Fuel injector ohms
Thread Starter
Instructor
Joined: Jul 2006
Posts: 177
Likes: 0
From: Eau Claire WI
Fuel injector ohms
Can anyone explain to me how to check the ohms on the fuel injectors. I am clueless when it comes to anything electronic. I have have never used a ohm meter. I am pretty sure I have a leaky fuel injector what should the numbers be and what am I looking for? Thanks!
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
By ohming the injector coils, it will not tell you if one of the injectors is leaking. You need to disconnect each harness connector from the injectors. Set the ohm meter at 20 (depends on what ohm meter you have). You will see two terminals on the injector. Touch one lead of the ohm meter to one terminal and the other lead to the other terminal. This will show up as a resistance on the ohm meter. The resistance should be 16-17 ohms. As long as all 8 ohm close to one another and all are over 10 ohms, then the coils are fine.
To test for leaky injectors there is a procedure to do. You will need a fuel pressure gauge to locate if there is a leak and were the leak is. In tank, FPR, injectors, ect.
To test for leaky injectors there is a procedure to do. You will need a fuel pressure gauge to locate if there is a leak and were the leak is. In tank, FPR, injectors, ect.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Your welcome. When you get time, try checking the injector coils and if they are good, we can help with locating a leak.....if any.
Usually when you remove the spark plugs one or more will have raw fuel on them,...if an injector is leaking.
Usually when you remove the spark plugs one or more will have raw fuel on them,...if an injector is leaking.
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
First.... the OHM check won't detect a leaky fuel injector.
A fuel injector leak means fuel is getting by the spring loaded pintle inside the injector.
That can be cause by a worn pintle and seat or something stuck on the seat or pintle that causes itr not to seal.
The motive force to move the pintle off the seat so fuel can pass into the injector nozzle is provided by an electromagnet inside the injector.
The electromagnet consist of a few hundred turns of wire that form a coil.
When electrical current passes thru the wire a magnetic field forms that pulls the pintle up against the spring pressure and fuel flows by the pintle and seat into the injector nozzle and out the nozzle end.
The nozzle end is comprised of a few tiny holes that cause the fuel to disperse into a mist as it leaves the nozzle end and mixes with the incoming air as it is passing by on it's way to the combustion chamber.
The electromagnetic coil wire is coated with a fuel resistant coating that provides insulation so that the wire coils don't 'short' to each other.
When all the coils are insulated from each other, the length of wire inside the injector is long enough to have a specific resistance that can be measured with an OHM-METER.
If the coil of wire is BROKEN the injector will not work at all. THe OHMETER will read OL (overload) or INFINITY.
If there are shorted turns of wire the injector coil will OHM check lower than normal.
The injectors for each 'BANK' (L98's) are wired in PARALLEL. BEcause of this if ONE injector coil had enough shorted coils the current thru that injector may rise to a 'critical' level.
Even though current flowing thru the wire creates the magnetic force to actuate the pintle valve, INCREASED current due to shorted coils will DECREASE the magnetic field.
In addition, the INJECTOR DRIVER or Output Stage in the ECM may not be capable of supplying the additional current for the bad injector and the GOOD INJECTOR currents may possibly be DECREASED. This condition can DRASTICALLY affect the performance of the engine.
In some cases the current could increase enough to open the protection fuse for the injector drive circuit.
Each of the TWO BANKS of injectors on the L-98 engine control system is individually fused.
Back to testing the INJECTOR COIL RESISTANCE.........................
I may be one ot two OHMS off but the factory specification is:
14 to 17 OHMS
To measure the resistance of the injector coil it's about as easy as One,Two,Three:
1) ON THE INJECTOR ELECTRICAL CONNECTOR pull the little clip 'lock' back and remove the electrical connector from the top of the injector.
2) PLACE YOUR OHM-METER on the LOW OHMS SCALE
The low OHMS scale will be similar to 0~100 ohms
If you have a 0~10 OHM scale use the next higher OHM scale.
Do NOT go above this to measure the electrical resistance on the injector coils. Nothing will be damaged if you do but your measurement won't be accurate.
For example if you used the 50,000 ohm range for this measurment you would see "0" OHMS on your meter. Even though the injector resistance was perfectly normal. So, use the LOW OHMS SCALE.
3) A set of clip leads come in really handy for this.
After placing your OHM-METER on the low ohm scale, place one of your test leads on one of the injector leads. Place the other test probe on the other injector lead.
There is NO POLARITY to be concerned with as the injector coil is just a few hundred turns of WIRE.
Read the OHM reading from the meter.
ALL the injectors should be in the range of 14~17 OHMS
If you find one or more that are out of the normal range it's good practice to replace them.
Having a resistance out of specification doesn't mean the injector won't work, in a lot of cases they still work to some extent and the engine continues to run.
