Hi All


My 1996 3.2 X300 has always started pretty instantly cold or hot until recently. Over the last 2-3 weeks, it takes a good 5 seconds of cranking before it will fire from cold. Once it has started it will re-start instantly unless left for a while.


My first thoughts were the camshaft position sensor, but would that not affect every start up?


Any help always appreciated.


Glen.

 

Yes, the cam position sensor logic is lost as soon a sthe Ign is turned Off.

Mine started that a long time ago, and I narrowed it down to the fuel pump inside the tank. There is a drain back valve inside the pump outlet, and it eventually starts to leak, and the fuel returns partially from the rail and the line.

The prime circuit, when the Ign is first switched On, should fill and prime the system, but as age creeps in, the pump has trouble doing so, and eventually dies totally.

A blocked, or simply old, fuel filter could also affect the priming efficency.

Less common, is the FPR (Fuel Pressure Regulator) bleeding off after shutdown.

 

Might want to check the air filter. Changing the extremely dirty filter on mine seems to have eliminated a similar problem (and a jump back to expected performance).

 

And it might be a very simple and cheap fix!

Is it slow on cranking as well, as if it's the battery giving up? But both battery and alternator check out fine?

First disconnect battery!!! This bit is important as you don't want sparks, shorts and other nasty things happening - trust me on this. You'll need to know your security code for the radio too

OK, if so, find where the main live feed comes through into the engine - will likely be through the bulkhead just in front of steering wheel into engine compartment covered by large rubber boot. Lubricate boot however as you don't want to tear it and carefully move back so you can see the positive cable and where it bolts through as assess condition - mine was less than pristine. Undo nuts carefully (mine cracked free easily), remove nuts and cable and out with wire brush and sandpaper.

Scrub, scrub, sand and polish until spotless around nut, bolt and cable end. Clean off all debris, go have coffee or drink, relax for half hour or so and repeat - I took a dremel with wire brush to cable end to get spotless. Clean again, apply grease liberally to prevent further corrosion (I need to do mine again as couldn't find copper or dialectric grease at the time), reconnect, tighten all up (will probably have done no harm to have removed nut on the stud that goes through bulkhead and thoroughly cleaned and retightened too), put rubber boot back in place, reconnect battery and turn ignition key - worked a treat for mine, immediate crank and start, voltage reading back to what it should be etc.

It's always worth a go

cheers

c

 

Thanks guys.


It cranks over nice and quickly, so I don't think it's a battery issue. The airfilter is nearly new, so the fuel pump theory looks favourite to me at the moment.


Keep 'em coming though.


Glen

 

Definitely try swapping camshaft position sensor. Worked for me with same symptoms (long crank, 2 seconds later it either started or misfired).

 

I'm having this problem with the lad's 96. Bob loaned me a fuel line he made from XJ40 parts, that fits a gauge. So now I know the problem is fuel pressure decay....just have to work out if it is a faulty regulator or check valve...





I rousted the lad from his game console to observe the problem:
tried but failed to attach the video. Basically, pressure builds rapidly at key-on when the pump activates for a few seconds, then decays to zero immediately when it shuts off.

I pinched the hose where you see the vise-grips in the pic, and that significantly retarded the decay. However, after further study, I see I was only pinching off the return line downstream of the gauge. So I've got more troubleshooting ahead of me.

 

If you can pinch-off BOTH the return and feed lines at the second the pump is shut off, you can trap the fuel. If it drops, then you might have a 'dribbly' injector.

If it holds, 'unpinch' one or the other to see if it feeds back to the tank through the pump or the regulator.

bob

 

Didn't have enough hands and vise grips to do that, but was an easy enough task to swap the regulator over from SpruceBruce. Same performance. So I guess it is going back through the pump, although swapping the regulator wouldn't rule out a dribbly-injector...but wouldn't that show itself in some bad or rich running? No codes and it's smooth as should be when it does start. Actually starts right up if you go straight from key off to crank and don't pause at pos II.

I guess I've gotta change my $12 pump!

As a check, I moved the gauge over to my 95, pressure came up to 35 or 45 (don't remember and it was a bad angle where I had it taped to the windscreen) but was still there 30 mins later, same press.

