Problems w/Autometer Tach connection to coil...

for some MSD boxes, one should use the tach input on the box (though people have ignored that before).

what does the neg coil wire do When you have the tach hooked up. i wonder if the tach is internally shorting the neg wire and collapsing the electrical field.

Distributorless Ignition Systems need tach adapters... No 5.0 Mustang had a DIS. It really sounds like your hooking it up wrong. I know I had my tach wired "wrong" on my 83... And thought the tach was broken... but I just had the + and - flipped.. Didn't effect performance, but I ordered a new tach thinking it was inop... but when the new one didn't work... I hooked it up to the + and it worked fine. lol. Then I just flipped the wires. Try it. Not gunna hurt the tach hooking it to the postive... Try and see.

Yeah, also.. If you use an MSD... atleast mine did this... I couldn't use the negative coil terminal anymore for tach referance.. It wouldn't work... I HAD to use the tach plug in on the MSD box for it to work.

all that wiring seems pretty simple, except for the red to the power. Id make sure that youve got the right hot wire (at this point anythings worths a shot).

Sounds like something shorted out and burnt out something in the ignition or a fuse now.

Start with the basics and begin troubleshooting...

Still doesn't solve your tach problem, but get the car running first and we can go back and work on that afterwards.

now that it wont start, do you get a ground pulse on the neg side of the coil (with the tach disconnected)?

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

1.) Remove push on connector from starter solenoid and turn ignition switch on. Place car in neutral or Park and set emergency brake. Remove coil wire from distributor & and hold 3/8” away from engine block. Jumper the screw to the big bolt on the starter solenoid that has the battery wire connected to it. You should get a nice fat blue spark.
Most of the items are electrical in nature, so a test light, or even better, a voltmeter, is helpful to be sure they have power to them.
No spark, possible failed items in order of their probability:
A.) MSD or Crane ignition box if present.
B.) Coil
C.) TFI module - Note: the car may fire off, and immediately die once the key is returned to the Run position if the TFI is bad.
D.) PIP sensor in distributor
E.) ECC relay next to computer - look for 12 volts at the fuel injector red wires
F.) Fuse links in wiring harness - look for 12 volts at the fuel injector red wires
G.) Ignition switch - look for 12 volts at the ignition coil red/lt green wire.
H.) Computer

2.) Spark at coil wire, pull #1 plug wire off at the spark plug and check to see spark. No spark, possible failed items in order of their probability:
A.) Moisture inside distributor – remove cap, dry off & spray with WD40
B.) Distributor cap
C.) Rotor
D.) Spark Plug wires
E.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil

3.) Spark at spark plug, but no start.
Next, get a can of starting fluid (ether) from your local auto parts store: costs a $1.30 or so. Then pull the air duct off at the throttle body elbow, open the throttle, and spray the ether in it. Reconnect the air duct and try to start the car. Do not try to start the car without reconnecting the air duct.
Two reasons:
1.) If it backfires, the chance for a serious fire is increased.
2.) On Mass Air cars, the computer needs to measure the MAF flow once the engine starts.
If it starts then, you have a fuel management issue. Continue the checklist with emphasis of fuel related items that follow. If it doesn’t, then it is a computer or timing issue: see Step 4.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html for a description of the test connector. If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. Beware of fire hazard when you do this. In pinch you can use a tire pressure gauge to measure the fuel pressure. It may not be completely accurate, but you will have some clue as to how much pressure you have.

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – Coupe & hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect for fuel escaping while pump is running.

Fuel pressure OK, the injectors are not firing.

A.) A Noid light available from Autozone, is one way to test the injector wiring.
B.) I like to use an old injector with compressed air applied to the injector where the fuel rail would normally connect. I hook the whole thing up, apply compressed air to the injector and stick it in a paper cup of soapy water. When the engine cranks with the ignition switch on, if the injector fires, it makes bubbles. Cheap if you have the stuff laying around, and works good too.

a.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on.
b.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at the rear of the upper manifold).
c.) No power and the 10 pin connections are good: look for broken wiring between the orange/black wire on the ECC relay and the red wire for the black 10 pin connector.


4.) Spark & fuel pressure OK.

A.) Failed IAB (no airflow to start engine). Press the throttle ¼ way down and try to start the car.
B.) Failed computer (not very likely)
C.) Engine ignition or cam timing off: only likely if the engine has been worked on recently).
D.) Firing order off: HO & 351 use a different firing order from the non HO engines.
HO & 351W 1-3-7-2-6-5-4-8
Non HO 1-5-4-2-6-3-7-8
E.) No start when hot - Press the throttle to the floor & try starting it if you get this far. If it starts, replace the ECT.

Loco5.0 said:

My guess is it's a bad coil. I'm going to get a new one & see what happens.

Click to expand...

To be sure, you need to test the wires at the coil (a new coil, with bad wiring or components upstream, will give you a shiny new coil and a car that still wont start).

a simple test-light has worked for me (though I dont know if that is acceptable to do). you really should have a test light and DMM. you can get the former on sale at Harbor Freight for 1 dollar and the latter goes on sale for 4 bucks at the same store. those are MUST HAVES for any electrical troubleshooting or installations.

good luck.

for reference, msd 6al will not have power to the coil with koeo. thats direct from msd.