Re:Which cylinder is blown?

Tyler wrote: Which cylinder is blown?

I am going to go with Cylinder #5.

It's an expansion tank system, too, which (in my opinion) adds a delay between TDC on the blown cylinder and a pressure pulse at the tank.

I could be wrong, and it will be interesting to find out, but I don't think there will be a significant delay. Liquids do not compress.

Tyler wrote: I guess the running test would also depend on if the suspect cylinder is blown badly enough that it'll leak under running compression pressures, or if it'll only leak under combustion pressures...

What I'm thinking is the combustion pressure should be significantly higher than the running compression pressure. So killing spark to the leaking cylinder might cause a noticeable reduction in the pressure spike.

Chad wrote: I could be wrong, and it will be interesting to find out

Yeah, about that... The truck is gone. :blush: Before taking stuff apart, we called the customer and they pulled the plug. I'm told it went something like this:

SA: "Hey Mr. Owner! So we found that you have a blown head gasket on your Ford..."

Mr. Owner: "Stop. I ain't fixin' it."

Sorry, we'll never know. :silly: I mostly wanted to put this to the group because I've never found a blown head gasket on a V8 using this method before.

My instinct was to start looking at when the pressure started increasing from its lowest point, which would make the suspect #2. :huh: But I definitely see the sharp increase that goes along with #5.

...but I don't think there will be a significant delay. Liquids do not compress.

Maybe not? I was thinking more about the air in the top of the expansion tank. It my head, it would act like a buffer. But I'm not a physicist.

Tyler wrote: My instinct was to start looking at when the pressure started increasing from its lowest point, which would make the suspect #2. :huh:

With an Absolute Pressure Transducer, this would be the case.

But I definitely see the sharp increase that goes along with #5.

Delta sensors have waning oscillations. So, in this case, the lowest point is, actually, the rebound of the pressure spike. You need to look for an...unnatural?...change in the pattern, indicating pressure change. That is how I look at them, anyway. It has served me, well, so far.

Maybe try pinching off the hose to the expansion tank to see if it makes a difference? That may tell if it is another variable to consider or not.

Nissan Technician

Let's play the game again! :lol: A different Ford 5.4L with another blown head gasket. '03 F-250. Have Modular engines always been known for head gaskets? :huh: 'Cause I haven't seen one before, then I see two in a month...

Zoomed out. Sync on #5. 1-3-7-2-6-5-4-8:



Zoomed in:



If we look for the upswing in the pressure sensor relative to spark timing, it sure seems like #3 is our prime suspect. BUT, the monkey learned from last time. I checked Mode $06, TID $53:



As usual, I've done no disassembly, so I don't know which cylinder is blown. But the PCM sure thinks #1 has a problem.

Unlike last time, this truck is getting an engine, so I'll be able to do some inspection on the old engine when I get it out.

:blink: This one is not so clear but, I'll venture a guess. The sharpest pressure change does coincided with the beginning of cylinder #1 compression stroke. This agrees with mode $06. But, the pressure increase, also, coincides with the second half of cylinder #8 compression stroke. It seems to me that if it were cylinder #1 the pressure increase would increase all the way to TDC but, it doesn't. It takes a little dive before TDC. And, then, looks like it gets another contribution from cylinder #3. :woohoo: I don't feel real confident in this guess but, :dry: I'll go with Cylinder #8



Is this a cranking waveform?

What happened at the end?

It, also, seems to me that the pressure increase begins too early in the #1 compression stroke. Pressure doesn't start to build in the cylinder until the intake valve closes. As a rule of thumb, this happens around 30°-50° after BDC. This pressure rise starts at about 17° after cylinder #1 BDC.

Chad wrote: Is this a cranking waveform?

What happened at the end?

NONEYA BUSINESS, THAT'S WHAT HAPPENED.
























Kidding! :silly: It was indeed a cranking capture. Here's another shot of the end of the capture:



I hadn't really noticed the extra tall pressure pulse until you pointed it out... :huh: Any theories?

Tyler wrote: Any theories?

Final stroke stopped TDC? Instead of traveling back down and decompressing?

Chad wrote: Final stroke stopped TDC? Instead of traveling back down and decompressing?

That's what I was thinking about. Plus, the water pump stopped turning, which I'm guessing has some kind of impact on the waveform.

When I get the blown engine out, I'll pull plugs.

Tyler wrote: I hadn't really noticed the extra tall pressure pulse until you pointed it out... :huh: Any theories?

That pulse portion of the trace appears to show two ignition events after the last #5 sync. It looks like you did stop the engine around TDC #8 which is the cylinder Chad thinks is bad.

Tip for telling whether you're looking at a cranking or running trace. 600 rpm is 100mS per rev or 200mS between 720* syncs. So anything 200mS or less is running. This trace is 600mS between syncs which is a healthy 200 rpm crank

Matt T wrote: This trace is 600mS between syncs which is a healthy 200 rpm crank

That's about the only thing this engine did very well. :silly:

Update! The F-250 engine came out this week. For reference, this is the waveform I started out with. Firing order 1-3-7-2-6-5-4-8, sync on #5:



So which cylinder was actually blown? That'd be... #4. :huh: I had to check all cylinders several times to be sure. #4 had coolant pooled up on the piston. All other cylinders appeared normal.

If I was a betting man, I'd have lost on this one. :silly: #4 was not on my radar. But maybe it should have been? This is the overlay Chad was kind enough to provide:



Marked up this way, it kinda makes sense! #4 goes all the way to TDC compression, then there's a slight delay until the pressure rises in the cooling system. Not a long delay, 17 crank degrees, but it's there. I'm sure the severity of the leak and the cooling system size has something to do with that.

Definitely learned something here. Stay tuned - the first 5.4L waveform I posted (from an '02 F-150) bought an engine, too. I'll be following up with that one when it gets pulled.

Tyler wrote: If I was a betting man, I'd have lost on this one. :silly: #4 was not on my radar. But maybe it should have been?

I lost, too. But, we all learned from this one.

#4 goes all the way to TDC compression, then there's a slight delay until the pressure rises in the cooling system. Not a long delay, 17 crank degrees, but it's there. I'm sure the severity of the leak and the cooling system size has something to do with that.

Something else to consider is that the sync is an Ignition event, which happens X­° before TDC. The piston chart overlay is positioned by an assumed TDC. It may by off by Y°.

Definitely learned something here. Stay tuned - the first 5.4L waveform I posted (from an '02 F-150) bought an engine, too. I'll be following up with that one when it gets pulled.

Awesome! I'm eager to see the outcome.

The engine came out of the '02 today. For anyone following along, these were the initial captures. 1-3-7-2-6-5-4-8, sync on #5.




And the leaking cylinder on this 5.4L is....

#5!

Which means, Chad won! Called it from a mile away:



I guess the takeaway from these blown V8's is that you CAN call the blown cylinder, it just takes a keen eye. For whatever it's worth to those following along, replacing cylinder heads or gaskets was not an option on either engine, IMO. Both had close to 200K miles, and both had been overheated repeatedly. It didn't really matter which cylinder was blown in either case - engine replacement was the answer.

Tyler wrote: Which means, Chad won! Called it from a mile away:

Thanks for the update!