Surging power 237

[Freightrain]

Well, okay.  Something is still awry.

New turbo, works fine.  I readjusted the linkage to get a better WOT on the pump.  Second trip out this past weekend over to Pittsburgh again(just out past Watts).  Trip over was fine.  Heading home Sunday evening I got about 1/2 way across the Pike and it suddenly started the "dropping power/boost" issue.  This seemed a bit worse then a month ago.  Seems the longer grades it would suddenly drop boost/loose power, then after a couple seconds come back.  It would repeat this randomly mostly on hills not so much on level ground.  But I wasn't into the power either.  It made it home okay, just lost speed on the hills.  Once I got off the highway it was fine in town.  Pulled up to speed easily and never hesitated.

Now, I threw a set of filters on it today just because.  They were a couple years old, but with the limited mileage they were far from used up.  I cut them both apart and neither had gunk/sludge in them.  Fairly clean looking pleats.

Secondly, I've noticed another issue this summer.  When letting off power to shift, the rpm drops like it should, but then as it gets to idle will just surge ever so slightly.  I have had to adjust my shift timing as typically it screws up my main box shifting. Compound not so much as it doesn't take as much rpm drop to get into gear.

The return spring on the pump arm is STIFF.  No way that it is not pulling it back tight.  I've readjusted the pedal a couple times to make sure everything is just right.  It does not appear to be holding the throttle up any.

I took it for a quick spin tonight after the filter change and it pulls fine.  I get it into 5th lo and lean into it and it goes up to 15# and just pulls away from traffic easily(kinda fun to do actually as you know the cars aren't expecting it).   I know I won't really see any difference til Saturday when I head out on the road again.  I was wondering, could the governor be an issue?  Could something in the pump be acting up?  Or is it just fuel related?  I don't have a pressure gauge and I know that would be a good think to have right now but don't have time to get anything installed and run into the cab by Friday night.

Pretty much all the fuel lines are within a few years old so I can't see that being an issue. Don't think the fuel pickup in the tank is a problem as the last trip is was acting up going over and there was more fuel them coming home.   It only seems like it happens under extended load, not short bursts.  I only have a couple more trips this year then I can tear into it if need be.

[Hobert62]

No answers, but some ideas anyway.     Are you sucking an intake hose or boot shut starving it for air?    If your fuel lines are a few years old they where from your other motor.   Is the suction line big enough for the turbo motor during a pull?     When it acts up what does it do if you take your foot off the throttle for a few seconds then get back in it?   

[Freightrain]

Intake is not closing up.  It is steel pipe with silicone connectors.

The motor has run strong with no issues at all most of the summer.  Just started the loss power about a month ago.

The lines from the tank to filters and then injection pump are all existing, but replaced them a few years ago so I know they are not damaged.  I don't think size is an issue as it ran fine up to this point.

If you lift off the pedal, then push again it doesn't really change, but by that time it would usually start to take off again anyway.  It gives the sensation of no fuel.  With the window down, you can just about here it "chug" as it slows down, then it revives and sounds strong again.

[41chevy]

Maybe look in the tanks?  Something by the pick up tubes that goes near it when angled on hills?   ODD

[j hancock]

Governor could be causing the surging.  Pump not keeping up on long pulls?  Pres. gauge will tell the tale.

Seems odd you go over fine and have issues on the way back.  Someone messing with you at the track?

[theakerstwo]

As for as the surge in the governor that is common with the pump.Its some wear in the governor and i have seen it many times.So with out spending alot of money on the pump rebuild i would live with it.As for as the loosing power i learned years ago you can guess all of the things that is not wrong with it but no way of know what it is untill you start testing.Its a fuel related problem and you need to get you a 100 psi liquid filled gauge which here they cost about thirty dollars.Run a # 4 hose from it being tied to the wiper arm down to a fitting that is between the sec filter and injection pump.I made a fitting years ago from two # six swivels that will go in line of the hose.Running down the road you watch that gauge and can learn what is going on there.Bt the psi dropping off with the lost of power it will be a restriction or sucking air or the check valve or some called it over flow valve having a problem.Another thing that i had a problem with on my B model when i installed a larger engine is on a damp night the little air cleaner i had on there that was made for the 673 engine was frezzing up and causing a lack of air to the turbo.I had a pryometer and it  was easy to find the problem.

[fjh]

Check the tank Vent ! ? I  Had a plugged  vent  recently, chased it for hours! cheap and easy if you check first instead of after you change the expensive stuff! 

[Freightrain]

Thanks for the ideas Glenn and Fred.

The vents are easy, so I'll check those first.
Yes, it drops boost as it looses power.  Doubt it is air cleaner freezing up as it has been plenty warm outside yet.  I will get a gauge and see what happens.  It is kinda random and would have to take a long drive to hope to have it repeat.  I might look into getting an electric version so I can mount the gauge permanently in the cab?

That overflow/check valve, is that the little brass fitting between pump and return line to tank?  Maybe it is returning more then it should?  Loosing fuel and power.

[theakerstwo]

Yes the over flow valve is the fitting on the return side of the pump were the return to the tank is connected.It its a old valve you can open it up to check and see if the spring is broken.You also have check valves in the suppy pump which may be hanging open causing low fuel pressure.A on and off lost of fuel pressure can be caused by a object being sucked up in the pick up tube. On my work truck I had same problem maybe three years ago so so i came home early and open up some fuel lines to find a large hard shell bug sucked up thru the supply line and into the inlet fitting of the primary fillter. I guess he had fell into the tank when fueling.

