OK, So I'm considering cleaning the MAF sensor and Throttle body assembly on my 91' Sovereign. I want to use the Seafoam brand with the hooked dispensing hoses into the throttle body.

I've read somewhere on this forum to beware of knocking the alignment of some sensor of sorts that can mess of everything. Help me on this, please... whatever that is I don't want to do it.

Getting to the throttle body seems to be more work than I have patience for, so my thought is to loosen the clamp enough to move the expandable piece back a half inch or so and let the Seafoam can hoses into the throttle body inlet area without dismantling a bunch of stuff over there.

Advise, warnings or a better way of doing this is appreciated.

Jagbro

 

Hi Jagbro,

I'm the wrong guy to ask about a shortcut method...

I like that Seafoam product and it is effective for periodic maintenance of an intake that is not too heavily carboned and gunked up. But if your intake and TB have not been cleaned in a while (or ever), Seafoam is going to make very little difference and will not give you the results you really want and need.

But it isn't nearly as difficult as you might think to do the job properly.

The MAF sensor is easy. Carefully disconnect the electrical connector, loosen the hose clamps and remove the MAF. Using zero-residue MAFS Cleaner Spray, flush the hot wire inside but take care not to bump it with the spray tube.

To properly clean the TB you really have to remove it from the intake manifold. The worst gunk is on the rear side of the butterfly valve or plate, and it's really difficult or impossible to clean it properly from the front side alone. And no gasket is used, so the mating surfaces of the TB and intake manifold are generally covered in varnish. Also, you really want to clean the EGR port that is behind the TB on the underside of the intake manifold, because it is almost certainly clogged with carbon. And you should also consider drilling drain holes in the case of the Throttle Position Sensor (TPS) and flushing it out, either with your MAFS cleaner spray or zero-residue electrical contact cleaner spray. Seafoam can't accomplish any of this.

While you're at it, wipe and flush the insides of the air intake pipes and breather hoses, use your contact cleaner spray to flush the electrical connectors for the MAF sensor, Intake Air Temperature Sensor (IATS), breather heater, oil pressure sender, TPS, brake master cylinder, coolant level sensor, O2 sensor, Idle Air Control Valve (IACV), etc.. And seriously consider cleaning the IACV itself while you're there.

It's really not as difficult or time-consuming as you might think. You can do all of this in a Saturday afternoon. Here are some links to photo albums that will help:

Air Intake Plumbing Part 1 of 2
Air Intake Plumbing Part 2 of 2
Throttle Body & EGR Port
Throttle Position Sensor Drain Holes
Idle Air Control Valve Stepper Motor

I know you don't want to do all of this, but you and your Jaguar will be really happy that you did!

Cheers,

Don

 

Thanks again Don,

So to be clear, I can SPRAY the hot wire inside the MAF. But do not touch it at all with anything, right?

Jagbro

 

What's happening is every 3-5 starts it just cranks and will not start, or may start and stumble a few seconds, then everything's good (like initially fuel deprived). But turn the key off, crank again starts up in 2 seconds. Never fails on this 2nd full crank. I've installed new plugs/ seals, spark plug wires, distributor cap/ rotor. Runs better than before, just this intermittent start up issue. Quite odd... That's what makes me think of air intake. I just bought it from a used car dealer 1 month ago, so I don't know if the MAF/ TB has every been cleaned (57,000 miles on OD).

Jagbro

 

You can touch it with the MAFS cleaner spray, but don't even touch it with anything solid like a finger or the red spray tube.

The Fuel Pressure Regulator (FPR) comes to mind, along with the fuel check valve. If proper pressure is not being maintained in the fuel rail that can lead to extended cranking in a cold engine or vapor lock in a hot engine that has just been shut off.

Another suspect would be the Crankshaft Position Sensor (CPS) - the next time it cranks and will not start, watch the tachometer while cranking. You should see about 200 rpm. If you see 0 rpm, your CPS is probably failing.

Cheers,

Don

 

Yes sir, cranked it again... and during the hard cranking the tach hovers at 200 rpm. Switch ignition off, then immediately crank again, starts right up without fail.

So I will check the FPR once I locate it.

Thank you...

 

It could be the fuel pressure regulator (or check valve) is allowing the fuel pressure to reduce when the car has not been run for a time.

If you turn the ignition key to on without starting the car, then off again, then back on again a couple of times, the fuel pump will prime the system several times (that half second merrp noise) - and raise the fuel pressure in the fuel rail. If the problem is caused by a drop in fuel pressure, then the car should start up quickly if you try this 'key cycling' trick.

