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Old 08-19-2004, 03:06 PM
Turbo Trans Am Turbo Trans Am is offline
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Default Boost problems

Hello everyone
I have read everywhere online that stock TTAs are supposed to run at 16.5 lbs. of boost, however, If I floor the gas in my car (3" Borla exhaust, 3" high flow cat, thrasher street chip, 9" k&n cone filter) TTA from a stop and keep the car at WOT, the boost will shoot to 16-18 and then drop down and hang in the 13-15 lb range through all the gears. Any clue as to what would cause this? The car had 55k miles on it and the turbo has never been rebuilt. The MAF pipe is bent a little bit going into the turbo due to over-tightening of hose-clamps. There is also oil on top of the intercooler by the side that goes into the throttlebody. Would a dirty intercooler & slightly bent MAF pipe cause this loss of boost? Is my car supposed to run at 16.5 lbs of boost at all times, or is it natural for it to just temporarily reach this figure and drop down a few pounds. I was told that the thrasher chip is supposed to make my car run at 18 lbs of boost, and that the Borla 3" exhaust with open baffle would probably cause an additional pound of boost. Anyone have a clue as to what is wrong?? I hope it's not time for a turbo re-build. How do you know if your turbo is bad? Thank you all for the help!
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Old 08-20-2004, 12:55 AM
Turbo Trans Am Turbo Trans Am is offline
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Default Re: Boost problems

I was having the same problem before I replaced the stock chip with a thrasher, so I doubt that is the issue. What are the pros of a manual boost control valve vs. an adjustable wastegate actuator? Any other ideas as to what could cause this? It almost sounds like a boost spike problem, except instead of spiking past stock boost settings & settling back down to normal, my boost spikes to stock setting and settles down to two or three pounds under normal. I appreciate everyone's help!
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Old 08-20-2004, 11:50 AM
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Question Re: Boost problems

Quote:
Originally Posted by Turbo Trans Am
Hello everyone
I have read everywhere online that stock TTAs are supposed to run at 16.5 lbs. of boost, however, If I floor the gas in my car (3" Borla exhaust, 3" high flow cat, thrasher street chip, 9" k&n cone filter) TTA from a stop and keep the car at WOT, the boost will shoot to 16-18 and then drop down and hang in the 13-15 lb range through all the gears. Any clue as to what would cause this?
The stock chip profile is set to have more boost in 1st and 2nd gears than 3rd and 4th. More in 3rd than in 4th, if you are really keeping track. So the behavior yor are seeing is not unusual. I would defer to somone familiar with the Thrasher programing to determine if they do the same thing.

Restrictions in the MAF pipe could be a problem for airflow. The higher flowing exhaust and cat could improve your peak boost levels. The K&N filter would as well. Detonation could cause the ECM to reduce your boost in severe cases. Are you monitoring detonation/knock or using a scan tool?
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Old 08-20-2004, 12:59 PM
Scott231 Scott231 is offline
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Exclamation Re: Boost problems

A manual bleeder valve....how Old School! The "problem" you are having is a combination of a 15+ year old spring in the wastegate actuator coupled with a high-flow cat that you are not supposed to be using with a Thrasher as those chips are for free-flowing exhaust sytems. The former however, is the bigger issue. Don't forget that you may be simply loosing boost cuz the ECM sees knock and is retarding timing.

As Scott Keller mentioned boost is highest in 1st and 2nd (however the stock chip does not know the difference, but the Thrasher does) with decreasing amounts in 3rd and 4th. The stock ECM has no way of knowing how much boost is being produced. Chips are designed however to run with a certain amount of boost that the user is in charge of attaining.

The stock TTA chip did allow for more boost than the stock GN chip because the TTA had the higher pressure fuel regulator. The weak spring you have in your stock actuator is allowing the actuator arm to move further than its engineers intended with the amount of pressure tha is being applied to it. Thrasher chips are not supposed to run at any exact boost pressure, rather the user is expected to have an adjustable wastegate actuator so that he can set it to acheieve the maximum amount of boost that he can run for the given level of octane he is running with his particluar Thrasher chip. The chip is designed to control the boost differential changes between gears, speed and time.

In your case all a manual bleeder valve would do is raise the entire boost curve in every gear. That is if you are seeing 18psi in lower gears and 15 in lower, the bleeder can get you to 20 and 17...still a 3-psi differential. Bleeder valves are just Band Aids to the real issue. You can get these bleeder valves at hardware stores for under $10 if you insist.
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Old 08-20-2004, 06:12 PM
Turbo Trans Am Turbo Trans Am is offline
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Default Re: Boost problems

The stock wastegate & actuator arm are on the car. Will getting an adjustable arm and making it shorter produce a different effect on the vehicle than installing a manual boost controller valve? The boost solenoid does have oil on & around it, to include where the hose leads off to the turbo & at the base of the solenoid. Is this an indication of a bad solenoid? What causes this oil leakage? Thanks for the info guys. I admit that I absolutely have a limited knowledge on these cars. Ttype6, I didn't mean to offend you in dismissing your solution. I thought you were implying that the new chip was causing problems. I really appreciate all the help, and I am learning a wealth of valuable information from you all.
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Old 08-21-2004, 02:47 PM
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Default Re: Boost problems

Quote:
Originally Posted by Ttype6
There is, also, no good reason not to buy an adjustable wastegate actuator. A manual boost valve and an adjustable actuator will do the same thing,make more boost. The boost valve becomes nessesary when you want to make boost pressures above 20 psi,so you do'nt need that yet.
I whole heartedly agree with the first sentence. I thought the TTAs already had one, but I may be mistaken. Regardless, having one in my opinion basically negates the need for an "adjustable boost valve". I've done without an aftermarket adjustable boost valve since buying my T, (13+ years) go reasonably fast, and things are fine. Sometimes simplicity is good. More complication begets more possibility of problems sometimes. *shrug* You do not have ****pit adjustability by using one, however.

I disagree sligtly with the "pressures above 20 PSI" comment as well. First, a stock turbo is out of its sweet spot above that point anyway. It become very inefficient; just heating the air greatly. And secondly, a high boost actuator (tighter spring) makes 20+ PSI no problem without a bleed valve, Grainger valve, or what have you. The same can be accomplished by adding an external spring hooked to the wastegate arm and a hole drilled in the actuator mount for extra tension, but doing it right is OK, too.
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Old 08-24-2004, 11:01 AM
Scott231 Scott231 is offline
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Default Re: Boost problems

Well, we are kinda moving away from the original questions 1) Why is my boost dropping, 2) Does a dirty intercooler cause the drop, 3) Is it supposed to drop a few pounds, and 4) is my turbo bad?

#1 & #3 answers are that the engine is supposed to run less boost in 3rd and 4th AND if the ECM senses engine knock it will retard the timing and boost.

#2 is No.

#4 is un-answerable as written. A bad turbo would not be the cause of a boost drop. However, your statement that there is oil on the boost solenoid could be an issue coming from multiple sources. The oil could be leaking out of the turbo and getting on the solenoid (if so, the intercooler will also have oil in the bottom of it - clean it out with some gasoline) or it could very well be blow-by from our breathers (a sign of rings or valve guides letting oil into the combustion chambers...some of which is normal).

However, we have not been told if the boost drop starts in 1st, 2nd or 3rd gear so it is hard to ascertain what boost problem you are referring to.
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