Sad engine diagnosis

[Ben]

Hi all,

Well I ended up buying a 1998 Version 5 STI 180kms

Well looked after car however all things must come to a end.

Was running a bit strange so I did a compression test and found cylinders 1,2,3 to be exactly this;

Except number 4. Which would not even read on the gauge... at all!

The car was idling rough and I pulled the Idle Control Valve and found this;

Gave it a clean but made no difference to idle problems.

The car is not using any oil or coolant.

It run\'s fine when driving other than coming out of first gear until 2000rpm. Boosts very well.

Spark plugs all looked like this;

Any thoughts? Only conclusion I can come up with is a burnt exhaust valve?

Was going to do a leakdown test but seems pointless as looks like I will have to take the motor out either way?

Comments welcome!

[Dvnt]

if theres no or bugger all compression on number 4 wouldn\'t that show up on the plug? have you double checked the compression reading possibly with a second tester?

[Rosssub]

No reading at all from number 4???

Did you have the throttle open during compression tests?

Same revolutions from each cylinder tested?

[Joker]

I\'d say #4 is the culprit

[Rosssub]

 Ben said:

Any thoughts? Only conclusion I can come up with is a burnt exhaust valve?

Or a Worn/Broken Valve Spring?

Do any of these Boost/Vac Gauge diagnosis pointers apply (maybe #4 or/and #5)?

Diagnosis of engine condition by measurement of manifold vacuum

Vacuum gauge indication/Possible engine condition.

1. Needle is steady but lower than normal position. This tendency

becomes more evident as engine temperature rises.

Leakage around intake manifold gasket or disconnection or

damaged vacuum hose

2. When engine speed is reduced slowly from higher speed,

needle stops temporarily when it is lowering or becomes steady

above normal position.

Back pressure too high, or exhaust system clogged

3. Needle intermittently drops to position lower than normal

position.

Leakage around cylinder

4. Needle drops suddenly and intermittently from normal position.

Sticky valves

5. When engine speed is gradually increased, needle begins to

vibrate rapidly at certain speed, and then vibration increases as

engine speed increases.

Weak or broken valve springs

6. Needle vibrates above and below normal position in narrow

range.

Defective ignition system.

[Ben]

Thanks ROSSSUB for that. I will pay attention to the rev needle more closely next time i drive it and report back.

Yes ZERO compression on Cylinder 4. I tried removing and testing on another cylinder again and then back to No.4 with no luck. I dont believe the tester is at fault as worked fine on all other cylinders plus its a Snap-On one not some $30 job from repco.

As far as im aware the needle does not fluctuate at idle when hot or cold.

The car idles nicely at around 500rpm / touching the gas pedal to bring the revs up to 1000rpm its rough as hell and shakes the car / 1500rpm onwards it runs fine , does not shake, boosts very well and smooth.

As far as vacuum lines I sprayed brake cleaner on every seal I could see and nothing brought the revs up.

Needs does not drop or rise suddenly except for when engaging the air con but nothing out of the ordinary

Like I said I have done 1200-1500km without the oil turning black yet nor and coolant being used.

Another test I did was open the coolant overflow reservoir and cranked it over - no bubbling.

No smoke out of exhaust hot or cold when boosting or cruising what so ever.

[Ben]

 Rosssub said:

No reading at all from number 4???

Did you have the throttle open during compression tests?

Same revolutions from each cylinder tested?

Sorry yes throttle open fully during compression tests.

Same revolutions of 5 each cylinder.

No reading at all on 2 seperate attempts

[Ben]

I should also note to you that we tried just putting a spark plug in the No.4 cylinder and cranking it over but could not hear any compression what so ever. Only sound was my poor starter motor trying to make something happen!

[Rosssub]

Surely a burnt valve seat would still show some compression, at least move the needle. Makes me think you have a broken/tired exhaust valve spring in number 4? Valves sitting open slightly. Unless it\'s a HG thing, just not showing in oil/coolant yet?

Any excessive valve train noise/ticking?

[Ben]

im not tooo technically minded with these things. Hard to hear as I have a exhaust system but when just revving it from the engine bay I can hear slight piston slap when you start holding the revs over 4k.

[Ben]

I shall try and take a video tomorrow which will probably be more helpful.

[Rosssub]

 Ben said:

im not tooo technically minded with these things. Hard to hear as I have a exhaust system but when just revving it from the engine bay I can hear slight piston slap when you start holding the revs over 4k.

I hope it\'s warm when you do that...

That could be the valve slapping/bouncing, from the soft/broken spring?

I wouldn\'t drive it at all, at least until you know what\'s wrong. If the valve retainer lets go or the spring collapses/something snaps, you\'ll have a big ass hole in your Piston/block.

