Dying fuel pump(s) behave like vapor lock?

cpav13 · Post by **cpav13** » 24 Jun 2012, 10:01

Hello All! I'm happy to join the forum. I just adopted a 1989 240 wagon with 200k miles and it's run like champ for the first month. (Took it camping, so it had lots of miles with me already).

I am trying to decide if a hot and long drive home yesterday could be explained by a failing fuel pump, and what role a disconnected vacuum hose connected to the pressure regulator might be playing in the problem.

The situation: Colorado is HOT right now. Boulder set a record yesterday for the hotest day since 1954 at 102 degrees. I had to drive about 40 miles through this heat, and as I was arriving the car started behaving like a vapor lock, with loss of power, missing, and then it died and would not immediately restart. I nursed it to a parking spot and once it cooled over a few hours, it started just fine and drove. But on the drive home, I was only able to make it about 15 miles before it would repeat: loss of power, stuttering, and then dying. In a gas station parking lot I opened the hood and noticed the vacuum hose connected to the fuel pressure regulator was disconnected. I reconnected it, thinking this could be causing a pressure issue, and went on my way. about 15 miles later, loss of power followed by stuttering and stop. Each time I could cool it for about 15 minutes and it would start up again. Overall, it was behaving much like a vapor lock, but even at 100+ degrees I'm unconvinced that the injected system could vaporize.

My thoughts, seeking your input: I suspect that I have a fuel pump going out, and the weak pump was overheating in the hotter-than-normal temps. I also fear that, if the pressure regulator was getting zero vacuum, this may have over-stressed the pump.

As I'm new to the Volvo 240 world, I was relived to discover that there was top access to the tank. But I'd love to be more confident before I drop the cost of new pumps.

Thanks all! Can't wait to get to know the community!

lummert · Post by **lummert** » 24 Jun 2012, 12:47

What was the level of fuel in the tank?

cpav13 · Post by **cpav13** » 25 Jun 2012, 08:59

Good question. The tank was about 3/4 full at the start of the trip, and just over half at the end. However, the asphalt it sat on all day was probably 130+, and has been for days. I'd expect the gas had to be sitting at 100+ degrees.

I've never had a car with a pre-pump/main pump style assembly. Is it always really obvious when your pre-pump is going out?

Cory

lummert · Post by **lummert** » 25 Jun 2012, 10:38

When the in-tank pump on my 88 765 failed the car would stall during hot 90 degree plus temps combined with low humidity. The tank was 3/4 full each time the car would stall. Eventually the main pump failed, too. The fuel that returned to the tank by way of the fuel pressure regulator is heated by the engine, heating the fuel in the tank even more. The main inline pump is not designed to pull fuel from the tank.

cpav13 · Post by **cpav13** » 25 Jun 2012, 11:59

That is promising. Thank you! Like I said, it's hot right now. As well, I'm assuming that the time the vacuum line was disconnected from the pressure regulator was leaving the pressure reg wide open, passing even more gas through the hot engine compartment, increasing the tank temp.

Anyone know a way to test a possibly failing (rather than dead) (pre)fuel pump?

Thanks!

lummert · Post by **lummert** » 25 Jun 2012, 13:09

My 88 765 has a fuse for the in-tank pump. By pulling this fuse while the engine is running the main pump will get very noisy if the in-tank pump is working. If the main pump is already making noise and the noise doesn't change when pulling the fuse, the in-tank pump is likely dead.

Disconnecting the vacuum hose from the fuel pressure regulator only allows the system to run at the line pressure (about 43.5 PSI).

cpav13 · Post by **cpav13** » 26 Jun 2012, 09:15

Thanks! I think I'll go looking for the fuse tonight. Although, I think the problem is intermittent, so I don't know if that will tell me much about the in tank pump, unless I catch it in a dead spot. However, I'm starting to feel confident I'm headed down the right path to figure out the culprit.

Thanks again!

nisan17 · Post by **nisan17** » 21 Jul 2012, 01:37

By what I've read I've had the same thing happen to me on my german auto. Spent $600 for a fuel pump change at a domestic car shop. Did the same thing again, then I took it to a foreign car specialist and it was a $12 fuel pump relay that was acting up!!! Now, I'm looking at threads again as my 91 740 non-turbo won't start, but I suspect it is the ext fuel pump as I don't hear it hum when I crank the car. But, I will check the relay as well and will also tap the pump itself with a solid piece maybe get the armature to turn. Let us know how you resolved this issue? Thanks