North American Turbocoupe Organization



Engine Drops Off In Power
Cullen Offline
Junior Member
#1
My 87 turbo engine all of a sudden decides to not idle well. And it drops off in power about the time the turbo boost really starts to pick up steam.
These conditions started while driving. When I get home I check the engine and find the two wire plug to the throttle is unplugged. I plugged it back in but still rough idle and a loss of power when the turbo kicks in. 
I have checked the timing.
Next thing is check the fuel pressure.

It really acts like a vacuum leak.

Any other suggestions?
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Mikey97D Offline
Member
#2
1. Check to make sure you have spark to each wire?  Easy quick check is to use your timing light on each wire to see if it strobes.
How old are your plugs, rotors, cap and rotor?
2. If you can borrow a smoke machine it is the best thing for finding vacuum leaks.  It could also be a boost leak once it starts building pressure it starts leaking.
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Jeff K Offline
Administrator
#3
There is no 2 wire plug that goes to the throttle body. Did you mean the 3 wire plug going to the TPS?

Sounds like you may have split or partly blown off one of the hoses from the turbo to IC or IC to TB (assuming you have the stock IC) or a vac/boost hose blew off the vacuum tree of off the IC. Both of these things have happened to me over the years.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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anasazi4st Offline
Senior Member
#4
(07-15-2020, 05:33 PM)Cullen Wrote: My 87 turbo engine all of a sudden decides to not idle well. And it drops off in power about the time the turbo boost really starts to pick up steam.
These conditions started while driving. When I get home I check the engine and find the two wire plug to the throttle is unplugged. I plugged it back in but still rough idle and a loss of power when the turbo kicks in. 
I have checked the timing.
Next thing is check the fuel pressure.

It really acts like a vacuum leak.

Any other suggestions?

If it’s a big enough vacuum leak you might be able to hear it, a WOOOSH or whistling. As Jeff suggests, it could be one of the thick hoses that connects the intercooler (if you have that) to the turbo and/or throttle body.

One day last year I started to hear a WOOSH on acceleration, and I had no power. The lower hose that connects the Intercooler to the turbo outlet elbow had split.
Another proud dues-paying member.

1987 Turbo Coupe w/T5OD, 8.8 axle, grey smoke; most options. Got it in 1991 with 41K miles: 3 turbos, 2 heater cores, 1 T5OD full rebuild, 5 clutches, 1 head gasket, 2 Teves II ABS units, etc. later....
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Cullen Offline
Junior Member
#5
Thanks gentlemen,
Here is what I found. Since my project it a true Frankenstein I had adapted an 87 Ford turbocoupe fuel pump to Mazda Miata parts in a custom tank. The sock came off the bottom of the pump due to rubber disintegration. The pump had sucked material into it and probably pumped some material on to the filter. And probably the injectors.
I found this by putting a fuel pressure gauge inline with the fuel rail. The pressure was lower than usual. I took it all apart and then the fuel pump stopped turning all together. I am sure a piece of material got in the gears of the pump.
I changed the filter as well but the the car still does not idle. It starts great and revs well but when I let off the pedal it drops right past 1000 rpm and dies.
I then took out the injectors and tried to clean them but had little luck. An injector business locally soaked them in their solution but it still will not idle. I have ordered new injectors.
The two terminal wiring plug goes to the can shaped body right over top of the throttle position sensor. It is called the throttle air by-pass solenoid. This part is an 85 Turbocoupe. Again, my 29 Ford pickup is made up of 16 different model A Fords. The suspension, brakes and steering are all a Mazda Miata. The engine is an 85 Turbocoupe but I have added an intercooler and am using 87 electronics.
Can anyone tell me how this air by-pass solenoid works and if it failed after the plug came off, could this be causing my inability to get the engine to idle?

This little truck is quick as heck and handles like a sports car. I have expected some hiccups being it is such a combination of cars.
Thanks, Cullen
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vegas_ss Offline
Senior Member
#6
Try setting the base idle and TPS... there is some info from the tech section in the link below.  You can remove the Idle Air Controller and try to clean it up, may want to have a new gasket for that.  Injectors are most likely not contributing to your idle issues.

Idle TPS Adjustment
1987 TC, 5sp, Boport Stage 3 Head/2.1 Cam
1996 Impala SS
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Cullen Offline
Junior Member
#7
Thanks.
The problem I am having is I can not get the engine to stay running. If I stay in the seat and keep revving the engine to 2000 rpm it runs fine but as soon as I let off of the accelerator, the rpms go immediately to zero. I am trying to double check my timing but can’t keep it near 1000 rpm.
All of this started when it was driving fine and evidently the sock came off the fuel pump and sucked in material to the fuel pump, lines, filter and maybe beyond.
When it started running poorly, I barely made it home where I looked the engine over. That is when I saw the plug on the Idle Air By-pass was disconnected. I plugged it back in but the engine would not idle down. As I tried to drive it, it was bog down upon trying to accelerate, like it was starved for fuel. I checked the fuel pressure and it was lower. Then I took out the fuel pump and saw the sock was off and there were materials in the tank from dissolved rubber and even some small metal.
I replaced the pump and filter and the fuel pressure came back up to about 42 lbs When not accelerating but would drop a bit when accelerating the engine rpm.
I have a new Throttle Position Sensor but have never checked the Air By-pass.
It is crazy that this project went from running great to being ill in a matter of a mile.

This fuel tank was a custom build. The builder built it with my pump, fuel level sender etc all installed. When I replaced the pump, I cleaned out a lot of metal shavings and minor metal “dust” with a magnet. I should have taken this tank apart and checked to see if it was clean on the inside but that is hindsight now. This why I think the injectors May have some small metal particles blocking fuel at idle.

Cullen
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