My mechanic tells me the reason why I have a problem starting the car,after the car had been driven for an hour or so is because the output of the alternator is low while the engine is warm/hot. In fact the car would start after 1/2 hour or so of waiting. Last weekend I was not able to start the car at all while sitting on my driveway under the brazing sun,but the same thing happened at night... Anyway the mechanic says the output from alternator was below 13 volts.
He put a new one on and he is getting 13.5 volts now,but he says that he is not happy yet,that needs around 13.8 volts...
My questions are: Is his diagnose correct as far as the non starting problem?
Is he right as far as the alternator output? What kind of Amperage should the alternator have? 80 or 120 Amps? I dont know what he is using... 1990 740 GLE
16 Valve...Along the way some electric instruments stopped working : radio,washer pump,horn,speedometer...
Tks for yr suggestions

When you say it does not start, does it crank properly?
If so, then obviously the alternator has nothing to do with it. If it does not crank, then yah it could be a poor charging system.
BTW we typically change only the voltage regulator assembly at the back of the alternator, rarely the entire alternator would need replacement. Is your mechanic one who works on cars like this, or changes oil and tires on GM vehicles?

Check for fuel and spark. Most cases it's the fuel pump relay, i nthe center of the dash o nthe relay cluster. Resolder the PCB, or just get a new one, cheap enough.

Could also be the RPM/crank sensor, usually at that age they function intermittently. If it does not detect crank, it will not engage power to the fuel pumps.

Since it's heat related, it could also be the fuel check valve stuck open. heat causes a vapor-lock effect. The valve is a bit of a pain to replace, but cheap to buy at around 10 bucks. I think on your car it's at the assembly with the main pump and filter under the car.

You said you have the 16v. Take caution. The timing has a few major weaknesses, if you don't update them your engine will self-destruct if you lose the timing. The 16v (b234f) is unlike the 8v (b230f) as it is an interferance engine, meaning pistons hit valves upon timing loss:

- You need to be sure of the condition of the main belt, along with the bottommost belt that drives the balance shafts;
- The idlers as well as the timing tensioner need to be in top shape, with belts tension well adjusted;
- The most overlooked weakness is the oil pump pulley bolt, which is driven by the timing belt, unlike the 8v volvos. Microfractures occure and it breaks off, causing timing loss. Don't ask me how I know. Replace the bolt with one from the dealer at around 5 bucks every few years.
- Another overlooked weaknesss is that the early 16v models used a plastic-like gear at the bottom balance shafts, which sheared after years and caused timing havoc. That needs to be retrofitted to the later model metal ones. Not sure about your 1990, it falls around the middle.

Best of luck, enjoy!

Greg Mustang
Montreal
Canada

Greg:
Tks for your info. I did nt specify it in the original post,but the car
when doesnt start,DOES NOT CRANK AT ALL. It's like you have a dead battery,except the battery is not dead. I turn the key,all the lights go on on instrument cluster,hear the fuel pump,but I get no crank.
So do u think the problem is with the alternator? Should I get a 120 AMP alternator? Should I dismatle/replace the instrument cluster as some of the instruments dont work,maybe for lack of enough juice? I dont think problem is with starter or neutral safety switch...BTW I changed the Timing belt 25K ago.
Tks again
Avelino

13.5 volts is plenty.

Your mechanic sounds like a bit of a kook. 13.5 will be just fine and aside from voltage what you are really concerned with is amps. It should say right on the side of the alternator what it is rated at, unless he stuffed in some kind of wildcat POS model alternator that does not have it's specs right on it like a Bosch/factory Volvo one does. According to Vadis your car came with an 80 amp alternator but that changes up a couple of times. So, while an 80 amp unit is correct for your car you may find a 120 amp model that fits and will work. As a rule you can always put in an alternator with a higher output rating but if you are never going to use that much current then it is a waste of money.

Mark