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Bad Chuggle/Fishbite Problems

H

Hobosnax

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Location
Oregon
Howdy Guys, long time lurker but first time poster. Thanks for having such a great forum for 6.5 owners, it was part of the reason I own one. Now to my problem.
I have a 1995 2500 6.5T that I bought about 5 months ago. Great condition with 100k miles on it, all stock except for a Banks exhaust. It has always run great, started easy with barely any smoke, ran smooth with no smoke and never had much blowby. The prior owner put a new injector pump on it at 99k, I have the receipts to prove it. I bought a new D-Tech PMD and put it in the front bumper with a 12 volt fan/heatsink on it, and left working PMD on the pump for backup, (didn't want to have to take the intake manifold off). I also hot wired the lift pump to a 12v ignition source in the cab because the OPS was out, (PO had been driving it that way not realizing it wasn't working, and it didn't really change how the truck ran once I got it hooked up).

So the other day I was driving at highway speeds and got two fishbites/hiccups in the space of about 5 mins. Has never happened before. I also notice that the throttle pedal seemed a little unresponsive, I had to tap a couple times to get it to respond during that trip.
Later in the day I am leaving home and the power just drops off and the truck dies, cranks good/fires but wont hardly idle, and throttle is very unresponsive, (I cant give it enough fuel to keep it going), chugs hard and blows black and white smoke/misses about half the time.
I roll half a mile back to the house backwards on a dead stick, (thank goodness we live in the bottom of the canyon).

The way it died suddenly seemed to indicate PMD/electrical problems, so I cleaned all the grounds I could get to (Six?) and battery terminals, swapped to the known working PMD on the pump and removed filter harness from optical sensor. No change.
Checked fuel pressure at the T drain valve: about 4.5 PSI idle and 3PSI at 2000 rpm (running rougher than a cob though so who knows), plenty of volume.

Pulled fuel line at top of the IP and found air in the line. Pulled the fuel filter housing: filter(about 5k miles old) and tiny screen are clear, normal amount of junk in bottom of housing. Replaced fuel lines that go to drain valve and injector pump, replaced the O rings at the heater assembly and WIF sensor. Cut a fresh end on the supply line coming from tank, (but didn't replace whole line), and tightened fittings at the LP. Checked for air again and it seemed to be cleared up.
Bled 6 injectors, (couldn't get to the two under the turbo, the one against the firewall passenger side the exciting enough with the truck running and a bare turbo).
Idled the truck for 15 mins or so and it seems to nearly be cleared up, will almost idle smooth and rev smooth, but occasionally still misses/bites a bit, especially at higher RPS. It is doing it enough that I don't trust to drive it. Sometimes it will idle smooth for 30-60 seconds only to miss/chug and belch a big cloud of black smoke.
Could it still be working air out of the system? Could it be a sticking injector that was brought on by the air issue? (It is probably due for them, at 111k miles and I have no proof they aren't originals so they probably are).
I am planning on running it a while longer and bleeding the injectors again and seeing if it clears up 100%. I really don't want to have to remove the turbo to get the last two injectors, but if the consensus is there I spose I will have to. Or maybe I have another issue as well (coolant temp sensor, optic sensor, some mystery gremlin).

Any advice, sage or otherwise, would be greatly appreciated.
 
Whew, sorry about the wall of text, just remembered something else. Checked codes with a paperclip and only showing a repeating code 12.
 
What is the fuel pressure from the LP. A pressure gauge you hook up temporarily or install is priceless. Lift pumps fail on these often. You don't need to crack lines to purge air. You can also have air leaks from the LP or tank pickup assy rusting out. A clear return line on the IP for testing will let you know when you eliminate the air leaks.

#1 test in the GM book is test for and eliminate air in the system.
 
Checked fuel pressure at the T drain valve: about 4.5 PSI idle and 3PSI at 2000 rpm
Click to expand...
Is this the best place to check it? It sure is the easiest. Lift pump is new in the last 5k miles.
How do you get at the tank pickup assembly? Cut a hole or remove the bed is what I am afraid you are going to say.
If you don't crack the line at the injector to remove air do you just run it out? I was worried it would just compress the air and not be high enough PSI to pop the injector and let it out. We routinely crack inj lines on other diesels to bleed air so it was just habit.
I will put a piece of clear tubing on the return line and watch for some air bubbles again.
 
Update:
A piece of clear tubing on the return line, (the little loop right behind the oil filler cap) shows no air bubbles while running(unless they are so small/fast that I cant see them), but when I shut it off some bubbles came up from the return manifold and floated in the top of the tube.
When I put the clear tubing on I had to introduce some air into the system, perhaps it is still working that out?
I will let it idle for 20 mins or so and see if smooths out.
 
