need some insight into whats happening with my engine. background story is i was planning to get the car remapped and a few weeks before i had a coolant leak. turns out it was the water pipe that runs off to the throttle body so we just did the delete mod as it was leaking at the t junction of the pipe. so all good again and i book the map session. car made 339 bhp (bug sti) and mapper said it went well. so i get the car home and im pootling along to the shops next day and steam pours out the bonnet. wtf! so i pull over and theres coolant pi$$ing out onto the block from somewhere. so i nurse car home and to garage next day. mechanic phones to say theres another coolant leak this time from the pipe under the header tank which runs under the inlet and joins at the other side of the block. so inlet manifold off etc to get to it. so i get the car back yesterday and seems to be all ok. i did notice the heaters wre not blowing as hot as before but the water temp seemed to be lower than before so i put that down to the fresh coolant change which was done after the pipe repair. one thing i did notice is my boost gauge is not working (defi) so was planning to ask mechanic about that one. i cant see any obvious vac pipes not connected tho. so i take the car for a blast round some local country roads to blow out the cobwebs and see how the new power feels. car sems to pull well and all seems ok. have a slow run home to let things cool down and when i pull up and sit idling while i gather up my house keys etc i immediately notice the oil pressure on the defi is bouncing about very eratically! its never done this since i have owned the car. it also feels like its hovering on the verge of cutting out /stalling. the revs are not fluctuating at all though and sit at a constant 5-600 rpm as usual. i have checked the oil level and its fine. there is no knocking or clunking noises from the engine and when accelerating the pressure is normal at 6 bar and it pulls ok. there is no oil in the water or water in the oil that i can see and its not overheating. easy thing to check is the oil pressure switch but beyond that what could be going on? a mechanical gauge fitted where the switch is should give a reading of the oil pressure? seems strange the revs are not fluctuating along with the pressure gauge movements? any ideas would be helpful as im running out of money to keep throwing at the car and if its something fatal it might be time to move on regarding this car. thanks for looking.

 

Either you have a faulty sender, However if its jumping like that I'd have suggested its drawing air into the lubrication system. The back plate screws on the oil pumps have been known to come loose

 

update on this, there is a vac pipe off. its on the inlet manifold. im guessing its where the gauge should pipe to. when i put my finger over it the engine seems to speed up and seems to be ticking over normally. there is another loose vac pipe there as well so im guessing the mechanic has piped it up wrong. need to find some pics of a gauge install so i can see how it should pipe up. fingers crossed it is just this thats wrong.

 

That would make sense as to why the boost gauge isn't working. But odd that the revs were not fluctuating in your first post which is why I suggested the oil pump screws. Not too worry I hope its an easy fix for you