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Had my car on the rollers today, sorted a few vacuum hose leaks so runs much better. However my boost peaked at 19psi at 3k but then dropped to 11 at 6.3k. Which resuled in 240 ish bhp at flywheel. The question is should the boost drop off like this?.
As discussed many many times - YES - boost tails off towards the red line. On my setups for K24 with no wastegate tampering or other tweaks its ~1.4bar max in the mid range and ~0.8bar at the redline. Multiply that by 14.5 for psi. You are a bit low in the mid range.
Its hard to see your graph properly - but looks like a boost leak or its holding back in the mid range. What fuel are you using ?
Could be coil packs holding you back too - you wont necessarily detect misfires.
Could be MAF out of spec as well, but I'd get a proper boost leak check done first.
COmpression good ?
Spark plugs tight ?
Fuel pressure ? - what are the AFRs from your plot ?
COmpression test requires a cylinder compression gauge - bout 20 quid - insert to each spark plug hole (all plugs out and hall sender disconnected)... Then floor the throttle and crank the engine to build up pressure - you are looking for big differences acros the engine. Best done cold IMO...
Fuel pressure needs a special gauge as well - bit more expensive - maybe best done at a garage this one - it does indeed T into the fuel line... You'll want to see the right pressure (4bar) above whatever the manifold pressure is. So idling with 0.5bar vacuum you'll see ~3.5bar fuel pressure... Then with 1bar boost you should see 5bar fuel pressure... This tests the FPR is working.
AFR requires another special guage which can piggyback on your lambda probe in the downpipe, or use a test port further up the downpipe. Can't remember the thread required for a probe. Best checked by a specialist if you are new to this - rolling roads often do it - but I cant see it on your graph.
Again - boost is supposed to tail off - otherwise the turbo dies with heat exhaustion (unless its a monster modified turbo).
I still think air leak on the intake system is your problem... Just think that the pipework from MAF to the throttle body has to airtight - and that all the control tubes (narrow braided stuff) off the inlet to various other things also needs to be air tight... This is to ensure that the engine ingests all the air that it has measured and that it has correctly measured all of the air if you get my drift...
That or maybe a sick/tired MAF - tried another one yet ?
Paul
Originally posted by MarkT
@ S2central
I have been using super unleaded, 98 RON.
Sparkplugs were torqued on the day as a check due to them notoriously loosening and popping out.
How do you do compression test, that may be the next check?, oil pressure is 1.5bar when at hot idle.
Haven't checked fuel pressure,how would this be done, I presume a gauge plumbed into the fuel line somewhere.
AFR is that checked with the gas analyser up the exhaust, if so the results were perfect and the lamdba was working perfectly also
Could a weak waste gate spring cause the boost to tail off?
I must admit the sound of her on the rollers is awesome, when your in the chair you don't fully hear the noise!.
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