
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    Am I not mistaken that your pressure test rejected the rings as suspects? If the pressure has not increased significantly, then the valves are probably letting go?
  • #3 10686076
    mimokd
    Level 10  
    Posts: 41
    Rate: 45
    I was told that if it rises, it's the ring's fault, so I gave up...
    Does this apply to sealants or the head to make ...?
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    #4 10686087
    pit1976
    Level 15  
    Posts: 134
    Help: 9
    Rate: 68
    Well, you were told well, but it didn't grow
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    #5 10686093
    trans-serwis
    Level 39  
    Posts: 4854
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    mimokd wrote:
    I was told that if it rises, it's the ring's fault, so I gave up...
    But they didn't tell you how much to increase the pressure after the oil test. And all your work in the dog's ass.
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  • #6 10686265
    mimokd
    Level 10  
    Posts: 41
    Rate: 45
    Does this mean that the valves or seals are leaking...?
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    #7 10686286
    marek49ae
    Level 24  
    Posts: 636
    Help: 57
    Rate: 252
    Sealants only seal oil, not compression. Some valve does not close, or the seat is burned out, or the head is cracked in the vicinity of 1 cylinder.
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    #8 10686291
    ftp.kowal
    Level 36  
    Posts: 2943
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    You have leaky valves. A normal mechanic wouldn't put it on without even reaching the valves and replacing the seals, not to mention planning.
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    #9 10686336
    jofa-j1
    Level 17  
    Posts: 210
    Help: 16
    Rate: 102
    More like a repair head. You can try replacing the valves themselves. Remove the old ones from the low pressure cylinder, check for tight fit. Lap in the new paste, install new seals and springs. Check the tightness (e.g. with kerosene), how it will hold the head. If the engine has a high mileage, replace all seals in one job. When installing the tappet glasses, remove the oil from the oil chamber because you may have one of the valves ajar later. GOOD LUCK
  • #10 10686527
    mimokd
    Level 10  
    Posts: 41
    Rate: 45
    Thanks everyone for the advice...
    I'm getting to work...
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    #11 10688081
    zeimp
    Moderator on vacation ...  
    Posts: 5260
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    Inspect the valve control hydraulics carefully. This is a common fault in these engines (as well as in 1.4/60 and 68 HP engines - there it is common ...).
  • #12 10689137
    kortyleski
    Level 43  
    Posts: 12262
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    But firstly, such an underestimated compression on one pot will not cause such strong symptoms as you describe, and secondly .... The error read is not related to this pressure ...
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  • #13 10689171
    ladamaniac
    Level 40  
    Posts: 5317
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    Check for left air, manifold, rubber connections, pneumothorax, EGR. Maybe you can tell us what the vacuum in the intake manifold is at idle.
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    #14 10689295
    wopor
    Level 32  
    Posts: 1995
    Help: 175
    Rate: 702
    If the pressure is well measured, the first cylinder does not hold pressure, and hence the uneven work and as zeimp wrote in his wisdom :D it may be the control and leakage of the valves themselves, and by the way, this repair and diagnosis is poplin, this knowledge was given to you by the butcher?
  • #15 10691344
    kortyleski
    Level 43  
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    batigol66 wrote:
    T5 show me where it says that he replaced the head gasket or where it says that the head was planed?

    I'll write you back for my friend. We assume that since he was replacing the rings, he did not do it through the muffler, but took out the pistons through such four holes visible quite clearly after removing the head. It can also be assumed that no one in their right mind will put the head on the old gasket and without planning. So he replaced.
  • #16 10691406
    ociz
    VIP Meritorious for electroda.pl  
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    kortyleski wrote:
    and without planning

    And why is that? Only plan when needed.
  • #17 10692473
    wopor
    Level 32  
    Posts: 1995
    Help: 175
    Rate: 702
    kol ociz with such repairs as above, they unscrew as they please and the deformation is ready and ... and how to check that the adhesion curves? -these are the dilemmas of those who fix it -it's such a piece of metal eeeee it's definitely good, I'm not making fun anymore because kol.zeimp went to the moderators, he'll give me a banana :D
  • #18 10692614
    zeimp
    Moderator on vacation ...  
    Posts: 5260
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    wopor wrote:
    I'm still not laughing because kol.zeimp went to the moderators, he'll give me a banana :D


