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Fuel injector scope signal
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milling machine
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Dec 22, 2012, 11:44 AM
Post #1 of 16
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Fuel injector scope signal
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There is nothing wrong with my vehicle but I have a question about the scope pattern for fuel injectors. When you see the hump in the pattern indicating that the injector is mechanically opening--I have one that the hump is not as well defined as the other ones are could this be an indication that it could be gummed up
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nickwarner
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Dec 22, 2012, 11:58 AM
Post #2 of 16
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Re: Fuel injector scope signal
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If you could post that waveform up here that would help a lot.
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Discretesignals
Ultimate Carjunky
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Dec 22, 2012, 12:06 PM
Post #3 of 16
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Re: Fuel injector scope signal
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Is this injector current or voltage your monitoring.
I believe as long as the pintle hump is visible the injector is operating mechanically. If it had a drive-ability problem concerning that cylinder, then it could possibly be an indicator of something going on. You also have to understand that not all injectors are built the same, so you may see some variances.
just to add:
When you are watching injector current, the hump is the pintle opening. If you are watching injector voltage, the hump is the pintle closing.
Not all injectors show humps in their waveforms, so be careful.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 22, 2012, 12:49 PM)
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Sidom
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Dec 22, 2012, 12:47 PM
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Re: Fuel injector scope signal
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Yea go ahead and post a pattern if you can and tell us what kind of scope you are using.
Those open & closing humps are usually hard to pick up and not all scopes will show them....
The opening hump you usually have to use a current probe to see but the closing one can be seen on the voltage side if the scope is good enough.
You aren't talking about the firing voltage are you?
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Discretesignals
Ultimate Carjunky
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Dec 22, 2012, 12:57 PM
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Re: Fuel injector scope signal
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This guy is my hero....probably Sid's too.
http://www.youtube.com/watch?v=NXrd1fYwj1o
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Sidom
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Dec 22, 2012, 1:30 PM
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Re: Fuel injector scope signal
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Yup very good info....and he also showed how a snap test can help spot a lean injector which can really help pinpoint a trouble spot, quickly.
If he ran a dual trace with a current probe that would of picked up the opening hump and then again they can be hard to see but just seeing one hump is really all you need to see. whether it's opening or closing, that tells you that mechanically the injector is working.
The one advantage to looking at the closing hump is you can also spot a weak or broken spring. If you get multiple closing humps, that tells the the pintle is bouncing on the seat due to a bad spring.....
Man, the new Verus has a really nice screen. Your Pico is also has no problem picking those up.....I'll have to admit with a Modis, it is a bit of a challenge to pick those up sometimes.....
The part I luv, is with all this high tech stuff....after pinpointing the trouble spot....The next step in flow chart???? Beat the cr*p outta it.........lol........Hey...it's a valid test....
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Discretesignals
Ultimate Carjunky
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Dec 22, 2012, 1:42 PM
Post #7 of 16
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Re: Fuel injector scope signal
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Flow charts can lead you to the edge of a waterfall too...lol It would have you ohm checking the injector harness, replacing the PCM, and who knows what else. It has been a long time since I've used a flow chart, but they can be good for getting an idea what to check and what is going on in the circuit that a wiring diagram doesn't provide. (sometimes)
One other thing that you can use to catch a stuck closed injector is the first look pressure sensor connected to the fuel pressure regulator's nipple. Have one channel on the injector and watch the pressure pulses in the fuel system. An injector that isn't opening or restricted will have an abnormal pressure pulse or no pressure pulse at all.
I wonder if you can watch pressure voltage changes on a returnless fuel system at the fuel rail pressure sensor to see fuel pulses? Time to break out the scope..
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 22, 2012, 1:48 PM)
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Sidom
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Dec 22, 2012, 1:51 PM
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Re: Fuel injector scope signal
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Yea flow charts can be good or bad....They are only as good as the guy/guys that wrote them, so if there is a scenario some one missed, then you will spend a lot of time testing, with the ending box as replacing the PCM and then still having the same problem...
