355 What's wrong with this injector waveform ?

I would swap the two "bad" injectors with good ones to establish whether the two injectors are really bad or not.

 

Would a noid light simulate a good injector (for the purpose of reading waveforms)?

 

I do not have an answer but WHEN you rebuild the injection harness you will be shocked at the high level of ferrari wiring. We wire wrapped better in the 1960's. Even if that's not the problem building robust wiring is a good thing.

 

Googling the subject, I get the impression that noid lights are simply LEDs, so I doubt you’d get any sort meaningful waveforms from them.

 

All injectors were tested on my bench and cleaned 2 times
They all fire right from idle to full speed on the injector tester.
They also all flow very close to each other from 20 lbs fuel pressure right to 60 lbs

 

On the bottom left of the Micsig you can read the voltages max and min they are a little blurry

 

Here is a post of cylinder 4 where you can read voltages that it should be

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Has the ECU been changed? Does the ECU have individual drivers for each injector?

 

No not lately but I bought a spare ecu years ago from salvage for a good price when f1 ecu’s were cheap
I did try it before

 

Have you tried simple continuity checks between the ECU and the injectors (with harness shake checks?

I'm just worried that the injector-specific wiring is shorting to something unrelated. You may not find it with simple wiring checks.

Someone once sent me a photo of some engine harness wiring damage (under the plastic sheath). I don't know how he found it as there was no obvious/visible external signs of damage.

 

The 355 injection, both 2.7 and 5.2, is sequential (separate switching channels in the ECU).

Since all injectors are good, the absence of flyback spikes on the "bad" cylinder suggests either bad injector driver (switching transistor) or bad microchip channel that drives that switching transistor. It appears that the injector is switched "on" and "off" (missed occasionally) but it seems that the switching "off" (cutting the current flow) is not "sharp" (sudden) enough to produce the flyback spike. The reason why I suspect the switching transistor and not the wiring is the fact that the flyback spike is absent all the time, i.e. still absent even when the graph shows that the injector was switched on/off (the wiring conducted the injector current at the time) but no spike. If there is some resistance in the wiring (poor contact somewhere), if the current switching on/off goes through, the spike should go trough even easier as it has much higher voltage than the on/off switched basic voltage.

I may be wrong with my "theory" but, in any case, I would try with another known good ECU.

 

All injectors share the same power (12v) from a fuse and the ECM has individual grounds controlled by mosfets aka “drivers” — basically relays on a circuit board—- each driver has a voltage suppressor or storage capacitor which either hold the “fly back voltage “ or lets it go to ground so that the high voltage doesn’t spike the control board

I put notes on the screen of my laptop scope explaining. The waveform

As far as the form provided earlier I do not see the injector holding the voltage do to no aka fly back or spike after ECM commands or supply’s ground
I feel if the wiring is check and no short to ground on the ECM side and good 12v going to the affected injector you probably have bad drivers or voltage suppressors in the ECM

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Actually, there is no fuse for the injectors on the F355. Power comes from the battery through a relay.

 

Yes you are right I has trying to shorten my explain of the power side of the injector because the others are working

One thing I do not understand clearly the setting on the scope being use would like a better pic of that

Also the hook up to the injector should be

Red probe to the trigger wire from ECM and the black probe to good ground


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Well, not the first time, but the experts do seem to think the waveform points to the ECU. Was the noisy (resting) waveform explained?

Is the fault identical on 2 & 3 cylinders? Did Grant change the ECU because of this problem or did this problem appear later?

Either way, it’s going to get expensive or time consuming. If there was a common wiring problem on, say, cylinders 1 & 2, instead of 2 & 3, at least you'd have a chance of finding the fault in a thinner part of the loom, but with 2 & 3, there is no adjacent wiring until the harness gets very thick. Without specialist tools to identify intermittent, high resistance points (e.g. Time Domain Reflectometers), you would be very lucky to find the problem without cutting up the entire harness.

Are there any more cheap ECUs available? I’m finding relatively cheap parts in Australia (but limited availability). The Aussie dollar is even lower than the Canadian dollar. What's the part number, Grant? 174846?

 

Yes as per the sheet 11
Also test fired with Leonardo and they all worked very consistently

 

I would say it’s not the ecu only because when I tested the used ecu it ran the same on a test drive

 

These are the same signals zoomed in
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Original ecu is in now again due to no difference on test drive

 

I did not specifically look at which wire went to which, I was consistent though from the pigtail. So wave forms should have been the same
If looking at injector the right wire would have been the same on all checks because I was consistent

 

Well, that should eliminate the ECU (assuming the same cylinders were involved). Is there something we are overlooking in the waveform?

Regarding the bad waveform, is there a signal* at the injector at all times or is it just the way the waveform has been adjusted. i.e. can you position the waveform vertically to give an arbitrary zero/start point? Is that what the "(Level)" control does?

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Is the vertical scale the same in the good and bad waveforms?

I don't think it's an earth issue as the ECU main earth is used for all injectors.

 

Watch, and listed.