New rebuild #4 misfire

[Ooowillow]

Where to start
95 6.5 fresh rebuild
First time I fired it up timing is off 8 dev. Got the timing set but the truck runs very rough about 1000rpm
Used tech two meter to turn off each injector one by one to narrow down which Cylinder is giving me the problem. Number four. When I turn off all the other injectors one by one I notice a difference in the RPM but on number four no differents. Found a fuel leak on the pump at the number four line thought that was my problem but it didnt fix it
Swapped the injector from 1 to 4 to see if problem followed the new injectors. Issue is still at numbe four
Checked all fuel lines to make sure they were ran to the correct cylinders
Ended up taking it to the dealer for help
They can't figure it out
Any thoughts
Pmd is less than 6 months old
Engine has 30 min on it

[Robyn]

Hello and welcome to TDP from a fellow Oregonian

Get a compression test on number 4
If comp is OK then the issue has to be the Rebuilt IP

To avoid issues when doing the test, unplug the fuel shut off solenoid on the IP
This is the round gizmo near the front of the pump the sticks up, just unplug it from the harness, then make sure the engine will not start.
Do your test.

Getting at the glow plug on 4 will be best done by removing the rubber flap in the wheel house (tire and wheel off) Easy access to the GP

Crank it to get 4 hits on that cylinder then read.

Who did the rebuild ???

Keep us in the loop

Missy

[sctrailrider]

I would open the injector line while it's running and see if any fuel squirts out.. maybe a clogged line from a dirt dobber???

[racer55]

Are you certain that you are chasing the correct cylinder?
Some scan tools report the cylinder in the firing order they are operating and NOT the physical location of the cylinder-can't say for sure that is how a tech II works but have seen the problem before.

[DmaxMaverick]

Are you certain that you are chasing the correct cylinder?
Some scan tools report the cylinder in the firing order they are operating and NOT the physical location of the cylinder-can't say for sure that is how a tech II works but have seen the problem before.

The Tech II will identify the correct cylinder and bank. This was brought to light soon after the introduction of the Duramax. Many tech's were having issues troubleshooting cylinder-related problems. The Duramax cylinder banks are opposite that of previous Chevy/GMC V8's. I've seen some of the off-brand scanners identify by the firing order, which isn't a bad thing necessarily, but can cause confusion if you don't know about it.

[phantom309]

all the injector lines in the correct order?

[Ooowillow]

[QUOTE=Ooowillow;306602]Where to start
95 6.5 fresh rebuild
First time I fired it up timing is off 8 dev. Got the timing set but the truck runs very rough about 1000rpm
Used tech two meter to turn off each injector one by one to narrow down which Cylinder is giving me the problem. Number four. When I turn off all the other injectors one by one I notice a difference in the RPM but on number four no differents. Found a fuel leak on the pump at the number four line thought that was my problem but it didnt fix it
Swapped the injector from 1 to 4 to see if problem followed the new injectors. Issue is still at numbe four
Checked all fuel lines to make sure they were ran to the correct cylinders
Ended up taking it to the dealer for help
They can't figure it out
Any thoughts
Pmd is less than 6 months old
Engine has 30 min on it


Update
Replaced the fuel line to number 4 just incase that was the issue.
Still running rough
Ready to sell
I have way to much time and money into this truck feeling very frustrated
When I took the intake off I touched the intake to the glow plug relay by accident got quite a arc. Now my glow plug light will not come on unless I put a lead from the go side to the output. Thought I fried the relay so I bought a new one but still have to jumper it to get the glow plugs to turn on.
Just to be clear glow plugs are new, light comes on if I put a jumper cable onto the output of new or old relay
Any more ideas?

[Ooowillow]

Injector lines installed correctly

[Ooowillow]

Huh
I have the intake off and the truck is running rough
On a whim I desire to shut it down and u plug the optical sensor.....
Seems to run much much better.... Can these be cleaned or do u have to replace them? Anyone in oregon have a spare or an old pump with one one it?
What is the purpose of this sensor and why would the truck run Better with it in unplugged?

[racer55]

With the OS unplugged the truck will run in limp mode.

OS can be confused by air in the fuel so rule that out by replacing the IP fuel return line with clewar diesel rated fuel line and then with the truck safely parked and idling-watch the clear line for bubbles.
Bubbles indicate air in the fuel usually entering pre LP.

They can be cleaned/replaced but it is precision work:
http://www.mamut.net/royh/newsdet9.htm

Your local stanadyne rebuild shop might be a good place to source a good used OS if need be.

On a 95 there can also be problems with the OS electronic noise filter-it can be removed and the remaining harness plugged into the OS-but you should also get enough ferrite core from radio shack to have a piece over each OS harness wire.

