North American Turbocoupe Organization



Boost rises, then falls - Fixed - New Problem!
Protouring442 Offline
Member
#1
What I have:
1988 Thunderbird Turbo Coupe
5-speed
Stock IHI Turbo
Gillis Valve
3" Exhaust
Bosch Bypass Valve

What it does:
When I floor it, boost rises with a corresponding increase in acceleration. Then, after it reaches a good 18psi (on the stock gauge), the boost then starts to fall. While boost falls, there is a corresponding decrease in the acceleration rate.

If I adjust the Gillis lower, the boost rises and falls just as before, though the upper limit will be lower. I'm thinking that the wastegate doesn't close once it has been opened due to the pressure in the diaphragm not being able to bleed off. Any other thoughts? Where does the pressure in the wastegate diaphragm bleed off?

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Bill
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Pete D Offline
Administrator
#2
The pressure should bleed off through the bleed hole in the gillis valve. Make sure it's not blocked.
Pete Dunham


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Protouring442 Offline
Member
#3
Quote:Originally posted by Pete D:
The pressure should bleed off through the bleed hole in the gillis valve. Make sure it's not blocked.
Seems the hole was a bit small... The hole in the Gillis (and I am assuming it was a genuine Gillis as it came with the car) was about 1/32. I enlarged it to 1/16, and the boost problem is solved. It now holds boost quite nicely.

On to my new problem! It breaks down at higher RPMs under full boost. Back off to approximately 3/4 throttle, and it runs fine. As I have just recently tuned it, and I am experiencing no pinging, I am thinking it is the coil not putting out enough current to fire the plugs at high boost.

Any recommendations on a coil?

Thanks!

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Bill
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Pete D Offline
Administrator
#4
Your valve is probably not a Gillis. I've had several in different cars and not had the problem you are experiencing.

What do you have your plug gapped at? If it's the stock 0.035, try closing them to between 0.030 to 0.032. Some people run a little less than that.
If that doesn't fix it. try another coil.

What are you running for a fuel pump?
Pete Dunham


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Kev Offline
Posting Freak
#5
MSD coil is a direct bolt in replacement.
Part #
MSD Blaster Ford TFI Coil #8227
Kev
1988 TC 5spd
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junkedturbo Offline
Senior Member
#6
Never waste your time or money on an aftermarket ignition, always go stock in this catagory.

Think of it this way! With project bolt-on, Matt runs his mustang at 30psi with NO2 and the funny thing about it is you look under his hood you see MOTORCRAFT?

The motorcraft ignitions in are cars run quite well(handling past 400whp), is vary affordable, and cooperates quite well with the rest of the engine and computer.

When buy ignition parts from companys like MSD, Mallory, Pertronix, ACCEL, ect. all your paying for is the name! If you need another coil an OEM will be just fine.

My car ran like crap with an MSD coil, ACCEL 8.8 wires and E3 plugs but when I changed it all with motorcraft most of the hessation went away Smile
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Protouring442 Offline
Member
#7
Quote:Originally posted by Pete D:
Your valve is probably not a Gillis. I've had several in different cars and not had the problem you are experiencing.

What do you have your plug gapped at? If it's the stock 0.035, try closing them to between 0.030 to 0.032. Some people run a little less than that.
If that doesn't fix it. try another coil.

What are you running for a fuel pump?
The pump is supposed to be a Walbro, though I did not install it. I also have an Adjustable Fuel Pressure Regulator. It definitely seems to be electric rather than fuel starvation, and there is no pinging to indicate the mixture is leaning out. Tomorrow I will look into purchasing a new coil and plugs and see what that gets me, but I have a hunch they will fix my problem.

From there, I want to make a few full throttle runs while monitoring the fuel pressure to ensure all is well in that department.

Thanks!

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Bill
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Ryan H Offline
Posting Freak
#8
I had an Accel coil in my rather stock 5.0 Mustang, it didn't work worth a crap. I ended up putting a rusty, probably 20+ years old JY coil in it to fix it. Works great now!
'88 TC Smile Walbro 255HP, Stinger FMIC, PIT BOV, Pro 5.0, Kirban, RR cam, FRPP strut tower brace, T3
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Protouring442 Offline
Member
#9
Ok, replaced the coil and the plugs, and now it goes like hell! It does run a hint rougher at idle however. I gaped the plugs at .026, so I may move them up to .030 and see if that helps.

Thanks Guys!

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Bill
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