Piston Slap: Bullish on Ford's Electronic Automatic Temperature Control? (Part II)

I have another question about my 1989 Taurus LX wagon, but I wanted to let you know that your diagnosis of my automatic climate control was dead accurate. (Well yeah, I’m awesome like that. – SM)

I didn’t think it was the AC compressor clutch because I used a hot wire to put power directly to the terminal on the compressor while the engine was off and I could see the clutch pull against the pulley. But after your response I tried something different — I pulled the AC clutch power wire out of the connector to the relay module and connected power to that wire while the engine was running. I could see the clutch pull against the pulley, but it was slipping.

This was almost two years ago. You posted my question a day or two after my daughter was born, and I was also busy fixing my 1988 Mercury Sable LS (which needed a new heater core, ignition switch, battery cable, coolant, and I installed an FS-10 compressor and AC lines).

So anyway, that question for you:

In early December I took the ’89 Taurus LX for a test drive, and it started backfiring under light throttle when it was warmed up. There was either steam or smoke slowly rising from the lower back area of the engine. I pulled out the spark plugs and they looked terrible — worn electrodes and excessively large gaps — so I installed new ones and did a test drive again, with similar results. This time the engine stalled a couple of times, which might have more to do with the fact that I didn’t gap the plugs, so they’re a lot tighter than the .056″ gap specified. The check engine light isn’t on, and the temperature gauge is reading much higher than it should, but still in the normal range. I didn’t continue the test drive long enough to figure out if the electric fan was not coming on, or if the thermostat is not opening, or if the new water pump is bad. It’s hard to diagnose a leak because the car has sat outside for so long that condensation is on a lot of parts. I’ve changed a water pump before on this, and a 3.0 Vulcan engine, so I’m pretty sure I did it right, and I was careful about the orientation of the new thermostat. I know you’re not supposed to open the radiator cap when the engine is hot, but I did that anyway, and a geyser of rust-colored coolant shot up, so I know the coolant system is holding pressure. I’m at a loss as to why the engine is backfiring so badly after it gets warmed up. Could one of the new parts be defective?

Sajeev answers:

While I revel in my successful diagnosis (on a vehicle within my wheelhouse) I cannot contain my jealousy at your collection: the UR-Taurus/Sable had such a profound effect on my 9-year-old self.

On to your question: the odds that your mis-gapped plugs or cooling issues (you need to flush the rust, burp it, etc.) are the misfire’s source is unlikely. The source is likely one of the numerous wear items discussed here that are likely in any 30+ year old car. Especially, if I recall correctly, on a Taurus with well-over 300,000 miles on the clock!

So check them all: I’d start looking for vacuum leaks, testing fuel pressure (between 30-40 psi for these Fords), and cleaning the Mass-Air Flow Sensor (with the right cleaner!). Hopefully that works, but the link in the paragraph above is a pretty comprehensive to-do list.

And I know about such lists: after spending five figures on my (formerly) $900 1989 Lincoln Continental Signature Series I can say I truly enjoy the end result. The Taurus was an amazing platform for the era, but it’s still competent performer and full of merit today! Uh oh, I feel a Craigslist-style ALL CAPS rant coming on…

YOU TTAC PEEPUL FIND ME MINT CLEAN 86-88 MERCURY SABUL LS SEDAN RITE NOW 4 MY LINCO-TAURUS PLZ

[Images: Ryan the OP and Sajeev Mehta]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.