Misfiring after work done on exhaust

I've had an exhaust gasket replaced in shop and when I drove, and ever since, there is a misfire. I replaced an oxygen sensor where the diagnostic tool said it was an issue (after replacing spark plugs and wires) but it still remains.

I bought the oxygen sensor online and when it arrived it was packaged poorly, with no protection and the box was crushed. I'm wondering if it got damaged. Is there a way to check the sensor and do anyone have any suggestions?

Thanks from Newfoundland, Canada!

More info to help,... the Disco runs pretty well and then bogs down. If I release my foot from the accelerator, it picks right back up again but goes boggy again. It's up and down.

I tried to view posts to see if there are any others who may have had the same problem but to no avail and there are a lot of posts! My eyes are now watering from reading so many lol...

This has started as soon as I was driving away from the shop after having the gasket replaced... go figure

I'd take it back to the shop and tell them to do it properly.

Sounds like the air/fuel mix is all wrong, by releasing the accelerator it's getting the right mix then it all goes wrong.
thats what I think but I could be a million miles away.


Stu

Assuming yours is a V8 it could be a number of things. I've had all manner of strange running/starting problems with my RRC which is similar to the Disco.

You might try disconnecting the air flow meter and then seeing if it runs reasonably smoothly. Be aware that the ECU warning light will come on and it will use a lot of petrol but it might give you a clue. If it runs O.K. you may have a duff air flow meter or a problem with the ECU. Quite why this would happen after a gasket replacement is a bit strange....could be nothing more than a coincidence. Then again I could be barking up completely the wrong tree.

One other thought.

I believe you will have a 14CUX ECU. In theory you can fool the injection system by changing the tune select resistor. Can't remember off hand what value you need but if you put one in from a non-cat RRC the ECU will not look for Lamda sensors and will run quite happily. If swapping the tune resistor makes it run better then it might suggest the Lamda (Oxygen) sensor(s) are either lazy or not working at all. Do check to make sure changing the tune resistor won't damage your catalytic converter (coz I don't know).

hope that helps ya.

Can you confirm the type of EFI system you have,if its a NAS spec car you probably have GEMS not 14 CUX.The way to tell is by the plug leads,if they come from a coil pack behind the plenum chamber its Gems,from a front mounted distributor its 14CUX.

Thanks classic, I'll print this info off and see if I could trace it with what you said. I don't know where the locations of the components are off-hand but will consult the Rave manual for specifics. It seems to be chocked full of specs.

eightinavee - the coils are behind the plenum near the firewall so I suspect a Gems? Is there something specific to look for there? I replaced the plugs and wires.

The running of the Disco is strange. It starts perfect but seems boggy for a bit and then can all of a sudden pick right up and pull like a train. Then it will slacken right off and even putter along! When I slack off the accelerator and pushes it again it will pick right up for another little while.

It's drivable but I'm thinking this may damage the cat.

But I still love the Rover!!

Piranhaboy said:

Thanks classic, I'll print this info off and see if I could trace it with what you said. I don't know where the locations of the components are off-hand but will consult the Rave manual for specifics. It seems to be chocked full of specs.

eightinavee - the coils are behind the plenum near the firewall so I suspect a Gems? Is there something specific to look for there? I replaced the plugs and wires.

Click to expand...

If you got coils you ain't got a 14CUX ECU, so my earlier suggestion is unlikely to help. Eightinavee will be your best bet coz I don't have any experience of the Gems injection systems. That said, do thoroughly clean the plenum and make sure there are no vacuum leaks.

Good Luck.

Right on classic. I appreciate your time in answering. I did take a listen for vacuum leaks but probably should shut the engine off and listen then?

I just purchased a Onboard Diagnostics tool and will hook that up to check the codes. I assume there is a clever landy owner who's up on the codes??? (crosses fings) lol

Incidentally it's a 98 Disco 1 with a 4.0 V8 and advanced evaporative loss emission control. Beauty little thing she is, and I get some looks driving her!! ... so hence the need for improvements on the performance! (- I'm talking about my Disco here! )

Paul D said:

I'd take it back to the shop and tell them to do it properly.

Click to expand...

Hey Paul, I did take it back - a few times now and they are baffled. They checked with the mechanic who did the gasket job to see what he may have done but he insists he didnt' do anything besides fix the gasket. He also said the parking brake cable was twisted. I bought another new one but found the other one was fine! It just wasn't hooked up and was a little stiff.

They did put the diagnostic tool on it and gave me a few codes. I'm going to put my OBD on it to see if I get the same ones and go from there.

I tried the OBD II tool last night and got 9 codes! They all seem to have to do with the misfire. It seems the downstream O2 sensor heater is gone but does that affect the fuel trim? I read it only told if the catalytic converter was working or not. I'm assuming the ABS rough road line low fault doesn't contribute to the problem...

P1191 - Oxygen Sensor Heater Circuit Open Downstream
P1317 - ABS Rough Road Line Low Fault
P0300 - Random/Multiple Cylinder Misfire Detected
P0307 - Cylinder 7 Misfire Detected
P0305 - Cylinder 5 Misfire Detected
P0304 - Cylinder 4 Misfire Detected
P1316 - Misfire Excessive Emissions Fault
P1314 - Misfire Catalyst Damage Fault Bank B
P1313 - Misfire Catalyst Damage Fault Bank A

Does anyone have any idea what might be the cause for these codes and how I might approach solving the issue?

