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Fighting a high idle...HO swap related

Recently finished the HO conversion on my 1988 T-bird Sport Coupe. I put in a '88 Mustang GT motor, Explorer upper/lower intake, 70mm BBK TB/EGR, under drive pulleys, 1-5/8" shorties, 2.5" BBK offroad H, Flowmaster lers. Also used stock HO injectors (orange top) and a BBK FPR w/ gauge. The car also still runs SD w/ a DA9 computer and T5, I did not do the MAF conversion.

Here's the problems.

First....high idle. It hold steady at 1200rpm. Friday I tore the intake off to search for vacspooge leaks and found none....all the lines are either hooked up or plugged if not used. Also cleaned the TB, IAC and blocked off the EGR (it was in the way of the FP gauge). I adjusted the throttle screw and it did not help.

Second...it's got a sputter. When setting still at idle (1200rpm) it sounds like it has a miss. The FP is steady at 39#, drops to mid 30's when floored. When adding fuel and setting still (under no load) the sputter is mid-RPM (2500-ish) but floor it then it rips to 6K. The other sputter is driving....when accelerating smooth it goes along good. Floor it and the car goes flat, not fall on its face flat, but just does not go any faster. Back off the pedal a little bit and it picks up smooth.

I also tried to check the TPS voltage today. It was reading 1.7-1.9. I slotted both sides of the TPS and got it down to .97 with the key on and 1.17 when it's running.  The idle is still high and still has the miss at idle.  It was raining so I did not take it for a ride, hopefully Sunday I can take it out.

When stopped on the road I can rev it up to 4K and side step the clutch...it will hone the tires and rev to 6K nicely till I lift or the car catches up to the tires. Occassionally when I do this and lift, it will pop back through the TB.

I think that is about all and I'm not leaving anything out.

Any ideas??? Looking for help here......want to get this thing going.
1988 T-Bird Sport Coupe--5.0 HO, MAF swap, 1-5/8" shorties, BBK/Flowmaster exhaust, Explorer intake, 70mm Edelbrock TB, T5, B&M short throw, Centerforce clutch and PP, disc brake TC rear w/ 3.55's, TC front brakes, '98 Cobra springs, DIY SFC's, other misc .  14.05 @ 98mph with launching too low and shifting too high.

Fighting a high idle...HO swap related

Reply #1
How old are your plugs, wires and fuel filter? Plugs gapped correctly?  No plugwires crossing or touching each other?  I would think a 70mm throttle body would be pushing it on an SD setup. Any codes or CEL?  Maybe you have a dirty injector?

Fighting a high idle...HO swap related

Reply #2
The TB size aint an issue.  I'm of the opinion that you need to reset your base idle.

http://sbftech.com/index.php/topic,1031.0.html
-- 05 Mustang GT-Whipplecharged !!
--87 5.0 Trick Flow Heads & Intake - Custom Cam - Many other goodies...3100Lbs...Low12's!

Fighting a high idle...HO swap related

Reply #3
X2, also the voltage for your tps shouldn't change if the car is on or off.

Do a idle reset, run codes, check grounds, and work from there.
Quote from: jcassity
I honestly dont think you could exceed the cost of a new car buy installing new *stock* parts everywhere in your coug our tbird. Its just plain impossible. You could revamp the entire drivetrain/engine/suspenstion and still come out ahead.
Hooligans! 
1988 Crown Vic wagon. 120K California car. Wifes grocery getter. (junked)
1987 Ford Thunderbird LX. 5.0. s.o., sn-95 t-5 and an f-150 clutch. Driven daily and going strong.
1986 cougar.
lilsammywasapunkrocker@yahoo.com

Fighting a high idle...HO swap related

Reply #4
If you can disconnect the IAC and set base idle to 600 RPM, you don't have a vac leak problem...

As mentioned, the voltage should not change with the engine running, if there isn't a wiring issue you may have a bad ECM... Anything over 1.1v(maybe even a little less) will cause a high/hanging idle, I like to see voltage around .85 to .90v max(forget the set to .99999 , it's BS)... You can reinstall the orig ECM long enough to verify voltage is or isn't correct with it...

Once the base idle is correct, then set TPS voltage...

Fuel pressure should hold 39psi at WOT, if not you have a restriction(maybe clogged fuel filter) or weak pump...

Fighting a high idle...HO swap related

Reply #5
Quote
Fuel pressure should hold 39psi at WOT, if not you have a restriction(maybe clogged fuel filter) or weak pump...

How are you measuring/checking the pressure?
-- 05 Mustang GT-Whipplecharged !!
--87 5.0 Trick Flow Heads & Intake - Custom Cam - Many other goodies...3100Lbs...Low12's!

