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Engine starting to miss and gets worse after a long run

dbrannon79

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Hey guys, I thought I woult get some input for you all on a weird issue the just started to show up. the other day I was out running around and noticed the engine was starting to miss out. it wasn't terrible, was thinking that I just need to finish replacing the injectors since I just replaced the 4 on the drivers side and haven't mustered up the courage to remove the turbo and break bolts to get the the passenger side. but as more time went by the engine was at the point it felt like a gas motor with a bad set of plug wires during acceleration, this was while I had been driving for about 2 hours. it was late at night when I got home so I left it for the next day to look at. the next morning I went out and low n behold she was running fine with no missing at all! Warmed the engine up and went out for a test run, I couldn't get the engine to act like it was again. she still has the occasional random miss or spit but not like it had been doing the night before. I felt like something electronic was getting hot and breaking down, but not sure. I checked the lift pump which I had recently replaced, it had good pressure. replaced the fuel filter for good measure and looked all over for any sign of fuel leaks on the injectors. I found one injector behind the turbo that the return hose had some slight seepage but nothing that stuck out like a sore thumb. I have already relocated the PMD away from the engine but was thinking that the PMD might be causing this. I shot the heat sink on the PMD with a temp gun after running around town for a bit and it showed 150 degrees! Mind you the engine never gets over 180. just had the radiator tank replaced so I know it's not overheating. I thought this might be a little hot but wasn't sure. It's currently zip-tied in between the brake lines from the master cylinder and the ABS motor under the hood. I know it needs to be moved out where some air can get to it better but I figured it should be in a better place than mounted down in the intake valley. What do you guys think could cause this type of missing? am I looking in the right place or are there other things I am overlooking?

Thanks in advance
 

MrMarty51

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Might have been a chunk of carbon stuck between a valve and its seat. Become dislodged after a cool down cycle.
I thought that removing the turbo on My 2000 K3500 was going to be a bolt bustin project. Not so, They all come off without a hitch and I have had the turbo off of there twice now.
I aint saying that Yours couldn't be different but this one was a lot easier than I thought it was going to be.
 

Will L.

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Do you have clear line on the ip fuel return? Check for bubbles.
If not every hardware store sells 1/4” clear tubing. You need 5-6” lkng but they sellit by the foot. Keep the other scrap piece for replacement of this one in a few years when it yellows. I suggest two new screw style hose clamps at the hardware store while your there.

get those other injectors in there. Not a fun afternoon but needed. Buying them is what stops many and sounds like you already did that.

Once you have the new injectors in there, if it is still missing: crack injector nuts one at a time to id which cylinder(s) is misfiring. Make sure you witness fuel spitting out of each as you do it.

do you have a scanner?
 

dbrannon79

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Do you have clear line on the ip fuel return? Check for bubbles.
If not every hardware store sells 1/4” clear tubing. You need 5-6” lkng but they sellit by the foot. Keep the other scrap piece for replacement of this one in a few years when it yellows. I suggest two new screw style hose clamps at the hardware store while your there.

get those other injectors in there. Not a fun afternoon but needed. Buying them is what stops many and sounds like you already did that.

Once you have the new injectors in there, if it is still missing: crack injector nuts one at a time to id which cylinder(s) is misfiring. Make sure you witness fuel spitting out of each as you do it.

do you have a scanner?
I had borrowed a scanner a before and there was no codes. havn't seen any engine lights come on or flash yet. I'll have to get those other four injectors in there soon. it's not a constant miss just every once in a while it'll hiccup so to speak but this one evening it was really running like crap trying to get on the highway going home. Drove it to work this morning and it never missed a lick! will bad injectors start having fits when they've been running a few hours constantly? the way it was running that night was similar to a gas motor ignition coil does missing under a load. I'll have to try the clear tubing thing too. one other thing I did before that trip was fill up the fuel tank, but I don't think that had anything to do with this. since my wife runs doordash delivering food, I may pick her up and run the truck around for a few hours this evening and see if I can make if do this again. It did take a good long drive before it started acting up and this morning heading to work it ran fine!
 

Will L.

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Yes, sticking injector will cause misfire, dead cylinder, and a bad injector can have it shoot a fine stream and destroy a piston. If it’s running good at the moment I wouldn’t expect the nightmare stream, but sticking one definitely.

When you do the clear line, you will get a tiny bubble trapped in there- no worry.
If more than one trapped bubble like a stream or frequent supply of individual bubbles is what to watch for. That is indicating air is getting in the fuel lines somewhere and needs to be fixed.
 

ak diesel driver

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When it's acting up again I'd do the OS and CPS tests. Could be a heat related electrical issue. Definitely do the clear line and get a fuel pressure gauge on there where you can see it while driving. 94-95 had OPS issues
 

dbrannon79

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Forgive me for asking but what is the OS test?

I did get out there again today, drove around town for about 2 1/2 hours running deliveries with the wife for doordash! after about 2 hours it started the occasional misfire more often but never got anywhere like it did the other day. the misfiring it was doing I feel is due to the other 4 injectors I haven't replaced yet. Although it started (what I thought) acting silly around the last delivery and while heading home. the engine started running extra smooth like it chewed and finally spit out a piece of carbon or something! it felt like it wanted to move while sitting at a couple of traffic lights!! so with clear traffic I punched it a couple of times and both times it threw us back into the seats, not enough to burn rubber but seemed like it had more power to go or maybe it was just having a moment.

I don't really know the history of this truck since I've only had it for about 3 months. now I am wondering if it's just ether really carbon'ed up or might have or had some kind of restriction in ether the fuel lines or exhaust. Ive already cut out the cat, that was one of the first things I did since when I bought it. Someone had cut a section of pipe out between the cat and the muffler and left it like that. I decided then to remove the cat and re-attach to the muffler due to the noise.

