Low Compression in cylinder # 2.

[speed]

Hi all,
I bought my NA6 a couple of months back and I've been working through a variety of issues.
I'm now at a point where I'm not sure what to do next.

Yesterday I ran a compression test with the following results.
Dry: 190/160/185/190
Wet: 205/170/205/205

Manga_blue has pointed out that I may have a dodgy valve in cyl #2.

I'm also experiencing a lack of power down low, especially once the engine is warmed up.
Engine bay heat also seems excessive.
When I pull up from even the most sedate of drives, the exhaust tinkles like mad.
I don't believe that I have a water cooling issue and the motor has not over heated.
No pulley's appear to be wobbling.

I was hoping that fixing the compression issue would also fix my other symptoms.

So far I've replaced the battery, alternator, coil pack, leads, plugs, exhaust manifold gasket, fuel filter, oil, oil filter and have cleaned out the throttle body.
My AFM still has the round metal plug in it but not sure if touched by a previous owner..

My timing is set at 14 degrees BTDC.

I look forward to any advise or suggestions that you may have to fix my issues.


Thank you,
Speed

[hks_kansei]

Could be a stuck/burnt valve.
I know that cars running on LPG can have valve burning issues (LPG burns hotter IIRC) but I seem to recall that timing and mixtures can also play a part.

How was the spark plug on #2? black and sooty? or white and crusty?



unfortunately the only way to see a burnt valve is to take off the head and look at the valves, it will also give you a chance to check the head gasket while you're there (and change it, you'd be silly to leave the old one in if you've goen that far)

[Sailor]

Check valve clearances. A bit of recession can close the clearances and you get leakage

[manga_blue]

Diagnosis depends on where it's getting too hot and under what running conditions you get it.

If the heat is up at the head and top of the headers and most of the crackling noises are coming from the headers then you could have problems with excessively lean mixture or retarded spark. Given that you've already checked 14btdc then lean mixture is possibly the cause. Lean causes excessive high combustion temps, poor power and fuel consumption with risk of damage piston, chamber and valves. Lean mixture often shows as pale grey deposits inside the tailpipe.

If the heat is all in the cat convertor then that indicates that there's fuel being dumped into the exhaust, either through rich mixture or misfires, and it's being burnt off in the cat. Rich causes poor power and fuel consumption, excess piston ring wear. It's harder to pick up at the tailpipe because of it being burnt off in the cat (unless it's really bad and you've got greasy black stuff on the rear bumper). It sounds like you've already done everything you can to minimise misfires except check that the CAS is working reliably.

In closed loop (low-mid throttle and less than 4000rpm) the ECU uses just the O2 and ECT sensors to set mixture. In open loop (mid-full throttle or greater than 4000rpm) the ECU uses its inbuilt fuel map and AFM, IAT ad ECT sensors to set mixture.

[93_Clubman]

I bought my NA6 a couple of months back and I've been working through a variety of issues.

What were the other issues? I ask as they may or may not be related, & the additional info can help us in answering.

Try resetting timing to 10 degrees BTDC to see what happens.

Also results from compression testing can be quite variable as you'll see from the following: viewtopic.php?f=29&t=59832

OP's previous post re this issue for background:
viewtopic.php?f=18&t=53999&p=775722#p775722

[NitroDann]

Have you confirmed that the timing is at 14 degrees using the psitons as opposed to the crank pulley. I have seen a lot of slipped crank pulleys which will lie to you about timing when using a light.

Use a stiff wire or long screwdriver in the number 1 sparkplug hole to confirm that the pulley is accurate and that your timing is in fact at 14. Its free, quick and will eliminate any timing based possibilities.

Dann

[speed]

How was the spark plug on #2? black and sooty? or white and crusty?

Yes it was on the black and sooty side.

Check valve clearances. A bit of recession can close the clearances and you get leakage

Noted and now on my list.

Diagnosis depends on where it's getting too hot and under what running conditions you get it.

If the heat is up at the head and top of the headers and most of the crackling noises are coming from the headers then you could have problems with excessively lean mixture or retarded spark. Given that you've already checked 14btdc then lean mixture is possibly the cause. Lean causes excessive high combustion temps, poor power and fuel consumption with risk of damage piston, chamber and valves. Lean mixture often shows as pale grey deposits inside the tailpipe.

If the heat is all in the cat convertor then that indicates that there's fuel being dumped into the exhaust, either through rich mixture or misfires, and it's being burnt off in the cat. Rich causes poor power and fuel consumption, excess piston ring wear. It's harder to pick up at the tailpipe because of it being burnt off in the cat (unless it's really bad and you've got greasy black stuff on the rear bumper). It sounds like you've already done everything you can to minimise misfires except check that the CAS is working reliably.

