OK, Grant... I learned something !


I had of course, done the "human test" on the MAP sensor. HHMM... I suppose there may have been some vacuum leakage, but it's so difficult to determine.
So, broke down, and finally bought a hand operated vacuum pump.
poop
No matter how violently I attempt to "pump up" the vacuum... I can't get it to read past MAYBE 2 in vacuum. When you consider that an engine typically goes down the highway at around 14-15 in vacuum...
I think I found a problem.


I'll take it apart, and see.

 

Well one.

Like I always say, "Simple cars for us simple folk". No special talents required to own and maintain one.

These early V12's are simply not rocket science, just plain OLD.

 

Oh, Grant, you're going to be SO proud of me ( the new guy here ) ...


Removed the Manifold Pressure Sensor.
Carefully ground off the heads of the 4 rivets that hold it together, and punched them out.
Geez... complicated little bugger, isn't it ?
Anyhow, I think I determined how it functions.
Unfortunately, unless it's just the O-ring seal that is leaking, I am unable to come up with another cure for the leak.
so...
Lets' see if I can CONFIRM that this thing is the enemy.
I removed that little "button" that fell out anyhow... you know, the one that the bellows presses against.
In it's place, I lightly threaded in a rounded head, short sheet metal screw.
This made the "point of contact" to the centre of the bellows, about 1/4" higher ( closer ).
When the two halves are assembled, the position of the internals, is manually relocated closer to what it would be, if there was a good vacuum signal.
Re-installed it... without the vacuum hose on ( redundant at this point ).
Started the engine.
WAY WAY WAY better.
This particular sensor, has the allen key adjustment, and it IS still useful in the state that the unit is in at the moment.
made a couple turns of that, and was able to almost eliminate the over-fueling condition.
Needless to say though, I would suspect that loading the engine, would cause a lean condition. That's OK at this time. At least I KNOW what's causing it.


I DO have a new temp sensor coming in next day. Pretty sure that it was also contributing to the problems.


Bad news is...
I think that I'd be best off, to get a new Manifold Pressure Sensor for this car. Not sure where to go though.

 

You have done very well.

I like the sense of adventure you have, must be some Aussie in ya somewhere.

If that bellows disc thing is not cracked, then the seal is the only vac leak left. The fact it is better now, points to it being the issue.

I have no idea where a new one would be sourced from. It is a BOSCH part.

Up there, try the likes of XK Unlimited in San Louis Obispo. They have helped me over the years with odd stuff, and they do actual restorations in house.

I will stooge around when time permits and see what I can find, maybe a Bosch part number even.

 

OK, did some basic searching.

The "basic" Bosch numder is 0 280 100 ??? for the Manifold Pressure Sensor (MPS or MAP in some languages).

I DO NOT know the last 3 numbers.

I found some on ?Bay USA, and they are ending in 100, 122, 010, etc. As I said, heaps of cars used this system, Volvo, Porsche, Benz, Citroen, etc.

Maybe your old unit has a number on it, or even a sticker wih the number.

I am sure I have notes on this system somewhere in all the boxes in the shed. I wil go digging when I can, but it may be a day or 3.

 

Told ya I had it somewhere, just needed to have a drink and "think", damn.

Go to page D92, and you find your Jag.

Bad news, NO pressure sensor listed, bugga.

Look at page D102, and the Merc V8 4.5ltr, with D Jetronic system, and the pressure sensor is listed as 0 280 100 112. Pretty close engine spec.

Remember this is the "Grand daddy" of todays EFI systems. NOT at all fussy in any sense of that word.

Maybe some time using google etc may find what you want, or even someone that rebuilds these things.

They are the PRIME fuel sensing item in the D Jetronic system.

Bosch EFI catalogue.pdf

 

Some Aussie in me ? Well, Canucks are kinda like Aussies... just not quite as crazy !

Grant, you've gone through an awful lot of trouble for me, and believe me, that has given me the priceless "experienced" information that I needed, so I can fix this thing.

And, talking about fixing...
The manifold pressure sensor ( MPS )....
I think I fixed it !
Yes, it looks like the only place it could leak, is the O-ring seal for the two halves.
Replaced that, put the little button back in, and bolted it back together.
I was able to create a form of an idle ! Though it tends to mis-fire and stumble some.... it is a hundred times better.
Installed the new $85 temp sensor that I got today. That may have made a bit of a difference, because after I put it in, I had to fool with the allen key set screw in that MPS.
In my efforts trying to lean out the mixture, I had messed with the fuel pressure regulators again, so, I'll have to re-set them properly tomorrow.

