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NTC 335 low power


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By Tattoo - Sunday, November 10, 2019 2:23 PM
I have the privilege of pulling the equipment trailer to football games and band competitions for our local high school marching band. My truck is a 1968 K123 with Cummins ntc 335. The entire combination when loaded weighs 45300 lbs. I kind of expected to be able to pull that pretty easily, but when we're on the interstate I have to keep the fuel pedal on the floor pretty much the entire time. On a flat stretch of highway we can reach 75 mph but any kind of an uphill will slow the truck down. If it's a moderate hill, I have to downshift and the truck will slow to 50-55 mph.

The engine coolant temp never goes above 175 degrees. The pyrometer typically reads about 900 under max load and the turbo can max out at 17 psi of boost.

For the Cummins guys out there, what do you think of my numbers? Any thoughts about where I should start to try to wake this thing up a bit?

Thanks.

Bryan
By Newto - Sunday, November 10, 2019 4:35 PM
Hi Tattoo,

your numbers do suggest that its a bit of a slug!!!!!!!

A standard 335 puts out around 28-30 psi of turbo boost......& 17 psi my immediate thought is that you are down on fuel pressure.

Things to check are...

1. Are you getting full throttle at the fuel pump lever?
Get someone to push the throttle pedal to the floor while you watch and see if the throttle lever on the fuel pump breaks at the spring.

If not then the fix is easy......adjust linkages to get full throttle.

2 if you are getting full throttle then you should check the fuel pressure (under load) by fitting a fuel pressure gauge with a flexible line into the 1/8 gas plug on the side of the shutdown valve on top of the pump. Fuel pressure should be around 185 psi....if not you better find a Cummins mechanic to adjust it for you.

3.Does it blow any smoke??...Grey/White on startup indicates a loose injector set.....black under load (without good fuel pressure) may indicate a worn turbo.

4.Also check the usual maintenance items....is the spin on fuel filter only about 3/4 full when you take it off????....if its full its blocked!!!!..get a new one!
and air cleaner.....is it clean and free of dirt and crud???....blocked air cleaner will also contribute to black smoke under load.

There's some homework for you Tattoo......good luck and don't forget to report back....

Cheers,

Newto
By Tattoo - Tuesday, November 12, 2019 2:39 PM
Thanks for that Newto. You've given me some direction. I like your theory about low fuel pressure under load. I don't have a fuel pressure gauge with that kind of range, but I'll work on getting my hands on one.

I had a few interesting thoughts after reading your post. I'll start by saying that I've owned the truck for probably 4 years now and have been driving it bobtail most of that time. The boost had never gone above 17 psi but I never knew what the correct range should be so I just chalked that up as normal. The lack of power really only became obvious with the trailer on it and trying to maintain highway speed.

Also, I had recently replaced the head gaskets and installed jake brakes. It was the first time I had worked on one of these engines and I struggled with the injector settings. My first attempt resulted in very loose injector adjustment. The truck ran when I was finished but smoked like a locomotive. The interesting part is that it made at least 30 psi of boost that way (gauge was pegged) and more power than I had ever remembered. I've since managed to get the injectors properly adjusted which eliminated the smoke and brought the boost and the power back to what has been normal for this truck.

Anyway, thanks again and I'll post again when I know some more.
By Newto - Wednesday, November 13, 2019 9:59 AM
Well Tattoo.......you've just about solved the problem!

The loose injector set would allow the injectors to "dribble" extra fuel into the combustion chamber between firing strokes thus giving a bigger bang & more turbo boost.

I suggest you find a Cummins mechanic that can adjust your fuel pressure for you....(you need a different size fuel button) because its obvious now that your fuel pressure is low.

