1993 L idle rpm spontaneously goes too high -- on the road

[AlaskaFestivaGuy]

I struck out again this morning. The shop had a top-of-the-line Snap-On tester, but lacked proper cabling for Festies. I wrote down the "buy this cable, adapter, etc." info message and left v/m for his Snap-On rep over in WV inquiring about purchasing the required stuff.

I'll try the O2 thing in Saturday daylight.

[AlaskaFestivaGuy]

An auto electric shop 13 miles outside of town to which I was referred just told me "We have the equipment" (like I haven't heard that multiple times already) but also claimed "ODB-1 does not save codes -- the problem must be happening 'right now' for it to provide any diagnostic info."

Does that make sense?

[AlaskaFestivaGuy]

I just placed an order with AutoZone Pittsburgh for "MAF, O2, TPS, and every other available sensor for 1993 Ford Festiva."

Any other suggestions beyond the 3 sensors listed above?

[WmWatt]

Nope. They all have the ICM chip to signal when to send the pulse to fire the spark plugs. ICM was initially called "transistorized points" because it replaced the mechanical points connected to the distributor shaft which were opened by a cam to signal the pulse.

BTW The problem has gone from fast idle to stalling?

[AlaskaFestivaGuy]

Yes, I remember "points and condenser" during tune-ups on my Fiat 128 and fleet of split-windshield VW Kombis!

It has actually progressed in the direction of (almost) stalling. This morning, I had to drive up a long hill (Pittsburgh has lots of hills) with some bozo on my rear bumper and was losing power, even in second gear. Our of sheer habit/desperation, I "pumped" the accelerator and made it to the top.

[WmWatt]

Sorry , missed the question above. Yes the computer stores OBD1 transient trouble codes. Mine did that last winter. Haynes manual confirms. You have to clear the codes by disconnecting the battery and depressing the brake pedal to remove them.

[AlaskaFestivaGuy]

If "clearing the codes" is done by pressing the brake pedal (for how long?) with the battery disconnected …

1. Where does electrical power come from for the ODB unit to sense that the brake pedal is pushed and then to "clear the codes?"
2. Where exactly is ODB (or its functionality) physically located? Is it inside the ECU?
3. Alternatively, is there perhaps a capacitor somewhere that holds a charge for a period of time after the battery is disconnected in order to sense the brake pedal and clear the codes?

[WmWatt]

"The Onborad Diagnostics (OBD) system is equipped with a computer which stores the failure code until the diagnostic system is cleared by disconnecting the negative battery cable then depressing the brake pedal for a perod of five seconds or longer." Haynes manual page 6-5

The positive bettery cable is still connected so there would be a source of current to power the computer and detect a closed curcuit at the brake pedal, the same brake pedal switch presumably which lights up the brake lights?

I don't know the physical location of the OBD computer.

I doubt there is a capacitor, just some computer memory kept alive by the car battery as a parasitic draw. Just guessing.

[AlaskaFestivaGuy]

Aha … I missed the comment about disconnecting the NEGATIVE battery cable (only).

I replaced the O2 sensor (which was quite sooty) and the ECT sensor between injectors #1 and #2. I purchased a TPS (but have not installed it) and have on order a MAF, arriving Monday.

I took it for a 20-min test drive in stop-and-go somewhat-hilly traffic and did not experience any problems, even with the temp gauge showing fully warmed up. On the next non-rainy day (when tow trucks are more readily available!), I'll do a more thorough test, including steeper hills and a stretch of Interstate.

I'm still not comfortable with shorting wires together to see if the OBS will "pulse out" a code on the check-engine light while so far from home. I haven't disconnected the battery, so whatever code it has in its silicon brain should hopefully stay there for a while.

So I spent about $300 for parts, about what I could have paid a shop to fiddle with trying to OBD1 it for 3 hours and possibly accomplish nothing.

[WmWatt]

Sounds good. Fingers crossed.

[AlaskaFestivaGuy]

A month later and running just fine. So it must have been the O2 and/or ECT sensors. I've had it up to 80 on the Interstate with no problems.

[ricko1966]

I think festiva is some version of eec not obd1 and can't be read with scan tools.Ford use to use electronic engine control system ,eec eec4 eec5 etc.and you had to use a breakout box which nobody has.Ground your sti connector and turn on the key and count light flashes to retrieve codes.I would put up a pic of what to ground, but all my pics are to big of file size, hopefully someone else can post a pic for you.