Cylinder Dead - I think - How do I confirm?

[NXTLEVL]

Hi guys

I've got a problem I need some help with. I went to the strip this weekend and on the drive home the car was running very poorly. Felt like it was a cylinder or two down. I've felt this before when a plug wire came off of a coil so I know exactly how that feels and this feels like that. I don't have any check engine lights and no other signs anything is wrong.

My first thought was to get out my pyrometer and check each primary tube to see which cylinder wasn't firing. This didn't produce any usable results as cylinder to cylinder I saw temperatures vary by 100 degree at idle. Anywhere between 390 and 510. Mind you this is through wrap as all my exhaust is wrapped completely.

My second idea was to use HP Tuners and check cylinder misfires. This produced NO results, literally. I didn't see a single misfire captured either on the current or historical channels. I thought that was weird but again, I didn't have any codes come up indicating I had a misfire this time or the time the plug wire fell off which makes sense I guess since the cylinder is technically totally dead and not misfiring.

Which leads me to this post. Where do I go from here? I'm nearly 100% sure a cylinder is not working but how do I track it down? Physically, HP Tuners?

[cmack]

I had spark problem, it was blowing out spark (only at wot), even though it was gapped correctly. After searching, I found cyc #4 and #6 both hard torched spark plug wires (MSD). The looked fine from top, once you removed them, the underneath of wire was torched. I still had my OEM wires, replaced them and problem resolved. I also did not have any cel. You can test resistance of wires, those two of mine failed.

[NXTLEVL]

I've inspected all wires and I just went out and put a timing light on each one and they all showed as firing. Now I'm back to square one. If I have no codes, HP Tuners says I have no misfires and the timing light says all coils are firing I'm not sure where to go next. It's a twin turbo car and getting to ANY of the plugs is a nightmare so I'm very hesitant to pull them and take a look especially if I have no evidence of a spark issue.

Given I have no real idea where to start now this thread will probably be jumping around a bit. Here's a random question that I should know the answer to. The valves on the charge side of the turbos (going to the intake) I believe are bypass valves. See picture below. These are open at idle and closed when the car is off. I'm assuming that's correct. I've never really looked at them before and wanted to eliminate that as a potential issue.

[morepowerjoe]

Your post would probably be better in the forced Inductions V8 thread. But I'll try. That looks like your blow off valve. As far as I know you don't want boost at idle, so yes it would be open at idle. As far as your misfire goes, you can still have a wire fire to a bad plug. I'm going to bet you have a fouled plug or possibly a broken plug or two and the only way your going to find out is to take out the plug and physically inspect it.

[NXTLEVL]

Yeah.. :(

I know that's probably what needs to happen. Well, I'll post back in a week once I get the plugs out. LOL

[NXTLEVL]

Plugs out and every one of them looked perfect. One was slightly wet but nothing major. New plugs in, all the wires I broke getting them off are replaced and the issue is still exactly the same. So I'm back to square one.

What I really need is some guidance around how to diagnose cylinder health via HPTuners. Plug access is nearly impossible so doing things like compression and leakdown are out of the question. Are there any pseudo methods to look at individual cylinders to at least try and narrow down where an issue may be?

[joshnmn]

Are all of your trims looking like they were before? If you have a spark issue it will show lean on the affected bank.

[NXTLEVL]

Unfortunately, I don't have any logs to compare to and I'm such a newbie with HPTuners and I'm not even sure how to include that channel or what the values should be. At this point I'm not sure it's even a spark issue.

I was researching how to test for cylinder issues and what I read most was about commanding a certain idle RPM and then shutting down individual injectors and seeing if that made a different to the idle quality/sound as a way to determine if there was an injector issue. I was going to try that but then I thought, wouldn't I see a fueling issue when I look for misfires? Or if the injector was not firing at all would it still not record a misfire as the cylinder is technically completely dead?

The I got to thinking even darker and thought what if I wiped out a cam lobe? Good fuel, good spark, good cylinder temps but reduced or eliminated valve action. I figure it would still act like it was down a cylinder but wouldn't show a misfire? Just spit-balling at this point...

Any help is appreciated.

Does anyone know how to command an idle RPM and shut down injectors? Is this even a good next step?

