I have a 6.5 TD 3500 frequently my engine rpms surge up to 3000 or so. It used to just go up and then just drop down immediatly and still does when idleing but recently when driving at speed the engine will surge and not stop until I turn the ignition off. when surging it blows thick black and or white smoke which it does not normaly do. Sometimes I can Drive 30 miles without a problem and others It does it after only 10 miles and when it is not surging it runs excellent no smoke or loss of power. I recently changed the fuel filter. I also had a wire burn and melt out of the connector I repaired the wire which I am pretty sure was for the headlights as I only had high beams before repairing and it plugs into the steering column right where the signal light lever is. I am pretty sure this not related but thought maybe something in the cruis control was affected.
Is your Service Engine Soon or Service Throttle Soon light coming on at all when this happens? If so, this will tell you more than I can just by guessing. Since the truck has a drive-by-wire throttle, it's not likely that a simple broken wire in the steering column would cause your symptoms. In fact, if the ECM suspects anything wrong with the electronic fuel management system the first thing it does in most instances is disable the cruise control. The most classic problem with these engines is the Fuel Solenoid Driver (FSD), which is the little black box that controls the fuel injection pump. These things have a finite lifespan because they are bolted directly to the FI pump and the heat they produce is a killer.
Although I have not heard of a bad FSD causing the symptoms you describe, it is possible that it has some relationship. The more common symptoms are hot stalling and loss of power. If you suspect a failing FSD and catch it quickly enough you can get away with simply replacing it (disconnecting the stock unit, leaving it mounted on the FI pump and installing a new one on a device called an FSD Cooler on top of the motor using the original harness -
30-45 minute job). A new FSD with calibration resistor runs about $250.00 and an FSD Cooler about $150.00. This only sounds expensive, but if you let it go too long it can fry the optical sensor inside the FI pump and can cause the pump itself to fail - VERY expensive ($1800.00+). If it weren't for this issue with the FSD mounted directly to the pump body, the DS4 electronic FI pump would be a very reliable unit (this is the classic difference between something working well on the test bench vs. working when mounted inside the engine bay of a truck receiving regular use).
Just as basic advice, I also recommend that since your truck is a 3500 and pre-1997 that you also install the post-1997 high flow water pump with dual thermostats and crossover. The earlier versions of the 6.5L TD had issues with burn-through of the head gaskets around the rear cylinders when the truck was used for heavy hauling and towing. The new pump setup increased coolant flow and virtually eliminated that issue - a good precaution on one-ton trucks that are expected to work for a living.
The Service engine and service throttle lights are not coming on at all. I also have an OBD2 code reader and no trouble codes are showing up at all. I am going to try and replace the FSD as a local mechanic told me that 9 of 10 times that is the problem but he told me that there were two modules the one on the pump and one in the glove box. I have come to place very little confidence in any of the local mechanics. The truck has 250000 km on it and the injector pump has never had any work done on it so it is probably a good idea to change the FSD anyway.
Thanks for the help I relaced the FSD and its seems to have solved the problem. I foung a new unit with a cooler that mounts remotly farther back on the intake manifold away from the heat and boosts torque. since you leave the old one in place it only takes about 15 min to install. The price is higher though $950 Canadian.
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