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7.3L IDI Diesels (Not Power Strokes) Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

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Old 01-16-2009, 03:18 PM   #1 (permalink)
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Missing / Popping 7.3L

My 7.3L has began a missing sounds once warmed. I thought it was possibly an injector but now that i have done some more checking on it , I am almost sure it is a valve guide. I had it idling this morning and once it began to warm I heard the random thudding through the exhaust. I had read to listen for a "chuffing" through the intake. When I pull the turbo hat off the intake it was popping through the intake, almost sounded like a fire cracker in a tin can but not as loud. I am really thinking it is an Intake valve guide, and the poppping through the intake was causing the turbo to flutter making the noise through the exhaust. But what I have read is there would be a chuffing through the intake and not a popping.
Has anyone else experienced this. Sounds like I will be pulling the heads back off sometime soon when the weather warms a bit.

Any help or Ideas are appreciated, I have already called around for prices on getting the heads work done and it looks like it will cost about $250 not counting gaskets, so I would like to get some more info from people before I tear into it completely.

The bad thing is I had the heads off a month or so ago for all new gaskets but the engine ran good before, so I just checked all the bearing and cylinders and didn't bother the heads. I had never had a 7.3l have a valve guide problem before so I didn't think to even check that.
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Old 01-16-2009, 07:11 PM   #2 (permalink)
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More info about your truck would be helpful.
If it is popping not chuffing through the intake there are a couple of things to check before you pull the heads.
Try to determine which bank the sound is coming from by loosening the injector lines one at a time. If the noise goes away when one is loosened that is the bank. Remove the valve cover on that side. You will be looking for a bent exhaust push rod, very worn or damaged exhaust rocker or anything else that would cause that exhaust valve to not open. You may need to crank the engine over to ensure the cam and lifter are moving properly. If there is an exhaust valve not opening it can 'backfire' through the intake making the popping sound you are describing.
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Old 01-16-2009, 09:50 PM   #3 (permalink)
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Just watch the pictures......... regarding the valve guides, however as stated above rockers or pushrods could be damaged.

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Old 01-17-2009, 01:08 AM   #4 (permalink)
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Originally Posted by suv7734 View Post
More info about your truck would be helpful.
If it is popping not chuffing through the intake there are a couple of things to check before you pull the heads.
Try to determine which bank the sound is coming from by loosening the injector lines one at a time. If the noise goes away when one is loosened that is the bank. Remove the valve cover on that side. You will be looking for a bent exhaust push rod, very worn or damaged exhaust rocker or anything else that would cause that exhaust valve to not open. You may need to crank the engine over to ensure the cam and lifter are moving properly. If there is an exhaust valve not opening it can 'backfire' through the intake making the popping sound you are describing.

Truck is a 90 F250 4x4 5 Speed. Engine has a little over a 100,000. I swapped the engine into my truck because the truck it was engine was damaged after it rolled (not flipped) over a hill and tore up the front of the truck and frame. The truck belonged to a family member and they gave me everything to convert my truck over to a diesel except the tranny I had to end up getting another one. I had heard the engine many times before and had even driven the truck with no problem. After the wreck the truck was started and everything ran fine, but it was not allowed to reach operating temp because radiator was shot from the accident. The engine had a lot of oil leaks on it, so before I put it in my truck I put all new gaskets and seals in it, including head gaskets, everything looked really good when it was apart (this is not the first engine I have had apart either).I didn't have the head redone because of the relatively low miles and how well it ran before and everything looked good. I put it all back together, stuck it in my truck and it cranked right up. I tried everything out and it was great. I finally got the proper radiator in it so that I could try it out on the road and try the turbo out and when I first get it up to temp it starts this crap. So now here we are. That is all the history I have on the motor.

It only pops through the intake after it has ran for a few minutes and then it gets worse as it warms, does that sound like a rocker arm , it seem that would also cause a problem when cold, but crazier stuff has happened? When cold it runs perfect. I will know for sure tomorrow, when I try to run it some more and try the injectors one by one. I was planning on doing that and pulling a valve cover tomorrow anyway so hopefully, it will point to something. I would much rather it be a push rod or a rocker than having to remove the heads and buy new gaskets again.

Thanks for the suggestions and help, more info is welcomed.