Increased fuel pressure will bring the turbo boost up higher & quicker which will also ( if you have an AFC style fuel pump) open the air/fuel control bellows quicker which should help in acceleration.

cheers,

Newto
By Tattoo - Sunday, November 24, 2019 3:19 PM
So I spent several hours working on the truck today. I replaced all 6 fuel injectors with reman units because I suspected that I had cracked 1 or 2 injector cups when I was having all that trouble with the injector adjustment. I did discover 1 cracked injector cup that was causing the truck to smoke lightly all the time. The other 5 injectors appeared ok. After the injector replacement, the truck runs noticeably better and does not make so much as a wisp of smoke.

The next thing I did was install a fuel pressure gauge and take the truck for a test drive. I'm attaching a pic of the fuel pump. You'll notice the braided line I installed which runs inside the cab and has the pressure gauge attached to the other end. I was able to hold the gauge in my hand and monitor fuel pressure while driving.

http://forums.aths.org/Uploads/Images/411b3902-9cdd-4a1c-ac94-8ea7.jpg

Here are my fuel pressure numbers...
at idle 0 psi fuel pressure. I was surprised by that. Is that normal?
at 1500 rpm in 8th and 9th gear, pedal on the floor 110-125 psi
at 2000 rpm in 8th and 9th gear, pedal on the floor 140-155 psi
At low rpm there is almost no boost. At max I never saw over 16 psi.
The needle on the gauge flutters a lot at higher rpms, but I think my numbers are reasonably accurate.
1500-2000 rpm is the range where the truck would fall on its face while pulling the trailer.
What do you think of my fuel pressure numbers?
I wanted to pull the button out of the fuel pump to see what it is but I ran out of time.

Thanks.

Bryan
By Newto - Sunday, November 24, 2019 10:31 PM
at idle the fuel pressure is usually pretty low....like 10 to 17 psi so if your gauge is calibrated towards higher pressure readings then idle may not show.

as for your max pressures......you are still down about 30 psi as a rough guide.

Good news is ..........you have an early fuel pump (pre AFC) so you can shim up your fuel pressure by removing the large circlip behind the throttle lever and pull the throttle shaft out.

In the shaft there is a hole which is partly blocked by an internal screw in the throttle shaft.

Usually that hole is somewhere between 1/2 & 3/4 blocked by that screw.Removing the screw and adding shims so the hole becomes larger will increase your fuel pressure.

Once the hole is more than 1/2 exposed the fuel pressure gain drops off and you may need to do a button change for big fuel pressure gains but up to 1/2 way open shims should fix your pressure problems.

The only issue you may have is if Mr Cummins put a ball bearing into the throttle shaft end to stop you tampering with the fuel pressure.
Some balls were soft and could be drilled....some were hard and needed an oxy torch to spit them out.......WARNING!!!.....point the throttle shaft away from humans and delicate receptacles
if you need the oxy torch option!!

Newto




By terry sillik - Monday, November 25, 2019 1:34 PM
Are you checking boost under a load? terry
By Tattoo - Wednesday, November 27, 2019 1:49 PM
Yes. All of my gauge readings were taken while driving. Thanks.
By Tattoo - Thursday, November 28, 2019 12:04 PM
Very helpful Newto! Thank you.

I had the opportunity to work on the fuel pump today and have a Thanksgiving feast with my family. It's been a pretty good day!

I discovered that my fuel pump button is a #27. On your advice, I pulled the throttle shaft and found that the fuel opening is just over 1/2 way open. By eye, I'd estimate that it's 55% open.

There's a seller on ebay offering #10 and #5 buttons with a housing gasket and a Cummins sticker! for $25. I'm inclined to order a 10 button and see what it does for me. Not sure what I'll do with the sticker though.

Maybe open up the throttle shaft a bit too?


What do you think?

Also, I found some great videos that explain the pt fuel system on youtube. Here's a good one.

