Hi Jag lovers,

i am new to this forum , am from holland and i had several jags before this one. Bought it from a friend and here is my issue:
the car was stored for about 20 years.
50.000 km original.
1987 with 2.9 engine
i went for the MOT and failed on emmission test.
9,5% co2 ,
the xj has new spark plugs (ngk) , i checked them after 1 week and they were black.
what i suspect:
fuel pressure valve on the front side of the injector rail. Pulled the vacuum hose of it but no fuel is leaking, but the next day i took out the injectors and after pulling the first one out it came out with high pressure..
after o wanted to remove the fpv, on the rail side nothing happened but on the return line there was really a lot of pressure and fuel coming out..
then i loosen the tank fuel cap…psssst vacuum sound and after i could easily unscrew the bolt of the return line without pressure or gas coming out..looks like something is blocking the return line.. i put air in it with a compressor and the line is not blocked since i hear the gas bubbling with the gas cap removed…
what can i check from this point?
Thank you all

 

Check for vacuum leaks, loose vacuum lines etc. Unmetered air entering the engine will cause the computer to compensate by enriching the fuel delivery.

Larry

 

hi Larry,
thanks for your reply.
i already checked all vacuum lines, there are not so many i could find, where can i find a sheme of the vacuum lines?
and would a vacuum problem cause so much difference in co2 ?normal value 1/2% now almost 10% , so ten times more… And so much pressure on the injector rail?

 

Hello Mike, sorry not familiar with the 2.9 engine, possibly check the parts diagrams at https://parts.jaguarlandroverclassic...j6-xj12-parts/

A broken hose or a badly fitted large corrugated air hose at the throttle body can be a source of unmetered air.

If your rail pressure is too high seems to me that the regulator is not working properly?

Leaking injectors can also richen up the mix ..the computer can compensate for a rich condition within a small range but outside of that range it will usually flag a check engine light and show a code on the VCM.

 

Hi larry,

thanks again.
the high rail pressure is solved.
this was because the return hose after the FPV was blocked because of air blockage in the tank..when i removed the tank cap there was no pressure on the return line anymore.
the engine ran smooth on 6 cilinders but still it was sputtering out of the exhaust and a very high c02 9.8%
i sprayed brake cleaner all over the engine to check for leaks but it didnt affect rhe running engine at all.
what i suspect:
coolwater temp sensor, the car was stored for about 20 years..
inside the car the temp goes max 2 stripes after a long ride (20/30km) , but can this affect the co2 so much?
or injectors..i took them out, the filters were clean but i didnt test them, maybe take the complete rail out tomorrow and crank to see what they do..
a friend adviced to put a cup of atf oil in the benzine tank to clean them..

fpv : it doesnt leak when i take off the vacuum hose but is there a way to test it? O think its working because i saw the amount of pressure after the fpv into the return line so i assume its not blocking?

 

The fuel cap should be vented. You might check on why thats not working. Did you drain old gas or mix with new? Does the car have any symptoms? Hard start, rough running, stumble etc?

 

If the car doesn't warm up, thats your problem IMO. Coolant temp sensor malfunction will cause major issues. They are widely available and reasonably priced. Change it.

 

Hi all,

i dont know what i should check for the tank cap to be vented..can i just drill a hole in the tank cap? Or is it easy to troubleshoot?

and i ordered a new temp sensor with the 2 wires for the ecu and also the one for the dash indicator( if i put this wire on mass the temp is max in the dash so i assume it is working but to be sure i ordered both sensors.

 

By the way Jerry,
I think old gas is mixed with fresh gas, but i inspected the tank from inside..looks clean👌
the car starts quickly,
but has a rough idle.sometimes it gets better and sometimes its rough again..
i also ordered a new gas filter. Tuesday i will replace the sensors and see what it does..and after i will replace the gas filter and see then what its effect is

 

Getting back to the gas cap, I went out and looked at mine. I have 2 styles but the venting mechanism is hidden up under the top cover on both. I hadnt given it much thought but that all "modern" gas caps should be vented, and having looked I'll admit that i am not sure how you could check it without breaking the cap. Sorry to mislead. Hope I can Actually help next time.

 

hi Jerry,
i think the gas cap isnt vented but the tank should be. I opened my gas cap but there is only the mechanism under it which makes this clickclick sound once you close it very strongly to prevent that your wife cannot open it the next time 😂
if you know what i mean..