North American Turbocoupe Organization



Help diagnosing poor boost (8 PSI) '88 - 5-Speed
TgrPrl Offline
Member
#1
I have a hunch, bear with me b/c I'm doing my best to be somewhat intelligent without having the same mechanical skilll as y'all. I haven't been able to get into the turbo yet to diagnose if that is in need of TLC, but I observed an exhaust leak at the coupling between where the pipes split and the cat. Makes sense to me that this is what is causing the boost to be about 8 max, right?

If there is not a relationship here, can someone instruct me on the best way to get at the turbo. I loosened the intercooler but am afraid if I get it off then I'm not going to be able to get the bottom boot back on.
1988 Black TC - Stock for now.
155K on the odometer.
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Bill S. Offline
Senior Member
#2
An exhaust leak anywhere after the turbo shouldn't hurt boost (if its a big enough leak it actually might help Smile )

The exhaust pressure from the engine is what spins the turbo's turbine (which spins the compressor wheel to pressurize the intake track). If there is a leak before the turbo (would be between the head and the manifold or the manifold and the turbo) or in the wastegate then some of the exhaust would not be pushed through the turbo resulting in lower performance.
Theoretically you could just dump the exhaust directly after turbo with only positive effects because the engine doesn't have to push the exhaust alllllll the way down allllll that tubing to the back of the car.

The bottom coupler isn't that hard to get back on just take your time. It may take a few attempts to get it seated properly but nothing crazy.

Is your car an automatic? They maxed out at 10 psi if I'm not mistaken. If you have a manual and your boost control solenoid isn't working right that could cause a lack of boost above 10 psi also.

Also are you reading this from the stock gauge? those gauges aren't always the most accurate (the xr7 i have is reading 2psi right now... there is no engine in it)

I hope this helps Smile good luck
'88 TC T5
'85 XR7 Roller
Mods on hold pending swap.
Stinger header & mBC on shelf
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TgrPrl Offline
Member
#3
Thanks Bill. The car is standard and I am reading off the stock gauge.

Could you instruct me on how to check the boost control seleniud? You had to know that would be the next question! :-) thanks in advance.
1988 Black TC - Stock for now.
155K on the odometer.
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Bill S. Offline
Senior Member
#4
the solenoid is the black puck on the passenger's side by the IRCM and air filter box. It has two vac lines and a 2 wire electrical connector.

I just thought of something else... are you running premium or regular fuel? the computer should only run 10 psi with the switch in the reg. position...


First I'd run the codes, that will give you an idea if the computer thinks the solenoid is connected. I'd also check to make sure all of the vac lines that are connected to the turbo/wastegate/solenoid (that general area) are intact.

Another thing that you might want to check for is boost leaks. The couplers between the turbo and intercooler and throttle body can develop cracks that are hard to see. You might want to pull the intercooler off (really not that bad) and make sure everything is in ship shape.

Did the car ever get further into the boost? is this a recent thing? is this every gear or just some?
'88 TC T5
'85 XR7 Roller
Mods on hold pending swap.
Stinger header & mBC on shelf
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TgrPrl Offline
Member
#5
Thanks. I am running premium with the premium switch on. The boost issue is the same across all gears. I do recall it getting closer to 15 prior to being stored for nearly 10 years (with annual starting to help keep things in check).

I'm going to print out your feedback and take it to my friend who has a shop and can help me try to isolate this.
1988 Black TC - Stock for now.
155K on the odometer.
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ridgeback Offline
Member
#6
sounds like my bird. I took it out of retirement because I was short on a car and it seemed to run fine but week in the boost with an occasional jerking while in boost. I started simple and changed the cap & rotor (it needed it anyways), adjusted the timing and WOW....I haven't been able to spin the tires like that in years!!!!! Unfortunately, the next day it died on me...something not right with the distributor or something. misfires like crazy.... oh well back to the forums to solve my problem.
Ron

Black 87 TC, 2nd owner since [email protected], [email protected]
Current Mods: Gillis valve @18psi. K&N Cone. Removed AC components, New: Esslinger Aux. Shaft, Seals, Melling Oil Pump, Heater core. Ranger cam & rollers, new tower bearings, Walbro 255 fuel pump
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TgrPrl Offline
Member
#7
Bill S - you are right - it is the boost override selenoid. Now I have to hunt for one of those.
1988 Black TC - Stock for now.
155K on the odometer.
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Cerebral Offline
Senior Member
#8
If you mean the boost control solenoid is bad, simply get an aftermarket one. U cant find the stock one, and you can buy an adjustable one off ebay for 20 bucks. I have one and it works great. Plus you can set the boost to whatever you want.
1987 Automatic TC- parts car

1987 5 Speed TC, K&N on Vam,Boost controller, T3, Bob's Log, Stinger 3 inch exhaust with Magnaflow, FMIC, Forge Dual Piston B.O.V., Ranger Roller, Esslinger Adjustable Pulley, Boport Drop in Valve Springs, Pyro Pete Clutch
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Pete D Offline
Administrator
#9
Tgrprl
What problem did you find with the stock boost conroller?

the original boost control solenoids (bcs) are obsolete. You can probably find a used original, as lots of people go to aftermarket boost controllers. Most of the stock ones have become brittle and it can be easy to break them,especially where the hoses connect.

The advantage of aftermarket controllers is they are adjustable allowing you to dial in more boost than the stock setup would give you. You can also dial in boost levels inbetween the min and max levels of the stock bcs. There are several brands and prices can vary between $20 to a few hundred.
I'm partial to the Gillis valves, www.boostvalve.com Not the cheapest but very reasonable and they come as complete kits with complete instructions.

There are some relatively cheap ways to raise the boost level but the adjustability isn't there.
Pete Dunham


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TgrPrl Offline
Member
#10
I didn't find it Pete - my mechanic did the trouble shooting for me. His shop software had some codes that figured out the waste gates are working properly etc, so it is likely this he said.
1988 Black TC - Stock for now.
155K on the odometer.
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