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poulrais

poulrais

Well-known member
Joined
Sep 8, 2006
Location
Quebec, CAN
Hi,

There's a weird thing happening on my 740 Turbo (1991)... It's totally stock but I'm running an MBC on the turbo. First time I start in the morning I will get steady boost (15-18 PSI) without any problem. If I do 3 or 4 hard acceleration runs then the boost will not hold as well and I then get a max of around 8-9 PSI. If I then hit the highway and cruise at 75 mph for awhile, not going in the positive of my boost gauge, I can get full boost for again 2 or 3 accelerations and again after that boost will not hold. Any idea about what could be causing this behavior? I'm thinking my turbocharger is about to give but could this be a wastegate problem. Is there something else regulating boost on these cars? I'm using 94 octane gas by the way.

Thanks!
 
+1, take a look at the wastegate.

Honestly, if your car is 100% stock, I would be very worried about running 15 to 18 PSI with the stock tune. It is only a matter of time before something breaks.
 
Well the car has 335,000 kilometers on the odo so I guess it's ok if something breaks... I'll probably install a adjustable FP regulator to boost the fuel pressure a bit but it's not pinging at 15 -18 PSI on 94 octane for now. Anyway, if it breaks, it'll be easier to pass the wifee's hold on dought for a rebuild!!!:-P:-D
 
And thanks for the pointers on what could be the cause. I'll take a look at the wastegate tonight. By the way, sorry for my ignorance but why would the actuator be so heat sensitive? Is there a diaphragm in there that is giving up? Can this be repaired or should I install another actuator?
 
also check for cracks inside the turbo around the wastegate hole, and check for cracks in the exhaust manifold (usually at the backside that faces the engine block, where the 4 runners come together.
 
Is the CBV something that can be bypassed of fooled? I also noticed a small amount of coolant coming out between the turbo and manifold's flange when I start the engine cold. Guess the bearings sleeves must be worn. Pretty sure it's not a HG issue since I changed it not so long ago and there's not coolant in the oil or vice-versa.
 
2fast242gt said:
if you still have a stock turbo.. 15psi is doing nothing with the 13c.
Click to expand...

Uh... What do you mean exactly? I understand I'm pushing this turbo quite hard at 15-18 PSI and I would understand if the pressure was coming down all the time because of turbocharger wear but it does push a lot of air sometimes and somewhat dies after a fews hard accelerations... I just want this one to die and be certain it's dead before going for an upgrade.
 
yeah, keep it at a little less then 1 bar duder.

that tiny little hairdryer is superheating the charge.
 
Well I would believe this could be the cause but it use to deliver the boost all the time... Could this thing be running hotter than it use to? I'll also check the intercooler for it could still be full of sh.. from the last blown head gasket. I know this must be somewhere is this forum but I feel a little lazy so what is the best (and cheapest) turbocharger upgrade for these cars?
 
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