I recently acquired a 1983 mark 3 jaguar xj6 4.2 with 130k miles, it has recently gotten brand new spark plugs and a distributor. The first thing I did was remove both tanks and send them in to get a resin coating to stop rust. I also added in 2 low pressure filters before the change over switch each side, I tested the fuel pump and it had very low pressure, so I lived with it for about 2 months. I had black soot mixed with water coming out of the exhaust at idle, and sometimes itll smoke badly when accelerating. It kept cutting out in traffic and I had to quickly put it in park and start it with no issue. It also lacked power when in low rpm, and sometimes I would start it and it would start and idle perfectly, then sometimes it would crank for a while and have a rough idle. I found it would run better after driving it for about 30 minutes. So today I decided to get the knew pump and put it on. But now the issues have gotten much much worse. I also took off some of the wires for the injectors to put in new hoses. But now it was a problem to start, and it will not keep running unless I accelerate. It runs so terribly, I took it for a test run and as I put my foot down it wants to cut out. The engine shakes a lot when I idle it. I've now taken the air flow sensor off to clean it. It does seem that it is an air sensor, it's got the symptoms of flooding. But I have no idea what sensor or if it's another fuel problem
Another problem which I don't know if it's related, is that the speedometer is out by 10-20km/h and the battery sometimes doesn't go up to 13v. Please can someone help, its pretty much the only car I have available and I want to go to a show with it on friday.

 

to me it sounds like the AFM (Air Flow Meter), not the fuel pump.
Check that all the hose connections are seated from the air filter canister all the way to the 90 degree aluminum intake elbow, and that there are no cracks in the bellows (accordion) hoses.
If every connection checks ok, you might need to substitute the AFM to prove it is not causing the problem, or do the Resistor Fix to the AFM. (that fix is another story and only certain people know how to do it). œ

When I purchased my '84 it was spewing black smoke and soot and stalling too. It fixed itself after a few times driving it. The car had been sitting a long while when I bought it.

​​​​

 

Thanks you very much, I have taken the AFM off to clean it and I'm putting back on now. I'll also check that bellow, it must the AFM because it's seems to be flooding. Mabye it's even because of the 7th injector? Should I try disconnect the wires from it?

 

the Start injector you call 7th, operates only for a moment, leave it alone, it doesn't flood the engine.

 

This might help

https://www.jag-lovers.org/xjlovers/xjfaq/efirich.html


What's your tire size?

Not good. Low voltage can definitely cause running problems.

As a first step check that the alternator belt is tight.

Do you have a volt meter to verify the voltage? The dashboard gauges are not always accurate.

Cheers
DD

 

Thankyou all I found a break in the rubber part after the AFM, I changed it and still have problems. I was thinking that the "start" injector was staying on, i disconnected it but the issue got worse, I tried running the car and disconnecting the AFM wires but it just stalled showing it's working, I'm going to try run it without injector cleaner in the fuel, mabye the return vacuum pump is gone for? Any more suggestions?

 

[QUOTE=Doug;2848710]This might help

https://www.jag-lovers.org/xjlovers/xjfaq/efirich.html




What's your tire size?


original size.



Not good. Low voltage can definitely cause running problems.

As a first step check that the alternator belt is tight.

Do you have a volt meter to verify the voltage? The dashboard gauges are not always accurate.

ill check and mabye bring my auto electrician in to see.

 

replace the CTS like Doug said. They are inexpensive and they do go bad.
Coolant Temperature Sensor.

 

I'm going to:
take spark plugs out and inspect
Test vacuum thingy
Check temperature sensor and wires
Put the old pump on
check thermostat
Try fuel without injector cleaner
Change the ecu
And then test injectors

 

I had one of these cars for 14 years, (a 1980, worst year for quality, but that's another story !!). In all these years I never had trouble with the ECU, or the MAF. Basically, there are two inputs to the ECU that give the main info for the engine to run, the rest of them being just trims. These two are (1) Mass air flow - from the MAF unit, and (2) engine temperature. Of course this assumes that everythingin the EFI system is working as it should, like the fuel pressure at the fuel rail. I had to replace my fuel pressure unit once; it wasn't working and the fuel pressure was too high. Roger Bywater of AJ6 engineering who worked at Jaguar when this analogue system was under development in the 70s has written a piece on the EFI system on the XK engine: -
https://www.jagweb.com/aj6eng/42efi/index.php
It's a very good read and may give you clues to where to look.

 

I'm going to test my return valve, mabye put the old pump on and see how it runs for now

 

I found the issue is the pressure release valve, it's not working, I have to order from england but its incredibly expensive, im going to see if i can buy an aftermarket one, but what's the pressure must it release at?

 

If you are in the US, go to SNG Barratt US store.

Are you asking about the Pressure relief valve for the Fuel Tanks ?
Or the pressure relief valve for the oil pressure ?

 

This pressure release valve and i live in zimbabwe, southern Africa so very little jag support, ive got someone in SA who does it but he doesnt have them.

 

Fuel Pressure Regulator

Cheers
DD

 

What pressure must the fuel line be?

 

36 psi when cranking the engine

Pressure when running can be a couple PSI lower or higher depending on engine load

Cheers
DD

 

I had a leaky cold start injector that was leaking fuel and flooding the engine. You could remove it, and test for leaks. It was very hard to find a replacement unit that was reasonably priced. Wish I had an extra one lying around, but I don't I wonder if there are VW or other brands that used the same thing.

Vacuum leaks were a big issue for me, that solved many of my problems. The other big issue was the tedious job of checking all ground wires and ground straps, Doug told me to do that early on. I finally bit the bullet and that make a big difference towards that elusive smooth idle. My idle now is pretty amazing, god knows how many hours and how much money I spent in search of this.

I joke with my wife that the reason society is filled with enormous conflict is that humans have an "advance" statically set for high rpm (conflict) and acceleration (competition for resources), not for idle. I haven't figured out the analogy of a vacuum leak yet.

 

Thankyou all very much I'll update you.

 

I found it was the regulator and so I've gotten an aftermarket adjustable one, having to get an adapter made up to fit.