Boost cut? Ignition problem? I have know idea what is going on.

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Amontgomery

not so sad 10psi
Apr 1, 2008
166
0
0
Cleveland, MS
I went out for a ride last night and got on the gas twice, the first time the turbo spooled up fine, then at about 7 psi it shuttered hard once or twice, after that it went straight up to 11 psi or so. I had a shimmed turbo so that seemed normal. It had no boost cut at the higher levels of boost. But did have a CEL. I got home and diagnosed, code 34 as I posted yesterday.

Second ride last night, pulled EFI fuse for a minute and plugged it back in. Rode for a bit to warm the car up and did a pull. This time, no shutter but hit boost cut at higher boost. No CEL or codes. I figured it was just boost cut.

Today, I pulled the shims off of the wastegate actuator and went for a ride. Same old thing, let the car warm up then do a pull. Tonight shutters from 7 psi and wastegate opens fine but with the car shaking hard. This happens in first and second gear but when the car gets to third and about 80-100 which is going by very fast BTW the car is running perfectly, look at the boost gauge and it is pegged out around 11 psi or so, no shims just on its own. I know the wastegate opens because I revved the car standing beside it today and watched it open, about 3/4 of an inch of travel in the actuator rod so I am assuming it is opening all the way. The weird thing was even though it was boosting very high at the higher speeds/gears it was running perfectly smooth and pulling WAY harder than it was at lower speeds.

I am thinking it could be a sticking wastegate actuator but I watch it open when I stand beside the car and rev it with my hand.

I am also thinking it could be boost cut but it is coming in way to soon at almost stock boost pressures.

It could also be ignition related, the sparkplugs that are in the car are old according to the guy I bought my car from(Chris, gixxer750) so I am thinking that could be part of the problem.

It might also be worthy of note that the car stays revved up when it is in park after driving. I am thinking that might be some stickage in the linkage but I have no idea.

I also have a idea that it might be a Throttle Pos. Sensor going out, but the car is not throwing a code for anything at all.

Car info;
89 Supra Turbo
Divorced down pipe 3" all the way back w/o catalytic converters
mild port and polish rebuilt head
thick hks headgasket
6m crank and rebuilt bottom end
cone air filter conversion
 
A

Amontgomery

not so sad 10psi
Apr 1, 2008
166
0
0
Cleveland, MS
If it opens when I rev it by pushing the throttle linkage why does it stick when it does have load on the engine?

And wouldn't revving the engine produce enough pressure to spool up a turbo and in doing so also create enough pressure to open a wastegate?
 
Justin

Justin

Speakers?
Mar 31, 2005
1,699
0
0
40
Spokane, Wa
Amontgomery;1012702 said:
And wouldn't revving the engine produce enough pressure to spool up a turbo and in doing so also create enough pressure to open a wastegate?
Click to expand...

Absolutely not.
 
A

Amontgomery

not so sad 10psi
Apr 1, 2008
166
0
0
Cleveland, MS
So you are saying that revving an engine with no load on it whether in park or neutral should produce no more exhaust pressure than an engine idling? And in producing no more exhaust pressure would not spool a turbo or produce any boost at all.

Please explain the physics behind this.
 
A

Amontgomery

not so sad 10psi
Apr 1, 2008
166
0
0
Cleveland, MS
I will read up on it. Though it does seem to be counterintuitive.

Regardless, the wastegate actuator moves when pressure is applied via a hand pump with a guage at about 8-10psi as it should. So the hardware of the turbo system seems fine though I could be wrong.

I am curious as to why it smooths out at higher speed and higher gears. I would figure that the more load from the faster speed with air resistence, higher gears, ect. would make the problem worse not better.

And under half throttle it has the same shudder/blip just not a prolific. Right before it reaches the maximum boost that it will reach for the session that I am gassing on it( if I am only on it part of the way it will only reach 5 psi or so and the blip is at 3 or 4 psi, where if I am full throttle the blip is at 7 or 8 psi and maximum boost is about 9-10psi.)
 
GrimJack

GrimJack

Administrator
Dec 31, 1969
12,377
3
38
56
Richmond, BC, Canada
idriders.com
The fact that your RPM doesn't drop to where it should after driving leads me to believe that you have a leak in your intake tract somewhere. I'd suggest building a boost leak tester and finding the leak(s).
 
A

Amontgomery

not so sad 10psi
Apr 1, 2008
166
0
0
Cleveland, MS
I am replacing all of the intake piping in a week or so with aluminum hard piping to see if that will help the problem. I will be removing as many of the joints as possible and having the entire intercooler piping welded with the only joins being at the throttle body, inner fender, intercooler, intercooler, and turbo. At the same time I will be replacing the plugs and flushing the coolant system.
 
A

Amontgomery

not so sad 10psi
Apr 1, 2008
166
0
0
Cleveland, MS
Well I have eliminated the high idle from my list of problems. The idle control cable had come loose from its mount next to the throttle body. Just has the shutter at about 7psi or so, I watched today, it happened at 3500, 4000, 4500, then smoothed out before it shifted. Only in first and second gear though. Third gear feels like it has it but it is not nearly as pronounced as at lower speeds. Though this may be that the car is going fast enough that the air pressure on the outside of the car acts as a dampener making the shake less noticable.
 
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