91gt cranks but won't start

[TimB91gt]

Hello to all i would like to ask for help with my 91 gt. Today I put on a new belt the smog system has been taking off my car by PO. I pulled the coil wire off the coil pack and not the dist in order to bump the engine and roll the belt in to place. put the coil wire back on and now the car only cranks but does not fire.

So far I've checked to see that i still have spark all the way through the ignition system to the number 1 plug. Fuel pump is coming on and cycling like normal I pulled plugs and confirmed they are wet with gas. Car will not fire on starting fluid. I've checked voltage at the inertia switch the switch is good. but I only have 5 volts on the green wire which from what i can tell from the wiring diagrams comes through a set of contacts on the fuel pump relay. I just recently found this forum and printed off the cranks but won't start check list to work through tomorrow

Is it possible that the spark from my coil pack next to the starter sol caused a fuse link to blow in the harness or some how got back to my computer?


Thanks for any help you can provide.

 

[jrichker]

From the orginator of the Cranks OK, but No Start Checklist for Fuel Injected Mustangs - work the checklist and the checklist will work for you. Don't skip around, start at the top and work your way to the bottom.

 

[TimB91gt]

Update on my car, This morning when i went to pull car into garage to perform cranks but won't start check list the car fired right up. Shut it off and back to cranking without starting. I preformed checklist only to find no problems. how ever when I crank the car while pulling out the plug on the tfi connector and pushing it back in I can get the engine to crank and run, car idles at 1,000 rpm I've replaced the tfi and still have the same issue. I've tried to crank the engine with the spout pulled out to check the pip module, still only cranks is there any other way to tell if the pip is bad?

 

[Noobz347]

If this is happening while you're pulling on the harness to the TFI then I might suspect the harness going to the TFI.

Shoot the wires while moving them around and see if you can find an intermittent break.

 

[TimB91gt]

I've tried that, I actually have to unplugged the connector from the TFI and push it back in several times while cranking the engine to get it to fire.

 

[Noobz347]

Maybe try cranking while tapping on the dizzy/TFI/connector with a rubber mallet?

 

[TimB91gt]

I will give that a try tomorrow after work. Sometimes I find it best to walk away and give things a rest before you get to frustrated.

Thanks for your advice.

 

[jrichker]

From the Cranks OK, but No Start Checklist for Fuel Injected Mustangs

1.)
B.) PIP sensor in distributor. The PIP sensor supplies the timing pulse to trigger the TFI and injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed. See paragraph 5A – Using a noid light will tell if the PIP is working by flashing when the engine is cranking.

5.) Fuel pressure OK, the injectors are not firing.
A.) The PIP sensor in the distributor tells the computer when to fire the injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed.
A noid light available from any auto parts store, is one way to test the injector circuit to see if the injectors are firing. The noid light plugs into the fuel injector harness in place of any easily accessible injector. Plug it in and try to start the engine: it will flash if the injector is firing.


If you determine the PIP is bad:
The PIP is a Hall Effect magnetic sensor that triggers the TFI and injectors. There is a shutter wheel alternately covers and uncovers a fixed magnet as it rotates. The change in the magnetic field triggers the sensor. A failing PIP sensor will often set code 14 in the computer. They are often heat sensitive, increasing the failure rate as the temperature increases.

The PIP sensor is mounted in the bottom of the distributor under the shutter wheel. In stock Ford distributors, you have to press the gear off the distributor shaft to get access to it to replace it.

To remove the gear, first you drive out the roll pin that secures the gear to the shaft. Then you get to press the gear off with a hydraulic press or puller. When you go to press the gear back on, it has to be perfectly lined up with the hole in the gear and shaft. I have been told that the hole for the pin is offset slightly from center and may require some extra examination to get it lined up correctly.

Most guys just end up replacing the distributor with a remanufactured unit for about $75 exchange


PIP problems & diagnostic info
Spark with the SPOUT out, but not with the SPOUT in suggests a PIP problem. The PIP signal level needs to be above 6.5 volts to trigger the computer, but only needs to be 5.75 volts to trigger the TFI module. Hence with a weak PIP signal, you could get spark but no injector pulse. You will need an oscilloscope or graphing DVM to measure the output voltage since it is not a straight DC voltage.

See http://www.wellsmfgcorp.com/pdf/counterp_v8_i2_2004.pdf and http://www.wellsmfgcorp.com/pdf/counterp_v8_i3_2004.pdf for verification of this little detail from Wells, a manufacturer of TFI modules and ignition system products.

 

[TimB91gt]

Okay so I've went through again and checked the pip and TFI module and I do get a flashing test light I get a pulsing light at the injectors. This afternoon when I got home the engine started up after sitting all night started up 10 times then nothing. Idles a little high when running. Still can get engine to start if I plug the TFI connector into module while cranking engine. Any ideas?

 

[2000xp8]

What kind of tfi module did you buy?

 

[TimB91gt]

The only one I could find at my local orielys I belive it is a master pro. It was a cheap one. Should I suspect it to be bad out of the box? Ikve run the cranks but won't start check list and according to that my TFI is working correctly. lead of test light on on coil wire probe on other wire light flashes while cranking.

 

[2000xp8]

Well, do i think it's your problem? I dunno.
Do i think it will be a problem? Absolutely.

Replace it with one from ford, aftermarket ones rarely make it 6 months.

