E7 Mechanical Stumbling & White Smoke Intermittently

[Salpolit]

Hi everyone,

We recently installed a new to us E7 mechanical engine in our RD as our old engine bit the dust. The new engine runs fantastic, no blowby or anything. Main issue is when revving the engine up quickly, it will stumble a bit and blow some white smoke but then it will "catch up" and everything will be fine. What is weird is when you go slow revving the engine up, it doesn't do it.

Also, when the engine is fully warmed up it barely does it if at all. Only seems to do it when colder and without much of a load on the engine. Other symptoms/potential issues are cylinder 2 & 3 fuel lines are currently leaking out from the head so we are going to replace those lines as well as pull the injectors and install new O-ring kits on them to ensure they are sealing properly. Is there anything else that can cause this?

I read on the VMAC I engines the econovance can cause this issue but being that this is fully mechanical without any wires going to the pump I can't see how that is a possibility.

What do you think?

[Joey Mack]

''fix what you know is broke''  pop test the injectors, that is if anyone has the tool and the knowledge,  I usually remove the fuel lines to inspect the ends for a groove worn into it from the injector and the injection pump..  I use 320-400 grit emory cloth to dress the ends up, and blow them out with brake cleaner. the straw for the brake cleaner works good to get that done.  

[Salpolit]

Thank you. I'm going to check those out hopefully it's something stupid! I'll report back what we end up finding

[JoeH]

How many hours are on the motor? Any clue? I think you're headed in the right direction trying to take care of the leaky injector lines. I'd start there before pulling injectors, but my maintenance history relies heavily on how durable Mack trucks are.  

[Salpolit]

@JoeH no clue unfortunately. Motor seems healthy, zero blowby and holds 70psi oil pressure when cold and 30 when hot. Was hooked to an Allison in an MR before this so hopefully she had a decently easy life.

We won’t see the new lines til Friday so my plan of attack is yank the injectors, check them over, and if they look suspect we’ll just throw a new set in along with the new lines. Fingers crossed!

[fjh]

12 hours ago, Salpolit said:

@JoeH no clue unfortunately. Motor seems healthy, zero blowby and holds 70psi oil pressure when cold and 30 when hot. Was hooked to an Allison in an MR before this so hopefully she had a decently easy life.

We won’t see the new lines til Friday so my plan of attack is yank the injectors, check them over, and if they look suspect we’ll just throw a new set in along with the new lines. Fingers crossed!

The injectors should be pulled!  in my experience fuel leaking at the line at the head, alot of the time its coming up the return side of the injector past the oring  and the fuel lines are not the issue they seldom fail ! Just sayin! and with the stumble Replace or pop test as Joey mentioned ! Wouldn't buy lines till I replaced at least The orings on the injectors or the injectors them selves! by the way you need only the top two orings on the injector the third oring is not necessary they will only supply you with  the two orings and the sealing washer now! I have used this technique with good results! (  As you install the injector snug the injector into place then loosen the the hold down leave it just snug Then tighten the line . then torque the injector after the line is tight this allows the injector to self align if it needs to before its torqued ) 

Just something to try!

[Salpolit]

Thanks guys. Pulled injectors today and wow they were bad. All loaded with carbon and dripping fuel. Hope we didn’t wash down any cylinders too bad!

6 pack of new injectors on order, hoping to have them in by Tuesday next week. I’ll report back how it goes 

[R.E.D]

Use some grease or Vaseline to make sure  the crush washer sticks to the injector tip .Torque lines to appropriate torque specs , if you're replacing them it should be with the new single nut style.While your there , wouldn't be a bad idea to check overhead.Just my .02 ¢ .

Red

[Salpolit]

No luck! Still runs bad with new injectors. It runs great when holding RPM at any rpm but stumbles, smokes, and backfires a bit when stomping on it.

I noticed this solenoid looking thing from a picture I have on the back of the old injection pump on the old engine. Issue is I already sent that engine back so don’t have a clue where it goes/what it does.

Would this affect the pump or timing at all?

[Salpolit]

This is what our current pump setup is. am I missing anything that could affect the timing or anything related to this issue?