However it's a roll of the dice on how much fuel the injector will pass when the electro-magnetic field isn't at the design strength.
One thing is for sure. The AIR VOLUME headed to the cylinder is NOT changed just because an injector fails to add the desired fuel amount.
So, you 'could' end up with a lean cylinder if the injector coil is not 'up to spec.'.
If you have a leaky injector the likely result will be just the opposite.
The affected cylinder will likely receive an enriched mixture from the fuel that passes the injector that isn't figured into the 'Fueling Algorithm' in the ECM code.
Even in this case the closer to WOT (wide open throttle) the engine is operated the closer the fuel mixture will become to 'normal'.
This is why it can be difficult sometimes to logically diagnose this type problem. The effect of the fault changes dynamically with throttle opening and becomes 'confusing' to diagnose.
Good luck and HAVE FUN dagnosing you engine!
A fuel injector leak means fuel is getting by the spring loaded pintle inside the injector.
That can be cause by a worn pintle and seat or something stuck on the seat or pintle that causes itr not to seal.
The motive force to move the pintle off the seat so fuel can pass into the injector nozzle is provided by an electromagnet inside the injector.
The electromagnet consist of a few hundred turns of wire that form a coil.
When electrical current passes thru the wire a magnetic field forms that pulls the pintle up against the spring pressure and fuel flows by the pintle and seat into the injector nozzle and out the nozzle end.
The nozzle end is comprised of a few tiny holes that cause the fuel to disperse into a mist as it leaves the nozzle end and mixes with the incoming air as it is passing by on it's way to the combustion chamber.
The electromagnetic coil wire is coated with a fuel resistant coating that provides insulation so that the wire coils don't 'short' to each other.
When all the coils are insulated from each other, the length of wire inside the injector is long enough to have a specific resistance that can be measured with an OHM-METER.
If the coil of wire is BROKEN the injector will not work at all. THe OHMETER will read OL (overload) or INFINITY.
If there are shorted turns of wire the injector coil will OHM check lower than normal.
The injectors for each 'BANK' (L98's) are wired in PARALLEL. BEcause of this if ONE injector coil had enough shorted coils the current thru that injector may rise to a 'critical' level.
Even though current flowing thru the wire creates the magnetic force to actuate the pintle valve, INCREASED current due to shorted coils will DECREASE the magnetic field.
In addition, the INJECTOR DRIVER or Output Stage in the ECM may not be capable of supplying the additional current for the bad injector and the GOOD INJECTOR currents may possibly be DECREASED. This condition can DRASTICALLY affect the performance of the engine.
In some cases the current could increase enough to open the protection fuse for the injector drive circuit.
Each of the TWO BANKS of injectors on the L-98 engine control system is individually fused.
Back to testing the INJECTOR COIL RESISTANCE.........................
I may be one ot two OHMS off but the factory specification is:
14 to 17 OHMS
To measure the resistance of the injector coil it's about as easy as One,Two,Three:
1) ON THE INJECTOR ELECTRICAL CONNECTOR pull the little clip 'lock' back and remove the electrical connector from the top of the injector.
2) PLACE YOUR OHM-METER on the LOW OHMS SCALE
The low OHMS scale will be similar to 0~100 ohms
If you have a 0~10 OHM scale use the next higher OHM scale.
Do NOT go above this to measure the electrical resistance on the injector coils. Nothing will be damaged if you do but your measurement won't be accurate.
For example if you used the 50,000 ohm range for this measurment you would see "0" OHMS on your meter. Even though the injector resistance was perfectly normal. So, use the LOW OHMS SCALE.
3) A set of clip leads come in really handy for this.
After placing your OHM-METER on the low ohm scale, place one of your test leads on one of the injector leads. Place the other test probe on the other injector lead.
There is NO POLARITY to be concerned with as the injector coil is just a few hundred turns of WIRE.
Read the OHM reading from the meter.
ALL the injectors should be in the range of 14~17 OHMS
If you find one or more that are out of the normal range it's good practice to replace them.
Having a resistance out of specification doesn't mean the injector won't work, in a lot of cases they still work to some extent and the engine continues to run.
However it's a roll of the dice on how much fuel the injector will pass when the electro-magnetic field isn't at the design strength.
One thing is for sure. The AIR VOLUME headed to the cylinder is NOT changed just because an injector fails to add the desired fuel amount.
So, you 'could' end up with a lean cylinder if the injector coil is not 'up to spec.'.
If you have a leaky injector the likely result will be just the opposite.
The affected cylinder will likely receive an enriched mixture from the fuel that passes the injector that isn't figured into the 'Fueling Algorithm' in the ECM code.
Even in this case the closer to WOT (wide open throttle) the engine is operated the closer the fuel mixture will become to 'normal'.
