99 & up 7.3L Power Stroke Engine and DrivetrainDiscussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.
Fluctuating throttle around 1500 rpm at light loads
2000 7.3 PS Diesel, 149k miles, bone stock. No check lights are on. New air filter, recent fuel filter. The cam position sensor has been replaced by the PO but may have 100k+ miles on it:
When driving slow speeds (30 - 50 mph) and around 1500 rpm the throttle fluctuates even though my foot is in the same spot. Sometimes the throttle gets to be more more (power and rpm go up) sometimes it falls off to less (power and rpm are less). At WOT and idle, all things are normal. This happens all the time but it seems it is more pronounced when the truck is "cold" (Los Angeles).
I have searched the forum but haven't found anything that sounded like my symptoms. How do I go about diagnosing this? I have a road trip coming up and don't need this out of the hole!
I'd say you probably have an issue with your EBP system "hunting" if it's accompanied by intermittent hissing in time with the power loss. Especially if it's happening in cold temps. It's pretty common for the tube extending from the front of the passenger side exhaust manifold up to the EBP sensor to plug with soot. That makes the sensor slow to react to changing valve position, so the valve in the turbo outlet overshoots then undershoots where it should be.
My truck did that early in it's life, and it took three warranty trips to the dealer to finally get a tech who checked it "by the book" and wound up replacing the EBP solenoid that controls the oil flow out of the actuator chamber in the turbo pedestal.
First thing you should try is removing the sensor tube and cleaning it out. You could also just unplug the intake air temp sensor, which will disable the system. But that should only be a temporary measure, as it will affect other things as well. The other way to completely disable the EBP system is to unplug the soleniod wiring connector located at the bottom front of the turbo pedestal.
Thanks for the input! I'll give the tube a cleaning. I had very good fuel mileage on this truck when I got it and it certainly hasn't gotten any better. Maybe there is a connection.
If I can not resolve this in the next few days, do you think I can take a road trip with such a condition or can it get worse to where I'll be stranded?
I cleaned the tube yesterday. It was pretty gunked up, especially in the last turn before the sensor. The truck wasn't cold when I went for the test drive. However, I could feel better throttle response - almost peppy at low rpm / partial load. I could not get it to reproduce the surging / fluctuating throttle. I won't celebrate yet until I had a chance to drive it from a cold start, but I think this may as well have been it!
In hind sight, the way this issue started, it is consistent with something clogging up / going bad slowly. It would show the symptoms maybe as early as a year ago and it was very mild. Then it got a little worse over time until it was blatantly obvious something was funny.
Thanks A LOT and I will give another update in a week or so.
To answer you question on whether it would cause a problem long-term. Most likely not. What happens with the EBP system is that it's engaged only until the engine oil temperature reaches a certain point, so even if you hadn't cleaned out the tube, you'd only have to put up with it until the engine had fully warmed up. I experience that most every day in the winter, and can feel when the engine temp reaches the EBP cutout point. The engine suddenly runs quieter, and the boost gauge pops up to normal.
On a long trip it would be a pretty minimal issue, only bothering you on the first few miles (maybe 3-5) of your trip. If you let it warm up completely before taking off, it wouldn't do it at all.
I have the same problem, and its not the EBV valve. It has gotten worse, especially when its really cold out, the rpm's go up and down bad? I was told it could be HPOP sensor, TPS, its defenitly and fluctuation in fuel pressure, not sure where to start?
Last edited by customhaying4u; 01-02-2010 at 05:53 PM.
If you're experiencing it underway, and have confirmed it's not the EBP system, then it could be a sticky IPR (Injector Pressure Regulator). Could also be a bad accelerator pedal assembly. You could check that with a multimeter. Pull the plug to the pedal and with a multimeter, check for smooth change in resistance as you move the pedal slowly.
If it's happening at idle, try pulling the connector off the ICP sensor (right behind the alternator on the head) and see if it smooths out. If so, that's an indication that the sensor is bad.
If you're experiencing it underway, and have confirmed it's not the EBP system, then it could be a sticky IPR (Injector Pressure Regulator). Could also be a bad accelerator pedal assembly. You could check that with a multimeter. Pull the plug to the pedal and with a multimeter, check for smooth change in resistance as you move the pedal slowly.
If it's happening at idle, try pulling the connector off the ICP sensor (right behind the alternator on the head) and see if it smooths out. If so, that's an indication that the sensor is bad.
Thanks,
now that I think about it, it has been fluctuating at an idle, I will try those tips out and get back, thanks so much.
You could check that with a multimeter. Pull the plug to the pedal and with a multimeter, check for smooth change in resistance as you move the pedal slowly.
If it's happening at idle, try pulling the connector off the ICP sensor (right behind the alternator on the head) and see if it smooths out. If so, that's an indication that the sensor is bad.
I tried checking for ohms, but it doesn't change, what am I doing wrong, also I played with the ICP sensor, ( I have an SP diesel module that plugs into the ICP sensor, so I will leave that unplugged for a while too)not sure if it made much difference..it seems to be better, but it has warmed up to in the 30*F range from in the teens....I'm going to change the oil tomorrow since its close anyways.
Thanks,
I tried checking for ohms, but it doesn't change, what am I doing wrong
There are three terminals in the connector for the AP sensor. If you probe across the two outside pins, you'll just be reading the resistance of the coil. Move one of your meter probes to the center terminal, which will be the wiper terminal. Then you'll get a change in resistance as the pedal is moved.
thanks,
I was looking at the wrong plug, I checked it and it seems to move steady, didn't see any bad spots, I'm going to town now and pick up some oil. I been using Delo 400 15/40, and I'll see how its running without the programmer.
Thanks
I noticed that the voltmeter moves when the really bad surging happens. This happens when I take off when its cold...but I'm still having the issue at 1500rpm's. I also noticed that the truck is running worse when using the new fuel that the state of Oregon has mandated that all fuel be biomixed. I have some fuel left over from pre-bio and my truck runs better....so thats whats going on right now.
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