Misfire code (and misfire)

[Lendawg]

Hello all,
I am getting a P1316 code on my D1 (Misfire causing emissions).
Occasionally, it is accompanied by a P0304, which will clear itself in short time. The P1316 comes in as "pending" coincident with the O2 test finishing. Turning off the ignition and restarting clears this. However, the code comes back when a later test finishes, and immediately sets as a hard fault.
It has a noticeable miss when idling (in drive w/ brake applied, let up slightly on brake pedal and you can feel the truck lurching with each revolution). It also has an audible tick per revolution.
Here's what I have done:
-Changed the #4 plug and ohmed the #4 wire (I am waiting on a set of Magnegor's in the mail).
-Tried pulling off the #4 wire while it's running, and I didn't notice any difference. The wire would spark to the manifold, though.
-Did a cranking compression test and the #4 and others come up to 125 psi.
-Vacuum gauge is steady at 17"hg at idle. Depress the accelarator and it drops to 2"hg...release and it rises to 23"hg and quickly returns to 17"hg.

I have read everything there is to read online about Discovery misfires and misfire codes. There seem to be a lot of suggestions, but no one has stated any absolute fixes.
I have sized up some repair shops, and they seem to know less than me, and that just won't do!
I am in NJ, and I only have a short time left to pass the MV inspection.
I am open to any suggestions.
Thanks for reading.
Lendawg

 

[discomike]

What year and how many miles on your truck??
What octane gas do you use?I bet if you went outside when it is dark and watch your engine while it is running, it may look like a Xmas tree cause of your plug wires.
Not knowing what year it is I don't know if you have a distributot or not, but if you do how does your cap look, and carbon tracks?
Mike J.

 

[Lendawg]

Thanks for the quick response, DiscoMike.
My Disco is a 1996 with 110k miles on it. I use the highest octane available every time (I think it's 91-93, not too sure)...and I just ran two tanks of gumout FI cleaner through her.
I have tried the arcing check in the dark, and I didn't see anything. I will try it again, but as I mentioned...I have a set of wires on the way.
I have 4 coil packs (as I'm sure you're aware). I tried to ohm them out, but they confuse me...I would think that ohming from the tower to chassis would show a high resistance, but I get infinity on them. Ohming between towers on a pack gives 0 ohms.

Thanks,
Lendawg

 

[discomike]

Well I will be interested to see how it runs with the new wires. I found that running Bosh Platium Plus 4's works really well with the Magnacors.
Mike J.

 

[Lendawg]

Yes, I am very keen to see what new wires will do. I am about ready to hand this thing over to a mechanic, or god forbid...the dealer!
I'm keeping my fingers crossed.

On the subject of troubleshooting misfires, I read last night about using an infrared thermometer to compare the temp of the exhaust manifold segments outside each exhaust port. I don't have an IR thermometer, but I do have a temp probe for my multimeter. I think I will give that a try. I'll let you guys know how it went.
In the mean time, I am still all ears for any further suggestions.
This is my first LR, and there still may be time to save me and make sure it's not my last!

Take Care,
Lendawg

 

[discomike]

Keep the faith,Magnacor to the rescue.
Mike J.

 

[Lendawg]

I'm almost afraid to write this, but...
After pumping the Sea Foam into every lifeline of the poor truck, I left it for the night. When I warmed her up this morning and took her for a ride, all the tests completed and there were NO codes!
TOUCH WOOD!!!
If it lasts til tomorrow, I'm heading straight for the MV inspection place and get this done at last.
Wish me luck,
Lendawg

 

[discomike]

I know SeaFoam is good but that is a surprise.
Mike J.

 

[Lendawg]

You would be correct in your surprise.
The bloody light came on again this morning, just as it reached operating temp. The same code (P1316) was there again.
It seems to stay out as long as the motor is reved up, as it is always at idle that the light comes on.
I did some further troubleshooting this afternoon...
Pulling off one plug wire at a time with the engine running, the #4 was very obviously not contributing to the fight. The plug is not fouled, though, so I am now thinking fuel injector or whatever controls it (ECU??).
Thoughts?
Anyone know how to check an individual FI?

 

[discomike]

I am thinking you need to verify the spark from the coil pack to the plug, make sure you are getting a good spark. Then get back and we will brain storm some more, ECU is a possibility, but lets don't go crazy yet. Injector will be the next thing to look at.
Mike J.