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Douglas Walker
10-04-2008, 08:53 PM
I just got my project running. I put a sc motor in a 88 mustang. Last night was its first time on the road under its own power.

Ive been working bugs out of it all day and setting up the t body. Ive got the idle down and the tps at .96 It idles great and while driving it runs perfect if you stay in vaccum.

When you get into boost the motor just craps out and bucks and pops. Its a fresh rebuild mods
42lbs injectors
76cl maf w/ correct sample tube
75mm Prof. products t body
255lph pump
all new ss braided fuel line
8an russel fuel filter
Com cam with .520 lift
ported heads new valve job.


Brand new motorcraft plug wires w/ autolite 103s gapped at .035
I checked the plugs after a few miles and they are dry and nice and tan. also no vac leaks, i used half a can of brake clean and it didnt change the idle.

The fuel pressure is around 38lbs at idle.

Looking for some ideas on how to fix this problem. It is not tuned yet.

Thanks
Doug

TSC89
10-04-2008, 09:15 PM
I had the same problem a couple of months ago. I put brand new plugs in my SC and it started bucking in boost but ran fine in vacuum. I found that one of the new plugs had a hair line crack in the ceramic that ran from the top to the base.

MagpoweredSC
10-04-2008, 09:16 PM
It sounds to me like bad plugs/wires. Mine ran like crap under boost, changed the plugs and wires to quality ones and it ran like a champ.
New sock on the fuel pump? Verified that coil works? Bad ground? Check these things.


Mark

Douglas Walker
10-04-2008, 09:27 PM
I pulled all the plugs and they looked good. On the wires I know you can ohm them but I dont know what the ohm should be.

New sock on pump, Coil worked just fine while in the original car, Got the battery in the trunk With0 gauge wire. Good Ground from battery to body. Computer grounds are all hooked up. One grounding strap from block to frame.

The battery is only pushing 10.84amps since it will not charge but the alt puts out 14+ amps. So maybe the battery is the problem or part of it

MagpoweredSC
10-04-2008, 09:58 PM
Yeah with only 10.84 volts on the battery that would cause weak power to the coil under hard load. The battery is not taking a charge and prob is causing your problems. I would get a new battery and verify voltage again while connected and not running and make sure your voltage is not slowly dropping, to me that would indicate something drawing amps and needs to be found. You should have a ground from chasis to engine and then engine to chasis. Make absolutely sure your eec is grounded properly and no pins are f'd up also. How is idle and medium load (5-8lbs of boost) seem?

Mark

Douglas Walker
10-04-2008, 10:05 PM
Yeah with only 10.84 volts on the battery that would cause weak power to the coil under hard load. The battery is not taking a charge and prob is causing your problems. I would get a new battery and verify voltage again while connected and not running and make sure your voltage is not slowly dropping, to me that would indicate something drawing amps and needs to be found. You should have a ground from chasis to engine and then engine to chasis. Make absolutely sure your eec is grounded properly and no pins are f'd up also. How is idle and medium load (5-8lbs of boost) seem?

Mark

I just tried a different battery and it has enough juice to start the car without a jump. The volts are fine and no drop. I have chasis to engine but isnt that the same as engine to chasis? All I remember is the one ground cable on the pass side of the sc besides the main battery ground on the drive side. ill recheck the computer grounds but im pretty sure they are fine.

Idle is fine and driving in vaccum is good. About 3k rpm it starts bogging and just barely into boost it will start to buck.

Im gonna run down to the shop and check for codes and fuel pressure.

MagpoweredSC
10-04-2008, 10:25 PM
Hmmmm...
Enough juice to start without a jump? Well, I would still verify with an ammeter.

With it being a swap there are many issues that could arise. I would do what you said and verify things. I have no idea how you wired it so something stupid could be causing this.

I would still expect plugs/wires maybe a dis module.

Mark

backtobirds
10-04-2008, 11:12 PM
You definitely need a tune. Just curious, what PCM did you use, and how did you adapt the ignition harness?

Douglas Walker
10-04-2008, 11:46 PM
Hmmmm...
Enough juice to start without a jump? Well, I would still verify with an ammeter.

With it being a swap there are many issues that could arise. I would do what you said and verify things. I have no idea how you wired it so something stupid could be causing this.

I would still expect plugs/wires maybe a dis module.

Mark

Battery volts engine off are 12.3, its on the charger for the night. Its been sitting in my 97bird for 3mo with zero drive time so it needs some juice.

KOEO test
Codes
29,96,67,82,85,83,88,84,31
most of them were because the items just arent there anymore. and are not needed for computer. I have to take the time to read them all though, I just glanced at them while scrolling down.

I couldnt get a KOER because the scan tool died and I couldnt find the Power cord for it.

I Checked the fuel pressure and I think its my problem
Car running at idle 31psi with vac on
with vac line off 38psi
Not sure why its higher with the vac line off???

So ill check the inline filter and probably pull the tank and check the pick up screen. I have a feeling it may be plugged over since I did get the tank completely clean.

One last thing Im not sure if my aftermarket boost gauge is accurate. but it says I get up to 30" of vac at times? Ill have to try another gauge tomorrow.

Doug

decipha
10-05-2008, 12:04 AM
fix those codes

aint no way you pullin 30kg of vac... no way!