By Tattoo - Thursday, November 28, 2019 12:57 PM
After looking around a bit, I'm finding other buttons available online... #15 #20 #22
By terry sillik - Thursday, November 28, 2019 1:15 PM
Tattoo (11/27/2019)
Yes. All of my gauge readings were taken while driving. Thanks.
By driving do mean with a trailer and load? terry
By Tattoo - Thursday, November 28, 2019 2:50 PM
terry sillik (11/28/2019)
Tattoo (11/27/2019)
Yes. All of my gauge readings were taken while driving. Thanks.
By driving do mean with a trailer and load? terry


So my first post in this thread contains gauge readings that were observed while pulling a loaded trailer on the interstate.

The post I made a few days ago with a picture of the fuel pump and fuel pressure readings was done after driving the tractor bobtail.

Any thoughts?

Thanks.

Bryan
By Newto - Friday, November 29, 2019 2:42 PM
Tattoo....

#10 is WAY too much.....in a 444 pump that one puts out around 240 psi........

I would try the #20 button....you can then play with the throttle shaft opening to either increase or decrease it a little.

Button sizes don't go down in single number increments.....from your #27 they drop to a #25 then #22 then #20 then #17.

the #20 should be close to the money.....

cheers,

Newto
By Geoff Weeks - Saturday, November 30, 2019 3:21 AM
Tattoo (11/28/2019)
After looking around a bit, I'm finding other buttons available online... #15 #20 #22
You can order any button made from Interstate McBee, find a dealer in your area or use an online dealer. they are cheaper than buying off E bay and you can order a selection so you can dial it in.
By Tattoo - Sunday, December 08, 2019 6:59 AM
Somehow Newto correctly diagnosed my truck problem from the wrong side of the planet!

I installed the number 20 button (bought a few/ 20 was the 1st one in) on my fuel pump yesterday and took the truck out for a ride. On the fuel pressure gauge I picked up roughly 30 psi. The gauge now reads between 175-200 psi with the throttle wide open, approaching governor rpm limit in high gears. The needle on the pressure gauge is steady as fuel pressure builds to roughly 100 psi, but under higher load and above 150 psi it flutters a lot. Turbo was able to produce a little more boost under the same conditions... I recorded 18-19 psi max (about a 2-3 psi gain). I'm driving the truck bobtail so I'll end up at top speed in high gear and we're done building boost at that point.

I haven't yet been able to truly test it pulling a loaded trailer and we don't have another marching band competition scheduled until February so it'll be a while.

I suspect that the truck will pull the trailer better this way and build more boost while doing so. Does that make sense Newto?

I'm also considering sending the pump out to be rebuilt and bench tested if I can find someone to do it. The excessive fuel pressure gauge fluttering has we wondering if the fuel pressure legitimately is surging under max load.

Thanks again for the help!
By Newto - Sunday, December 08, 2019 10:06 AM
Well done Tattoo!!

Its not uncommon for the gauge to flicker like that when not under constant full load.We used to use the average of 1/2 way between high & low as a gauge....

200 - 175 = 25 divide by 2 = 12.5 + 175 = roughly 187 psi .....very close to the money.

Rather than spend money at a fuel shop if you have spare cash I'd give that old VT turbo the boot & fit a Schwitzer/Borg-Warner either 4LHR or HT3B turbo.

If you fitted a p/n 196390 4LHR Turbo you won't get into any arguments about whether you need auto-lash jake screws....because you don't!!

That VT Turbo you are running is pretty primitive.....(and it looks like its still struggling to make decent boost). Even a single entry HT3B turbo will work better than what you have.

Just putting it out there!

Cheers,

Newto

PS....Do you believe I can fix Cummins standing on my head down here?.........lol
By Geoff Weeks - Sunday, December 08, 2019 11:36 AM
Tat, don't know where your at, but Spencer Diesel in Spencer, IA did a bang up job for me. I mostly take care of my own pumps but this one "grenadied" on me under load and I needed a whole new pump.
When they saw mine, they replied they had never seen so much broken in a pump that came off a running engine. They came highly recommended to me and I found the work to be top notch, have over a year in on the new pump and the engine runs great.
By Tattoo - Monday, December 09, 2019 3:57 PM
That's a great recommendation Geoff. Much appreciated! Btw we're out of York, SC just a few miles south of Charlotte.
By Tattoo - Monday, December 09, 2019 4:03 PM
Newto (12/8/2019)
Well done Tattoo!!