In closed loop (low-mid throttle and less than 4000rpm) the ECU uses just the O2 and ECT sensors to set mixture. In open loop (mid-full throttle or greater than 4000rpm) the ECU uses its inbuilt fuel map and AFM, IAT ad ECT sensors to set mixture.

If anything, seems to be running rich, maybe my camshaft pulley is out a tooth.
It happens every single time I drive it. Once warmed up she is gutless down low.
Bearable for about 5 mins when cold but I never rev a car out until it's reached operating temperature.

I bought my NA6 a couple of months back and I've been working through a variety of issues.

What were the other issues? I ask as they may or may not be related, & the additional info can help us in answering.

Try resetting timing to 10 degrees BTDC to see what happens.

Also results from compression testing can be quite variable as you'll see from the following: viewtopic.php?f=29&t=59832

OP's previous post re this issue for background:
viewtopic.php?f=18&t=53999&p=775722#p775722

Other issues were:
Battery was wrong type - Replaced
Alternator had a dodgy voltage drop box attached - Replaced
Exhaust manifold gasket was leaking - Replaced.
Thermo fan dead and air con fan was connected to thermo fan wires and ran with ignition - Fan replaced and wiring corrected.
Oxygen sensor also replaced, chasing power issues.

Other stuff was removing non-working alarm and re-wire stereo and speakers - Stereo now works properly.

I've tried dropping the timing back to 10. Runs far worse, meaning more sluggish.

Have you confirmed that the timing is at 14 degrees using the psitons as opposed to the crank pulley. I have seen a lot of slipped crank pulleys which will lie to you about timing when using a light.

Use a stiff wire or long screwdriver in the number 1 sparkplug hole to confirm that the pulley is accurate and that your timing is in fact at 14. Its free, quick and will eliminate any timing based possibilities.

Dann

No I haven't. Do you mean to confirm that the piston in cyl 1 is at top dead centre and see if the marks on the pulleys line up or that the piston is as high as it will go. Sorry, not sure how I can tell it's at 14 with a screw driver.

I'm very grateful for every bodies input.


So far it's sounding like my timing belt is out combined with a valve issue.

[sailaholic]

Dann how is pulley slip possible on a b series engine? There is a keyway that keeps the crank aligned.


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[manga_blue]

So far it's sounding like my timing belt is out combined with a valve issue.

The belt could be out but most likely you've got a mixture/spark issue. The compression issues are minor - I've seen engines with much worse compression than that making very good power.

Good point about the pulley, Dann. The other free, quick and easy is to put a timing light on it again and check that there's no pulley wobble while it's running and that the position of the timing mark stays pretty constant. That should give you a dynamic view of timing mark slip and of the quality of the CAS signal.

After that then:
Lean: Check entire intake system for air leaks, fuel pressure regulator weak, fuel pump pressure/delivery, injector blockages and spray patterns. Replace fuel filter and PCV valve.
Rich on closed loop: replace O2 sensor (single wire ones are only good for 60,000kms anyway), replace ECT sensor.
Rich on open loop: replace ECT, check AFM and IAT operation/voltages, fuel pressure regulator stuck

[manga_blue]

Dann how is pulley slip possible on a b series engine? There is a keyway that keeps the crank aligned.

You're kidding us, right?

[hks_kansei]

Dann how is pulley slip possible on a b series engine? There is a keyway that keeps the crank aligned.

Harmonic balancers are two parts, the centre which lines with the keyway, and the outer, which has the timing marks and pulleys.

there's usually a bonded rubber donut between the two, if the bond breaks, the outer pulley can shift, moving the marks.

[manga_blue]

Also this :

[hks_kansei]

No I haven't. Do you mean to confirm that the piston in cyl 1 is at top dead centre and see if the marks on the pulleys line up or that the piston is as high as it will go. Sorry, not sure how I can tell it's at 14 with a screw driver.

With the piston at TDC the timing mark should line up with the TDC mark on the scale, if not, it's out.


Timing lights work by lighting when the spark goes, since that happens X degrees BTDC the light goes on just before TDC, and shows the mark at the same point.

[sailaholic]

Dann how is pulley slip possible on a b series engine? There is a keyway that keeps the crank aligned.

You're kidding us, right?

Nope, but obviously having a brain fart.

My memory, is everything is positively located unlike the later engines that just rely on an interference fit.

Apart from a damaged key / keyway (which I wouldn't have described as "slip". I don't see how the pulley could be out of rotational alignment.


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[hks_kansei]

Apart from a damaged key / keyway (which I wouldn't have described as "slip". I don't see how the pulley could be out of rotational alignment.

see my post above re: rubber insulated/located.



the lefthand pullleys were supposedly from a burned out MX5, the rubber separator things melted and the two halves separated.
The righthand one is a normal one.