boost problem

[nickkrmr]

i seem to be having trouble with my turbo, it will boost fine and once i get up to 4 or 5 rpms it will die out and make a big bang noise then it will pick back up, it doesnt do it every time but does it alot, any ideas what the problem, could be, i have a small boost controller, when i take it off, the boost goes up to 14lbs but i feel no boost at all, when i have it one, i feel the boost in the car, any help would be apperciated thanks

[Indiana]

Stock boost gauge isn't actual pressure its ECU calculated from the MAF and other sensors and its just a guess.

You might have bad spark plugs or the wrong plugs, the vac. adv. might be bad, the injector clips dirty, the ignition timing off or it might just have too much boost its detonating and the knock sensor is saving your motor you need to give some more details but here's some links for you so you'll know how the stock fuel system works.

 

http://www.b2600turbo.com/Spark%20Plugs.htm

http://www.b2600turbo.com/distributorvacuum_advance_unit.htm

http://www.b2600turbo.com/ECI%20System.htm

[Caliber308]

i seem to be having trouble with my turbo, it will boost fine and once i get up to 4 or 5 rpms it will die out and make a big bang noise then it will pick back up

 

Is it a "BIG BANG" noise, or just a "Slight" miss ?? Tell us a little more about your car.What year, Stock? If not,Turbo and Modifications.

 

CALIBER 308

Edited September 22, 2010 by Caliber308

[nickkrmr]

its usually sounds like a miss and a lose of power and then it comes back, its an 89 starion, all stock, new injectors clips, oem spark, i replaced almost everything on the engine, ,

[Wolf87Conquest]

If you are hearing a slight "pop" and then it seems to lose power...then pick back up, it sounds to me the wastegate is opening. If the fuel doesn't have enough octane...it'll "pop" the wastegate early. It's why there is a wastegate and needs to function properly (sounds like yours does) so when boost pressure rises too high for the engine...it "pops' diverting exhaust pressure away from the turbo.

Remember...even as the engine has a low static compression ratio...the turbo boost pressure artificially raises comp ratio. Every pound of boost is a pound above normal atmospheric pressure....so, once pressure gets above what the engine can handle, usually controlled by a set pressure on the wastegate, or from computer signal. If computer signal, the sensors play a role in what the computer "sees" and acts accordingly.

[nickkrmr]

so how do i fix this, do i put a boost controller on and lower the boost or is there another way to fix it, thanks for the info also,

[Wolf87Conquest]

I'm not sure of what it is you want to do..is it get more boost? Running around 5K RPM is getting close to redline.

Think about this...you have a 2.6 liter (about 155 ci) pretty much half a Chrysler corp. 318 and giving close to 200 hp. (stock 318 gives 150 on a good day). There is a limit to how much boost this engine can safely handle. Higher boost will shorten engine life as it will put more stress on crank and rods, not to mention the head is aluminum and is the top of the combustion chambers.

Wastegates are there for that very reason...to limit how much boost the engine will get. Like I mentioned before...the wastegate "pops" when that limit is reached. It can be a set pressure on the wastegate, or controlled by the computer. If computer control...the sensors are the computer's "eyes" and that feedback from sensors are what governs the computer's actions.

Higher octane fuel should allow for higher boost levels..at least in theory. Higher boost also means higher compression ratios..pressure has to go somewhere. An example...you build a "race ready" engine with a static comp ratio of 12/1...it would not run on regular pump gas...the octane is too low. For that comp ratio, octane would need to be around 100 or higher. Then you decide to put a supercharger on it...further raising comp ratio...so an octane of say 110 or more would be needed.

[Indiana]

http://www.kb-silvol...on=read&A_id=57

 

That chart will tell that for stock pistons and boost pressure of 20psi your effective compression ratio is 16.2:1 and that's on pump premium fuel.

 

That's not so bad IF some other things are considered and they go hand in hand. Chosing the correct spark plug and its heat range is one and then there is the one that makes the most difference, its the one that you are stuck with no matter what and is another reason for an MPI swap and what costs the big bucks to get tuned by someone EXPERIENCED and that's the total ignition timing. Your distributor is limited as to what it can do and the intercooled dist. allows a higher mechanical advance then a vac. adv. unit retard max of 7degrees. For higher boost you can have added safety by using a non intercooled distributor that has less possible total timing. The vac. adv. units are the same. The ignition maps in the MPI software you choose is where all that magic happens not in those fuel tables. The fuel tables are there just to maintain the end air fuel ratio you want but for changing boost conditions and to max out power all through the range that's where it takes time. You need to have EGTs to measure this and this is where experience and paying for it won't cost you your engine. You might think that stock pistons suck but this is NOT TRUE AT ALL. Having a lower CR to start with allows you a larger tuning window and higher possible boost pressures. Some of those quick ETs from those famous cars are using lower CR pistons and its for a reason. Someone tells you that your motor running 20psi boost is a bad thing, you'll hear this all the time from a few on here but there's a big difference if your base CR is at 8.5:1 with that same boost pressure. You'll end up at 19.8:1 and now you are where its more important for things like detonation to not happen, to not lean out for any reason, to not rev too high or pull too long so that combustion temperatures are slowly raising your coolant temperature and its happening way before that slow to react coolant temp. sensor or gauge sensor can show you. This is when preignition happens and pistons melt and you never knew why. Its not about the boost pressure its all about ignition.

Edited December 16, 2010 by Indiana