Curing fuel line vapour locks
The first ‘to- do’ task on the list for the Jaguar E-Type this month was to complete the fuel bypass piping where fuel can be bled from the inlet union on the front SU back to the tank in an effort to reduce fuel vaporisation. This was a common occurrence when trying to restart the car with high under bonnet temperatures experienced after completing a run on hot days and hopefully the bypass will resolve the issue.
The symptoms were a continual fast ticking of the fuel pump as it tries to clear the vapour in the line and lack of fuel flow into the float chambers. I had drilled and tapped a suitable thread in the centre of the front SU union then fitted a threaded elbow for a rubber hose. This was piped to a solenoid valve mounted on the inner splash guard and then onto a ¼-inch copper tube.
I’d measured and bent this copper tube to follow the path of the fuel inlet line from the engine bay to the rear of car adjacent to a rear suspension cross member. A hole was drilled at the front of the boot and a second piece of copper tube bent so that it connected to the front bit and went over the top of the cross member into the boot.
The two sections of copper tube were then joined with a brass compression union and a rubber hose was used to connect the copper tube to a fitting I'd attached to a removable plate on the tank top.
The solenoid valve was operated from a switch fitted to the centre console so that fuel was only bled back to the tank when necessary. The system tests went well and when the ignition was switched on the fuel pump could be heard ticking as fuel filled the SU float chambers and then stopped when they were full.
Energising the solenoid resulted in the fuel pump starting when fuel could be heard returning back to the tank. I'll have to wait until summer and some hot weather to see if the operation of this valve clears the vapour lock.
Prior to restarting the car, the cooling system required filling, so the required quantity of concentrated inhibitor was poured into the header tank and the complete system filled with rain water from our filtered water tank and the complete system checked for leaks.
Other areas were then given a final check before the plugs were removed and the engine spun over on the starter motor until there was a good oil pressure reading on the gauge. Next, the plugs were refitted, leads connected and eager anticipation followed in preparation for a start. Thankfully the engine burst into life on the second prod of the starter button and all sounded great. So I reversed the car out and took it for a short run to the end of our road and back again. The engine, gearbox and brakes all seemed fine, so as the car was in a decidedly grubby condition after sitting with the cover off, I gave it a good clean prior to returning it to the workshop.
A simple wash and leather off had the E-Type back to its sparkling best and prior to refitting the boot boards they were cleaned and treated with vinyl conditioner. The other trim in the rear hatch area was also given the same treatment, so the car was looking spick and span inside and out.
The Jaguar was once again raised on the hoist to check the timing with a timing light. After replacing the distributor the ignition had been set statically, which was now checked. The timing light is connected to the front (number six) plug lead and as the timing pointer and marks on the front pulley are on the underside, the car needs to be raised to allow a clear view. The
setting was checked with the distributor vacuum tube disconnected and required a small adjustment to meet the 10° BDTC specification.
Now that the suspension had settled it was time to check the front wheel alignment, which I was expecting to need some adjustment, as the track rod ends had bee replaced during the upgrades. If the replacement components are identical to the old, it is possible to retain the alignment by using the lock nuts as a guide to repositioning the new joints.
In this case it was not feasible, as there was a variation between the two old ends, both of which were different to the new ones. I have owned the E-Type since 1986 and during my ownership haven’t changed the track rod ends, only ever replacing the rubber boots.
I measured the difference between the old and new ends as best I could and made the necessary changes during reassembly but had expected some final adjustments would be required. Two string lines were used for the initial measurement, which confirmed that the wheels were almost parallel and required adjusting to meet the specification of 1.6mm to 3.2mm toe in. It is relatively easy to make the adjustments on an E-Type, as the ends are accessible from above with the bonnet open. After adjusting the toe in to 2mm and tightening the track rod end lock nuts, the setting was checked using a Trackrite gauge, which confirmed the string line measurement.
The following day when I went to start the car to check the SU balance, I operated the switch for the fuel return to be greeted with silence indicating a problem, most likely with the solenoid. A check on the solenoid failed to detect any audible click when the coil was energised. An electrical resistance check indicated the coil was okay, so the valve needed removal for further investigation. This valve was an eBay purchase where the specification confirmed that it was suitable for petrol, but I was not overly surprised when I found the rubber seal on the base of the plunger had swelled but only by a slight amount. So I was surprised that the valve would not operate.
A check on the dimensions of the plunger and armature confirmed there was minimal clearance for the plunger to lift, so I used the lathe to remove .75mm from the top of the plunger, which solved the problem. If I get further issues in the future I will replace the seal with a material compatible with modern fuels.
The carburettor airflows were checked and found to be fine, which was to be expected as they had not been touched since removal, so I went on a longer test run that confirmed the gearbox noise had disappeared, as had the clunk from the differential.
When the car returned home with a hot engine and pressurised cooling system. I checked for coolant leaks and found a couple of the new hoses were weeping, which was quickly fixed by tightening the hose clamps. What was a concern though was that the heater valve was dripping from the valve itself, not the hose connections.
The valve is sealed with a diaphragm that also allows the open/close movement of the shut off element, which I believe I replaced 20 years ago, so I shouldn’t be complaining. I rarely, if ever, use the heater but did open the valve to ensure the heater drained during removal of the old coolant and that all air was expelled when refilling.
It’s great to have the E-Type mobile once again and I'll take it on a longer motorway test run to ensure all is okay prior to using it on a club run.
I have owned the E-Type since 1986 and during my ownership haven’t changed the track rod ends, only replacing the rubber boots