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Old 06-20-2010, 12:10 PM   #1
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Default Replacement Engine not running quite right...

Hi folks,

I am hoping someone may be able to offer some suggestions to my "little" issue...!

I have a 1990 MX5 BBR Turbo, which has been Megasquirted by its previous owner (amongst a number of other things inc larger injectors, one piece exhaust, oil cooler, intercooler etc) up to approx 198 bhp.

The previous owner also fitted a 94 engine (still 1.6)... I recently ruined that engine by running very low on oil - the oil pressure gauge appears to be faulty.

Now the issue - I have just replaced the engine myself (with my bro's help who knows a fair bit about cars, I know a bit but am certainly no expert) including new gaskets where required (obviously), and though the engine starts with no issue and sounds pretty smooth it lurches at WOT from about 4000rpm under load... So obviously all is not well.

The replacement engine comes from API who appear to be well respected, so I don't doubt the engine itself is good (it is of the correct type and age to directly replace the one I inadvertently knackered), and all the ancillaries and manifolds have been transferred from the previous engine (including injectors of course). I have also transferred the coil pack and CAS over as the new CAS was a bit squashed and the coil pack looked a bit corroded in places.

I have just set the timing with the MegaSquirt instructions after changing the CAS, so that should now be correct (set to 10deg BTDC fixed, then -10 to enable spark advance).

I realise that all engines are a bit different, so is this potentially the cause and it just requires retuning (which I would not do myself but find a professional to do this for me, in which case can anyone suggest a tuner who knows mx5/miatas and MegaSquirt, near sth London/Surrey UK???).

Or does that sound unlikely in which case are there other things I should check before going that route?

Any pointers much appreciated!

Dave
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Old 06-20-2010, 12:14 PM   #2
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Hi folks,

Any pointers much appreciated!

Dave
You do know that the oil pressure gauge is not an oil contents gauge right?
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Old 06-20-2010, 12:23 PM   #3
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Yeah I did read that somewhere, but surely the amount of oil in the engine will have a significant effect on the oil pressure and therefore the gauge reading will be related to oil level?
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Old 06-20-2010, 07:46 PM   #4
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Your HLA are your oil level indicator. If they're clicking you need to add oil. Or check the dip stick, dipstick.
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Old 06-21-2010, 11:49 AM   #5
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Yeah I did read that somewhere, but surely the amount of oil in the engine will have a significant effect on the oil pressure and therefore the gauge reading will be related to oil level?
The oil pressure gauge reads only oil pressure and WILL NOT CHANGE until the oil level drops below the oil pick up and the pump sucks air from the crankcase. At this point, air being less dense than oil, the oil pressure drops to zero and you Fark your engine.

Here ends today's lesson. Now go check your dipstick children.
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Old 06-25-2010, 12:02 PM   #6
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Guys,

Thanks for your responses, but I wasn't asking about how to use the oil gauge - I've already suffered due to that (hence the new engine) so I will be checking the dipstick regularly now!

Question is: Any ideas on what to check (potentially in MSPNP?) since fitting the new engine? It should be the same engine as before, and it ran fine before (so the tune was fine for the last engine) but at about 4000rpm @ WOT it lurches... Runs beautifully until then, and is also fine up to red line up to about 85-90% throttle.

Is it just that something is likely to require amending in the tuning? As mentioned, the car was tuned when I got it so have not used MSPNP, MegaTune, whatever, before so don't even know if this is likely to be something that needs doing ? I.E. retuning for the new engine? Or is it more likely to be mechanical? Wondering if the replacement engine that came from a reputable company and was apparently tested, could have an issue?

Unfortunately searching online for someone having done similar is not helping - been searching on this for weeks...
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Old 08-04-2010, 03:23 PM   #7
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Answer is: Knackered Megasquirt... New OMEX being installed, mapped, etc professionally...
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