loss of torque...wtf? - Ford Powerstroke Diesel Forum
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Old 07-14-2014, 07:59 PM
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loss of torque...wtf?

'97 crew cab, 4wd, 4:10 gears, 168K miles, 3" down pipe
last year I completely gutted my cat. then I got a 4" exhaust from the (gutted) cat back. Nice turbo whistle. tons of low end torque...i thought.
I don't tow much. Sold my big *** boat a couple of years of ago, kept the truck. I had the opportunity to tow about 2K pounds yesterday up and down some 7 and 8 percent grades in the Colorado mountains. In town she runs fine. Very little smoke. She just runs.
Going up the mountains (empty at this time) she was struggling to stay at speed, constantly down shifting, up shifting, then back again. And tons of smoke.
When I hooked up to the trailer and 2 ATV's it got worse. The truck fought even harder to just get going. At one point going up an 8 percent grade, she only managed to hit 45 mph and I was in it. I pushed in the tow/haul button and when she down shifted the EGT's hit 11,000, even more black smoke, and just barely moved. I let off the accelerator til the EGT's backed off. By this time we had crested the top of the pass. Going down hill the EGT's were normal (well, yeah, no load) and going up the next hill I had momentum carrying the truck and trailer so she did OK, but once momentum was gone and I had to accelerate, she lugged hard with a **** ton of black smoke.
Once we were out of the mountains and back on flat ground she did fine. A couple of hills here and there but nothing to speak of.
I noticed a lack of high end torque as soon as i gutted the cat last year. And then a bit more when I got the 4" exhaust. So what happened? Do I need some back pressure? Should I get a performance muffler to add some back pressure? That would be a hell of lot cheaper than a new cat. I really don't want to go back to a cat...unless that is what is needed.
I just want to know what happened and how to correct it. These trucks are capable of towing an incredible amount, but I was having trouble with only about 2000 lb's. Please advise.
Thank y'all so very much
T
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Old 07-14-2014, 08:40 PM
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Sounds like you were not getting any boost. Do you have a boost gauge? Check for exhaust and boost leaks.
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Old 07-15-2014, 01:29 AM
Can you hear the derail??

 

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^^^ this sounds exactly like your problem, check the impeller wheel too
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Old 07-15-2014, 03:53 AM
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It's not the cat. I took mine right out 2 weeks ago (no inspection up here) and the change was more, not less power. The factory cats on these trucks are a joke....

Do you have access to a scanner?
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Old 07-15-2014, 03:54 AM
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i will third the boost/exhaust leak
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Old 07-15-2014, 04:58 AM
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I do have a boost gauge. I was so intent on keep my eye on the EGT's I didn't even look at the boost. I thought about that very thing after I got home that night? So having an open exhaust system would not make it harder to pull? It's not back pressure, it may the turbo?
Can I pull a vacuum and check for leaks?
Thanks to all. I really appreciate it
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Old 07-15-2014, 10:28 AM
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Post-turbo back pressure is bad, and will reduce power. You definitely don't need to add more restriction to the exhaust.

It sounds as though you're not getting much boost. There are several common things that can cause this.

- Do a boost leak test. You can get a little adapter gizmo (or make one with some PVC pipe) that goes over the turbo and pressurizes the intake system. Due to sucking oil through the crankcase vent, the various boots tend to get oily and stop sealing. I can almost guarantee you have boost leaks, since that's the default state of these trucks...
- Look for exhaust leaks pre-turbo. Exhaust getting out before the turbo means it won't spin the turbo as fast.
- While you have the boot off for pressurizing the intake system, inspect the turbo compressor wheel. It shouldn't be missing chunks or rounded off.
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