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Old 04-10-2017, 08:08 AM
Baxterdown's Avatar
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Join Date: Jun 2014
Location: Fort Lauderdale, FL
Posts: 257
Need help identifying a strange stall and noise

Hi guys! I need your help identifying a strange stall and noise. Here’s the scoop.

I took my 72 280SE 4.5 out for a ride Saturday. The car had been parked in the garage for about 4 weeks. It started on the second turn (as it always does) with no problem. I drove it for about 20 minutes to a restaurant (half hour stop), then about 10 minutes to a friend’s (10 min stop), then about 30 minutes to run an errand (5 mins stop). Then, on the way home the car started stalling.

About 10 minutes into the drive home, I got to a stop light and the car started to stall. I put it on neutral quickly and gave it some gas and it recovered. But, from that point forward, whenever I got to a stop or light, the car would stall. Pressing hard on the brake and giving it a tad of gas would keep it running. And, it ran perfectly ok while moving. But the second I would let go of the gas at idle, it would stall.

The engine wasn’t overheating. The gas tank was at 3/4 full and oil pressure was good. Here’s a quick picture I took while at a stop light.

Now, onto the noise. Sometime along the drive I started to hear a noise coming from the back of the car. I had heard that noise before. But I had only heard it before when I shut down the engine. Now, typically I drive with the stereo on; I wasn’t on Saturday. So, maybe the noise has been there all along and I just hadn’t heard it before.

It’s a winding noise that would run for about 30 seconds after I shut down the engine and then would come to a stop slowly. No, it’s not the power antenna. :-) This noise is on the back of the car. Also, the noise keeps going even after I cut the power and take the key out of the ignition.

This time though, the noise kept going for almost five minutes after the engine stopped and I took the key off the ignition. I took four videos.

Here’s what you’re going to see:

Video – 01
Pointing the camera at the fuel pump (microphone is down toward the ground) from the drive’s side. As you can see, the fuel pump and filter are brand new. With that said, I don’t think it’s the fuel pump because I had heard the noise before the pump was replaced.

Video – 02
Pointing the camera at the fuel pump from the passenger’s side (same thing, microphone toward the ground).

Video – 03
Pointing the microphone at the fuel pump (camera toward the ground) from the driver’s side. You can hear the sound start to sputter here. This was about three minutes after the engine shut down. I was baffled the thing was still going!

Video – 04
Camera pointing to the gas tank relief valve. The valve is brand new and you’ll notice it is different than the OEM part. The W108 valves do not exist anymore so I had to use the valve from an SL when I replaced it.

A few things to keep in mind. You guys might remember I redid the undercarriage last fall. At the time, I had all fuel lines replaced. I also replaced the gas pump and filter, and gas tank relief valve as I mentioned above. The fuel sender unit is new as well. I replaced it last summer and bought the unit new from MBCC.

I showed the video to my mechanic yesterday and he thinks both the stalling and noise might have something with pressure building in the gas tank. He asked that I drive the car again and try to replicate the issue. Then when the car stalls, he asked that I remove the gas cap, check to see if it’s hard to turn, if the sound it makes is a swoosh or a pop to indicate inward or outward pressure, and see if that will alleviate the symptoms.

I'm going to wait until Saturday to take out the car again. I can only drive it after work during the week and I don't want to risk getting stuck at night.

In the meantime, please let me know what you guys think.


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Old 04-11-2017, 02:17 PM
Registered User
Join Date: Oct 2012
Posts: 6,382
You might be working on two problems.

The stalling sounds like water in the tank. It happens when the seasons change and we have cold weather and then hot and then back to cold. A quick way to figure this out is to dump two quarts to rubbing alcohol into the tank. The alcohol will bind with the water and when the alcohol burns in your cylinder it will drag the molecules of H2O with it. You might notice a slight loss of overall power but the stalling will stop. That is, if the problem is water in the gas.

The noise sounds like the fuel pump and it is pumping against a blocked line and relieving back to the tank. The pressure is much higher when this takes place so the whole thing is working harder than ever. Reach up under there and feel the pump when it is doing this. It should not only be buzzing but hot to the touch. (Well, maybe warmer than seems normal since higher pressure is dissipated as heat.)

You may have a stuck fuel pump relay. Find the relay and then, when it starts doing this, pull the plug off the relay. It should be in the engine compartment and easy to access. You might pull the plug off before testing this just to make sure the plug will come off with a slight tug. After all these years those electrical connections can be quite tight the first time you go to unplug one.

Of course you could also pull the positive wire from the fuel pump. I just think the relay would be easier to unplug.
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Old 04-11-2017, 08:41 PM
meltedpanda's Avatar
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Join Date: Mar 2003
Location: Central Ky
Posts: 5,954
Ok , I agree with idle , I think it is a vacuum issue or a stuck relay , or both or related - vacuum issue causing a hard push or pull symptom pump stuck on?

stalling, have you checked the fuel return valve ?
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