    In your case, probably not, because the "mocking" you write about makes sense (we both know that), so cool ;)
    And that you can learn a lot on the forum (e.g. replacing the rings and assembling on the old gasket), it's a different story ... I'll wait for the author's response to the topic and it will probably be closed.
  • #19 10692886
    wopor
    Level 32  
    Posts: 1995
    Help: 175
    Rate: 702
    This is how I gather to describe the correct engine repair technology on my own. but on the other hand, there is so much on the web that I have an inner reluctance :D but it's good that they are like kol zeimp and other young people (probably young :D ) that they want me only "an old man and maybe" :D and we will probably never know what the author had in mind.
  • #20 10693230
    mimokd
    Level 10  
    Posts: 41
    Rate: 45
    For a detailed explanation of the whole situation, I will describe what was done ...
    New head gasket but no planning (I know what you're thinking). I got bad information for sure when it comes to diagnosis but now it's too late...
    I did all the work myself so you can make fun of it - I'm abroad and that's why I'm trying it myself because it costs a fortune here...
    How do I deal with the head, I will let you know if I succeeded and the pressure in the manifold, unfortunately, I do not know how it works ...
  • #21 10693680
    przem27
    Level 30  
    Posts: 1317
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    T5 wrote:
    batigol66 wrote:
    Replace head gaskets.
    Did you read the first post? Do you think the rings are exchanged?


    I know someone from the area who pulls the box and the shaft because it's cheaper (work according to g is supposedly not costs :) ) and the client pulls the gasket so "you can" 8-O .
    greetings
  • #22 10693804
    ftp.kowal
    Level 36  
    Posts: 2943
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    przem27 wrote:
    I know someone from the area who pulls the box and the shaft because it's cheaper (work according to g is supposedly not costs :) ) and the customer for the seal pulls so "you can".
    greetings

    My friend will write in what engine it was because I do not want to believe in such things.
  • #23 10693922
    przem27
    Level 30  
    Posts: 1317
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    Rate: 495
    The F9Q engine, it came to me a week after the ring replacement operation (supposedly), after passing the "crazy diesel disease" dictated by economics, the heart transplant only helped (along with the gearbox).
    greetings
  • #24 10694067
    ftp.kowal
    Level 36  
    Posts: 2943
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    Rate: 1829
    Maybe I misunderstood something. A colleague I wrote in the previous post that the latter pulls the pistons down after removing the shaft, right? But do I misunderstand.
  • #25 10694104
    przem27
    Level 30  
    Posts: 1317
    Help: 131
    Rate: 495
    That's what I wrote, embellished with sarcasm if my friend didn't notice, straightening, in my opinion, he did nothing but cashed the money, (because what about spraying the bottom of the piston? :) saying that he replaced the head gasket, he privately boasts that this is how he deals with naives. It seems to me that we just threw the topic in the trash with a stupid polemic on rhetorical topics, if your friend has any more questions, I suggest you pm me.
    greetings
  • #26 10696851
    wopor
    Level 32  
    Posts: 1995
    Help: 175
    Rate: 702
    kol despitekd, at least I'm not making fun of you as a user, only from these "hit diagnoses", unfortunately, you need to acquire some knowledge and practice to give the most accurate causes of the fault, in real socialism I had to learn and gain practice and innovation in ideas on how to fix lack of some access to machinery and equipment for repairs, which sometimes caused a headache from brainstorming :D , now it's just a pleasure for me and work and access to info and gadgets (locks, etc.), and by the way, I once saw a repair of the replacement of the crankshaft in the former USSR performed in a ditch as a channel and after the repair the engine worked quite decently ZIL alone :D , Regards
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Topic summary

✨ The discussion revolves around a Skoda Octavia 2001 1.4 16V experiencing low pressure in cylinder 1, resulting in uneven engine performance and power loss. The user reports a persistent low pressure reading of 8.5 in cylinder 1, despite replacing the piston rings. Responses suggest that the issue may stem from leaking valves, a burned valve seat, or a cracked cylinder head. Recommendations include inspecting the valve seals, replacing the valves, and ensuring proper head gasket installation. The importance of checking the valve control hydraulics and potential air leaks in the manifold is also highlighted.
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FAQ

TL;DR: Cylinder 1 shows 8.5 bar (≈40 % below the 14 bar of the other pots) and “You have leaky valves.” [Elektroda, ftp.kowal, post #10686291], pointing to burned or mis-seated valves rather than rings; inspect head sealing, hydro tappets and manifold leaks first.

