Fuel injectors last a long time, but sooner or later they're gonna fail —and when they do, a cylinder misfire is what you'll be dealing with.
In this tutorial, I'll show you how to do a fuel injector resistance test to find out if one has suffered an internal electrical failure.
If your test results show the injectors are OK internally, I'll also explain what else you can check to get to the bottom of the misfire issue you're chasing.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 4.7L V8 Jeep Grand Cherokee: 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
WIRING DIAGRAMS:
- Fuel Injector Circuit Wiring Diagram (1999-2001 4.7L V8 Jeep Grand Cherokee).
- Fuel Injector Circuit Wiring Diagram (2002-2004 4.7L V8 Jeep Grand Cherokee).
CYLINDER MISFIRE DIAGNOSTICS::
INJECTOR SPRAY PATTERN TEST:
Symptoms Of A Bad Fuel Injector
After spending more years than I care to count turning wrenches, I've seen fuel injectors fail in a handful of predictable ways. The three most common are:
- Internal electrical failure: The injector shorts out or opens up inside, and when that happens, it simply stops spraying fuel.
- Clogged nozzle: Carbon and varnish build-up choke the injector, so it can't deliver the right amount of fuel or the right spray pattern.
- Wiring or signal problem: The injector itself may be fine, but without power or a proper trigger signal, it won't fire and no fuel makes it into the cylinder.
Whichever way it happens, a faulty injector is gonna make the engine stumble or misfire at idle or when you hit the throttle.
The tricky part is that the PCM doesn't always throw a dedicated "bad" fuel injector trouble code when this happens. But if it does, you'll usually get one of these:
- P0201: Injector #1 Control Circuit.
- P0202: Injector #2 Control Circuit.
- P0203: Injector #3 Control Circuit.
- P0204: Injector #4 Control Circuit.
- P0205: Injector #5 Control Circuit.
- P0206: Injector #6 Control Circuit.
- P0207: Injector #7 Control Circuit.
- P0208: Injector #8 Control Circuit.
From personal experience, I can tell you that around 90% of the time, when you do have a bad fuel injector, you'll see a misfire trouble code:
- P0301: Cylinder #1 Misfire.
- P0302: Cylinder #2 Misfire.
- P0303: Cylinder #3 Misfire.
- P0304: Cylinder #4 Misfire.
- P0305: Cylinder #5 Misfire.
- P0306: Cylinder #6 Misfire.
- P0307: Cylinder #7 Misfire.
- P0308: Cylinder #8 Misfire.
And well, the other symptoms your vehicle may experience are:
- Lack of power.
- Bad gas mileage.
- Check engine light (CEL) is on.
Where To Buy The Fuel Injectors And Save
If your testing shows the injector is bad and you're ready to replace it, the ones below are quality parts from trusted brands I've used for years —and I have no hesitation recommending them:
1999-2000 4.7L V8 Jeep Grand Cherokee:
2001-2007 4.7L V8 Jeep Grand Cherokee:
Disclosure: As an Amazon Associate, I earn from qualifying purchases. If my tutorials help you, using these links is an easy way to support the site at no extra cost to you. Thank you!
The Fuel Injector Resistance Test
The fuel injector resistance spec (for the 1999-2007 4.7L V8 Jeep Grand Cherokee) is 10.8 to 13.2 Ohms with the injector at ambient temperature.
You can check this quickly with a multimeter set to Ohms mode. This simple resistance test will tell you right away if the injector has an internal issue.
If the injector has failed internally, you're going to see one of two results:
- Open circuit problem: Your multimeter will show infinite resistance. On a digital meter, that usually shows up as the letters OL.
- Short circuit problem: In this case, the injector has shorted inside, and the multimeter will read right around 0 Ohms.
NOTE: If you're new to fuel-injector or misfire troubleshooting and need a little more background on what we're doing here, check out this in-depth guide. It walks you through the whole process of diagnosing a cylinder misfire —whether it's a bad or clogged injector, or something else. I strongly recommend it (it'll save you quite a bit of time and a ton of frustration): How To Troubleshoot A Cylinder Misfire -P0300↔P0308 (1999-2007 4.7L V8 Jeep Grand Cherokee).
Alright, here are the steps:
- 1
Disconnect the fuel injector from its electrical connector.
NOTE: Start with the one you suspect is the culprit and at least two others for comparison.
Of course, you can go ahead and check all eight if you'd like. - 2
Turn your multimeter to Ohms (resistance) mode.
- 3
Touch the multimeter leads to the injector's two spade terminals.
Don't worry about polarity here —it makes no difference which lead (red or black) goes on which terminal when measuring simple resistance. - 4
Record the resistance reading that shows up on your multimeter. Make a note of which cylinder that injector belongs to as well.
- 5
Repeat the process on any other injector you want to test.
NOTE: You can continue with the rest of the injectors to have readings for all eight.
Here's how to make sense of what you just measured:
CASE 1: The fuel injector's resistance is within spec —or, if you checked all eight, they all came back within spec. This confirms the injector's internal windings are in good shape.
Even so, the injector you tested (or one of the eight, if you tested them all) could still be clogged or restricted —or the misfire could be coming from something else altogether.
If you've pinpointed the misfiring cylinder, confirmed it has spark (its ignition coil checks out), its compression is good, and its injector's resistance is within spec, then your next move is to check that injector's spray pattern. This tutorial shows you how:
If you haven't identified the misfiring cylinder, or confirmed its getting spark or its compression yet, I recommend this guide. It'll walk you step by step to the root cause:
CASE 2: One injector shows a resistance value way out of range. This means the injector is faulty and needs to be replaced.
If you're ready to replace it, below are injectors from trusted brands I've relied on for years and confidently recommend:
1999–2000 4.7L V8 Jeep Grand Cherokee:
- Standard Motor Products Fuel Injector - MFI - New - FJ481 (Amazon affiliate link)
- 812-12136 Remanufactured Fuel Injector (Amazon affiliate link)
2001–2007 4.7L V8 Jeep Grand Cherokee:
- Standard Motor Products FJ475 Fuel Injector (Amazon affiliate link)
- 812-12144 Remanufactured Fuel Injector (Amazon affiliate link)
More 4.7L V8 Jeep Grand Cherokee Tutorials
You can find a complete list of tutorials for the 4.7L V8 Grand Cherokee in this index:
Here's a sample of the tutorials you'll find in the index:
- How To Test The Throttle Position Sensor (1999-2004 4.7L V8 Jeep Grand Cherokee).
- How To Test The Fuel Pump (1999-2004 4.7L V8 Jeep Grand Cherokee).
- How To Test The MAP Sensor (1999-2001 4.7L V8 Grand Cherokee).
- How To Test Engine Compression (1999-2007 4.7L V8 Jeep Grand Cherokee).
If this info saved the day, buy me a beer!
