Bad running after new head gasket - cause?

[rogerthechorister]

Yes, I was getting to both of those ideas, but if going carbs I think a pair of sidedraught Webers would be more fun - I've played with balancing twin downdraught 2BBL Strombergs and Solex in my FIAT days and I could get a 500 rpm tickover and a glorious induction howl up to 6,500 RPM - It took 2 hours and if I was lucky it could last for all of 24 hours. And christ knows what my emissions were.

Recommendations for a whole new EMS?

[Laird Scooby]

The main reason i suggested the Strombergs is it would be relatively easy to keep your turbo with them - i'm not fully au fait with everything that would need to be done but they're more or less plug and play. You might even find there's a suitable manifold available off the shelf too, as the old 140 series ran twin Strombergs, i think in certain markets so did the 240 series and as the engine in yours is more or less a development of both of those there's a good chance of finding one.

As for a recommendation for a new EMS - the one that comes to mind for me is the Weber Alpha . I have no experience of this at all but i do know it's a popular choice when people have converted carbs to injection and reading all the "blurb" on it it certainly seems capable of doing what you need it to do.

[rogerthechorister]

Can't think of anything else to change.

"Expert" is talking about re-changing the ECU and EZK - the new EZK still gives no reading on either my pulse counter or his Volvo diagnostic.

Last ditch changes will be injector resistor pack, cleaned injectors, cleaned throttle body, and radio suppression relay.

Then we will have changed every single bit. Every single one.

Don't know what to do now.

[Laird Scooby]

I still think it's something silly. Like a trapped/pinched/disconnected hose somewhere on the vacuum and/or pressure side of the engine management system or a disconnected sensor, incorrectly set timing or something along those lines from when the HG was repaired.

I know that probably isn't helpful just now but you've checked everything else as you say and that's the only thing left it could be, except maybe that radio suppression relay. Just a thought - are there 2 hoses (small vacuum or pressure) on the turbo? If so i wonder if they were unintentionally swapped?
I had something similar on my 740 except it was the hoses feeding the heater matrix - result, no heat unless you were sat idling then only luke-warm. "Reversed" them (corrected in otherwords) and lo & behold i had a working heater again!
If two of the small hoses have been unintentionally swapped (eg wastegate and MAP sensor) this would result in some very strange behaviour under load - could be worth checking where every small hoses goes to and comes from before finally pulling your hair out.

[averill]

Originally Posted by rod25

Sounds to me like Timing to me , mite be out by a tooth .

I agree, this was my first thought immediately.

[foggyjames]

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

[rogerthechorister]

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.

[Laird Scooby]

Originally Posted by rogerthechorister

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.

..........and a partridge in a pear tree!

Sorry to be a little facetious but that's a pretty exhaustive list of parts to "fix" it!

With all those various different parts, i'd be inclined to say that (assuming all new sensors are fine) then what they're measuring must be wrong.
In other words, back to what i've previously suggested, something along the lines of a vacuum hose incorrectly connected, pinched, split or similar where it can't be seen, or at least not easily seen. What about the hose between the air filter and AMM and/or turbo and those parts? A slight misfit on one of those could cause an air leak (either in or out) which would cause problems too.

[foggyjames]

I had a feeling the two might not be connected. In that case, I think we're looking either at a boost control issue, or fuelling. Respective causes could be Turbo+ messing up, or a weak wastegate actuator, and an EMS fault (fuel supply, faulty sensor, etc) or a boost leak.

I think an important next step will be to monitor AFRs via a wideband lambda sensor (preferably with a bung in the downpipe), to see if it is going either rich or lean during the flat spot. I would also monitor boost pressure via a calibrated gauge. If it's "flat" rather than misfiring, one of those pretty much has to be wavering during the flat spot, and that will tell you a lot about what's going on.

cheers

James

[Diesel-do-nicely]

if you skim a head , on the 940 the cam timing will then be slightly retarded, if the rest of the bits, made at various plants with tollerance here and there all ad up with this timing issue to a bit more retardation (ie scottish rugby lineout coaches) you may get a wierd flat spot.
All i can suggest is that you check the rotor arm and cap again , and do the cam timing with a dial gague down a plug hole , dont assume a timing mark is accurate, has a cam or crank pully woodruff key been left out perchance ?
seen it before 3 times
and after removing the bonnet put an apprentice in the engine bay with a strobe light to see if the timing is correct when driving at the relevant rpms, while he is there he could read the pressure of the fuel supply if you have a gauge.
We once had a "harmonic" in a vw corrado , it hesitated at high loads, but it was about 1400rpm, 2800rpm and very noticable at 5500 ish, on a very clever tech boys vag diagnostic roller he found the fuel pump drew huge current at these rpms for no reason, changed the fuel pump and it cured it