Explorer DOA (long, but please bear with me)

[jkesselr]

Okay, so here is the story: My borther recently bought a 91 Explorer that doesn't run. I don't know explorers well, so I can't tell you what trim level it is, but I can tell you that it is a 4.0 with all of the options (4X4, power windows, seats, locks, leather, moon roor, etc). As I said, I am not familiar with teh explorers, but I am a pretty good wrench, so I started with the basics. It read 39 PSI of fuel, but there is a buzzing that never seems to quit under the hood (back near the center of the plenum / coil pack area. It sounds like a fuel pump, but I know they are in the tank on those. Anyway, I used an inline spark checking tool and only saw spark on two cylinders the front right and rear right on the coil as you look into the engine compartment. The rest had nothing. I tried to follow the coil diagnostic sequence in the Chilton, but only part of it worked. Checking the 4 pin connector on the coil, I hooked one probe to the bat+ terminal and read .6-.7 ohms when I touched the other three terminals with the other probe. The range is from .3 to 1.0 so I was well within spec. I then tried to check the secondary resistance by touching the coil pins (on the 4 pin connector) and their respective plugwire towers on the coil pack. The meter didn't even move (on any of the scales). I really think the issue is spark, he is tight on cash and I don't want him to have to buy a coil pack that he doesn't need. Any thoughts? Also, before we started playing with it, it would turn over and sound like it was trying to fire (the turning would pick up for just a very split second, but it would never fire). After we took the coil out and did all of the tests, it doesn't sound like it is ready to kick any more, it just cranks and cranks and cranks. Could this be some other sensor that coulb be causing the computer to shut of power to the coil almost immediately? Please offer your suggestions and provide a breif explanation of how to check the things you suggest. I may also need a quick description of where to find relays or whatever as I have spent all of about 1.5 hours working on an explorer in my entire life. Thanks guys for all of your help!!!

 

[dogfriend]

You should read between 6.5 to 11.5 k ohms (6500 to 11500 ohms) on the secondary side of each set of coils in the coil pack. Probes go on Cyl 1 &5, 2 & 6 , 3&4 to read each coil.

I recently had to replace a coil pack that was reading about 12.5k because I was getting a misfire under load. The coil pack cost $120 from Napa, so you want to be sure before you replace it.

It occurs to me that you could have a problem with the ICM (ignition control module) aka Thick Film Ignition module - this is the next thing to check if the coil and wires check ok.

 

[dogfriend]

Here is some info on the Distributorless Ignition System used on the Explorer. Dead Link Removed

This is a copy of the Chilton manual at autozone.com. If you can get a copy of the Haynes manual, it has some good info along with pictures of the components in Chap 5.

 

[jkesselr]

When checking the secondary, I have the coil out of the car and am checking from one of the 4 pins on the connector to a pair of wire towers, is this correct? I ask because I am getting nothing! Does this sound right? The ICM is the black box that mounts to the core support right behind the passenger side headlight, correct? What is the tesp procedure for this? Thanks for your help!!!

 

[Opera House]

I question the test method

There are three high tension coils. None of the secondaries have a connection to ground or 12V primary. Basically a spark plug on one side is in series with one on the other side of the engine. If you removed more than one spark plug wire at a time and inserted your tester, it would look as if some plugs were not getting a spark. If you got spark on two plugs, I bet the rest are fine.

 

[dogfriend]

Originally posted by jkesselr
When checking the secondary, I have the coil out of the car and am checking from one of the 4 pins on the connector to a pair of wire towers, is this correct?

No, according to my Haynes manual, you test the resistance between the wire towers - for example between tower 1 and 5. This is because both cyl 1 and 5 share the same coil.





I ask because I am getting nothing! Does this sound right? The ICM is the black box that mounts to the core support right behind the passenger side headlight, correct? What is the tesp procedure for this? Thanks for your help!!!

Yes, the ICM is mounted to the radiator support. You can get it tested at some autoparts stores (Autozone, Napa) or you can test with a digital voltmeter.

Here's a couple of threads related to ICM:

Bad Tach

Hesitation, stumbling