What conditions need to be met before the fuel injectors fire?
#1
What conditions need to be met before the fuel injectors fire?
doing some early morning brain storming before i try and work on my car again tonight, im trying to diagnose why my primary injectors wont fire
-My fuel pump primes
it builds 3 bar of pressure
-I have fuel in the rail, i checked when i pulled the primary rail, primed pump, fuel poured out
-I applied power to each primary injector, they click and were even squirting the small amount of fuel left in the rail.
-I used a multimeter and placed the leads in the fuel connector harness side in both connections, had a friend crank it, and the mutimeter would read voltage, ex: crank,crank,6v,4v,12v,8v repeat itsself, so this means i have power coming to the harness.
-egi fuse is good.
-i have spark, power fc turns on, etc, just wont squirt fuel.
But with the rail in, when i crank the car no fuel squirts out, how exactly do they fire, is there constant power to them all the time?
does the ecu just add a ground to complete the connection causing it to fire?
does this mean i have a bad ground somewhere if every other condition is good?
and where does the injector harness ground itsself,/ any other related grounding points.
Thanks in advance!
Adrian
-My fuel pump primes
it builds 3 bar of pressure
-I have fuel in the rail, i checked when i pulled the primary rail, primed pump, fuel poured out
-I applied power to each primary injector, they click and were even squirting the small amount of fuel left in the rail.
-I used a multimeter and placed the leads in the fuel connector harness side in both connections, had a friend crank it, and the mutimeter would read voltage, ex: crank,crank,6v,4v,12v,8v repeat itsself, so this means i have power coming to the harness.
-egi fuse is good.
-i have spark, power fc turns on, etc, just wont squirt fuel.
But with the rail in, when i crank the car no fuel squirts out, how exactly do they fire, is there constant power to them all the time?
does the ecu just add a ground to complete the connection causing it to fire?
does this mean i have a bad ground somewhere if every other condition is good?
and where does the injector harness ground itsself,/ any other related grounding points.
Thanks in advance!
Adrian
#2
rotorhead
iTrader: (3)
Are you positive they're not firing with everything assembled? You can use a test light or perhaps a mechanic's stethoscope to check if the solenoid in the injector is engaging. You should be able to view injector duty cycle on the Commander to see if the ECU is trying to fire them or not. Ideally you would take logs with a Datalogit.
Yes, the ECU engages the injector drivers (field effect transistors, wikipedia that) to pulse the ground for the injectors.
There are four ground wires for the ECU. The wiring diagrams show where they run to.
does this mean i have a bad ground somewhere if every other condition is good?
and where does the injector harness ground itsself,/ any other related grounding points.
and where does the injector harness ground itsself,/ any other related grounding points.
#3
Are you positive they're not firing with everything assembled? You can use a test light or perhaps a mechanic's stethoscope to check if the solenoid in the injector is engaging. You should be able to view injector duty cycle on the Commander to see if the ECU is trying to fire them or not. Ideally you would take logs with a Datalogit.
There are four ground wires for the ECU. The wiring diagrams show where they run to.
There are four ground wires for the ECU. The wiring diagrams show where they run to.
should i start by checking the injector pins at the ecu, 4w/4x/4y/4z? for continuitywith a ground, are these the power signals? would that show if there is a short somewhere.
are the injector pins supposed to have constant power with the ign on? i only get power once i start cranking, this seems normal, just thinking outloud
Last edited by ILoveJDM; 04-06-11 at 02:27 PM.
#4
Radioactive Rotary Rocket
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During cranking there is a fixed amount of fuel being injected. It's a special map used just for cranking, like 200 rpm. I think temperature effects how much, but besides that the ECU ignores everything else. So if you aren't getting any fuel during cranking, you have something seriously wrong.
If you really want to diagnose this, you need someone with a scope. You need to probe your primary injectors with the special probes that can fit into the connectors and making contact while the connector is plugged in. Then setup the scope to show all the injectors on the same screen and start cranking. You should get a nice digital sine wave. A multimeter won't be quick enough to give you a good reading here. That is going to tell you where the electrical problem is: either the wiring harness or the ECU.
If you really want to diagnose this, you need someone with a scope. You need to probe your primary injectors with the special probes that can fit into the connectors and making contact while the connector is plugged in. Then setup the scope to show all the injectors on the same screen and start cranking. You should get a nice digital sine wave. A multimeter won't be quick enough to give you a good reading here. That is going to tell you where the electrical problem is: either the wiring harness or the ECU.
#6
You can use a led diode with resistor about 560ohm to the + of injector connector and the - of the led to the other side of connector and simple check if it light when you crank.
Just to know pfc didnt have fuse protection for the outputs so it is possible to fail the transistor array in the pfc board like arghx said.
Another test that you have to do is with multimeter negative probe to ground and the positive to constant + of the injector connector you must read stable 13,6 volt with the key to on.
If it is less under 12,5 then your problem is in the egi relay circuit and not on the pfc.
Just to know pfc didnt have fuse protection for the outputs so it is possible to fail the transistor array in the pfc board like arghx said.
Another test that you have to do is with multimeter negative probe to ground and the positive to constant + of the injector connector you must read stable 13,6 volt with the key to on.
If it is less under 12,5 then your problem is in the egi relay circuit and not on the pfc.
#7
Another test that you have to do is with multimeter negative probe to ground and the positive to constant + of the injector connector you must read stable 13,6 volt with the key to on.
If it is less under 12,5 then your problem is in the egi relay circuit and not on the pfc.
If it is less under 12,5 then your problem is in the egi relay circuit and not on the pfc.
Ok so i did this
postive connector to the injector plug, and neg to the chassis,
i get 3.0v dc on both primary plugs.
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#8
you will have battery voltage on one terminal anytime the key is on (it will only be 13vdc with the alt charging)
the other terminal will be "open" until the ecu fires the injector which it does be allowing a ground path
get a noid light.
or a high impedence test light
put the clip end of the light on the battery POS
probe the injector clip on the pin the is controlled by the ecu(no battery voltage) and crank the car
the light will pulse if the ecu is controlling the injector. just like a noid light
now if what you are saying is that with the multimeter neg attached to a seperate good ground (like the batt neg terminal) you only have 3vdc on the injector clip well that is the problem.
what is the battery volatge when doing the test?
the other terminal will be "open" until the ecu fires the injector which it does be allowing a ground path
get a noid light.
or a high impedence test light
put the clip end of the light on the battery POS
probe the injector clip on the pin the is controlled by the ecu(no battery voltage) and crank the car
the light will pulse if the ecu is controlling the injector. just like a noid light
now if what you are saying is that with the multimeter neg attached to a seperate good ground (like the batt neg terminal) you only have 3vdc on the injector clip well that is the problem.
what is the battery volatge when doing the test?
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