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

 

[dbrannon79]

@nycxjeremyy I would put my finger on having air in the lines. if you haven't done it already, remove the return hose from the IP and replace it with a piece of clear tubing. you can get the clear tubing from your local home depot in the plumbing section. it does not need to be fuel rated. it's 1/4" line. there will be an upside down "U" shaped piece of hose about 6" in length attached to the top of your injection pump going to a steel line by the timing cover. this is the return, Once you have this replaced with clear line, start the truck and let the fuel flow for a minute or two purging air that you got in it with replacing the hose. then from there watch it for any flowing bubbles. also when it's off and sitting you should only see a very small air pocket, nothing more. of the clear line empties over night or when starting up and running you see bubbles flowing through it, you are sucking air from somewhere.

most of the time the air is getting in from behind the lift pump to the tank. this could be any connections or even inside the tank with the fuel pick up tube.

Next step is to check your fuel pressure at the IP inlet. Harbor freight sells a fairly cheap fuel pressure test kit that comes with a tee which you can plumb inline at the IP. if you have a stock lift pump, you should see 8-9psi with the key on and should maintain at minimum 5psi at idle. if at any point you see pressure at 1psi or lower, you are starving the IP of fuel and causing damage.

let us know what you come up with on the clear hose and then with fuel pressure.

 

[nycxjeremyy]

@nycxjeremyy I would put my finger on having air in the lines. if you haven't done it already, remove the return hose from the IP and replace it with a piece of clear tubing. you can get the clear tubing from your local home depot in the plumbing section. it does not need to be fuel rated. it's 1/4" line. there will be an upside down "U" shaped piece of hose about 6" in length attached to the top of your injection pump going to a steel line by the timing cover. this is the return, Once you have this replaced with clear line, start the truck and let the fuel flow for a minute or two purging air that you got in it with replacing the hose. then from there watch it for any flowing bubbles. also when it's off and sitting you should only see a very small air pocket, nothing more. of the clear line empties over night or when starting up and running you see bubbles flowing through it, you are sucking air from somewhere.

most of the time the air is getting in from behind the lift pump to the tank. this could be any connections or even inside the tank with the fuel pick up tube.

Next step is to check your fuel pressure at the IP inlet. Harbor freight sells a fairly cheap fuel pressure test kit that comes with a tee which you can plumb inline at the IP. if you have a stock lift pump, you should see 8-9psi with the key on and should maintain at minimum 5psi at idle. if at any point you see pressure at 1psi or lower, you are starving the IP of fuel and causing damage.

let us know what you come up with on the clear hose and then with fuel pressure.

Will try this tomorrow if I can, thank you so much for this

 

[Will L.]

The fuel pressure listed is higher than needed for a db2. You want 5 psi range and when you get to 7 or 8 it will force the advance in timing.

My money is on air in the line.
The 911 and related stuff for gelling is horrible for these older ip (injection pumps) and pop injectors. If you can get some winter blend and flood the tank with it, maybe drain half whats in there first then add winter- that would be better.

Ideally you want to add a stainless steel T fitting between the ip inlet and the king nipple where the rubber hose goes to it. The factory size there is 5/16”. Third side of the T is 1/8” for a pressure sensor to a permanent mounted fuel pressure gauge in the dash. Low pressure wipes these pumps out. The inline one recommended above is fine for fast diagnostics. Long term do the in dash gauge.
Also the rubber lines for the rest of the fuel system- SAE30R9. The original stuff doesn’t withstand the modern fuel they force us to buy.

 

[nycxjeremyy]

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):

New video by Jeremy

photos.app.goo.gl

New video by Jeremy

photos.app.goo.gl

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

 

[dbrannon79]

Don't be too quick to point the failure at the injection pump. go get a piece of clear hose and use it to replace the return hose. I paused your video to take a screenshot of the hose you need to be clear so you can see if you are getting air in the system.

 

[nycxjeremyy]

Don't be too quick to point the failure at the injection pump. go get a piece of clear hose and use it to replace the return hose. I paused your video to take a screenshot of the hose you need to be clear so you can see if you are getting air in the system.

View attachment 91819

Ill give it another look/try, if it is getting air somewhere, finding the leak and stopping it will not be a fun day

 

[dbrannon79]

Next once you have the clear hose in place of the hose I circled in the post above, then run the engine. look for bubbles flowing.

Then you need to check your fuel pressure to the IP. follow the rubber hose that connects to the back of the IP back to the fuel filter. you need to find a place you can tee into and put a pressure gauge at. since your on a base, some of the mechanics should have a low pressure gauge you can run a hose from with a tee. ideally you want to read fuel pressure between the filter and the IP, but you can connect the tee before the filter just to see what the lift pump is doing. the reason we say to go between the filter and the IP is so that we see that the lift pump is able to push fuel past the filter.

here is another screenshot of where the fuel comes into the IP at. if you look under the intake with a flashlight you will see a rubber hose connected where I have again circled in this photo.

 

[nycxjeremyy]

Next once you have the clear hose in place of the hose I circled in the post above, then run the engine. look for bubbles flowing.

