Hi all,

Here's the history, some of which may or may not have anything to do with the misfires:

My wife's '98 Disco started missing and experiencing the general lack of power. Prior to this, she had a weird problem where the gas tank wouldn't fill up all the way. It was as if something was blocking the fuel from entering the tank fully, causing some splashing back and tripping the fill sensor on the gas nozel. Filling the tank very slowly seemed to work and there were no problems with the way it drove and no idiot lights came on, so I ignored it and threw some mystery oil at it. Eventually it started filling normally, so when I started getting the misfires I thought it was related in that I thought I might have partially clogged the fuel filter. I can't quite recall if the fuel gauge stopped working before or after the tank started filling properly again, but they were about the same time. I changed the filter, and on the spark end of things, changed all the plugs and ignition wires. The plug in cylinder 6 was wet and smelled of fuel and the wire going to the plug in cylinder 5 was pretty badly damaged. The original codes were as follows:

0305 (cylinder 5 misfire)
0306 (cylinder 6 misifre)
1316
1314 (I think, that one may have shown up later)
and something LR specific, 3999 I think.

Now, in full dislosure, I admit that we drove the Disco for a good while with the misfires before I tried to fix the problem. I know, I know, terrible, no good thing to do. Anyway, I cleared the codes and we drove for awhile to see if it got better. I figured it might take a bit to flush out whatever crap may have accumulated in the cylinder during the time that it wasn't combusting. It seemed to get better at first, then got worse not long after that. I re-read the codes and now I'm getting:

0302
0304
0306
1314
1316
3999

The only lead I had from that was that all the cylinder misfires were on the same bank, so I figured I had probably fouled the upstream O2 sensor, or both the upstream and downstream O2 sensor on that side by sending non-combusted gas over them and that I had probably done some damage to the cat as well, but hopefully all could be burned off or restored without having to replace, if I need to, I'll cross that bridge when I come to it, first priority is to get all 8 cylinders firing again. Anyway, I tried to do a diagnostic by swapping the two upstream sensors to see if the problem would switch sides, but for some reason I thought it would be easier to cut and splice than disconnect the wires since I initially had some trouble getting to the connectors. Unfortunately, I cut the supposedly good one too close to the sensor and didn't have enough free wire to splice properly... so, both upstreams got replaced and no splicing was performed in the end. I've only driven the truck maybe 5miles since replacing the sensors, but so far, not much has changed. It's still sluggish and it's still missing. I reset the codes before driving it and the only one that's come back (so far probably) is 1314.

I really don't want to keep throwing parts at this to fix and, if you haven't noticed, I'm an amateur on my best day, but I'm willing on the weekends. So, a few questions:

1) Do the downstream O2 sensors contribute to the com's info, or just the upstream ones? Will I need to replace them too?
2) Did I just waste a ton of time and cash replacing the upstream sensors?
3) is fuel pressure in the rail, or something else fuel related a more likely culprit?
4) What diagnostic steps should I be taking? My seat of the pants protocol doesn't seem to be working too well.

Your help MUCH appreciated. If I missed a question that I should be asking, please answer that one too.

Thanks in Advance,
John

 

I can tell somebody's excited........

Welcome to a tiny slice of heaven.

From a good source the 3999 is the ECM having a bad day. It's a LR programming error. Ignore it, it will go away once the others are untangled.

After the ECM goes into closed loop the rear 02's play a role in fuel trim. By the codes your getting on one side I'd say you have too much fuel entering into the motor. Check your plugs again. Any that are wet are an injector staying open. Any that are black are injectors staying open too long to compensate.

Tighten up your intake manifold, you'll be surprised how loose the bolts are. I suspect a little vacuum leaky is going on. 35Nm - 26 ft/lbs.

You need a copy of the Rave. http://www.landroverresource.com/


Misfires are always a pita since so many things contribute to them. Start with the bolts and grab 2 more 02's for the rear.

 

One other question. How many miles on the truck?

 

Can you describe the lack of power ? Does it idle okay ? Or is it a dead miss ? Does it stumble off idle as if it is running rich ? How is it a highway speeds ? - Just trying to get a little more info.

 

Welcome to your newest worst nightmare.

Where are you, look at lots of other posts and update your signature with lots more info like most of us have.

 

Thanks for all the quick attention and questions! So, I'll take them' in reverse order:

I'm in Austin, TX, the truck's a '98 Disco I with ~115,000 miles. I'll add that stuff as a rider to my threads for future posts.

The lack of power is most noticeable when trying to get up to high speeds. Basically, pedal to the metal doesn't do a whole lot quickly past 60mph. It does eventually get going, just really sluggish. I almost don't notice it when first starting the truck and driving in around town speeds up to 55 mph. The idle is real shaky and it coughs a bit at stop lights. After it's warmed up and coughing at a stop for a couple minutes, it might sputter a little when getting moving again, but not that bad.

I'll mess with the intake manifold bolts tonight, the downstream O2 sensors will take a couple days to get in once I order them... if I end up needing them. Also, if tightening the bolts on the intake fixes the problem, where do I send a thank you gift? I can offer a lovely, well-mangled, upstream O2 sensor and a witty card.

 

I had this problem with my '96 Disco -

http://www.robisonservice.com/servic...n_fouling1.pdf

It would buck at about 55-60. It felt like a hard miss, almost like going over
railroad ties or something. I went through a bunch of wrong answers from
supposedly Land Rover techs before I brought it home and did the job
myself. I pulled the heads, took them to a good shop and they went over
them good and shimmed a couple of valve springs, valve job, the works.
I believe it was due to the previous owner using cheap, low octane gas.
Don't mean to scare you, but it happens. I ended up soaking the lifters
in MMO, replacing the head gaskets of course and getting a good valve
job. My labor was free, and shop work and gaskets all together was
about $500. Been running like a champ since.

 

DiscoJag,

That's what I want to avoid if I can. That link is extremely helpful if I get to that point though.

Since it's all happening on one bank, I think it is most likely to be a problem with the fuel delivery on that side (pressure in the rail or something like that) or the fuel mix as directed by the com on that side, which is why I went to the O2 sensors. The loose manifold on that side sounds like it makes sense too. I'm really hoping it's not something more systemic like the head overhaul you went through, of course it could just be dumb luck that everything's on one side now.

Luckily, no hard misses yet. I've had to do a head rebuild on a far less fun (low mpg, commuter) vehicle before and even with the far more fun to work on Rover, I am REALLY hoping I don't end up having to go down that route.

 

I hope it's nothing major, but it's not the end of the world if you do have to pull the heads. Best of luck. Keep in touch.

 

Our Land Rover 1997 D1 had that exact problem.
Every once in a while it felt like you were running out of gas - at speed.

The shop had to keep it a week and used a code scanner on live data mode to diagnose the O2 sensors were acting up.

This is before I fixed the Rover myself..

Well, I would:

1) Replace all 4 O2 sensors.
2) Replace the vehicle speed sensor

Once they did all that - our D1 was purrrrfect.

I had replaced the fuel pump to try to correct this problem and it did NOTHING to fix it.
I also tried to replace the fuel filter..

The ECU seems to (here is a technical term) wig out when the O2's are faulty on a D1 and it stumbles at speeds of 50 to 70MPH.

Been there - lived it. Felt the bucking.
Panic in your soul as you figure you will be walking ---

But, it never dies. It will keep going.