Hey all,
went north for the Holiday weekend hauling my slidein camper (2000lbs) and small fishing boat. While sharing the road with other diesels it really seems like I was lacking in power. There was a pretty strong head wind (20mph) and going up hills, she wouldnt go any faster than about 74mph. I had some new GMC diesels hauling 35ft 5th leave me in the dust. I wish I could drive another truck similar to mine to see if its just me or if my truck is getting tired. The turbo whistles when at 70mph, but at 60 I dont hear it much. My only mod is the 6637 air filter. Pickup has 155K miles, just changed oil, fuel filter, and cleaned fuel line screen. Pickup is 1996, 4x4, 4:10 rear, auto tranny. Is it just me? When do you normally hear your turbo? I also have a very LOUD roaring noise when going down the highway. Seems like it starts about 55mph and just resinates through the cab. Maybe now I am just paying more attention.

Thanks,
Jeff

 

well the newer truck will always have the advantage but with the gearing you have that load should have that affect on your truck. Granted thats a big head wind but I think you should have gotten over 74 MPH. THe roaring noise could have been the fan clutch especially if you were working hard. though normally it should be the other way around in that it should be on at lower speeds and off at higher speeds. So it may or may not have been the issue.

 

sorry, thought i started a new post

 

I have held my 95 PSD w/3.55 gears at 90-95 for half hour straight. Don't know what the RPM was but I would guess it was close to 3k. It won't hurt it one bit. especially cruising at those speeds. Idle is usually right around 500-550.

 

How can I tell if the cooling fan clutch is bad? It used to be when I was empty I would get that roaring sound between 55 and 65 and once I hit 70+ it would smooth out and get quieter. I wonder if a driveshaft U-joint or diff would make that noise? I did notice when I was hauling a bobcat the other weekend I could feel the truck slighty vibrate when accelerating.

tjbeggs, I'm assuming you were empty going 90+ mph?

I would especially notice the lack of power if I would slow down to 60mph at the base of a hill, then try to climb. Most of the time even I shifted out of OD, it took forever getting to 70 and thats about all it would go with the pedal to the floor.

 

Yeah just a quick midnight run to the hospital cause my dad was having chest pains.

The fan clutch can be tested though not very scientifically. With a cold engine you should be able to spin the fan by hand with some resistance. It should only free wheel about 1 turn or less when you giv eit a spin by hand also. So it should have some resistance but not so much that it is nearly locked up with the pulley but enough slack that is will spin 1 turn or less.

 

Here's some reading on the subject....



Fan Clutch Test

NOTE: The following test does not apply to the 6.0L diesel. For the 6.0L diesel, refer to the Powertrain Control / Emmisions Diagnosis (PC/ED) manual.

Spin the fan blade (8600) by hand. A light resistance should be felt. If there is no resistance or very high resistance, the minimum and maximum fan speeds must be checked as follows:

Fan Clutch Test — Minimum Speed Requirement

Use a suitable marker to mark the coolant pump pulley (8509), one of the fan blade retaining bolts and the crankshaft pulley (6312).
Connect a tachometer to the engine.
Install a throttle adjusting tool.
Connect the Digital Photoelectric Tachometer.
WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and run it at approximately 1,500 rpm until the normal operating temperature has been achieved.
Operate the strobe light at 3600 rpm for 7.3L diesel engines, and aim it at the coolant pump pulley. Adjust the engine speed until the light flash and the coolant pump pulley mark are synchronized.

Aim the strobe light at the fan blade bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).
The fan blade speed must not be greater than 2,000 rpm on 7.3L engines.

Turn the engine off.

If the fan blade speed was greater than 2.000 rpm on 7.3L diesel engines, install a new fan clutch (8A616).

Fan Clutch Test — Maximum Speed Requirement

Perform Steps 1 through 5 of the Fan Clutch Test—Minimum Speed Requirement.

NOTE: The temperature of the air hitting the fan clutch should be above 96°C (205°F) for maximum fan speed.

Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille (8200). This will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.

Place the climate control function selector switch in the MAX A/C position and the blower motor switch in the HI position.

Adjust the strobe to 3,600 rpm for 7.3L diesel engines.

WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and adjust the engine speed until the strobe light flash and the coolant pump pulley mark are synchronized.

Aim the strobe light at the fan blade retaining bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).

If the fan blade speed is less than 2,850 rpm on 7.3L engines, install a new fan clutch.

Rick....

 

Same deal for my truck although I was hauling about 8000 pounds and the outside temp was about 110. However, at anything above 60mph, the engine was making so much noise, I could hardly stand it. Once it downshifted for a hill, it sounded like it would blow up running at 3000 rpm. However, the sound was very similar to when my 460 would get hot and the fan clutch would kick in to cool things down. I am going to test the fan clutch but maybe it's just because it is so damn hot right now.

 

Another thign to check for your low power is to unhook the conenctor for the MAP sensor which is located ontop of the heater box. and it has a rubber line going to the intake area. just unplug the electrical connector and drive the truck. If it has more power chances are you need a MAP sensor.

 

Anyone have a pic of the map sesor? I would like to try unplugging it to try TJs idea.

 

Well no pics but I will explain where its at. Ok passenger side of the engine compartment mounted on top of the heater box. I think its actually screw tot he cab but its right above the heater box. It has a small 1/4 inch rubber line going to it as well as an elctrical connector that I think is three wire. The rubber hose goes tot he passenger side intake plenum. Just unplug the connector.

I guess I have a few more location pictures to add to my collection.

 

Thanks will check it tomorrow

 

If the MAP sensor needed replacing, wouldnt that throw a code?

 

Not always. I just read about a guy who had low power for like a year (since he had owned the truck) he unplugged that thing and it was like a new truck. Replaced the sensor and it was good to go. No CEL no codes.

BTW You have a message!

 

how much are the map sensors and where is it?