940 Starting problems

Eric Kropp · Post by **Eric Kropp** » 08 Aug 2010, 18:39

I have been having problems with my sons 940. We (me and the 940) have been having stating problems for some time. I eventually traced it to two bad fuel pumps.(yes, really, both were dead) I replaced both of them and the filter and all seemed to be fine for a fair amount of time, 6 months or so. Now it occasionally chooses not to start for a bit. Let it sit for an hour or so and will start. I changed the fuel relay behind the ash tray, because I had one and that made no difference. What I do know is that it is charging good (like 15volts good at the alternator) but it reads 13 volts at the battery while the car is running. I also know that some times you can have enough voltage to crank the engine and not have enough juice to trip the relay....bad battery?.....

Eric

Post by **billofdurham** » 09 Aug 2010, 11:30

What is the reading at the battery when the engine isn't running?

Bill.

Eric Kropp · Post by **Eric Kropp** » 09 Aug 2010, 18:47

Looks like it is juuuuuust above 12 volts when the engine is not running. It appeared to be the same at the alternator also when the engine is not running. The only reason I have a hunch it is the battery is; when I was diagnosing the fuel pump/s I noticed that some times there would be enough battery to turn the engine over,( and I don't mean just barely turn over) and not enough to trip the fuel system relay and supply juice to the pump/s. When I would drop a charger on the battery, the relay would trip with in a minute. This battery has always seemed like there is very little reserve.
Eric <><

Post by **billofdurham** » 10 Aug 2010, 11:34

I work with this table for batteries - courtesy of Wikipedia:

The open circuit voltage, is measured when the engine is off and no loads are connected. It can be approximately related to the charge of the battery by:

Open Circuit Voltage (12 V) Open Circuit Voltage (6 V) Approximate charge Relative acid density
12.65 V 6.32 V 100% 1.265 g/cm3
12.45 V 6.22 V 75% 1.225 g/cm3
12.24 V 6.12 V 50% 1.190 g/cm3
12.06 V 6.03 V 25% 1.155 g/cm3
11.89 V 6.00 V 0% 1.120 g/cm3
Open circuit voltage is also affected by temperature, and the specific gravity of the electrolyte at full charge.

So if you are "juuuuuust above 12 volts when the engine is not running" you could be down to 50% or less charge.

Bill.

Eric Kropp · Post by **Eric Kropp** » 14 Aug 2010, 11:21

So I went and purchased a digital multimeter and it showed 12.43 volts with out the engine running. So my guess is the battery is good according to the chart above. I also checked it at the alternator with out the engine running and the voltage was the same, indicating that the connection is good from the battery to the alternator. I have not checked it with a hydrometer yet. Any ideas?

Eric

Eric Kropp · Post by **Eric Kropp** » 15 Aug 2010, 12:04

Just a thought. When I changed the fuel injection relay, down by the ash tray, I replaced it with and "NOS" one that was made in 1991. Do you guys think there is any problem with that. Should I get a new after market one from Auto Zone?

Eric

Eric Kropp · Post by **Eric Kropp** » 02 Sep 2010, 18:07

Haven't found out what the problem is yet. Have a little more info. It just up and died while my son was bombing down the freeway this afternoon. All of the usual red and orange lights came on on the dash. This is the second time it did that. The first time was in a parking lot at 5 or so mph. All the red and orange lights came on that time too. This time he was going 65 mph or so. Wouldn't start, had it towed and it started up about and hour and a half later. I have yet to be able to catch it at a time that it won't start so I can check the fuel pump and the pressure in the manifold. Has anyone had any bad luck with the high pressure fuel pumps from Auto Zone? What do you guys think about me using a "new" NOS fuel relay when I replaced it? Ideas?

Eric

Post by **billofdurham** » 03 Sep 2010, 12:26

In all this trouble has it set any codes?

"NOS relay." Does NOS stand for Nitrous Oxide System? If so the relay is specifically for circuits that require 4+ amps to operate. Also as the relay is marked 1991, what sort of usage had it before you put it into the 940?

When the engine dies the warning lights should come on.

Bill.

Eric Kropp · Post by **Eric Kropp** » 03 Sep 2010, 23:23

I don't have the scanner to check codes. One thing I do remember (just came to me when you mentioned codes) is one time a repair shop saw a code for a knock sensor when the check engine light was on and I think there was a code for the mas air flow sensor. The mechanic thought the codes were the result of some thing other than bad sensors, so he cleared them. That was at least a year ago. Could that cause no spark? NOS means "new old stock". It is a Volvo relay for the fuel system. It is a new relay that was still in the box, but made in 1991. Here is what I found out today. It died and I was able to find out the fuel system seems to be fine to the injectors. I found out that it had no spark....for a while. I took the coil wire off the distributor and "propped" it in position about a 1/4 inch from the valve cover and got no spark when we cranked it. Then a little while later it had spark. I changed the coil wire to no avail. I think I will scrounge a coil from pick-and-pull tomorrow and give that a go. I am thinking....hoping that what ever it is, is something that is breaking down when it gets hot

Eric

Post by **billofdurham** » 04 Sep 2010, 11:37

You don't need a scanner to read the codes on the 940 nor on your 240. There is an On-board Diagnostic (OBD) unit in the engine compartment and the instructions for its use are pinned at the top of the forum.

Bill.