how do I test a coil and fuel injectors?

supercommuter · Post by **supercommuter** » Thu Jun 30, 2011 1:05 pm

Been running like crap, got a P0304 for misfire in #4, then that went away but still running crappy, and now a P0200 for fuel injector and a P0300 for misfire in multiple cylinders.

I've already replaced the plugs, and am going to do plug wires tonight. Next step I guess would be the coil, but I'd like to test the coil and injectors before I start throwing parts at it.

Can you Ohm out the coil and injectors, or check for certain voltage? I have a multi-meter and know how to use it, just need to know what to check for and where. Thanks!

Johny · Post by **Johny** » Thu Jun 30, 2011 2:20 pm

supercommuter wrote:Been running like crap, got a P0304 for misfire in #4, then that went away but still running crappy, and now a P0200 for fuel injector and a P0300 for misfire in multiple cylinders.

I've already replaced the plugs, and am going to do plug wires tonight. Next step I guess would be the coil, but I'd like to test the coil and injectors before I start throwing parts at it.

Can you Ohm out the coil and injectors, or check for certain voltage? I have a multi-meter and know how to use it, just need to know what to check for and where. Thanks!

I don't think the coil is your problem, it may be one of the wires because before I changed mine, I was getting misfires too. Check the resistance on one of the wires, and compare it to a good one.

For testing the coil, I think you can attach the two pins to 2 of the terminals and check for conductivity. Or put a screw driver with a rubber handle to the terminal and have someone start the car for you, and watch for spark. I've seen someone do that before, but not too sure how safe that is

Post by **occasional demons** » Thu Jun 30, 2011 8:05 pm

IIRC, the injectors are 12 - 14 ohms. But that won't tell you if it is clogged, etc.
In addition to the above posts...
A bad o ring at the injector, or IM runner can cause a miss also. The vacuum leak can alter the fuel path enough that cylinder will lean out and miss.

The Accel coil I had just gave me a good time trying to find my miss/backfire in the IM. No CEL/codes at all. At least you have some codes.

Check the connectors for any corrosion on the coil/injectors, too.

If you have some jumper wires with small alligator clips you can put 12 volts to the center pin, and ground the outer pins. When you break the ground(s) the related coil should fire. If not, it is dead. This is far more saturation time than it will get at cranking/running, so if it won't fire with this test, it is more than likely done.

If you do one coil at a time, be sure just that set of wires is sparking. If there is any spark from the other pair, the coil is bad. I suspect this is what was happening with the Accel. Randomly firing both coils at once is not good. My ghetto blaster has passed the torture test with flying colors. :/

OB · Post by OB » Thu Jun 30, 2011 10:13 pm

^With as much voltage as the coil puts out when it fires, I don't know how good of an idea this is. I guess it's not much different than using one of those spark testers that you ground to the head (simulated spark plug).

There are two coils listed that could have come as OEM equipment. Not sure if one is SRT, one non SRT, but the FSM shows:

Weastec (Steel towers) - 0.45-0.65 Ohms Primary / 11,500-13,500 Secondary

Diamond (Brass towers) - 0.53-0.65 Ohms Primary / 10,900-14,700 Secondary

Spark plug wires (ohms):

2280-7290

Note, the SRT wires have identical ratings, EXCEPT #4, which is 2686-8062

Post by **occasional demons** » Thu Jun 30, 2011 11:30 pm

The only danger is if you hold onto the plug wires/ends. The best way would be to put a spark plug in each wire. Then be sure the plugs are grounded. On the car, this may mean wrapping bare wire around them, and attaching it to the body of the car. As long as the ground is good, you are safe. (Just don't stand too close to the fender, with metal zipper equipped pants.)

If the secondary voltage was back feeding to the primary input, (The connector) the PCM would be toast by now)

If they are not oem wires, the resistance value can vary greatly. Parts store wires are generally junk.
(The daughter's 1gn currently has the NAPA wires it came with. Any water at all on them causes violent misfiring. And they don't appear to be too old. The car only has 43000 miles. There was prolly nothing wrong with the original ones, other than age.)

The Taylor Spiro pro's I have are now 7+ years old, 98,000 miles. They still average about 300 ohms each. I can blast them at the car wash, and the engine never misses a beat. Cost:$42.00, about the same cost as Mopar, or parts store junk.

But if they are over 10,000 ohms each, for as short as they are, yeah, pitch 'em.

supercommuter · Post by **supercommuter** » Thu Jul 07, 2011 11:13 am

Okay, I've got 12.5 K accross the towers on the coil.

I then checked the terminals where the plug connects to on the side of the coil, and it's pretty much 0 Ohms across the center pin and either of the outer pins. What does that mean?

OB · Post by OB » Fri Jul 08, 2011 12:11 am

supercommuter wrote:Okay, I've got 12.5 K accross the towers on the coil.

I then checked the terminals where the plug connects to on the side of the coil, and it's pretty much 0 Ohms across the center pin and either of the outer pins. What does that mean?

Those should be the primary readings. I imagine one is hot, and the others are grounded independently by the PCM to energize each respective coil.

supercommuter · Post by **supercommuter** » Fri Jul 08, 2011 8:18 am

So what should it read across the three pins at the connector?

supercommuter · Post by **supercommuter** » Fri Jul 08, 2011 9:52 am

Alright, I've got .9 Ohms at the Secondary, about 3K Ohms on the plug wire, and 12.9 Ohms at the injector.

Does that sound right?

2GN.ORG

how do I test a coil and fuel injectors?

how do I test a coil and fuel injectors?

Re: how do I test a coil and fuel injectors?