Worsened chugging

[Chevy vanguy]

Hi. I have an 81 Pontiac Bonneville with 5.7. 203,000 miles. I am trying to figure out why it loses it's prime. Every morning, I have to prime air out of the fuel filter to get it started.

When it's warm and driving, it dies at a stoplight. Then when I start it, it runs and acts like nothing's wrong.

I don't get it. Help?
Thanks.

[Diaric]

have you checked if the fuel pump is working. The priming to start in the morning sounds like an air leak, but the stalling sounds like more.

[Deezel]

Check for any leak. Any dampness around any fuel fitting can allow air in and the fuel to drain back to the tank. The fuel filter tends leak air in. Have you replaced the filter.

[Chevy vanguy]

I have replaced the fuel filter twice this month and to no luck. Air leak is my first suspicion, but I don't show a trace of diesel fuel dripping underneath the car. With worsened chugging, it makes me think the fuel line is clogged with sediment... as it used to belong to a farmer up in Nebraska. Might have to drop the tank and find out.

How do you determine whether the fuel pump is working?
Many thanks for your responses and help, I really do appreciate it!
Scott

[57diesel]

Describe to us the priming process you are using? Just wondering if perhaps its not a priming issue but something else you are doing in the process that is letting it start.

I presume this still has the stock mechanical lift pump? Also the stock filter?

What parts have you replaced since you have owned it?

[Chevy vanguy]

57diesel- The priming process I did was loosen the fitting on the outlet of the fuel filter. After few cranks, it starts up. Still idles slower than normal.

I bought the car in September 2010, I've replaced batteries, glow plugs, glow plug controller in January 2012. It ran beautifully until the fall of 2012. I've replaced the box fuel filter twice in November 2012. I've only put on 25,000 miles since I got it.

I should let you know I'm not an expert on fuel system, but I am going to also assume that it still has the stock mechanical lift pump. And filter too probably.

Thank you!
Scott

[Chevy vanguy]

Found the leak! It's under the car, by driver's seat! Between the driver's side floor and the driveshaft. The floor underneath is soaked. I couldn't get my big body underneath to pinpoint the leak, but I'll find out pretty soon.

[Chevy vanguy]

It's the fuel line between the fuel pump and somewhere by the oil filter. Will keep you posted. Thanks for all the help!

Keep yourselves safe from the snow storm tomorrow.

Scott

[57diesel]

Getting the leak figured out will likely solve your problem.

Seems like a strange place for a leak, I thought the fuel lines on those cars were always along the frame rails. The fuel and brake lines always rust where the clips are that hold the lines to the frame. The floor is wet inside the car? Or you just see fuel dripping off the transmission? If its off the transmission I wonder if its something leaking around the filter or injection pump? The intake / valley area on the olds is pretty deep and can hold a fair amount of fuel. There is a drain tube at the back that leads to the back of the block so anything that comes out of it will tend to drain down the transmission.

The stock lift pump on these cars was a mechanical pump just like the gas cars had, just mounted lower and upside down. Its under the ac compressor. One of their failure modes was to rupture and pump a little air in along with the fuel. The other failure mode was to either leak fuel into the crankcase or out the bleed hole.

Stock fuel filter was that metal can with the 2 fittings and wing nut. Many people put on some sort of aftermarket filter with a water separator.

[tqwrench]

I experienced a similar situation with a fluid leak from a pipe this weekend, but it was the 1/4" brake pipe to the rear of the car, on my 84 Olds 98 350D. I'm waiting for the other shoe to drop and find Diesel all over the right frame rail. 57Diesel was correct, they tend to leak where the clips are. The reason I posted is I wound up using a newer product to repair my leak, a copper-nickel-iron alloy brake pipe that is ridiculously easy to work with, it's called Ni-copp, I got it locally. In my case I had to do about 7 feet of 1/4" brake tube (by the time I got done with all the bends and curves), the rear hose and since they also had a roll of 3/16" I did the lines coming out of the brake hose to either wheel cylinder. This stuff is rated for brake pressures and will never rust. Well worth the money I paid for it since I had to do it all on my back in the driveway. I don't think I'll ever use steel tubing again.