7.3 running very rough - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 4 (permalink) Old 10-30-2014, 02:34 PM Thread Starter
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7.3 running very rough

I have a 7.3 that I had problems with after sitting over the winter. I replaced the starter, two new batteries, new fuel filter. I pumped the fuel tank out and put new diesel in.

The truck will crank in 3 seconds. It acts like it initially does not want to turn over, then trying the second time, will turn over and crank. Before all this, it cranked and blew white smoke. Now, the smoke is black or maybe a blue color. It will smoke up the yard in about 2 minuets. It's just dark smoke now.

The engine will run, but lopes when it initially starts. Like it has a high lift cam in it. It will run at 700 RPM, then run up to 1200 RPM then back down to 700 RPM. But, only if I sit with my foot on the pedal. I let it run like this for about 2 minuets. Then it will run at 700 RPM and idle. But, it acts like it's missing on a few cylinders.

I have put Hot Shot Secrets, in the oil, as this is supposed to free stuck injectors. But I don't know if I should just let it sit and run for awhile.

Could this be due to a severely stuck injector, or completely failed injector?

I check the Glow Plug Relay and it test OK. Other control modules bad? And, just by letting it sit over the winter, would electrical components just fail?
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post #2 of 4 (permalink) Old 10-31-2014, 05:37 PM
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Without diagnostic tools, it harder to find the cause. You need to be able to look at lie data of the engine running to see which cylinders are misfiring.

The first thing I'd check is the engine wiring and make sure a critter didn't use you wiring as a home and chew through anything. Checking the electrical components with a multimeter is a good start, and won't cost you much even if you have to order a $5 multimeter from Harbor Freight. The under valve cover harness and the valve cover gaskets are good places to start your checks.

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post #3 of 4 (permalink) Old 10-31-2014, 06:54 PM Thread Starter
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Let me add this, this truck ran fine, before I let it set up. 0 to 80 mph in no time flat. Ran perfect. I did crank it a few times, but as it got colder, and the batteries got weak, I just didn't fool with it, TOO cold! If, it is several stuck injectors, how would I determine which ones?
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post #4 of 4 (permalink) Old 10-31-2014, 11:55 PM
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The only way I know of to check is with a cylinder contribution test. You will need the appropriate scan tool to do this. The only other thing I can think of is to disconnect the wiring harness going through each valve cover individually and see what happens. If disconnecting one of them makes no difference, then you probably have a wiring harness issue causing the truck to only run on four cylinders.

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