Hello Techs,

This vehicle is fixed. The primary purpose of this post is to discuss cause and effect of scan data and ultimately show how powerful the PS3423a is.

Vehicle is a 1995 Chevrolet Camaro with a 5.7 liter VIN code P engine. This LT1 engine is sequentially fuel injected and utilizes an Optispark (ABITS) type II distributor which is the vented style.

Several modifications have been done and I’m not aware of all of them. It has been supercharged and the PCM has been chipped. There is a boost pressure and air/fuel gauge mounted under the IP. The LH pre-cat O2 sensor wire has a blue scotch lock on it which feeds the A/F gauge. There is a 5 speed trans in place of the original automatic. And to top off this mess, there are headers!

Complaint is lack of power when slightly accelerating. First thing I do is check for any DTCs. There are two codes for the skip shift solenoid. Imagine that! The PCM was programmed for a Borg Warner T56 6-speed trans. I just ignored it.

As I’m approaching highway speeds in fifth gear I noticed sort of a “fish- bite” or “chuggle” sensation. I then start recording this on the Tech 2. I gave it a little more throttle and it became more pronounced. I get the car back to the shop and upload my snapshot. Have a look.



What would be your next move?   

         Hello there.
  The O2 sensor is a voltage generator.The only way to measure the voltage on a single wire 02 sensor is to ground it( through the Scope or DMM).The a/f ratio gauge likewise will not work if it is not grounded and becomes a drawer of amperage-as it  grounds, somewhere in it's circuitry, some of the entire current produced by the O2 sensor.
       That will cause a lowered voltage signal by the sensor to the ECM.
        The ECM is interpreting that lowered voltage as lean, and attempts to enrichen to correct.
 I agree with Jarvis-Samuel and I think the  Air/Fuel gauge is the cause of the  problem.

Hello Gentleman, hope you do not mind my playing along?

Afraid I am not overly familiar with Chevrolet fuel trim stategy but is it not odd that the primary long term fuel trim increased without a consistant increase in the primary short term when the throttle was snapped?

Paul Summers

Thank you Mr. Grotti

Shaking my head I missed it on my first look but bank 2 has a perfect stoichiometric block learn value of 128 while bank 1 has a block learn value of 158 which indicates that the PCM is enrichening the A/F mixture to compensate for a lean condition based on oxygen sensor feedback. 

If I am on the right track I will have to do a bit of homework as I am unfamilair with the engine control system.

Paul Summers

Hi Edwin,

It had a lumpy idle. Fuel trims at idle were 128, 121, 128, and 118. At 2000 rpm, they are like what you see on the graph. I didn't go to WOT, but at 81 % throttle angle, the left O2 was 905mV and the RH was 870mV. I did current ramp the injectors and they were ok. Also I attached the First Look Sensor to the fp regulator and the waveform looked perfect.

There is no intake vacuum leak. Idle fuel trims would have shown this more so than off idle conditions when the intake air pressure is higher.

Do we have excess O2, or lack of HCs, or a combination of having too much of both?

Nothing wrong with being curious. Try this out.


Ignition problem? You tell me. 

Autonerdz Productions presents this flash movie of ignition on this '95 Camaro. This is at idle when the engine is running a bit lumpy. 

http://www.autonerdz.com/flash/95camaro.html


 

Correct, The OE ignition system does not provide multiple sparks. However, which I should have mentioned in the beginning, this has a Crane Fireball ignition controller. I believe it is a HI-6S Digital Multi-Spark Ignition (an inductive design).

No need to see the coil current ramp. The problem is isolated to one cylinder as seen in the movie. From left to right, the firing events are 5718436572. This is using #7 as a sync because it was easiest to get to. A faulty coil would have shown up in other cylinders as well.

You want to see ignition control? You did. I think what you meant was ICM inputs, correct?

Let me explain a little on how this system works. There is no CKP sensor. There are two CMP sensors which are of the optical variety. One disc has two sets of slots in it it. There are 360 slots for high resolution which are equally spaced apart. This is used for timing control. The other eight slots which are of different widths tells the PCM which plug is being fired. Both signals are sent to the PCM. The PCM then sends an ignition control signal to the Ignition Control Module (ICM). Naturally the ICM will control the coil.

Is there a triggering problem? Not at all. We are isolated to a single cylinder.

Now its time to determine from the secondary ignition capture of where the fault is based on the irratic spark line disturburbances.

Correct, The OE ignition system does not provide multiple sparks. However, which I should have mentioned in the beginning, this has a Crane Fireball ignition controller. I believe it is a HI-6S Digital Multi-Spark Ignition (an inductive design).


