Half rate tach and 223/224 Continuous

[fastpakr]

I finally started troubleshooting my '94 2.3 a little bit tonight. It's been throwing a CEL since I bought it. Can't run KOER codes because it goes into FMEM immediately (although after a clear it will pass KOEO). Stored codes are 223 (Loss of Dual Plug Inhibit Control) and 224 (PCM detected coil 1,2,3,4 primary circuit failure). Primary visible symptom is a half rate tachometer. When I first bought it I diagnosed a failed coil pack (and had it tested before replacing), but that repair did not resolve the issue.

Tonight I verified power to both coils from the ICM/DIS module. Also traced continuity from each of the four coil signal wires back to the ICM - no problems there. When those tested good, I verified continuity from the PIP and DPI pins at the ignition module back to the ECU. No problems there either.

Since the truck runs, I assume it's safe to trust that the other wiring to the ignition module is good (seems that it would keep the system from working at all?). Based on this, I'm ready to replace the ignition module. Can anybody back me up on this diagnosis or point me towards something else that should be checked first? I've got the Mitchell manual for my truck, but the troubleshooting steps for this issue are written based on using several pieces of diagnostic gear I don't possess. Any pointers from those with experience here would be greatly appreciated.

 

[Rattler]

If the truck runs ok, you might be getting old codes. A friend of mine told me about pulling the SPOUT sensor out of it's plug, and unhooking the negative terminal for about thirty minutes or so. It's real easy to do, and it is a lot cheaper than a ICM. All of your Ford dealers carry it, and in Houston I got one for around $10.00 IF you should need one. It seemed to quiet mine down by just removing it for a while after getting codes a couple of years ago.

 

[fastpakr]

Thanks, but no - this is not an 'old code'. It is set instantly when trying to run a KOER test, even after clearing all codes properly (not by leaving the battery unhooked).

You bought an ignition module at a dealer for $10?!?

 

[Bryan22]

i got those same codes, turned out to be combination of a bad ground at the ICM, bad plugs and bad wires. does the truck run ok? does it ever just decide to lose power for a second then pick back up again, or just shut down alltogether?

first thing i would try before replacing the ICM is running a wire from the bottom left bolt (looking at the motor from the front) to a good ground somewhere. It's a mojor PITA getting at that bolt, but that single bolt was causing me a lot of problems for a long time till someone on here pointed me in the right direction (mine was missing the bolt alltogether).

 

[fastpakr]

It's not intermittent at all. The tach has never been anything but half rate, even for a second. Plugs and wires have been replaced as part of the tune up I did almost immediately after getting the truck. I'll double check the block ground.

 

[Sevensecondsuv]

The other coil pack.

Only running on one coil will cause the half rate tach. I've had this very same problem multiple times on mine (only once was the truck's fault )

The half rate tach is a dead givaway that something is wrong with one side of the ignition and not the other. The truck wouldn't run at all if it was a bad ICM. At least that's been my experience with bad ICM's.

 

[Bryan22]

i never thought of that though with 1 coil pack or the other. that's pretty good info, especially if i had a tach . did you ever get it figured out fastpakr? was just thinking too, if that was your problem, from what i've read the passenger side coil is the one that fires on cranking, so it'd have to be the drivers side coil pack. Could test it by puuling the easiest plug to pull on the drivers side and check for spark.

 

[fastpakr]

No, I've had a limited amount of time to work on it. I'm going to test the coils tonight before I go to bed. I did find last night that the frame ground isn't attached at all. Looks like the bolt was sheared off at some point. It was naturally hanging naturally against the frame so I didn't catch it until I physically pulled on the cable.

For what it's worth, I did find several discussions of ICM failures on some other forums with my symptoms so it is at least possible.

Thanks for all the suggestions. I'll post back when I have more test results.

 

[rangerbum]

As far as the tach goes it could just be wire problems. When I installed my tach i only read half the RPM, due to having dual plugs per cylinder. Mine was all about the connection.
If that's it it would be the connection that leads to the coil pack, but could be the pack itself.

 

[fastpakr]

Again, unrelated problem. You miswired your aftermarket tachometer. This is an OEM system.

 

[fastpakr]

No, I've had a limited amount of time to work on it. I'm going to test the coils tonight before I go to bed. I did find last night that the frame ground isn't attached at all. Looks like the bolt was sheared off at some point. It was naturally hanging naturally against the frame so I didn't catch it until I physically pulled on the cable.

For what it's worth, I did find several discussions of ICM failures on some other forums with my symptoms so it is at least possible.

Thanks for all the suggestions. I'll post back when I have more test results.

Follow up...
I just tested the coils. Primary resistance on both packs tests fine. The rear coil pack tests fine on secondary resistance. However, I'm showing an open circuit when measuring secondary resistance on the front coil pack. What's got me most confused about this is that the truck will only barely run when disconnecting the front (apparently bad?) coil pack, but when disconnecting the rear pack that tests fine, it starts and runs fine. For the life of me I can't explain why it runs ok on the bad coil pack but hardly at all on the good one.


Edit... Ignore the above. Must have had a bad connection. I rechecked both coil packs and they tested fine. Swapped them around as well with no impact. I assume the front coil pack handles the normal compression stroke spark events and the rear coil pack handles the emissions round?

 

[AllanD]

I would give a long angry loo at your wiring harness.

EVERY TIME I've seen problems with a DPIS 4cyl there's been something
broken, melted or corroded in the harness.

If that truck were here I'd obey the dictates of my previous experience and
wrap the back of a stanley knife blade with a blob of duct tape and I'd
start "exploring" inside the harness wrap.

At the very least I'd start flexing parts of the harness looking to make borderline problems "worse" for diagnostic purposes

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[fastpakr]

I'd already pulled my module before seeing Allan's reply, so I went ahead and had it tested at the local Advance Auto. It failed miserably, and they wanted $130 for a new one. A nearby junkyard sold me a used one for $40 that passed the test at Advance. With it installed, I'm finally getting a normal tachometer reading and both ignition codes are gone. For the first time since buying the truck last Fall, I was able to run KOER tests.

Thanks to all for their help. I can't stand buying parts until I'm sure of the diagnosis - you guys helped me sort that out. Nothing like paying $40 for one used part rather than paying a shop for a couple of hours of diagnostics and new parts.

 

[Bryan22]

good job. you were right all along

 

[fastpakr]

No real pride about that, just glad it's resolved. Looks like the second half of this is going to be straight forward too. Got a 172 on KOER, ran through the troubleshooting sequence until determining that the sensor isn't switching at all. I'll grab a new O2 sensor tomorrow and throw it in.