Injectors not firing.

Topic: Injectors not firing. (Read 2072 times) previous topic - next topic

Injectors not firing.

April 02, 2009, 12:27:41 PM

I tried to start then engine I dropped in, and it cranks over, but I'm getting no fuel. Fuel pump is on, and there is fuel in the lines, but the injectors are not firing. I tested the leads, and I got a .26V reading with key on, and a -.6 reading while cranking. We tested my brothers Mustang, and it read 0 while on, -1 while cranking. (Wasn't sure which was positive lead or not, but I measured the same way.)

The new engine is a 351W with 24lbs injectors. I have a cobra computer (for a 5.0, but I thought it would just run lean) and a 96 cobra MAF (it calibrated for the 24, of thats what I read online.)

Does anyone think the computer is to blame, or something with the wiring?

Injectors not firing.

Reply #1 – April 02, 2009, 03:55:55 PM

The red wire side of the injectors should have 12v with the ignition in run.
This comes through the EEC power relay being picked. Since the fuel pump is running, the EEC power relay is picked.

The EEC pulses the ground on the other wire to the injector.

Injectors not firing.

Reply #2 – April 02, 2009, 04:08:20 PM

Injectors not firing.

Reply #3 – April 02, 2009, 06:46:05 PM

Check for spark. If the computer doesn't see a pulse from the TFI module it won't fire the injectors (because it won't know when to fire the injectors).

Injectors not firing.

Reply #4 – April 02, 2009, 08:21:38 PM

I have spark. The first thing I checked. The TFI is new too.
Ran a voltmeter from the red wire to the neg battery post with the key in run, and it read 10.6. So did the other wire. The other wire is a ground, right? Is it always on, turning off when the injector fires, or the other way around?

Injectors not firing.

Reply #5 – April 02, 2009, 09:01:07 PM

The injectors should have a 12V feed any time the ignition is on. The computer switches the ground on and off to fire them. They will not have ground until the computer gives it to them. You're getting that voltage reading through the injector itself (power is going through the red wire, then through the injector, then into your volt meter). If the injector was "firing" your reading would be "0".

If you've only got 10.6 volts at that red wire you've got a problem.

Injectors not firing.

Reply #6 – April 02, 2009, 09:24:53 PM

If the injectors are used and have been setting for some time they may be stuck... Had this exact problem on a buddies F150 I gave him a set of 19lbers for... It would only fire one cylinder, the other seven were stuck... Wound up reinstalling his originals...

Had the problem again a couple weeks ago, on another set of used injectors with only 10K on them... I replaced the right bank injectors (chasing a interminent miss at idle) in the old Grand Marquis and it missed like Hell, till it ran about five minutes then cleared up...

Injectors not firing.

Reply #7 – April 02, 2009, 09:48:53 PM

You think all 8 would be stuck? I'm getting no firing at all. I soaked them in Seafoam before installing.

And I'm not sure how true that 10.6 is, cause I went out to recheck it, and the battery was pretty low. I don't see how it could be going through the injector, cause I pulled the wiring harness off of it to check...

Injectors not firing.

Reply #8 – April 03, 2009, 12:26:47 AM

Check and see if any local car parts stores have a "noid light".
It plugs into the injector cable and will blink if the EEC is firing the injector.

Injectors not firing.

Reply #9 – April 18, 2009, 01:29:53 AM

Ok, radio shorted out. I wanted to fix that first so I don't kill my battery.

I got a noid light, and it lights up. Dim at first, but then brighter. Can't really tell if it's blinking real fast, or alway on. Guess I might lift one side of the fuel rail up tomorrow, see if I'm getting anything. Any more ideas. I would think if they are getting signal, they would have to fire...

Injectors not firing.

Reply #10 – April 18, 2009, 02:24:12 AM

you can unplug the injector, jumper power and ground to each injector, listen for the click.

4 of the 8 i bought from tom were stuck (wouldnt click),, I gottem to free up by standing them upright inside a wood block with holes drilled.

filled them up with 3 in 1 oil and let them sit for a helava long time. Put power to them and they clicked.

A guy down here told me to boil some water, drop them in by a string one at at time in the water for about 1 min,

dry them off and put power to them. It works for him when they are stuck. He said it expands things inside and frees up the moving parts.

Injectors not firing.

Reply #11 – April 18, 2009, 10:51:41 AM

The noid light should defiantly blink... An injector pulse is similar to the spark from a single plug wire while cranking...

A open TPS circuit will put the EEC in dechoke mode and shut off the injectors...

Injectors not firing.

Reply #12 – April 18, 2009, 01:05:02 PM

Put the noid light on another vehicle so you can see what it's supposed to look like.

Injectors not firing.

Reply #13 – April 18, 2009, 07:41:05 PM

The light was pulsing, I got a better look at it when I had some help. Never totally went off, but definitely getting brighter.

I ran 12v to one of the injectors, and sure enough, it clicks.

If the EEC shut down the injectors, it wouldn't send a signal, right? I don't see how else it would stop it...

Injectors not firing.

Reply #14 – April 18, 2009, 10:02:09 PM

Have you checked your pressure at the fuel rail? Maybe your fuel reg got damaged in the install and is passing all the pressure back to the tank.

Does it run if you squirt some fuel into the intake?
-dz