OK, that makes more sense. When I first saw that I was disturbed by it and I did not get passed that. Wow, this is an inductive Multi-Spark ignition system and not a capacitive ignition system? Very interesting. Does this system only multi-spark at idle? Is this to achieve a smoother idle?


No need to see the coil current ramp.

Maybe, just for fun.

The problem is isolated to one cylinder as seen in the movie. From left to right, the firing events are 5718436572. This is using #7 as a sync because it was easiest to get to. A faulty coil would have shown up in other cylinders as well.

Like I said before I could not get passed the multi-spark. Would the firing events be 57218436572? I never thought it was a faulty coil.

You want to see ignition control? You did. I think what you meant was ICM inputs, correct?


Yes that is correct. I wanted to see if the inputs match the outputs.


Now its time to determine from the secondary ignition capture of where the fault is based on the irratic spark line disturburbances.


The problem is in cylinder number 5. I see good conductivity at the start of the firing line and normal spark KV. At first the air fuel ratio is normal but some where in the middle there is a lack of conductivity. It does not look like it is running lean to me but rather a lack of HC and 02. I think it may be a mechanical problem on the cylinder. I would want to hook up a vacuum gage or use the First Look sensor to verify if this is the problem.  Depending on the results I may do a cranking and running compression test.   

Edwin

With the firing order of 18436572 and the pattern being synced/triggered by #7 cyl, I believe at this point that #5 is exhibiting a fuel distribution issue, and the First Look sensor is not indicating a restricted flow to any cylinder, I suspect a faulty /poor spray pattern from that injector.

Edwin -

Your observations on the fuel trim numbers may be correct.  But I think that they could be caused by an ignition misfire. 

First, the fuel trim numbers are from the vehicle accelerating under load on a test drive (do we know only one cylinder was misfiring at the time?).  The secondary ignition waveform was captured at idle (do we know what the fuel trim numbers were at idle?).

Second, the short term fuel trim for bank 1 really wasn't that high (133).  This could be easily be caused by a single cylinder misfire.  I could be completely wrong here, but I believe that the high long term trim for bank 1 is showing the cumulative effect of the misfire over a long period of time.  In other  words:

Misfire occurs --> O2 swings low --> More fuel added (short term nudged slightly higher) --> Long term follows and is nudged higher --> 

Misfire occurs --> O2 swings low --> More fuel added (short term nudged slightly higher) --> Long term follows and is nudged even higher --> etc.

Of course each time fuel is added it actually does more harm than good since the cylinders don't need more fuel.  It is just that the O2 sensor sees excess unburned oxygen and doesn't see the unburned HC's from the misfire.  So, the computer responds by over fueling.   Additionally, this actually makes the engine run worse since it now has gone from having one cylinder misfiring due to an ignition fault to now having four over fueled cylinders.

Though I must add that I would be the first to admit that my understanding of fuel trim diagnosis is not as good as I would like it to be.

loren

Edwin,

I need to elaborate on something here. I pulled those idle trims numbers off of the tail end of my recording. This was after a decel sitting at the intersection ready to make a turn. My focus was more on traffic rather than how the engine was running at the time. It is very possible that the engine was running ok at that time. I wasn't watching trims at the time I captured secondary. The idle instability was not consistant. I'm not so sure I could pick out an intermittent misfire using fuel trims regardless. No, I didn't attach a vacuum gauge, but that is a very good suggestion. Something very basic that often gets overlooked even by me. I assure you there was not a mechanical issue. When I seen the ignition capture, one thing came to mind. There is a ____ to ______. What is your method of converting counts to percentage regarding fuel trims?

Man, I was hoping you guys didn't catch that rotor KV being higher than plug KV on that first event. Anybody want to take a stab at it? It doesn't happen during the next firing of #5.

Romain, take a look at the third strike on the first series of strikes for #5. Poor injector spray pattern?

No, you didn't get wrong information. What I said is true. It did have a lumpy idle and the trims I gave are correct. I should have mentioned the lumpy idle was intermittent. Sorry, that is my fault. I did see where you drifted off the right path is why I mentioned it. You are doing real well with this Edwin, I'm glad you joined in on this post. My apology for misleading you.

Wouldn't you agree that FTs would not necessarily reflect an intermittent misfire?

Hi All,
        
     I am not a fan of secondary ignition diagnostics. I am of the firm belief that one thing can look too much like another.