Edit: You may be lucky (if possible) and it\'s just a valve so far out of adjustment (shims) that the valve\'s not seating/sealing properly???

[Ben]

yes definitely warm when I did that hah. Unsure what i will find really. The car was like that when i bought it and supposedly the person i purchased the car off said its been doing it for \'a while\' so god knows how much driving has been done on it - I know I have done 1500kms so far.

I will take your advise and put the car into storage until I have time and some money set aside to take the engine apart and see what I have. I will be doing all the work myself I would just rather not pull the engine to pieces only to have it sit there for a month while I gather funds together! I am already planning on worst case scenario and have been looking on STAPARTS at cost of rebuild components.

Thanks again for your input Ross

[Rosssub]

No worries Ben, good luck. Take it to a \'pro\', or offer some beer and ask one of these Guys to come have a look at it with you. Fingers crossed it may be an easy fix or something simple you\'ll laugh at. But worst case scenario it could ruin your engine (full rebuild/replace). :-[

[Ben]

Yeah i\'m fortunate to work in the automotive industry and can get genuine and aftermarket parts at a reasonable price as well. At this stage I will leave the car and buffer up some money to plan for the rebuild before splitting the motor open. Will post a update as to what I find. Thanks again.

[funkytown]

what happens when its running and you pull the lead off #4? compared with pulling off another lead.

sounds definately head related and not piston / bottm end.

[Ben]

 funkytown said:

what happens when its running and you pull the lead off #4? compared with pulling off another lead.

sounds definately head related and not piston / bottm end.

When running nothing changes when pulling lead. I also pulled the injector while running and made no difference to revs or engine idle.

[funkytown]

and that #4 sparkplug is not oily or overwise pitted or the tab smashed against the center pin or different colouring?

etc etc etc etc

further points at the head. I would be borrowing or getting a scope to have a look in that bore before removing the long block or stripping the motor down personally.

that injector is ticking away when plugged in though ah?

[Rosssub]

 funkytown said:

further points at the head. I would be borrowing or getting a scope to have a look in that bore before removing the long block or stripping the motor down personally.

Are you thinking a hole in #4 piston/broken rings etc?

Edit: Or to view Valve seats/Valve operation?

[funkytown]

nah it surely cant be piston but investigating to rule it out is super sensible, but i guess if its anyting fopar on a valve a quick scope will tell you how farked or if even the piston has touched the valve. and therefore reasonably salvagable.

if its touched its bent valve and $$ headwork required = scrap head, and probably scrap piston minmum and the bore could be scored.. so scrap the shorty...

so forget touching that motor - just scrap the lot and start again imo.

so it all escalates quickly. if its a spring you could EASILY get to it and test with out even splitting the block. if its valve not sealing then thats just a bit gay and splitting is required.

all im saying is get the full picture before commiting $$.

[Ben]

Yes sound very helpful funky. Turns out my friend has bought a bore scope so I will be able to investigate next week =).

Yes I dont want to split the block till I know exactly what is wrong with the engine.

Im trying to get at least 3000 set aside before starting work and i figure that should cover most things needed.

Everyone says use a V7 STI Shortblock? Are these quite strong. I have had a look online and also on trademe however they seem to be hard to come by?

[funkytown]

they come and go in terms of supply but they are semi closed and have phase 2 crank set up so generally good for about 250wkw.

more than most ppl need imo.

3000 might be wildly over what you need, or wildly under

[Ben]

Haha i dont plan on going for a race car. 200wkw would see me absolutely fine =)

[soopersubaru]

Connect air compressor to #4..Rotate engine carefully and listen for the hiss., Sump?,Exhaust? ,Intake?, Or does the radiator cap lift?...Simple Leak down test. This will answer what is at fault. Head issue in all probability.

[Ben]

Well, just a quick update;

I have started to pull down my motor. Everything that has come off is actually in really good nick! Does not look like the engine has been apart before. Intake manifold / Intercooler is clean. No gunky residue inside. VF28 turbo , no shaft play or damage to fins.

Still a bit confused as main issue is 0.00% compression on number 4.

Turned crank manually - all valves moving up and down.

Pulled head off number 4 - piston looks fine from top view. Block slightly scored but nothing out of ordinary.

Top of valves all look in place and seat well, little carbon build up but nothing to be alarmed about.

No sign of head gaskets leaking.

Have noticed one bearing is completely screwed, quite a lot of play when you give it a shake.

At this stage I thought I would have found a chip in a valve or a gaping hole in a piston or something. Nothing, almost concerning I have a major problem, taken motor to bits and have not found a cause yet- not much more to take apart!

Am just about to take the head off the the other side and fully disassemble the block. Will update soon.