Sputtering M38, going with the flow and headlight woes in this installment of Tech Tips
Something not right with your historic military vehicle? Steve Turchet answers your questions on how to keep ’em movin’!
Best Guesses
Q: Tech Tips is always the first thing I read, being a military vehicle mechanic in training thanks to my M38, which I bought 3 years ago. I have a puzzle that I hope you can solve. I was driving the jeep about a month ago on the road at 50 mph. Suddenly, the engine began to sputter and made that gasping sound that you hear when an engine runs out of gas. Then it died, and I stopped. The fuel gauge showed between 1/4 and empty, so I knew it was low. I poured in the gas from my jerry can and after some long cranking on the starter; the engine started again, and I was on my way. Everything was fine. But a week later; the same thing happened, but this time the gas tank was almost full. I thought there might be water in the gas, so when I got home, I drained the gas tank, but did not find any water. Then my jeep did the same thing again. I checked all the gas lines and the filter. No leaks or clogs. I’m stumped. —Mark D.
A: It sounds as if you’ve checked most of the obvious causes for your problem, beginning with the most obvious — running out of gas. While there could be several other reasons this is happening, and some of them have nothing to do with your M38’s fuel system, but I’m going to take two guesses. One: have you considered vapor lock? Were they hot days when your jeep died? Was the engine temperature hot? Were you climbing a hill? Two: check out your fuel pump. While one may usually regard a fuel pump as being like a light bulb that either works or doesn’t, it may sometimes give warning signs before it fails completely. Since you mentioned your engine made the sucking sound that usually indicates fuel starvation, I’m going to stay with the fuel system, rather than suspect an electrical or ignition problem, and suggest that your fuel pump might be failing. Another possible indication of this would be if you pulled the dipstick and smelled gas in the engine oil, though this is not always the case when a mechanical fuel pump is failing.
M38 Memo
Q: I have an M38 that I’ve driven in a number of parades since I got it around 2006. I have had to do a number of repairs/fixes, some because of the work done before on it. One thing that seemed to be a problem was the carburetor/fuel pump. Both are older original types, but I don ‘t know how old. After fixing the gas tank, checking out the in-tank filter, changing an inline filter that was added (close to the engine), and after checking the screen on the carb, I started on the fuel pump. One of the first things I did was take the line apart at that added filter to check out the gas flow from the pump. After turning the engine over for a while, the flow seemed to improve and become more steady. Odd? Yes. I then checked the pressure. I had more than the minimum. Odd again? Yes. Just for the heck of it, I pumped more gas into a can. It seemed to work well. Since that time, I’ve not had any issues that I can relate to the fuel pump. I think what I did was to clean out (flushed) some little debris that may have gotten caught in there, maybe on the surface of the valves that caused it not to work well. So, I have suggested to some that they do a “flush,” then follow with some more checks. Also, because of the time that these were made, I add oil to the gas and only use 100% gas. Semper Fi. — Paul S.
A: Thank you for the input, Paul, and your experience should be helpful to other HMV owners.
Headlight Help
Q: I have an M38A1D. When I restored it about 10 years ago, I put a new wiring harness with turn signals on it. All of the lights were working good until last fall, when the headlights quit working. I put new sealed beams with the correct connections on, but still no headlights. The stop light, brake light, turn signals, instrument lights, and blackout drive light all work. Thinking it may be the switch, I put a new one on. Still no headlights. I tried another switch and the headlights worked until I turned them off, then they would not come back on. I have used a circuit tester to check the wires and wire 16 from the switch to the dimmer does not have any power. Still, all of the other lights work. I am thinking it may be a broken wire inside the plug that plugs into the switch. I hate to put a new wiring harness on as they are expensive. Is there any way the plug can be checked? — Lowell May
A: Sounds as if you’ve done the logical thing and traced the problem. Have you checked to see if you’re getting power to the dimmer switch? If so, then it would seem the problem might be in the switch. They do eventually wear out, or sometimes just get corroded inside, especially on vehicles that sit a lot. Sometimes they can be taken apart and cleaned. Like many M-Series components, the same dimmer switch is used on many vehicles from that era, so it shouldn’t be hard or expensive to find a replacement. You might also try stepping on the dimmer switch or pushing it with you hand a few times. This might clear it of any internal corrosion. Hope this helps. Please let us know what you find.
Send your favorite Tech Tip or question to Steve Turchet at military@aimmedia.com
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