Knowing a system, most of the time you can eliminate 1/2 the system with some intitial testing and then focus on the problem. A flow chart you have to test out the whole system (until you find a problem), step by step and that is where some guys get into trouble, by skipping some steps "cuz it looked good"......oops.....
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milling machine
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Dec 23, 2012, 9:16 AM
Post #9 of 16
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Re: Fuel injector scope signal
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I was using a analog scope I am just a DIY-- it was a voltage measurement I did not realize on a voltage measurement you would be looking at the closing of the injector I thought I was watching the opening also I do not know how to post pictures or videos on the internet-This vehicle was a Ford explorer six cylinder--But as I think one of you said that this is the spring action that this hump waveform is connected with maybe this is an indication of partially sticking injector--Also I have another question how often does a scope actually help you solve a problem-- so far the scope has never actually helped me solve anything but has actually thrown me off the track a few times causing me to replace good parts for nothing also I knew a Ford mechanic and he said they do not use scopes at his dealership
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Sidom
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Dec 23, 2012, 1:24 PM
Post #10 of 16
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Re: Fuel injector scope signal
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What you can do it up load the waveform to an online photo sharing site like photobucket or something and then just click on the image, copy it and then just paste into the body box here when you are typing your message...
As far as how often does a scope help? Lol..that is a loaded question.... I can't speak for everyone one just my own personal experiences....1st there is 2 modes, seconday ign patterns and low voltage patterns and that is what we are talking about here. I would say the percentage is very high with techs who are familar with ign scoping and a lot lower on the other end. You have to realize that a scope is just one tool available to a tech to help him find a problem and is not the only way to find that problem.. You said your buddies shop doesn't use scopes, that doesn't surprise me, there is a lot of shops/techs that don't use scopes.
It's like any new tool, whether it's a scanner, voltmeter, anything......There is a learning curve, how to hook it up, how to set it up and then most importantly, knowing what you are looking at, what is good & what is bad.
As far as finding the smoking gun, I would say the percentage is low. Most of the time you are looking at good patterns but in a way that actually could be considered in helping to find the problem because you can rule this out or that out as being good and some tests are more definite that other ones......
Take that closing hump on the injector waveform, you can see how hard it may be to see if you don't know what you are looking for and in that video, if you noticed that small spike the tech said "don't worry about that, it's just noise"...He was right it was just noise. Noise is a glitch or interference that really isn't hurting anything but is showing up on the pattern. Then again there is a curve to be able to reconize noise that isn't a problem as opposes to something that is going on that is creating a problem....
If I had to pick one of the best time saving tests, it would be a relative compression test. You use an amp probe on a battery cable and just crank the engine. On the screen it just looks like a line of humps but each one of those humps represents a cylinder AND compression...If you get a pattern of 7 humps, straight line, 7 humps, straight line, this would tell you that you have a cyl with zero compression. This test seriously take about 2 minutes to run at the most. How much time would that save you on a diag on a Ford F150 5.4 with a miss where you suspected low compression. If you've ever had to run a regular compression test on one of those, I think you would agree, you couldn't do it in 2 minutes....but if you don't use a scope, then I'm sure you would have a compression gauge, could pull all the coils & plugs, hook up your gauge, have a helper crank the engine for you & check the cyls, one by one and either confirm the low cyl or comp is good and move on to the next step.......
Now your buddy could come back and say, if the cyl had zero compression it would set a code helping to narrow down the cyl and an experienced ear can hear low compression on cranking and he would be right but even trying to do a manual compression test on one cyl...there is no way you would ever be able to do it faster than you could with a scope (as long as you are familar with the scope & setting it up)
personally I try to use ever tool available to me to help find a problem. Some guys don't like scopes and never will, thats fine, like I said it's not the only tool there is to find a problem, there is always different ways but on some jobs its way faster.
