looks like it is trying to turn on the injector but no current is going through when it cuts out.  Is that something that would be in the injector winding?  If it was a open I would not think there would be voltage at the supply and contorl side at the same time.  Am I anywhere on the right track?

Hi Sam,

Would you agree that an injector winding fault will be more than likely consistent?

Also, I agree with your statement in regards to an open. We wouldn't see supply voltage on the control side if it were open. What if there was high resistance instead? Would this not show us supply voltage while the circuit was unloaded?

Hi Sam,

I sent you the psd file.  You can open it with the current software.  Just switch converters in the software.

If any other Pico users want to have a closer look:

http://www.autonerdz.com/downloads/mf.psd

         I have to admit I was confused by what thought I saw in the movie.  An engine that seemingly was running alternately between mostly four cylinders and no cylinders without rpm change? The download sure helped. The rpm was fluctuating! Blowing UP one signal sure helped me to see a problem.

          BTW don’t ever try to play Techardy with Matt. Nice guy nervousness but cool as a cucumber under fire   What a natural! Thanks for the cool capture Matt!

I read good pertinent stuff in a manual by Linder (of injector reputation) and in a waveform reference manual by Motor.
  Linder calls these injectors TBI injectors(TBI was a peak and hold injector in GM applications).I noticed ours have a pattern like the peak and hold.One injector fires all six poppets at once, thus ,once per revolution.I think the reference voltage is perhaps a modulated cam position signal -maybe a hall effect with six vanes-the injector would fire once per crank revolution.That would be why we see a consistent injector firing every third cycle of the reference voltage, once per crank revolution..SO, the signal for the injection for the cam position is fair to good.
         In the Motor reference manual is a case history of a bad peak and hold injector- the shorted injector ruins the driver. I think it looks like the injector in our case follows the pattern of a shorted injector because it has low or non-existant voltage peaks(That is the way MOTOR explains it)-they ought be consistently around fity or eighty volts depending on the system.Ours are all over the place.I could say it ruined the driver because of the way the driver is firing the injector(that is what happened in the case history -the shorted injector ruined the GM injector driver-new PCM time).It looks like the driver has no rhyme or reason to the way it fires the injector and it looks like the short is an intermittent that would only get worse.
 They put diodes in the COP spark systems in series with the secondary to prevent voltage surges from it going backwards into the PCM and shorting it.
                    This explanation is relative to the books I have read, but not due to practical experience.Practical experience can be embarassing.Go to open forum and read about mine today for sure.
   

Quote:


Fisher,

There are no signs of a shorted peak and hold injector in that capture. If that were to happen, we would see a quick vertical rise in current at turn on to about the midway point typically, and then ramp up at an angle to about 4 amps. Current limiting would kick in and lower it to approx 1 amp. This doesn't hold true for a saturated switch style injector. Since there is no current limiting feature with that type, we would see higher than normal current peaks accompanied by the quick vertical rise at turn on. You are correct in stating that the voltage peaks are dimished with a shorted P&H injector, however, we would still see current flow until it got to the point the driver shut down. Remember what Tom said, "everything is there to diagnose this vehicle." A shorted injector taking out the driver is not there. Hope this makes since.

What a great capture. 8)  Thanks Matt... It sure looks like a bad ECM driver to me.

Edwin

Here is what I see:

1: 0 Amps when the fuel injection drops out, which indicates either an open or high resistance in the circuit.

2: Power feed to the injector stays steady at ~14 V, which indicates no problem on the power side.

3: Ground is still being pulled low to 0 V, which indicates driver in computer is functioning and no volt drop on ground side.

4: No inductive kick (along with no ramp up in amps), which indicates no magnetic field in injector coil.

5: Still ~ 14 V open circuit voltage on the ground side of the injector, which indicates injector in not open (as pointed out in earlier posts).

My conclusion: injector coil is failing with excess resistance when hot or excess resistance at the connector to the injector.  I'd take a close look at the connector to the injector and if no problems found would replace the injector.


A couple of additional things that I also noticed from the psd file:

1: If you zoom in on the amperage when the injector drops out you will notice a very small noisy amperage reading.  This supports the excess resistance idea.

2: If you zoom in on the time right before the injector drops (for example 1800 mS) you will notice that the current starts ramping up well after the drive pulls the ground to zero.  This is why I think that excess resistance at a connection could be a factor.  I would check the injector connector for terminal tightness, corrosion, etc before condeming the injector.

Lots of other cool detail in the capture also, but the above is what I would key in on for a diagnosis.

loren

Is there really a timing issue going on (900 mS - 1100 mS and other spots) or is extra fuel being delivered asynchronously?  I may be way off or not looking carefully enough, but it looks to me as if there is a regular consistant injector pulse pattern with extra asynchronous pules added to increase fuel delivery at times.

I am keying in on the loss of amps pointing to a high resistance issue in either the injector or the connector to the injector.

loren

  I thought about the O2 sensor and how it reacts to what could be no fuel.I thought about how the first frames show no current draw and thought that the firing will anyway show a mass of oxygen which the sensor interprets as lean;it only REACTS to oxygen.SO, too, I dont know what pattern should normally show on these injectors.I know that the injector doesn't fire itself.
  So, to me the driver looks bad unless it is supposed to fire in mutiples-like that Ford system for secondary-at idle IT fires mutiple strikes.
   One of my school books says heat is an issue with bad connectors.

