Eratic behavior from an 85' 6.2 (more below) requesting help please (Two vids in one)

[Nycxjeremyy]

This is genuinely confusing me, the first half of the video is of it idling, it then began to surge out of nowhere, this is all after I changed the fuel filter, added howes additive and used diesel 911 to ungel the fuel last week, it actually ran relatively well after doing that and then today it began to surge again.



The second video is of me starting it after leaving it alone for 1.5 hours (30°F), notice how it behaves when attempting to start



Failing IP? Lift pump failure? Air in the lines? I'm not sure anymore, this is driving me insane, i don't know anymore, any help would seriously go a long way.



Video: https://www.reddit.com/r/Diesel/s/tkmbTC6sbC

[Robyn]

How many miles are on the injection pump ????

It sounds like the issues could be a failing injection pump.

Has the rig sat for a long period of time ????

Bad fuel left in the tank can create all sorts of problems.

Air in the injection pump will purge through pretty quickly.....

Gelled fuel can cause problems .......Before you get into tearing things apart.
Pump out the fuel tank and replace the fuel with good clean winter blend fuel.....
Make sure you have clean fuel coming to the filter and to the injection pump.

If the issues persists then the injection pump is likely the cause of the surging.....

Keep us in the loop.

[Nycxjeremyy]

1. Motor has 78K miles on it
2. Not since I bought it last year
3. It has winter diesel since where im stationed at (SD) it can get very cold so all the pumps have em, that and I run Howes additive to help aswell

------
So we actually took it to the on base DIY shop and did a smoke test, there was a indeed a bolt missing on my turbo which we fixed immediately, but the surge was not remedied



I took it out for a test drive and when i rolled up (letting off the throttle) it began to surge again



Missing bolt on Turbo: https://photos.app.goo.gl/iYM9csxDiYaNyAw56



Surge at idle: https://photos.app.goo.gl/G3vtcf6rsojggC4g7



Hard start (took 7 tries):

https://photos.app.goo.gl/UshScC3UKLt8p5EN8

https://photos.app.goo.gl/Ahb3dKVVzBVuZA1f9





I definitely have a faster time getting up to speed, but the surge is still there, a friend of mine who does own a 6.2 is adamant it's a failing IP, but I've been told that it could be the Lift and/or Fuel pump, but I don't know anymore, I'm about to throw in the towel here.



If it is an IP, it's going to be an expensive repair, im just an E3, don't necessarily have all the funds in the world

[Nycxjeremyy]

1. Motor has 78K miles on it
2. Not since I bought it last year
3. It has winter diesel since where im stationed at (SD) it can get very cold so all the pumps have em, that and I run Howes additive to help aswell

------
So we actually took it to the on base DIY shop and did a smoke test, there was a indeed a bolt missing on my turbo which we fixed immediately, but the surge was not remedied



I took it out for a test drive and when i rolled up (letting off the throttle) it began to surge again



Missing bolt on Turbo: https://photos.app.goo.gl/iYM9csxDiYaNyAw56



Surge at idle: https://photos.app.goo.gl/G3vtcf6rsojggC4g7



Hard start (took 7 tries):

https://photos.app.goo.gl/UshScC3UKLt8p5EN8

https://photos.app.goo.gl/Ahb3dKVVzBVuZA1f9





I definitely have a faster time getting up to speed, but the surge is still there, a friend of mine who does own a 6.2 is adamant it's a failing IP, but I've been told that it could be the Lift and/or Fuel pump, but I don't know anymore, I'm about to throw in the towel here.



If it is an IP, it's going to be an expensive repair, im just an E3, don't necessarily have all the funds in the world

[Nycxjeremyy]

Thoughts sir?

[Yukon6.2]

If it is the IP they are cheap if you shop around, i used to buy new military pumps off of eBay for less that $300.00
I would look for an air leak in the fuel system.If you have the original stanadyne fuel filter with the rectangle filter the base has a spot that crud sits in and will corrode through the aluminum.
My 90 did that, made for hard starts, which got harder the longer it sat. Can't remember weather it surged or not.
I drilled out the spot and threaded it for a 1/8" pipe plug, of course its on the bottom of the filter base. It didn't leak fuel out as the suction through the corosion just let air in.

