# Ca18det



## HachiRoku_UK (Dec 5, 2002)

Hi Guys, I am new to the 200SX and I have a question about it. I noticed an odd characteristic in the way the engine revs. The engine revs smoothly up to 4000rpm then suddenly the revs surge quickly to 5000rpm as though the clutch where slipping. The vehicle speed continues to build well and the boost doesn’t fall off. the revs will then settle around 5000rpm briefly before continuing smoothly on. This is not clutch slip as that has been replaced. There are some other points regarding boost pressure too but I can go into more detail if anyone is interested or can help maybe. For info the engine has a bleed valve and BOV.


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## Guest (Dec 7, 2002)

Give me all your mods, and go in more depth, then I shouldl be able to help.


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## HachiRoku_UK (Dec 5, 2002)

Hi, Thanks for your reply. As I said before I’m quite new to the 200 SX and bought it as a cheap project to experiment in tuning it. The engine is completely standard apart from a Diaphragm type blow off valve, a basic mechanical bleed valve and NGK-R (copper) cold range plugs. It also has a boost gauge. Before the bleed valve was opened the standard boost was measured at just 8psi max, which I thought odd, but accepted as I have seen many cars fall within 2 or 3psi either way of the factory stated boost. I used the bleed valve to raise the max boost to 10psi but I began to really notice the rev surge more. I found that if the boost is increased further, the surge occurs lower in the rev range. Otherwise the car seemed to run well at 10psi, it then blew its head gasket. I repaired this; while in the engine I found it good condition internally. I am sure the gasket failure is not related to the pressure question as the car had been stood for some time before I bought it. The inspection of the failed gasket seemed to indicate corrosion from the coolant water behind the gasket fire ring. The daily use I gave the car after its long vacation would have quickly acted on the corroded area of the gasket. I have seen similar failures in long stood Hachi’s I have worked on.
Additionally I have noticed that the boost gauge needle becomes quite erratic at max boost. I have since had reason to suspect the gauge I am using, which may explain the original 8psi reading too? I have a new gauge in front of me on the desk right now as I write, but a cracked rear disk has changed priority for fitting the new gauge. What this new gauge will tell me I don’t know, Ill wait to see. I suspect the old one was well full of shit.
The surge effect is only noticed in the higher gears (3rd to 5th); in 1st and 2nd I haven’t noticed the effect. However the engine has cut out around 5000rpm in 2nd gear on 2 occasions as if the FCD had cut in, but at only 10psi? I don’t know unless the current gauge turns out to be very wrong when I change it.
I hope you have some ideas for me,
Phil.


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## HachiRoku_UK (Dec 5, 2002)

It looks like the new clutch the car had fitted a while back, wasnt actually fitted..... Easy mistake for a guy selling to make I suppose... Anyway looks like it was nothing more than that. Thanks for the offer of help Killersilvia.


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