This is why it can be difficult sometimes to logically diagnose this type problem. The effect of the fault changes dynamically with throttle opening and becomes 'confusing' to diagnose.
Good luck and HAVE FUN dagnosing you engine!
Last edited by VetNutJim; Mar 28, 2007 at 01:08 PM. Reason: Spelling Correction
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
By ohming the injector coils, it will not tell you if one of the injectors is leaking. You need to disconnect each harness connector from the injectors. Set the ohm meter at 20 (depends on what ohm meter you have). You will see two terminals on the injector. Touch one lead of the ohm meter to one terminal and the other lead to the other terminal. This will show up as a resistance on the ohm meter. The resistance should be 16-17 ohms. As long as all 8 ohm close to one another and all are over 10 ohms, then the coils are fine.
To test for leaky injectors there is a procedure to do. You will need a fuel pressure gauge to locate if there is a leak and were the leak is. In tank, FPR, injectors, ect.
To test for leaky injectors there is a procedure to do. You will need a fuel pressure gauge to locate if there is a leak and were the leak is. In tank, FPR, injectors, ect.
Racer
Joined: Dec 2006
Posts: 367
Likes: 0
From: Beaver Dam Kentucky
First.... the OHM check won't detect a leaky fuel injector.
A fuel injector leak means fuel is getting by the spring loaded pintle inside the injector.
That can be cause by a worn pintle and seat or something stuck on the seat or pintle that causes itr not to seal.
The motive force to move the pintle off the seat so fuel can pass into the injector nozzle is provided by an electromagnet inside the injector.
The electromagnet consist of a few hundred turns of wire that form a coil.
When electrical current passes thru the wire a magnetic field forms that pulls the pintle up against the spring pressure and fuel flows by the pintle and seat into the injector nozzle and out the nozzle end.
The nozzle end is comprised of a few tiny holes that cause the fuel to disperse into a mist as it leaves the nozzle end and mixes with the incoming air as it is passing by on it's way to the combustion chamber.
The electromagnetic coil wire is coated with a fuel resistant coating that provides insulation so that the wire coils don't 'short' to each other.
When all the coils are insulated from each other, the length of wire inside the injector is long enough to have a specific resistance that can be measured with an OHM-METER.
If the coil of wire is BROKEN the injector will not work at all. THe OHMETER will read OL (overload) or INFINITY.
If there are shorted turns of wire the injector coil will OHM check lower than normal.
The injectors for each 'BANK' (L98's) are wired in PARALLEL. BEcause of this if ONE injector coil had enough shorted coils the current thru that injector may rise to a 'critical' level.
Even though current flowing thru the wire creates the magnetic force to actuate the pintle valve, INCREASED current due to shorted coils will DECREASE the magnetic field.
In addition, the INJECTOR DRIVER or Output Stage in the ECM may not be capable of supplying the additional current for the bad injector and the GOOD INJECTOR currents may possibly be DECREASED. This condition can DRASTICALLY affect the performance of the engine.
In some cases the current could increase enough to open the protection fuse for the injector drive circuit.
Each of the TWO BANKS of injectors on the L-98 engine control system is individually fused.
Back to testing the INJECTOR COIL RESISTANCE.........................
I may be one ot two OHMS off but the factory specification is:
14 to 17 OHMS
To measure the resistance of the injector coil it's about as easy as One,Two,Three:
1) ON THE INJECTOR ELECTRICAL CONNECTOR pull the little clip 'lock' back and remove the electrical connector from the top of the injector.
2) PLACE YOUR OHM-METER on the LOW OHMS SCALE
The low OHMS scale will be similar to 0~100 ohms
If you have a 0~10 OHM scale use the next higher OHM scale.
Do NOT go above this to measure the electrical resistance on the injector coils. Nothing will be damaged if you do but your measurement won't be accurate.
For example if you used the 50,000 ohm range for this measurment you would see "0" OHMS on your meter. Even though the injector resistance was perfectly normal. So, use the LOW OHMS SCALE.
3) A set of clip leads come in really handy for this.
After placing your OHM-METER on the low ohm scale, place one of your test leads on one of the injector leads. Place the other test probe on the other injector lead.
There is NO POLARITY to be concerned with as the injector coil is just a few hundred turns of WIRE.
Read the OHM reading from the meter.
ALL the injectors should be in the range of 14~17 OHMS
If you find one or more that are out of the normal range it's good practice to replace them.
Having a resistance out of specification doesn't mean the injector won't work, in a lot of cases they still work to some extent and the engine continues to run.
However it's a roll of the dice on how much fuel the injector will pass when the electro-magnetic field isn't at the design strength.
One thing is for sure. The AIR VOLUME headed to the cylinder is NOT changed just because an injector fails to add the desired fuel amount.
