My 1990 xj6 4.0 engine, it’s been giving me a headache, it all started when I washed the engine. I had a sudden oil leak from the valve cover, so I wash the engine, remove the cover and replace with new gasket, change the spark plugs and air filter, had to remove the air box in order to remove the filter, there was no way to remove filter on it. I blew air on the engine and electrical connections, let car sit for 24 hrs before I started. Start with a little hesitation or shake, was minimal like a 5% of a 100%. It bother me so I when to my friend house to se if he could find the problem, he told me that the EGR valve was not working correctly, he tried to plug the valve and it got worse, so it was connected back on. I left his house and when I came to stop sign,the car shut off. Check engine light was on on code fuel44 fail44.So I changed the Egr valve and the Egr solenoid, check engine light was off for 35 miles of straight driving, then it came on,check and it was given code failed 26, air leak, replaced some vacuum lines, then car started running rough and code 44 came back on. I have treated the gas tank with sea foam gas treatment 2 full tanks at different weeks, I did notice that it was speeding more gas than usual and back of muffler were black and you can hear the missed of engine, the rpm was going crazy, this have been going now three months. I have changed the fuel filter, 02 sensor and cleaned the the throttle body mounted on the car. The car ran like a 97% better, only lasted one day…

So one day ran soso and the next day ran like crap, shutting down, had to hold the gas around 800 rpm’s just to get it out till the car reached temperature, it did it for a wild, so after I changed the 02 sensor it was the opposite, now it runs like a 95% when is cold for the first 3 minutes, then it starts to running rough and shutting off at the lights or stop signs.
There is a sensor that I don’t know what it is, is between the mass air flows sensor close to the throttle body in between the two big air hoses. That sensor is loose at top where the connector is, loose from the bottom of connector attach to the sensor copper nut.

I’m posting some pictures,

 

I’m a new member, still don’t know how to used the forum, but I appreciate any suggestions on my issues I’m having with the car. On one of the pictures there is a sensor that I disconnected, does anyone knows what kind of sensor it is.
thanks

 

That’s the Intake Air Temp sensor.

Wish I had a quick answer for your questions but there a few culprits. Plus, the two faults can integrate with each other.

Washing the engine on this car can be a bit of a pill. Usual culprits for after washing it is water in spark plug wells. Check relay blocks for corrosion or anything abnormal. I would check for vacuum leaks by spraying the connection with brake clean and see if idle changes.

Jag lovers has a pretty good e book:
https://www.jag-lovers.org/ebooks/vi...40&Vsection=12
Following some of these diagnostic steps will be helpful. If you don’t already have a manual, I really would urge you to get one.

Good luck!

 

That sensor is the intake air temperature sensor. Obviously the car is running very rich. Test that sensor and the computers' coolant temperature sensor- there are 2 next to each other at the front left on the thermostat housing and the one wire one is for the dash gauge. The process for testing them is very similar and is located in the stickies section. If I recall, cold they should have 5 ohms resistance and heated to 100 (?) degrees they should have .5 ohms. Also, sometimes when you plug an O2 sensor in, one of the connectors will back out of its plug. Make sure all 3 of those wires are making good contact. I can't quite see in the pic, but make sure the maf sensor plug is all the way in and of course check all the grounds. There are several on the intake manifold. Sorry if this doesn't make much sense, I'm at work and going off memory. Good luck.

 

Thanks to all for responding,
I apologize for not responding earlier, but I was working on the car. So the air temperature sensor I think is bad, you can rotate the female plug that mount to the nut counter clockwise without moving the nut. I wonder if that’s one of the problems I’m having. Also I did spray some throttle body spray cleaner on the big air rubber hose were the clamp goes, definitely there is a small leak, the RPM when up. I did it four times no doubt about the air leak.

I will order does parts and hopefully that should take care of the problem. I have other work that needs to be done, I will keep posting

thanks

 

The vacuum leak is what is causing the problems. Those air temp sensors always rotate and never come out in my experience.

 

Thanks for letting me know about rotation of the air temperature sensor, yes I was breaking my head trying to figure out how it comes out. I tried to unscrew pulling upwards, no luck.
Thanks again

 

Very easy to pinch or cut into the large corrugated hose at the throttle body while fitting the large clamp, causing a vacuum leak ...and of course the hoses don't last forever either.

