Ok, so here's the deal. I took my truck on a 1200 mile round trip to see family for thanksgiving, and on the way there the truck ran great. I averaged 19.67 MPG, but I was empty and not pulling a trailer. So then on the way back I was pulling a 24 foot flatbed trailer hauling a steel flatbed that I am going to put on my truck (weighs a couple hundred pounds). The truck had no power and got 10.32 MPG on the return trip. Also the ABS and BRAKE lights are now on and when I rev above 2300 RPM's I can hear a hissing noise from behind the dash, it sounds like it is comming from right behind the airbag on/off switch area, but it is hard to tell for sure (also it makes this noise even in neutral revving the engine).I also noticed that I was getting no black smoke at all, not even when I would go into a long hill and push the throttle all the way, it almost feels like I don't have any throttle after 3/4. I was having to down shift, and barely dragging over the top at 45-50 on hills that I usually pull in 5th at 70-75. So I stopped and looked things over and found nothing obvious wrong, so I unhooked my van aken chip to see if that changed anything, it didn't seem to make any difference, actually maybe a little less power if anything.At first I thought that I wasn't getting any boost pressure (I don't have a gauge on it), but if that is the case I should have black smoke. It feels like it isn't getting enough fuel maybe.Any ideas of what I should be looking at would be greatly appreciated, because I have to take it again this weekend on a snowmobiling trip.Thanks in advance Oh, I also pulled the codes and only got a P1693 code, I can't get the cheap code reader that I borrowed to show the companion codes that would go along with the P1693 code.

Was your boost pressure the same? Sounds like you have a leak between the turbo and intake manifold somewhere.

Unfortunatly, I don't have a boost gauge or EGT on the truck yet. They are now on order along with a fuel pressure gauge.

I'd roll with the idea this is a boost leak too. How is the turbo plumbing, connectors and hosing? In particular, check the boot. If you have a friend you REALLY TRUST, have then brake boost the truck to give 3-5 PSI while you listen around under the hood.... soapy water on the elbows and boot could help you pin point a leak... I dont' think our trucks will throw fuel at an engine that is not getting compreable boost, but I could be mistaken. Anyone else? Ideas?

Ok, so here's the deal. I took my truck on a 1200 mile round trip to see family for thanksgiving, and on the way there the truck ran great. I averaged 19.67 MPG, but I was empty and not pulling a trailer. So then on the way back I was pulling a 24 foot flatbed trailer hauling a steel flatbed that I am going to put on my truck (weighs a couple hundred pounds). The truck had no power and got 10.32 MPG on the return trip. Also the ABS and BRAKE lights are now on and when I rev above 2300 RPM's I can hear a hissing noise from behind the dash, it sounds like it is comming from right behind the airbag on/off switch area, but it is hard to tell for sure (also it makes this noise even in neutral revving the engine). I also noticed that I was getting no black smoke at all, not even when I would go into a long hill and push the throttle all the way, it almost feels like I don't have any throttle after 3/4. I was having to down shift, and barely dragging over the top at 45-50 on hills that I usually pull in 5th at 70-75. So I stopped and looked things over and found nothing obvious wrong, so I unhooked my van aken chip to see if that changed anything, it didn't seem to make any difference, actually maybe a little less power if anything. At first I thought that I wasn't getting any boost pressure (I don't have a gauge on it), but if that is the case I should have black smoke. It feels like it isn't getting enough fuel maybe. Any ideas of what I should be looking at would be greatly appreciated, because I have to take it again this weekend on a snowmobiling trip. Thanks in advance Oh, I also pulled the codes and only got a P1693 code, I can't get the cheap code reader that I borrowed to show the companion codes that would go along with the P1693 code.

Boost leak was my first thought too, but I couldn't see/feel/hear any leaks in the intercooler boots. I'm starting to think that mabye it is in limp mode??

Ok, so here's the deal. I took my truck on a 1200 mile round trip to see family for thanksgiving, and on the way there the truck ran great. I averaged 19.67 MPG, but I was empty and not pulling a trailer.

So then on the way back I was pulling a 24 foot flatbed trailer hauling a steel flatbed that I am going to put on my truck (weighs a couple hundred pounds). The truck had no power and got 10.32 MPG on the return trip.

At this point I normal ask for error codes and fuel pressure?

Also the ABS and BRAKE lights are now on

Here is the write up on that...

http://mopar.mopar1973man.com/cummins/2ndgen24v/abs/abs.htm

and when I rev above 2300 RPM's I can hear a hissing noise from behind the dash, it sounds like it is comming from right behind the airbag on/off switch area, but it is hard to tell for sure (also it makes this noise even in neutral revving the engine).

