Hesitation from change in electrical load

[eternalphoenix64]

'87 Ranger w/ 2.9, manual, and 4x4

So this truck has been a massive project in electrical gremlins.

Lost function of fuel pumps, turned out a ground became 12V somehow and a 12V became ground. Replaced wiring harness and it runs.

Was super cold-blooded and had a hesitation, so ended up replacing both fuel pumps (turned out to be the in-tank one causing the problem).

Now the truck starts and runs GREAT. Except when I give it a sudden power draw (such as when I initially turn on the fan or headlights or blinkers), there is a brief hesitation in the engine.

Things that have been done to this truck since I bought it:
Both fuel pumps replaced
Battery replaced
O2 sensor replaced
Belts replaced
Tune up (TFI module, plugs, wires, cap, rotor, and coil)
Water pump replaced
Wiring harness replaced
Computer replaced
TPS replaced (there wasn't one)
Battery ground cable replaced
Starter solenoid replaced
and I think that's it.


I'm wondering if the alternator is to blame (have to double check, but pretty certain it is internal voltage regulation), but I'm open to other possibilities if anyone has encountered the same problem before.

 

[RonD]

Test battery voltage with key off
12.3 to 12.8 volts is expected
12.3v is 5 year old battery
12.8v is new battery

Start engine
Battery voltage should now show 13.5 to 14.9volts, that's the alternator and voltage regulator working
It should be above 14volts for a few minutes to ReCharge battery after starter motor drained it.
Then voltage will drop down to about 13.5volts to run all the truck's electrics and Maintain Battery's 12volt charge
Running over 14volts all the time will "cook" the battery

Voltage regulator is what varies the voltage coming out of the alternator.
say engine has been idling a few minutes and Battery Voltage is now 13.6volts
Turn on the Head Lights, voltage should drop a bit then come back up to 13.6volts, that is the voltage regulator reacting correctly to extra power draw and increasing the alternators output.
Leave lights on and turn heater fan to High, you should see the voltage drop and then see it come back up.

This is while engine is idling
If voltage drops but doesn't come back up, then raise RPMs on the engine and see if voltage comes up to 13.6volts, if it does then Voltage regulator is OK but one of the three Fields in the alternator is bad.

An alternator has 3 Fields in it's case, each field generates AC voltage as rotor spins inside, each field has a set of Diodes that convert AC volts to DC volts.
All 3 Fields are needed to get full AMPs/Voltage from an alternator.
If a Field fails then alternator can not generate enough amps/volts at lower RPMs to maintain the 13.5volts.
Increasing the RPMs allows the other two Fields to generate more AMPs to compensate for the fail Field.

A failed Field is the old "why are headlights dimming at idle?" question, because voltage is dropping below 13.5v and your eyes notice it.

Vehicle makers spec alternators with about 30% more amps than needed for stock electrical system
So if you have a 90amp rated alternator your vehicle probably needs about 60amps with EVERYTHING on
90 Amp rating is with engine at 2,000RPMs, not at idle
At idle you probably have about 70amps, with 3 working fields, if one fails then you drop below electrical needs for ALL electrics on, at idle RPMs

 

[adsm08]

One of your battery cables is loose. Probably at the starter relay.