1996 VDP 4l - runs rough after 30 mins

My 1996 VDP 4litre runs perfect for about 30 mins then starts missing and finally refuses to run at all. Leave it for a couple of hours to cool down and it behaves perfectly for another 30 mins or so.
When the problem starts, the Rev Counts goes to zero with every cough and splutter, but returns to normal revs indication when you play with the throttle to keep it going.
It does not throw up any codes, (cheap basic OBDII reader). Fuel filter is new and pressure is good; tried it with the fuel press relief out of circuit and no difference.
New plugs and coil-packs. Cleaned the throttle body, Map and MAF. New air filter. Opened up the CPU, dry as a bone, no sign of cold joints or terminal fungus.
New battery, good charge rate.
Any ideas?
Cheers
Dino

I forgot to mention that I have the EGR blocked off so as to eliminate it from the equation.
Dino

Welcome.-
Get a second opinion, I‘m just thinking loud, but either a sensor cutting out (crankshaft, but then why no codes?) or it happens as the car switches to lambda feedback/closed loop. Is there a way to read the fuel trims, and does it throw no codes that lead somewhere while it is cutting out and dying?
Either something gets hot, or something is sending false information. Maybe have a go at disconnecting the lambda probes, see what happens.
What if you drove it somewhere you could let it cool down again without being in the way, to see what exactly goes on beyond idling?

Good luck
David

When it stops, crank the engine and see if the rev counter shows<>200rpm
The CPS does not AFAIK throw a code, my AJ6 XJ40 certainly didn’t when it was earthing out and stalling the engine (always at a set of lights and usually when I was at the head of the queue!)

Hi Robin,

what is the significance of 200rpm?

When it stalls, sometimes cranking can get it to run very roughly but enough to get the steering and brakes to work if rolling down hill, but any loading for even flat roads stalls the engine.

My best thought is that something gets hot after half an hour and when it cools down, it runs again.

Cheers

Evan

Hi David,

thanks for the response.

Additional info:

When it stalls, sometimes cranking can get it to run very roughly but enough to get the steering and brakes to work if rolling down hill, but any loading for even flat roads stalls the engine.

My best thought is that something gets hot after half an hour and when it cools down, it runs again.

By lambda probes, I assume those are the oxygen sensors?

How to read fuel trims??

Cheers

Evan

If your not getting codes…………
Go to gas flap
lift flap
does the LITTLE RUBBER CHRISTMAS TREE EXIST?
IS it blocked with leaves or dirt?
That vacuum lock will cause that.
Or remove the black tree and blow with an air hose GENTLY.
Its that or crap in the tank shifting over.
Is the gas old or sitting for months or years?
Its all related to that.IMHO
Try a BIG bottle of chevro techron fuel injector cleaner ONLY CHEVRON…It willeat the crap out of the pickup screen
Good luck
gtjoey1314

Exactly. But, half an hour is a very long time to warm up and I wouldn’t crawl under the car for now.
The crankshaft sensor sounds good so far.
I don’t know whether the car even reports the fuel trim information, all I know is some basics not tied to the Jaguars.
So I‘d start by what Robin wrote.
Vacuum in the tank is another great suggestion!
It would lean out as if the pump was on the way out. Giving it throttle would help a little. Any load would kill it after it ran for a while. Might have shown on the short term fuel trims, but not certain. Start there, lift the flap, allow in some air!

David

Yes, vacuum in the tank sounds very possible.
Thank you gentlemen, I will report back.
Cheers

The significance of the 200rpm is that is shows the CPS is working, no movement on the rev counter generally no CPS signal to the ECU.

I had the same thing happen on a old Rang rover , ok when cold , then stopped after about the same time , turned out to be the main HT lead coil to cap , replaced it with a copper one all was well !

No wires or cap on a x300
Check the Christmas tree and last fill up

1 Like

Hi Guys…not sure what you mean by “Christmas Tree”.

I released the gas cap and there was a “whoosh” as air rushed in. Definitely a vacuum in the tank and the cap hasn’t been off for 4 months.

How to clean that little vent thing by the side of the cap?

Cheers

Dino

I think we might have something
You should have a little vent plastic tree or a hole next to the cap?
Is the hole plugged or loaded with junk?
Is the gas 4 months old?
Put a big bottle of chevron injector cleaner
The black bottle only after 10 minutes add NEW highest octane you might have fixed the problem
You have a vent issue or crap is sucked to the screen and you have to break it up
The chevron will break it up!!!

Sorry pull up the little tree low air or go gently with a hanger type wire
Now the hoses could be crushed inside the quarter but I doubt that…right
Gtjoey
So if that line is clean the bottle was used by jag in 1995 96 97 and beyond for the injectors and the tank screen
How old is the gas