Wierd Missing Sound

[91f2504x4]

I got a wierd problem, I am not sure what the deal is, I got a few ideas but I really want to see what everyone else thinks. I finished the swap in my 90 f250 a couple weeks ago and got everything together and just got the right radiator in it yesterday so I could finally run it up to operating temp and try the turbo out.

Well this morning I was moving it around and it ran out of fuel, gauge works sometimes and other times doesn't I had to make pickup tubes and the first one I made was too long and now it is a bit too short and it runs out when there is still plenty of fuel in the tank, but anyway. I got more fuel put in it, bled the system and it started right back up and was running great as usual. Well I drove it back down and parked it by the garage and was letting it warm up and it sounded like a really faint thud thud thud, almost like a miss but not quite, the longer it ran the more prominent it sounded, the idle never fell and it would still rev good but it started to get more noticable until you could really hear it in the exhaust, right now the exhaust is just straight 4 inch out of the turbo so it is pretty loud.

The wierd thing is there was no smoke, like an injector had failed so I checked to make sure I checked all the lines to make sure I didn't leave any loose and sure enough they were all tight.


The truck ran really great up until this point and it still revs good and runs good but it has that flutter at idle almost like it is missing.

Some history on the engine:
1990 7.3l a little over 100,000

It was in a family member's truck that slipped out of gear and went over a hill totalling the truck, engine has a little over 100,000 but had a lot of leaks, so I put all new gaskets and seals, including head gaskets. So far nothing is leaking. It was always hard to start for them so I went through the glow plug system putting new terminals and a new wire here and there. I advanced the timing maybe 1/32" from where it was then and now it starts great, it is in the 20's outside and it starts on what sounds like the second rotation of the engine.


Would advancing it too far cause this type of sympton? I wouldn't think so but I am looking for anything to avoid just throwing money at it. I might pull the valve cover and check all the lifters and make sure everything is ok there but it done this at idle so I would think all is well there too, I just had it apart a month ago.

Any Ideas?

 

[91f2504x4]

I have been doing some reading around and it seems that there have been other people who have had the same problem and for them it was exhaust valve guides. I am worried this is correct and I am having the exact symptoms that the others I have read were having. It is smooth and calm at when cold but as it gets warm it starts to ch ch ch until its a thud thud thud thud when it finally gets warm, it almost sounds like a very mild lope. It has plenty of power and it never done this before when the previous owner had it. I didn't even mess with the heads when I had the engine aparts other than to clean the surface for the gaskets to seal on. I heard the truck run plenty of times before it was wrecked and I hate to think the valve guides when bad just sitting in the garage for a month. I didn't mess with anything in the heads because the truck ran so good before and it had no problems.

I will try loosening each of the injectors to see which of them makes a difference to see what cylinder it is, and then I will swap the injectors and see if the problems moves with the injector or stays in the cylinder. If it stays with the cylinder I am going to pull that valve cover and check for side to side valve movement. I would much rather it be an injector as I just put new head gaskets and all in the truck and hate to waste money on another set of head gaskets on it.



Does anyone else have any better ideas? I am going to be busy for a couple days so it might take me a while to fix this problem.

 

[69dieselfreak]

fuel pick up tube you made them it might be that your picking up air from somewhere in your tank id start there go for the cheapest thing first
but thats where id start

 

[91f2504x4]

The pickup tube is all metal now except for where the two pieces of metal meet (butted togehter) and there is a piece of rubber attaching the two with 4 hose clamps on it. The metal is cut to length and there is no rubber on the bottom. I wouldn't think it would run fine when cold then then start the miss if it was because the fuel pickup. I didn't use rubber so I would know for sure it wouldn't be crimped after my initial rubber pickup tube.

I have just been through all the fuel lines, and also the ank selector works great. The intank pickups are good, I have a holley red fuel pump right in front on the selector valve and it has brand new rubber line running to the fuel filter. I can push the schrader valve in and fuel comes out good and fast.