I'm thinking about pulling the intake and replacing all the rubber fuel lines from the IP to the filter and go further if possible to the steel lines off the tank, along with new valve cover gaskets and the last 4 injectors of course! with this I would find out just how bad the carbon buildup really is. I gave it a good look and I just might be able to access the injectors behind the turbo with the intake and the valve cover off :) Just curious though, do these engines have adjustable rockers like the old chevy 350's did or are they fixed like the newer engines. thought I would check and adjust the rocker clearance while I was in there if needed. I know, I'm thinking too far ahead on maintenance, not really sure how soon I would take on this kind of job between work and how far the dollar will stretch!
 

Will L.

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Don't pull the intake yet. new parts that are not required and possibly new defective (which occurs to frequently) can complicate diagnostics of a different issue.

OS is Optic Sensor, the black square thing on top of the ip. it works in conjunction with the CPS crank position sensor.
Unplug one then start truck. It will be hard to start but should start. Then turn of truck plug it back in and unplug the other one. Same thing, hard to start but should start. If you find it will not start the item still plugged in is at fault.
 

Rockabillyrat

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When you say it wanted to "move while sitting at a traffic light". Did it feel like it was pushing though the brakes? That could be a TCC issue. When are you noticing the misfire? At idle? under heavy load? under light load at cruising speed? A slipping TCC can feel just like a misfire. Usually that will be under a light load at cruising speed. I diagnose those by watching the TCC slip on the scanner. A long hill is the best place to get it to act up.

The more information you can provide on when the misfire is occurring the better. I play 21 questions with customers alot so I can drive it under the same conditions they do to recreate the issue.
 

WarWagon

Well it hits on 7 of 8...
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The PMD is how old? If you can't touch it you can blow it for electronics. Consider this PMD cooked. Get it out from under the hood ASAP and use a new one. It's not ' I know I need to do it' : it's this delay just cost me a $PMD$ !

As always check again for codes. Not all turn the light on.

Air in fuel is step #1 for a reason. Without a clear fuel line on the IP return you are wasting your time and money. I chased a kinking shut hose for years, but, the clear line indicated air when the engine quit.
 

dbrannon79

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I started thinking about what you said about the PMD and all and remembered that when I relocated it, the old one that’s still mounted on the IP was working that I had just wanted to relocate it. So I decided to reconnect the one mounted on the pump to see if it acted any different! Boy did it!! But In a bad way When I started it up it ran like crap and bad misfired and bucking while trying to idle. So I swapped the connection back to the one I relocated. Started it up and still missing and running really crappy! I knew I was moving wires around trying to connect the IP mounted PMD so while it was running I started poking at the harness around the IP. Low n behold I touched the harness going to the OS that seems to have some sort of small square black box before going into the engine harness and it straightened out and ran fine. I’m not sure what that black box is that the wires go in one side and out the other the to the OS connector but while playing with it tapping with a screwdriver it misfired a few times! I guess I need to replace the harness or at least take it all apart and look for broken or corroded wires and connections. I tried to attach a photo of the little box maybe y’all know what this is.

Thanks
 

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dbrannon79

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From what I can see the is the OS filter. You don't need it throw it away as far as you can!
a noise filter! is this for the radio? I would have never thought that, I was thinking it was some kind of diode or something to prevent voltage backfeed! I will definitely remove it tomorrow after work.
 

dbrannon79

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I sure hope so! gonna remove it this afternoon and go doordashing with my wife again tonight and see what happens. although I discovered my water pump leaking :arghh: so I guess a cooling upgrade is in the works real soon! I hear there is a great benefit by using the 97' year model pump, fan clutch and Duramax fan blade. I probably need to check the timing chain at the same time since this beast has 270k on it. my wife is telling me it's tuning into a money pit! But we all need to have toys :cool:
 

Rockabillyrat

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I'm not married... yet. But I've already been practicing moving the decimal point to the left when I talk about what I spend on truck parts with my GF. Her dad was a car guy so she is used to it😅
 

dbrannon79

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Well, I am happy to say that I think the problem was found! After removing the OS filter, I went out doordashing with the wife for a solid 5 hours ( even had the AC running to keep her comfortable ) and the truck never skipped a beat. not one single misfire all afternoon .

I did notice after about an hour into driving that the sound if the motor having the urge to go while sitting at the traffic lights came back! this time I payed more attention to it. taking my foot off the brake didn't lurch the truck forward at all, after a while of feeling it I thought it might be a sunken motor mount and I was just feeling the vibrations from the engine running, though I couldn't feel the tweaking when taking off like you would with a bad mount. the only thing I could think of was maybe the fan clutch was engaged and the fan blade might be causing more load on the engine. I know this is an older truck that I really don't know anything about, there's a lot of things it might be, bad mounts, exhaust vibrating against something under the cab, AC compressor causing the engine to work harder. ether way it doesn't seem to be causing any problems.

one thing I am curious about is what I found inside the upper intake! while I was removing the OS filter I pulled the upper plenum from the intake to get to the connector easier. to my surprise there was some kind of grainy like black stuff inside the intake. not a lot, but there was one area directly under where the rear center bolt goes to hold the plenum, where some was piled up. The rest was bassicaly lightly sprinkled all around and clung to the insides due to the oil film that was coming from the tuna can on the valve cover (which I need to replace). I got it out with a rag and it came off easy but was grainy like sand. I think it was carbon but Ive never seen it semi-loose and sand like just laying in the intake like that. could that have come from the turbo or is this just oil that's getting fried in the intake over time that was coming from the CDR valve, A.K.A tuna can? there is no EGR on this engine so it wouldn't have come from there. other than this, I am happy that the missing is gone :D
 
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