Hi All

I hope everyone is surviving this very interesting 2020!

I had a road trip over the summer and got some gas in a very rural area, leading to some misfire codes. Refilled later on the I-95 home and everything returned to normal so I put it down to bad gas. However, these codes have now returned.

I'm getting multiple misfire codes on different cylinders, and truck now has close to 100k miles. I recently had it serviced by a LR specialist and plugs were replaced as part of this. I've done the following:

Cleaned Throttle Body
Replaced MAF
Replaced All 8 Coils.
Replaced PCV Valve.
Ignition Capacitor (replacing today)
Cleaned Electrical Connectors

None have made any difference to reduced engine performance. Yesterday the truck threw up lean codes on Bank 1 and 2 but the power was restored for a brief time before reduced performance warning returned. I decided to run some live values to see if I could spot any trends and it seems the majority of misfires are happening on cylinder 8. Once the engine cooled I checked plugs 2 and 8, and 8 has a definite orange ring at the bottom of the porcelain. I watched a useful British Atlantic video which hints at possible coolant leak.

So, given the above, Am I looking at a leak (exhaust fumes smell sweet) and how can I further diagnose? I'm desperate to do as much as possible and learn, but equally, if the job is requiring a specialist, I'd rather not tinker further and get it into the shop.

One last thing, my Gap Tool only lets me monitor 6 cylinders, 4 and 7 are missing from the live values options if I recall. That can't be correct, can it?

Thanks

 

Some first thoughts:

Re-check your spark plug gap?
They should be: NGK IFR5N10 (LR005253), 1.5 mm (.060") gap
What brand coils did you get?

If cylinders 4 and 7 are missing from the live values, that seems to be an issue.

Swap coils on 4 and 7 with ones that the IIDtool can see:
Does the problem move away from 4 and 7? Then it might be bad coils.
Does the problem remain on 4 and 7? Then it is not the coils - but maybe the wiring leading to the coils.

 

I'll check spark plug gaps tonight and revert. Plugs are NGK Iridium and only have at most 1500 miles in them.

I've tried swapping coils but that's not helped or changed anything. I replaced with all with new Duralast coils but same performance; no marked improvement anywhere, which leads me to believe it something else. I've seen some articles say gaskets could be shot. If so, what's the best way of testing? o2 Sensors perhaps was mentioned in another thread.

The IID doesn't show cylinder 4 or 7. I don't actually think the issue is here, unless the computer somehow just cannot find or recognize all 8 which is a big concern.

The good thing is I've now got workshop space so I can finally do a lot of this myself just need a little steering as I'm running out of ideas.

 

Can you post each CEL code you are getting for us to see?

May help someone be more specific in potential fixes.

 

If you pull the plugs, do a compression test. Rent a tool kit if needed. A compression test, at this point, is like going to a doctor and getting a blood pressure test as standard procedure. This can tell a lot if something is going on, or if you have a potential blown head gasket where coolant is entering.

For the issue with missing cylinders, I would contact GAP.

 

Thanks for the input.

I'll get out to the workshop tonight and pull the codes. I can get a compression tester from Autozone. Worth buying one though, as they seem pretty reasonable in price.

 

I cleared all codes yesterday after switching around coils and plugs to test. Here are the codes coming back:

P0306-00 (E8) - Cylinder 6 Misfire Detected
P308-00 (E8) - Cylinder 8 Misfire Detected
P300-00 (E8) - Random Misfire Detected
P0313-00 (E8) - Misfire Detected with Low Fuel
R0316-00 (E8) - Misfire detected on start-up (first 1000 revolutions)

 

Spent the evening doing compression test (which I quite enjoyed I a strange way). Here’s what I found:

Cylinder 1, 148psi. Plug had a little oil. Plug gap .040.
Cylinder 2, 145psi. Plug gap .040.
Cylinder 3, 147psi. Plug gap .040.
Cylinder 4, 142psi. Plug gap .040.
Cylinder 5, 161psi. Plug gap .040.
Cylinder 6, 145psi. Plug completely sooted. Plug gap .040.
Cylinder 7, 169psi. Plug gap .040.
Cylinder 8, 147psi. Plug gap .040.

I spoke with gap and sorted the tool issue. Ran live values and Cylinder 6 is misfiring like crazy.

 

Very good info to have and keep on hand. The compression numbers dont look scary. A couple are a little higher than the others but not out of spec and could just be variations cause by the testing itself.

I am starting to lean towards corroded connection at the ECU behind the starting battery. If you have not, I would pull the battery and disconnect the computers back there, verifying there is no corrosion.

 

I’m curious about the plug gap.

My manual says .060”