If he has ever had a timing chain jump on a V/6 on the bank without the cmp (actually it doesn't matter it could jump on the bank with the cmp cuz he doens't use a scope so a cmp/ckp waveform wouldn't help him) then the only to options to confirm that jump would be to tear it down and line up the marks or use a pressure transducer to take a running compression waveform and check the valve timing on the screen......
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milling machine
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Dec 23, 2012, 4:01 PM
Post #11 of 16
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Re: Fuel injector scope signal
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Thanks for the answer
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Discretesignals
Ultimate Carjunky
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Dec 23, 2012, 5:54 PM
Post #12 of 16
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Re: Fuel injector scope signal
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I think a scope is an important tool for a technician because it actually lets you see what is going on in an electrical circuit. There are some things that you can do with a scope that you just can't do with a multimeter or see on a scan tool data stream. These computers are processing information very quickly and small glitches can cause big changes. I'm currently building a library of known good and bad waveforms on different vehicles. There is a group of techs in IATN that have compiled waveforms of all kinds of different things on all kinds of different vehicles. It can be compared to catching and cataloging butterflies.
Even the factory service information on some models such as Ford and Nissan are showing waveforms patterns for signal comparison. I'd really like to see someone catch the bad coil setting a P1320 fault on a Nissan 3.0L using a multimeter only. Ain't going to happen.
I've caught bad COP coils, used it to troubleshoot an AC problem which lead me to a bad condenser, caught a few bad cam and crank sensors, and used it to help me find a problem with a TAC system on a Saturn. When used right it is a very helpful tool. When used with other tools and other strategies, you can become one bad ass tech...LOL. Techs are also find new ways to use a scope to check things and even creating their own software to set the scope up for particular functions. It's constantly evolving.
The main advantage of a modern DSO, besides helping you understand more about electronics and signal monitoring, is the ability to record and catch glitching.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 23, 2012, 6:07 PM)
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milling machine
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Dec 24, 2012, 1:47 PM
Post #13 of 16
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Re: Fuel injector scope signal
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Maybe Car Junky can start a section for problems concerning scope troubleshooting some DIY are getting scopes because they hear about them especially on u-tube--that is why I have one but as said again if you are not that expierenced at reading signals you can easily misinterpret them causing the replacement of good parts
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Sidom
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Dec 25, 2012, 12:57 PM
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Re: Fuel injector scope signal
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Not a bad idea.....I would definitely have more interest in that section than say..........Motorcycle seat repair?????
The only downside I could see to that is, with the large percentage of techs who either don't or won't use scopes I can only image the split is even greater with DIYers....
You have one, can hook it up and understand what you are looking at....My guess would put you in the top 5% of DIYers....
My memory sux but I'm getting flashes now about you getting this old scope a while ago.....What type of scope are you using????......I would love to see some waveforms...... You would probably have to take a pic with a camera and up load that, take picture of the scope to....
I've used those analog scope before and personally the big plus they have over the new ones is the waveform. The old ign scopes I use to use had functions like yours where you could use the lower voltage ocillascope for different things. I don't know if it was,, the screen size or what but they had beautiful patterns that were really easy to see stuff.
If you could put all the bells & whistles off the new DSOs into an old analog scope (more than 1 channel, storage, zoom, etc) I personally think that would be one of the best out there.....
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Discretesignals
Ultimate Carjunky
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Dec 25, 2012, 5:58 PM
Post #15 of 16
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Re: Fuel injector scope signal
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motorcycle seat repair is a hot section....lol
I would like to see a section devoted to test equipment and how to use it. Don't know how many posters that come in here and don't have a clue on how to use a DVOM, noid light, or even a 12 volt test lamp.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 25, 2012, 5:59 PM)
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Tom Greenleaf
Ultimate Carjunky
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Dec 25, 2012, 9:23 PM
Post #16 of 16
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Re: Fuel injector scope signal
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At least half of the sections should go now. "Use of tools and equipment" could be one new spot. Leave a ton of assorted stuff to plain "Open Posting" and focus as few areas as possible - T
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