31psi at idle is toooo low... crank it up to 40
your fpr is acting normal... don't worry

battery isin't the problem dont waste your time thinking it is

other than whats been said my sc was bucking because of:

sc belt tensioner was weak and the sc belt was slipping
bad coil

but the main reason was because of my stripped crank, the bolt holding the harmonic balancer was jb welded on because my crank was stripped.... it spun perfectly round and didn't wobble at all. But it was causing the crank sensor to read wrong and was making it buck only under boost.

backtobirds
10-05-2008, 12:40 AM
Battery volts engine off are 12.3, its on the charger for the night. Its been sitting in my 97bird for 3mo with zero drive time so it needs some juice.

KOEO test
Codes
29,96,67,82,85,83,88,84,31
most of them were because the items just arent there anymore. and are not needed for computer. I have to take the time to read them all though, I just glanced at them while scrolling down.

I couldnt get a KOER because the scan tool died and I couldnt find the Power cord for it.

I Checked the fuel pressure and I think its my problem
Car running at idle 31psi with vac on
with vac line off 38psi
Not sure why its higher with the vac line off???

So ill check the inline filter and probably pull the tank and check the pick up screen. I have a feeling it may be plugged over since I did get the tank completely clean.

One last thing Im not sure if my aftermarket boost gauge is accurate. but it says I get up to 30" of vac at times? Ill have to try another gauge tomorrow.

Doug

Fuel pressure should be 39-45 psi with the vacuum line off. Vacuum lowers the pressure. So when you open the throttle, vacuum goes away, and the pressure increases.

I did get some pretty high vacuum numbers, but only under extreme conditions, like decelerating in gear.

Douglas Walker
10-05-2008, 01:43 AM
fix those codes

aint no way you pullin 30kg of vac... no way!

31psi at idle is toooo low... crank it up to 40
your fpr is acting normal... don't worry

battery isin't the problem dont waste your time thinking it is

other than whats been said my sc was bucking because of:

sc belt tensioner was weak and the sc belt was slipping
bad coil

but the main reason was because of my stripped crank, the bolt holding the harmonic balancer was jb welded on because my crank was stripped.... it spun perfectly round and didn't wobble at all. But it was causing the crank sensor to read wrong and was making it buck only under boost.

Cant fix the codes if its not part of the car anymore
Code
29 C No input from Vehicle Speed Sensor (VSS)
31 O,C,R EGR Valve Position (EVP) sensor out of range (low)
67 C Clutch Switch circuit failed (3.8L SC only)
82 O Supercharger By-pass Solenoid circuit failure (3.8L SC only)
83 O High Speed Electro Fan drive circuit failure (3.8L SC only)
84 O EGR Vacuum Regulator (EVR) circuit failure
85 O Canister Purge circuit failure
88 O Electro Drive Fan circuit failure (3.8L SC only)
96 O,C Fuel Pump circuit open, battery to ECA


Im gonna look into these
82 O Supercharger By-pass Solenoid circuit failure (3.8L SC only)
96 O,C Fuel Pump circuit open, battery to ECA

I am only using the stock fuel pressure regulator

XxSlowpokexX
10-05-2008, 09:09 AM
maybe you have a fuel pump issue..Get a FP gague to see whats happening top end

the-big-e
10-05-2008, 11:05 AM
You could have a leaky intake gasket.....

The PO of my 90 XR-7 spent thousands of dollars trying to fix it.....

You could barely drive it because it would buck and back-fire as soon as it would go into boost.....

Couldn't find it with carb cleaner or starter fluid tricks.....

I used a length of vacuum line to find it....

Put one end in your ear and probe around the intake on both sides.....

I found mine leaking near the back of the engine under the TB.....

Douglas Walker
10-05-2008, 05:02 PM
Pulled the fuel filter and it was clean. So i pulled the tank and found that the sock was packed with crap. So I reflushed the fuel tank again and bought a new sock. Ill try it again

thanks
Doug

Cougarfetish
10-06-2008, 12:14 PM
My car did the exact same thing about a month ago, spent a long time posting and reading, reaplaced coil DIS and tried lots of different leak tests etc. Ended up being the faulty spark plugs cause I used single plat, and not double plat. Don't rule out the plugs yet, simplest thing should be first thing you try.

-Derek

Douglas Walker
10-07-2008, 08:51 AM
It was just starved for fuel. The new sock did the trick. I have to say shaving off some unneeded weight from the sc body really brought that v6 to life. Now time for a tune and tires.

thanks for the help
Doug

89XR7TD
10-07-2008, 07:29 PM
What did you end up doing with your SC? It looked pretty cool!!!!

Tom

Melon
10-07-2008, 09:37 PM
I believe he sold it to a local guy. After that, I'm not sure where the car went, but I remember Doug saying he just couldn't get away from it :D

Doug - when you do get the chance to come tune, I assume you'll be heading to Lincoln and talking to Dan?

-Melon

Douglas Walker
10-08-2008, 06:35 PM
What did you end up doing with your SC? It looked pretty cool!!!!

Tom

It was just a headache kinda car. Not sure what it was but its still always broken. I removed all items and replaced them with stock then watched the car go to junk. they tore it up pretty bad. But its in good hands again. im helping bring it back to life. the best part im not paying for it this time.

Melon.
Ya Ive already talked to Dan about setting up a time. Im havings some issues with the tranny but in the mean time since the set up is close to my old one. Ill use the SCT chip from my old car. I thought maybe we could set up a meet when I make the trip.

89XR7TD
10-08-2008, 06:44 PM
Mine has been down for a while now!!!

Well goodluck with the Mustang!

Tom

Douglas Walker
10-08-2008, 10:29 PM
I did more damage to mine in the garage than I ever did on the road. I think I pushed and pulled it futher than I ever drove it. But when it ran, Man it was a good time.