flubyux2

iTrader: (1)

I've got a secret that I'll share with you. I am a stranger to rdx's but no stranger to factory forced-induction cars, specifically Japanese made.

Every forced induction car runs the risk of overboosting. Overboosting can be caused by numerous, uncontrolled and/or elemental variables. Mechanical and electrical failures or hiccups can result in overboosting. These hiccups can be either accidental or intentional. Accidental occurances typically happen due to a sequence of events. Intentional events of overboosting happen from things like the hondata reflash or external boost controllers or peripheralcomponents which allow more efficient operation of the turbo such as air filters, intake systems, down pipes and exhaust systems.

Overboosting results in a higher-than-intended manifold pressure. The calibration of the factory ECM uses a fuel and ignition timing advance
map (3d, in the x,y and z axis). These lookup tables dictate how much fuel and how much timing should be administered at any given rpm vs manifold pressure. Let's say that the x axis is rpm: 0-8000. The y-axis will be manifold pressure: -25in/Hg- 21psig (this is roughly a 2.5bar range, 1 down and 1.5 up). While the fuel map may go to 21psi, the fuel pump and injectors probably won't support the airflow volume. Conversley, the little turbo is likely well out of it's safe-operating range after 15psi. This is where an overboost protection limiter is necessary.

Acura has Implemented safe guard to prevent overboosting from damaging their vehicles. Going over the safe limits can cause lean conditions and high intake temperatures. These conditions cause detonation or uncontrolled propagation of the flame front. The flame doesn't start at the spark plug and/or doesn't travel at it's normal speed. If the intake charge reaches it's autoignition temp, a flame can start somehwere else in the cylinder, before the spark plug fires, and travel at more rapid speeds. If this happens, severe engine damage can occur. Engine failure is one option. I've seen enines that have produced 700hp (and capable of holding 1000hp) bend a connecting rod and blow a hole in both sides of the block.

Fuel cut is how you prevent this from happening. When the driving conditons or variables cause this to happen, the safe guard essentially shuts the engine for a split second. Since this usually only happens at high rpms (when peak load and boost are possible), a split second can be as many as 100 engine revolutions with Zero fuel, thus Zero power. People characterize this as "hitting a brick wall". It can sometimes be accompanied by a fireball or pop from the exhaust (in unrestricted systems) or a pop from the intake. The intake side noise isn't a backfire. Since this motor is direct injection, it's impossible for unspent fuel to exist in the intake tract, hence no "fire". What you are hearing is a rapid stop and redirection of charge air a full pressure exiting thru the airbox/filter.

Hope this clears up any concerns

flubyux2

iTrader: (1)

Edit: pertaining to the folks actually experiencing this annoyance, it's happening because all the varialbles are culminating at the same time. Boost is load dependant. Idle and cruise is lower load than towing and acclerating. The higher the rpm, the more boost is possible... And the opposite is true. One thing that's happening here is that and upshift from 1-2 gear is essentially forcing the engine with a 6700rpm, full-boost load down to a 5500 rpm with the same load causes the boost to increase. This results in a boost spike. This is when the fuel cut is employed. It's purely accidental and just the nature of turbocharged engines mated to automatic transmissions. Only time and experience from real world testing can give a designer info necessary to tune out this quirk. Fortunately, I already know what needs to be done: retard the timing during the upshifts. Maybe a reflash will become available that can combat this problem

princelybug

iTrader: (16)

Nice info! BTW, I sent you a PM.

MMike1981

the engine isnt direct injection.

cwepruk

Nice attempt to throw a whole bunch of useless knowledge out that doesn't pertain to the issue. The car isn't direct injected, the car doesn't overboost. It's not a fuel cut. Usually happens after a transmission shift and the boost dies down.

You actually think we all have overboosting problems?

cwepruk

Since I can't edit the above, the issue doesn't occur at full boost, doesn't occur at WOT and their is a bypass valve to vent excess pressure. Boost tapers off during the shift, and before the turbo hits full spool, it sputters.

MMike1981

what i was thinking as well, but you wrote it hahah

cwepruk

I could understand if this was datalogued by the guy or he was some Acura insider, but the post is speculation followed by a bunch of tangential tech.

My intial post came across a bit harsh, but I couldn't edit it so whatev.

wspy

And I could'nt be bothered to say anything on the "tech" shpeel either!

As you said ,... whatev ;-)