C20XE early engine block with late valve head

Varnis9

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Hello guys

My C20XE has an early bottom end, merged with a late cylinder head (Motronic 2.8 ecu and wiring loom with all sensors). The engine has never run properly during idle. When on cruise though it works sweet, The symptoms I have are:

  1. Sometimes the engine starts on second crank
  2. Rough idle
  3. When it starts it sticks at around 3000 rpm then drops to 1000 ish after a few minutes
  4. Smells fuel at exhaust
I have replaced almost all sensors, took ecu wiring out and checked all good, no ecu fault codes, checked timing and fuel pressure at 2.5bar as it should.. I have started thinking maybe it is an incompatibility between old bottom end and late cylinder head?

Can anyone share some light on this?

Thanks
 

AndyB-Redtop

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I doubt very much it’s anything to do with incompatibility between the head and block. Unless someone has made a real bodge job of matching it up.... it sounds more likely to be an electronic/ECU issue. If the engine had a distributor initially, your problem may lie in the loom conversion from M2.5 to M2.8. There are many different types of sensors between the 2
 

Varnis9

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It looks like the 2.8 was transferred as a whole, cylinder head and sensors, to the early bottom end. Wiring has been sliced open checked for shorts, broken wires all good, replaced connectors and pins. Still to no avail..

Loosing my mind with the car now.. Not sure if it is something to do with timing difference between early crank and late camshafts?
 

Varnis9

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Round or square tooth belt/pulleys? I assume you are running an M2.8 ECU ? Have you tried changing your MAF/Lambda sensor ?
It s got round teeth pulleys. Changed lambda and afm with genuine still no luck. Yeah running 2.8 ecu.. You got any suggestion pal?
 

Varnis9

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Replaced 3 of those fuckers, also checked wiring all good. Also checked voltage with engine off gives a solid 12v.
 

AndyB-Redtop

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There is a difference between the early/late camshafts, well, only that the exhaust cam isn't as long on late than early to drive the distributor. The later has a different profile on the end for the coil/ignition sensor. Doubt that is your problem though because if the head was just bolted on, you already have the right cams on the engine because it runs. The cam lobe profiles should be exactly the same "Standard". Are you running non standard cams, i.e. higher profile/lift cams? If so, these might need tweaking/retarding slightly...…. But then you say it runs sweet when cruising...… :confused::hmmm: Have you tried a compression test on your cylinders? Thinking of your 3000rpm on idle, what's your "blow-by" Crankcase pressure like going back to the inlet manifold through the 2 breathers from the head?
 

Varnis9

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Done both compression test and engine air leak test all good within specs. The engine runs standard cams. Not sure about that blow-by pressure through the breathers. Can I measure that?
 

AndyB-Redtop

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If your compression/air test came back good, then there should be no worry for blow by from the crank, through the breathers to the inlet. That can be ruled out. I just thought if you had poor compression, you’d have a lot of blowby going back to inlet, thus causing rough and high idling.
 
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Think later ones had blue injectors rather than cream and cars with traction control had a black coolant temperature sensor and the rest are blue. Not sure if there compatible with each setup but worth looking into.
 

Varnis9

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According to my ecu part number its off an astra 1993-94 not sure if that's "late" or early!
 

Varnis9

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Going to try the icv adjustment hopefully it will make a difference
 

Varnis9

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Any suggestions on the second crank engine start issue? I have checked on the pressure regulator and the pressure does not pick up during first crank...
 
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