Hopefully this makes sense!

 

The fuel pressure regulator sits on the fuel rail towards the front of the engine. It looks like this:

 

To supplement the FPR photo posted by db, here's a shot of the fuel rail with the FPR in situ near the forward (left) end of the rail:




Cheers,

Don

 

So I spent some time going through a similar issue. It turned out to be that the check valve in the fuel pump has lost its ability to hold pressure with ease so I added an inline check valve and all is well now. Im setting a day to clean my intake either way since the car can only benefit from it. Dont want to confuse you with my input but it's something to look into if you're still having starting issues once you've cleaned the the intake. Check out my thread "Im Back" for clues to a fix. My car is a 1994 so the check valve is built into the pump. Not familiar with the 1991 models but yours may be easily replaced as you already have an inline check valve. If you're unable to locate a Jaguar valve, I read that Volvo used the same valve and those are still being sold

 

Thanks all!

 

Don this seems to be the likely issue. After the engine has sat a while and is cold, I clicked the key to the on position until I hear the little buzz that you mentioned. When this is done it cranks right up without fail. So I'll be changing out this Fuel Pressure Regulator soon. I've seen hem for around $50 here and there...

Jagbro

 

Hi Jagbro,

In addition to replacing the FPR, I would recommend replacing the fuel check valve if you have an external fuel pump, or adding a check valve if your pump is in the tank. Sorry I can't remember the year of your car - it helps if you add the year, model and engine displacement to your signature.

If you have an in-tank pump, it's easiest to just add a check valve to the fuel feed line that runs alongside the fuel rail and connects to the rail at the firewall end. I got my check valve and 5/16 in. hose barbs from McMaster-Carr (mcmaster.com) for $25 or so. Choose a check valve with seals suitable for gasoline (fluoroelastomer, if I recall correctly - the Buna-N seals are for water). See my photo album in the link in my signature.

Cheers,

Don

 

Curious John and Brewtech. I see your advise on changing out my Fuel Pressure Regulator. But why would it it be necessary to add a "Check Valve", isn't that what the FPR does? I have a a 91' Sov with in-tank fuel pump (so I have read)... Does the check valve look like what's below from McMaster?

JagBro

 

Hi JagBro,

The FPR is a type of valve that resists the flow of fuel to maintain the proper pressure in the fuel rail so the injectors can atomize the fuel rather than dribble it into the intake. If the only resistance the FPR faces is the pressure developed by the fuel pump, then as soon as the fuel pump is turned off, the pressure dissipates back through the pump and into the fuel tank. This sudden loss of pressure allows the fuel in the rail to suddenly boil, or vaporize, creating classic vapor lock: no liquid fuel in the rail to feed the injectors.

Check valves are one-way devices, allowing flow in one direction but preventing flow in the other direction up to some maximum breakdown pressure. They are used in various ways in the fuel system. A check valve placed after the fuel pump works with the FPR to prevent backflow and the sudden loss of pressure in the rail when the pump is shut off or is momentarily starved of fuel, as in cornering with a nearly empty tank. In the late XJ40s ('93-'94), this check valve is part of the evaporative flange on top of the fuel tank. On earlier XJ40s the check valve is just before the fuel filter.

A check valve placed before the fuel pump in the bottom of the plastic fuel pump canister serves to keep the pump primed so it doesn't run dry when fuel in the tank is low and sloshing around.

In the X300, a check valve in the fuel tank port for the return line that carries unused fuel from the rail back to the fuel tank helps keep the surge pot full to prevent pump starvation. The surge pot is a "dish" formed in the bottom of the tank to keep a pool of fuel available at the inlet of the pump.

The valve I used on our '93 was from McMaster-Carr and looked something like this:



With hose barbs that thread onto the ends of the valve that look like this:




Here's a link to photos of the check valve I installed in our '93:

Fuel Line Check Valve Installation

The Jag-Lovers forum is updating its photo storage so the larger images aren't currently available, but you can still see the thumbnails.

Cheers,

Don

 

This check valve may be more of the issue of cold cranking than the regulator, you think?

 

They both have to work together, so if one is not performing optimally it can cause longer cranking times before sufficient pressure builds in the rail.

 

I'd say "hot" cranking rather than cold!

IIRC the later 40's (maybe early ones too) have a built-in couple of seconds cold cranking delay to allow the oil to get pumped up top before the motor fires up.

Larry