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Old 06-26-2005, 05:45 PM   #1
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How to check if injectors are firing?

Like it says, how do I test to see if the injectors are firing?

...I'm having my no-start issue yet again. It's happening more frequently now. I have the correct fuel pressure, and I'm wondering if maybe the injectors aren't even firing.
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Old 06-26-2005, 06:39 PM   #2
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buy a noil light. it plugs into the injector harness and blinks of they are getting power.

http://www.etoolcart.com/browseprodu...ht-NM5559.HTML
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Old 06-26-2005, 09:00 PM   #3
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$5 or so at Pep Boys in the tools aisle...
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Old 06-26-2005, 09:26 PM   #4
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A noid light will not tell you an injector is firing fuel. It will only tell you the ecu or distributor is commanding fuel. The only way to tell if an injector is actually firing is to remove the fuel rail or do the "leakdown" check per the GM manual.
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Old 06-26-2005, 10:04 PM   #5
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Deleted answer as it does not relate to the no start question.
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Old 06-26-2005, 10:33 PM   #6
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Quote:
Originally posted by John Millican
A noid light will not tell you an injector is firing fuel. It will only tell you the ecu or distributor is commanding fuel. The only way to tell if an injector is actually firing is to remove the fuel rail or do the "leakdown" check per the GM manual.
Its the quickest and easiest way to tell if they are getting a signal to pulse or not. If they arnt there ya go. If they are then do a leakdown test and pop off the rails if needed.
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Old 06-26-2005, 11:03 PM   #7
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To find an individual injector gone bad, I'd understand the leakdown test, but this is for my no-start problem. Assuming that I am actually getting the inector pulse, what are the chances of multiple injectors all with the same intermittent failure.

Almost non-existant.

...I just re-read my post and realized that you guys may not be familiar with my problem. I'm having trouble with the car not starting. I'm trying to eliminate the possibility that for whatever reason, the injectors aren't being told to fire. The noid light with do that for me. I realize that it will not find a bad injector.
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Old 06-26-2005, 11:09 PM   #8
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Just dso you know one shorted out injectr can kill either a whole bank of them or maybe both banks due to it shorting the driver in the ECM. If it wont start first check spark and injector fire and see which your loosing.
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Old 06-26-2005, 11:19 PM   #9
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What else would cause me to have the injectors not firing?

I was gonna have the injectors cleaned, balanced and blooped anyhow, so regardless of what I find, I'm gonna yank'em and have 'em done.
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Old 06-26-2005, 11:28 PM   #10
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are u sure its not just that hot start problem?
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Old 06-26-2005, 11:42 PM   #11
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That's exactly what I think it is......

......and I still don't know WHY it's happening!
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Old 06-27-2005, 12:20 PM   #12
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Quote:
Originally posted by Abubaca
To find an individual injector gone bad, I'd understand the leakdown test, but this is for my no-start problem. Assuming that I am actually getting the inector pulse, what are the chances of multiple injectors all with the same intermittent failure.

Almost non-existant.
.
Not true. I had a complete set of 8 fuel injectors I bought from Street and Performance. All of them were bad.
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Old 06-27-2005, 12:23 PM   #13
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The distributor ignition module fires the injectors under 350rpm (during cranking), after that the ecu takes over control of the injectors.

If you have a cheap parts store ignition module in your distributor get it out now and replace it with an AC Delco module. Don't forget the special greese under it or even the Delco one will fry.

This may of may not fix your problem but it is good insurance.
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Old 06-27-2005, 01:28 PM   #14
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Quote:
Not true. I had a complete set of 8 fuel injectors I bought from Street and Performance. All of them were bad.
...but to ALL fail and cause a no start condition, and then ALL fix themselves and work. ...and then all fail again later? Don't get me wrong, I hear what you're saying, and they're gonna be cleaned/checked regardless. If nothing else than to eliminated any doubt.



Quote:
The distributor ignition module fires the injectors under 350rpm (during cranking), after that the ecu takes over control of the injectors.
So if when I test the injectors they're not getting a signal to fire, that means that for whatever reason the ignition module isn't sending the signal? ...Whether it's faulty, or if it's something else? That makes sense. I've replaced the module, but it was NOT AC delco. It worked fine for awhile, then the problems came back. ...but of course it could be coincidence. It may not have been the module at all. REgardless, I'll get an AC Delco piece this week.
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Old 06-27-2005, 02:57 PM   #15
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Bad injectors will funtion until the driver(inj driver) board overheats and shuts down :-) Once it cools it will refire.


Other fun things are pickup coil in the distrib and the module.

When these dont outirhgt fail, they tend to act up in overheat/high tempature conditions first and then die completely.
(or cause weak pulse/signal to ecm resulting in weak spark and/or intermittnet injection)

Other thing is Vats issues. Dirty and worn key or ign lokc barrel or even broken or intermittent wire connections there. Possible module too, but I havent seen a moduel fail in my own experience.

later
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Old 06-28-2005, 03:02 AM   #16
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Quote:
Originally posted by Abubaca
[B I've replaced the module, but it was NOT AC delco. It worked fine for awhile, then the problems came back. ...but of course it could be coincidence. . [/b]
You said it yourself, the ingition module fixed it "for a while". That's because parts store modules are very much junk. It's not coincidence. A good Delco module will set you back around $60 compared to $30 something at a parts store.

The only other thing in the crank fuel system is teh pickup coil and wireing between the ignition module and ecu. The ecu injector drivers don't come into play untill the engine is started (over 350rpm's).
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Old 06-28-2005, 08:13 AM   #17
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I'm gonna pick up an ACDelco mod. this week. I won't get to do much more "testing" till the weekend though.

Thanks!
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Old 06-28-2005, 08:29 AM   #18
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Quote:
Originally posted by Abubaca
I'm gonna pick up an ACDelco mod. this week. I won't get to do much more "testing" till the weekend though.

Thanks!
When you install the new module, be sure to use the heat-sink grease as indicated. It supposedly helps conduct heat from the module to the dist body and keep it cool.
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Old 06-28-2005, 01:45 PM   #19
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Oh don't worry. I learned that the hard way a few years ago.
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Old 06-28-2005, 01:45 PM
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