Then you need to check your fuel pressure to the IP. follow the rubber hose that connects to the back of the IP back to the fuel filter. you need to find a place you can tee into and put a pressure gauge at. since your on a base, some of the mechanics should have a low pressure gauge you can run a hose from with a tee. ideally you want to read fuel pressure between the filter and the IP, but you can connect the tee before the filter just to see what the lift pump is doing. the reason we say to go between the filter and the IP is so that we see that the lift pump is able to push fuel past the filter.

here is another screenshot of where the fuel comes into the IP at. if you look under the intake with a flashlight you will see a rubber hose connected where I have again circled in this photo.
Thanks again for this, ill see what I can do

 

[dbrannon79]

Ill give it another look/try, if it is getting air somewhere, finding the leak and stopping it will not be a fun day

If you do find bubbles in the clear hose once it's running, we can all bet $$ the air leak will be somewhere between the back of the lift pump ( located underneath on the frame) and the fuel tank. think of it this way.... your truck is a 1985. it's 40 years old.... any rubber hoses or connections are getting pretty brittle, dry-rotted and cracking. would you run tires that old? of course not, if they held air they'd pop in the first 10 miles!! same goes for rubber hoses.

Now I am going to take a step back and correct myself, @Will L. can correct me too... your truck might have a mechanical fuel pump on the engine. anyway, there will be rubber hoses attached to the top side of the fuel tank that go to the frame which then connect to steel lines.

these steel lines go first to the lift pump before they go to the fuel filter on the engine. follow these lines and you will find all the rubber hoses that will eventually need replacing.

Again I will let @Will L. step in here because I don't know if they used mechanical lift pumps in 85.

 

[dbrannon79]

BTW, in case I didn't mention it... your truck is a true gem, don't throw in the towel. Yes the 6.2/6.5 diesel are a dieing bread. but put in the time and patience, that truck will out last anything new on the market!

 

[ak diesel driver]

They did in 84 for sure

 

[dbrannon79]

@ak diesel driver where was the mechanical lift pump at on these engines? I assume it goes where the turbo oil drain goes into the block same place like on a small block chevy gas engine?

 

[nycxjeremyy]

Id like to thank you all for your help in this matter, this is really narrowing it down and hopefully next week on weekend pass (military) we can do the clearl line trick and see once and for all if it is indeed air in the system

the DiY shop on base actually has an old head army mechanic (I'm AF) who did tell me to look into replacing the Fuel Pump and Lift Pump as both are certainly old and dated and it could also help perk it up, i may look into that aswell

And for clarification, my Motor is an 85 (mechanical pumps, etc) while the Blazer itself is a 90s one, the motor was swaped out by the previous owner

 

[dbrannon79]

That is certainly a beauty you have there!

easy check to see if you have an electric lift pump.. look under the rig on the inside of the frame rail near the drivers door for this attached to the steel fuel lines. if there is nothing along the inside of the frame on the drivers side, then you have a mechanical lift pump on the engine.

your IP is mechanical too, but that is the pump you don't want to deem as failed yet.

 

[nycxjeremyy]

That is certainly a beauty you have there!

easy check to see if you have an electric lift pump.. look under the rig on the inside of the frame rail near the drivers door for this attached to the steel fuel lines. if there is nothing along the inside of the frame on the drivers side, then you have a mechanical lift pump on the engine.

your IP is mechanical too, but that is the pump you don't want to deem as failed yet.

View attachment 91822

I've been under the Blazer a few times and haven't seen anything like that, i found the mechanical one though, which my friend replaced last year (I was out of state when I lended him the truck, he did it on his own) so I suppose i can rule that out.

 

[dbrannon79]

I looked up a lift pump for an 85 blazer 6.2 diesel and got a photo of what it looks like. this will be mounted on the engine block on the passenger side towards the front. there will also be another rubber hose from it to the steel line on the frame maybe 6-8 inches long. if he did replace it, that rubber hose can be the source of your issues with letting air in the lines.

others will chime in soon, but if the lift pump is there on the block, how does your turbo drain oil back into the pan? this lift pump is for a non-turbo style engine.

 

[nycxjeremyy]

I looked up a lift pump for an 85 blazer 6.2 diesel and got a photo of what it looks like. this will be mounted on the engine block on the passenger side towards the front. there will also be another rubber hose from it to the steel line on the frame maybe 6-8 inches long. if he did replace it, that rubber hose can be the source of your issues with letting air in the lines.

others will chime in soon, but if the lift pump is there on the block, how does your turbo drain oil back into the pan? this lift pump is for a non-turbo style engine.

View attachment 91823

Yup, that's it, I remember now, he bought it off rock auto, it was made by Delphi

Edit: it was replaced a year ago, never gave issues then, id be surprised if it'd be causing issues now

 

[dbrannon79]

having this style mechanical lift pump also makes me think it can be the issue with the surging too. as it is pumped by the cam pushing on a rod which presses on the lever of the pump.

Others correct me if I am wrong here. if this pump is pulsing pressure up and down not keeping up the demand for the engine. the engine runs lower idle RPM as it's in-between the cam stroke on the pump causing the surging right after letting off the go pedal..

 

[dbrannon79]

Yup, that's it, I remember now, he bought it off rock auto, it was made by Delphi

Edit: it was replaced a year ago, never gave issues then, id be surprised if it'd be causing issues now

Rockauto is full of chineesium knockoffs and copies of the "real" parts. you have to be careful what you but from them..

this makes me lean more towards you having a failing lift pump. as well as possibly needing to replace the rubber hose that feeds this pump too!