 

A 'dribbly-injector' will usually show up on the next start cycle. Rich mix and chugging on the fuel soaked cylinder.

bob

 

aholbro1,

The X300 check valve is part of the outlet port of the fuel tank, and as far as I know it is not replaceable, but before you replace your fuel pump again, it might be worth adding a new check valve to help the FPR maintain pressure in the rail. Here's how I did it on an XJ40 using inexpensive parts from McMaster-Carr, including a check valve with a fluoroelastomer seal safe for gasoline. You can add it in the same spot where you connected the fuel pressure test gauge:

Fuel Line Check Valve Installation

Cheers,

Don

 

Don,

While that may be true, I know the replacement pump has a check-valve in the outlet. I've got the original that I removed around here, somewhere...when I run across it, I'll check it for a check-valve as well. I'd be surprised if they put redundant check valves in 'em; one in the tank outlet and one in the pump....I'd MUCH rather have redundant pumps! Where do you obtain the obscure knowledge that the check valve is in the tank outlet port? I'm curious as I imagine the source documentation has other good gems in it.

I like the idea of the separate, in-line, check valve. I'm much less excited about crawling around under the car and cutting into the (apparently) no longer available fuel line to fit one. While it would be no less work than changing the pump, I'm thinking of fitting one to the pump discharge hose inside the tank. Rather than trying to cut this one and work down inside the tank, just remove it from the pump, fit a check valve and short length of hose to connect to the pump:



Any thoughts?

 

I remember when I worked at the VW dealer in the 1980s there was a TSB for an additional fuel pump check valve for a faulty one in the Bosch 'K' Jetronic pump. It was an 'add-on' ck valve for the banjo fitting on the pump discharge. Check valves in series is not a problem.

A few years later I worked at a British Car Repair shop (Back to British Cars) and we had a Rolls Royce in for vapor lock/long cranking due to a faulty 'K' Jetronic Pump. Rolls dealer wanted $800 for a new pump. I called over to the VW dealer I used to work at and asked if they still had the 'ad-on' check valves for the Rabbits. He said "Yea and they are still $10."

I put one on the Rolls and called the customer to come get the car. He was SHOCKED that the repair bill was so low.

Just add one on the supply line somewhere. I like the McMaster Carr one Don B referenced.

bob

 

Hi aholbro1,

Here's the diagram from the AJ16 Engine Management System Manual that shows the location of the check valve, but I just realized this diagram shows the valve on the return line, so that one is to keep fuel in the surge pot from draining back toward the fuel rail and starving the pump:




I recently installed an OE Denso pump in a '97 but didn't pay any attention as to whether there was a check valve in the pump outlet, but now that I realize that port valve is on the return side, it would make sense for the pump to have one too.

If you want to add a check valve (which definitely will not hurt anything as long as it's installed in the correct orientation), don't worry about putting it under the fuel tank as I did while I had the IRS out. The first place I installed it was in the flexible inlet hose at the fuel rail, and that's where I would recommend you put yours. I didn't notice much if any difference in performance between the two locations, and installing it at the fuel rail is a simple 15 minute job.

As I mentioned, I got the valve and the hose barbs from McMaster-Carr, and I think the total cost was around $25 plus postage.

Cheers,

Don

 

This is brilliant stuff guys, I will install a check valve and let you know what happens.


Just one thing. The check valve in the return line in the schematic above seems to be against the flow of fuel thus preventing any fuel getting back to the tank. That can't be right.

 

I sure looks that way, doesn't it? I'm going to look for another diagram to see if this one has the check valve in the wrong port or aiming the wrong direction....

 

I think it is correct, just a bit fuzzy. You can just make out a ball at the top and the "V" of the seat at the bottom. So it stops the fuel going back towards the engine and emptying the surge pot as you say.

 

Harrumph! I'll need to take another look at JEPC when I get home. Could swear that it calls the line attached to the Fuel Pressure Regulator the "Fuel Feed line" and the one connected to the back of the rail the "Fuel Return Line." Which caused me great confusion in trying to understand how pressure could ever be maintained in the rail by the regulator and a check valve at the pump/supply. If the other way 'round, as depicted in Don's drawing, above, it makes much more sense.

Either I misread JEPC...or it is wrong.

Further inspection of Don's schematic yields this gem: (Check valve location varies, XJ6-XJ8) and yet the page title is: "AJ16 Fuel Delivery and Evaporative Emission Control System" I missed that part where they offered the AJ16 in XJ8's!

I didn't misread it:
(but the JTIS calls it right: Fuel feed hose connects to the fuel rail. Fuel Return Hose connects to the pressure regulator.)

 

In the '93-'94 XJ40s, there are two check valves, one in the bottom of the fuel pump canister to keep it from draining and starving the pump, and one in the evaporative flange that works with the FPR to keep the rail pressurized. I wonder if there is one in the X300 evaporative flange?

 

The check valve in the return line is a good thing when the tank is removed for pump replacement. Removing the return line from the bottom of the tank with fuel IN THE TANK will get you wet and the flow would NOT STOP if no check valve present.

Check valves in both lines trap the fuel.

bob