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Old 01-17-2009, 09:10 AM   #5 (permalink)
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After the wreck the truck was started and everything ran fine, but it was not allowed to reach operating temp because radiator was shot from the accident
You did run it with full coolant in it though.......

when you started the engine.........did you just crank it over. On most occasions after rebuild I recommend rolling the engine over several rotations by hand to allow the lifters to bleed down. If they are not bleed off ........the valves or pushrods will/may/can be bent. My suggestion is to remove the rocker covers and check..... rolling the pushrods on a sheet of glass will show any bends. Also remember copper end to the top on installation.
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Old 01-17-2009, 11:57 AM   #6 (permalink)
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Originally Posted by cdnsarguy View Post
You did run it with full coolant in it though.......

when you started the engine.........did you just crank it over. On most occasions after rebuild I recommend rolling the engine over several rotations by hand to allow the lifters to bleed down. If they are not bleed off ........the valves or pushrods will/may/can be bent. My suggestion is to remove the rocker covers and check..... rolling the pushrods on a sheet of glass will show any bends. Also remember copper end to the top on installation.
I didn't personally start the engine as I didn't want to run it with the front of the engine and the front of the engine making contact with each other. The radiator formed to the shape of the front of the engine. I had to replace all the pulleys because they all were crushed. The person who owned the truck wanted to start it to show me how good it ran even though I said "no don't worry about it, I know it runs good." But when I pulled he hoses off to remove the radiator, anitfreeze went everywhere, so it had at least a good amount in it and it wasn't ran very long anyway, I kept telling him that's good you can shut it off, so he finally did.

I turned the engine over many times before it actually starting, when I was bleeding all the fuel lines. I don't see the valves making contact with the pistons because the lifters are not blead. If the timing is off then possibly but the timing was right. If the valves made contact when the lifters weren't blead, wouldnt it bend something everytime you cranked it, the lifters only pump up so much and the valves wont hit the pistons then, so why would they hit when you first crank it? Sorry I might be missing something, if I am please let me know. The thing that is really wierd is when it first starts up it runs perfect with no popping or missing, but after a couple minutes and the engine begins to warm it starts the popping, almost like a lifting is bleading down and not opening an exhaust valve or something. I would think if a pushrod was bent it would pop and miss even when first started, but it runs fine then.

Please don't think I am arguing, I am just thinking out-loud and if my logic is off let me know.
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Old 01-17-2009, 01:37 PM   #7 (permalink)
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Only thing with running an engine without FULL coolant is the heads do heat up fast.... the same happens when air is trapped in the upper block due to a jammed bleed off check ball in the upper coolant manifold. See my photo link.... for the upper coolant manifold. Did you have to change the oil filler/timing gear cover where the Injection pump is and did you remove it with the IP attached.

If the popping comes out of the intake, related to valves would be my first choice. I had a broken valve spring once that cause something similar....... the springs are 2 parts inner and outer. To check for worn guides.... ensure piston is below TDC ...press down on the valve stem 1/8 inch and wiggle it.... any abnormal visible wiggle is bad.

Quote:
If the valves made contact when the lifters weren't blead, wouldnt it bend something everytime you cranked it, the lifters only pump up so much and the valves wont hit the pistons then, so why would they hit when you first crank it?
If the/a lifter(s) are full of oil and not bleed off completely in time the piston will/can contact the valve(s). There is no more than about 35 thousands gap between piston and valve. So a lazy lifter or one not bled down has a great chance of causing touching.
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Old 01-17-2009, 02:23 PM   #8 (permalink)
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Only thing with running an engine without FULL coolant is the heads do heat up fast.... the same happens when air is trapped in the upper block due to a jammed bleed off check ball in the upper coolant manifold. See my photo link.... for the upper coolant manifold. Did you have to change the oil filler/timing gear cover where the Injection pump is and did you remove it with the IP attached.
I took the pump and the cover off to seal everything because it had so many leaks, front timing cover came off as well, I line up the 0s on the crank and cam gear and the Ys on the cam and injection pump before putting the front timing cover back on. It starts great and runs fine when cold but as it warms it is popping on one cylinder. I started up on first try even at 6 degrees F yesterday. I had actually ran the truck a few times before it started to do this.

The day this started I had just got all the turbocharger piping hooked to the intake and I was seeing how it would spool. It had been running for about 15 minutes and it was kinda stuck on a hill in 2WD due to no bed and no weight on the rear end. I goosed it a few times to get it out but ended up having to crawl up under it and put it in 4wd (I am waiting for a new shifter). I easily got up the hill in 4wd so I drove it back down into the drive way to check everything under the hood, when I got out it was running perfect with no problem so I was check over everything at idle looking for leaks when I started to hear and abnormal very very faint missing sound, I thought it was almost in my head at first. I kept trying to figure out where it was coming from and it sounded like I could hear most prominently in the exhaust but it also sounded like it was possibly in the intake but no enough to tell. I shut the truck down thinking for sure it was an injector until the next say when I read about valve guides. I went out started the truck to let it warm and after idling for only about 5 minutes it started sporadic missing / thudding (much sooner than the day before, it took 15-20 minutes the day before to start). I pulled the intake hat off like I had read, thinking it would hear a chuffing but I heard a popping. Almost like a firecracker in a popcan but not quite as ear cracking.

I am going out today to diagnose as soon as I get bundled up, that stinking wind will cut right through you out there.
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Old 01-17-2009, 05:07 PM   #9 (permalink)
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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.
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Old 01-17-2009, 05:34 PM   #10 (permalink)
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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.
Good News

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...and now it runs like a sewing machine.
They must have really loud sewing machines where you live
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