For another suspect, look at the fuel pump strainer in the gas tank. The pump can be replaced two ways. You can buy just the pump and motor and stuff that into the housing once that is removed from the tank. The second way is to buy the complete assembly including the housing and fuel level sending unit. The second way gets you a new strainer already snapped onto the fuel pickup.
I just encountered this for the fifth time less than four days ago. The interesting thing is the symptoms are quite different between carbureted engines and fuel injected engines. This happened to me twice on two different cars in the mid 1980's. Both had carburetors. After about fifteen miles, the strainer became clogged with debris floating in the tank, or they collapsed internally to block the pickup tube. The problem is always insufficient fuel volume. With a carburetor, the slower the engine runs, and the less load it is under, the better it will run. At higher speeds you cannot get enough volume to keep the float bowl full. As a point of interest, the first time I ran into this, my instructor showed us how to remove the hose from the mechanical fuel pump on the engine, open the gas cap, then use compressed air into the hose to blow the "sock" off the pick-up tube. This solved the stalling on a 1972 Chevrolet. You still have the fuel filter in the carburetor to keep the gas clean.
The third time this happened, it was on my 1988 Grand Caravan with fuel injection. Now the symptom was the faster I drove, the better the engine ran. This acted up for the first time four hours from home, west of Minneapolis, on the hottest day of summer. There was a little sputtering, just enough to get my attention, when I left a stop light, then it ran fine for another thirty miles. The engine stalled when I coasted up to my turn-off, and would not restart for about ten minutes. My suspicion is the strainer was being pulled closed by the vacuum, and needed time to slowly stretch out again. The fellow I was doing business with suggested a different highway to get back to Minneapolis, but he did not mention there was a stop light every five miles. I got to be an expert at stuffing in into "neutral", stopping the engine, then coasting to the light just as it turned green. Nursed it all the way to the city that way, then it took me four hours to get through it thanks to road construction on all three bypasses. Once back on the highway, it ran fine all the way home.
The second time this happened to the same van, I was pulling a huge tandem axle enclosed trailer, but I had a fuel pressure gauge clipped under the wiper arm. Normal fuel pressure is 45 psi. When under load, and again only on a really hot day, the pressure would slowly drop to 20 psi, and the engine still ran okay. Once it hit 15 psi, the sputtering would start. I found that by lifting the accelerator pedal for just an instant, the pressure would pop back up, then give me a good fifteen to twenty seconds before I had to do that again. I nursed it fifty miles that way.
Both times the solution was to replace the strainer that is clipped to the fuel pump housing. Cost was $9.00. The strainer for the two carburetor cars was three bucks.
Now I am driving a 1994 Grand Voyager. Coincidentally, just made another trip to Minneapolis, but it was cooler that day. A few days ago I made a forty mile trip, and the stalling showed up for the first time just as I started coasting to the turn-off. Visited with relatives for a few hours, then hopped in and the engine started right up and has been running fine ever since. I am carrying a scanner and a fuel pressure gauge with me for when it is needed next.
The symptoms are different, as I mentioned, with fuel injection. The more load the engine is under, the better it will run. The stalling occurs when the largest volume of fuel must be pumped, ... Which is during coasting. To explain, when a molecule of gas is getting ready to leave the tip of the injector, there is two forces acting on it. One is intake manifold vacuum that is pulling on it, and the other is fuel pressure that's pushing on it. Fuel pressure is basically held constant by the pressure regulator, then the engine computer is programmed to pulse the injectors open a very precise amount of time calculated from manifold vacuum on Chrysler's, and the amount of air passing through the mass air flow sensor on all other brands. The issue is when you are coasting, manifold vacuum goes way up, and that would tug really hard on the gas to pull it out of the injectors. That would lead to an excessively rich mixture, loss of fuel mileage, and increased emissions. To prevent that, the fuel pressure regulators had a vacuum port that was connected to intake manifold vacuum. When vacuum goes up, it pulls on the spring-loaded valve to cause it to maintain a lower fuel pressure. As vacuum increases, pressure decreases, and the net difference stays the same. The rich coast-down mixture is avoided.
Here is where the strainer becomes the problem. The fuel pump is designed to move way more fuel per minute than the engine will ever need. Of the fuel it pumps, only a tiny percentage is tapped off to go into the engine. All the rest, possibly ninety nine percent, goes through the pressure regulator and right back into the tank. The regulator presents a carefully-controlled restriction that keeps fuel pressure at specs. That restriction limits the volume of fuel the pump has to move.
When you are coasting, manifold vacuum acts on the regulator to lower fuel pressure. That means it is a lot easier for the gas to push its way through the spring-loaded valve and go back to the tank. With less restriction, the volume goes way up, and that is when the plugged strainer becomes a factor. Not enough volume can get through it, so pressure starts to drop below what the regulator is set at. The harder the pump works, the more it puts the strainer under a vacuum and forces it to collapse even more and block the pick-up tube.
Had I figured this out the first time this happened in Minneapolis, I would have removed the vacuum hose from the regulator and plugged it. That would cause fuel pressure to go up very high, but with maximum restriction through the regulator, volume required to keep up would be real low. For my current problem, I am carrying a hose pinch-off pliers and I am going to experiment with pinching the fuel return hose. That will also drop volume needed real low and keep pressure real high. I expect to see black smoke from the tail pipe, but it should get me home without having to walk!
I do not have an answer as to why this only occurs on really hot days, but the first time it occurred on my 1988 in Minneapolis, it acted up a little in town the next day, then not at all over the entire winter and next spring. The other potential clue leading up to this is I needed to drive a truck for two weeks, and I let the van sit. Some people express a concern about mold feeding on the alcohol in today's gas, and I am wondering if that is what clogs the strainer. Most other people have just one car they drive every day, so it is constantly getting fresh, new gas dumped into the tank.
To argue against that, I have an 1980 Volare, (carburetor engine), and a 1993 Dynasty, (fuel injected), that get driven so rarely, they both have gas in the tanks that is over five years old. Have not had a problem with either one, but they both have very low miles too, so I am not sure what factors influence this failure. I can tell you heat is involved, but I do not know why.
Sunday, May 13th, 2018 AT 5:40 PM