We know the driver grounds an already hot or positive injector... ,( those aren't PNP injectors; the signal isn't 'upside down') so, it would be easy for a break in the ground wire between the ECM and the injector to ground the injector as there is so much grounded metal for to do that with,but- the "asynchronous" are still associating with the regular timed pulse they are firing ahead of of it I mostly noticed.The third pulse is part of the the other two, it is with the driver; it is voltage of the driver(it's gotta be!).
A firing pulse due to a broken ground ought occur at ANY point in the engine operation.
  Do you notice that the reference signal is kind of unhappy?It seems to ramp up almost a volt really gradually before the on signal and then distinctively on it's off signal there is an associated dropout or spike in the injector voltage trace.That one seems to become the third injector pulsation, the other two being the ones that look like a peak and hold?
 

Quote:


   Yeah the reference is the first signal I blew UP cause I noticed it was lifting off ground but it repeats the lifting consistently across the waveform while the injection pulses are not consistent so I dismissed it as being a cause. I don't think the reference off alignment to the noise in the injector voltage trace is a problem for the same reason of its consistency VS. injector turned on inconstancy. I agree with you though Fisher, Im gonna sit back now and see what others have to say.

OK, game over.  Thanks for playing    We discussed this in Group Therapy last night too.

A lot of good ideas and many of you are on the right track.  Loren (Maki) nailed it with the most complete and accurate response.  He said it better than I could, but I'll blab anyway...

1.  The asynchronous pulsing of the injector is a normal injection strategy.  It can do this on accel or trying to catch a stall.  It's just a distraction and can be dismissed for now.  There are much more important elements in the capture that tell the story.

2.  The lifting off ground of the reference (chan B) is a circuit voltage drop caused by the coil current.  It's normal.  At time 4420ms you can see clearly a coil ramp and fire in the reference voltage drop.  Zoom in 2x vertical on channel B to see better.  You see the induction ramp, current limit and cut off.

3.  The voltage is present on channel A injector drive (neg side) when the injector is not active so the circuit is not open.  However, during the event, when the injector is grounded, no current flows.  So, we know there is excessive resistance somewhere.  We have a bad connection.

4.  The distance between the lowest point in the injector voltage waveform on channel A and ground is the circuit voltage drop from the test point at the neg side of the connector through the PCM driver, the PCM grounds and all the wiring to bat neg.  Just like using your DVOM to do voltage drop testing on a starter circuit, the circuit must be active to see the voltage drop.  If the bad connection was anywhere between the channel A test point and ground (PCM driver, PCM grounds, etc) then we would see that in the voltage drop.  We don't.  The injector is flat on ground the whole time.  Therefore, we know that the bad connection is not anywhere after the channel A test point toward the PCM.

5.  Channel C is on the power side B+ of the same connector.  It shows no drop in voltage during the events.  If the bad connection was toward the power supply from the channel C test point, we would see the voltage fall.  We do see this voltage dip when current flows in the circuit.  It's minimal and to be expected.  We can even see an upside down injector current signature there if you look closely.  But not when there is no current flowing.

6.  Conclusion:  The bad connection is between the channel A and C test points.  Since all that is under the upper intake plenum, it's time to get out the wrenches.  We know what we are looking for and where to find it.






Waveform databases are great, but we can't do lab scope diagnosis by simply comparing waveforms.  We have to be able to analyze, using the system knowledge and the behavior of circuits.  I always say, slow down you'll be faster.  Don't rush off to do another hook up until you fully understand what you have captured already.  You may not need any other captures.  The answers to all your questions may already be right in front of you.

Nice logic Loren you could see the forest right through those darn
asynchronous trees 

  Not sure I see a potential stall as the cause of asynchronous pulses though.

Here’s why,

1. The time between reference pulses at the beginning of the movie (with no injection –445ms for example) is 17 ms or so.

2. Then (at 0ms) injection returns and the time between references decreases to about 12-15 ms (slightly higher rpm for quite a while) and then, out of the blue at 910 ms the asynchronous trees start growing.

3. Then injection goes away again and while there’s no injection and the time between references has increased to about 25 ms (surely it’s closer than ever to stall) at the 2800ms mark injection returns but without async pulses.

I don’t know what the answer to this is, I just hate not knowing. But that’s the way it goes sometimes.

Enjoyed the game all. 

Ok Tom,

Ya suckered me in. I have to say that is a fantastic capture that Matt did. Just excellent work.

So here is what I see.

I see a consistant injector supply voltage. As a matter of fact you can see the load imposed by the injector when it's operating propely. Since the voltage drop on the supply is consistant during the peak injector turn on load of about 4 amps I'm going to rule out a voltage supply issue right up to the  test point. (I'm assuming that he's backprobing right at the injector connector) 

The ref signal looks fine to me so I'm going to rule out a control side (logic or input) issue.

When the failure occurs it appears that all the current flow goes away. The trigger side of the injector appears to be normal pulling nearly all the way to ground with the exception of a lack of inductive kick. The lack of the inductive kick tells me that there was a lack of a magnetic field formed.  This is due to the lack of current flow.

What could cause this?

Since we have a lack of current flow I'm going to rule out shorts to ground or a lack of resistance in the circuit. Either would cause an increase in current flow.

Since we don't have excessive resistance we must either have a lack of voltage or excessive resistance.

I know source voltage is good up to the test point so I can rule out everything in the voltage supply up to that point. 

The trigger occurs when it appears that it should. It also appears to remain near ground when it should. If the driver in the ECM was failing and could not retain the ground (failed to allow current flow) on the trigger side I would expect to see the voltage ramp up during the on time. It doesn't do this.

I'm only left with two choices, either there is a high resistance connection right at the injector terminals themselves or the injector is intermittently going high resistance under load.

I'd sell the injector and perform a pin drag test when I was replacing it.

That's my story and I'm sticking to it.

Just hope like heck I'm not wrong;-)

Jon