Loss of power at 60+mph
 

Hello all! been having an issue and not really getting any advice in the tech forum so thought I would give it a shot here :)

My 91 cummins engine seems to be having an issue but only when I try and go faster than 60mph. It will cruise around town just fine but once I'm on the freeway trying to go over 60(OD AND TC engaged) it craps out on me and I can feel a LOT of vibration in the gas pedal. Things chill out once I let off the throttle and cruise 55 mph or so, not sure what's causing the problem. I did use some diesel fuel treatment 2 tanks ago so I thought maybe I had clogged the fuel filter from all the gunk in the tank and lines moving forward so I replaced that, I also thought I might have had a weak lifter pump so I replaced that as well. Still have the same problem, engine hates life over 60 mph any help would be appreciated :)

anyone?

Any recent work on the fuel system?
Any exhaust smoke when this occurs?
Do you have any gauges fitted? Tacho, EGT, fuel pressure?
Have you checked the pump is getting full travel when the pedal is pressed?
Have you tried holding it in a lower gear and going to or above the same RPM?

Nothing other than a bottle of diesel fuel treatment 2 tanks ago. I did have to take the gas pedal off about two weeks ago and bend it upwards a bit. When I traded for it a month ago you couldn't push the gas pedal all the way without smashing it into the carpet, now I have full travel on the throttle linkage arm and am no longer pushing with all my might into the carpet.
boost was only around 10-15 lbs with 650 egt during this problem on the freeway, no noticeable smoke during the problem. My sister drove behind me yesterday and said it does smoke a lot just following me around.
No tach yet, I ordered the signal converter off ebay 2 days ago so I can get a signal off my w terminal and hook it up to my gas tach in the dash.
Also have a fuel pressure gauge on the way in the mail!

I feel like I am able to exceed the rpm's without any problems around town with a heavy foot, I'll know more once the tach is set up in a few days.

Have not forgotten you, been busy
OK, smoky around town but not when getting on it.
Certainly sounds like lack of fuel.
Lets see what the gauge shows when you get it installed.
Is the fuel tank from a gas engine? Have you removed the strainer from the pickup?
Quick check, tank cap off and blow air back through the line to the tank. Prime and bleed the system and see how it goes.
Cheers Steve

Oh no it will smoke a lot if I mash it driving around town, esspecially going around 40 mph with the TC locked up. My sister said it was excessive when she drove behind me but would go away once I was up to speed. It just craps out over 60mph.
Yes it's the original gas tank, I didn't have any problems priming the system when I installed the new lift pump. That's a good idea though blowing air towards the tank to check for restrictions. It has a 45 gallon tank and it's halfway full. hope I don't have to drop the tank :D

I'm still waiting on my banjo bolt in the mail, got the gauge though :tu:

I mean yes smokey around town not when having this issue at 60mph+

Well I got the fuel pressure gauge installed. I'm getting around 6-7 psi at idle, 4-5 cruising around, and got it down to 2-3 going 45mph up hill. I have yet to try and cruise down the freeway as I feel like I might have found the problem. What do you guys think, drop the fuel tank and clean out the screen filter? I already replaced the lift pump and still has the same symptoms so I feel like that's not the problem, although it's possible.

Did you try blowing air back through the lines? If it improves then you need to hunt what was causing the restriction.
For diesels they don't usually run screens on the fuel pick up, if using a gasser tank the screen is usually removed.
By chance did the original set up use an intank pump? Be a bit of restriction drawing fuel through that.
Cheers Steve

Haven't tried blowing air back yet. I don't have an air compressor, do you think blowing in a tube with my mouth would do any good? Yes it has the original 45 gallon gasser tank from factory. I feel like they are sucking fuel through the original pump in the tank as I still have a fuel gauge. I'll drive it around a bit more to empty the tank so I can drop it if need be, still has over half a tank :/