Fighting a high idle...HO swap related

Reply #6
Fuel pressure should not drop off at WOT. Change your filter. If that doesnt help, put in a bigger pump. The stock pumps are only good for 75 lph and probably less if its old. You might be able to improve the idle by adjusting the tps. I would check the timing also.

turbo charged 94 Cobra engine/440cc injectors/megasquirt /5 speed swapped (T5)/maxbox upper intake/70mm PP throttle body/AJE coilovers/2003 Mustang control arms/S.T. sway bars/ES rear control arm bushings/11" brake conversion/manual rack conversion/8.8 TC rear with rear discs and a welded diff/3.73 gears/PLX wideband/199mph speedometer/Aeromotive FPR/CNC hydraulic hand brake/cobra R wheels/....ect.

Fighting a high idle...HO swap related

Reply #7
A brand new stock pump runs around 35psi under loaded wot, tested off the fuel shcrader. Could be my harbor freight guage too. As long as its 30-40psi, it has nothing to do with your idle.

Replace your tps. It should read below 1.2 volts at idle, but more importantly, it should not have any dead spots while throttle goes up. With key off, run the throttle up. Any dead spots, and its garbage. Fix this very first. I would also worry about the lower intake sealing well, which can cause a leak.

Check the ground wire for the ecm, its right next to the battery. You voltage might flucuate some if you have a bad ground.
Quote from: jcassity
I honestly dont think you could exceed the cost of a new car buy installing new *stock* parts everywhere in your coug our tbird. Its just plain impossible. You could revamp the entire drivetrain/engine/suspenstion and still come out ahead.
Hooligans! 
1988 Crown Vic wagon. 120K California car. Wifes grocery getter. (junked)
1987 Ford Thunderbird LX. 5.0. s.o., sn-95 t-5 and an f-150 clutch. Driven daily and going strong.
1986 cougar.
lilsammywasapunkrocker@yahoo.com

Fighting a high idle...HO swap related

Reply #8
Quote from: V8Demon;386880
How are you measuring/checking the pressure?

I have a guage right on the BBK regulator.
1988 T-Bird Sport Coupe--5.0 HO, MAF swap, 1-5/8" shorties, BBK/Flowmaster exhaust, Explorer intake, 70mm Edelbrock TB, T5, B&M short throw, Centerforce clutch and PP, disc brake TC rear w/ 3.55's, TC front brakes, '98 Cobra springs, DIY SFC's, other misc .  14.05 @ 98mph with launching too low and shifting too high.

Fighting a high idle...HO swap related

Reply #9
Quote from: Dan B.;386897
I have a guage right on the BBK regulator.

Are you checking with the vacuum line on or off?
-- 05 Mustang GT-Whipplecharged !!
--87 5.0 Trick Flow Heads & Intake - Custom Cam - Many other goodies...3100Lbs...Low12's!

Fighting a high idle...HO swap related

Reply #10
FP?  With vac line on.
1988 T-Bird Sport Coupe--5.0 HO, MAF swap, 1-5/8" shorties, BBK/Flowmaster exhaust, Explorer intake, 70mm Edelbrock TB, T5, B&M short throw, Centerforce clutch and PP, disc brake TC rear w/ 3.55's, TC front brakes, '98 Cobra springs, DIY SFC's, other misc .  14.05 @ 98mph with launching too low and shifting too high.

Fighting a high idle...HO swap related

Reply #11
Also swapped the TPS for another one I had.  Still reading way high.....1.7. Should I slot the holes on this one?
1988 T-Bird Sport Coupe--5.0 HO, MAF swap, 1-5/8" shorties, BBK/Flowmaster exhaust, Explorer intake, 70mm Edelbrock TB, T5, B&M short throw, Centerforce clutch and PP, disc brake TC rear w/ 3.55's, TC front brakes, '98 Cobra springs, DIY SFC's, other misc .  14.05 @ 98mph with launching too low and shifting too high.

Fighting a high idle...HO swap related

Reply #12
Check the voltage with the TPS removed from the TB, if it's still high you have a bad TPS, wiring or ECM issue...

Fighting a high idle...HO swap related

Reply #13
Quote from: Dan B.;386962
FP?  With vac line on.

In park this is actually normal for the pressure to drop a little when you check with the vacuum line in place.

Read the following thread:  http://www.foxtbirdcougarforums.com/showthread.php?18145-Vacuum-increase-at-part-throttle-!!-Apparently-It-s-OK-in-park....-Solved!&highlight=
-- 05 Mustang GT-Whipplecharged !!
--87 5.0 Trick Flow Heads & Intake - Custom Cam - Many other goodies...3100Lbs...Low12's!

Fighting a high idle...HO swap related

Reply #14
I saw a little tidbit in that thread about fuel pressure drop after shut off.  I noticed that mine drops down to the mid 20's soon after shut off.  You saw something about dropping to 30 a certain period of time after shut off being acceptable.  If mine is dropping so fast and lower than 30#, does that indicate something??
1988 T-Bird Sport Coupe--5.0 HO, MAF swap, 1-5/8" shorties, BBK/Flowmaster exhaust, Explorer intake, 70mm Edelbrock TB, T5, B&M short throw, Centerforce clutch and PP, disc brake TC rear w/ 3.55's, TC front brakes, '98 Cobra springs, DIY SFC's, other misc .  14.05 @ 98mph with launching too low and shifting too high.