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Dead Injector -- diagnosed by fuel pressure damper pulse.

posted May 19, 2016 11:20:38 by AndyMacFadyen
Dead miss on 1.6 Rover 45 ---- 4 cylinder EU3 --- wasted spark plug top coils, returnless fully sequential injection, no scharader valve, in-tank pressure regulator pulse damper on fuel rail. Misfire code for #3 cylinder, exhaust manifold colder on that cylinder.

Current ramped the coil sharded by cylinders 2 & 3 looked normal and good spark on no 2.
I swapped the shared coils over betwen 1&4 and 3&2 misfire didn't move, #3 spark plug looked okay.
Fuel injector not easy to access for current ramp so tried my Autoditex Firstlook sensor.
Connected to the pulse damper vacuum port and plugged off the manifold vacuum tube.

I used a low pass filter and had the upstream oxygen sensor disconnected to force open loop the result was clearer cut than I expected

Before injector change.



After Injector change.
[Last edited May 19, 2016 15:19:54]
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6 replies
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Noah said May 20, 2016 11:17:37
Nice job as always Andy! How necessary is it to make sure the system status in open loop during this test? Not criticizing, just curious.
Massachusetts, USA
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AndyMacFadyen said May 20, 2016 14:39:06
I think running open loop produces more useable wave form if the engine is misfiring. My reasoning is in open loop the injector durations won't be hunting up and down in reponse to the O2 sensor output. If there is a bad misfire the injector durations will be all over the place even if it is an ignition fault.
One of the problems with method is that every engine type is going to produce a different pattern and different brands of sensor are going to produce different looking signals.

Originally I a made a home built sensor using a 2 dollar piezo acoustic guitar pickup (somtimes called a contact microphone) it worked but the signal looked nothing like the offical Autoditex FirstLook see image below.


[Last edited May 20, 2016 14:43:34]
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Tyler said May 22, 2016 21:30:50
Originally I a made a home built sensor using a 2 dollar piezo acoustic guitar pickup (somtimes called a contact microphone) it worked but the signal looked nothing like the offical Autoditex FirstLook see image below.


I've done the same, and had some success using it in the exhaust and intake. That last picture REALLY illustrates how much better the FirstLook is. I just have a hard time getting over the price tag...

Excellent work, sir! Just curious, did you ever find out what the exact failure was with this injector? Stuck closed, poor spray pattern, restriction, ect. Not poking holes in your diag, just trying to relate the failure to the pattern observed.
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AndyMacFadyen said May 23, 2016 08:12:17
It was an electrical open, if the connector had been easier to acess it would have been easy to find. In retrospect I could probably have found it with a stephoscope but these days I reach for my Oscilloscope without even thinking about it ----
I was lucky to have a similar known good engine to to compare it with or it would have been a more difficult call. Most of the engines I look after have very similar injection systems so I will use the test again and try and build up some experience with it.

I think I could have made the homemade tool work better but life is too short. Initially I was disapointed in the AutoDitex tool but using a filter and changing scope aquisition settings produced a usuable waveform. I tried both the scope's built in filter and an external hardware filter both nicely cleaned up the waveform.

I tried looking at exhaust pulses but I am not sure what use I could get from it. on Friday I am off for 14 days vacation in Italy but when I return the next test I am going to try with it is looking at crankcase pressure pulses.

It is difficult to compare the price of equipment between North America and the EU when stuff gets shipped either way the price rockets. My Autoditex sensor was a fairly reasonable at £50 (70 US dollars or 62 Euro) from http://www.scantool-direct.co.uk/automotive-oscilloscope-tools.html

I think if I was looking after a fleet of vehicles this type of sensor could be a very useful for regular condition monitoring and preventative maintance, essentially by finger printing the engine when new and you could track wear and tear on the engine.
[Last edited May 23, 2016 10:49:09]
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Tyler said May 25, 2016 02:21:18
I tried looking at exhaust pulses but I am not sure what use I could get from it. on Friday I am off for 14 days vacation in Italy but when I return the next test I am going to try with it is looking at crankcase pressure pulses.


I've experimented with crankcase pulse testing, kinda had a hard time making something of it. Initially, I wanted to use it to ID leaking rings, but it didn't really show up on the scope, even on cars that I knew had ring sealing issues. Might have been user error? Let us know if you have any success!

It is difficult to compare the price of equipment between North America and the EU when stuff gets shipped either way the price rockets. My Autoditex sensor was a fairly reasonable at £50 (70 US dollars or 62 Euro) from http://www.scantool-direct.co.uk/automotive-oscilloscope-tools.html


Whoa, $70? Value! I was thinking about the SenX model, that I can't find for less than $300. Even with shipping and a BNC-to-banana adapter, I'm still ahead.
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MattWhite said May 26, 2016 11:48:38
Definitely sold me on one Andy. Great work man.
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