[evintho]

I wanna thank mgman75 for helping me get this far.
http://forum.turboford.org/cgi-bin/ultim...059504;p=0

Now it fires right up, runs for 2 seconds then dies! I've got 40lbs of fuel pressure at the rail (fp gauge on the rail). Just replaced the TFI too. It's gotta be in the wiring. '89 Mustang N/A harness modded for VAM/boost/bap/etc. Worked fine for 4 years on Thunderstang. LA3 ECU. Generic ignition switch. It starts but seems like the ECU isn't allowing it to run. Power runs from the BATT to the starter solenoid to a terminal block to the ignition switch. I've traced the wires a dozen times. I have wiring diagrams and EVTMs. Here's pics of my starter solenoid, terminal block and ignition switch.


STARTER SOLENOID.................


[Image: Starter%20solenoid_zpshlhnihxy.jpg]

1) Circuit #32 to TFI
2) I added this wire. To center stud (start) on ignition switch.
3) Hot at all times. Power wire to terminal block.
4) Circuit #38 to EEC relay.
5) Circuit #36 to alternator plug. 3G conversion.
6) To alternator power output stud. Fused.
7) Main POS battery cable.
8) To starter motor.


TERMINAL BLOCK...............


[Image: Terminal%20block_zps2fq0epbu.jpg]

1) BATT power to fuel pump relay.
2) BATT power to fan relay.
3) BATT power from starter solenoid.
4) BATT power to ignition switch.


IGNITION SWITCH..............


[Image: Ignition%20switch_zps0xdlxtk8.jpg]

1) Hot at all times from BATT stud on terminal block/solenoid.
2) Circuit #16 to TFI/Coil/EEC relay.
3) Circuit #687 to O2 sensor.
4) Power wire to fuel pump relay.
5) To small top stud on starter solenoid.


There are 6-7 wires I eliminated from the harness but they shouldn't have anything to do with the running of the motor. I'm turning to you guys 'cause I have no more options! I've gone as far as I can go. I need expert Turboforder's help!!

[TurboRay]

Soooo.....what "quits" when the engine dies, John? Spark? Fuel pressure? Injector signal?

I suppose there's nothing wrong with picking up the TFI's "start" signal from the solenoid - but, AFAIK, that pin (3rd from top) on the TFI is usually energized from the "start" position on the ignition switch. Is the TFI being powered (4th pin from top) by the "ignition" terminal on the switch (IOW, switched batt voltage)? Is it grounded at the bottom pin (6th)? The top two TFI pins are PIP and Spout, respectively. :dunno:

[evintho]

I'm not sure what quits, Ray. As I said, FP stays at 40psi. Injector signal? Not sure. I would assume the spark quits.

The 3rd TFI pin (START) is circuit #32 that goes directly to the small stud on the starter solenoid.

The 4th TFI pin (TFI PWR) is circuit #16 that goes to IGN on the ignition switch. There are 2 other wires that branch out from circuit #16. One to the coil and one to the EEC relay.

The 6th TFI pin (IGN GND) is circuit #259 that goes into the tin foil shield along with the wires from TFI pins 1&2 and travel to the ECU. #259 connects to pin #16 in the ECU labeled 'TFI Module'. There is a bare wire coming out of the shield that's connected to a good chassis ground. Not sure where the other end is.

[ThunderFaux]

Damn it! Wish I could help, GET THIS BABY GOING!!!

[77Pinto]

If you are running a VAM do you have any air leaks between the VAM and the engine?


Bill

[evintho]

Originally posted by 77Pinto:
If you are running a VAM do you have any air leaks between the VAM and the engine?


Bill

No. Everything's tight. I really think this is a spark/ECU/wiring issue.

[TurboRay]

If you've got a timing light with an inductive-pickup, fire the engine with the trigger pulled to see if it stops flashing as the engine dies.....indicating a cessation of spark. If it continues flashing, yet the motor dies, I'd restart it on 3 cyls with a noid light connected to one of the injector plugs, to find out if the injector pulse is ceasing.

Your description of the engine dying after "2 seconds" of running, is sorta indicative of the engine burning up any fuel remaining in the manifold after "delivery" has stopped. :dunno:

[jimtash]

Disconnect the VAM.

[twan374]

If #2 is supposed to be hot all the time it's in the wrong spot. The starter only gets juice when the key is in the start position thats why when you let go of the key the starter is disengaged and no more juice at that terminal. So basically when you let go of the key you are shutting off the ignition. Move it to the large bunch of wires that are hot all the time from the battery. and see what happens. Also I see a heavy ground to chassis. The ground cable should go from the neg battery to the engine block then to the chassis in most cases thats the best route

[Alex L]

i think that ign switch is wired up mostly correct, the left lug is hot for run/start, and the center lug is the output for the starter motor relay. normally i run the TFI and O2 sensor off the EEC relay instead of the switch to keep the wiring tidy, but if the switch can handle it, go for it.

not sure what reference you're using for circuit numbering, as my 84 reference has completely different ones! so we'll work in broad strokes.

the ECU will prime the injectors for a few ms on power up after priming the fuel pump for 2 seconds. sounds like that part is OK.

it then waits for the TFI to start sending a PIP signal to reenable the fuel pump and start firing injectors during cranking. PIP is usually dark blue, edge pin on the TFI, pin 56 at the ECU. the TFI will self fire at 10 deg advance until it starts receiving SPOUT from the ECU. SPOUT is yellow-green, right next to the PIP on the TFI, and is ran to pin 36 on the ECU. the bare ground/shield wire should only be attached to ground on one end!

it sounds like its just firing off the priming pulse, and never actually getting to a run state on the ECU. you never mentioned if the fuel pump is running or not when the engine cranks?

if you turn the key on, crank to start, let it die, then immediately crank again without power cycling the ECU and it doesn’t start, its just running off the priming pulse. if it does fire again and dies again after a few seconds, its a metering issue.

you can also check for the ECU / TFI changing from 'crank' to 'run' by a timing light. if it stays at 10 deg, its the TFI in limp/start mode; if the ECU goes into run mode, the spark should jump to 25~30 deg advance.