[Nycxjeremyy]

I already have an IP from a CUCV on its way, my boy who owns a CUCV 6.2 gave it to me for $200.

As for the Fuel Filter, it has a spin on with a water separator as the previous owner installed it, the fuel filter was swapped out last week (added additives and everything) and the 6.2 still revs up and down only to then loose power

[JohnC]

Does this engine have EGR? Faulty EGR has been known to cause surging.

[Yukon6.2]

I already have an IP from a CUCV on its way, my boy who owns a CUCV 6.2 gave it to me for $200.

As for the Fuel Filter, it has a spin on with a water separator as the previous owner installed it, the fuel filter was swapped out last week (added additives and everything) and the 6.2 still revs up and down only to then loose power

You will have to change the shut off solenoid from 24V to a 12V one. It's not hard you just have to be careful to make sure the shutoff solenoid gets install correctly.

[RudyJ]

Sorry your having so much trouble with your 6.2. I'm no whiz at the 6.2 but if it all started when you changed your fuel filter, I would start there. It could be the water separator, or the fuel filter itself. Just a thought, hope it helps. RudyJ

[More Power]

...this is all after I changed the fuel filter, added howes additive and used diesel 911 to ungel the fuel last week, it actually ran relatively well after doing that and then today it began to surge again...

Air in the fuel lines, as the cause of surging, should be eliminated before jumping to the pump replacement conclusion. If the engine ran well before this incident, this new surging problem is not likely to be because of a failing fuel injection pump.

How much time has the engine been running since the surging began? These fuel injection pumps are little hydraulic pumps. Diesel fuel is not compressible, but air is. Air in the system messes with fuel delivery in a big way, and can create a range of problems.

Air, if that's the problem, should eventually work its way out. I'd also look at supply pump operation as a potential contributor. A bad lift pump can cause some of this, but...

[Robyn]

Put a clear plastic tube on the return line from the top of the IP
Bubbles in the return flow are a tell tale sign of trouble.
An air leak into the supply line between the tank and the lift pump.
Possible air leak in the tank in the fuel level assembly and pickup tube.

Give the clear tube a try and see if you get bubbles in the return line.....

[Nycxjeremyy]

Video of the air test is up! Please let me know whay you all think



https://www.reddit.com/r/Diesel/s/rZMjyYOR5y

[Yukon6.2]

Hold your throttle wide open to purge the air out of the pump faster...
Looked like it cleared up when it was running

[DmaxMaverick]

If you're getting that air at every or most cold starts, check/change the fuel filler cap. It must be a "Diesel Fuel Only" cap, and in good condition. A gasser cap vents differently, and a failed vent on a Diesel cap can cause issues with the fuel system just the same. A minor leak that would otherwise go unnoticed, causing no issues, can be exploited by a poorly vented system.

[Robyn]

That huge amount of air is getting into the system prior to the lift pump.
A fuel line between the tank and the lift pump.
Rubber hose between the frame rail steel line and the lift pump
The hose at the tank connection or the line on the tank sender assembly and pickup sock.
I have seen the steel line in the tank assembly crack or rust through

IF YOU ARE CAREFUL VERY CAREFUL
You can add a TINY bit of air pressure to the tank filler and see if fuel leaks out on the ground....

Possibly a failed diaphragm in the lift pump ....These usually leak fuel....not always

You should not see any air bubbles in the line NONE

[RudyJ]

which filter did you replace, the one on the firewall or the one on the intake? Is the one on the firewall square or round. I feel like your problem is in the filter or filter housing. I'm sure you filled the filters with diesel when you installed them, but you never know. Anyway I think they had trouble with those square ones in the past. Did you oil the filter gaskets before tightening them up, it could be getting air around the gasket or could have had some trash or rough spot on the filter housing. When I change mine I put auto transmission fluid and diesel in them as the transmission fluid will help clean the injectors. Those are a few things to check, it doesn't take much to give you an air leak. Hopes this helps.