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Why won't my truck start and gets poor mileage?

I recently bought my uncle's 1996 379 with 470 Detroit. It is fleet truck plus; single air cleaner and exhaust, not full gauges, but more than the minimum. He got between 6.7-7.2 mpg. He hauled for the California State Penetentiary, and got good rates. His maintainance attitude was "I can't afford to be broken down. Parts will be replaced before they break." The bearings in the engine were changed because the pan was leaking. Once the pan was off, he had the shop change the bearings.

Before he parked it when he stopped working, he took it to Peterbilt to have them change the injectors. They seemed to be leaking, and it was more cost efficient to change thm once the rockers were off anyway. The shop changed only one, so that seemed to be the only thing it needed when I bought it from him. He had started it occasionally, and moved it, but essentially it was sitting for 3 years.

Once I got it out to Chicago, I had problems starting it, because it did exactly what he said it did due to the injectors, however it is colder here, so it wouldn't start. I had the injectors changed (all six, even the one that had been changed were bad), but the fuel pump broke on the next trip. The fuel was midly diluted, proving the injectors were bad. When the shop changed the pump, it wouldn't start, so they put it on the computer, which showed ECM failure. Knowing that other problems will show the same failure code, they hunted down loose connections and broken wires. 3 days later, without having to change the ECM, the truck was running.

It still will not start without ether below the 40 degrees and cold engine. in the high 20s and below, it needs someone spraying ether while cranking for it to start. When it starts without ether it cranks for a little while, then hits on 2 or 3 cylinders, and die. When it finally starts, it idles 400-500 rpm, and won't take the throttle. After about 20-30 seconds, it suddenly picks it up, and goes to fast idle, and will take the throttle.

The mechanic at the shop doesn't know why, so he called Detroit, and they hav suggested that maybe the rings are tired due to the mileage (860,000) but as it doesn't smoke or burn oil, that doesn't seem to be the problem. Another suggestion is it is an ECM problem, and it doesn't fuel correctly until the ECM warms up. My uncle has told me it sounds like it has a leak between the fuel pump and the injector, and sucks air. He told me to look at the fuel line from the pump to the engine for wetness, but there is none. The filter plate does have some liquid on it, perhaps that is cracked.

Further, the truck gets awful mileage. The last 2 fillings were 5 mpg and 4 mpg. Although I drive faster than the speed limit was when the truck was in California, I go slower than posted speed limit in the states I drive, IL, IN, IA, WI and OH, about 62. I haul rail containers, and I would expect my mileage to be less than hauling dry van or reefer, but not this bad.

Further, on Tuesday, when I got 4 mpg, the truck ran poorly. It took forever to get up to speed, and the load I had felt 10k pounds heavier than it was. Yesterday, when I got 5, it pulled much more comfortably.

Normally, when I take over a truck, I improve the mpg, and have driven several trucks above 7, and one above 8, and that one was hauling containers, so I am not the problem. Please help!

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sounds like it's being starved for fuel. Change the filters, change the fuel lines and possibly injectors. This might fix both problems.

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I've heard a bad bull gear on a Detroit will also make it hard starting? Food for thought...

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Steven will be eternally grateful.
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