Why it matters: Fixing the real leak source avoids €500–€900 in avoidable parts and labour.

Quick Facts

• Factory compression spec for VW/Skoda 1.4 16V (AUA/BBY): 10–15 bar; max 3 bar spread [VW SSP 220]. • Minimum drivable compression: ≥7 bar per cylinder [Bosch Handbook, 9th ed.]. • Hydraulic tappets cost: €12–€18 each, replacement time ≈1 h per cylinder [Skoda ETKA 2023]. • Typical EU head skim + valve grind: €180–€320 [AutoBild, 2022]. • 10 % compression loss ≈3 % power loss [SAE Paper 2019].

What does OBD-II code 16490 on a Skoda Octavia 1.4 16V mean?

Code 16490 indicates an implausible signal from the manifold–barometric pressure sensor G71/F96. It flags when intake vacuum or altitude correction goes outside the 10–108 kPa map expected by the ECU [Elektroda, mimokd, post #10686034]

Does low compression in one cylinder trigger code 16490?

No. The code monitors the sensor circuit, not cylinder pressure. A single 8.5 bar cylinder will not set 16490; it only worsens idle quality [Elektroda, kortyleski, post #10689137]

Why didn’t the oil-test raise compression much in cylinder 1?

If oil adds <1 bar, rings seal acceptably. Compression stayed at 9.5 bar, so the leak path is through valves, head gasket, or a cracked head [Elektroda, Ture11, post #10686054]

How can I confirm whether valves or rings leak?

Run a leak-down test: 1. Bring cylinder 1 to TDC, apply 4–6 bar shop air. 2. Listen at intake, exhaust, dip-stick. 3. >20 % leakage and a hiss at the intake/exhaust confirms valve issues [Edd China, 2021].

Can faulty hydraulic tappets mimic low compression?

Yes. A stuck tappet holds a valve slightly open, dropping compression by up to 4 bar and causing misfire [Elektroda, zeimp, post #10688081]

Should the head always be skimmed when replacing the gasket?

Measure warpage with a straight-edge and 0.05 mm feeler. Skim only if out of spec; removing unnecessary material shortens head life [Haynes Manual 3927].

What compression range is acceptable for the 1.4 16V engine?

Service spec is 10–15 bar with no more than 3 bar variation between cylinders [VW SSP 220]. Anything below 7 bar needs overhaul [Bosch Handbook, 9th ed.].

Will 8.5 bar on one cylinder alone cause severe stalling?

Idle may roughen, but 8.5 bar usually reduces power by about 8 % and rarely stalls an engine unless another fault exists [SAE Paper 2019].

Can an intake manifold leak imitate low compression symptoms?

Yes. Unmetered air raises idle speed, creates uneven running, and can set 16490 even when compression is fine [Elektroda, ladamaniac, post #10689171]

What is a quick 3-step leak-down test procedure?

  1. Warm engine, remove spark plug, set piston to TDC compression.
  2. Attach leak-down gauge, regulate to 100 psi reference.
  3. Read percentage loss; >20 % signals internal leaks Cylinder Leak-Down Basics.

What are the repair options if valves leak?

Lap or replace valves, install new stem seals, and pressure-test the head. Parts cost ≈€120; labour 4–6 h [AutoBild 2022].

Should I replace all valve stem seals when the head is off?

Yes. Seals cost <€1 each and prevent future oil burning; doing all at once avoids repeat head removal [Elektroda, jofa-j1, post #10686336]

Which other components should I inspect alongside the head?

Check EGR valve, vacuum hoses, and rubber couplers for cracks. Leaks here skew the manifold sensor and mimic baro faults [Elektroda, ladamaniac, post #10689171]

What happens if I keep driving with one low-compression cylinder?

Long-term operation raises exhaust temperature, risks catalyst melt, and can increase fuel use by 15 % [OE Emission Study 2020]. Edge-case: piston may overheat, leading to ring land failure.
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