Happily taking the X300 into town and after about 7 miles I give the throttle a bit of a boot and the engine starts spluttering and misfiring. It limped along for a bit and then I pulled over. Bonnet up had a look round. It would idle a bit rough but OK but it wouldn't pull at all or indeed rev smoothly. Rescue service got me home and he had no real idea what it was.

I checked the ODB errors and there were none which I think rules out coils and injectors?

We both thought it was like fuel starvation so maybe the fuel pump is failing. I checked the fuse and also swapped the relay for another one in the trunk. I also fiddled with some relays up by the air filter

Now it runs sweet as it always did.

If the pump is failing would you get an intermittent problem or does the pump have to pressurise to a certain level for the injectors to get enough fuel to run at all?

There is plenty of fuel. It's petrol. The tank breather is OK. the fuel filter is a year old.

It did seem odd that giving the engine a bit more load precipitated the problem.

I'm hoping that one of you will say - ah that's clearly ....

Mike

 

Mike,
You hadn't by any chance just refuelled? I'm wondering about a little water in the tank...

 

Yes it was filled recently by a friend who used it while I was away. I did wonder about dirty fuel but it does seem a bit unlikely as now it revs cleanly to 4,000 rpm

However, I took it for a longer test run having made sure a friend was available to tow me home and it was fine until I asked for a bit more go-go and then it basically wouldn't pull above 4,000 rpm

I am now wondering if cleaning the MAF would be a good idea?

 

Sadly, no.

The OBD on these cars isn't all that great. For example, over the years of my X300 ownership I had several coil failures with nary a trouble code set.

I'm not suggesting that you do (or don't) have a coil or injector problem. But, 'no codes' is not proof positive that you don't

cheers
DD

 

Jings. I think I'll approach the soft underbelly first though which I regard as the MAF and then the fuel pump. I guess the local garage can test the fuel pressure for me.

 

That's good, but unless the car is misbehaving *at the time the fuel pressure is being checked* you might not get a conclusive result.

This might be one of those cases where you actually hope the symptom becomes worse and/or more consistent...so as to increase your chances of zeroing-in on the problem.

Cheers
DD

 

I have an extended hose on my fuel pressure gauge so that I can tape the gauge to the outside of the windscreen while driving the car under the questionable conditions. Unfortunately, without a connection port, it is a major PITA to connect the gauge to an X-300.

 

I'm going to try cleaning the MAF as a first step and hope that helps.

Then I might just change the pump anyway if I can get a known good one cheap enough.

 

They're on eBay for about $15

 

Before I got into removing the tank, I would at least give the filter a go.

 

I suppose you are right although it's only 3,000 miles old.

 

I cleaned the MAF and took it for a test drive and it span up to 6,000 rpm without complaint which is nice but leaves me wondering if that's just good luck or a fix. I suppose only time will tell.

Having bought a fuel filter I think I'll fit it.

 

Have you checked the coils using the dark test? That is, put inside of a dark building and watch the coils through a paper towel holder. If a coil is going bad you will see a light show. Get new coils from Japthug.

 

No, I haven't but I will. The rescue guy and I both felt it wasn't that sort of problem but it's worth checking.

 

Just managed another test run and it's much worse when the engine is decently warmed up if that tells anyone anything. Cold it revs well but at full running temperature it just won't pull above 4k rpm and started to misfire a bit around 2-3k although that did clear.

Maybe it is coils?

 

Checked the coils in the dark (we had a handy power outage) and no problem.

This being a 1994/5 X300 how many oxygen sensors will it have and am I right in thinking they are difficult to change?

Given that the problem appears at high temperatures I'm guessing it's a closed loop problem and hence most likely an O2 sensor issue.

Reasonable thinking?

 

Should only have a pre cat O2 sensor since its pre OBD2. May have 2, one for each seperate manifild, not sure, you can see them if you look under the sheild. Would a UK car even have OBD2 since it was a US thing?

 

Having looked there are two visible in the engine bay one on each downpipe. But I assume if I have a cat then there should be two more further down.

I'm not getting any errors on the OBD reader I have though although I do understand this car is not fully to spec.

 

The costr of an OBD scanner which will trend chart your O2 sensors is pretty small these days compared to the cost and trouble of changing parts "in the dark". You can watch the OBD voltages and pretty quickly get an idea if you have a bad sensor.

 

I do have a reader but it doesn't get much out of this car. The recovery guy was from the local Jaguar dealership as it happened and his van had the full Jaguar diagnostic kit but he said it just wouldn't talk to the car properly. He was pretty keen to have a roadside fix as they get a reward for that.

However, suggest a suitable bluetooth model and I'll try and find a similar model in the UK. My current one id very simple.

Incidentally may I ask when in closed loop mode does the MAF contribute anything to the mixture control or is it all lambda sensors at that stage?

Also what does the temperature sensor just beyond the MAF contribute in closed loop?

Mike