Thanks

From the sounds of it I would imagine it's overfuelling - P1314&P1313 can mean that the misfire is likely to cause damage to catalyst A&B. P1316 is misfire is causing excess emissions This could be caused by faulty O2 sensors. Not 100% but your's may have 4 O2 sensors (or more) - 2 pre cat and 2 post cat.
I would clear the codes (using the OBDII software or disconnecting battery for 5 mins - make sure you have the stereo code if applicable). It shouldn't throw any new codes until it warms up and goes out of closed loop. Can't see how they would have damaged all the O2 sensors but they are fragile. I'd check all the sensor pigtails for damage, also check and make sure the shop plugged the airpump and EGR lines back in properly. Did you say yours has enhanced smog equipment on it?

Thanks rojbarker, good info to start from. I only replaced one O2 sensor - the upstream driver's side. That one came in the mail in its original box (which was crushed flat) and envelope. No bubble protection or anything of the like.

You're right, there are 4 sensors. 2 are upstream of each cat and two are downstream of the cats. It looks like one of the downstream O2 sensors is need of replacement, for sure by the OBDII data.

Sensor pigtails... are they the wire leads and plugs from the O2 sensors?

Airpump and EGR lines. I never checked those. I'll have to look them up in my Rave CD for locations of the components and respective lines.

I'll clear the codes and see what comes up. Once again, thanks rojbarker.

Hope it helps somewhat, it's hard to diagnose problems like this sometimes.

Yeah the pigtails are the sensor leads - not 100% sure why they're called they as they're not curly...!

Check out:

Oxygen Sensor Information

Some interesting information and how to test your sensors to rule them out or identify them as the culprit.

As for the EGR and airpump, your MAY not have an airpump but it should have EGR - this will be linked into the exhaust manifolds somewhere - if it hasn't been reinstalled correctly after the gasket change, that could cause problems.

At least you're getting some codes - my Camaro is OBDI and it has to be really running like a dog before it'll trip a code!

Thanks again...

I did as you said, I erased the codes and then drove the Disco home for lunch (not to feed the Disco but meself! ) . After returning to work () I hooked up the OBD II again and a single code appeared. This is what I got in the freezeframe:

DTCFRZF P1316 (Misfire Excessive Emissions Fault)
FUELSYST1 CL_Fault
FUELSYST2 CL_Fault
LOAD_PCT (%) 53.7
ETC (CELSIUS) 78
SHRTFT1 (%) 24.2
LONGFT1 (%) -2.3
SHRTFT2 (%) -25.0
LONGFT2 (%) -2.3
RPM (/min) 1847
VSS (km/hr) 64

Ok, I have a misfire, but I knew that. There are two CL_Faults in the two fuel systems. I'm not sure what that means. Nor do I understand the numbers in the short and long term fuel trims but the short term numbers are on the opposite side of zero! Hmmm... something standing out big-time here.

Is this making any more sense to anyone else?

That Oxygen Sensor testing information is awesome rojbarker. I'll give that a check later at the Bro's garage. There are two ways to test - one with installation and a bench top test. This will most certainly help. In fact, I may strip all sensors from the vehicle and bench test them all and replace any that fail. Good call dude!

I hoped that may help, good luck with finding which one is wrong.

Pulled this off a website when searching for FUELSYST CL:

"FUEL STAT 1 = Fuel System 1 Status: Fuel system status will display more than just Closed Loop (CL) or Open Loop (OL). You might find one of the following messages: OL-Drive, indicating an open-loop condition during power enrichment or deceleration enleanment; OL-Fault, indicating the PCM is commanding open-loop due to a system fault; CL-Fault, indicating the PCM may he using a different fuel control strategy due to an oxygen sensor fault."


The long term fuel trim is the value that gradually changes and tunes the PCM so a negative or positive value of a few percent seems about right. Short term is calculated instananeouly while driving - accelerating quickly, etc. I think that a negative on bank 2 and a positive on bank 1 of 25% seems quite high so it may well be overfuelling - I assume cylinders 7 & 5 are on the same O2 sensor in the manifold pre cat, hence why you got codes indicating misfire on those cylinders specifically. That last part is just speculation though on my part!

Thanks again rojbarker. I tried a simple test of actually disconnecting the new O2 sensor I replaced and lo and behold, the engine ran very well! It seems to be using it's other sensors to determine fuel trim. Now it only misses at high speeds but the key word here is HIGH speeds. It pulls like a train at typical city driving but is still a slight problem. It seems the new sensor is defunct. The shoddy shipping protection didn't protect at all.

I am now looking at prices of O2 sensors online. I'm going to pick up two. Does anybody have any good sources they recommend?

Thanks for the help so far!

I'd say Bosch know what they're doing - they invented the O2 sensor if my memory serves me correctly. Stuck a couple in my Camaro and they're fine - plus they're not that much more expensive than other brands. Just my opinion mind you, could be different on Landy's.

Glad you've got closer to sorting it.