Common rail diesel  Interference suppression 

When it was time to get a larger vehicle because the family was growing in size physically and socially ( they now drag their friends along ) I thought it was time to trade in my little Diahatsu Feroza Four wheel drive ( petrol engine fully suppressed by me for HF . )  which stood me well for 11 years , and get a much larger vehicle . I needed something to tow the family fizz boat , be able to visit amateur radio  club repeater sites on farm hill tops and have plenty of seats  with seatbelts for all occupants. so I opted for the new Isuzu  ( GM ) "Bighorn"  or "trooper" if  your Australian ,  It is a large vehicle with plenty of room , heaps of grunt , and available in Diesel ,  I have always wanted a diesel  .Thought it would be great for Ham radio . NO Sparkplugs!! therefore   no ignition interference!   how wrong i was . The new 3.0L double overhead cam Turbocharged diesel engine is a computer controlled common rail diesel, 40% more powerful than the old 3.1 L donkey of earlier model Isuzus and really thrifty on fuel and with much lower exhaust emissions  BUT you should hear the noise on HF !!! give me back my old Feroza! I should have known anything with a CPU was going to generate noise  and i didn't expect to hear the "click click click "of ignition coming out the speaker of the icom 706! no way  could the noise blanker quash that ! so i had to get tough .

The common rail diesel does not have the standard  mechanically driven injector pump . In the Isuzu 4Jx  type engine , there are injectors feed from a  high pressure fuel line but they are hydraulically  actuated but electronically controlled .  Imagine the injector  as a medical hypodermic syringe full of diesel fuel  that sticks into the cylinder  . the plunger of the syringe is forced down under great pressure by a small hydraulic ram  which is feed from a separate very high pressure engine oil  pump . The valve to open and close the  high pressure oil is controlled by an electric solenoid ( read amps , fast rise and fall square waves )  by the engine management control CPU  and timed to coincide with  compression  ignition around top  dead centre of the piston travel .  This electronically controlled system works very well and does a marvellous job in making the engine run well , gives fine control  and great fuel economy . BUT the HF noise is horrendous.

I mounted my HF helical antenna on the back of the vehicle by way of a flat plate bracket that mounted over the 3 holes that holds the spare wheel onto the rear door , the antenna base is at roof height and can hinge forward flat onto the roof ,if I want to go into a car park building,    Make sure you have a good bonded earth for the  HF radio in the car . I mounted my whole Icom 706 MkIIG in the consol of the vehicle . and ran the power cables with a ferrite suppression  bead , straight to the battery ( later on I mounted the SGS239 Auto antenna tuner in under the spare wheel  at the back of the vehicle .. ) 


I had a 20 over 9 noise level, totally  HF unworkable, so I started to tackle the problem . OK lets see where it is coming from  ie what is radiating the signal . These days motor vehicles are built in an effort to be  audibly quiet and comfortable ,so a lot of components are rubber mounted. No low impedance electrical contact  there !! DC continuity is usually provided by earth return wiring that may be ok for 12v DC flow but will be a high RF impedance ,no way is it going to bypass Rf noise. I  went and did the standard metal to metal electrical  bonding using my favorite material , copper braid stripped out of RG6 half inch coax.  I bonded the bonnet to the body at the hinges  and where the bonnet closes at the front 


bonnet bond                                     battery bond earth                                     front lower contact point bonnet


   upper contact point  bonnet   ( self cleaning!!)

see photos..  and don't forget the sand off the paint to get good electrical contact , .When you have tightened up all the bonding screws give the area a good coat of waterproof wax like spray grease to inhibit rust. ( CRC  soft seal)  I ran an extra bonding braid from the battery earth straight to the body . I them bonded the exhaust pipe to the chassis rail midway down the underneath and at the tailpipe end using copper braid and a large stainless  hose clip 


 stainless hose clip on exhaust  ,                                                 engine to firewall bonding 

this is always a problem spot as exhausts get hot   and there will  be corrosion of bare metal after a while,  you can protect the area with a spray of VHT  high temperature spray paint . The bodywork  of modern motor vehicles is mounted on rubber !!  don't forget to climb underneath and earth the body work to the chassis at each "corner" of the vehicle   this was a prick of a job on this wagon as you needed to undo nuts  set up long threaded bolts to get the braid in the correct position . While there you could bond the transmission to the chassis rail .

At this stage the HF noise was starting to come down to a respectable S9 !!!  ha ha .  not good enough yet buddy !! want to be able to work 10m AM !!  so it was into the engine compartment and concentrate around the ECU  box. This is a large flat aluminium box with a HUGH bunch of cables coming out of it !! 


