Cylinder 7 misfire

[Siia109]

The Rolling Restoration on my '97 4.0L SE7 has shown me that cylinder 7 seems to be the problem child.

- The compression test was 138 dry and 155 wet which was 10psi less than the next nearest
- Large amount of carbon / oil in this cyl.
- Cat 1 / Sensor 1 has a consistent high reading
- P0300 = Random / multiple misfires
- P1316 = Misfire excessive emissions fault
-Pending 0307 - misfire cylinder 7 (First time yesterday this came up)

Help me define "misfire" as my limited knowledge this could mean everything from a valve is stuck or injector or an ignition issue.
If the cylinder has excess oil then that would point to rings and not head gasket which would correspond to the low compression - correct? Of course to fix it means the heads are coming off anyway.

What am I missing? Or what can I check to help focus on the issue.

Thanks in advance.

 

[Grum.man]

First thing I would do is swap the spark plug and wire from cylinder 8 and cylinder 7 and make sure the problem is the cylinder and not a plug or wire. I don't think 138 psi is low enough to cause a misfire. Are you sure it's excess oil and not excess fuel? Oil could be blow by on the rings or leaking valve seals. If it's excess oil it could have fouled the plug causing a misfire. You could put a bore scope in cylinder 7 and look for any cylinder wall scaring.

 

[1of40]

Is it consuming oil between changes? If this engine hasnt seen regular use at op temps, good oil/filters, good top tier high octane fuel then I'd try to get things cleaned up first.

 

[LRDONE]

It's likely going to have some blow by if the cylinder isn't burning right. I'd do some simple stuff to rule out some simple things. Plugs, wires, Bg product through the fuel system etc. From that point you could read the spark plugs to point you in the right direction. 138psi is a little low but if you can get it to come back a alive for a little while I bet that number will increase a bit.

 

[Siia109]

Yes - new plugs and new wires, new oil, new filters. The ignition coils are new from the PO. Been running injector cleaner but not getting the higher octane since high compression and Land Rover are not synonymous. But I will run a couple of tanks through it and see what happens.

She is blowing oil when the revs are at 2000 +RPM - so she is burning oil way more than my 3.9L in the D90. I figured when the oil pressure rises it is getting forced pass the rings and burned off creating the deposits as well as the smoke. It's definitely blue smoke not white.

Is the definition of a misfire by the manual simply a none ignition or is it lacking full detonation? Thinking a misfire could be fuel, electrical, timing, valve, compression...or a combination? I certainly don't feel or hear anything different, the RPM didnt drop or stumble as I was sitting idling with the Ultragauge plugged in and the Pending 0307 code alarm went off. No check engine light came on either.

This car is almost to digital for me - LOL!

Thanks guys...

 

[LRDONE]

The random misfire could be caused by anything. A random misfire is measured by crankshaft speed or the lack of crankshaft speed during a combustion stroke. The camshaft position sensor is how the ecm knows which cylinder is the problem. If you're burning oil that bad then it's time to pull that motor and make it new again.

 

[kris812]

I ohmes a NiB set of wires I just bought.. found one of the short ones double the resistance of the longest one.. that new wire was bad.. worth looking into! Also I think, not sure, you can swap plugs on the same coil to test if issue follows the coil.. but normally they die on both sides and you'll have 2 misfires.

 

[1of40]

Yes - new plugs and new wires, new oil, new filters. The ignition coils are new from the PO. Been running injector cleaner but not getting the higher octane since high compression and Land Rover are not synonymous. But I will run a couple of tanks through it and see what happens.

She is blowing oil when the revs are at 2000 +RPM - so she is burning oil way more than my 3.9L in the D90. I figured when the oil pressure rises it is getting forced pass the rings and burned off creating the deposits as well as the smoke. It's definitely blue smoke not white.

Is the definition of a misfire by the manual simply a none ignition or is it lacking full detonation? Thinking a misfire could be fuel, electrical, timing, valve, compression...or a combination? I certainly don't feel or hear anything different, the RPM didnt drop or stumble as I was sitting idling with the Ultragauge plugged in and the Pending 0307 code alarm went off. No check engine light came on either.

This car is almost to digital for me - LOL!

Thanks guys...

If you suspect or determine ring failure you might want to consider piston soaking with Berryman B12. Done right it's very effective at loosening things up.

 

[Siia109]

If you suspect or determine ring failure you might want to consider piston soaking with Berryman B12. Done right it's very effective at loosening things up.

Wouldn't "loosening things up" cause more blow by? With 127K miles on it Im thinking she has settled in with gunk proving key "assistance". Or is that your goal - clean out the gunk and then see how bad it is to confirm my fears of pulling the engine out?

 

[terryjm1]

Wouldn't "loosening things up" cause more blow by? With 127K miles on it Im thinking she has settled in with gunk proving key "assistance". Or is that your goal - clean out the gunk and then see how bad it is to confirm my fears of pulling the engine out?

Ive had engines that sat for long periods where the rings would get stuck in the pistons. “Loosening up” the rings solved the problem. But, those were engines that sat for years.

 

[1of40]

Wouldn't "loosening things up" cause more blow by? With 127K miles on it Im thinking she has settled in with gunk proving key "assistance". Or is that your goal - clean out the gunk and then see how bad it is to confirm my fears of pulling the engine out?

Yeah, the objective is to free-up the rings so they can do their job better.

 

[Siia109]

Sounds like the cheapest as well. Thanks - I would not have tried this.

Matt

 

[kris812]

Seafoam can also do the same thing.. but yeah a stuck ring is bad.. anything to free it up including the Italian tune-up helps