Injectors not firing...

[stangzroastrice]

Ok on my 90 Mustang, I'm starting my 347 for the first time, and I'm getting fuel pressure, spark, and everything else except my injectors aren't firing, so the car doesn't even sputter or anything while starting... Here's the deal... According to the multimeter, on my injector plugs, I'm getting 12 volts when I touch the hot lead and ground it to the chassis or the injector harness's ground itself manually. When I try to touch both leads, I get nothing with the ignition switched on. When the car is being cranked over, I get 1 volt when touching both leads so I have no idea whats going on ... Any suggestions?

 

[90mustangGT]

I think your have a connection problem on the ground side of the injectors. Maby Jrichker will chime in...

 

[HISSIN50]

Your meter might be averaging readings. There is a constant 12 volt feed from the EEC relay to each injector. Then computer pulses the ground to each one (this pulsed ground is how the computer varies the injector pulsewidth). I would grab a noid light from the parts store (3-5 bucks) and use it since it has very quick on/off dwell.

If you really dont have a ground pulse, the car obviously wont fire. At that point, we would need JR, Tom, etc.

Also make sure you dont have a pegged TPS reading, as that will kill the injector pulsing.

Good luck.

 

[stangzroastrice]

Yeah so it seems like they're getting power considering i get that constant 12 volt feed and when cranking the motor, it gets a 1 volt reading on the meter, but since the pulse is so quick, the meter doesn't catch it... I'll try the noid light idea but one question, if the TPS is pegged does that mean the injectors wouldn't show a reading at all? or just won't pulse considering like I said, I did get that 1 volt reading when cranking with the meter.

 

[JB66]

Make sure you have no wires pinched anywhere. Try it with the TPS disconnected. You obviously have power to the ECM, but the TFI module doesn't seem to be getting the necessary info to the injectors. I think pins 12(#3),13(#4),14(#5),15(#6),42(#7),52(#8),58(#1) and 59(#2) are the grounding signals for the individual injectors, if it comes to that. Also make sure the ECM is fully grounded.

 

[jrichker]

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.


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 10 pin connectors.

Follow JB66's instructions and use an ohmeter to check out the resistance btween the injector wires and their respective computer pins. There should be less than 1 ohm resistance.

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

 

[stangzroastrice]

ttt