ECU   unit with bonding straps and bypassing                         earth strap from rubber mounted ECU to body 

Out with the Fluke scopemeter  ! I measured  very fast rising 60 V spikes going positive and negative on the injector control cables (so they have active opening and closing !!)  I wound flat copper braid around the injector control cables  soldered it together and earthed it at each end .. made a small improvement . 


note:  Initial  braid cover on solenoid control wires                     Ferrite toroids on positive and negative  to ECU 

I also clamped ferrite suppression  beads onto the multi cables that go to the ECU.  Now I did make a small  low pass filter of ferrite beads and feed through caps and put them in series with the injector control lines  , (i did try bypassing the solenoid  control   wires with 0.1 uF 300v caps but the upsets the fuel injection timing and the engine does not like it when idling ). this produced  an additional benefit.  The biggest effect I found was  by passing the 5 solonoid control cables ( one is the common earth return ) as a complete 360 degree loop thru a large clamp on ferrite bead . and in finding this  on hindsight ,i would try this as my first attempt in ECU suppression. we are now down to a very acceptable level of ignition interference . 

To get lower in interference level , you have to fiddle with the position of bonding  straps around the motor and ECU  but i think the worthwhile effort become exponential  with respect to the achieved results. There was places midway along the ECU bonding strap where if you touched it to the  fuel primer  metal the noise would drop even more /  You will find that there are low level carriers at different frequencies across the HF band ,  emanating from the ECU , some even have a real digital "note" to them 

 I hope this has been of some use to someone  when i get some spare time I may have another concerted effort to improve things even more .

MK2  Mods   Nov 2011   success !!!
I was still determined .  I had time  and inclination to improve the current situation , I suspected that if I completely screen the injector leads from the  ECU  up to the rocker box cover . this  surely must improve the situation , The last time I did this was on my 1979 Honda Accord  and in those days I was able to work the oscar  series of satellites 2m up and 10m down mobile with no vehicle noise what so ever on ssb .
I had at my disposal an injector wiring harness from the 4JX-1 Isuzu common rail Diesel ,this was a good find as I was reluctant to pull the rocker box cover off to expose the twin camshafts and the  injector solenoids,to see what was inside ....  I peeled the  black cable wrap of the pink injector wires to leave them  bare,

 earth return and 4  injector solonoid control lines 


Using the notation on the  loom connector  grey  /black  plug ( there is letters stamped on the side)  I isolated  cable  A, the common return for all injectors ,  G,H,J,K  ( there is no " i"  just  like in the  word Team!) are the individual injector  cables ,   I traced the wires from the loom  injector thru the large grey/black  plug to the  ECU  Unit ,  I then one by one pulled out each corresponding pin out of the grey/black  plug  ( poke a long thin rod down the inside of the square hole in the pin  and you will unclip the pin from inside the plug and the wire will pull out )  but  before you do you will have to take off ( unclip) the grey cable holder  off the top . Mark the cables permanently  A, G  H  J   K ,
So you dont get lost , start with one cable , lengthen it , slip on the braid and connect it completely before doing the next injector cable then you wont make a connection mistake

I soldered the extension cables on, so I could go directly from the  cylinder head to ECU,  the soldered joints had two layers of heat-shrink, and then I fed the cables thru  the correct length  of RG58  Braid from old coaxial cable   ( as measured against the  modified lead  ) feed you wire in through the side of the braid about 30mm up from the end and do the same at the other  end this  will give you 30 mm tassels of coax braid  to connect to at each end and not interfere with the  wire in the centre . The rest of the grey black plug carries 5 other sensor cables ,they where left as they where found .. . The 5  braid tassels at the cylinder head end were collected together and soldered to a large connector and bolted to a convenient unused  spare thread on the intake manifold ,                  That is the injector end earthed.

I have now used old  RG6 braid to cover  wires  

I did exactly the same at the ECU  end , gathered the coax tassels together  and crimped them into a bolted type connector  ,soldered it   then drilled  a small 3mm hole in the outer rim of the ECU ( where it can do no damage ) and bolted the tassel connector the the ECU  case . I slipped about  3 large Ferrite beads over each of  the wires where they connected to the ECU  hoping these will help absorb some RFI  but I dont think they do a lot to be honest , ( ended up removing them when I soldered the toroids on )  A mobile run showed a huge  improvement in "injector  Noise" on the  IC706 radio .
  I found that when I stopped  on the side of the road in a very quiet RF  location and  opened the bonnet  ,and while listening to the radio on HF  ie 18 Mhz  "touching"   (finger capacitance)
I replaced the large ferrite  beads  with computer board  Toroids 

computer motherboard torroid    compared to hc49/u  xtal

 This the five cables at the ECU  end with series torroids 

the injector return cable induced  more  noise than "touching"  the injector cables going into the ECU . So I came back home and placed a small switch-mode power supply toroid with heavy wire ( I obtained from an old  computer motherboard ) , in series with the "common" wire  going into the  ECU  . That  dropped the noise  even more ,  so I used     more of these and put one in each  braid shielded lead at the ECU end , that were feeding each  injector solenoid , to see if I can eliminate all injector  noise completely !  I glued the computer  torroids together with  hot glue to vibration wouldnt break the solder  joints ...   Well now the "ignition " noise on the HF bands on ssb  is down to scarcely audible stage where quiet atmospheric noise is easily heard , even in AM  mode the  HF noise is low enough never to be a problem .  I have absolutely no audible engine "ignition" noise above 24 Mhz , not a peep on AM  mode.  even at 2m    !

Its taken me a while but it has now been worth it         .................73 de Mike   ZL1BTB


                                                          back to home page