If you had gauges you might be able to tell if it actually a boost leak by the loss in boost pressure. But in neutral there truely isn't any boost pressure buit... Maybe 5 PSI reving it hard.

I also noticed that I was getting no black smoke at all, not even when I would go into a long hill and push the throttle all the way, it almost feels like I don't have any throttle after 3/4. I was having to down shift, and barely dragging over the top at 45-50 on hills that I usually pull in 5th at 70-75.

Sound like a fuel issue... Need to know what you fuel pressure is...

http://mopar.mopar1973man.com/cummins/2ndgen24v/fuel-pressure/fuel-pressure.htm

So I stopped and looked things over and found nothing obvious wrong, so I unhooked my van aken chip to see if that changed anything, it didn't seem to make any difference, actually maybe a little less power if anything.

At first I thought that I wasn't getting any boost pressure (I don't have a gauge on it), but if that is the case I should have black smoke. It feels like it isn't getting enough fuel maybe.

Any ideas of what I should be looking at would be greatly appreciated, because I have to take it again this weekend on a snowmobiling trip.

Thanks in advance

Oh, I also pulled the codes and only got a P1693 code, I can't get the cheap code reader that I borrowed to show the companion codes that would go along with the P1693 code.

Comes back to the basics... You need to find out what the error codes are... and what you fuel pressure is like...

http://mopar.mopar1973man.com/cummins/2ndgen24v/fuel-pressure/fuel-pressure.htm

http://mopar.mopar1973man.com/cummins/2ndgen24v/obd2-error-codes/obd2-error-codes.htm

I will be taking the truck into the shop on thursday, to have them pull the rest of the codes and check fuel pressures. I really don't think that it is a boost leak, because of the lack of black smoke, also maybe I should describe this hissing sound a little better, it sounds more like a vacum leak, like mabey a heater control vacum line is cracked. and it will only happen when the I rev over 2300 RPM's, it is not dependent on load or speed, because it will do it when sitting still in neutral. This is all very good advice and I appreciate any and all thoughts or ideas on this issue. If anyone has anymore ideas I would love to hear them and get this thing figured out because it has me baffeled.

It does sound more complicated than just a boost leak the more you talk about it. You won't get any smoke with a leak though because the computer will not give much fuel to an engine with no boost, and having no fuel and no boost you would have no power. This is true even back to 1st generations, they have a spring that the boost pressure pushes against which then lets the pump give full fuel once boost is built. If trucks didn't have anything like this, the guys that floored it at stoplights would black out the intersection every time.

How much blow by are you getting from the crancase vent? This is a clue of if you got a vacuum leak. When you do have a vacuum leak the vacuum pump becomes a air compressor creates excessive by blow. :eek:

I did notice that I have more blowby than I used to. There is enough that the front axle is covered in oil residue from the crankcase vent. I didn't even think of the vacum pump being a problem. How would I diagnose the vacum pump?

Well its a matter of chasing down all the plastics tube and checking for cracks, leaks, bad rubber, etc... Basically either the vacuum pump works or it don't but if the vacuum pump is bad its either leaking engine oil or the power steer and brakes are out... :eek:

The other thing I noticed this morning is that the heater isn't blowing hot air, so I got out and checked and the heater hoses are hot, so I am wondering now if I have a vacume leak, maybe the heater blend door isn't moving which is causing it to blow cold air. Also now that you mention the brakes, they feel very stiff and grabby, if that makes sense, anyway they aren't working as they should, I just figured it had something to do with the ABS light being on, but maybe not huh?? Also the steering wheel is hard to turn, but I just figured that was because it was -6 degrees the last few days here.

The other thing I noticed this morning is that the heater isn't blowing hot air, so I got out and checked and the heater hoses are hot, so I am wondering now if I have a vacume leak, maybe the heater blend door isn't moving which is causing it to blow cold air.

Actual the blend door is controlled by a stepper motor on the passenger side floor. It not even vacuum driven but there has been issues with the blend door breaking.

Also now that you mention the brakes, they feel very stiff and grabby, if that makes sense, anyway they aren't working as they should, I just figured it had something to do with the ABS light being on, but maybe not huh??

Yes it got a lot to do with the ABS light on... The ABS light is telling you you got a speed sensor out since you didn't say anything about speedometer I'm going to assume your front axle speed sensors are shot.

Also the steering wheel is hard to turn, but I just figured that was because it was -6 degrees the last few days here.

When was the last time you changed your power steering fluid? PS fluid should be flush and changed every 30K miles. If the fluid is dark and nasty then yes it needs to be changed.

How old is your fuel filter?