North American Turbocoupe Organization



Too much boost with stock BCS
Qwertys Offline
Senior Member
#1
After doing a mod that Walsted suggested (removing the mesh in the stock airbox). and putting the vacuum hoses to how they should be with a FMIC installed, i went for a little drive.well, it did boost quite well, perhaps a little too much. it very quickly hit 18 PSI and the overboost buzzer went off. that thing is loud, and scared the crap outa me. luckily i did not hear any detonation.
the problem is, i have the stock BCS installed, it shouldn't be getting that kind of boost, should it? could the BCS be broken? whats the best way to tell?
'85 TC BPV and Ford FMIC
'88 TC Kirban AFPR, Autometer Boost, FP and A/R Gauge, 8.8 to 4.10 rear, Walboro 255lph Fuel pump, Garrett GT3071R T3/T4 Dual Ball bearing Turbo, Custom AWIC.
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oldraven Offline
Senior Member
#2
What was this about vacum lines again? O_o

I've got to try that.
I'd like to think my life has a soundtrack, and it sounds just like the white album.

1987 Turbo Coupe, 5-spd. Candy Apple Red w/ Charcoal Smoke Accents, k&n drop in, 2.5" duals. Stirring from her winter slumber.

http://www.cardomain.com/id/oldraven

http://www.cardomain.com/id/doasa
http://www.cardomain.com/id/jeepishltd

CAW!!
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Gregg Offline
Senior Member
#3
Too much boost???? What's that?
Gregg
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Keith Nubel Offline
Posting Freak
#4
Did you move the vacuum hoses to the tapping that's after the intercooler in the tube going to the throttle body? I relocated mine to the stock position because it over boosted. Just curious.

------------------
85.5 TC 5 speed, Ranger Roller cam, 3" exhaust system, manual boost valve, large VAM, SVO PE computer, front mount Motorsport intercooler & sport grille, ported upper and lower intakes,flow matched injectors, ported E6 manifold, 245/45/17 wheels & Tires,140 mph speedo,Motorsport lowering springs, under restoration
1985 TC
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Qwertys Offline
Senior Member
#5
thanks keith, i might try that. i figured the vac line was after the IC because it allows the IC to pressurize fully before it started limiting boost. i guess the IC hoses are too restrictive and allow too much boost to enter before it gets back to the WGA.
'85 TC BPV and Ford FMIC
'88 TC Kirban AFPR, Autometer Boost, FP and A/R Gauge, 8.8 to 4.10 rear, Walboro 255lph Fuel pump, Garrett GT3071R T3/T4 Dual Ball bearing Turbo, Custom AWIC.
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Walsted Offline
Posting Freak
#6
BCS stuck open = 15-16 psi

BCS stuck closed = 10psi

18psi = something else going on. I don't know how you have your lines set up now, but if your wastegate, boost gauge, and boost warning buzzer are getting their readings from a vastly different source, (such as one or two pre-intercooler and one or two post-intercooler,) that could be the cause. In your shoes, I would make sure that everything is getting a reading after the intercooler, since that is what matters.

Hope this helps.

(Edit for spelling)

[This message has been edited by Walsted (edited 05-12-2004).]
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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Qwertys Offline
Senior Member
#7
unfortuantly, i dont think i can have it all hooked up post-intercooler. on the FMIC install directions, the vacuum tree gets its pressure from pre-intercooler with a line going from the inlet elbow, to the outlet elbow, then to the vacuum tree. the BCS is supposed to get its pressure Post intercooler.

there is a metal line going from the inlet to outlet, so i dont think i can replace that. the boost warning buzzer is right next to the EGR solonoid right?
you think it was just the gauge seeing the surge?
'85 TC BPV and Ford FMIC
'88 TC Kirban AFPR, Autometer Boost, FP and A/R Gauge, 8.8 to 4.10 rear, Walboro 255lph Fuel pump, Garrett GT3071R T3/T4 Dual Ball bearing Turbo, Custom AWIC.
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Walsted Offline
Posting Freak
#8
The boost warning buzzer IS right next to the EGR solenoid. You are right.

I would say that all lines, even metal ones, can be rerouted, but this is California. My smog inspectors may not look at it, (they checked condition of the lines real closely last time, but not routing, from what I saw,) but your's might check both. So, given that, I would just dis(regard/connect) the buzzer, especially if you didn't hear detonation or experience a decrease in accelleration(sp?) due to the knock sensor kicking in.

Hope this helps

------------------
Mike Walsted - NATO member
1986 5-speed TurboCoupe and 1985 5-speed XR7
Mike Walsted - Sold my 1986 5-speed TurboCoupe
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Qwertys Offline
Senior Member
#9
actually, when i saw the boost gauge go from 15 to 18, there was another good jump in speed, quite noticable...
I think what i might do, is find the line that goes to the boost guage, and hook that line, solo, to the post intercooler line, or perhaps i could 'T' it to the Overboost Buzzer.
I looked into Aftermarket boost gauges, and the clerk said 60$... if it was like 20-30$ that'd be more reasonable.
'85 TC BPV and Ford FMIC
'88 TC Kirban AFPR, Autometer Boost, FP and A/R Gauge, 8.8 to 4.10 rear, Walboro 255lph Fuel pump, Garrett GT3071R T3/T4 Dual Ball bearing Turbo, Custom AWIC.
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Pete D Offline
Administrator
#10
In stock form, the vacuum tree is fed by the big line coming from the fitting on the top front of the upper intake. This is post intercooler. In turn the OB buzzer and EGR are fed from the tree and see "net" boost. The stock boost gauge is also fed off the vacuum tree.

There is no reason you can't "T" off devices from the vac tree ports

Quote:unfortuantly, i dont think i can have it all hooked up post-intercooler. on the FMIC install directions, the vacuum tree gets
its pressure from pre-intercooler with a line going from the inlet elbow, to the outlet elbow, then to the vacuum tree. the BCS is supposed to get its pressure Post intercooler.

That is not the source for the vacuum tree. That is part of the supplemental vacuum for the speed control. The vacuum tree is sourced ONLY from the upper intake.

In contrast the stock BCS gets it's source from the compressor outlet )pre intercooler)
Pete Dunham


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