I'll be back

 

ooooooh, it wasn't THAT simple ! Yes, I solved the leak at the body of the MPS, with a new O ring. Yes, I did start over, and re-set the two fuel pressure regulators to about 28 PSI.
The stupid thing would then start, run OK for a few seconds, then commence it's over-fueling again.
Took apart the MPS again. Took out that double "brass bellows" again. This thing is exposed to atmospheric pressure, through the hole for the allen key adjustment provision. All I could come up with, is that the bellows must be leaking somehow.
Decided to "pressure test it", with compress air. CAREFULLY blew air into the opening, while having the bellows submerged in water.
AHAH !
Little bubbles all around the perimeter of the one that does the expanding.
I applied a bit more crimp to that seam, and tried again. WAY better, but still not sealed.
I then applied the scientific approach.
Very carefully, very cleanly, applied a uniform bead of high quality engine silicone, around all seams, and let it cure.
It's back together.
Still not great ( random mis-fire ), but the MPS seems to be very sensitive to adjustment... just as Grant said it should be.
The engine will now consistently sort of idle, and I can get up to highway speed without too much "pedalling" the throttle. Probably still a touch lean.


At the moment, I'm done with it, until the new distributor cap; shows up on Tuesday.
I have a concern about the one on there... seems that it may be "distorted" / out of round, due to evidence of the rotor having made a nasty gouge through 3-4 consecutive terminals inside.

 

.

just reread this , noticed you an old 348-409 Chevy guy!

i bought NEW 1959 Chevy Impala with the very rare(i didnt know at the time) factory 348 Special Hi-performance 3 dueces engine,4 sped in the floor(only 1959 sold in Boston Mass at that time),positrac.

factory stock engine had 11.25 comp.ratio, solid lifters, heads big valves and ports nice cast headers larger exhausts.

ports where big enough, late 60/61, i bolted on a 409 dual 4 barrel aluminum intake manifold and carbs, every one said wouldnt work, well nobody on the street beat me in a race,for 1 1/2 yrs!

by then 427s from Ford, mopar, and GM where showing up, i did the BAD thing and took the engine out and put it in a 34 Ford Coupe, chevy drive train, 1st time out at the strip cranked out an 11.5, at 124mph.

then the musical chair engine went into a 1957 Chevy Belair H/T, it was a formidible car even then!

and just comes to mind; guys around said 348 cant rev, well after market tach said 7000+ more times than i can count, also engine never gave me any form of trouble!

just a little old time memories.

 

HAAHH !! Ronbros !
great history... and darn nice car you had there.. all of them.
Me ? ... a 409 guy ?
uuuhh...
don't open THAT can of worms...
you have NO IDEA !
I own, built, and drive the fastest NHRA legal Stock Eliminator 409 Chevy... 1962 BelAir sport coupe, 409 / Jerico 4 speed / 5.13 gear. Shift at 7000-7200 RPM, goes through the traps at 7250 RPM... high 10's @ 123 MPH.

 

Almost forgot !
on topic


I just installed the new distributor cap. It then took 15 minutes to get the engine to fire up ??????????????
I dunno ????
After it was running, I went for a drive, and got it warmed up.
Yes, the 'thumping" miss is gone. However, the random sputtering is still going on, and I'm constantly chasing the setting on the MPS.
One good thing, is that the random mis-fire seems to be 90% on the left bank only.
That in itself, is a HUGE accomplishment.

 

my approach on 1978 XJS V12 F/I system,(pic shown). this programmer lets me adjust fuel, rich or lean in 1% changes, at all rpm and load conditions!

standalone SDS,simple digital systems, calgary CA.

for me it was much easier to figure out, and eliminates or find all the 30yr old corroded parts. with new modern parts, most available at local car stores!

i replaced the injectors with some after market parts, tests showed 4-5 stuck and most just not balanced and volume all over the place! also with adjustable FPR.

an important thing with a 12 cylinder cap, proper rotor to terminal phasing, it can cause irratic sputtering, hard starts,etc. also check for weak spark only when cranking,install relay full juice to coil when crankin.

 

Even MORE info, and what appears to be a final solution. Thanks, Ronbros !
Trouble is, I can't justify throwing the bank account at this thing ! I just need it to be acceptable.

