ignition mystery

[JustinSchick]

Hello folks,

If any of you are subscribed to the SHOTimes lists, you're probably already painfully aware of my saga. If not, let me try and describe it start to finish:

I had a little problem with a alternator belt that was too short, putting the tensioner pulley too close to the battery. Unfortunately I didn't catch it soon enough to avoid one big mess.

Mess cleaned up, I dediced to be nice to my car and do some maintenance. That included an oil change, intake cleaning, IAB valve swap (to a newer ATX style), and new plugs. Nobody had Motorcrafts in stock so I used Autolites. They are indeed slightly longer, but my Taylor wires still covered the plug wells adequately.

Got it all buttoned back up and the troubles started. At first it was very intermittent, usually only at startup. Then a couple weeks later the symptoms would occur after it had warmed up, sometimes repeatedly during a single trip. Now they're pretty much constant (every time I start it - I don't drive it anywhere anymore). The CE light illuminates, the tach goes off by quite a bit, and it runs super rough and rich, barely wanting to idle. Codes include 212 (IDM / SPOUT failure), 215 and 217 (coil failures).

I swapped the cam sensor with a spare I had on hand. Then replaced the coil with a used one purchased from Al Fitz. Then the DIS with a new one. Then the PCM (X2J) with a used spare I had. Then the crank sensor with a new one. Same results after each step. Now this evening, I checked the IDM and SPOUT circuits. For reference, IDM is pin 4 at the PCM and pin 12 at the DIS. SPOUT is pin 36 at the PCM and 5 at the DIS. Both circuits showed just 0.1 ohm, so I assume they're not grounded out.

My current plan is to take the intake back off, swap those Autolites out and check the resistance on my plug wires. Beyond that, I have no clue what to do next. I'm pretty much at my wits end and thinking very seriously of parting the thing out and getting something with more displacement and RWD. I love this car, but need more reliability than this out of my daily driver. If you have any ideas whatsoever, they would be greatly appreciated!

Justin
silver 92 SHO in KC MO
205k and trying to keep it counting quickly

 

[projectSHO89]

Justin,

If your "big mess" included battery acid, all bets are off.... However, I would suspect acid damage to the wiring at the DIS module, specifically those leads that run to the coil.

Verify that both bottom DIS mounting screws are installed, that thermal heatsink compound was used, that the crossover tube is properly grounded to the heads, and that the rear grounding strap between the head and the firewall are installed properly.

O'Reilly's and AutoZone both carry the new Motorcraft FM plugs for our cars. Less expensive than the PP version, also.

When you say your "tach goes of a bit", is it rising, lowering, or what? Magnitude of change?

Are you encountering erratic starting? That is, only starts after several attempts?


A few ideas.

Steve

 

[JustinSchick]

Thanks for the reply Steve.

In addition to ohming the SPOUT and IDM circuits, I also did the three coil wires between the DIS and the coil. All seemed to be fine. Part of my troubleshooting also included cranking the engine over while watching for PIP and CID signals.

When I did the new DIS I used the goo that came with it, and cleaned up each contact point between the crossover tube, brackets, and intake. Good idea on the ground strap though, I'll check it tonight.

Other than rough and rich it starts up fine, first try. When the problem was erratic, the CE light would come on, and the RPMs on the tach would pretty much get cut in half of the real value. A few minutes later the light would go out and it'd run perfect again.

Good to know those FM (fine wire?) plugs are ok to use. I guess the big question is, can crap plugs and wires generate these codes? I guess if plug(s) weren't firing, it'd make sense that the DIS wouldn't reply to the PCM with the IDM signal.

Justin

 

[projectSHO89]

I guess if plug(s) weren't firing, it'd make sense that the DIS wouldn't reply to the PCM with the IDM signal.

Justin

The IDM signal is a summation of the three coil drive signals and requires both CID amd PIP signals as prerequisites. It is generated in the DIS module and fed back to the PCM as a monitor signal and to the dash to drive the TACH.

It would require an extraordinary fault in the ignition secondary system (plugs and wires) to cause it to **** the actual coil drive signals.

The most common reasons for a drop in the RPMs indicated by the tach combined with Coil X codes is a faulty DIS, faulty coil, or an open circuit in the interconnecting wiring.

If you can catch it in the act, measure each of the three coil drive signals at the DIS using a DVM on DC volts. I would expect a reading of 7-11 volts on a properly operating signal line with the engine at idle. An open drive in the DIS module would cause a Vbatt reading. A reading of Zero would indicate an open circuit between the DIS and the coil (including the coil).

Steve