[Freightrain]

Interesting.  I know the hand pump was dried up when I got the motor.  I had to get it working(tear down/lube up) to prime the system to test run it.  I had the supply pump apart and saw the 3-4? check valves(forget exactly).  Might check those also.  Might be just weak enough that under a heavy draw it is not pushing enough fuel.  Like I said, around town is fine.  

I don't think it is the pickup tube as it won't do it just sitting or driving around town.   Still like to put a gauge on it to see.  I know autometer offer electronic high pressure gauges.  Not sure if the pulsing will make them hard to read(digital readout), thus a liquid filled mechanical would be better.  They offer an isolator kit for car fuel pressure, but likely not rated to 100 psi.

[Freightrain]

Just as a side note, I have a big water separator spin on filter next to the drivers tank, then the typical original secondary(canister) up at the pump.  Doubt anything could get very far up the line with it set up this way.

[gearhead204]

as said before check fuel flow, be sure to check the filter heads, I've seen chunks of rubber (from a failing hose to a plastic candy wrapper ) caught in the drillings  or rust flakes caught in the banjo bolt drillings, also some times the banjo bolt may have a screen or check valve located in them so make sure all fittings are clean. I will often pressurize the tank and check fuel flow thru all related hoses then the low flow will often be easily spotted.    

[farmer52]

Larry,

In addition I am thinking you might be getting air in the fuel system.  Check your fittings and lines on the upstream (suction) side of the transfer pump.  A fuel gauge on the supply side is a good tool.

[Freightrain]

I'll check all the fittings.  

 

Edited September 27, 2016 by Freightrain

[Freightrain]

Are those little check valves interchangeable?  Could I use the one off my 673 or are they rated at different pressures?  Are they typically available new, easily? I have a VIN from a firetruck or just use the pump number?

[gearhead204]

I have never heard of  pressure regulating check valves ( but some days I don't know squat) I would say swap'em

[Freightrain]

Picked up a gauge at Summit yesterday and a nylon tubing kit to hook it up.  Just need to dig through my fittings box to hopefully have enough to attach it?  Hope to get into it Friday night, as I have to leave Saturday morning!!  Ugh.  Got a 2 hr drive, I'm keeping my fingers crossed........

[theakerstwo]

What most guys did was was take a #6 swilve and cut back short and then braze a #6 brass fitting to it and that way you have a #6 male on one end and a #6 female on the other end of you tear fitting.Then put it in line of you line from the filter to injection pump.have a port from the fitting to your gauge hose.That way you are reading after the filters.Also this reading needs to be taken unload.

[Freightrain]

Well, I found a 1/4" T that I could thread into the pump, it gave me two ports.  One for fuel in and one for gauge.  I can use 1/4" plug to seal it off when not needed.

I started the truck, it runs at about 15# at idle.  Any fluctuation of RPM does not really make it move a lb or so.  Good?  Bad or Ugly?

I tried to remove the check valve.  Wow, that's been in there for 40 sum years and wasn't coming off without a fight.  I gave up on it for now, will wait to see if anything else comes up before trying to unscrew that from the pump.

I pulled two of the check valves from the fuel pump(the top two-easiest to get to).  Look okay, springs intact.  Surfaces are smooth and flat.

[Freightrain]

Well, looking in my book, it says I should have 20# of fuel pressure.  So I pulled the pump off my 673 and put it on.  Yup, still 15#.  Well, going to drive it tomorrow and see what it does under load.  I took a quick run up the road bobtail and with a little boost the fuel pressure really falls off, like under 5# or so(hard to read across the cab and out the window as it is mounted to the air cleaner).  With the possibility of rain I couldn't strap it to the wipers!

Gotta get to the race tomorrow so wish me luck.

[theakerstwo]

Larry remenber it can be restriction or air and its easy to make a sight gauge with a clear plactic hoses.If it was you over floe valve bad it wouldnot have 15 psi at idle.A way to checkthe overflow valve with out pulling it off is use some vise grips and mash the fuel return line to the tank partially closed.The take a reading and if the valve is bad then the pressure will hi or stay up.Done close the return off too much.This will prove if you suppy pump is good and tell you what the overflow valve is doning. That is if you have a good supply to the supply pump.

[Freightrain]

Should the pressure stay at 15# or drop off with acceleration?  How low is normal/OK?

Lines are all near new so shouldn't have a problem.  I pulled vent line off and it is open.

Going to top off tanks.  Didn't have issues when full.  Maybe have issue with suction line in tank?

Edited October 1, 2016 by Freightrain

[theakerstwo]

I wish that i had a dime for all hoses that i have found in my life that was new but has a flapper over one end so dont forget that.I always said that if you have 28 to 30 psi under load you will get full power.On any engine i dont want the pressure to drop at full thottle unload more than 5 psi over a no load condishion.

[fjh]

9 hours ago, theakerstwo said:

I wish that i had a dime for all hoses that i have found in my life that was new but has a flapper over one end so dont forget that.I always said that if you have 28 to 30 psi under load you will get full power.On any engine i dont want the pressure to drop at full thottle unload more than 5 psi over a no load condishion.

Agree with that statement Glenn!  15  is min I want to see wound up I like 25-30 If ya  have to disassemble the drain back valve and stretch the spring! 

[j hancock]

Mack OEM spec is between 18-24 psi at full load for a 237.