[DmaxMaverick]

This is usually a reliable indicator of a failed IP. Some folks have had success repairing the OS, but it's not for the faint-of-heart. Much of the time, even if you're fully capable of doing it, it still fails. IP overhaul is indicated, in most cases. You can continue with it disconnected, but you will be running in limp mode all of the time. This will eventually have other consequences, so correction is imminent.

However, as Racer said, verify you aren't getting significant air in the fuel. That, and other things such as high concentration biodiesel or died fuel, can also have an affect. The optical sensor relies on a light beam through the fuel to accurately determine the parameters, so essentially anything that may affect that, can cause issues.

[Ooowillow]

I will try the clear line
When I replaced the fuel filter I noticed it was black. First time I saw this truck sat for 3 months am I think grew some algee so...
I replaced the fuel tank when I did the rebuild. Gauge was reading very full and when I hit a half tank on the needle I was out of fuel. Gauge is still reading off even with the new sending unit
I also noticed some very bubbly fuel when I bled the air valve on the top of the filter housing.

How does air get into the lines and up to the ip?

I disconnected the electronic noise filter on the optical sensor harness and plugged the harness back in. The truck still ran poor so I put it back in.

Is it safe to drive it with the sensor unplugged and never replace it

[racer55]

first take 2 minutes and click user cp at the top of the page,then click edit signature and fill in the box with year make and model of the truck.

then every post you make from then on will have that info at the bottom so we don't have to go back to the beginning to look it up.

the air gets into the system at a hole or a leaking area,were any o-rings left out when you changed the sending unit or lift pump-every threaded fitting requires an o-ring?

With the OS noise filter removed you should get enough pieces of ferrite core from radio shack such that you can fasten a piece over every OS harness wire.

[Ooowillow]

Could it be a grounding issue?
The engine ran fine before the head gasket blew...
I don't understand why the pump or optical sensor would be acting up no with a fresh rebuild. Anyone have a wiring diagram for the engine compartment?

[Ooowillow]

Racer
Which line is the return line
I put a clear line from the canister filter to the intake of the IP and didnt see any bubbles when the truck is running
Did I check the correct line?
Or is the return line the line that goes from the injectors back to the tank?

[racer55]

Return line is the 1 at the frt of the IP that connects to the metal TEE that the injector return lines fasten to at the frt.

[ken93]

Are the glow plugs new? Did you check the glow plug for function. Dont think your getting any less of a miss unplugging the OS, just an increase in idle speed from limp mode. Might seem less at slightly higher rpm. Air in your return will cause a random cylinder misfire, enough air will cause multiple cylinders. Your problem is one of only a few things, lack of compression(bad rebuild), bad glow plug, fuel delivery issue. If the issue doesn't follow the injector, you can pretty much rule it out. Just because the IP is delivering fuel, doesn't mean it is the right amount or at the right pressure to "pop" the injector.
First thing I would do is swap the glow plugs around, If no change, then swap the glow plug wires around. If you have a multi; meter, you can check the continuity of the plugs. Take wire off plug, test from male prong (pos) to the hex of the plug (gnd). Also check ohms. Ref. Another glow plug for a base reading of ohms.
If the problem hasn't shown itself yet, we move to fuel. We know it isn't the injector, so you have to either rent a fuel pressure pulse tester (digital tool for testing IP line pressures) or have it tested.

Some additional info would be helpful in tracking your issue down.

Are you getting smoke at exhaust? If so what color? Smell raw fuel? Any strange noises?

[racer55]

The techII most often requires an OBD1 expansion module to work properly with an OBD1 vehicle,perhaps some updates to the techII allow for both in a stand alone version-I am not as up on its patches and firmware as people who use 1 everyday for years?

[Ooowillow]

First I want to thank you for taking the time to help me

Update
Lines 4 and 5 were the first installed 5 then 4. 4 is a bear to get to...
I installed clear fuel lines on the ip feed line and both of the return lines. The return line from the pump is free of bubbles, the feed line from filter is free of bubbles, return line that goes back to tank has a couple bubbles now and again

Pulled the pump had it tested and it test good

Replaced optical sensor because Walt at ss deisel said he was 100% sure that was the problem.... Didnt change a thing...still runs rough white smoke. Unplug optical sensor and it runs smooth exept it misses at high rpm 3k or so

Haven't finished testing the lift pump
I can hear it run....

How do I check the crank sensor? When I put my Dvm on the ground plug of the crank sensor wiring harness and touch the other lead to ground I have no continuity like I have on the other sensors

I am running the engine with the intake off but it runs like crap on or off. I bring that up because the two sensors on the intake are not pluggedand the egr is not installed or plugged in. Again I have the intake off to get to all of the lines and the ip.

Will try to test lift pump this week

When I crack the valve on the top of the filter housing it always hisses air.... But no bubbles in the clear line from filter to ip

[Ooowillow]

Fuel tank and sending unit are new
10 gallons of fuel in 25 gal tank
Fuel filter is new