7.3 slight miss, knock, but compression and injectors seem OK... What could it be?

QuercusRubra

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99.5 F550 7.3 Powerstroke 4x4 ZF6

Makes a knock when driving that has a metallic ring to it. Sometimes it's barely there in the diesel noise, occasionally it's so loud that nobody can miss it.

Computer is reporting cylinder contribution failure on #4 and #8. However, I swapped them with #2 and #6 and the cct failure stayed on #4/8. All 8 are new rebuilt from Full Force diesel. New glow plugs, new vc gasket, new icp sensor, ipr valve, cps sensor among others. Completely resealed fuel and hp oil systems with hutch mod, regulated return, hp oil x-over, no fuel or oil leaks up top, except for drin valve just started and possibly the ebp valve leaking a bit of oil when active, but the valley is clean.

I just did a compression test pretty much cold and dry, tho a little oil was likely in the cylinders from the glow plug holes. I vacuum out the oil from on top of the glow plug before I remove it, but there's probably a little anyway? Found all cylinders between 380 and 425, but #8 is one of the highest the middle ones are a bit lower, but I don't think that's a lot, is it?

HPOP at idle is a little under 600psi at startup and a little over 500 hot., maxing out around 2800 with 35% duty cycle, (to the best of my memory). Fuel pressure is solid 62 to 64 always.

Pulling the electrical plug to each cylinder whe its running makes it stumble pretty badly on each cylinder. About the same to my ear.

So what's causing this knock, puffs of smoke at the tailpipe, shaking engine/cab like it's missing and cct failure, but compression is pretty good and compression is really good on one of the failing cylinders, and the failure didn't follow the I jector to a new cylinder?

I'd say it starts well and has pretty decent power. I can tow a 13k trailer 30 to 40mph up a moderate hill from a stop, and I'm weighing a little over 23k total

When I got it, the fuel pickup was pretty bad, and my theory was it sucked a lot of air and killed the injectors? There were times when it ran OK, and times when it was a challenge to make it over a bridge on a flat highway goi 30 to 40 mph, and it would pour out smoke. And it leaked buckets of oil and fuel, I think. When I got it back it could start/run/drive OK, but when I Rev it up or under hard load it cackled walnuts going through a grinder and made a huge cloud of smoke.

What kind of internal damage could this situation cause? Could it make a rod knock? Given that you can't run a powerstroke low on oil I don't really know what makes a rod knock?

See my other videos in this: compression tests on each cylinder, cold starts.

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greenskeeper

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What's your fuel pressure @ idle and under load?

Have you ever rebuilt the fuel pressure regulator?
 

QuercusRubra

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I have the Dieselsite regulated return kit along with the hutch mod (in tank pickup) and hp oil xover. Fuel pressure on the regular output is always a solid 62 to 64. I wonder if I should try turning it up a little, tho 60 should be plenty, right?

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paramax55

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Why did you have the injectors rebuilt? What was the problem before? When did this problem start?
 

QuercusRubra

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I bought it with reportedly bad injectors. Stomp on the throttle, it would sputter or hesitate, make a bunch of smoke and make a scary loud kackl like grinding up walnut shells. Even when sitting if reved to a certain point, maybe 1500 it would start to billow a cloud of smoke and kackle or whatever it was.

Dropped the tank and it looked bad, lots of sludge, umbrella off, all in rough shape. My guess was it was suckling air, which would kill the injectors.

Also, a few times on my drive from Florida to NY, it had so little power that holding 35 to 40mph was hard. It would smoke then, also.

So to make a long story short, I did a lot of work and now I'm just trying to diagnose these symptoms that don't really make sense to me.

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paramax55

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That can make a difference - you bought the truck with a problem, put some parts on it, and it's still broken... Are these the same injectors, just sent in and rebuilt? Or a completely different set? Dumb question, but did you change the oil? And have you verified the quality of the fuel? You said there was a bunch of crap in the tank - how did you clean it and are you sure it's clean? After you did all the work, did the truck change at all?

The truck can run OK with completely F-ed up injectors. I know because I used to run WMO fuel in mine and I had to swap/clean my injectors all the time. Can you monitor high side oil pressure and fuel pressure while you are driving? You can use a cheap bluetooth OBD2 device and watch your parameters on the phone using Torque Pro as you drive around. Any of my bad running I've been able to trace back to high side oil issues or fuel pressure issues.

Oh, yeah... one other thing... how far have you driven it since swapping the injectors? It can easily take 20 miles to get all the air out of the high side system and it will do ALL SORTS of strange crap in the mean time (surging, clattering, stumbling, etc...).
 

QuercusRubra

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Thanks for your response. The truck does run better now than when I got it.

These are new rebuilt I jectors, not my originals rebuilt.

I removed the tank, scrubbed inside and rinsed it well. Replaced the pickup with the Dieselsite hutch mod kit and the inline spinon filter.

I have changed the oil 3 times... Long story.

I have a fuel pressure gauge in the cab, reading off the pressure regulator. I also have the torque pro app running. HPOP press is aro 470 idling warm, and peaks out around 2800. Fuel pressure was reading solid 62 - 64... I just raised it to 68...havent run it enough to know if that did anything.

I'm confident the air is out of the system. I've worked it pretty hard.


