77 XJ12

I morphed the below engine timing thread into a fuel starvation thread.

https://www.jaguarforums.com/forum/x...timing-102173/

Outta be stand alone.

Long story short. Intake backfiring and dodgy engine revving. Sometimes revs ok but soon goes into the backfiring mode.

So I follow Grant's advice and pop the little plug out of the right fuel tank. Three ounces of gritty fuel. I think, OMG this thing is packed solid. So I pull the big plug waiting for the woosh and nothing. It's farkin' empty. I can see up inside the cavern.

Gauge reads 1/4 tank full in one and 5/8 in the other.

Gonna pull the other plug now for the hell of it. Odds on finding petrol?

The job was easy though. Pulled the bottom body shroud and side bumper without issue. 20k garage queens do have some upside.

 

AHA, Smiths/Lucas sender units, you guys should know better by now HAHA.

 

I hear you. I'm learning.

Left side is bone dry, too.

I am simply outta gas.

 

Maaaaate, you need some SERIOUS drinking time, take a break, a day or 3 will do.

 

Well, if you've got the 1/4 panels off, then its a short step to removing the fuel tanks for a refurb, or replace. New ones are still around and were advertised on UK supplier ads in my Jaguar Enthusiast Club magazine just this month.

Not cheap, though.

 

Hey Fraser,

Good to hear from you.

Think I got lucky. Tanks are in fine shape with some crap in them that looks like fine coffee grounds when dried. When wet from petrol, the stuff can be ground between thumb and finger into a puree. Thinking basic varnish from old fuel knocked off the walls from the Seafoam I had the owner dump in in June.

Flushed each tank through with 1/2 gallon of fuel - about six times - until the debris backed off to a minimum. Tank screens were "mint" - so I think.

Cranked engine and checked flow before main fuel filter. Moderate flow - each tank flowed the same rate. It was not spurting through the hose but it was plenty to run the engine - says the noob. Have no idea what volume per minute should be.

A few backfires through intake transitioning to warm under load when driving - then subsided. (Gunk in an injector or two?). A few passages of driving were very different than before, like Quadrajet secondaries kicking in on a GM big block. But still unimpressive overall.

Revs more smoothly and freely than ever before. Attribute that to new bushings on throttle linkage. Have not dialed it in though.

 

Pfffff. This does not have to be mutually exclusive.

Took the car out tonight and I got rubber in second gear. I am not kidding.

Makes sweet noises like never before. Big time happy heavy breathing under load. Let me demonstrate. "BWAAAAAAAA, Bwaaaaaaaa. Bwaaaaaa". Skinny *** steering wheel keeping it in the center o' the road. Young girls without tops rushing to the side of the road waving and screaming "Pick me, Pick me"

You get the picture.

Um, long story short, the linkage bushings seem to help pretty good.

 

I found cellulose thinners very good for cleaning fuel varnish off the components.

 

Why remove the valnaces unless one is pulling the tanks.

the valances have a rubberoid plug that removing it allows access to the large drain plug.

The rubberoid things are usually destoed in the process. But, if concours requirement is not an issue, the cars do just as fine sans them. or there are ways to close the hole with more elegant gates.

 

Good point. Like I said the car is a cream puff/garage queen and I have yet to encounter a stubborn fastener. I took one valance off, given it's easy, to just see what things look like behind it. I also thought the tanks were partially full and I had a big job in front of me.

On the other side I removed the phillips head machine thread screws on the inboard side and was able to slide out the fat 3" disc without messing it up by just putting a little pull down on the valance.

Thanks Frances. Is this through flushing or mixing with fuel? I have run a gallon of lacquer (cellulose) thinner through a half full gas tank on a couple of cars trying to cook deposits out of catalytic converters that were throwing inefficiency codes without issue.

 

No, only for cleaning dismantled parts, but if you can set it up, you could flush lines out, but you have to beware of the affect of cellulose thinners on plastic and rubber-like parts in the system. I would not mix it with fuel and run the engine, you can get commercial products for adding to fuel to clean fuel injection systems. Obviously if your tanks are looking good then rust particles do not seem to be a problem. I once replaced the flexibles on the fuel return valves using hose that was sold as fuel line, only for the petrol to dissolve them from the inside and dump a load of rubber particles in the tanks which then blocked the gauze filter. It took me a couple of weeks to work out what had happened and it was only when I inspected the lines that I found them to be very floppy, and thought, aha, why is this line like this ? The inside had almost disappeared and a few more weeks would have seen the thing leaking petrol onto the floor. I had to flush out the tanks and once this was done, and the correct hoses put on, the car was its old self again.

 

Ouch. Think what cellulose/lacquer thinner would have done to them. Same thing but much faster.

I performed pressure testing and found the rail pressure to be 28 psi using either tank. Pressure comes up quickly when cranking and is steady except when revving (car stationary) up to about 5,000 rpm then it drops into the low 20's. This may or may not be an issue. I am a little confused by this as the injector pulse/duration will be near maximum at that rpm and it makes some sense that pressure will drop (stand alone) but aren't there regulators to keep the rail pressure constant?

The thing I don't think is right is that there is no standing pressure. I turn the key to "on" and I hear the fuel pump run for a couple of seconds. I see the pressure go up then instantly drop. Start the car and I see the 28 psi. Turn car off and it drops to zero instantly.

Given it's a quasi Bosch system with cold start valves, there needs to be fuel at the cold start valves - all the time. Maybe not pressure when cold but at least gasoline. I pulled the CSV hose off to connect the pressure gauge and there was no fuel. It was wet at the fitting but no fuel dripping.