Another common fault is over-tightening the clamp at the plastic elbow end of that hose causing the elbow to buckle inwards, also creating a vacuum leak. The OEM corrugated hose is rather expensive but luckily there's an affordable replacement available. This aftermarket hose is a bit lighter weight which also makes refitting a bit less of a struggle.

https://www.rockauto.com/en/moreinfo...SVZqjmJc%2F6Pg

 

Thank Lawrence for your reply, I just received the extension hose, it looks and feels strong. I bought it at Amazon $58, every one else was in the $80+.. I guess I will find out on the weekend is there is other houses crack. So far I’ve been driving for two days at 95% ok, around 135 miles. It has not been turning off at stop lights, around 600 - 700 RPM fluctuating at times. Let’s see how close I get to the 100%. LOL

Thanks again

 

I replaced the throttle hose this morning, no change was made. For the past 3 days it has been running around 95 - 97% better, but today I when on a 30 miles trip, on my way back to the house I was 15 miles from home and was stuck on a traffic jam, after 5 - 10 minutes the car engine stopped running, try to get it running but it keep going off, waited few minutes but nothing. Try again and was pressing on the gas pedal and was able to get it running at 2000 RPM but was shocking and after 25 seconds it went off. After 25 minutes I decided to check the fuel pump, somehow my mom turned the ignition on and the car started, I was able to drive it to four blocks away from the house before it stopped running. After 10 minutes crank the car up and was able to get it home.

I noticed that the transmission didn’t go into the last gear and I was doing 60, when I let the gas pedal off, it when down fast, that was around one mile away from the house. I guess I have to check under the car to see if there’s something disconnected from the transmission like a vacuum hose, and also check the fuel pump.

I’m posting a picture of the old throttle hose, found something like paste in it, not sure if it came from the oil hose connected to air throttle elbow, also the new hose I replaced.





Amazon $58

 

Sorry, I forgot to post the old throttle air hose. I have no idea was that paste or grease.

 

It looks like bearing grease. Is it possible someone put way too much to try to make ihe hose easer to slip on?

 

Hi Jerry,
I have no idea what it is, doesn’t smell like grease but it is a good amount of what ever it is.
Thanks

 

Usually there is an accumulation of oily sludge in the corrugations, most of us clean that out after each winter. It's a mixture of condensation and oil vapour from the engine breathing system which directs fumes from the cam cover back into the intake. Normal XJ40 stuff.

 

Hi Lawrence,
I was worrying about that paste looking thing. I have not touched the car for 2 days trying to get my head clear before I get back to the lovely xj40 issues. I guess it was not used much in the past 2 1/2 years, driving only 1,500 miles compare to this past two months that I have put almost 1,000 miles. I think I have a fuel pump issue.
Thanks

 

Question; can the fuel pump be a part of the code Fuel 44.
The reason I asked is because I use to hear the pump sound inside the car, then the last couple of weeks the sound got louder, I got down on the floor and touched the line going into the fuel filter, that hose was vibrating strongly, you were able to get a hand massage. LOL
then last Friday after most of the day driving around on my way back home stopped at a traffic jam, the car went off , I was not able to started back up, let it sit a couple of minutes and nothing. I waited around five minutes and this time I pressed the accelerator, I was able to bring the rpm to like 2,500 for only like 30 seconds before it died again. After 25 minutes I decided to see if I can listen to the pump while my mom turns the switch, the car started up and was able to stay running, I drove around 15 miles before it died off again. I was around 4 blocks from the house, I waited like 10 minutes before I crank it up again and it did. I was happy that I made it home, I couldn’t hear the noise of the pump running, I got on the ground and touched the line going into the fuel filter and the vibration was not as strong as it was two weeks earlier, didn’t sounded as loud as it was before. Does this mean that the fuel pump is going bad. I will appreciate some input.
Thanks

 

Hi my Jaguar forums friends,
I have been working on the XJ40 idle problem, the air leak disappeared when I replaced the throttle big hose, I also removed and cleaned the idle control valve. My RPM when down to 600 and the car was running at 97% fine. I drove it yesterday around 15 miles with no problems, I was driving today and pulled up to parking lot at the bank, put the car on park and was running all of the sudden when off with no hesitation, just quick running. Drove a mile down the road and parked again, no problem whatsoever. Got in the car and drove for two miles and parked again and the car quit running again, no hesitation or check engine light on. Two hours later I was showing the engine to my uncle, started the engine and was running for like ten minutes when it stopped running again, tried to get it running but it wouldn’t stayed on, waited a while and tried few more times and was not able to make it start. When under to check the gas pump while the engine was turning, didn’t feel the pump running strongly like it used to do before.

Will appreciate any feedback, or were to start at this point.

 

Fuel pumps are a common cause of this failure. Does your car have an external pump? I had thought that Jag went to in-tank pumps in 90, but am frequently shown wrong. If it is external, then it should be easy enough to run a wire and test it for proper function. Definitely check the pumps' relay too, they are often suspect especially if they are blue. You can swap with any other "block" relay to test that- the a/c one is usually convenient, i think. If the pump is in-tank, it will be worth reading fellow member "etaent"s recent thread about his pump debacle. There are several threads on fuel tank removal you can consult about that if you havent already. Good luck.

 

Hi Jerry,
I haven’t checked the pump, I checked the spark plug and there is no spark, I have to find out what is the problem before I can check the pump,
thanks