240 Alternator and fuses weirdness

mschultz373 said:

but in terms of applying field flashing - that means my alternator is still partially working for the time being? fundamentally, if it is NOT below the battery voltage static - i.e without car on - then the alternator is doing its job?

but at 13.4V with the car idling, the bottom line is that a new alternator is basically in my future? regardless of the brushes or regulator? shouldn't the voltage, ideally, be 14V at least?

Click to expand...

Yes, the alternator is charging the battery. You do not need to mess around with field flashing because that is not your problem. If you want to try an acid test, with the engine running switch on the headlights, 4 way flashes, the heater fan, radio and any other electrical loads that you can think of. Watch the voltmeter. If the voltmeter drops to the battery voltage you know that the alternator has limited ability to supply charging current. This could be an internal alternator problem or it could be a wiring problem. If the alternator is able to maintain the voltage at 13.4 volts with all that load you are probably OK to go.

The 13.4 volt operating point is lower than ideal and may be a sign that the regulator may be out of spec, or damaged or that you have a nasty wiring problem. I don't think the 13.4 volt operating voltage confirms that a new alternator is mandatory. Since your brushes were not worn down a new regulator might fix the problem; however, I am more inclined to believe that you might have some wiring problems. I had an 1987 745 T which had the Volvo biodegradable wiring. I thought the charging system wiring was separate from the engine wiring harness. If you have the original charging system wiring you may have some issues there.

to be clear, which I wasn't, the volt drop I measured was alt case to negative battery - testing the alt ground wire. i'll perform the others this morning, but my plan of attack is to clean up or replace the alt ground wire.

i replaced the engine wiring harness with a dave barton one last month.

is my voltage at D+ terminal OK? Or too low? Bentley says it should get battery voltage, which makes me think it should be 12.4V instead of ~2V?

here's the full volt drop measurements:

idling in P w/ fan on full, AC on, radio on, lights on
battery = 13.35V
battery + to alt B+ = 174mV
B+ to alt case = 132mV
alt case to engine block = 285-300mV
engine block to batt - = 15mV
batt + to starter = 61mV
starter to alt B+ = 113mV

battery posts to clamps were <15mV

300mv drop from the alt to the block is a lot. Try running a redundant ground..


What's the issue with the charging system?

yeah, i'm going to clean up the alt ground wiring points first and then see what the measure is.

the other volt drops are in spec, i.e. under 200mV.

i was just asking what voltage at alt D+ ought to be - if it's supposed to read as battery voltage (~12.4V) or if my read of ~2V is acceptible.

thanks for your continued time and help yall!

so I cleaned up all the washers, terminals and screws and areas for alternator ground and B+. I also put dielectric grease on all the metal parts. here's my measurements after:

battery @ idle nothing on = 13.85V
battery @ idle fans/AC/radio/lights ON = 13.48V
battery + to Alt B+ volt drop = 161mV
alt case to engine block = 174mV

so my cleaning up clearly helped the grounding, but I am still not happy with the battery charge being <14V.

but it looks to me that fundamentally, the alt is basically working, though not as well as it should. could the voltage regulator need replaced? that's the only thing I can think of since the brushes and the wiring appears to check out.

Just so you know, silicone dielectric grease is an insulator. It works well as an external coating to stop oxidation of electrical connections - just like any other grease. If you want to improve the electrical conductivity in a bolted electrical connection you need to use something like Ox Guard which is a grease with fine metal particles embedded in the grease (available at Lowe's Home Depot, lots of places).

Check the service manual for the car. 13.8 volts may be within spec for a non adjustable regulator at idle. If your .161 v and .174 v drops were measured under load that totals .335v which is close to your load vs no load voltage difference. You did not do the battery negative to chassis ground voltage measurement. If you have some drop there that could explain the difference.

With a heavy electrical load on the alternator, measure from the B+ stud to the frame of the alternator (or its ground connection). If you have a higher voltage there then the voltage drop is somewhere in your external wiring. If the B+ to frame voltage is down around 13.8 volts, then it may be a regulator that is at the lower end of its spec range or it could be some kind of regulator problem.

Edit:
As an additional observation, a voltage above 12.4 indicates that the alternator is probably supplying the electrical load of the car. However, to restore charge in a battery within a reasonable period of time the voltage applied to the battery really needs to be a minimum of 13.8 volts. Also, what is happening to your voltage when the engine is spinning faster than idle. If the voltage climbs to 14.4 volts at 2500 RPM then you should recharge the battery quickly.

thanks for the info.

all my previous measurements were under load - lights, AC and fan full, radio.

this is what I am getting now:
battery @ idle w/ load = 13.25V
battery @ idle w/ load @ 2000rpm = 13.35V

B+ alt stud to alt frame= 13.55V

engine block to battery - = 18.4mV
battery - to chassis ground = 18.3mV

bentley manual says battery should be at least 12.6V with key off and at least 14V with engine running; but the troubleshooting principle is that, if the voltage does not increase from rest to running, then there is a fault with the charging system. so I am not in precise spec, but i am in accordance with the principle.

bentley also says that, in lieu of a load tester, run the engine @2000rpms with electric load and battery should not fall below 12V. so I am in spec here.

