Hey Guys,

for you who followed my hard cold start journey my know i have problems when starting from totally cold and then a slithly rough idle and low power. Its a V12 H.E engine.

I thought i leave it that way but then i was just too annoyed by the problems.

I did already measure the fuel pressure befor but now i noticed that the pressure meter i used is laggy and does not drop by its own. Anyway, i got a new one and did the test again.

Following things i noticed:
- When i turn the ignition the pump primes for a few seconds. It takes about 1-2 seconds for the pressure to rise up to 25-30psi. As soon the pump stops it drops to zero immideatly. If i do it again, its the same..pretty low pressure and then drop to zero.

- as soon as the engine runs it rises up to 60psi.

Ok the high fuel pressure would mean my engine runs too rich, what would explain the rough idle and the low power and the fuel smell from the exhaust.

The low fuel pressure and the drop to zero would explain my cold start issues.

BUT there seem to be two problems in the fuel system. One of them i found: the high fuel pressure is caused by high pressure in the return line. To test i unplugfed the line after the fuel regulator and put a line to a bottle - and suddenly i have a perfect 35psi at idle.

The previous owner did put in new tanks since the oöd ones were rusty - the filters in the injectors were kinda messy when i renewed them. so i assume there is a blockage in the return pipe....maybe in the fuel cooler? where would you guys start the search?
It has to be between the fuel pressure regulator and where the line splits to the two tanks because it does not change when i switch tanks.


Ok thats problem 1.
Problem 2 is the low pressure and the instant drop when priming the fuel line. it also is pretty low while cranking...maybe 20psi. The fuel pump and filter is new.
I know there is a check valve between filter and engine. i was thinking this may be broken...but the fuel pump also as a check valve - since the pump is new, even if the other valve is broken it should work. or am i wrong there? anyone has a idea what could cause the low pressure and the instant drop while starting?

 

OK.

1) Get down and dirty, and LOOK at the metal return pipe under the LH side of teh car. Particularly near the jacking points. Tyre fitters etc, are reknown for NOT using the jacking points and crushing that line. I have had/seen many over the years.
Fuel cooler, dunno, I ditch that sucker on day 1 of ownership.
If thats OK, I will will leave it to the Series Guru's to carry the thread. MY V12 HE have all been the XJS version, only PreHE in my fleet with 4 doors.

2), Injector/s stuck open and dribbling fuel and pressure off. Cold start Injectors are common for that.
The Loom is above #1 on any "to do list", and they are failing very regularly now due to age, nothing sinister.

TPS is set too high, thus triggering the Injectors as soon as the Ignition is switched ON. That would also affect Cold Start.

 

i had all injectors out and tested, none was leaking. My car does not have cold start injectors. So they should be fine.

i will have a look on the throttle position sensor. I did not find a description how to test the new one in my books. is there a reading for this?

i guess the sudden pressure drop when the pump stops could come from a broken check valve since there is also a connection from that valve to the return pipe?

 

You are NOT listening.

Injector integrity is NOT the subject of my suggestions.

Good on ya for cleaning them.. I have never, ever cleaned any Injector on any of my Infected cars, they are a robust little sucker and do what they do for a million kms, One of mine has 163K to go to reach that distance, and the Injectors are is installed in Coventry in 1976.

If the loom, or TPS, is not as it should be, the system WILL trigger Injectors whenever the Ign is in the ON position.

Simple engines these V12's.

So, you prime the thing, the pump stops on the timer, the pressure drops, the Ign is still in the ON positionm so the ECU etc etc is alive and kicking.

 

i understood you - i just wanted to tell that a leaking injector would cause the same problem and i can say that they do not leak.

The injector loom does work when running, so the triggering of the injectors should be fine. Leaves the TPS and the loom of the TPS.
I will check that, unfortuny my workshop manual only writes that you need a lucas test unit for the new TPS.
I can also try to listen if the injectors operate when i turn on the inition. you can hear them very clearly with a stetoscope.

Can someone explain how the fuel air bleed valve with the check valve works?

 

The TPS is checked with a voltmeter. I can explain later if nobody chimes in sooner.

The check valve on the air bleed works (or doesn't) work as expected; nothing unusual. As for the air bleed device itself I've never investigated exactly how it operates

Are you still running two fuel pressure regulators? Just curious. I'm not sure if the the inlet regulator could have any bearing on your problem. Need more coffee.

Cheers
DD

 

yes i am still running two pressure regulators. I was thinking about the inlet regulator too, but when its clogged up i would expext too low pressure at the rail - not too high

 

The RH is NOT a pressure regulator as such. It is more a pulse damper, and mostly removed. Caues more issues than it was meant to solve.

MY TPS Doco attached.

 

Thank you, today i followed your instruction and adjusted the TPS. It was at 0.263V. Now its at 0.339V.
While doing it i payed attention to the injectors.

1. They do a short burst as soon as i turn on the ignition. Not very effective since the fuel rail has no pressure then at my car.
2. With ignition on but engine not running they do a short burst when i open the throttle quickly. Its not how far i open it but how fast i open it. Also not effective since the pressure drops to zero as soon as the pump stops.

Is that normal behaviour?

I am still questioning why the pump does only build 30psi on ignition on but 80 when the engine is running?

steps now:
1. clear the return line to get a decent pressure when the engine is running
2. put a check valve between the air bleed and the fuel filter. The check valve in the air bleed valve appearently is made of gold so i put in a aftermarket one in the line.