I wouldnt make sense to me that it would run good when cold but then when warm it would flutter through the exhaust because of a bad pickup tube. I will check again, although I have checked it 5 times already when I was having troulble with the rubber one crimping. Just to rule that out I will run a hose straight from a jug of fuel into the pump avoid the selector valve and all.

 

[91f2504x4]

I am not going to jump to the conclusion of valve guides already but that is realy the only thing I have seen that makes sense to the symptoms I am having. Hopefully it is just an injector issue that I can trade out easily without having to pull everything back apart already but sometimes crap just happens. I have just come to the reality that I have this kind of luck so there is no reason to think it is something simple

The thing that sucks is valve guides only cost about $25 but the labor to get them done is going to cost quite a bit, if that is what it truly is.

 

[Black dawg]

ive had injectors cause a funny sound/miss out the exhaust. its pretty dang hard to isolate a partial miss by cracking injector lines.

 

[91f2504x4]

It seemed pretty constant once it warmed it, it was really noticable through the exhaust. At first it was fairly quiet, but the warmer it got the more obvious the miss was. I might also try testing glow plugs to see if any of them have significantly lower reading than the rest, pointing to a misfire condition. I think I will also pick up an IR thermometer to check temps that way, to find the cylinder with the problem.

 

[91f2504x4]

Ok so I had a few minutes earlier to crank her up and take a listen again. Even at 6F this morning it fired right up, but I could tell the batteries are a little weak. It cranked up normal and sound good until it began to warm up and then the thudding started coming through the exhaust. I had read if it were a valve guide problem you could hear it "Chuffing" through the intake but instead when I pulled the turbo hat off the intake it was popping out the intake, at first it was random but the longer it ran the more constant until it was once a rotation and pretty rhythmic with the engine so I think it is just one cylinder. Has anyone else ever had this problem? I am thinking for sure it is an intake valve guide now. I am also thinking that the sound wasn't coming from the exhaust that much at all but instead was causing the turbo to flutter when it popped through the intake making the sound in the exhaust.

ANY IDEAS?

 

[typ4]

check valve springs. Pull the covers and run it and see if there is smoke coming around the guides, it will cook a spring and cause this. A exhaust valve not opening will also cause this but you should have a valvetrain rattle to go along with

 

[91f2504x4]

So do you think it could possibly be a bad valve spring, causing the intake to not shut completely once it begins to warm up.

I will pull the valve covers off tomorrow and have a look for a warn valve guide or a bad spring.

I have also heard that these have problems with breaking valve springs. But when it is cold it runs perfect, as it warm though the popping begins.

 

[typ4]

That is strange.

 

[91f2504x4]

I wanted to run it more and do more testing but the popping was so bad I was afraid it might drop a valve soon or something. It is worse today that it was the other day.

I also unhooked and hooked up the cold timing advance, to see if it had any effect on the popping but it didn't. I gave it throttle slowly to see if it got better or worse and it stayed proportional to the RPMs.

 

[Agnem]

Be concerned. Joe Lewis' truck did just this same thing. Sounded fine when it first started, but started to make a noise after a moment or so. Turned out to be a major valve issue.

 

[91f2504x4]

I am thinking that mine is the worn valve guides or something with the exhaust valve not opening, hopefully I will know by tomorrow. If I know I will be sure to post what it is, I hate reading post where people just describe my exact problem but then they never come back to say how they fixed it, they just leave you hanging, the need to put a resolution post.

 

[91f2504x4]

Ok I got it figured out and fixed. I checked the injectors one by one and they all made a difference but #4 made the least, so I pulled that valve cover off and the Exhaust rocker arm bolt was loose, I pulled it out and somehow it was a little stripped. I never noticed this when I put it together, must have been one of those days when the wife was yelling at me to do something else. It must have already been stripped because I torqued all of them down to 20 ft lbs. I put a new grade 8 bolt in there and retorqued all of the rest of them to be sure none of the rest of them were bad and now it runs like a sewing machine.