North American Turbocoupe Organization



Can't Boost past 12psi
TCLover82 Offline
Member
#1
I recently deleted my stock BCS to try and get more boost, (vac line hooked straight to the barb on the turbo inlet), and I still can only boost to 12psi. I understand the the stock IHI unit is good up to 17psi. What exactly is holding me back from getting the other 5 psi? Some sort of vacuum bottleneck or something???
'88 Thunderbird Turbo Coupe - 120K miles, 99% Rust-Free, 351W/AODE Swap coming soon!
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Pete D Offline
Administrator
#2
Try this: This is a cheap, easy method that still feeds a signal to the WGA so that the turbo doesn't over boost.
Disconnect the two lines that go to the stock (broken) BCS from the BCS. Leave the other ends of those hoses where they are. Connect those two disconnected ends together using a blue electrical butt splice connector. This will give you around 16-17 psi of boost max and insure that there is a boost signal going to the WGA.

quote:Alright, i just took off the lines going the BCS and capped them both. The car is still overboosting. The idle is much much better now.

What you have there means there is no boost signal going to the WGA, so it's going to overboost. It does, however, eliminate the leaking stock BCS, so the car should idle better.
Do what 4cammer72 and I described and all will be good, unless the WG truely isn't operating. You won't know until you do what we described
Pete Dunham


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TCLover82 Offline
Member
#3
That is exactly what I did. Only I used a new piece of hose to connect them directly, instead of with the original lines. The ends of the original Vac lines went to the barb on the top of the turbo inlet, and to a brass L shaped piece on the side of the turbo, which then went from there under the turbo to the WGA. Now they are all connected together. Vac Barb>Brass Piece>WGA. Wastegate seems to be working fine, as it only boosts to 5 psi at 1/4 to 1/2 throttle, never seen it overboost even once.
'88 Thunderbird Turbo Coupe - 120K miles, 99% Rust-Free, 351W/AODE Swap coming soon!
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Pete D Offline
Administrator
#4
What gauge are you using to get boost readings? The stock gauge may not be accurate.

Make sure the turbo shaft is in good condition.
Have you taken the compressor inlet tube off the compressor (2 fasteners) and checked the turbo shaft for side and end play. There should be almost no perceptible side play and end play. Do the blades touch the housing or back plate when checking for play? Are there any witness marks on the compressor housing?

Take the boost line hose off the WGA diaphram. Using a regulated pressure of 9.5 psi applied to the diaphram, watch the rod to the WG. It should only move a few thousandths of an inch if it moves any further, the spring is weak and allowing the WG to open early (too much) which slows the buildup of boost
Pete Dunham


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TCLover82 Offline
Member
#5
Ok, I will check all those things out asap, and report back.
'88 Thunderbird Turbo Coupe - 120K miles, 99% Rust-Free, 351W/AODE Swap coming soon!
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Not B Anymore Offline
Administrator
#6
Does it feel like it's only boosting to 12psi?

Like Pete said... Stock gauge could be off or the hose from the vac tree to the gauge could be cracked & leaking. Try to get a hold of an aftermarket gauge for testing.

Wouldn't hurt to pressure test the intake to see of you have a leak opening up under boost.
Brian Leavitt
'86 TC 5-Speed -- MS2x w/COP | 83 lb. injectors | T3/T4 50 Trim Stage 3 .63AR | Full 3" Exhaust - No Cat | Motorsport FMIC | Ranger Roller | Ported E6 | Walbro 255HP | Kirban | 20psi | 120-amp 3G | 8.8" 3.55 rear | '03 Cobra Wheels
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KY Bird Offline
Member
#7
About two years ago I had a throttle position sensor that was starting to go bad, causing me to lose several pounds of boost. You may want to run the codes to see if anything comes up.

Bill
300K and still ticking

'88 TC Silver (Titanium Frost) Mach One, 5-speed, K&N, 14* timing, dual 2.5" exhaust, tripminder, the rest is stock
'87 TC Parts Car RIP
'03 Escape, Killed in Action
'08 Taurus X Baby Mover
'89 Buick Reatta
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TurboCoupe50 Offline
Posting Freak
#8
If your TC is automatic, 12psi is all you're going to get(been there done that)... Orifice in the fitting is different so allows a quicker bleed off time vs the 5 speed...
1988 Turbo Coupe331 AOD

1972 Comet GT

1969 Fairlane Cobra 428CJ 4-Speed
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TCLover82 Offline
Member
#9
^ I think this man has hit the nail square on the head. As not only had I suspected the Brass Fitting before, a quick search on Turbo Ford revealed that others with 88 Auto TC's have had the same problem, and that changing the Brass Fitting to one from an older T3 car allowed the boost to rise up to 17-20psi afterward. Wonder if porting the stock fitting would work? If not, looks like I'll be searching the local junkyards for a T3 equipped car.

This is on my stock gauge btw. Feels likes it's only boosting to 10psi, gauge says 12.
'88 Thunderbird Turbo Coupe - 120K miles, 99% Rust-Free, 351W/AODE Swap coming soon!
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