Injector staying wide open, when iginition is on
#1
Injector staying wide open, when iginition is on
Hey guys, i have a 1987 vette, that im having trouble getting to run properly. The way it runs seemed to be getting worse and worse each day.
Tonight after replacing the plugs, with new acdelco plugs, after maybe 2 mins of idling, the plugs literally were black completely carbon fouled. I clean them and tryed to start the car again, and the starter wouldnt budge the motor, took the plugs out, of 4 & 6, and gas literally spilled out of plug holes!!!!
With the ignition turned on , engine not running, all 8 injectors are recieving voltage, i took the connectors off and put a test light in each injector harness connector , ALl lit up.
With the fuel rail pressurized, i individually connected each injector , (with ingnition on) and each one, once connected clicks, and i can literally hear fuel spraying, and the fuel pressure drops. This is with the ignition on, but engine not runing. BTW (If the ignition is off and i hot wire the fuel pump, the rail holds pressure)
The injectors are only supposed to be fired when the ecu recieves a reference signal from the distributor. What would cause them stay open only with ingnition on. im leaning to the computer being bad, but i have no check engine codes, and the diagnostic mods works fine.
If anyone has any experience with this kind of problem help would greatly be appreciated.
Tonight after replacing the plugs, with new acdelco plugs, after maybe 2 mins of idling, the plugs literally were black completely carbon fouled. I clean them and tryed to start the car again, and the starter wouldnt budge the motor, took the plugs out, of 4 & 6, and gas literally spilled out of plug holes!!!!
With the ignition turned on , engine not running, all 8 injectors are recieving voltage, i took the connectors off and put a test light in each injector harness connector , ALl lit up.
With the fuel rail pressurized, i individually connected each injector , (with ingnition on) and each one, once connected clicks, and i can literally hear fuel spraying, and the fuel pressure drops. This is with the ignition on, but engine not runing. BTW (If the ignition is off and i hot wire the fuel pump, the rail holds pressure)
The injectors are only supposed to be fired when the ecu recieves a reference signal from the distributor. What would cause them stay open only with ingnition on. im leaning to the computer being bad, but i have no check engine codes, and the diagnostic mods works fine.
If anyone has any experience with this kind of problem help would greatly be appreciated.
#2
The ECM pulls one side of the injector connetor to ground the other is tied to 12 volts. They are seperated into two banks of four.
So either you have a shorted harness to ground or a ECM that is stuck on for some reason.
What happens if you disconnect the ECM ?
So either you have a shorted harness to ground or a ECM that is stuck on for some reason.
What happens if you disconnect the ECM ?
#3
would pulling the ecu fuse, do the same as diisconecting the physical wiringto the ecu? I figured if i had a short in the harness, it would only be on one set of injectors, the both sides are driven separately?
#4
Pulling the fuse will not be the same as disconecting the harness at the ECU. Do disconect your battery before doing this to prevent any damage.
Here is a link to some info you may find helpful.
http://www.diy-efi.org/gmecm/ecm_info/1227165/
Here is a link to some info you may find helpful.
http://www.diy-efi.org/gmecm/ecm_info/1227165/
#5
Safety Car
sounds like a short on ECM side to ground some where. Is it possible you pinched a wire? To test there i would pull the Injector fuses to remove the +12VDC and prevent any more fuel from spraying then using your test light you can check to see if the ECM is sending a signal (Ground) to the injectors.
Last edited by FD2BLK; 11-21-2005 at 09:36 PM.
#6
Le Mans Master
Agree on a short to ground in the injector harness, right side. Change the oil before you start it. Also, rotate the engine by hand until each cylinder is at TDC and then use a vacuum pump to suck out the fuel. Squirt some 30 wt in each hole and then with the fuel pump disabled, crank the engine over until the oil flows out of the holes.
#7
tommorow im planning to find the short,
I have a few pages from the sevice manual. It shows there are 2 wires d15 and d16, that come from the ecu to drive the injectors. does anyone know the routing of the whole injector circuit? Where does the power come from? Any key places to look for a short? I have a voltmeter, and a continuity test light how would i go about finding the short?
I have a few pages from the sevice manual. It shows there are 2 wires d15 and d16, that come from the ecu to drive the injectors. does anyone know the routing of the whole injector circuit? Where does the power come from? Any key places to look for a short? I have a voltmeter, and a continuity test light how would i go about finding the short?