Update 2: Solved
Tried letting it idle for 20 mins, ran rough the whole time. No visible air in clear return line while running, but some bubbles up when truck is shut off (is this a bad thing? seems like a silly questions but doesn't seem to be affecting how it runs)
Tried disconnecting the CTS, truck idled up and still ran rough.
Tried disconnecting the optic sensor: Bingo. Truck runs smooth as silk and throttles up smoothly. SES light has come on obviously. Perhaps some of the fuel additives I have been running have melted some crap loose that fogged the lens, or perhaps its just time for it to go. Is there any way to disable the OS and just run with the CPS? Other than trading it in for a 92/93. . .

Next question: Where is a good place to get a new optic sensor? Dealer item or is there any better place to get them?
 
Hobosnax said:
Update 2: Solved
Tried letting it idle for 20 mins, ran rough the whole time. No visible air in clear return line while running, but some bubbles up when truck is shut off (is this a bad thing? seems like a silly questions but doesn't seem to be affecting how it runs)
Tried disconnecting the CTS, truck idled up and still ran rough.
Tried disconnecting the optic sensor: Bingo. Truck runs smooth as silk and throttles up smoothly. SES light has come on obviously. Perhaps some of the fuel additives I have been running have melted some crap loose that fogged the lens, or perhaps its just time for it to go. Is there any way to disable the OS and just run with the CPS? Other than trading it in for a 92/93. . .

Next question: Where is a good place to get a new optic sensor? Dealer item or is there any better place to get them?
Click to expand...

I would check your local diesel shop or IP rebuilders,or stanadyne affiliate.
 
Try cleaning the OPS with industrial acetone.
Mark exact location before removal.

After shut down it is normal to have a small air bubble in the top of the return line
 
The 6.5 can purge it's own air. 1-2 lines for severe air lock is all you need. Make sure you are getting 100 RPM when cranking.

Have you eliminated the filter harness that plugs into the optic sensor? Trace the optic sensor plug back a few inches. A black cube is the filter. You can unplug the filter and connect the harness directly to the optic sensor. This can verify it isn't the problem.

Air should be gone after engine startup. Fuel moves really fast in the lines. Use a flashlight to look for small bubbles or look for them immediately after shutdown. As in have a friend shut it off while looking at the line with a flashlight.

Air from the IP side is a air leak in the suction side of the system. If air is bubbling back from the injector side - not sure. I would suspect a sticking injector allowing air in the system. Have a couple pop tested to see if this is happening. The return system will drain back into the tank with an air leak, but, a return system air leak aside of an injector sticking is not an issue. Fuel leak is an issue...

Lift pump pressure is good as you posted.

Fuel tank drops by removing the straps, disconnecting the 2 fuel lines and fill neck hoses. A floor jack is helpful.
 
Howdy guys, thanks for the help/replies.
Bison: I assume you meant optical sensor not oil pressure sensor? Or I could just be getting my acronyms mixed up.
WW:
Hobosnax said:
. . .and removed filter harness from optical sensor. No change. .
Click to expand...
But unplugging the optical sensor does smooth it out, like I said, so I think I got the air out of the system and that the OS is screwed, I will try washing it with acetone.
Lets say I took it out already, and the guide I was using was upstairs on the computer and I was in the shop and I might have not marked the position correctly.
It doesn't appear to have hardly any play left and right. How tight of tolerances are we talking about here? Like less than a millimeter? Is it something I can dial in manually or will I need a scan tool to tell me the fuel numbers.
Thanks again for the help, hopefully this shadetree mechanic can get his truck back on the road with out destroying the IP.
 
Had a very similar issue last night. Drove 80 miles, no issue pulled off the road to stop at mini mart, truck bucked and shut off. Started right back up. Then, driving home several hours later. Intermittant bucking that increased in frequency and died. Would not start. Checked the usual suspects and then swapped out PMD. Started right up. Shut it off and reconnected the PMD and started right up and ran fine. Same thing happened about a year ago. Contacts seemed clean and they are lubed, but I'm wondering if the PMD connectors are really finicky. I don't know what kind of resistance would render it inoperable. It's annoying when it happens and usually in the most inopertune times and places....
 
Final Update:
Tried washing the bad OS in acetone and it didn't really fix the problem, maybe helped some, or maybe I imagined it. Installed the new OS and just eyeballed/threw the dice on the position. I felt confident it was in the right place. Cleared the codes, (which there was a mess of after unplugging the OS: 17,18,35,43,92,95,97,98), and the truck runs great. Smooth at idle, can hold steady and smooth at 2000rpm, runs great around property but haven't had it out on the highway yet. Seems to run better than it was, but some cruising will tell for sure.
Thanks everybody for the help
 
Got it through Ott's Friction Supply, a HD brake/truck place in Portland, Oregon. Have family that works there and have worked with them in the past mostly, was my first call. Ended up being about 300 bucks. Cheaper than a new IP pump I spose.
 
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