injector resistance readings
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 38
Likes: 0
From: PHILLY PA
injector resistance readings
can 1 take an ohm reading to the injectors with the car not running/or ignition switch on??? seems my mechanic is telling me he can`t because he needs power /or ground to the injectors,,is he right?
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
He is full of it. Turn it off after full warm up, measure between contacts on each injector and record the reading. Let the engine cool completely and take the readings again. You don't need power for a resistance reading.
Racer
Joined: Sep 2007
Posts: 393
Likes: 0
From: Bartonville Illinois
I did notice a small diference taking the readings after injectors were hot, from the cold readings Better readings HOT.
You can't take Ohmeter readings with voltage applied to a circuit. It will not work and will probably ruin your meter.
If you didn't misunderstand what he was wanting to do, then I would say you need a new mechanic.
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 38
Likes: 0
From: PHILLY PA
sorry badduck...i failed to mention that my car,will not start,,,CRANKS..but will not start,,,it all started when he changed out 3 injectors,,ran well for 2 days,,then it died,,towed it back to him ,he say`s there is no pulse to the injectors (noid light),changed ecm`s,Notta,,fuel pressure good,,fuel filter and pump,,good,,,,i`m leaning toward the other injectors,,,and i`m asking for a resitance test for the injectors,,,and that`s what brings me to my original post,,,,i`m not a mechanic,,but people are asking me " what`s the resistance of each injector when cold",,,that`s why i asked can it be done with out car running?,,,,thanks
Pro
Joined: Sep 2006
Posts: 702
Likes: 2
From: Conyers Ga
You not only don't need power to take an ohm reading, it's recommended to remove the power SOURCE when doing it. Tell him to read Ohm's law.
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Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
he`s saying he can`t take readings because of no power/or ground to injectors,,because car wont start,,thats why i`m asking is he right?
You must UNPLUG the harness from the injector in order to make the resistance measurement across the contact pins of the injector...
he say`s there is no pulse to the injectors (noid light),
Supporting Vendor
Joined: Mar 2008
Posts: 1,762
Likes: 14
From: Cumming Ga
sorry badduck...i failed to mention that my car,will not start,,,CRANKS..but will not start,,,it all started when he changed out 3 injectors,,ran well for 2 days,,then it died,,towed it back to him ,he say`s there is no pulse to the injectors (noid light),changed ecm`s,Notta,,fuel pressure good,,fuel filter and pump,,good,,,,i`m leaning toward the other injectors,,,and i`m asking for a resitance test for the injectors,,,and that`s what brings me to my original post,,,,i`m not a mechanic,,but people are asking me " what`s the resistance of each injector when cold",,,that`s why i asked can it be done with out car running?,,,,thanks
Advanced
Joined: Jan 2008
Posts: 75
Likes: 0
From: hinton ia
in my opinion at this point it dosent really matter what the resistance of the injectors is if they arent being pulsed i believe that the injectors are constatly supplied power and the computer cycles the ground to make them pulse. if you have power but no ground the drivers are probably bad if you dont have power at least we narrowed it to the power side of the circuit.
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
sorry badduck...i failed to mention that my car,will not start,,,CRANKS..but will not start,,,it all started when he changed out 3 injectors,,ran well for 2 days,,then it died,,towed it back to him ,he say`s there is no pulse to the injectors (noid light),changed ecm`s,Notta,,fuel pressure good,,fuel filter and pump,,good,,,,i`m leaning toward the other injectors,,,and i`m asking for a resitance test for the injectors,,,and that`s what brings me to my original post,,,,i`m not a mechanic,,but people are asking me " what`s the resistance of each injector when cold",,,that`s why i asked can it be done with out car running?,,,,thanks
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Check both injector fuses first, with an ohmeter! To measure resistance on an injector, the injector must be unplugged in order to gain access to both of its terminals, so it really doesn't matter if the ign is on or not, but it doesn't make any sense to unplug an injector and measure the resistance of the injector coil with the ignition on! If the mechanic thinks the ign has to be on, then he isn't familiar with fuel injection and you need to look for a more informed mechanic! See if you also have spark while cranking because the ECM uses the distributor pulses to time both the spark timing and the injector timing.
There is value in measuring the d.c. resistance (what an ohmeter measures) because a very low resistance can burn out the injector fuse/s, but for injector operation, d.c. resistance is a very poor measurement. A turn to adjacent turn short in the injector coil cannot be seen with an ohmeter and it can ruin the injector operation, but if you have an impedance bridge, you can easily find a turn to turn short.
There is value in measuring the d.c. resistance (what an ohmeter measures) because a very low resistance can burn out the injector fuse/s, but for injector operation, d.c. resistance is a very poor measurement. A turn to adjacent turn short in the injector coil cannot be seen with an ohmeter and it can ruin the injector operation, but if you have an impedance bridge, you can easily find a turn to turn short.
Last edited by jfb; May 21, 2008 at 08:54 AM.
Racer
Joined: Sep 2007
Posts: 393
Likes: 0
From: Bartonville Illinois
Instead of spending the money paying this mechanic, may I suggest you spend about $60 and buy a Digital volt meter. You can learn to check some of this stuff yourself. There are posts on this forum about darn near anything and mechanics are pretty expensive these days.
You can always take the car back to him if you can't figure it out.
You can always take the car back to him if you can't figure it out.
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
OK I've stayed quite long enough, stiff the mechanic, it sounds like he'll do you more harm than good ($$$$). I agree with allot of folks. You should take the money you would spent on a mechanic and invest it in the tool it takes to get the job done. AKA ohm meter. With forum help and your willingness to learn you'll feel better about a corvette accomplishment. Once you diagnose this problem you can approach a mechanic and he'll won't be so likely to take advantage of you if you can communicate with him.