[fjh]

There is no timing advance on what you have how ever you can check and set the timing!   Just wondering is the engine equipped with dyna tard?  hard to see there! If so pull the engine brake relay or disconect at the head and see if this changes your issue! I see two pictures here one with a jake switch replacing the original pump cover swiTch ! Is the clean one the engine you are using now???  I think you have a dynatard switching issue here! It will make the engine brake apply in a light load application if left on and not set correctly ! ! Disconnect at the head to be sure! a rubbed wire to ground will set the thing off!  If the stumble goes away you have your culprit!   NOTE If your using the built in switch on the pump theres a specific way to set its a bit tough to explain but will try  if you confirm what your up too there!

My opinion!

 

[Salpolit]

The old engine had a Jake on it, this one doesn’t. That makes sense what that solenoid was for, actuated the Jake’s! Totally forgot about that

[Salpolit]

I have a call in with a company we use for diesel injection services. He told me idle lift pump pressure should be approximately 25 psi and go up from there as RPMs raise.
 

Currently idle is at 18 psi and then when we rev the engine up, the pressure increases slightly but then when it starts stumbling, it goes down towards 15 psi even while the RPMs are up. Once the stumbling clears up, the pressure will go past 30 psi.

 

I’m hoping we are on the right track here, thinking bad lift pump?

Edited October 10, 2023 by Salpolit

[fjh]

Yup 15 is too low! You need to be at least 20 full load! You also need to be sure the tank is vented and have no bad lines prior to the pump ! Any restrictions prior to the pump will cause what you got there! The spring in the return T there could be weak or broken also take it apart and look before condemning the pump!

[doubleclutchinweasel]

There you go!

[fjh]

On 10/10/2023 at 9:21 AM, Salpolit said:

I have a call in with a company we use for diesel injection services. He told me idle lift pump pressure should be approximately 25 psi and go up from there as RPMs raise.
 

Currently idle is at 18 psi and then when we rev the engine up, the pressure increases slightly but then when it starts stumbling, it goes down towards 15 psi even while the RPMs are up. Once the stumbling clears up, the pressure will go past 30 psi.

 

I’m hoping we are on the right track here, thinking bad lift pump?

So did you nail it?

[Salpolit]

Waiting for the new lift pump to arrive, hopefully Monday it’ll be here. Going to throw that in and see if it changes anything. Fingers crossed!

[JoeH]

My 95 e7-350 mechanical had a bit of a stumble at one point.  Almost sounded like the name brake was trying to come on under acceleration.  I changed the fuel filters and it went away. Been 3 years now? Could be a lift pump at the borderline of spec, the truck does have 24,000 hours.

[Salpolit]

Update:

Lift pump finally arrived. Changed that and no change. Decided to run the overhead, found most of the cylinders loose but 2 of them were tighter than normal. Adjusted everything into spec and that made the engine run better and eliminate any haze when idling.

Still does the misfire though. I took the truck for a drive today and noticed that it only does it when taking off and starting to build boost (or revving it at idle). Once the truck is running down the road, you can lug the engine down and everything and it won’t sputter again until it has a “light load” condition like idling or coasting.

I noticed it does it significantly more after coasting in gear. Could this be some type of a stuck valve or wet stacking?

[JoeH]

Humor me, change the fuel filters. If you already did, then do it again.

[Joey Mack]

Yep... 

[fjh]

On 10/19/2023 at 3:05 PM, Salpolit said:

Update:

Lift pump finally arrived. Changed that and no change. Decided to run the overhead, found most of the cylinders loose but 2 of them were tighter than normal. Adjusted everything into spec and that made the engine run better and eliminate any haze when idling.

Still does the misfire though. I took the truck for a drive today and noticed that it only does it when taking off and starting to build boost (or revving it at idle). Once the truck is running down the road, you can lug the engine down and everything and it won’t sputter again until it has a “light load” condition like idling or coasting.

I noticed it does it significantly more after coasting in gear. Could this be some type of a stuck valve or wet stacking?

Agree with  the filter thing too! Also did you check pressure after the pump change did it come up to spec?

[Salpolit]

We replaced fuel filters multiple times, only thing I can think is maybe I have some bad diesel. Running K-100 in it seems to help.

Loaded 14 ton in the truck today and with a load on it, it barely does it if at all. Seems to only do it under very light load circumstances. I think I’m going to live with this for a while and hope that running some fresh fuel through the truck will help. The fuel is only about 3 months old and it came out of the same tank as our other fleet trucks. But moisture maybe got into the tanks while the truck sat for the engine swap.

I’ll report back when we have a resolution!

[Joey Mack]

Have you looked in the tanks for algea and worm's?

[Salpolit]

Haven’t checked yet, I’ll take a look tomorrow to see what’s in there