     When I look at the #5 pattern it looks like to me it could be caused by a poor injector spray pattern. (as Romain pointed out)

    When I look at the #5 pattern it looks like to me it could be caused by EGR turbulence (as Romain pointed out)

    When I look at the #5 pattern it looks like to me it could be caused by turbulence from a valve sealing issue. (as Romain pointed out)

    When I look at the #5 pattern it looks like to me it could be caused by a loose spark plug.

   When I look at the #5 pattern it looks like to me it could be caused by carboned valves soaking up fuel on #5.

   When I look at the #5 pattern it looks like to me it could be caused by maybe something else that doesn’t occur to me. 


   Personally the only thing I believe it’s possible to see for sure in secondary ignition patterns are patterns of normal, high and low resistence.

    When I take a look at #5 pattern all I feel confidant in saying is that I see high resistance in the burn line. However since Carl seemed to highlight the rotor gap I’ll do what I don’t like to anyway and take a SWAG and say:
   
       When I look at the #5 pattern I see high resistance in the burn line that looks like to me it could be a crossfire to another cylinder ......or it could be something else that doesn't occur to me.

       If block learn of 128 is 0 LTFT then I guess 158 / 128 = 1.23 would mean an LTFT of +23% ? The clues from the block learn if Edwin and I are doing close conversions sure don’t add up though. I'll have to go along with Edwin here. A +23 or +26 sure indicates a lambda issue that could easily be single cylinder lambda related misfire. Maybe this truck has another bank 1 issue totally unrelated to the misfire. I don’t see an ignition misfire causing this much +LTFT

    Darn! I hate trying to do this with secondary patterns. They make me SWAGGER 
   
    Personally when it comes to misfires give me a vacuum guage,O2 waveforms, and most times FT’s (but even better a gas analyzer) any day 

Hi JT,

Nice to hear from you.  I know you and me have traveled this road before about secondary ignition wave forms.  You definitely make really good points. 

Carl, I like to use fuel trims and a vacuum gage for misfires to give me a direction where to go.  You asked if I used fuel trims for an intermittent misfire, that would depend...  If the system cannot give you fuel trims, I like to use the gas analyzer along with a vacuum gage and the O2 sensor.  You didn't give me the wrong information, but the way you presented it, it made it seem to me that those fuel trim numbers were happening at the same time as the misfires.  In order to use fuel trims for misfires the misfire has to be happening at the same time.  The way I was calculating fuel trim as a percentage was like John is calculating it, except I was using total fuel trim.  Definitely John put it the best way by saying that this is a SWAG because we don't have any fuel trim numbers, vacuum readings, or gas readings.  So if I was to take a SWAG at it now, I said you have a possible ignition misfire and it cross firing to another cylinder under load and maybe two cylinders are misfiring causing those high positive fuel trims under load.  Is the rotor gap the same in the other cylinders?  Can you give us more detail?  Can you post the secondary during the acceleration?

Edwin

The problem was indeed an ignition misfire. The header tube had melted the 90 degree plug wire boot. The boots on these MSD wires are real thick. I had great difficulty removing the wire off of the plug because the tube was so close. The only way I would have been able to replace the entire plug wire would have been to remove the supercharger. Instead I replace the boot only with a smaller one and wrapped heat cloth around it. Poor header design.

Like Edwin mentioned, I didn't think this was a single cylinder igniton misfire based on the trims. Another thing is, it didn't feel like a typical ignition misfire. My initial thought was a fuel delivery issue which is why I started testing injection. When those tests passed, I scoped secondary. When I looked at that capture, I figured this had to be a leak to ground. I'm thinking of one of two possibilites. Either the plug ceramic is carbon tracking, or there is a leak to ground from the wire itself. A clue that really helped was the first series of strikes. Two strikes outside the combustion chamber, one strike inside, and the last one outside.

You guys are sharp. There were some really good suggestions.

I thought it was impressive to still see the rotor notch with this much time on the screen. There is some serious sampling going on there.

I have no idea why the rotor KV was higher than the plug KV. Maybe a bug got caught between the rotor tab and the cap tower?   

Thanks for playing along guys.

Lean trim is what I first thought of on your #5 Carl.  Similar except yours didn't have an upward (lean)
burn line curve before the high resistance as in this example.

http://www.members.aol.com/bgoode007/leantrim

The next thing I thought of was high resistance in the plug or the wire (snap at the top) Still not a match
to yours though since your firing line kv was fairly normal.
(These are known conditions of secondary idle and snap I did some time ago for my own satisfaction.)


The bottom idle and snap on these was from a spark outside the cylinder and is really confusing.
You would assume that a spark outside the cylinder would be low resistance and the idle capture on
this one seems to confirm this. The confusing part
of this is the snap outside the cylinder.

