'97 VDP 4.0L. I'm trying to diagnose a P0300 code. I have a cheap basic OBD2 scanner. I'm wondering if there's something affordable out there that might give me more useful data. I'm not sure how advanced the diagnostics are on a '97 but it might help steer me in the right direction.
I recently replaced all 4 O2 detectors and now I'm getting frequent misfires, causing the CEL to flash and the engine to lose some power. I don't know how they'd be related to the O2 sensor replacement but it's definitely way worse since I replaced them. I was thinking maybe the CAT is clogged because reading up on symptoms of that they seem similar to what I'm seeing but I'm not sure.

 

Have you checked for a vacuum leak?

 

Other than just taking a good look around the engine bay, no I haven't. What's the best method for finding that?

 

Better do a smoke test if you are smoker :-) Or just blow the non-smoker air into the intake. Remove the airfilter box and choke the MAF sensor inlet with something like rubber glove, or plastic bag or whatever else. Then remove the breather hose near the IAT sensor on the intake bellow and blow into. If there is a major leak you'll find it. Also how old is your air filter?

 

There is a hook up map for the O2 sensors , and I would not expect the new O2 sensors to hone in immediately , every new O2 sensor has its own " nuances " and the ECU needs time to learn them

For a good engine regulation live data observation in a savable and sharable graph you can share there is a ELM - 327 device that plugs into the OBD2 port and extracts the information to either a through bluetooth smart phone or USB port cable to a common laptop ( but not both )

They're on E - bay around 12 dollors US free shipping and need additional software ( cost and learning curve ) to bring out full feature of live data otherwise just reads and resets CEL codes

There are waaaaaaaaay too many Youtube videos on the ELM - 327 as it's like they learned how to use a door knob and they must show their sophistication by shairing that on Youtube ,

There is one I had that shows you what you need to wrap your head around to learn

Your most important parameter IDs ( PIDs ) are :

Short Term Fuel Trim bank 1

Short Term Fuel Trim bank 2

Engine Coolant Temp ( this determines if the ECU is going into full fuel trim / mixture after warm up and O2 sensor reading so the ECU can calculate proper fuel trim for smooth running as well as emissions )

RPMs

There are a few examples of X300 contributors with their graphs if I can pull them up

OBD2 live gauges displayed to tablet? - Jaguar Forums - Jaguar Enthusiasts Forum

Later you can observe the O2 sensors as you reformate the PIDs ( this takes some time as a learning curve ) but in the final end product you should have close to 0.0 % STFTs through all ranges of engine load and RPMs , + or - 3 % more realistic limited by the refinement ( data size ) of your data " maps " or data arrays in the ECU

The O2 sensors have a heating element inside for the O2 sensor to read correctly

You can have a blown fuse # 10 right engine bay fuse box or the sensor can be bad from stock as a new part

Remember the X300 takes a special Titinia based O2 sensor

 

The O2 sensor codes have cleared with the new ones installed. They are the correct type.
I have an Autel OBD2 reader that I think can read the fuel. I'll check it out.
I just pulled the plugs to have a look. They have less than 10k miles on them. They have this orange ring on all of them.

 

BTW, these are Iridium plugs. I may just go ahead and change them to copper. What do you think?

 

This is a live date representation of a X300 with the 2 lines , Blue ( voltage on car ) and Green ( RPMs ) to show voltage regulator dropping out and showing the battery full charge state as that is drawn on during alternator VR failure ( car does stall )

There are other better examples from other X300 contributors like myself that did not save them as a file when looking at my live data ( amateurish )

 

There is a TSB on the correct plug of the cheap Champion copper # x , no exotics like platinum or iridium , there was some gap differences in TSBs though the years

There is a TSB on the staining ring but my not be an issue with correct plug

 

X300 TSB list as will be off - line until tomorrow

a couple for plugs and one for corona stain

JagRepair.com - Jaguar Repair Information Resource

 

The orange on the plugs is called Corona stain and is nothing to be too concerned about.


Did you replace the O2 sensors one at a time? Is it possible you mixed up the connections for bank 1 and bank 2 downstream sensors? - the connectors are identical and will plug in to either. It will cause bad running if you get them wrong.

The acid test diagnosis of swapped connectors is to look at Short Term Fuel Trim on Banks 1 and 2. If one is at +25% and the other is at -25% then it's pretty much nailed on that the connections are swapped. Any cheap OBD scan tool should be able to display STFT live data.

Note: engine management needs to be in Closed Loop for STFT to mean anything.

 

I double checked the downstream sensors and they appear correct with the left sensor going to the plug with the red wire. But i did notice fuel trim at + and minus 25. Short video attached.

 

The wire colours are not relevant. The ECU can be internally programmed to switch the sensors.

I can pretty much guarantee that your sensors are reversed. Swapping the connectors is free so try it and see what happens.


If you want more explanation, see this thread

https://www.jaguarforums.com/forum/x...etting-271801/

(If you don't want to read the multiple pages - jump to post #82 for the answer)

 

Thanks so much, I hope that's the answer. I'll try to swap them tomorrow. That connector is a bitch to get to but lucky for me I never did get its bracket back to it's intended location. I have it zip tied right now.

 

Why are we going down these various avenues, I have attached the details for code PO300 with possible causes, this should be of assistance to you and provide a guide to follow.

John Herbert
1996 XJR

 

145 F coolant temp looks low... Might be a thermostat issue. Or ECT sensor. Both of them are known to fail.

 

Thanks John, I hadn't seen that document.

 

I don't think the engine was up to temp yet. I ran out to take a look at the data so the car was only on for a couple of minutes.

 

There is one tiny reference to the closed loop coolant temp of 160 degrees or abouts in the Jaguar 801s doc that took me a long time to search once I was corrected by Vee

Somewhere along the way I got a higher degree lodged in my head and stuck to it

There is a Mod called the Lambda Mod to make the rear sensors connecters much better , haven't heard anything in a long long time on the original mounting but there are pics

If you don't see your 160 abouts coolant temp you may be at a thermostat or ECU connector condition check , the sensor itself is pretty cheap and is the 2 wire sensor atop the thermostat housing , the 1 wire sensor next to it is for the instrument cluster temp gauge which is not very accurate and is referred to as a dummy gauge

This brings you about in different directions as John stated but the main point is do not include / install a thermostat large O - ring , even if it comes with one , cracks thermostat housing ears when you crank down the bolts , many have done

 

I hate it when solutions start to pile up. You don't know what to do and what not to do. The posters can't keep up with what's been done and what hasn't.

Regarding the coolant. Nevermind the thermostat for now. Its the Coolant Temp Sensor that can cause something like this to happen. It's a common $20 part and should take you no more than 10 minutes to replace. If you've never replaced this sensor before, then it's time. The Coolant Temp Sensor plays a very important part in the startup and fueling of the engine. Please replace this sensor so it can be crossed off the list. Thermostat causes other kinds of problems, but nothing like this.

Also, spark plugs need to be copper type. Too many posts report issue when using iridium, or other exotic plugs. NGK BKR5e or Champion 71 (RC12YC) should be what you need.