It's draining off somewhere, I believe.

Check valve on the return line. Check valve at pump?

So, primary questions:

1. Is 28 psi rail pressure ok
2. Is the drop in fuel pressure - say 28 down to 20 ok when free revving to 5k?
3. Does the absence of residual/standing pressure indicate a problem?

Thanks.

 

The fuel pressure is maintained as absolute pressure against manifold vacuum. That's why the pressure regulator on the fuel rail has a pipe connected to the manifold. It then compensates for variations in manifold vacuum. Of course when you are cranking, there is no vacuum, and fuel rail pressure is high. There should be some residual pressure in the system, and the workshop manual warns about this when disconnecting fuel lines, but over time it does disappear. I think 28 psi is OK, but the only real way to check is to put a new pressure regulator on. The workshop manual (which you have, don't you !!), give the expected pressure.

 

Fraser, don't try to confuse me with the root cause for my questions.

Haynes manual is on the way. Owner has one and even a new one is only $20 plus shipping. He is sending it over. However, I have had the car for three months now so a robust kick in the rear is warranted.

Good news though. Was reading Grant's threads stressing the need for a decent gravity feed from the tanks to the pump. I had only put two gallons in each tank when I noticed the pressure drop to 20 psi from 30-ish psi under high stationary revs. I put ten more gallons of fuel in the right tank and revved the car to 5k again with NO drop in pressure using that tank. God bless Grant.

Also residual pressure does not drop instantly now. It takes about five seconds to go to zero where yesterday it dropped like a stone. Maybe just some gunk?

Engine is sounding very gnarly, but still a few intake backfires on the right side at idle. I do believe it is the throttle linkage not dialed in. So again, I will shut up until completed.

Keep in mind I work on Bugatti Veyrones (aka Chevy tie rod ends) and Maserati Boras (aka 1993 Buick Park Avenue heater cores) to bring the real money in so I can't work on the Jag full time.

 

Throttle linkage adjustment completed. All backfire issues are gone and car runs smooth save some light putt-putt (poof-poof that kick your hand back a little) type backfires from the right bank at idle only.

Car free revs nicely and delivers the deep nasty sound at high RPM's when warm. Very consistent. Way more like a sewing machine, if that makes sense.

Massive black gunk in bore and on throttle plates. I attribute that to the EGR valves that previously would kick in any old time except for the one that was stuck open. I blocked them both with shim plates but left them plugged in a few months back.

Adjustment task took several hours mainly because I was nervous.

Anyways, regarding putt putt out of exhaust, I read one thread from Grant about running on 11 1/2 cylinders and whacking an injector. Although it was a newer (HE I think?) car he fiddled with, I unplugged one injector connection at a time and found the bank 1A wire badly frayed, the rubber sheath thingie ripped and the connections were sporting naked and severed copper wires at the white connector that plugs into the injector. Also pins would slide back out of the white connector easily. Not so good.

Disconnecting the other five connectors individually would cause the exhaust putting/poofing at idle to double in intensity. When bank A-1 connector was removed, I could not pick up for sure that change had occurred. Given it is nasty, it's highly suspect.

I also need to check the TPS voltage. Not sure I fully get that thing but understand it will deliver different across the RPM range with a defined voltage at idle and talk to the control module Given the left side does not putt/poof, and smells "normal" and the right side poofs and stinks bad, I doubt it is the culprit.

Thanks all.

 

Bob,

Catching up with thongs. Been working, and went interstate to collect another Jag for me.

The PreHE has a Throttle Switch as apposed to a TPS, and setting them is quite fiddly, and daunting at first. If it were mine I would leave it be for now, as what I read sounds like a cylinder out, and that switch has zip to do with that.

If you want the procedure let me know, I have the factory book somewhere here, and I can scan it and email it direct. My Pre HE's never had issues with that switch. Whacking the injectors was a semi regular happening, as was the 2 PFR's (fuel pressure regulators), as they also stick with lack of use, and fuel contamination.

Those Pre HE injector plugs are a marvelous thing, NOT, and the wires popping out is sooooo common.

 

Thanks Grant!

Owner is bringing his UK based manual over Wednesday. It's not the factory manual. Was expensive. Bennings or something like that. Not Bentley. Although, that would be ok vs Haynes.

I have never felt this thing run with consistent power delivery until tonight. Took it out and wailed on it. There were some backfires that did not happen when free revving - all in the 2500-ish rpm range under load - but I am ok with that for the moment. Plenty of things to check up on for a car that has been sitting since 92 but the throttle bore clean out and linkage setting provided marvelous results.

 

Thanks for the nudge, Fraser

The good manual finally arrived today. It is the factory manual. BRG in color and still in the plastic wrapper. Sweet!

The issue with residual pressure has been isolated to downstream of the engine bay fuel filter. Pulled off the inlet hose and clamped on the fuel pressure tester. It's at 55 psi now and hanging - drops a pound or so every several minutes. Fuel out of inlet side was clean.

When I said the car was sewing machine like when idling, I had the air cleaners off and the air temp sensor was not connected. Changed the whole complexion of how it idled when re-connected. Not really in a bad way, a little less sewing machine like, but changed the smell of exhaust on the left side to now having some fuel in it rather than smelling almost too lean.

Nice thing with manual is I checked the resistance of the air temp sensor and it was spot on vs ambient.

Thanks for all the help and I'll surely have another thread popping up soon.