Liar, Liar, Pants on Fire

96 Chev Lumina Van 3.1 V6 71k miles, No Start

Most of you know from some of my articles how I approach a no start, in the case of this Lumina, the value of this method is made apparent.

The customer was coming in with it for some other work and it died on the way in and ended up being towed in as a no start.

Using my quick method of looking at a no start, I first checked the battery volts since most people try hard to restart to avoid a tow, battery was at 12.2 volts. Since this seemed adequate, I went ahead and turned the key on to hear the pump prime and it sounded ok. Fuel gauge reported a quarter tank of fuel. I cranked the engine and it started after about 8-10 seconds cranking.

In the shop it went for further testing. When faced with this situation, I will start it and leave it run awhile to see if the thing will die again and not restart. In ran for a few minutes and died and would not restart.

Back to my quick method, pump prime existed and sounded ok, cranked for 10-15 seconds, went to tailpipe no raw fuel smell.

Ok, so I have pump prime, good cranking, no fuel at tailpipe, so it has to be a fuel supply problem.

After hooking up mastertech, I have a cranking rpm signal, so I should have injector signal at injectors,and on 3.1 V6, these are impossible to get to without pulling the plenum. An easy way of checking them for operation is to steth them and listen for clicking of the pintle while cranking. They turned out to be operating ok.

Ok, so I have pump prime, good cranking, no fuel at tailpipe, injector signal, so it still has to be a fuel supply problem.

Now I go to the fuel pump relay and get a waveform,

Not much draw on this pump, pattern looks great.

After finding the repeater and doing the math, rpm is 7211, So whats the conclusion? low amps and high rpm means the pump is not producing any pressure but why? Is it getting any fuel? After looking at the tank I find its made of plastic (polypropylene to be exact) and what I heard as the pump prime was masked by the insulating properties of the tank (steel tanks are more amplifying with the sound of the pump and its pretty easy to suspect an empty tank by the sound of the pump. I have to start looking at them first. Listening at the filler neck may help eliminate this mistake. So now I hookup pressure gauge and find there is zero pressure at the rail. I add five gallons to the tank, and after a few pump primes, the pressure goes to spec's and the thing starts right up. Now the fuel gauge reads almost a half tank. So now I have to look at a gauge problem. Ultimately, I wasted some time here by not realizing the tank was empty, but by following my simple diagnostic routine for a no start, I found the problem. Staying with established diagnostic routines will always make you a better tech, so keep to them. Sometimes you may have to modify them slightly, but for the most part, try to keep it as simple and systematic as possible.