injector's are not spraying???

[tylerjames]

hi, my name is tye... i'am a new member to this site but if been using it for awhile i got a 94 silverado with the 5.7 350 that the injector are not spitting any kind of fuel i replaced the ecm in it and the ground from the block to the frame and also the one from the body to the frame... the fuel pump was another thing i replaced but was not the case... any idea's???

[manicmechanix]

Can you tell if the fuel pump comes on? You need to stick a fuel pressure gauge on it, but a quick and dirty test would be to unhook the feed line and see if you get a good stream of fuel into a cup when you turn the key to ON. See if you are getting spark. Make sure any spilled fuel has evaporated off before you Crank the engine or check spark of course . You can also unhook the injector connector and hook a test light acoss the terminals and see if it flashes during cranking. This engine is a TBI with a distributor right?

[tylerjames]

the fuel pump dose not turn on when the key is into the on pistion but when i start cranking it it will kick on... and i did the test light ideal for the injector's but with a noid light and it dosent flash or come on at all thats why i thought it was the ecm but i replaced it and still nothing... and i get spark to the plugs

[manicmechanix]

I'm not sure why your fuel pump wouldn't run for a couple seconds when key is turned ON but will run while cranking. But if your not getting any injector pulsing while cranking but you are getting good spark, it might be your ignition module. But first check fuses and with a test light hoked to ground check that you are getting
+12V to the injectors with key ON. You seem to have an elctrical problem or ignition module prob. If you had a service manual that covers the diagnostics that would help. Do you have a scanner? You can jump the diagnostic connector with a wire or paper clip and you should just get a code 12.

[Airjer_]

Are you sure you don't have a blown ECM fuse?

[2000CAYukon]

The injector pulse comes from the pickup coil which is converted to a DC signal by the Ignition Module. So a bad Ignition Module or pickup coil can cause the injectors not to fire.

//2000CAYukon

[Airjer_]

If the pickup coil is bad there would be no spark and no injector pulse. If the module was bad wouldn't there be injector pulse but no spark?

[j cAT]

Originally Posted by tylerjames

the fuel pump dose not turn on when the key is into the on pistion but when i start cranking it it will kick on... and i did the test light ideal for the injector's but with a noid light and it dosent flash or come on at all thats why i thought it was the ecm but i replaced it and still nothing... and i get spark to the plugs

with a voltmeter check for voltage at fuel pump....
with a fused wire jump fuel pump electrical connection....
make sure the fuel tank grounding point is clean and this ground/wires are properly grounded for fuel pump return...

insufficent pressures will cause your problem/fuel filter plugged..
all injectors not spraying fuel is usually the ground for them or no fuel pressure....

you have spark so the crank sensor must be working..

[manicmechanix]

Originally Posted by Airjer_

If the pickup coil is bad there would be no spark and no injector pulse.

Yeah I think so. Since he said he had good spark his pickup coil is working.

If the module was bad wouldn't there be injector pulse but no spark?

Not necessarily. The module has a reference wire to the ECM that tells the ECM to pulse the injectors, and even if the module is switching the coil (sparking the plugs) that doesn't mean the module doesn't have a problem in the reference circuit for the ECM.

This is what I think his problem probably is. It's a common problem really. I forget what color this ref. wire is but I think white or purple. There's a few ways to check it. Check the module output for the reference or stick a test light to +12V to the harness side and see if the ECM pulses the injectors every time the terminal is touched. I think is safe to apply 12V to the ECM reference but don't qoute me on it .

[2000CAYukon]

Wire is Purple/White. With Ignition on, and the 4 wire plug disconnected at the dist, momentarily touch 12V test light to the Purple/White wire on the connector. If the injector pulses, the ignition module is bad.

Most parts stores, can also test the ignition module.

//2000CAYukon

[jyount]

Originally Posted by manicmechanix

I'm not sure why your fuel pump wouldn't run for a couple seconds when key is turned ON but will run while cranking. But if your not getting any injector pulsing while cranking but you are getting good spark, it might be your ignition module. But first check fuses and with a test light hoked to ground check that you are getting
+12V to the injectors with key ON. You seem to have an elctrical problem or ignition module prob. If you had a service manual that covers the diagnostics that would help. Do you have a scanner? You can jump the diagnostic connector with a wire or paper clip and you should just get a code 12.

The reason the pump could run while cranking and not at key on is that it has redundant power supply circuits.
The primary circuit for power is thru the fuse and relay so on and so forth, the secondary backup though is that once the engine develops oil pressure it can send another power circuit if needed, not sure exactly how it flows thru circuitry, but it DOES have backup power supply, so long story short, he has two problems.
If you don't have injector pulse I would recommend at the very least go to Autozone(typed under my breath) and get a Haynes(also under my breath). At least it will give you some basic diagnostic steps.
It sounds to me like you have spent 500-1000 on parts that didn't fix a thing. A Haynes book is only like 22 dollars, money well spent sounds like. I don't know what your problem is for sure, but I would say to either get a book and do some diagnostics, or take it to someone who has books and diagnostic exp.
To often when I worked at the dealer someone would have a couple thousand in parts changing and we would fix something little for less than a hundred bucks.
Even if you can't afford to fix what they find, our shop, and alot use the same principles, would charge a flat 1 hour diagnostic fee, in other words, if it took all day long to figure it out, you only paid for an hour.
Good luck though, don't mean to offend you if I did, but sometimes you will spend alot more to try to fix it yourself than you would if someone in the know did it. Not to mention your time.

[manicmechanix]

Originally Posted by jyount

The reason the pump could run while cranking and not at key on is that it has redundant power supply circuits.
The primary circuit for power is thru the fuse and relay so on and so forth, the secondary backup though is that once the engine develops oil pressure it can send another power circuit if needed, not sure exactly how it flows thru circuitry, but it DOES have backup power supply, so long story short, he has two problems.

That'/s a good point. I understand that earlier GM fuel pumps were supplied power through the oil presure switch, but models in the later 90's and up weren't. I'm not really sure if his is the earlier or later style. He could also have problem with the ignition switch in RUN. I was really just saying that I was surprised that his fuel pump wasn't coming on in RUN but was during Start. He's definitely got a whole other problem with the injectors not cycling and it's probably related to the ign module as was explained earlier.

[jyount]

Originally Posted by manicmechanix

That'/s a good point. I understand that earlier GM fuel pumps were supplied power through the oil presure switch, but models in the later 90's and up weren't. I'm not really sure if his is the earlier or later style. He could also have problem with the ignition switch in RUN. I was really just saying that I was surprised that his fuel pump wasn't coming on in RUN but was during Start. He's definitely got a whole other problem with the injectors not cycling and it's probably related to the ign module as was explained earlier.

Not 100%, atleast 98% though , but I think a 94 should still be this way. But ya, hes got multiple probs.

[manicmechanix]

Originally Posted by jyount

Not 100%, atleast 98% though , but I think a 94 should still be this way. But ya, hes got multiple probs.

Yeah I think the change away from the oil pressure switch powering the fuel pump probably happened after '94 on most application. Well the original poster got some really good diagnostic advice, but for all we know he could have a bad fuse or open circuit somewhere. He's never got back with us and told us if he checked out the things we mentioned. Being an automotiveforums troubleshooter is a thankless job .