SEcond problem on my son's 1988 740. At the most inconvenient of times, the 740 will refuse to start. It doesn't turn over and no starter clicking sound. Then after a period if time a few minutes to a couple of hours, it will start as if there never was a problem.

A few threads have mentioned the neutral safety switch as a likely candidate but I had the safety switch out of the car and inspected and tested it closely and there doesn't appear to be a problem there. In addition, the car refuses to start in park or in neutral. When there has been a problem, I have tried moving the shifter when trying to start and nothing. As I indicated, if the car is left alone or a periodi of time it will start as if nothing was ever wrong. The problem is you never know how long you will have to wait.

Could it still be the neutral safety switch or should I look elsewhere?

Thanks for any tips.

 

the starter circuit is pretty damn simple. it COULD be the ignition switches starter contact I suppose, fromt here it goes through that neutral safety switch, and straight to the solenoid on the starter.

you could bypass the safety switch, just direct connect the two wires together and be careful not to try and start in-gear.

 

I ask my son to leave his 740 around so I could troubleshoot it. Everything seem to be fine. This afternoon, I was driving back home and I noticed that the wipers were running slow. Didn't pay tomuch attention to it at the time but abotu 10mins later, I realied that the car was about to stall out. I was able to turn onto a side road before I stalled out. I fully expect to have to call someone for help.

I noticed that if I turned the key everything would power up as it should but the car would not turn over. I tried moving the shifter to neutral but sill nothing. After a couple of minutes of sitting there, The car started up and I drove home. Wipers operated at the correct speed

I am going to check the battery connections toomrrow (daylight) but I have checked the negative connection to the battery.

Could the problem be on the positive side?

 

OK, time to check the charging circuit too.

first, put that dead battery on a 8-15 amp battery charger overnight. then take it off the charger a couple hours and measure the battery voltage with a digital volt meter, it shoudl be 12.something volts (if its very cold otu, it will read fairly low, if its 68F, fully charged is 12.6V). now, turn the ignition on, verify the alternator light comes on, start the car, verify it goes out, and measure the voltage, it should be at least 1V higher than your previous reading. if so, you're charging, if not, its time to diagnose the charging circuit. that alternator light is a critical part of the circuit, so its important that it lights before you start the car (this provides the alternator with 'bootstrap current').

 

Merry Christmas all.

It is bitter cold here.A fully charged battery gives 12V. With the car on, the voltage is actually .5V lower so I assume that is a "bad" thing <grin>. I am guessing that the alternator light is not on as there are only a couple of lights on and there is nothing I would recognize as an alternator or power signal. I am going to dig up my Haynes manual to see if there is any info there.

The alternator is only a year old. It was actually replaced after a similar occurence when traveling. The Shop said it was the Alternator so my son didn't have much of a choice as he needed to get back home.

 

its really important that the alternator light on the dash is working. its a red light, with a circle that has a box on each side, I think. it should come on when you turn on the key, and go out when the engine is started. if it doesn't do both those things, then its quite likely the alternator isn't charging, and your battery will run down as you drive.

the alternator light is connected to the ignition switch, and the D+ terminal on the alternator.

the last -no charge- scenario I debugged, it was the alternator GROUND that was bad, the alternator itself was fine

 

I have to shuffle the cars around to get the volvo into the garage. Just too cold outside to work on the car.

I did checked the ground at the alternator. 0 ohms between negative post on the alternator and the battery.

I did find a drawing of the instrument cluster lights for the '88 740. There is an alternator not working light (7th from the left) but it is never lit regardless of the key being one or the car running.

Over the years, before the charging was problematic, we would have problems with the car not starting (lights would come on but no starter clicking, nothing) then a few minutes later the car would start up as if nothing had happened.

I was focused the the neutral safety relay but Moving the shifter or trying to start in Neutral did not change things. Could both problems be related to a faulty ignition switch.

Is there a troubleshooting guide for "no Charge" that I could step through?

 

engine stopped, but key on, there should be ~ 12V at the D+ terminal relative to the alternator ground. if there isn't (which your lack of ALT light suggests), its possible the alt light bulb in the dash is fried, its an important part of the circuit. Replace that light before you continue, it might just fix the problem.

if the light is still not coming on, take the wire thats hooked to the D+ terminal, and connect it to a handy ground, turn on the key and verify the light comes on. if it STILL doesn't come on, its either your ignition switch or a wiring problem. Pin 15R of the ignition switch should be powered in II and START, there's a blue-red wire from there to dashboard connector D:4, where it drives the battery light, then C16 is a red wire to bulkhead connector B pin 22, red to connector A pin 4 (near the left fender) and red wire to the alternator D+ pin.




oh my pinouts are for a 1992 740/940, I /assume/ your 88 is very similar, but it might have a different dashboard connector, I dunno.

 

You have a battery/charging issue you have to address first; possibly a loose connection somewhere in the starting circuit.
To cure the possible lack of charge due to a dash light malfunction, all you have to do is rev the engine to 2,500rpm and the alternator should kick in...

