ignition problems

Im having a bunch of ignition problems too, sorry i cant help you, heres a bump for you

Bypass the MSD (May Suddenly Die) box and see if it gets better.

If that does not fix it start looking at the grounds and power wiring to the MSD.

Grounds are important to any electrical system, and especially to computers.

1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.

4.) All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or head bolt.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt for help troubleshooting voltage drops across grounds

That is some sound advice from JR. If you have the instructions for the box, do the opposite of what they say. the most important part is getting the box out of series with the coil (put the stock coil harness back on the coil).

When it wont start, do you know if you have spark and injector pulsing? That is a very good way to narrow the issue down, as you might find that you are missing neither, and that it is a burp in the tune (reminds me of hot start issues on carbed stuff).

Good luck.

jrichker said:

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

Click to expand...

Just curious where is the other ground go to from the tfi module? Is that aluminum foil looking wrap that the dizzy wires come through at the computer the shield ground right? I see a bare metal ground wire coming from that shield and it grounds on the car frame but where is the other end? the tfi or just stops in the middle of the harness and is connected to that aluminun foil stuff? If this is one ground where is the other? Thanks

87stangdiddle said:

Just curious where is the other ground go to from the tfi module? Is that aluminum foil looking wrap that the dizzy wires come through at the computer the shield ground right? I see a bare metal ground wire coming from that shield and it grounds on the car frame but where is the other end? the tfi or just stops in the middle of the harness and is connected to that aluminun foil stuff? If this is one ground where is the other? Thanks

Click to expand...

The other TFI ground wire grounds internally inside the computer.

The shield ground is the bare wire that grounds to the frame. The foil shield
protects the TFI wiring from the high voltage field produced by the spark
plug wires and keeps the TFI signal out of the radio. It is only connected to
ground at the computer end.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-90 wiring

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

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Diagram courtesy of Tmoss & Stang&2birds.