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| TBi injector waveforms; what to expect when testing | |
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| Topic Started: Jan 19 2010, 10:37 PM (612 Views) | |
| mwebb | Jan 19 2010, 10:37 PM Post #1 |
 
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 right click on image , select view image , click 2x to expand image TBi or throttle body injector , peak and hold waveform red is good blue is what you would see at the signal pin IF the ECM were not commanding or controlling the injector this is a Dual TBi system on a astro van , the blue signal has a poor connection at the signal pin of the PCM pin D19 even so you can see that the injector is powered up and voltage is good at 14.4 volts and because you can see supplu voltage on the signal side / pin of the injector you also know that the injector coil is not open , the positive supply pin is connected to the signal / control pin by the coil inside the injector . if you connect a test light to battery positive and the test side to injector signal / control pin IF the PCM is controlling the injector , you will see "blinks" in the test light IF the PCM is not controlling the injector or the injector driver has failed in the PCM there will be no "blinks" using a DVOM negative test lead to battery negative positive test lead to injector signal pin , set DVOM to duty cycle and there should be a value under 20% , what ever it is it must not be zero or 100% see the thread about "T" pins to see how to connect to the injector itself http://geometroforum.com/topic/2680128/1/#new  right click on image , select view image , click 2x to expand image after removing the affected connector D19 from the harness with exotic appropriate tools designed for the purpose (a "T" pin) and crushing the female connector slightly to restore the grip it once had and reassembling the harness connector this is the waveform , both injector's signal and current waveforms known good , not really this is a reman PCM , not installed by myself , notice the difference in the "ringing" in the "hold" driver on the blue injector these injectors and circuits are on the same car as it is running and a basic rule of thumb when doing this is they all MUST be the same they are not , one or both are bad - but the engine runs , and starts and the customer does not want perfection , he just wants to use the van ... so down the road it goes . ================================================= G13 or G10 with TBi has only 1 injector Edited by mwebb, Jan 19 2010, 10:40 PM.
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| mwebb | Feb 2 2010, 11:34 PM Post #2 |
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 right click on image - select veiw image - click 2x to expand image 1994 suzuki swift 1.3 g13 TBi at WOT snap note in upper left small full screen , the blue injector signal drops out after the rpm peaks and the throttle closes this is "Decel fuel cutoff ", is this TPS closed throttle switch good and adjusted correctly ? you betcha Decel fuel cutoff happens when engine rpm is over about 1200 rpm and closed throttle switch is closed , if it did not happen in this waveform , i would concentrate my attention on the TPS closed throttle switch 20.5" at hot idle is the intake vacuum with 1/2" of flutter , does this engine have one or more bad valves ? you betcha see burn line on cylinder 1 and 2 , firing order is assumed to be 1-3-4-2 the hash / turbulence in the burn line is caused by the gases that are escaping through the partially opened valve as they rush by the spark plug blowing the flame out , if the hash extended to zero , it would be carbon tracking or a mix of turbulence and carbon tracking flutter in the vacuum gauge can never be caused by carbon tracking fun with 2ndary spark waveforms , just like a EKG on a human , only better with higher resolution . last and least injector waveform , blue = signal at yellow black at the injector black = injector current about 50% duty cycle just after WOT snap peak this injector is bad , as marked by vertical current rise at the beginning of the current waveform and no oscillations but this waveform appears to be good the values in the little box are "good" values for those with scopes i will put up zoomed images of the burn line and injector current rise time to show the failures in greater detail Edited by mwebb, Feb 2 2010, 11:38 PM.
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| mwebb | Jun 4 2010, 09:12 PM Post #3 |
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a better more complete image with current and voltage  from a 1994 volvo with bank injection , but the waveform for a geo metro looks about the same a basic rule of thumb... is to expect about 2 ms or .002 seconds of on time per 720 degrees of engine revolution (subject to change based on engine load and conditions at the time ) so if you connect a test light from battery positive to the injector signal pin , you will see a faint blip / pulse as the engine idles OR as the engine is cranking with the starter assuming there injector is getting a signal from Mr ECM |
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10:04 AM Sep 7
