I've had the car in the garage for a little over a week installing a cold air inlet system. This morning that project was finished, so I hopped in and fired it up...started and ran fine. I drove it out of the garage and brought it back in so I could work on some cosmetic issues. Got done with those and tried to start it. The fuel pump comes on, and it cranks fine, but unless I floor the pedal it won't start at all. If I floor the pedal it'll run for about a second and shut down.

About the only other thing I've touched have been the vacuum hoses. Would this behavior be expected of a vacuum hose was plugged into the wrong place? I've not touched the fuel system.

This car has had the air pump removed, but it ran fine after that modification.

Thanks,

John
1987 XJS V12 (supposedly 61,000 miles).

 

I have an 87 XJ-S that I race. I removed all of the pollution controls and extraneous encumbrances on the V-12. The blower shouldn't make a difference as long as the check valve is holding. I removed and plugged those air injection ports. Really cleans up the motor and allows greater access too. I would suspect the fuel filter first or the fuel level. Could be a pinched fuel line too. It's a restriction any way you look at it.

 

Wild guess.

Are the vacuum hoses to the fuel pressure regulators attached?

No vacuum to regulators = max fuel pressure = over fueling = flooding.

Wide open throttle signal from TPS while cranking shuts off injectors to clear flooding. Once throttle is released the overfueling resumes.

I'll mull other thoughts after more coffee and I'm sure others will chime in

Cheers
DD

 

The only way it can truly flood is if there is no place for the fuel to go. The excess fuel not used by the engine is circulated back to the tank. That line is opposite the pressure regulator on the driver's side of the fuel rail. That's the line that goes through the cooler and back through the fire-wall. Once the pressure is achieved the excess fuel returns to the tank. It is cooled on it's return so it doesn't enter the tank as a vapor. It's a bit more difficult to flood a EFI engine. The injectors only pulse a metered amount of fuel when signaled to do so. If the cylinders are not firing than that's a different story. You can have excess fuel in the combustion chamber in that case. Check that return line. You can just turn the ignition on , disconnect the fuel line at the tank into a safety container to see if it's returning properly. Use a helper though. Spraying fuel can ruin a Jag quickly especially if it ignites!

 

I had and old XJS HSE about 10 years ago that was left in storage for some time. It was started regularly and ran fine. However one day it started perfectly and then stopped after a few moments. After a few seconds I turned the key again and it started perfectly, ran for a few moments and then simply stopped again. This pattern repeated.
I seem to recall it was a fuel supply problem, something to do with the solenoids in the boot that held a one way valve open or something. I hot wired this solenoid as a temporary fix but a new owner replaced it I believe.
Appologies to be alittle vague but your problem sounds similar.

 

I think you have him on the right track though. See if there is fuel flow and find out if the pump stops when the pressure comes up. Jags are like Rovers, check those pins and grounds constantly. Good advice Steve!

 

Right, but once once excess fuel is in the combustion chambers, it isn't gonna get back to the fuel tank :-)







Right again but if the fuel pressure is too high the metering is thrown off.




Good idea!


Cheers
DD

 

That return line seems suspect. I wonder if it's pinched off someplace. Don't hesitate to look in the trunk either where it connects to the fuel tank. A common test is to remove the return fuel line in the trunk and see if it's flowing when the ignition is turned on. Make certain to safely catch the fuel. If there's no fuel coming out then start working your way back to the injectors for restrictions.

 

Fixed! And I'm amazed at the solution (but shouldn't be)...

I kept thinking that it MUST have been something I did...and sure enough it was. I had unplugged the water temperature sensor and air temperature sensor to rewrap the wires. Searching through some old posts, I saw one concerning the water temp sensor, and how it can cause "issues". I went and looked at mine, and while it appeared to be seated correctly, it hadn't pushed it down all the way. I reseated it until it clicked into place, and damn if the thing didn't fire right up.

Besides being delighted with such an easy fix, I'm surprised that a water temperature sensor would be so critical, but obviously it is.

Thanks for all the input...I'm sure I'll need it someday, just not today!

John

 

I have always admired the looks of the XJS - V12.
Also most owners, as I understand things, do remove all the greeny pollution control equipment which seems to seriously limit the performance of this engine.
How well has your car withstood the ravages of time, have you been able to keep it in mint condition, & how is the handling when compared to a modern performance saloon?

 

If the sensor is flat-out disconnected the engine won't start at all, at least not in my experience. I've heard this either disables the injectors completely or increases the fueling so much that the engine won't run.

With the engine running you can unplug the sesnor and, if it follows the pattern, the engine will die right away.

Perhaps yours was *just* making a partial connection? Poor connection = high resistance = cold signal = extra fuel.

<shrug>

Anyhow, good sleuthing :-)

Cheers
DD

 

That's very interesting. I replaced my sensor with a conductive racing temp sensor. It certainly is a different type of sensor from the stock unit. Mine runs just fine with or without the sensor being hooked up. Sure am glad that you resolved the issue and the forum was helpful. Sorry about the errant advice.

 

My engine is completely stripped for racing though. You can't believe the room and access you have with all those extraneous systems off the motor. Especially the A/C..The HP increase is quite noticeable too. No cats on the exhaust either and no balance pipe for the straight pipe rocker panel open pipes. It's going to be very intimidating to others at 7K RPM.

 

Wide open throttle cuts off additional fuel so the flooded engine starts.

The poster would said EFI are hard to flood never owned Bosch EFI vehicles from the 80s. Those vehicles were real easy to flood. Coolant sensors are the major cause of over fueling on those old beasts. In the 90s Bosch EFI system performed a plausibility check of coolant temp vs. intake air temp.

 

peterlonz...I can't make any comparisons since this is the first Jaguar I've ever owned or driven. Whoever owned it before did, at least, seem to take care of the body and the interior. It had some rust in the usual places behind the wheels, but other than that was in remarkable good shape for being so old.

My problem with taking off the air pump and blocking various lines is figuring out which thins to block and which to not...probably another topic for another post.

Doug, maybe my use of the word "start" wasn't quite right...it seemed to start, but stopped so fast it was hard to describe :-). FYI, I did unplug it, and it did indeed die right away. When it warms up I'll put a meter on the sensor and see what its resistance range is. No problem about the errant advice...I'm sure one day I'll need it.

Thanks to all,

John