Its not uncommon for the gauge to flicker like that when not under constant full load.We used to use the average of 1/2 way between high & low as a gauge....

200 - 175 = 25 divide by 2 = 12.5 + 175 = roughly 187 psi .....very close to the money.

Rather than spend money at a fuel shop if you have spare cash I'd give that old VT turbo the boot & fit a Schwitzer/Borg-Warner either 4LHR or HT3B turbo.

If you fitted a p/n 196390 4LHR Turbo you won't get into any arguments about whether you need auto-lash jake screws....because you don't!!

That VT Turbo you are running is pretty primitive.....(and it looks like its still struggling to make decent boost). Even a single entry HT3B turbo will work better than what you have.

Just putting it out there!

Cheers,

Newto


PS....Do you believe I can fix Cummins standing on my head down here?.........lol






Very interesting! Perhaps I'll ask Santa to slide me a big old turbo under the Christmas tree. I feel like I've been reasonably good this year!
By Geoff Weeks - Tuesday, December 10, 2019 2:48 AM
Tattoo (12/9/2019)
That's a great recommendation Geoff. Much appreciated! Btw we're out of York, SC just a few miles south of Charlotte.
The guy who recommended them to me, said people send their pumps to them from all over the U.S. I just put mine in a bag (after draining as much fuel out as possible) placed in a box and UPS'd it to them. Never went and saw their shop.
By Tattoo - Sunday, February 02, 2020 5:32 AM
Ok here is my long overdue update...

I took Newto's advice and replaced my VT50 turbo with a Schwitzer 4LHR. I was able to find a brand new BorgWarner unit at M&D Distributors online for about $800 shipped. The turbo was basically a bolt-on. I only had to make slight adjustments to the orientation of the turbo's intake and exhaust housings to make everything line up. I made some noticeable gains with the installation of the turbo. For one, you can hear this turbo through the exhaust stacks whereas the previous turbo was inaudible. Anyone who says they don't like the whistle of a turbo is lying and cannot be my friend. This one sounds good! Boost starts to build much sooner in the rpm range (it's almost immediate) and initially maxed out at about 20 psi.

http://forums.aths.org/Uploads/Images/586de465-aab8-4179-8d18-f02a.jpg

Because I'm greedy and I always want more power, I went ahead and sent my fuel pump out to a local diesel shop in Charlotte, NC. I felt good about the shop because these guys recognized the pump code on it, just hadn't seen it in a while. We agreed that the strategy would be to rebuild it to spec. plus 10% max fuel pressure. The pump builder called me at the end of the week and stated that most of the internal hard parts were just flat worn out. He replaced the throttle shaft, tach drive and bushing, flyweight assembly and some other odds and ends. He finished the rebuild and ran the pump on the test stand with the #20 button that I had previously installed. 285 psi fuel pressure was the result. He did go back in and replace the button to get the fuel pressure down to 205 psi. on the stand.

What I learned is that by installing the #20 button as I had done earlier to increase fuel pressure, I was covering for a worn pump. Remember that I was getting about 185 psi fuel pressure on the truck with the 20 button, where the pump shop was getting 285 psi fuel pressure after the rebuild with the same button.

All of that said, I pulled the trailer yesterday for the 1st time this season. Truck is running strong. Throttle response is crisp. Turbo boost is up to 22psi. There is no smoke from the stacks after the engine is warm and my fuel pressure gauge shows about 180 psi average max.

I'm very happy with how the truck is running, but I think there may be a bit more that I can squeeze from this engine. I know it's not going to make 400 horsepower, but I do want to get the most power I can safely get.

