Bad Fuel Injector??

[rocky37]

My brother in-law has a 98 Nissan MAX with 120,000 miles. He took the vehicle to a local shop for a check due to very rough idle and CEL. He was told it was a miss fire in one of the cylinders. The shop said it can be the coil pack or fuel injector. The shop said to replace the coil pack because it was cheaper than the injector. So, my BIL ok’s the replacement of the coil pack and the car is running better but not perfect, still a little rough. This was about 2 weeks ago and now the car is running very rough again.

My BIL decides to replace the fuel injectors (online order). My question is, the shop should be able to determine if the fuel injector, coil pack or something else is bad that is causing the rough idle? I can replace parts until I find the bad part, but a tech. is paid to determine what is wrong and correct the issue.

My other question is, will a bad fuel injector cause a very rough idle with a CEL?

 

[Steve S]

yes but so can a coil or spark plug is it obdII? "should be" A good shop should be able to diagnose the difference .I would go to a real shop.

 

[rocky37]

It is OBD2. I expect a tech. to be able to determine a bad coil, spark plug or injector without guessing which is bad by replacement of items until the issue is corected. I know there to a way to test the coil pack, but I am not sure if there is a way to test a bad injector.

 

[mechtech2]

If he can wait a week or so, try running a bottle of good injection cleaner in the gas tank. Chevron Techron, Gumout REGANE, or Redline SI-1.
A compression or leak down check should be performed, then go after bolt on parts.

 

[brianl703]

Originally Posted By: rocky37
I know there to a way to test the coil pack, but I am not sure if there is a way to test a bad injector.


The way I've heard to do it involves using an injector pulser and a fuel pressure gauge. All of the injectors should drop the same amount of pressure when pulsed a given number of times.

The other way is with a cylinder balance test, which even the ECM in my 1988 Ford Mustang 5.0 supports. This cancels each injector in turn and notes the amount of RPM drop at idle. An injector that doesn't drop the engine speed as much as the others is reported by the computer at the conclusion of the test.

 

[Donald]

The best way to clean the injectors is to get a fuel rail adapter and run the car on fuel injector cleaner with the fuse or relay for fuel pump pulled. NAPA sells cans of cleaner for this use, its just a matter of getting the proper adapter.

However at the mileage you mention, the injectors probably do not have a perfect spray pattern. There are places on EBAY that will test/clean/rebuild fuel injectors for a decent price.

But a misfire means something is not right, a lot worse that a slightly bad spray pattern.

 

[bdcardinal]

a simple test is to start switching injectors and see if the misfire follows the change. you can do the same with coils.

the scan tool we use at work can do relative compression tests, power balance tests, coil tests, and injector flow tests without lifting the hood of the vehicle.

 

[PT1]

Originally Posted By: bdcardinal
a simple test is to start switching injectors and see if the misfire follows the change. you can do the same with coils.



This is what I do and it works like a charm! But only if it doesn't show on a TechII first.

 

[tunabreath]

Unplug the injector harness to each injector one at a time and see if there is a change in engine RPM.

Use a stethoscope at each injector to listen for a clicking.

If no clicking, use a noid light (available at auto parts stores in a set) to check for signal to the injectors.

 

[rocky37]

Thank you for all the help.