GregBBRD

And keep in mind that the alternators in these cars are pretty "lame"...especially with an automatic. Both fans running (at normal speed), both A/C fans running, the headlights on, and the rest of the "normal" loads can overwhelm these alternators. Add in a trick stereo with an amplifier and you can easily be dealing with a -20 or -30 amp situation.

Sean had a source for "rewound" alternators, which put out more low rpm amperage, which "cured" several vehicles.

ammonman

Thanks for the input Greg. You are correct (as usual) that the fans are what is using the current. The only time I notice the fans running at full speed is when the A/C is on and ambient temps are high. During these conditions the A/C pressure switch should usually be the "highest" input to the fan/flap control in my normal climate. The chart in the WSM indicates that fan voltage starts to ramp up from +8VDC at 15 bar (220psig) getting to +12VDC when the A/C pressure sensor sees around 18 or 19 bar (264 to 279 psig). At +35C (+95F) discharge pressure in a R134a system (mine has been converted) should be somewhere in the 16-19 bar (235-279psig) range if the later R134a charts in the WSM are anywhere close for an earlier R12 system that has been converted. I'll rig up some leads and see what the actual voltage is at the fans during high ambient with A/C running. I have completely replaced the entire cooling system (hoses, T-stat, WP, exp. tank, rad tanks, etc.) except for the radiator core. When I had the tanks off the radiator it was in decent shape with all the straight-through tubes clean and clear and no debris or visible deposits The dash gauge reads a needle width below or above the +190F line depending on ambient. I verified it is accurate +/-about 3 degrees using one of our $$$ thermometers from work to check radiator supply and return temps and water bridge temps near the gauge sensor after the cooling system refresh. I'll see if Sean has any info on the "extra output" alternator rewind option. If the voltage drop wasn't causing idle rpm to sag so badly I wouldn't be chasing this so hard. Plus I'm a stubborn perfectionist that just can't hardly let go of something not being "just right". I'm bad enough about this that I have to remind myself to stop trying to get that last little bit to perfection because I usually end up messing up an otherwise top quality fix.

Thanks again for sharing your knowledge and experience with us amateurs. It is appreciated.

Mike

ammonman

Just a quick update. The loaner Output Stage made no difference in the idle characteristics. Verified coolant temps today via direct reading digital thermometer. Car was idling in P and ambient is +92F today. Coolant temp leaving the engine floats between +192F and 194F measured at the Temp II switch. Coolant temp returning from the radiator measured at the metal cover for the thermostat floats between +167F and +180F depending on where you're at in the cooling fan cycle. The fans come on at about +177F return temp and the temp rises to +180F before falling down to +167F and the fans cycle off. I'm also beginning to ponder if the low idle at high ambient is due to an aging MAF not accurately measuring air mass as temp rises. I say this as I had a couple of stumbles yesterday on hard acceleration from dead stop to pull out into traffic. The car just acted like it fell flat for a split second before taking off.

Thoughts?

Mike

John Speake

The LH ECU, and hence fuel injection system is pretty well compensated for supply voltage variations. Similarly idle speed should also hold steady even when volts drop.

If the MAF is aged then when you put your foot in it and the LH goes open loop, the mixture will be weak. This weakening does get slightly worse with higher temps.

ammonman

Roger that. What will cause idle to drop as temp goes up? TBF isn't an issue. Crank play is in spec and I put eyeballs on the block web when I did the MM/OPG job. Intake has been refreshed with new seals, hoses, gaskets, throttle and flappy sealed bearings. Temp II, plug wires, caps and rotors, and O2 sensor have all been replaced in the past year.

About the only things external to the engine I haven't refreshed are the coils (yes, the leads are all corrosion free and tight along with the grounds), the ISV, TPS (it's adjusted correctly and both contacts work), MAF, and ignition amps. Oh, and the MAF connector hasn't been touched. All the grounds were cleaned a couple of years back and treated with corrosion preventer.

Mike