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Bad running after new head gasket - cause?

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Old Aug 10th, 2013, 19:14   #1
rogerthechorister
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Default Bad running after new head gasket - cause?

My Sport Edition ate her head gasket (and clutch) the last weekend in May - and I've just got her back from the very helpful garage at the end of the road.

Other faults found included a very cracked exhaust manifold (changed) a turboplus little hose not properly attached, and the vacuum hose to the brake servo leaking. Oh, and a weeping rear pipe seal on the waterpump thought to have been the cause of the H/G.

No she's running like a sack of sh1t and teh question is where to start. Using NO water, using NO oil. MPG within normal bounds. It may be my imagination but I thought the temperature gauge was at first sitting a fraction high, but after half an hour on the motorway it had gone to slightly below the middle in stead of a whisker above, but it rises to straight up or a whisker above pottering in traffic. The lambda light has come on three times (pulled no 1 fuse to re-set) and so far it has stayed off after the last time. Tickover dreadful - dithering with hiccups between about 300 rpm and 800 rpm lambda light flickering on at the lowest speed (but that's probably due to zero output from the alternator at those speeds) and occasional stalling. Chasm upon initial acceleration - but then feels lively in first to the red line. But by the time one gets to 3rd and 4th is is apparent that there is a huge flatspot containing hiccups between about 3,200 rpm and 4,200 rpm, diminishing as the turboplus takes hold. Running out to the redline in 3rd (in stead of the flatspot from 5,500 to 6,000 that she's had ever since I owned her). Of course I didn't try that in 4th, ossifer it would have been illegally fast, but it MIGHT (nudge nudge) have seemed similar.

On one of my favourite test hills I am about 15 mph down at the point where I have to break or go straight over a roundabout.

Where do I start hunting?

Possiblity 1 - build an Not-quite-OBD2 reader?
Possibility 2 - AMM and throttle body and oil breather?
Possibility 3 - it feels like electrical, to my trousers, so plugs HT leads dizzy cap and rotor arm?
Possibility 4 - keep driving, the brains might be re-learning the engine?
Possibility 5 - fuel pumps and Jimathon injector cleaning? ) It is Jimathon isn't it?)

Open to suggestions here folks!
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Old Aug 10th, 2013, 19:28   #2
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Default sensors

Have the sensors in the cylinder head been properly connnected that lie under the inlet manifold?
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Old Aug 10th, 2013, 20:56   #3
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Sounds to me like Timing to me , mite be out by a tooth .
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Old Aug 10th, 2013, 21:48   #4
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is the throttle switch in the correct position on the throttle body, are all the cables set as they should be.
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Old Aug 11th, 2013, 01:14   #5
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HT breakdown and/or weak spark will be quite severe leading to severe hesitation/stalling on the application of power or severely strangled power output.

If the emissions light is comming on, the fuelling is not correct according to the O2 sensor.

I wouldn't rule out timing belt, but I'd be looking for a post metering air leak first.
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Old Aug 11th, 2013, 04:08   #6
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I had a similar problem when I had a head gasket done at a local general garage, which had otherwise done a really good job. It was just some of the vacuum tubing not properly reconnected. In my case I'm pretty certain it was the ones on the charcoal canister that weren't connected properly.
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Old Feb 13th, 2014, 13:43   #7
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Quote:
Originally Posted by rod25 View Post
Sounds to me like Timing to me , mite be out by a tooth .
I agree, this was my first thought immediately.
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Old Feb 17th, 2014, 15:12   #8
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Gut feeling - this is something fairly simple, albeit well hidden. If I had it in front of me, I would start with the absolute basics. Has it had a compression and leakdown test? Has a second party checked the cam timing? I know the original garage checked it, but if they had set it wrong in the first place, they might be setting / checking incorrectly...! Having said that, the idle will be horrible all of the time if it's a tooth out. In fairness, I suspect it's neither of those, if it comes and goes - a mechanical fault of that nature ought to be ever-present. There isn't a cam sensor on an LH car.

Are the flat spots what I would call flat spots (i.e. it stops pulling), or staccato misfires? As a generalisation, flat spots will be caused by fuelling (or poor boost control), while misfires will be ignition.

I think "new man" is thinking along the right lines, but his shopping list is a little eye-watering. Ignition power stage tends to result in the car dying when hot, not poor running. It could be the coil, but if it has had a new one...! Has it had leads and cap / rotor? Apologies if that has already been covered.

I would resist the temptation to throw more money at it. If the only approach left is "throw parts at it", I'd buy another (fully working) car, and swap any parts thought to be suspect over, before buying new. I'm far from convinced that the ECU or EZK box will be dead.

Swapping engine management is likely to be more painful than fixing what you have, tempting as it might seem.

Does the boost gauge dip at all during the flat spots? I would bypass Turbo+, as that is a complex system, prone to malfunction and strange behaviour (certainly in the retro-fits I've seen), and risks muddying the water. Go with a hose straight from compressor housing to actuator. If that clears it up, try fitting an MBC at 12psi, to see the cause is the higher boost pressure, or Turbo+ itself pulling the boost back. Turbo+ monitors the knock sensor, so may well play silly buggers if it thinks something is wrong (real or otherwise!)

Gut feeling? Assuming compression numbers and cam timing come back as they should and the ECU is not showing codes, I would confirm that all ignition consumables (leads, cap and rotor) are fresh, then look at the fuel system in detail - pressure (3 Bar at idle?), age of filter, possibly injector cleaning. Then it's onto electronics, starting with the TPS (which is a twin switch (throttle shut, and WOT) - so could explain the poor idle, but not the on-load issues). I'd then either measure or just swap out other components until I smell a rat. If all smells of roses...hmm...tricky to say.

cheers

James
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Old Feb 17th, 2014, 16:41   #9
rogerthechorister
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Default Has had...

I believe has had compression test - but I can get another done.

What's a "leakdown test"? The engine is coming up for 200,000 miles so I'd expect static pressure in the cylinder to drop fairly fast.

Tickover is no longer horrible. The only remaining fault is the flat spot.

The flat spot is (as you say) just that the engine stops pulling. If I get it past the flat spot (tricky that with a caravan on the back) pulling resumes - until you get to the end of power on the standard cam which is not far away.

There are no staccato misfires.

Car has had

Air filter
AMM
TPS checked
Distributor checked
Distributor cap rotor arm and HT leads
Plugs
ECU
EZK
Ignition amplifier
Coil
Temperature sensors (the 2 under the inlet manifold)
Knock sensor
Injectors are away for cleaning right now.
Some fuel pressure testing done
All little vacuum hoses
Possibly not that bigger hose that is twin-wall and goes along the head
Downpipe
Lambda sensor
Recon turbo 6 months before the gasket went
Good 90+ mani after the turbo went.
Cat
Crank sensor
Earth strap
TPS checked.
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