So, you 'could' end up with a lean cylinder if the injector coil is not 'up to spec.'.
If you have a leaky injector the likely result will be just the opposite.
The affected cylinder will likely receive an enriched mixture from the fuel that passes the injector that isn't figured into the 'Fueling Algorithm' in the ECM code.
Even in this case the closer to WOT (wide open throttle) the engine is operated the closer the fuel mixture will become to 'normal'.
This is why it can be difficult sometimes to logically diagnose this type problem. The effect of the fault changes dynamically with throttle opening and becomes 'confusing' to diagnose.
Good luck and HAVE FUN dagnosing you engine!
A fuel injector leak means fuel is getting by the spring loaded pintle inside the injector.
That can be cause by a worn pintle and seat or something stuck on the seat or pintle that causes itr not to seal.
The motive force to move the pintle off the seat so fuel can pass into the injector nozzle is provided by an electromagnet inside the injector.
The electromagnet consist of a few hundred turns of wire that form a coil.
When electrical current passes thru the wire a magnetic field forms that pulls the pintle up against the spring pressure and fuel flows by the pintle and seat into the injector nozzle and out the nozzle end.
The nozzle end is comprised of a few tiny holes that cause the fuel to disperse into a mist as it leaves the nozzle end and mixes with the incoming air as it is passing by on it's way to the combustion chamber.
The electromagnetic coil wire is coated with a fuel resistant coating that provides insulation so that the wire coils don't 'short' to each other.
When all the coils are insulated from each other, the length of wire inside the injector is long enough to have a specific resistance that can be measured with an OHM-METER.
If the coil of wire is BROKEN the injector will not work at all. THe OHMETER will read OL (overload) or INFINITY.
If there are shorted turns of wire the injector coil will OHM check lower than normal.
The injectors for each 'BANK' (L98's) are wired in PARALLEL. BEcause of this if ONE injector coil had enough shorted coils the current thru that injector may rise to a 'critical' level.
Even though current flowing thru the wire creates the magnetic force to actuate the pintle valve, INCREASED current due to shorted coils will DECREASE the magnetic field.
In addition, the INJECTOR DRIVER or Output Stage in the ECM may not be capable of supplying the additional current for the bad injector and the GOOD INJECTOR currents may possibly be DECREASED. This condition can DRASTICALLY affect the performance of the engine.
In some cases the current could increase enough to open the protection fuse for the injector drive circuit.
Each of the TWO BANKS of injectors on the L-98 engine control system is individually fused.
Back to testing the INJECTOR COIL RESISTANCE.........................
I may be one ot two OHMS off but the factory specification is:
14 to 17 OHMS
To measure the resistance of the injector coil it's about as easy as One,Two,Three:
1) ON THE INJECTOR ELECTRICAL CONNECTOR pull the little clip 'lock' back and remove the electrical connector from the top of the injector.
2) PLACE YOUR OHM-METER on the LOW OHMS SCALE
The low OHMS scale will be similar to 0~100 ohms
If you have a 0~10 OHM scale use the next higher OHM scale.
Do NOT go above this to measure the electrical resistance on the injector coils. Nothing will be damaged if you do but your measurement won't be accurate.
For example if you used the 50,000 ohm range for this measurment you would see "0" OHMS on your meter. Even though the injector resistance was perfectly normal. So, use the LOW OHMS SCALE.
3) A set of clip leads come in really handy for this.
After placing your OHM-METER on the low ohm scale, place one of your test leads on one of the injector leads. Place the other test probe on the other injector lead.
There is NO POLARITY to be concerned with as the injector coil is just a few hundred turns of WIRE.
Read the OHM reading from the meter.
ALL the injectors should be in the range of 14~17 OHMS
If you find one or more that are out of the normal range it's good practice to replace them.
Having a resistance out of specification doesn't mean the injector won't work, in a lot of cases they still work to some extent and the engine continues to run.
However it's a roll of the dice on how much fuel the injector will pass when the electro-magnetic field isn't at the design strength.
One thing is for sure. The AIR VOLUME headed to the cylinder is NOT changed just because an injector fails to add the desired fuel amount.
So, you 'could' end up with a lean cylinder if the injector coil is not 'up to spec.'.
If you have a leaky injector the likely result will be just the opposite.
The affected cylinder will likely receive an enriched mixture from the fuel that passes the injector that isn't figured into the 'Fueling Algorithm' in the ECM code.
Even in this case the closer to WOT (wide open throttle) the engine is operated the closer the fuel mixture will become to 'normal'.
This is why it can be difficult sometimes to logically diagnose this type problem. The effect of the fault changes dynamically with throttle opening and becomes 'confusing' to diagnose.
Good luck and HAVE FUN dagnosing you engine!
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