Persistent misfire under load only

[Jimmy Brooks]

Sorry for your troubles. Why does your diagnostic tool seem to think it’s looking at a diesel engine? I’m not sure how trustworthy are the readings you’re getting.

It’s because this is discovery 5 and I’m using a gap tool G3 which doesn’t have the full reading capabilities, I know it’s weird but the information it provides is accurate, the actually issue is that it doesn’t provide much information. What I mean by that is I don’t have access to all of the live data but the the live data that I do have access to is accurate. My biggest issue is that I don’t have access to fuel trims or misfire counters. Anyway, I’m just trying to work with what I got and rule out as much as I can with my knowledge and other’s knowledge before spending $400 to upgrade the tool.

I know the fault readings are accurate because when I saw this for the first time I went to O’Riellys and used their scanner and it showed the Same codes.

 

[powershift]

Have you tried the SDD that is on the Jag forums? If you have paid to use AI then you've paid for stolen copyrighted material so pretty much anything is fair game now. I wouldn't give GAP another $400.

The way I did it was to put that money that would have been sent to GAP into a new laptop and then run SDD. Although I ended up spending $1k for an Acer Predator Helios NEO 16 with an i7 back in '23, its useful for more than one specific specialized thing.

The GAP tool can't do anything except plug into the truck. Its not like its dual purpose hardware where you could load a game on it or load maps. Acer has the best value and you can expand the RAM and HDD after purchase.

 

[greiswig]

It’s because this is discovery 5 and I’m using a gap tool G3 which doesn’t have the full reading capabilities, I know it’s weird but the information it provides is accurate, the actually issue is that it doesn’t provide much information. What I mean by that is I don’t have access to all of the live data but the the live data that I do have access to is accurate. My biggest issue is that I don’t have access to fuel trims or misfire counters. Anyway, I’m just trying to work with what I got and rule out as much as I can with my knowledge and other’s knowledge before spending $400 to upgrade the tool.

I know the fault readings are accurate because when I saw this for the first time I went to O’Riellys and used their scanner and it showed the Same codes.

I think I know what you mean, but I suspect you’re partially wrong. Witness my posts earlier (I think in this same thread) where I point out that it gives me information about the wrong cylinder. So yes, it may be accurate but wrong. As long as you know how to take that into account as you interpret results, you may be OK.

 

[Jimmy Brooks]

I think I know what you mean, but I suspect you’re partially wrong. Witness my posts earlier (I think in this same thread) where I point out that it gives me information about the wrong cylinder. So yes, it may be accurate but wrong. As long as you know how to take that into account as you interpret results, you may be OK.

I read the forum and I did the thing where you unplug the coil and see what it labels each cylinder. When I did it I unplugged cylinder 2 on the V6 layout and it called out cylinder 2 when I put the ignition on engine off. Did the same for cylinder 3 and it labeled it cylinder 3. Do you think the misfire codes would call out the same way as the coils did or do you think it would revert to the V8 (10-13) layout? If you think it reverts to the V8 layout then I might have to swap cylinder 5 injector (cylinder 4 on the V8 layout) to see if that fixes it.

I’m just still stumped by why it won’t call a misfire out at all. Part of me thinks it might not be a misfire. With the weird RPM behavior when im in park reving it up I’m starting to think it could be a throttle positioning sensor… but from what I’ve read those normally those throw codes when they’re bad.

 

[Jimmy Brooks]

Have you tried the SDD that is on the Jag forums? If you have paid to use AI then you've paid for stolen copyrighted material so pretty much anything is fair game now. I wouldn't give GAP another $400.

The way I did it was to put that money that would have been sent to GAP into a new laptop and then run SDD. Although I ended up spending $1k for an Acer Predator Helios NEO 16 with an i7 back in '23, its useful for more than one specific specialized thing.

The GAP tool can't do anything except plug into the truck. Its not like its dual purpose hardware where you could load a game on it or load maps. Acer has the best value and you can expand the RAM and HDD after purchase.

Is the SSD cheaper than the upgrade?? I’m just not trying to spend more money than I have to on a tool that realistically I would only be using on one car. I can’t get the money back that I already spent on the gap tool.

 

[greiswig]

Do you think the misfire codes would call out the same way as the coils did or do you think it would revert to the V8 (10-13) layout?

Here is how at least my GAP tool denotes the cylinders, compared to how the engine codes denote them (true cylinder numbering).

 

[Jimmy Brooks]

Here is how at least my GAP tool denotes the cylinders, compared to how the engine codes denote them (true cylinder numbering).

What does the codes mean vs gap. If I got a code for misfire on cylinder 4 on the gap tool would that mean drivers side middle cylinder or drivers side front cylinder?

I wouldn’t have a problem pulling another injector if it is the middle cylinder

 

[greiswig]

What does the codes mean vs gap. If I got a code for misfire on cylinder 4 on the gap tool would that mean drivers side middle cylinder or drivers side front cylinder?

I wouldn’t have a problem pulling another injector if it is the middle cylinder

“Codes” means when you pull a code, such as P0304, even with the GAP tool, the code itself is pointing to the appropriately-numbered cylinder. The GAP tool is just “reading the code” straight off the computer, not trying to interpret it. So P0304 would be #4, driver’s side front.

“GAP” on the other hand means that if you are trying to monitor live values for the #4 cylinder, you’ll want to ask the tool to look at #2 instead, because the live values seem to think there are 8 cylinders, with the odd ones all on the passenger side.

Note, however, that this is for a GAP tool that is configured to read the SCV6. I have no idea what your diesel-configured tool is doing.

 

[Jimmy Brooks]

“Codes” means when you pull a code, such as P0304, even with the GAP tool, the code itself is pointing to the appropriately-numbered cylinder. The GAP tool is just “reading the code” straight off the computer, not trying to interpret it. So P0304 would be #4, driver’s side front.

“GAP” on the other hand means that if you are trying to monitor live values for the #4 cylinder, you’ll want to ask the tool to look at #2 instead, because the live values seem to think there are 8 cylinders, with the odd ones all on the passenger side.

Note, however, that this is for a GAP tool that is configured to read the SCV6. I have no idea what your diesel-configured tool is doing.

the tool won’t even go as far as giving me a misfire counter for live data… I’m going to purchase this new tool to properly diagnose.

In the meantime, does anyone have any ideas why fixing a small leak in the PCV system would make a misfire/stutter in rpms so much worse?

 

[greiswig]

In the meantime, does anyone have any ideas why fixing a small leak in the PCV system would make a misfire/stutter in rpms so much worse?

If the fix didn't actually fix it and made the leak worse? Or if the previous leak somehow made an existing condition (rich mixture?) more tolerable on that bank? Or if the fix caused a barely-functional PCV valve to start malfunctioning? IDK