1st, I'm considering another button change. There seems to be a slight discrepancy between the pump shops max fuel pressure (205) and mine on the truck (180). I feel like that's probably the difference between running the pump on a stand vs. on the engine, or different pressure gauges, or both. I'd like to hear some thoughts about safe max. fuel pressure on a small cam 855.

2nd, I've read a lot about running another fuel line to the front cylinder head. The theory makes sense to me. Who has done it and what were the results?

3rd, I'm wanting to install a divided turbo mounting flange gasket. This apparently is a gasket that does not exist. I've looked everywhere. A while back I installed an updated pulse exhaust manifold with divided exit. Now I've installed this nice turbo with divided entry. I used the open undivided mounting gasket that came with the turbo, but I never felt good about that. In reading about the theory of how the pulse manifold works and the advantages of a dual entry turbo, why would you want to bridge those 2 distinct ports with an open gasket? I may end up making a divided gasket to see if there's any increase in boost. Any thoughts?

Thanks for the help along the way. I'm doing my best to record my results in the hopes that it may help others that come later.
By Geoff Weeks - Sunday, February 02, 2020 6:37 AM
Re dual fuel lines.
I have done it and also did dual return on one engine. Long and short is: I didn't notice enough for the bother of routing the line behind the fan drive.
Divided turbo and pulse manifold: the idea is to keep the volume smaller on either side to help with turbo lag, not to totally isolate the two chambers, I doubt you'd see any gain and you most definitely don't want that section of the gasket to "blow out" and pass through the turbine!
By Newto - Monday, February 10, 2020 10:11 AM
What Geoff said about the divided turbo mount gasket is right !!! For a time Cummins had a divided turbo mount gasket which then got superseded to the current open gasket p/n 3069177. So I'm guessing they may have had the odd centre strip burn out & cause some issues.
Schwitzer/Borg-Warner make the turbo & they supply an open gasket so trust their judgement.

As for dual fuel lines........when we were racing trucks (tractors) we used dual fuel lines only because of the amount of fuel we were trying to get into the cylinders....as Geoff said again...I doubt you would notice any improvement with the fuel pressures you are running.

Now ..........fuel pressure..........fuel pressure is the same as using a watering hose........turn the tap on full with no gun or trigger on the end of the hose and you just get a large flow of water but not much pressure so the water literally just falls a short distance from the end of the hose.
Place your finger over the end of the hose to create an orifice and the water squirts a lot further......same theory with fuel pumps.

So, if the pump room had 205 psi on their pump stand and you only have 185 psi on your engine then the orifice your pump is pushing into is larger than the pump stand so the pressure drops.
Only variable place you can lose that pressure is via the injectors.
First thing to do is re-check your injector adjustment !!!!
Using the outer base circle method with an inch pound tension wrench set the injectors to 72 inch pound as per Mr Cummin's specs then re-check your pressures.
If the injectors are a bit loose you will lose pressure.......then if you are still below the pump rooms 205 psi you can then play with button changes to get the 205 psi that they had......DONT EXCEED THAT PRESSURE THO!!
If the injector set doesn't bring the pressure up then it means the injector tolerances on the Barrel & Plunger are a bit loose so buttoning the pump will compensate for that.

Enough for now........hope that helps.

Newto


By steeltracs - Sunday, February 23, 2020 4:28 PM
Newto is right on with his info. Have you up graded to an after-cooler? By adding one it will drop your pyro-meter temps greatly enabling you to squeeze more power out of the small cam. Any after cooler from a big cam should work with slight plumbing mods if you have a FFC block and water rail ( more challanging if non FFC but I have made it work with custom made water pipe).
By steeltracs - Sunday, February 23, 2020 4:37 PM
Newto is right on with his info. Have you up graded to an after-cooler? By adding one it will drop your pyro-meter temps greatly enabling you to squeeze more power out of the small cam. Any after cooler from a big cam should work with slight plumbing mods if you have a FFC block and water rail ( more challanging if non FFC but I have made it work with custom made water pipe).