740 alternator problems

absit4040 · Post by **absit4040** » 04 Dec 2011, 22:23

Hello,
I have a 1990 Volvo 740 Sedan.
Background: In the past 2 years I have had the distributer cap, plugs, basic tune up, and muffler/exhaust repaired/replaced. In the past year I had the fuel pump and casing rebuilt/replaced and all the belts changed and a new battery.
Problem: Sometimes my car doesn't want to start asap in cold/windy weather, it has stalled twice when pulling away from a stop in cold/windy weather. When I am driving on the interstate the lights dim pretty badly.
Questions: Is a bad alternator the likely problem? Would fixing the alternator solve the stalling/hard start problems? Last question, shich bolt tensions the belt that goes to the alternator?
Thanks.

absit4040 · Post by **absit4040** » 04 Dec 2011, 22:43

...also when the car has had a hard time starting, it begins to turn over as normal but it feels like it isn't getting gas. My instinct tell me to hit the gas pedal, but I don't want to flood the engine... the times I have hit the gas pedal,it doesn't help anyway.

Post by **billofdurham** » 05 Dec 2011, 12:17

Welcome to Matthew's Volvo Site.

A bad alternator can cause all sorts of problems as can a slack alternator belt. Before diving in and replacing the alternator you can test it if you have a voltmeter or you can have it tested at any good car parts outlet, usually free of charge.

To adjust the belt there is a tensioning arm, part #7 on the attached. Slacken the mounting bolt #5, and the tension arm pivot bolt #8 just enough to allow the alternator to move and then adjust it with the tensioning arm. Correct tension is reached when you can depress the middle of the longest run of the belt 0.2 to 0.4 inches with firm thumb pressure. Tighten the other two bolts.

740 Alternator mounting parts.pdf: (122.01 KiB) Downloaded 410 times

Check and re-tension the belt if necessary. If this makes no difference then move on to the battery. Check the positive and negative leads for good, clean connections especially where the negative is attached to the body. If you have to take either of the leads off the battery to check/clean them make sure you have the radio code if one is needed. Always remove the negative lead first and move the connector as far as possible from the battery post. You can test the battery using a digital voltmeter. The reading you get shows how good the battery is:

Open Circuit Approximate Average Cell
Battery Voltage State-of-charge Specific Gravity

12.65+ 100% 1.265+

12.45 75% 1.225

12.24 50% 1.190

12.06 25% 1.155

11.89 0% 1.120

The table shows that even with a battery giving out 12.06 volts it is useless.

To do a quick test for the alternator start the engine and run it at a fast idle. Using the voltmeter on the battery terminals you should get a reading around 14 volts (13.5 to 14.4). If you don't get this reading it is time to have it tested professionally.

Bill.

absit4040 · Post by **absit4040** » 05 Dec 2011, 16:00

Wow, thanks a lot!

shegarty · Post by **shegarty** » 06 Dec 2011, 06:02

if you find that the alternator is not putting out the required voltage even after tightening the drive belt be sure to check the brushes/regulator - the alternators in these cars are pretty robust and you can usually get away with just replacing the regulator/brush pack - over time the brushes which are constantly in contact with a rotating shaft will wear out, crack or even sometimes disintegrate - easy fix and you don't even have to remove the alternator to get at them

absit4040 · Post by **absit4040** » 24 Jan 2012, 19:22

Hi All,

Thanks so much for everything and sorry it took me so long to respond with the answer.

So, I tested my electric system and all was fine. Car came back to life and would run normally for a few days and then have problems again. Eventually, just before Christmas my car died to the point that it wouldn't start back up. One day it finally kicked over, took it to my shop and again, it would run fine. With no problems, no symptoms, it was hard for my very honest mechanic to find the problem. He didn't charge me for the evaluation, 3 days went by, then the car would begin to stall at lights, lights would dim, it would have a hard time starting, etc. I took it back to the shop and finally it exhibited the problems I was having! My mechanic told me it was loosing RPMs and his first thought was the original Fuel Pressure Regulator. I left it overnight, next morning it was ready to be picked up and turns out it was the Ignition Control Module.

I really wanted to post the fix because I think this site is a great resource and I feel like there are probably a lot of people out there who might benefit from this information, especially since the Ignition Control Module is a easy repair - although very hard to diagnose.

Last, for Volvo owners live in St. Louis I would like to plug Loop Automotive. Their reputation here is no secret. In my 38 years I have never had a better experience with mechanics. If you have a problem you can't fix yourself, you'll be thankful for looking into their work. I know other Volvo owners who use them and everyone I know insists on their good work, integrity, and prices. Once they even preformed a simple fix for me for free. Seriously good people.

And thanks again Matthew's Volvo site. Even before I was a member I would look things up on here first.