 

[TimB91gt]

Okay thank you for your advice. I believe I will stop. At ford tomorrow and pick one up. I don't have a CEL on, should I dump the codes and see what I come up with ?

 

[jrichker]

Okay so I've went through again and checked the pip and TFI module and I do get a flashing test light I get a pulsing light at the injectors. This afternoon when I got home the engine started up after sitting all night started up 10 times then nothing. Idles a little high when running. Still can get engine to start if I plug the TFI connector into module while cranking engine. Any ideas?

I think we may not be communicating very well. I understand that the problem is that the engine does not start once it gets warm unless you remove the SPOUT?

Is that correct?


If that is correct, the problem is the PIP sensor in distributor. The PIP sensor supplies the timing pulse to trigger the TFI and injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed. This is a problem that gets worst on a warm or hot engine.

The PIP signal level needs to be above 6.5 volts to trigger the computer, but only needs to be 5.75 volts to trigger the TFI module. Hence with a weak PIP signal, you could get spark but no injector pulse. You will need an oscilloscope or graphing DVM to measure the output voltage since it is not a straight DC voltage.

 

[TimB91gt]

No sir that isn't exactly right. It wil start after sitting all night. Without letting the engine warm if I shut it off right away after starting it will not start back. If I remove just the spout it still will not start. I actually have to unplug the entire connector out of the TFI module then while cranking the engine plug the connector back into the TFI. I first suspected wiring on the harness but have determined it to be good. I'm stumped.

 

[jrichker]

You may have the wrong TFI module

Description courtesy of Tmoss
Well, if you include the SN95 style TFI, there are four TFI modules. Two for the distributor mounted style are black and gray and have the pins comming out of the top to plug into the distributor. The SN95 style also has black and gray modules without the pins because they are remotely mounted. The gray modules are "push start" modules.

Ignition dwell with the Push Start (gray module) system is controlled by the TFI module alone, and increases with engine rpm. The Ignition Diagnostic Monitor (IDM) signal on a Push Start TFI system comes from the coil negative circuit and is filtered through a 22k ohm resistor to pin #4 on the EEC-IV computer. The computer monitors this circuit to verify a coil firing for each PIP signal, and sets codes if it sees missing or erratic signals. Another feature that is unique to the Push Start TFI system is the start input on pin #4 of the module connector. This is wired into the starter relay trigger circuit, and signals the TFI module that the engine is cranking. When the module sees battery voltage on this circuit, the SPOUT signal is ignored.

In the early '90s, Ford began using a different TFI system on certain vehicles -- the Computer Controlled Dwell (CCD) TFI system. The TFI module on CCD TFI is always black in color. There are a few major differences between the two systems. As the name implies, with the CCD system, the computer controls primary dwell. The CCD TFI module still ungrounds (fires) the coil at the rising edge of the SPOUT signal, but now the falling edge of the SPOUT signal (which had no meaning to the Push Start TFI module) is used by the CCD TFI module to ground the coil. The PIP signal remains the same 50% duty cycle square wave, but SPOUT signal duty cycle varies according to how much dwell is desired by the computer.

Another major difference between the two systems is the IDM circuit. Pin #4 on the CCD TFI module, which was the start circuit input on the Push Start TFI module, is now the IDM signal, sent directly from the TFI module to pin #4 on the EEC-IV computer. This signal is still a filtered (low voltage) version of the ignition primary waveform, but is filtered internally in the TFI module rather than through an external resistor. There isn't any start circuit input to the CCD TFI module; the module infers engine cranking from a low rpm input from the PIP signal.
Since these two TFI systems are so significantly different, yet so similar in appearance, parts application problems will inevitably occur. A gray Push Start TFI module will plug right into a CCD system, and vice versa. To make matters worse, parts books are often incorrect on TFI module applications! With the incorrect TFI module installed, the vehicle will run, but drivability and MIL (malfunction indicator lamp) problems will result. For instance, if a gray Push Start TFI module is installed in a CCD system, the computer will not be able to control ignition dwell, and the MIL will illuminate with memory codes for the IDM circuit set, as the gray TFI module is incapable of generating an IDM signal to the computer. If a black CCD TFI module is installed in a Push Start system, dwell will remain fixed, since the SPOUT signal duty cycle never changes. If in doubt about which TFI module belongs on a particular vehicle, consult the ignition system-wiring diagram for the vehicle. If the wire going to pin #4 on the EEC-IV computer comes directly from pin #4 of the TFI module, it is a CCD system. If not, it is a Push Start system.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[TimB91gt]

I've got the correct TFI module. Should I be checking the output voltage of the PIP while the engine is running or cranking or does it not matter which way?

 

[jrichker]

Follow the link to the Wells article I posted. They describe the troubleshooting process in detail.

See http://www.wellsmfgcorp.com/pdf/counterp_v8_i2_2004.pdf and http://www.wellsmfgcorp.com/pdf/counterp_v8_i3_2004.pdf for verification of this little detail from Wells, a manufacturer of TFI modules and ignition system products.

 

[TimB91gt]

Hey everyone thanks for your help. I've found the problem and it is a combination of a couple things.
1) My TPS is bad.
2) My Temp sensor is bad.
Injectors were dumping fuel into cylinder and flooding the engine, and since the TPS is bad computer could not clear it out.

When I was pulling the TFI connector out and cranking then plugging back in it was keeping the injectors from pulsing.