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Can't build boost

897 Views 8 Replies 6 Participants Last post by  tpabayflyer
When I powerbrake, car only builds 3 lbs. of boost and i'm almost at WOT. I'm looking at cracked headers as possible problem. ANything else i should check out? Does the stock converter limit how much boost I can build?

87 GN Hardtop~Stock motor, Mease stock intercooler w/Duttweiler big neck,stock intake, stock tb and plenum, TE51 w/.63 housing, stock D5, MSD 50's, THDP, ATR 3" dual exhaust, big mouth cold air inducition, SMC alchy injection and egt gauge, MM boost command, PTE remote oiling system, Walboro 340 hotwired, 10 mm Magnecor wires, AC R43 plugs @.035 Adjustable regulator, ATR 3" maf pipe, B&M tranny cooler, Deep aluminum tranny pan, Dynotech shift kit, scanmaster 2.1, factory alarm, 21* Testa alchy chip, dual airbags, vdo gauges, autometer boost gauge, front braces and rear seat brace, Bilstein shocks, more mods to come
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Whats your line-off fuel pressure, and what kind of headers do you have? Whats your alky turn-on point, and what kind /size of tires do you have?

Also, it seems like you should have about a 3000RPM stall with that combo.

'87 T .030 overbore/ 240 cam/ heads port/ polish/ all 3in. pipes (exh and int)inc. MAF/ j&e pistons/ 42.5lb inj. +7th inj./ TE44/ Precision Frontmount/ houston DP/ METCO lower control arms/ and alot of other stuff I didn't think of /11.5in M/T's/ @ 21.5psi best ET ??.?? @ ???.??
Also, what were your O2's reading while spooling?
I hear this all the time about headers causing this problem' I dont beleave it possible with just a cracked header I think there would have to be a hole in it' a big hole to cause boost to drop that low, Both of mine had numerious cracks & I never had a boost control problem, I would look at the actuator & wastegate & make sure they are working properly & all vac hoses are intact & connected right first. I would also ck the turbo blades & shaft esp with that TE51.

To hell with 12's Im going for the 11's!

Keith Davis---
2001 Ultra Harley Davidson
93 1500 Cheby PU
72 Cheby 4x4
98 Monti Carlo LS
99 Grand Am
Astroroof, DigDash' TTA crank, Ported polished heads & intake' Jay's 62mm T/body & upper' 979springs" Weber 206 206 hyd cam" Manly SS valves, Steel center mains' PTE 51 Turbo, THDP" Postons headers, Hooker comp. mufflers' T.C. Orange stripe conv. SMC alky,Boost command, Scanmaster2, MSD50 inj, JL Chips" V4 IC' LT1 MAF & Translator' Nitto DR's 275/50/15, All the braces, All gauges VDO.
12.8 @ 102 is with stock setup no times for new setup yet.

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I agree with fast86 (and Elvis) on the actuator. Seems there are a few problems associated with the THDP. Perhaps a call to TH would be wise.

I got to the point where the boost dropped a pound a day until I was left with 5 psi. Although rare, it was the convertor that was plugged up. (A Postons hi-flow unit) It was from running too rich, that caused it-I believe.

Theree is a way to check exhaust pressure by going into the 0-2 bung with a guage. I've forgotten what the back pressure should be...sorry.
Is this a recent problem? When did it start? After adding a new turbo?

Pop off the THDP from the turbo and look at the carbon patch on the wastegate puck. The puck should be perfectly centered on the wastegate hole, so the exhaust residue should tell the tale. There was a run of PTE .63 exhaust housing back in the day that were off. I had one and the car couldn't get out of it's own way. Basically, the puck wasn't sealing off the wastegate hole, even when closed.

As for the header cracks.. yes they can cause slow spool if you are using a 'conventional' chip. If the O2 sensor doesn't get an accurate reading because air is being sucked in from a cracked header, then the ECM is going to add fuel because it is sensing a lean condidtion. Add fuel when you don't need it and you will have slow spool.


'87 GN - Stock Block, Stock Cam, Stock Turbo, Stock Heads, V4, MSD50's, TH DP, JayJackson 62mm TB, 16position MaxEffort Chip. 3680# with Driver
11.92 @ 111.77mph

'87 Mazda RX-7 w/GN Powerplant
12.37 @ 122.26 MPH
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Mr. T, I think my lin-off pressure is 43-44 but i don't trust the accuracy of the fuel rail gauge so I'll probably replace it. Still got the stock headers that probably are cracking but don't know how to check if its really cracked. alky turn on is 12 lbs. I have BFG radials(they suck) 255/60's and 225/60's up front. I know i need a 3000 stall converter but hard to get cash right now
. Didn't check o2's while brake boosting. Gonna have to do it again and I'll let you know. How do I check the wastegate and actuator to see if they are bad? What about boost lines? when I go check the blades and shaft what should I look for to tell they are bad?
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I am in the same boat.. all I get now is 13psi boost.... what is the deal??? it was 15-16 not too long ago.. I have a 17psi chip and I also adjusted the W/G actuator rod and it made no difference in total boost, just spun the turbo faster at lower rpm....I'm thinking a leak in the intercooler??? I have a 112K mile 87 GN...my hoses look kinda crappy so maybe I will replace them.. TBF
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