Edwin has seen this previously and pointed out that the snap outside the cylinder should not
have shortened the burn line and caused higher resistance than the idle wave.  I totally agree with
him. Theory tells you it shouldn’t but for some reason in this case it did.

Carl I know you and believe that what you found (spark outside the combustion chamber) was causing
your waveform high resistance on #5. Theory tells you if it’s a leak to ground it should cause low not high
resistance but for some reason in your case it did. Although maybe what I am calling high
resistance doesn't fit the definition. Maybe I should say varying resitance?


Quote:

Yes. IMO too many variables means secondary analysis doesn’t always fit the theory  

Quote:


  Unless the pcm detects a misfire and shuts down an injector
(and on a 96 GM I seriously doubt that to be the case)
I don't see an ignition misfire causing a trim that high either Edwin.
I suspect this engine had another issue totally unrelated to the
misfire driving the trim that high.

Carl,
                     No doubt about it my notes were correct. I specifically created and noted these conditions for the purpose of comparing the results and all the captures were made within about 15 minutes on the same engine.
           
         I wasn’t really interested in the firing kv at the time, more the burn lines. The reason the voltage range is wrong is because I was using Pico’s presets which the version I was using at the time scaled in volts rather than kv’s I guess maybe they prefer that in Europe? I can probably dig up the original psd’s if you really want to examine the settings I don’t know what they were other than whatever Pico had them set to.

         The small notes at the bottom of the high resistance pics are more specific as to the high resistance wire. It was actually two wires in series with a thexton spark tester in between to increase resistance. Snapping with the high resistance wire in place obviously did have the effect of using up the available energy and shortening the burn time. Why? I dunno. Doesn’t fit with theory huh? I guess this was actually two fixed environments however, one in the combustion chamber and one inside the thexton unit. Don’t see why that should have an effect though. At least no more so than a wire with high resistance.

         The middle “no problem” captures are labeled correctly . As to why would there be a longer burn within a fixed environment with snap than at idle, again, I dunno. You tell me. That’s part of my point. Maybe it’s an anomaly that’s engine specific (don’t know why it would be) but that doesn’t seem to fit with theory of this is how it “always” is either.

         I wouldn’t expect turbulence at all with a spark firing outside the cylinder. What’s there to cause it? True there’s no HC but to jump a gap without cylinder pressure you don’t need them. There certainly wasn’t any on my lower left idle capture with a thexton tester with a spark outside the cylinder. But then again there was turbulence when snapped. Of course maybe it depends on the gap it has to jump to find a ground. (But I didn’t change the gap on the thexton). Again part of my point. Too many variables I feel to name “absolute” circumstances.

         I’m not trying to argue any of this with you. I am sure that you do much more secondary analysis than I do. I’m not from Missouri but I do like to see things for myself. Maybe I just got lucky on this vehicle on this day with the controlled testing I did. Although this engine did run fine and showed perfect lambda on a 5 gas could it have had had another problem unknown to me that caused some of this? Could the spark tester gap rather than an actual wire caused some of these non-fitting results? I dunno, all I know is that I am still very skeptical that when it comes to secondary testing every engine will “fit” a set theory every time.

       Part of my problem is that I don’t believe in too many “absolutes”. My point is only that they are many variables that can affect secondary patterns. What if you have a vehicle with a high resistance wire and an over fueling problem at the same time? What is that secondary pattern gonna look like high resistance or low resistance? Again I dunno, do you? I guess it could depend on the severity of the resistance and the over fueling. I’m not trying to discourage anyone who is comfortable with secondary analysis from using it. I think most of the time the theories can and do fit and give excellent direction, just not “all” of the time  Sorry for the long winded response, just my opinions. 

Quote:


I'm sorry that you are still struggling with it Edwin. I don't quite know quite what to say other than I guess it's like the old Ripley show. I didn't just say the spark was outside the combustion chamber, I know the spark was outside of the combustion chamber. I was there.

Yes.

Carl,
LOL!!!! Actually after I asked the question, I already knew the answer, because you posted the injectors wave form and it looked perfect.  You are correct this vehicle does not disable injectors.

Edwin,

How would the PCM be able to identify which injector to disable? Is it possible to have a misfire monitor without a CKP sensor?

There are two CMP sensors which are of the optical variety. One disc has two sets of slots in it. There are 360 slots for high resolution which are equally spaced apart. This is used for timing control. The other eight slots which are of different widths tells the PCM which plug is being fired.

It seems to me that it knows what cylinder is being fired by your description. Right?

Yes, you could monitor for misfire without using the crank sensor, by ionization.

Edwin