 

OK, 5 coffees in, look out.

NO, Injector activity with Ign ONLY to ON indicates a short somewhere. Your adjustment of the TPS is fine, and it was too low, which would NOT have activated the Injectors.
Assuming the TPS volt rise as you open the throttle is SMOOTH, without "bumps", I would deem that part DONE. You may need an older Analogue meter for that test, as the damping in Digital stuff can block what you are looking for.

YES, activation as you quickly open the throttle is normal,. and designed as is.

30psi on 1st prime is "about" normal and enough to start the thing. Bear in mind, as soon as you hit Start, that pump starts again.

80 running, NAH, you got a problem. The pumps are "generally" 110psi DEADENDED.

I will think more during the day and come back later my time.

 

ok, i will try the following things:

- disconnect all injectors to see if the drop of pressure has something to do with the injectors. If they open and stay open after ignition on it would explain the somewhat low pressure at priming, the instant drop and the hard start....although i think that would also flood the engine and it would not start at all.
- put a 12V battery at the pump and see if it builds up pressure when it runs with ignition off.

The 60psi come from the blocked return line, i will sort that out first.

 

Simpler.

Unplug the TPS, that removes an aging item, and YES ir will start and run with that unplugged, just VERY slow to accelerate though.

If that still causes the Injectors to click, there are other issues.

 

are you 100% sure that there is normally no priming pulse on ignition on? i read somewhere else, where they had issues with the ecu signal that they should check for this priming pulse on ignition on since its independent from ignition and TPS.

 

NONE of mine, PreHE and HE have that "feature", and I see NO use for it.
As you have already stated, the rail is at zero pressure soon after shutdown anyhow.

BUT

I am down here, and we have NO strange emissions, hot start, whatever, on our cars.Simplistic in the true meaning of the word.

Your market, wherever you are, may well be different, but Ign Pulse Activation, NOPE.

Injector loom issues, hell yes, as that sucker goes live at Ign ON, and if there is a short, leakage (more common than beer in a pub), you got issues.

There is a thread in the XJS section, with pictures, about that very thing.
Coz I am generally a good guy, here it is
https://www.jaguarforums.com/forum/x...he-v12-279318/

 

You are for sure the expert with jaguars and i will work through that thread for sure. Just for your information, here is the thread i was referring to:
https://www.jaguarforums.com/forum/x...pening-176662/

The car was originally delivered to germany.

In theory the fuel rail should hold pressure and in theory the pump also starts with ignition. But in reality you are right, the rail looses pressure over time and the pump needs some time to build up pressure.
Anyway and here is the mechanical engineer speaking and not the jaguar expert:
Maybe its just a sort of calibration of the injectors. They close by fuel pressure and i noticed that if you apply pressure without operation some were leaking, but worked perfectly fine after the first click.

I did not notice the injector click at all since its at the same time as all relays operate. But i noticed it with the stetoscope on the injectors.

 

So i planned to clear the return line and put in a new check valve to get the fuelpressure cleared out.

But first i did some test to see if the issue is connected to the injectors and to find out why the hell i get 60psi at the running engine.

so i unplugged all injectors and the TPS and put the ignition on. Same as always, pressure goes up to 30psi and drops as soon as the pump stops.
Next i unplugged the fuel pump and put 12V right to it to see if i get to 60psi then. With continious running fuel pump i get 38psi. Then i applied vacuum and it drops with vacuum as it should.
But then i released the vacuum and the pressuee jumped right to 60psi). whaaat?

I changed the pressure regulator to a new one a few weeks ago in hope to get rid of the idle issue. Appearently the new one is broken. So i put in the old one.

Now the fuel rail holds pressure, runs at constant 38psi without vacuum, 32psi with vacuum. No drop when the pump stops. Basicly as it should be.

Well that means back to the scratch. i really hoped that would explain my issues. But the change to the bad regulator did change nothing how the engine runs.

Maybe i will build a new injector loom. But all injectors fire normal, so i would not expect it. is there a sure way to test it befor you do all that work?

 

My present and past HE V12s had/have a 2-3 second pump activation simply by turning the key "on".

FWIW.

More later

Cheers
DD

 

Mine were at 42-45psi NO vac, and varied 36 +/- running t idle.

I ran no RH "FPR" as mentioned earlier.

I only used OE FPR units when needed. Remember, most of my "work" was Pre Computer days, and YES, I am that old.

No fuel cooler, over run valves etc etc.

Injectors are fired in 4 batches of 3, which you know I think?

1/3/5A
2/4/6A
1/3/5B
2/4/6B

NOT sequential, and I have always assume they fire 12 at a time, but NEVER gone into to far, as I have never needed to.

My looms were a single RED for Ign feed to all 12.

Then a separate colour for each batch Earth trigger. Carefully splicing as I built it.
Simple and effective.

These looms today are causing a lot of weird things, and AGE is the killer, not the kms etc etc. An insulation leak to earth will actuate that batch.

The only way to properly test is to remove that loom, lay it out CAREFULLY, unwrap it, and inspect each wire for anything.
I did that once, then stopped and built a new loom, why waste time inspecting, this looks horrible, so move on McDuff.

 

Doug, i think we agree on the pump priming the fuel rail on ignition on. The discussion was, do the injectors fire a pulse at the same time as the pump starts. Its hard to hear since all the relays click at the same time.

anyway you convinced me - i will rebuild the injector loom since the car will sit for a few weeks anyway when i send the AAV to england for rebuild.