From time to time only when warmed up, either just off idle, or high(ish) load with low RPMs I get a mild stutter in how the engine is running.

It’s never stalled, and it only does it in gear, never while just sitting neutral or park.

I have gotten missfire conditions- no codes thrown, though- front time to time when I monitor with the Nanocom. I’ve set up screens in the Ultragauge to monitor fuel trims and O2 sensor performance, and have off and on looked into it, but frankly get busy and with as rarely as I drive the Disco (I’ll drive it regularly for a month or a few weeks, and then not drive it for a month or so) I’ve never really jumped in to fully resolve.

I’ve made off hand comments previously on this in various threads, but didn’t really address and can’t remember some of the advice that was given.

I’ve done a MAF, O2 sensors, cleaned the IAC and throttle body, done the PCV change, replaced the vacuum boost line, done the transmission fluid and filter (but I still have P0501 that I’m going to replace the VSS to address), and I think that’s about it.

I’ve got spark plugs to put in and was thinking about doing injector seals while I have the intake off, and possibly the valley pan gasket? Anything else you guys can think of I should e looking at? I have to believe this is a vacuum leak somewhere deep (thus injector seals) as it only happens in the conditions I put above.

I’m not really concerned about this as it’s happened off and on for a couple years now and never really hurt anything. At now just about 187k miles, the thing runs darn near like brand new and is smooth as I could ever ask for. I drive it like a total grandpa and rarely rev it over 3k RPM, but I also run nothing but tractor gas in it. I do a can or so of Sea Foam once or twice a year and have also done the intake cleaning where you put a hose in the can and run it straight to the intake.

I think it’s running fat as the economy seems to have dropped off a bit at just over 12mpg (it used to be over 15 most of the time- told you I drive it like a grandpa), which again leads me to think it’s a vacuum issue and is dumping more fuel to account.

 

So I’m still trying to track this one down. I drove the Disco today and it did stuttered pretty bad- sometimes even more under load.

It eventually threw a P420 code. It has done this before. In researching this, are the “catalytic converter cleaners” worth looking at? I just ran a couple bottles of Sea Foam in the tank and got another bottle of Lucas injector cleaner that I’ll run the next tank.

I had narrowed this down to needing to do injector seals, but a lot of stuff is saying the cats themselves are bad. I’m at 187k on the clock.

Could I have a bad injector? I thought there were codes for that, though?

I’m pretty stumped on this one and my economy seems like it’s getting worse.

 

Oh yeah, these were a couple shots of the fuel trims:

When I started monitoring during the drive home (stop and go most all the way)



Later the numbers for the long term trims dropped.



I monitored the O2 sensor page too but didn’t take any pics and can’t recall what the numbers mean anyway. I need to drive it again and compare and report…

 

How old are the coil packs? I presume plugs and wires are not ancient.

I ask because I recently had the cat converter code (P420), decreased MPG, but no studder. I also had a specific mis-fire code (cyl #1 fwiw). I knew I had a mangled plug wire on #1. I replaced coils when I did head gaskets at 145k (now 178k) so I kinda ruled them out.

Changing the plug wire (which I knew was compromised) fixed everything. MPG went from 12 to 14 and codes were gone.

I guess what I'm saying is, if the coils are 'old' and you are going to rip the top end apart, think about replacing them, and wires/plugs as well.

Heck, just start with plugs and wires since they are the easiest and cheapest to change.

 

@WaltNYC you, like so many people on this forum are such a huge help and make all this stuff fun.

In my research on the web and in this forum, I found another thread I started a few years ago regarding a different code but the same symptoms and I’m trying to compile all that data. There were a couple of other posts I made and great responses that I was trying to find to refresh my memory on things.

As I looked through how to actually use the UG and the pages I set up for fuel trims and O2 sensor performance I was reminded of some of the data I captured to help with analysis. I think the O2 sensors are working because up and downstream numbers are not mirroring and adjusting at what appear to be acceptable levels.

But on the fuel trims, the fact that I have negative numbers for short term an awful lot means it’s sensing lean situations due to too much O2 and thus dumping more fuel, which is then reflected in the high numbers for the long term fuel trim.

OK, that aside and why Walt’s input was so key: I too have seen cyl 1 missfires a good bit, but no codes.



I cleared things, reset adaptive values and went on my way. (Then of course didn’t drive the Disco for a while and forgot all my research and data and such). This is why I wanted to find the posts I made- and subsequent great responses- that basically lead me to think either a plug, maybe plug wire or coil were the culprit. But when I swapped the cyl 1 plug, it was not bad.



When I presented this, some folks mentioned this was more of a vacuum leak situation and eventually came to the injector seal being a source. Now enter Walt’s input coupled to that. Apparently one of the coils was replaced prior to my purchase and for some reason I thought they said wires as well. However, based on the similarities to Walt’s experience, I am back to a plug wire wince the plug was in good shape.

As such, my course of action is going to be to FINALLY do the plugs, and when I do those, I’m just going to do a bunch of “while you’re in there” activity: injector seals, coils, and probably wires.

This tells you how busy I’ve been over the last few years as my initial thread on this (https://landroverforums.com/forum/di...ources-115849/) was prior to moving to Euroville for a couple years and the Disco sitting in storage. I’m just finally getting to it- which is a lot of the reason I like Discos as they are very forgiving on stuff like this and soldier on until you can get to it- and I think now have a course of action.

Adding to my motivation for resolving this is our barn is almost done, which will give me a decent space to work with minimal pressure and I can do it at my convenience.

Thanks for pushing me in the right direction, Walt! I know I’m doing a bit of a parts throwing exercise, but these are all parts that frankly are mild consumable and have not been done since my tenure with this Disco, so a good idea just to add to a baseline.

 

Here's my two cents worth. High long term trims mean the system is adding fuel (nearly 15%) in order to compensate for high oxygen (lean condition). A tight motor should read less than 5% LTFT according to my mechanic. Resetting Adaptive Values should set LTFT back near zero. Occasional negative short trims shows the system is trying to maintain stoichiometry by pulling fuel. Since vacuum is higher with the throttle closed at idle, the short term could go positive to add more fuel, then on the road, when manifold vacuum is less, the short term could shift to negative, especially wide open. The total trim is simply the Long and Short added together. Total trim adds or subtracts from the base value calculated by the ECU for injector pulse width.

Looks like you are on the right track. I found grains of sand can work down to injector seals and potentially cause leaks. Clean well before removal. Will be interested to see LTFT decrease to better values after a few hundred miles with the repairs complete. If so, you found the vacuum leaks.

 

I like how you put this and agree, so thank you.

It may be one or all of the components I listed causing the stutter, with one more possible that I’m debating on (but probably won’t do at this time) and that’s injectors. In the coming weeks I’ll order the seals, coils, and wires, and depending on what I see I’ll decide on the injectors.

I’ve heard of folks hooking up individual injectors to a 9v battery to see about spray pattern/strength and while I have them out, it seems a good idea. I suspect they are good based on how smooth it runs, despite this issue (and obviously based on the data looks to be isolated to cyl 1), and if I test that one and it’s good, then I don’t think replacing them is really going to do much.

 

Thanks for your kind words.

Karlyn STI 721 8mm wires + NGK BPR6ES plugs work well in the P38.
BOSCH 0221503407 coil packs

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