#8
Melting Slicks
I had this exact same thing happen in my '86 I used to have. It was indeed a short like the others have said. The short was in the harness behind engine. I had to take the distributor out to get to it and unwrap the harness and trace all the wires. Come to find that two of the wires had rubbed through the protective coating and were shorting on each other. I don't remember what color wires they were and didn't really find out where they went so I can't help in that department though. Hope this helps.
#11
I just disconnected the ecmfrom the harness, and put the ignition on "on" position, and the injectors are not on ,
with the ecm connected, ignition on, the injectors all have power, and stay open.
In my oppinoin this confirms, that the ecu is the problem. Any other things to check? How much and wheres the best place for a remanufactored ecm??
with the ecm connected, ignition on, the injectors all have power, and stay open.
In my oppinoin this confirms, that the ecu is the problem. Any other things to check? How much and wheres the best place for a remanufactored ecm??
#12
Use a ohm meter to verify ECM the injector driver pins (D15,D16) are shorted to the ecm ground (D3 or D1).
You don't want the ECM connected to the harness when you make this check.
This will check the output driver on your ECM for a short.
Did you verify that you have 12 volts at the injectors when you had the ECM disconnected ?
You don't want the ECM connected to the harness when you make this check.
This will check the output driver on your ECM for a short.
Did you verify that you have 12 volts at the injectors when you had the ECM disconnected ?
#13
with the ecm disconected, the injectors got no voltage with ignition in on position. With the ecm connected they were getting constant voltage at all injectors with ingnition on position.
#15
Safety Car
Originally Posted by tsiawd1028
with the ecm disconected, the injectors got no voltage with ignition in on position. With the ecm connected they were getting constant voltage at all injectors with ingnition on position.
Then you have not confirmed the ECM is the problem. remember the ECM provides ground not +12VDC. With the ECM disconnceted check to see if a ground is present on the ECM side of the injectors. This test should be done with the ECM disconnected and all of the injectors disconected (Will read back through the injectors otherwise). Then use the ohm meter to check for ground on the injector connector, if no meter use a test light with one end conected to +12V and see if it lights when you touch the ECM side of the conector
#16
with the ecm disconected, the injectors got no voltage with ignition in on position. With the ecm connected they were getting constant voltage at all injectors with ingnition on position.
With the ecm connected, ignition in on position, all 8 injectors, are recieving power and ground, therefore "on"
then i disconected ecm, with ignition in on position, the injectors were not getting ground, and where "off" .They still were getting power , but not grounded. so they were off.
With a test light connected to 12v Bat+, i connected the other end to the ground wire, on each injector harness clip, i did not get continuity, if i had a short to ground in d15 and or d16, there would have been continuity in half or all injectors.
doesnt this point to the ecm being faulty?
i greatly appreciate everybodies help in this. Thanks
#17
Le Mans Master
Member Since: Dec 2004
Location: Myrtle Beach SC
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St. Jude Donor '05-'06
The best way to test the ECM is to get a known good one possibly from a friend.Problem here is if it is not the ECM might it do damage to it?Now let me get this straight can you start your car?If you can do you hear the injectors tapping?If the answer is yes to both I would swap the ECM.I am assuming the car was in open loop when it was running to rule out O2's.Just remember the dreaded intermittant short if the ECM swap does not fix it.If your not in a rush you could try the salvage yards for a know good one although I have only read a couple of horror stories about bad rebuilts and many satisfactory replacements.I think Autozone has them(at least for my year) and at if it is bad you can take it back pretty easily..
#18
In my last post the checks are for for the ECM out of the vehicle. If the injector drivers mearsure ~zero ohms to ground on the "ECM" pins then they are shorted to ground.
Keep in mind that if the electronic device opening the injectors were to fail the designer should would want the injector to fail closed not always open.
Keep in mind that if the electronic device opening the injectors were to fail the designer should would want the injector to fail closed not always open.
#20
Just trying to give a second way to confirm that the ECM outputs are shorted to ground.
I just don't expect the injectors drivers would short out. Instead I would expect them burn open.
Here is a ECM Schematic link for those interested.
http://www.cruzers.com/~ludis/
I just don't expect the injectors drivers would short out. Instead I would expect them burn open.
Here is a ECM Schematic link for those interested.
http://www.cruzers.com/~ludis/