P.S. Oil pressure is perfect, oil looks clean and shows no signs of metal, there are no unusual sounds, car fires right up every time, I drove it 110 miles home from the track with this issue present.

[Badbubba]

You could perform a relative compression check. Need equipment to do it. It measures the current from your battery as each cylinder goes through it's cycle. If a cylinder is down on compression, it will not require as much current, amps, for the starter, as compared to the other cylinders. Whether it be a spring, rocker, cam, rings, lifter, etc. You can set a trigger on #1 and then know your firing order and look at the current peaks. I haven't tried it, but supposedly if you hold the gas pedal down, the car will act as if it was flooded, so the injectors would be shut off. Be certain the throttle body is open. Leave plugs in. Could even try this by listening for even and consistent speed in cranking.

[Badbubba]

Originally Posted by NXTLEVL

Unfortunately, I don't have any logs to compare to and I'm such a newbie with HPTuners and I'm not even sure how to include that channel or what the values should be. At this point I'm not sure it's even a spark issue.

I was researching how to test for cylinder issues and what I read most was about commanding a certain idle RPM and then shutting down individual injectors and seeing if that made a different to the idle quality/sound as a way to determine if there was an injector issue. I was going to try that but then I thought, wouldn't I see a fueling issue when I look for misfires? Or if the injector was not firing at all would it still not record a misfire as the cylinder is technically completely dead?

The I got to thinking even darker and thought what if I wiped out a cam lobe? Good fuel, good spark, good cylinder temps but reduced or eliminated valve action. I figure it would still act like it was down a cylinder but wouldn't show a misfire? Just spit-balling at this point...

Any help is appreciated.

Does anyone know how to command an idle RPM and shut down injectors? Is this even a good next step?

P.S. Oil pressure is perfect, oil looks clean and shows no signs of metal, there are no unusual sounds, car fires right up every time, I drove it 110 miles home from the track with this issue present.

Could pull and replace each spark plug wire to find out what cylinder(s) make a difference with the miss.

[morepowerjoe]

Originally Posted by Badbubba

Could pull and replace each spark plug wire to find out what cylinder(s) make a difference with the miss.

That's what I would do too.

[Badbubba]

Originally Posted by NXTLEVL

I've inspected all wires and I just went out and put a timing light on each one and they all showed as firing. Now I'm back to square one. If I have no codes, HP Tuners says I have no misfires and the timing light says all coils are firing I'm not sure where to go next. It's a twin turbo car and getting to ANY of the plugs is a nightmare so I'm very hesitant to pull them and take a look especially if I have no evidence of a spark issue.

Given I have no real idea where to start now this thread will probably be jumping around a bit. Here's a random question that I should know the answer to. The valves on the charge side of the turbos (going to the intake) I believe are bypass valves. See picture below. These are open at idle and closed when the car is off. I'm assuming that's correct. I've never really looked at them before and wanted to eliminate that as a potential issue.

Since they are on the intake and vent to air, they are Blow Off Valves. From my experience, they should be closed. They open to prevent what is called compressor surge. This happens when the charge pipe has pressure and you lift off the gas, closing the throttle body. The pressurized air in the pipe will stall the turbo(s), potential damage. The BOV is what gives you that whoosh/pshhhh when you let off the throttle. A waste gate is used on the exhaust side with a boost controller to regulate boost. It bypasses exhaust gases around the turbo. The waste gate can be external, ewg, and vent to atmosphere or back into the exhaust. Or internal, built into the turbo. Also if it is MAF tuned, the open BOV is allowing unmetered air to enter the intake and cause poor running conditions.

[joshnmn]

The MAF is typically close to the throttlebody, downstream of the bov(s). It doesn’t matter if they’re open or shut, the engine is just getting air from different places. Whether it’s open or shut depends on manifold vacuum vs bov spring pressure.

[Badbubba]

Originally Posted by joshnmn

The MAF is typically close to the throttlebody, downstream of the bov(s). It doesn’t matter if they’re open or shut, the engine is just getting air from different places. Whether it’s open or shut depends on manifold vacuum vs bov spring pressure.

Going back and looking at his avatar and description, it appears it's a twin turbo. So then the MAF is most likely down stream, after the intake piping merges. Since having dual MAFs would be difficult. So, then, yes, you'd be correct. It would not be unmetered air. Single turbo could be either way.