That can make a difference - you bought the truck with a problem, put some parts on it, and it's still broken... Are these the same injectors, just sent in and rebuilt? Or a completely different set? Dumb question, but did you change the oil? And have you verified the quality of the fuel? You said there was a bunch of crap in the tank - how did you clean it and are you sure it's clean? After you did all the work, did the truck change at all?

The truck can run OK with completely F-ed up injectors. I know because I used to run WMO fuel in mine and I had to swap/clean my injectors all the time. Can you monitor high side oil pressure and fuel pressure while you are driving? You can use a cheap bluetooth OBD2 device and watch your parameters on the phone using Torque Pro as you drive around. Any of my bad running I've been able to trace back to high side oil issues or fuel pressure issues.

Oh, yeah... one other thing... how far have you driven it since swapping the injectors? It can easily take 20 miles to get all the air out of the high side system and it will do ALL SORTS of strange crap in the mean time (surging, clattering, stumbling, etc...).



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paramax55

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My high side oil pressure was down where yours it at idle until I cleaned my IPR. Now it's closer to 600 at dle, but I am running a tune. Fuel pressure is fine from what you're describing. My inline filter will clog occasionally and I don't even notice a difference until fuel pressure gets well below 40. Usually 20 is the magic number where I notice something isn't right, then I look at the pressure gauge, see what's going on, then pull into the closest parking lot.

Is it possible you have single squirt injectors with a double squirt tune? Or vice versa? If you bought the truck with a problem, someone could have installed a junkyard computer with the wrong tune to try to fix it. That will throw your timing all out of whack. And you could also try swapping the IDM with a known good one. They are usually all or nothing, though, so I wouldn't put it high on the suspect list yet.
 

QuercusRubra

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It's a new IPR valve, so I doubt that's it. But how did you clean yours? There's always a possibility of some bit of dirt getting in somewhere when I had everything all apart.

My impression is that if dirt did get in somewhere, it would probably make it all the way to the fuel injectors, are there any fuel or oil passageways on the way small enough to be blocked by a small bit of dirt?

It seems like moving the injectors around has ruled them out as a culprit.

I'd say little chance Full Force sent me single shots instead of the stock injectors. But I can't vouch for the pcm. The idm does appear to be rebuilt.

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paramax55

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I saw that you have a new IPR. That's why I memtioned that I have a tune because that can change the high side pressures. It's probably not the problem, but it's not hard to clean. If you do a search on youtube for "7.3 ipr cleaning" the best video is only about 3 minutes long. The key is using a sharpened scraper to get the plug out. You'll see.

I don't think you got a different type of injector than what you sent in. But you may still have something different than what the computer wants. Remember that the truck ran bad when you got it. If someone put the wrong computer in it before you bought it, it will still have the wrong computer. The injectors may match the truck, but not the computer. It's worth ruling out. If you pull the parking brake, the computer is right behind it (I think it was only 3 bolts). You should be able (if I remember correctly) to pop the cover off the back of the computer. It should have a sticker on it that says what bin it was programmed with. A little time in the googles should let you know what injectors that bin is designed for.

As far as the IDM goes... I burned up a couple of them over the years - then I found out why. Even a stock IDM will send 120V pulses to the injectors. When the fields collapse afterwards, it's like 8 miniature ignition coils trying to send all sorts of RF noise into the system. Ford wrapped a ground wire around all of the high voltage wires as a shield. That worked fine for the first 20 years or so, but eventually the ground ate through the casing for the 120V wire and started shorting it out. My symptoms weren't like yours, though. My single symptom was a truck that stopped running instantly.

That makes me think of something else... you mentioned that the IDM looks rebuilt. What if there was something that killed the IDM AND the computer... the truck stops running... replace the IDM and the computer... the truck runs like crap... tired of dealing with the truck... sell the truck...

I've had 2 things make smoke out the tailpipe... 1 is low fuel pressure (which shouldn't be a problem for you) and the other is dirty injector tips. But I've never had timing that was way out of whack from the wrong computer. I would think that bad oil pressure on the high side could do it, too.

Anyway, there are a couple of things to look at.
 

greenskeeper

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pull the valve covers, while it's "knocking" unplug one injector at a time, see if the "knocking" goes away. This will pinpoint which injector/cylinder has the problem

*edit* or smoking at cold start in the last video....if you disconnect an injector and the smoke goes away....there's your problem.

In the last video, does the smoke eventually clear up as the engine reaches operating temperature?
 
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paramax55

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He already posted that he tried unplugging injectors. He even pulled them and swapped them. He's also done a contribution test.
 

QuercusRubra

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Yes, when warmed up, I don't see smoke. Also, it runs much smoother.

I did unplug injectors, one at a time too, and they all made a big difference in idle, all about the same to my ear.

Maybe I'll leave the valve cover off with the truck outside overnight and see if unplugging an injector changes the smoke puffing.

Is it possible to drop injectors through a scan computer? I just have a Bluetooth adapter and my phone, which doesn't seem to offer that capability, but a friend of mine has an expensive snap on scanner, and I wonder if that would do it?

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greenskeeper

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does it smoke after being plugged in overnight (with a known good heater) ?
 

QuercusRubra

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The heater works, but I haven't tried it in this case. I can say that in the summer when it was hot it smoked just a little, I'd say not much. I'll try the heater now, for comparison.

So what would this tell you?

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