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Discussion Starter #1
Chasing my loss of performance problems, I'm down to two suspects, both of which appear to be faulty- the Trionic ECU (it's going back to Maptun again...) and the head.

I thought maybe cracked head or failed gasket as the plugs were not all the same colour (although that could be caused by poor fuelling due to faulty ECU). I also have traces of oil in the coolant, although I now suspect that may be a leak from the auto rad I fitted. A block test proved negative.

Anyway, I carried out a compression test on Friday and got the following results:

Cold 12.6 11.0 11.4 12.0
Hot 13.0 11.2 11.6 12.2
Oil 16.8 14.0

The "good" range according to the gauge is 10-14 bar.

I put a teaspoon or so of oil in two cylinders to see if I had a major problem with ring wear (I wasn't expecting it, they were only done about 30k miles ago).

I'm a bit of a numpty on this stuff, but according to Haynes, there shouldn't be a variation of more than 2 bar. I've got a difference between #1 & #2 of 1.8 bar (2.6 with oil added), which is close to the limit.

Haynes lists the following symptoms/faults:

A low reading on adjacent cylinders suggests a blown head gasket, but the block test was negative.

If adding oil does not improve it substantially, then leaking or burnt valves, or a blown head gasket are to blame- observe the relative difference between #1 & #2 3.8 vs 2.8 bar

If one cylinder is 20% lower (16% between 1 & 2)and the engine has a slightly rough idle (it does), a worn camshaft lobe is suspected.

And just to add insult to injury, having done all this and swapped out the ECU and injectors, I now have a misfire under more than about 0.5 bar of boost . I tried another DI (admittedly faulty itself, but only above 1 bar last time I used it) and the same result. I can't believe it's chewed another DI- this will be 3 in 4 months if it has!! Or has the demise of the DI been caused by the faulty ECU (I don't see how myself)

Any ideas gang, other than a can of petrol and a match?
 

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Discussion Starter #3
Originally posted by Leon (9-5 stg2):
[qb]If the gasket is split between 2 cylinders, a block test is unlikely to pick this up..
It only picks up combustion gases in the coolant..
IF you've oil in the coolant I'd be slightly concerned    [/qb][/b]
I think I've got a problem between two cylinders, too Leon, either head or gasket.

I'm not too worried about the oil- as I say, I suspect it's contamination from the auto rad I fitted a few months back. There's certainly no trace whatsoever of mayo on the dipstick. The way the oil casually floats on the surface also suggests it hasn't been introduced under high heat and pressure as there's no evidence of emulsification there.
 

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Discussion Starter #6
Originally posted by Scaero (ecopower stg0):
[qb]I think in Marks case it was 'where wasn't it cracked...        :rolleyes:  

Andrew [/qb][/b]
Ha F ha!

It was a recon one from Abbott, that I did get a partial guarantee with.

The cracks on my old one were around the spark plugs and between the valves, but not between the cylinders.

Right now though I just wish I knew what was causing the misfire- all was OK before I did the compresssion test
.

I'm stuck tho as to what might cause a misfire other than a dodgy DI... I
 

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Mark,
Not been around much lately so sorry for the delayed reply. I know that Haynes uses the 2 bar rule but I would say anything more than 1 bar difference signifies that something is not right. I've had a Saab engine with less than a 2 bar difference and then I found a blown hg when I dismantled it.

I'd say that since the oil did not reduce the difference, the cause is head related. Head gasket or valve seating must be the likely culprits. Whatever the cause, I feel that the head is going to have to come off.

Sorry

Alanb
 

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Discussion Starter #8
Hi Alan,

That's the conclusion I came to with my indy. We've certainly isolated one possible cause- the recon process appears to have involved fitting steel thread sleeves for the spark plugs, presumably because the threads had been stripped previously. These have come loose on the two cylinders that have the low results.

I'm not happy that the head had these and I didn't know about it- even if they arefitted properly, they will significantly reduce the ability of the spark plugs to conduct heat away. The plug fitted to the loosest sleeve showed significant signs of overheating... basically I think the thermal integrity of the head has been compromised by this so who knows what other damage may have been done.

Anyway, it's going back to the suppliers on Thursday this week, when I'm going to hang around whilst they pull the head off and conduct a diagnosis...
 

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Mark,

This mentioned suppliers didnt hapen to be a well known Saab tuning company with the first letter beginning with 'A' and the first letter of the second word beginning with 'R' would it???,

Pete
 

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Seems there are a few unhappy customers beginning to crop up in regard to said suppliers
,
I really would have expected better from them especially as they charge top money for there products/services - im very surprised they fitted a circumspect head to your car knowing the levels of boost/power you run.....
How do you stand in regard to solving the problem??,
Have said company agreed to fix and replace??,
I do hope this doesnt turn out into another 'BillJ' gearbox incident

Pete.
 

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I've still got my scratch that I got as a present...

It's also got a very slight whine, but that was like Bills back in mid Feb.

A
 

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Discussion Starter #14
Pete, I did get a guarantee with the head, which I feel should cover what's happened with it.

As with other parts of the car, the head is going to be subject to exceptional stresses given the state of tune of my car, and the fact that I do occasional track days. It's not unreasonable IMO for any supplier not to give a full gaurantee for such use but I am unable to see how a track day would precipitate the failure of the inserts.

Ref the whine, I've got it too. It was bad after the last rebuild, so the preload was adjusted. This made things better for a while but now it's come back again...
 
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