I was getting codes P1313 and P1314 set on my 98 Disco and checking the archives found comments from a fellow who said he eliminated the P1314 by cleaning the intake plenum and all its hose connections without removing the plenum itself. “You should see five vacuum lines coming off the plenum; Brake booster (medium length hard line), Fuel regulator (short), 2 x PCV (short), AEL (long hard line). There are no valves. Just two short hoses and an oil separator on passenger side rocker cover. Pull it out with pliers and clean all the gunk out.”

I removed the two hoses that run from the intake plenum to left and right valve covers and they were clear with nothing in them. The driver’s side hose had a kink in the bend so I cut some off one end to reduce the kink and I’d guess it is supposed to be a molded hose with a 90 degree bend, but this is a straight piece of hose bent 90 degrees. Am I missing some device that should be in one or both plenum hoses?

I removed the MAF from the air cleaner box top and from the plenum intake hose, and it was clean inside; the O ring on the MAF end that goes into the top of the air filter box fell out and had some kinks in it so it might not have been in correctly. I removed the big intake hose from the intake of the plenum and the plenum was not particularly dirty but I cleaned it and the butterfly with carb cleaner, brushes, and paper towels. I reassembled the intake tract being careful to place the O ring on the end of the MAF and I also sprayed the MAF male and female connectors with contact cleaner.

All in all I didn’t find much to clean and did not see a one-way valve in either hose from valve covers to the plenum that others have mentioned. Since then I’ve not had a P1313 set, but I still occasionally get a P1314 when climbing a steep hill slowly. I can drive on the open road without getting a code P1314; it just pops up when driving slowly under load. My code scanner says the #1 fix for P1314 is to replace the crankshaft position sensor; anyone fixed this by replacing the crankshaft position sensor? I’d have thought a bad CPS would have more effect than just an occasional misfire code at low speed under load conditions.

 

I had a 1313 and 1314 and another general misfire code before too. The dealership told me it was a cylinder 3 and cylinder 4 misfire. I did tuneups, etc., nothing got rid of the problem until I put an additive called Marvel Mystery in my gas tank and in my oil. Now the only code I have is an oxygen sensor code which I am buying an oxygen sensor to get rid of.

I have been having those codes for the entire 4 years that I have owned that truck and then all of a sudden I put that Marvel Mystery in there and those codes disappeared within a few days on a long road trip from TX to GA. that stuff must have unclogged something that was sticking.

You might try it and see if it helps.. You can get it from any auto parts store and some dollar stores sell it cheaper..

I know some people talk against additives but I know several people who swear by it and have been using it in all of their vehicles for years... It's definitely old school--been around for decades--and not very many people know about it..

 

Quote:

Originally Posted by colemtd

I had a 1313 and 1314 and another general misfire code before too. The dealership told me it was a cylinder 3 and cylinder 4 misfire. I did tuneups, etc., nothing got rid of the problem until I put an additive called Marvel Mystery in my gas tank and in my oil. Now the only code I have is an oxygen sensor code which I am buying an oxygen sensor to get rid of.

I have been having those codes for the entire 4 years that I have owned that truck and then all of a sudden I put that Marvel Mystery in there and those codes disappeared within a few days on a long road trip from TX to GA. that stuff must have unclogged something that was sticking.

You might try it and see if it helps.. You can get it from any auto parts store and some dollar stores sell it cheaper..

I know some people talk against additives but I know several people who swear by it and have been using it in all of their vehicles for years... It's definitely old school--been around for decades--and not very many people know about it..

OK, do you think it was the MM oil in the gas or in the crankcase? and how much did you try in the gas tank?

I had a fellow swear to me that MM oil in the crankcase of my 96 Jeep Cherokee would stop the lifter noise it had had since the first oil change I made after buying it used. I followed his suggestion of adding a quart of MM oil, drive 100 miles, and then change the oil. There was no change in the lifter clack so MM oil apparently does not solve all problems; the Jeep has run 100K with that clack.

I did try Seafoam in the Disco gas tank by putting a bottle down the vent hoses to try to fix the slow fill problem and I assume that bottle full would have found its way to the gas tank; this was after changing the plugs and wires which eliminated all the misfire codes except 1313 and 1314. I do still get the occasional 1187 "pending" (Heater Circuit Short Upstream Oxygen Sensor) but I haven't changed the O2 sensor yet.

So, what?...a quart of MM oil in a full gas tank? I changed the oil and filter 300 miles ago and figure one additive at a time is the best approach.

 

Well I don't know why you would have to change your oil after 100 miles with the MM in there, I don't think that would give it time to work. You have to read the MM label for gas tank usage but I think I use 1/2 bottle per fill-up and I only use it on long road trips. Yes I put a quart of it in my oil and I drove it over 800 miles on one one-way trip from TX to GA and that's when my codes disappeared..

 

I added a quart of MM oil to the oil and added some in the gas tank, but haven't driven very far and still get some P1313 and P1314 codes when climbing a steep hill; time will tell.

On the Charokee, It was due for an oil change at the time and the guy's recommendation was to add the MM, drive 100 miles, and then change it. I'll leave it in the Disco this time and see what happens.