 

I have the cluster out (easier than I expected). I have verified that the bulb at position 10 (battery charge failure) is good.


With the ignition in the on position, the battery charge failure light is off.
I removed the bulb and, with the key in the on position) tested the voltage on each leg. On both legs, the voltage is 11.5V. I expected one leg to be 0V. Since the voltage is the same on both sides, no current therefore no light?

I am assuming D+ lead is the small red wire at the alternator (near the larger + connection)? With the car ignition on (car not running), the D+ connector is reading 11V.

 

disconnect that D+ wire (yeah, the small red one) and connect it to a ground, and turn on the ignition and see if the light comes on.

if it does, then your alternator diode board is quite likely bad.

 

Yes, I connected the D+ terminal to ground and the lights came on. Is the diode board a replacable part?

Edit: If it is the diode, will that be detected if I take the part into AutoZone and have them test it.

 

The diode board for these alternators is not readily available... its inside the alternator, and is something that a rebuilder is supposed to test and replace/repair as needed.

sadly, cheaper rebuilders tend to just clean up the alternator, slap new brushes on it, do a quicky test and ship it.

 

Beyond the diode being bad are there any other possible causes. Is there something that that would also cause the "failure to start" when the battery is know to be charged? Before the charging problem appeared, my son had these mysterious problems with the car failing to start. LIghts would come on (don't know if all of them came on) but the starter would not turn over or click. A few minutes later, the car would start as if there never had been anything wrong.

Ian

 

that last symptom sounds like a loose connection somewhere in the starter circuit

 

Just a follow up to let you know that replacing the alternator resulted in the dahs board lights reacting as they should. I am charing the battery right now and will check the voltages with and without the car running to confirm that it is charging.

In the processing of pulling the dash apart, I found that a prior owner had installed a remote start system. MY son knew about it but it was never used as they didn't give him the clicker. I am going to cut all of it out later.

Now if I could only figure out why it sometimes won't start. I have a replacement neutral safety switch but I am not convinced that is the problem. If that was the problem, I would have expected the car to start if you moved the shifter around or tried to start in neutral as opposed to park.

I am guessing the starting problem is probably related to the ignition switch. The sympotmns again. Turn the key to the on position, the lights come on. Turn the key to the start position, light intensities don't change but the starter does nothing. Trying to give the car a boost does nothing. A few minutes to an hour later, the car starts as if nothing was ever wrong.

 

its either the ignition switch, the park/neutral safety switch, or the wiring in between them and the starter solenoid.

if you can find hte connector to the park/neutral switch, disconnect it and connect the pins together on the car side, this effectively disables that switch (so try and remember not to start in gear...)

 

85 volvo 740 new alternator, new battery, redid grounds to engine block and frame. Alternator tests 14.7 on bench. In car engine running 13.4 down to low 12's. Battery keeps going dead engine just is running on battery. Battery shows 12.8 with engine off. Just put in a new main engine wiring harness. Can't figure this out brain melt.

 

fully charge battery with an external battery charger. take it off the charge, wait a couple hours, use volt meter to read at battery terminals, should be about 12.6V (less if the battery is very cold, it is winter now). now start car and measure voltage again, should be about 1-1.2V higher, eg, 13.6V or so if you got 12.6V before starting.

if you see that +1V rise, then your alternator is working fine and should be charging the battery.

if you DONT see that 1V rise, then with the engine running try your volt meter from the battery + terminal to the alternator ground (watching out not to get cables tangled in the fan!!), this should be the same as what you saw on the battery + to -... if its higher, than your alternator ground is likely bad. also, test from the alternator B+ terminal (thats the big red wire) to the battery -, that should basically be the same as you see at the battery + to -, if its higher than the battery reading, then the alternator -> starter -> battery wire is suspect.

 

Pierce
I have been driving my son's van for the last several days to see if I can figure out why the car won't start on occasion and get a good description of the symptoms. It has happened a couple of time today. This last time, I got in the car turned the lights on, turned the key to the on position. The headlights are on full strength. Even turned the fan on. Turn the key to the start position. Lights turn off, blower turns off but car does not start. There might be a single click (seems to be coming from up front passenger side) when the key is turned to the start position but not the multiple clicks you often hear when the battery is too weak to start. I tried a moving the shifter to neutral to start but nothing. Tried moving the ignition key back and forth but nothing. If history proves true it should start soon but frustrating waiting for it

{EDIT} since it is generating a single click down low near the firewall drivers side, does this indicate the the solenoid is the culprit? or perhjaps wiring from the battery to the starter?
{Edit 2} Upfront near firewall on drivers side of Engine
{Edit 3} in the daylight, the car is starting but it would appear the the click was coming from the starter. I am guessing that the small post on the solenoid is the 12V coming from the ignition. The large cable goes under the front of the engine and directly to the positive terminal on the battery.