 

aaaaaaaaaaaaaaaaaand... ANOTHER symptom ! ! ! ! !
Fuel is "aerating" within the pressure side of the system. When opening the line at the engine, pressure seems to be stored in great quantities... fuel sprays out like foam... indefinitely. Like it's propelled by a fully pressurized compressor tank.
NO WAY can the fuel mixture be corrected, when half of what's going through the injectors, is air.

 

OK.

If that is the case then the return to the tank/s is restricted, or getting restricted.

NOT Jaguar related.

Years ago, I had that with a Detriot powered Genset. Weeks later we found that when the return hose was pushed over the barb fitting, a small "flap" of the inner lining of that hose had "peeled up". Engine ran fine until that flap "popped up" and closed/restricted the return line, engine overfueled and died.

Fuel pressure went thru the roof, so we knew it was in the return system somewhere.

PreHE FPR's can jam, and without reading this whole thread again, I think? you replaced them????.

The pump will "dead end" at about 110psi. That will flood the engine for sure.

The only way air can get in is on the "suction side" of the system, so maybe check that also. Any issues on the "pressure side" will have a leak obviously.

 

why do you think i went to a standalone system, 78 jag/bosch was old and junk(all kinds of potential problems), nope didnt need that kind of noise!

if it aint one thing its another, no doubt you will make it run, but not as good as the engine could.

 

Today, I disassembled the little junction in the trunk, and cleaned out the plugged metering jet that is in one fitting. All good now. Replaced those hoses.
Ran the fuel pump manually, and bled off the foamy fuel at the disconnected hose at the engine. Started flowing nice and clear , smooth.
Reattached it.
Connected the wire properly at the pump ( through relay ).
Cycled it a couple times.
Started the engine. Was a touch lean.
Adjusted the MPS.
Ronbros.... you say, "not as good as the engine could" ?
HEE HEE !...
Well, it sure DID run as good as it could. I mean MAN... did it run nice... for about 15 minutes. Then started leaning out. Adjusted the MPS again. Idled OK, but would not hold any RPM cleanly.
Then, when I went to re-start it... WAY too lean.. then too rich.. then lean.
When this thing sits for a while, it'll run pretty good. Then, act up again.


Yes, Grant, I know about that potential hose problem. I've replaced most of them.
I'll do the rest tomorrow.


Now, one thing I haven't mentioned...
The new fuel pump that I installed, is not a correct original. It is an aftermarket MSD unit, for general fuel injection systems.
I have a concern that this thing simply has too much go for this old style injection.
So much, that it's simply cycling too much fuel through the entire system, and causing a aeration.
I've seen this in engine oiling systems, when the pump is too aggressive ( pressure / volume ) for the bearings, etc.

 

On the way it seems.

The fuel pumps for these systems IS the standard "Universal EFI pump". Down here it is used on Ford, Holden, Merc, BMW, Volvo, SAAB, etc. The same pump is used on the XJ-S HE, S3 6cyl EFI, and V12.

I seriously doubt the pump is the issue, BUT, and there is always a BUT, if its one of those radical racing style, with serious flow/pressure capabilty, then you may be correct.

The constant leaning off, is maybe, the CTS, and/or is wiring.

It has been a seriously LOOOOOOONG time for this next item.

On the side of the ECU is a knurled knob that is the "Idle fuel trim potentiometer". Its ability to adjust the fuel idle mixture relies on HEAPS of other settings being spot on, and I would have to wade through my huge stack of notes to find that sequence list.

On our S2 V12 adjusting that knob could get the engine to belch black smoke, so it really does have the ability to seriously affect fuel trim, but only at idle from memory??.

 

That scares me, Grant ! I won't go near that thing, until all else is solved.


Yes, I'm concerned that this fuel pump IS one of those super duper things... even at only about $150.
Did some more reading on the subject. Found some info suggesting that excessive fuel flow through the entire system, can cause a "vortex" above / into the fuel outlet from inside the tank... thereby sometimes "gasping" air... creating bubbles within the pressure side of the system. Pump this into the low pressure return lines, and there's HUGE ait bubbles. Pump that into the tank... and there's a freaking toilet bowl, with an air hose blowing in it.... Then see what that super duper fuel pump starts drawing from.


The fuel full of air on the pressure side, really IS the symptom here. Need to stop that.

 

We have the correct pump at work for $130 AUS.

As I said before, there is NOTHING special about this system, and sometimes the "special" stuff, and "special" thinking, does more harm than the way Robert Bosch designed it, along wth his best mate The Prince Of Darkness (Sir Joseph Lucas).

Get the standard pump, be done with it, they work and work well.