alright gents,

i recently got my car mapped after its fresh rebuild and all running fine and covered around 1300 miles including run-in period then without any warning i lost all power and its running/idling like crap!!

i did a compression test on it fearing the worst but it was ok

i tried changing everything on the ignition side and when i started it i noticed alot of smoke coming from a resistor for the primary rail front injector, (i have kg parts rails with 850 and 1680 injectors)

i thought it may be this so have changed it today for a new one and its done exactly the same,

any ideas on what the problem could be and also how to fix it? and could it be a cause of it running bad??

cheers dudes

 

Sounds like there is a problem in the wiring related to the injectors, this could cause one of your injectors not to fire.


This is easier to describe with a diagram, but I'm not in the mood for MSPaint right now.

+12V switched power should connect to one side of the resistor.
The other side of the resistor should connect to one of the pins on the injectors.
The other pin on the injector should connect to the ECU.


This is how most OEM vehicles with factory resistor packs are wired. The resistor is essentially intercepting power to the injector, limiting the amount of current that can flow through the circuit when the ECU driver provides switched ground. This prevents 'too much' current from damaging the injector and/or driver circuit inside the ECU. For instance, if you connect 12V power to a 3-ohm low-impedance injector, 4 amps of current will flow through it, this is usually 'too much' and will likely damage both the injector and the ECU after a few minutes of operation. If wire a 6-ohm resistor as described above, the total resistance is about 9 ohms and about 1.3 amps of current will flow through it. In most cases, this is not 'too much' and nothing will be damaged.

If there was a wiring problem causing your 6-ohm resistor to get shorted to ground, it would see about 2 amps of current, which may be 'too much' for it to handle causing it to smoke. This is assuming you have a 6-ohm resistor... if your resistor is only 3 ohms it will see even more current and almost definitely cause smoke.

Long story short, check your injector and resistor wiring for a short to ground. This could be due to a pinched wire or insulation that has been cut or rubbed bare. It's not uncommon for solder joints to contain sharp spots (this is not the correct way to solder, BTW) which can eventually poke a hole through heat shrink or electrical tape.

Good luck!
-s-

 

wow thats the most informative reply i ave ever had cheers scotty,

i am going to tackle this later this afternoon (working at the minute)

when i rebuilt the engine i also re-wrapped the engine harness and did not notice anything but that was about a year ago now,

if it does have a short is it possible for me to run a new wire to leave the original redundant as i dont want to remove and strip the harness down again if i can?

cheers lee

 

No worries, Lee.

If the original wire is causing the short circuit, you will need to disconnect it in at least one place (either at the resistor or at the part of the wire that is connecting to ground) so it no longer connects the resistor to ground. Then you can run a new wire. Electrically, the circuit should work and it doesn't matter much if the wire is bundled with the main wiring harness or not.


Mechanically, if the new wire is not insulated from heat / moisture / mechanical damage it may live a shorter life than it would have otherwise. Much better to have crispy electrical tape a few years from now vs. crispy wires. If it were my car, I might run a new wire temporarily to make sure it solves the problem and then spend the time bundling it into the harness later.

 

right a little update,

i have been mad bausy with work so not had much time to have a look at it,

just out of curiousity i pulled the plug on the faulty injector and started the car, surprise surprise the resistor stayed intact with no melting/smoking?

is it looking like a dodgey injector then?

am confused

fault finding definately aint my forte

 

Test the injector. Apply 12v (+/-) to the injector connector pins and listen for a click. You can also test injectors with a multimeter set on resistance testing. If the injector coil is burned up you won't get any reading. If they are bosch injectors usually will read 5.1 ohms, stock injectors are somewhere around 12-13 ohms IIRC.

You can also use the multimeter to test the wiring, should see momentary flashes of 12v. Most autoparts stores also sell little flashing bulbs that plug into the injector harness to test the wiring.

 

cheers for all your help gents,

i finally through the towel in and asked my auto electrician to come and have a look yesterday,

within 5 minutes he noticed that the injector on the front primary rail was grounding out to the block and also had continuity between the connections, he also said in the 20+ years he has been an auto electrician he has never seen an injector ground to the block???

long story short i have just done a 3 hour round trip to pick up 2 brand new 850cc injectors and lets just say i am a happy man

cant beat the wonderful sound of a brap and it is running as strong as ever

yet again thanks for all your help guys