7.3L Diesel Stalls When Hot, Won't Start When Cold
Q I have an '01 Ford F-250, with a 7.3L diesel engine, which was purchased used. In July the engine began to shut off when warm. My mechanic traced the problem to the powertrain control module (PCM). We went on vacation to the mountains, where the temperature dropped to 45 degrees in the morning, and we began to have trouble starting the truck. (I would cycle the "wait to start" three times to get it to start the first time.) We have never had this trouble before, and we have camped when it has been down to 32 degrees.
I have changed the oil temperature sender and checked the glow-plug relay, as indicated in my repair manual, and I believe it is the PCM. My mechanic says no-he is checking the glow-plugs.
Could it be the PCM? And how do you test it when the temperature doesn't get below 60 degrees?
Simi Valley, CA
A It sounds as if we have two unrelated problems: (1) the engine stalls when it gets warm, and (2) the engine will not start when it is cold outside. To get an accurate answer to both problems, I went to the best Ford diesel troubleshooter around, Ford Master Tech Mike Kelly. I have known Mike for over 20 years now, and he has never failed to come up with a precise and clear answer. If there was an answer to be had, Mike is the man. Here's what he had to say:
"As to problem (1), I have only seen a couple of things that would cause a 7.3L that's running to stall. The most common is a cam sensor that is going bad. This is a temporary problem, and usually the engine will restart after it cools off. A code scan of the system having this fault will result in a code "P0340" and/or a code "P0344." I believe that this model year is included in a recall where the cam sensor will be replaced free of charge if it is the older black one with a gold hold-down bracket.
"The other common failure on this model that can cause the engine to stall is the fuel heater element coming loose inside the fuel filter canister and grounding itself on the canister body. Usually, this will blow a large 30-amp fuse in the underhood fuse box, requiring the element and the fuse to be replaced.
"Problem (2) sounds suspiciously like a glow-plug system concern since it only occurs with a cold engine. The first thing to do is to note the tailpipe while the engine is cranking. If the engine is smoking out the tailpipe and will not start, this indicates that all the fuel delivery components are supplying fuel just fine but the glow plug system is not heating up the air in the combustion chambers. Conversely, if the engine is not smoking out the pipe during cranking, there is a problem in the fuel delivery system.
"To check the glow-plug system, just unplug the nine-pin connector on each valve cover and measure the resistance to ground of each of the two outer pins in the connectors going into the engine. Optimum resistance will be 2.0 ohm or less. Any higher resistance will indicate a failing or failed glow plug or a melted wire or connector under the valve cover. If the glow plugs and wiring pass this check, then the most likely culprit is the glow-plug relay.
"The best check for this item is to put an inductive ammeter on the wire going to the glow plugs and turn the key on. The desired reading is 200 amps since a healthy glow plug will draw 25 amps. It is also very important to note that this relay looks like a starter solenoid, but has twin gold-plated internal contacts, and using one designed for a starter will cause it to fail in a short time.
"Also the two large terminals on the wiring to the glow-plug relay, that receive power from the battery and send the power to the glow plugs, have to be very clean and very tight to carry this amount of current. I always polish the eyelets with a file or a Scotchbrite pad.
"To test the system when it isn't cold out, you must insert a resistor in the plug going to the engine oil temperature (EOT) sensor to trick it into thinking the oil is cold. I have never seen this issue caused by a defective PCM, but nothing is impossible."
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