92 4.9 f150 injector problem
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Freshman User
Joined: Jul 2003
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From: florida
92 4.9 f150 injector problem
truck only runs spraying gas in it has new fuel pump and regulator
has over 30 pounds pressure
aparenly injectors aren't pulsing, weird thing is both wires at injector have full voltage all the time when key is on, replaced distributor and ignition module
no help still the same when turning motor voltage drops a little
i'm sure because starter drawing power but both are still the same when turning and doesn't break at all, like they are the same wire, shouldn't 1 be positive or neg and the other oppisite? a coil works these right?
can't see the injector being used as a ground because of o-rings.
any help would be appreaciated going crazy here, Michael
has over 30 pounds pressure
aparenly injectors aren't pulsing, weird thing is both wires at injector have full voltage all the time when key is on, replaced distributor and ignition module
no help still the same when turning motor voltage drops a little
i'm sure because starter drawing power but both are still the same when turning and doesn't break at all, like they are the same wire, shouldn't 1 be positive or neg and the other oppisite? a coil works these right?
can't see the injector being used as a ground because of o-rings.
any help would be appreaciated going crazy here, Michael
Junior User
Joined: Jan 2007
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From: Va.Beach
Heres something to consider, the computer for running all aspects of those controls has to have the proper voltage (12vdc), it only will operate to a certain level of low voltage and then it just doesnt function even if other things will. Your correct injectors do have a - as well as a + wire and they do not ground at the injector, but Im not sure if this voltage is 12 vdc. I do know this voltage is pulsed and may not be readable with a meter that reads only a constant variant.
Lead Driver
Joined: Nov 2002
Posts: 9,557
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From: Concord, NC
The injectors are fed +12V and the computer controls how long the ground is active to control the injector pulse width, which ultimately controls how much fuel goes into the engine. At idle/cranking speeds, you will see battery voltage on both injector terminals because the injector is active for such a small amount of time (probably well below 10ms for each pulse). A noid light will aid in determining if the injectors are firing. If you listen real close, sometimes you can even hear the injectors click when they fire. One other note, fuel pressure for an inline six should be above 50psi, although I can't remember the spec off the top of my head.
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From: florida
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Elder User
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This might seem silly, but I had the same problem with mine, and even though I had replaced the pump, the pump I put in wasn't any better than the one I pulled out. Try switching the ignition switch on and off a few times and see if it starts, that will prime it up a bit to get enough fuel pressure and see if it starts. If not, I'm betting as mentioned above, you're getting voltage, but not a good injector pulse. A noid set will help out loads and they'll only set you back about $10 for the set.
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Thread Starter
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Freshman User
Joined: Jul 2003
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From: florida
indy i already tried this many times and fuel pump works much better than old one.
from what i understand injectors should work even if you have no fuel pressure.
which means to me even with low pressure it would sputter or something.
hear no clicks and feel nothing when turning engine, pretty sure noid light would just say it's not pulsing. i certainly appreaciate anyone trying to help. you guys are great
from what i understand injectors should work even if you have no fuel pressure.
which means to me even with low pressure it would sputter or something.
hear no clicks and feel nothing when turning engine, pretty sure noid light would just say it's not pulsing. i certainly appreaciate anyone trying to help. you guys are great
Elder User
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Out of curiosity, have you checked the timing ? Maybe advance it a bit and see if it starts then turn it back to the original setting, and how many miles are on it ? Unless it's the computer not sending injector pulse or just something really off the wall like a shorted wire or something, I'm wondering if maybe, just maybe the timing is off a tad.
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Freshman User
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From: florida
what gets me is both wires having 12 volts with key on wether it's turning or not.
i understand if a coil shows voltage on both sides when used, but coil on injector is unplugged when i check for voltage.
and neither one fluctuates when turning.
i understand if a coil shows voltage on both sides when used, but coil on injector is unplugged when i check for voltage.
and neither one fluctuates when turning.
Elder User
Joined: Jan 2007
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Sounds like you're not getting the injector pulse then telling the injectors to spray. This is a longshot,, and I mean a longshot, but Oldsmobile had a problem in the Aurora that was doing something very similar to what you're describing, and after hours of work and lots of new parts, they found out the problem was in the ignition switch itself.
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Freshman User
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From: florida
yes i did try changing timing a little each way no help. leaning torwards bad computer or short in the wiring somewhere. 130,000 miles you guys are deffinatly great.
i have to go to bed now but will see if anyone has more ideas tommorrow thanks guys
i have to go to bed now but will see if anyone has more ideas tommorrow thanks guys
Posting Guru
Joined: Sep 2002
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From: Langhorne, PA
With a voltmeter all you will ever see is 12VDC on both sides..The pulse that drives one wire to ground potential is too fast to see without an oscilloscope of some kind. The pulse may be 500milliseconds, 100mSec, 10 milliseconds...a top-of-the-line the meter won't help, no meter movement (needle) could ever respond quickly enuf.