95 Disco 3.9CUX won't start. Now what?

Frobisher

Well-known member
Hi all,

For the first time since buying the Disco 8 years and 70K miles ago, it's finally DOA in the driveway. I've read lots of forum posts here, there, and everywhere, worked through ignition issues on the RAVE to try to sort it out, and nothing. Any directions you can point me in will be great. Thanks!

The situation:
AM going to work, turned over but didn't start the first time but turned on with second try. I thought I noticed an unusual sound with that start and hoped it wouldn't come back to haunt me. I really can't describe it well, maybe like a little thump or something on start. Drove fine to work.

PM leaving work, turned over but no start. Everything lights up, fuel pressure on the rail (checked with a squirt on the Schrader valve and it seemed strong), and the battery is good.

I appear to be getting air but no spark. I've exchanged the rotor arm, distributor, and coil with known good ones. No dice. Ran V1-V4 ignition tests from the RAVE, and if I did them correctly, all test the way they should except "replace the coil" (V3 maybe?). It's like everything is good until then but no spark on the lead leaving the coil. I get measured current coming through but I can't get it to spark. Weird.

The fuel pump turns on and I can hear air coming in through the intake. The immobilizer has been bypassed with a button and hotwire ignition, so that shouldn't be an issue.

Most of the issues over the years have leaned more toward the easy solutions, so I'm avoiding tearing things open until I've tried all the simple stuff. I thought maybe I bumped a wire on the coil when I was re-arranging the area where the jack and ramp are supposed to be stored, but everything looks right. One of the connectors on the coil is a little loose but it's been like that for a while. Maybe it finally went south? I'm not sure.

That should give the most recent background. Thanks for any suggestions or directions you're willing to offer.
 

pmatusov

Technical Excellence Contributor
Callsign: AK6PM
Do you have a timing light? It'll help you with ignition issues.

14CUX feeds the signal from the coil to the ECU - if there are no ignition pulses, ECU stops the fuel pump. Look for the wires going from switched terminal of the coil - there should be two of them, one going to the ignition amplifier, another - to ECU. It is not uncommon for one of them to break connectivity at a sharp bend.
 

Rwollschlager

Well-known member
Lack of tach suggests loose or broken connection at the coil, clean, inspect and tighten all leads on the coil. The coil needs a sense from the ignition amp module to fire. So if the coil has a bad connection it may not be getting the signal to fire.
 

Frobisher

Well-known member
So,
1. I put the timing light on lead from the coil: no spark.
2. Checked the terminals at the coil: they all seemed to be secure at the spades.
3. Checked voltage on the V1 - V4 tests. V1: Battery + to -, 12+ volts; V2: Battery to + coil, less than 1V; V3: Battery to - coil, less than 1V; V4: amplifier to ground, less than 1V.
4. Bonus test: coil + to -, 0V.
5. Just now tightened all the connections on the coil just to be sure. No change.

It would appear tests V2 and V3 failed, so that should possibly mean bad coil, but I swapped in a "known to be working" coil. Basically, I'm at the same place as with my other coil.

I'm a little bit stumped, but it appears that easy stuff may be over.
 

pmatusov

Technical Excellence Contributor
Callsign: AK6PM
It is super easy to check if coil is good:
- leave +12V feed on the coil terminal, disconnect both connectors going to (-) coil terminal.
- Grab a spare spark plug (or use any from the truck), and any of ignition leads - connect the spark plug terminal to the coil high-voltage output, and ground the thread of the plug.
- turn on the ignition, verify that you have +12V on the (+) coil terminal.
- using a test lead (or any wire), short the (-) coil terminal to the ground (engine block/heads/intake plenum/whatever).
You should see and hear a spark. If you don't, chances are that the coil is bad.
If you see and hear a spark, chances are that the coil is good.
Next comes the ignition amplifier.
- from the previous test, leave the spark plug connected as it was to the coil.
- reconnect both connectors to the (-) coil terminal.
- turn on the ignition, and have somebody else crank the engine.
If you see and hear repeated sparks, likely both ignition amplifier and coil are good.
If you don't... Before you decide that the ignition amplifier is bad, remove the distributor cap, have somebody crank the engine, and verify that the rotor is moving.
Let's go from there.
 

rocky

Well-known member
Probably not your cause, but do you have access to another 14cux unit?
I had a mystery intermittent everything except spark problem. Pulling the 14 cux revealed water coming out of it, and a mass of corrosion inside.
 

rover4x4

Well-known member
I had a broken wire between the ignition module and coil. It was a "factory" relocation kit for the stock ignition module. It was hidden in a plug, in a harness. Seems your troubleshooting has been thorough.
 