You do NOT need to be above 14V.

in which case, does it simply appear that I need to keep my eye on the alternator ground wire? currently it checks out in volt drop but it was the only stand-out problem.

thanks for your time and help everyone.

my car made the 11hr trip. battery @ idle when getting gas was 13.68V during day, 13.48V at night with lights on.

i did have one blip. about 3hrs in, I hit a patch of very slow stop-and-go traffic on the interstate. i was stopped, waiting, for about 5min when suddenly my car died. I tried to start it and it would crank and, if it did turn over, then immediately die. I wrestled with this for about 10-15min - no blown fuses, no obvious wiring issue. I rapped on the fuel pump and top of the in-tank unit a few times, thinking that may jump-start either if one had stalled. i don't know if that helped, but after 15min or so, the car started and i was able to drive to the exit.

i was not able to replicate the condition. so i drove on.

the car did totally fine the rest of the 8hr trip. averaged 70-80mph, didn't dip much below 70 on hills even. when i stopped for gas a few times, i turned the car off and she would start up and drive fine.

after thinking of it more, i really doubt it's either fuel pump, since a fuel pump fault would presumably not allow a car to operate normally for 8+hrs. additionally, in april, i replaced the hall effect sensor and had troubleshooted the entire ignition system then, making me doubt if it's an ignition issue. finally, i put a fresh lh2.2 MAf in the car just a few weeks back - so again, i doubt it is the MAF.

my hunch is the IAC. mine has been finicky since I took it apart (stupidly), and I've intended to replace it with a known good unit. my manual lists faulty IAC as a possible cause of engine starting then dying.

i'll look into more tomorrow and write back. thanks again everyone.

Good that you were able to make the trip mostly successfully.

Be aware that the motors on electric fuel pumps usually fail during a restart. They will run, you will shut the car off and they will not restart. Repeated attempts to start may get the pump running and rapping the high pressure pump may sometimes jog the pump rotor a bit to allow a restart. If you get the pump to run it will usually continue to run until you shut it off. Depending on the commutator segment that the pump brushes land on when it shuts off the pump may restart or may not (literally a roulette table). When these conditions occur my past experience has been that complete failure is 1 day to 1 week away.

You should be able to tell if the pump is the problem. When you switch the ignition key to the run position (but, do not engage the starter) you should be able to hear the fuel pump run for 2 seconds as it goes through its prime cycle. If you don't hear that prime cycle that is normally an indication that the pump is dead. However, given your other wiring issues I would also check the wiring and pump relay. My recollection is that the engine will run if the pre pump is dead; but, will not run if the main pump is dead. I do also seem to recall that a failed pre pump can lead to an early grave for the main pump.

more diag today seems to confirm both pumps are operational.

voltage @ fuse for main pump = 13.84V (car on), volt drop of <30Mv
voltage @ fuse for in-tank unit = 13V, volt drop <30mV

in-tank unit is getting battery voltage and is drawing 3.21A. good.

jumpering from fuse 6 to fuse 4 to power main pump confirms that main pump is working also. it turns on. however, it does sound more like how cleanflametrap puts it on his site: "A hint is sometimes given by the noise the main pump makes when it is either starved for fuel input or electrical input. Instead of the smooth low pitch hum this positive displacement Bosch pump emits when all is well, a raucous buzzing noise warns it is trying to pump vapor along with the fuel." I will check the electrical wiring to the main pump tomorrow.

regarding fuel pump relay, i put a new unit in in late March. did not check but presume it is still good.

IAC appears fine. outer terminals yield 43 ohms resistance, inner terminals yield 22.5 and 20.6 ohms. not far from the 40/20 spec.

I was unable to check the continuity at the TPS. I cut off the TPS connector off my old harness, but still i couldn't measure anything. i am chalking this up to operator error and will need to check my meter's manual on how to test continuity (i know....), and re-test.

i checked my MAF too. resistance for the idle pot check (terminals 2-6) is 20.66 ohms, which is in range of accepted 0-1000ohms. However, my heated wire reading is 36.31 ohms on my meter? my meter was indicating it was 'k [ohms]' so I am unsure if that means the reading is actually 3.631 ohms or the 36.31 ohms. I know, i am still getting my meter chops together. but i may need to run the heated wire test again.

car will start normally, and I drove it to grocery and back today with no issues. it does seem like I have less acceleration than before my trip, though. and the idle in park is surging and low. the idle has a rhythmic ramping-up surge to it, cycling every 2secs or so. i have been pulling my hear trying to get that idle to settle and be normal for the past month....it seems that the idle screw is NOT doing anything, even with the IAC terminal grounded out. again, this makes me suspect, despite the test, a faulty IAC.

my general thinking is: confirm main pump is getting adequate power and wiring is good. then look at TPS and IAC again.

EDIT; while I am here, can I ask, honestly, am I deluded in thinking an 85 240 could be a 100% reliable car for 10hr+ trips? on one hand, old volvos are synonyms with reliability. on other hand, everyone says old cars are inherently less reliable. i love this car and will keep it regardless, but should i get a camry/civic for road trips and use the 240 as a local car only?

[deleted]

A fuel pressure test would be a good step to confirm that both pumps are operating correctly.

[deleted]

a week later and my car is still driving normally. i haven't had any break downs or strange fuel issues - the only persistence is an intermittent surging idle at start in P that disappears when I give the car throttle.

if you have the car sorted out. it is reliable for trips. carry spares though and have AAA.

thanks for the replies and inspiring confidence in the car.

i still wonder if I am chasing a gremlin here, given the 'car died on highway for 15min then started and ran for 9hrs' incident described herein earlier; and yesterday, my car started then died twice coming out of a parking spot. I had the AC on slightly and the stereo; turning off the AC allowed the car to start and drive normally without dying. If it's relevant, the heat index was 100F+. I seem to be able to run the AC after starting while driving without any faults (well, except that the AC doesn't blow very cold)

anyway, not sure if these could all be connected or if I am just worrying.

There is a delay relay for the a/c. It prevents the a/c from running during starting if you leave the a/c on. Makes the a/c wait till about 20 seconds after starting before it runs. If that relay fails to give you the delay. Then it can be hard to start your car with the compressor engaged.