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Discussion Starter · #1 ·
On top of everything else...
I was out playing last night (nice and cold!!)
and I was getting major hesitation in third gear as it was coming on full boost (above 1.4 bar)
does the same in 4 th but not so violently
hesitation really quite severe (like hitting the overboost)
My only thought is the DI is dying...
It does not owe me much... its comng up to 90k miles on this one, with all of this at elevated horsepower.
checked all the hoses and all of the usual stuff

Any Ideas ?
 

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My DI only showed signs of failure when hitting about 0.9 bar. Any less and it behaved perfectly well. Felt like a misfire/shudder and recovered immediately if I let the boost drop a little. Bore no relation to rpm, only boost.
 

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Mine has similar symptoms - in fact it started well over a year ago. The DI and either the AMM or throttle body were replaced (Can't remember which) but with very little effect. Seems to be worse when pulling hard in higher gears - and better with aircon switched off (takes the compressor out of circuit). Also seemed slightly better with new plugs. If you ever find out what it is please let me know!
 

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Yes, that's just what happened to mine on the way to a PE rolling road day abut a year back. Fortunately I was able to borrow another and the problem was solved.
 

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Might be the MAP sensor. Check the there's no condensation or dirt in the tube. (not overly familiar with the setup so if there’s no tube then ignore my suggestion)

Also as you’re running higher boost there may be a couple of changes you can make to the MAP sensor setup so it gives more accurate readings. MAP sensor should be mounted on the car body and not the engine. The tube connecting the MAP sensor to the intake manifold should be quite short (not more than 1 meter) The sensor should be mounted higher than the port on the intake manifold. The port on the manifold should not be shared by other devices (like idle control valves) You can also insert a restrictor in the tube so the pressure does not pulse through the tube. If the pressure is pulsing through the tube the MAP sensor will read rapid pressure fluctuations instead of smooth pressure build-up.

Again - not entirely familiar with the setup on the 9000 so disregard irrelevancies.
 

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Discussion Starter · #9 ·
I have ordered one from elkprats so should get it on wed as well as 4 new sparkies..
If the pressure is pulsing through the tube the MAP sensor will read rapid pressure fluctuations instead of smooth pressure build-up.[/b]
I remember some-one telling me about this

This might be causing my premature boost decline

Any Idea on a restriction?

btw spot on with the reccomendations on how the map sensor should be fitted
that is exactly how it is fitted on the 9000..
 

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Maybe it would be worth checking the readings at that crucial moment. I.e. hook up a volt meter and drive till it starts to happen and if your voltmeter shows something similar to the feeling your getting then suspect the MAP sensor. Also the MAP sensor could be limited in it's capability and may be only able to read up to a certain pressure. You might need a more capable device. Wonder if the ECU would notice / accept a different sensor?
 

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Originally posted by ejenner:
[qb]Also the MAP sensor could be limited in it's capability and may be only able to read up to a certain pressure. You might need a more capable device. Wonder if the ECU would notice / accept a different sensor? [/qb][/b]
Correct. The stock sensor has a limit of 1.65bar. For their higher levels of tune, Maptun use a 3 bar sensor. IT think it's fitted with an adaptor kit. However this can only be used with MY94 onwards Trionic (once again us MY93 lose out! )

The restriction to stop pulsing is an interesting idea, but I think that is normally overcome by the use of a particular spec tubing between the manifold and the MAP sensor. It's much stiffer walled than the rest of the vac tubing, and should be kept as short as possible.
 

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Discussion Starter · #12 ·
gave the di a good clean and re-lubed it
Also fitted a narrower gauge tube to the 3 bar map sensor...
result ?

hesitation gone
also seems a lot smoother the boost comes in in a nice rush
Early days and I do think the di is still on the way out ...

The map sensor measures pressure ...
the ecu interprets this and looks at rates of rise etc to determine what to do
now the 3 bar map sensor will be more sensitive to pressure fluctuations
(assuming the fsd is the same as a standard one)
so excessive noise will get in the way of the ecu interpreting boost rise rates etc
My engine runs pretty lumpily and there must be lots of spurious "noise" so a damping mechanism
(which could be physical..restriction on the pipe
or electrical)would help it to run as it should

this seems to be happening at the moment

watch this space

 

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So your using a different gague? If it's working then I guess it must have been pulsing. The rigid tube sounds like a good idea.
 

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If you have pulsing in a tube that continues, it's likely to be a resonance. The aim is to change things to put the resonant frequency of the system outside the range of the triggering frequencies, or their harmonics. Any change might do.
 
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