Frobisher

Well-known member
It is super easy to check if coil is good:
- leave +12V feed on the coil terminal, disconnect both connectors going to (-) coil terminal.
- Grab a spare spark plug (or use any from the truck), and any of ignition leads - connect the spark plug terminal to the coil high-voltage output, and ground the thread of the plug.
- turn on the ignition, verify that you have +12V on the (+) coil terminal.
- using a test lead (or any wire), short the (-) coil terminal to the ground (engine block/heads/intake plenum/whatever).
You should see and hear a spark. If you don't, chances are that the coil is bad.
If you see and hear a spark, chances are that the coil is good.
Next comes the ignition amplifier.
- from the previous test, leave the spark plug connected as it was to the coil.
- reconnect both connectors to the (-) coil terminal.
- turn on the ignition, and have somebody else crank the engine.
If you see and hear repeated sparks, likely both ignition amplifier and coil are good.
If you don't... Before you decide that the ignition amplifier is bad, remove the distributor cap, have somebody crank the engine, and verify that the rotor is moving.
Let's go from there.
Thanks for such detailed directions. So far, no spark on the coil check.

Negative on the amplifier check as well. Just to be sure, spark plug threads are grounded by laying on the block. Is that sufficient to produce a spark?

I know this isn’t rocket science, but…
 

Frobisher

Well-known member
Probably not your cause, but do you have access to another 14cux unit?
I had a mystery intermittent everything except spark problem. Pulling the 14 cux revealed water coming out of it, and a mass of corrosion inside.
Not available, but my ecu is under the passenger footwell. Thats not as wet as the driver side, but it gets a little damp. It doesn't seem as likely, though, but good to check. Thanks. Anything’s possible.
 

pmatusov

Technical Excellence Contributor
Callsign: AK6PM
Thanks for such detailed directions. So far, no spark on the coil check.

Negative on the amplifier check as well. Just to be sure, spark plug threads are grounded by laying on the block. Is that sufficient to produce a spark?

I know this isn’t rocket science, but…
It should be.
 

Frobisher

Well-known member
And the rotor is spinning. Never having looked before, it’s surprising how slowly it goes round on start-up. 60 rpms, maybe?
 

Frobisher

Well-known member
New coil installed and still no change. I even reversed the terminals on the coil thinking maybe I mixed them up. That produced a very weak spark. It looks like maybe this deeper in the system. The voltage test checks tor the amplifier, so I figure that’s good. Maybe?

How did it work to drive 4 miles, then totally not have a spark 9 hours later?
 

Frobisher

Well-known member
Latest update:
1. I direct-wired the coil to the battery and got a spark off the negative lead and a bit of a spark out of the lead line from the coil grounding through a spark plug on the valve cover. Therefore, coil is good, coil lead to distributor is good.

2. Checking the ignition amplifier, I get the following:
-continuity amp to coil is good
-continuity amp to distributor is good

-blue wire from distributor to blue wire going out to coil 98 ohms
-blue wire from distributor to red wire going out to coil 105 ohms
-red wire from distributor to red wire going out to coil 187 ohms
-red wire from distributor to blue wire going out to coil 180 ohms
-ground from red/blue clip from distributor is good

I'm not sure what all this means just yet, but it's all I could figure to measure. It seems like it's saying the ignition amplifier is good. Or not. I'm really not sure why there's resistance from red to blue, but I'm still trying to figure how the amp works. Or maybe doesn't. Reading about that is tomorrow's homework assignment.
 

Frobisher

Well-known member
To wrap up this mini-saga, I worked my way back and forth battery through to distributor, swapping out the amplifier and coil with known good and ultimately new, all to no avail. I don't like to throw parts at a problem unless I know it's really the solution. In the end, these were cheap enough to try and since they continued to produce no spark, it had to be the distributor. As it turns out, the pickup coil in my distributor decided to pack up and quit seemingly out of the blue. It was as dead as a red shirt beaming down to a planet with Kirk and Spock.

A used one from a friend did the trick with a test spark the size of a July 4 firecracker, so I buttoned everything up and the 3.9 liters of CUX goodness roared to life. A little bit of playing with the timing and it sounded just fine. 9 miles later, it died on the road, so I deadsticked it into a pizza shop lot. It turned out this time it really WAS the coil. And that would be the brand new one, so I go home to get the old one, and I now appear to be good to go. We'll see what happens tomorrow am.

Maybe I fried the new one with a short session of reversed polarity. Maybe it was not one of Bosch's better budget units. We may never know.

Thanks for the help to all those who contributed. Anybody finding this thread later, be sure to check the pickup coil leads on the side of the distributor. It makes it look like you have an ignition coil issue, so when all else fails, follow the wires. Test it for ohms (2000-5000) through the 2 pins, and when you rotate the arm, you'll get a low voltage reading. If you get nothing or 0.L on your meter, "He's dead, Jim."
 

rocky

Well-known member
Bad Bosch coil? Wouldn't be the first. There was a batch of bad ones they shipped out a few years ago. We had a bunch of them around here. Knee jerk reaction is to carry a spare one on trips.
 

Frobisher

Well-known member
Great to hear it worked out. How many miles on the distributor? Was it the original 70k?
I’m fairly certain mine was the original distributor at 203k. My friend’s replacement (Jagspeed Motorworks of Latrobe, PA for locals like yourself) is of the same vintage but perhaps slightly less mileage.

To add a little insult to injury after all this effort, I ended up with massive hesitation uphill. I checked the timing repeatedly, but it turned out to be a fuel filter so clogged it practically needed a stent! And right at the 30K “time to replace me” mark. These kinds of concurrent yet unrelated issues really make for adventure.
 
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