STALLING issues

My ‘73 petrol Land Rover Series 3 has been having stalling issues. It will seem to be tuned properly, running great, but at about 15 minutes into most test drives it will stall out. Usually at a stop sign. Then it will not start up until it sits for 5 minutes or so. It’ll have a stale air or faint burn smell when I pop the bonnet (not a fuel flood smell) - can’t tell from where. It will start up after waiting, with lots of cranks and gas. It’ll get me back home and runs great at high speeds but it will stall again, sometimes during slow driving. I would appreciate any suggestions. I’m stubbornly trying to fix it myself, but I’m about ready to take it to a pro mechanic. (any suggestions in San Diego area? I've called around and many won't take on old Rovers anymore). Please tell me if I’m missing something really basic. Pardon the lengthy details. Until this, it was running solid for 25 years. Including many middle-of-nowhere Baja runs with no troubles.

Perhaps describing the first stall could give indication... After a common 30 minute freeway drive it backfired big upon deceleration off the freeway, then went a mile before the first of the now familiar/frustrating stalls.

First suspect was fuel. It is getting good flow, but I replaced the fuel pump anyway. Flushed the tank (no rust), checked for clogs. Then rebuilt the 15 year old genuine Zenith. Did the flattening trick in case of warping. Seems clean and functioning. Still had the stalling. Bought a new RN ‘replacement’ Zenith. No difference. New fuel line and filter, at proper angle ( to avoid vapor lock). During a gasping stall while moving at about 10 mph, a cyclist was along side and he stopped to say it sounded like it was fuel starved. I think I’ve tried every mixture variation (lean/rich), but usually stay near the specs - following the carb plaque by the radiator.

Second suspect was ignition. It was running a Pertronix reliably for 10 years with a Lucas coil. Reverted back to new points for a day just for giggles but it did not help. Tried a new Accuspark distributor with a new coil. Still stalled. Now a new Pertronix distributor which seems to run good with a new Lucas DLB101 coil. (maybe still a coil issue?).

Third suspect was for exhaust leak. Did a smoke test and saw no leaks but a mechanic friend told me to replace the gaskets anyway, so I did all from carb to manifolds to engine. Installed a new brake booster (fun times!). A vacuum gauge placed at the manifold pipe going to the booster shows a steady needle.

It had an engine rebuild a few years ago. Compression is even - about 115 in all four (on a home test gauge). Valve clearances are triple checked and perfect. Timing is set TDC, trying slight variances A-B. Rotor points to plug 1 when TDC. New plugs and wires. It still has the stock air filter, PCV valve (new diaphragm), and stock Cooper fume vent and breathers, etc. Replaced the head gasket a year or so ago. The exhaust and muffler are clear - unclogged.

A couple of neighbor veteran car guys have had a go at tuning it. They’ll say the engine sounds really good and strong. They’ll set the carb confidently their way. It seemed perfect again but sure as heck it stalls later on the test drives. Making carb adjustments during the return doesn’t help. Even in the driveway, I'll set the idle steady at 750, but the rpm will suddenly drop to 400 or so, or stall with a tough re-start. Maybe a bad electrical ground? Maybe some sort of vapor lock with the fuel tank/vapor tubes? It has a new vented fuel filler cap.

Any guess is appreciated! Cheers, Ty

I also have a '73 Series III, and have had somewhat similar symptoms. I had two problems: vapor lock causing the engine to stall after a hot restart, and inability of the fuel pump to deliver enough volume at high engine speeds, also causing the engine to die. Two problems, perhaps related.

First - when my engine stalled after a hot restart I pulled the hose off at the carb inlet, cranked the engine over, and observed no fuel delivery to the carb. Looked like vapor lock to me. I figured a new fuel pump would fix it, but it didn't.

Second problem - went through three replacement fuel pumps and rebuilt the original pump before I got a pump that solved the fuel starvation problem at high engine speed/load. Diagnosed it all as a fuel delivery problem by running the engine with a fuel pressure gauge hooked up and mounted temporarily on the dash. It ran at about ½ psi most times, but dropped to zero psi at speed. After ten or fifteen seconds of zero psi the engine died. I installed an electric fuel pump (in series with the mechanical one) that put out a minimum of 2 psi at all times and the truck ran great. When the pump was switched off the engine would again die at speed. Ironically at this time the mechanical pump was a good one, but it struggled to pull fuel though the electric pump. When I replumbed the fuel lines so the two pumps were in parallel instead of in series the mechanical pump would work satisfactorily, and continues to do so. No more high speed stalls.

As far as the dying after a hot start - the weather turned cooler in the middle of me installing another fuel pump every couple of weeks. I did switch to running ethanol-free fuel for the summer, and I'll find out next summer if that's the fix. Apparently the ethanol boils in the hot fuel pump and fuel lines before ethanol-free fuel will. I got an app called "Pure Gas" for my iPhone that shows the gas stations selling ethanol free fuel. Down side is that the stuff costs more than premium gas.

Back to the mechanical fuel pump - suggest you run your truck with a fuel gauge installed. I had to hunt around awhile to find a gauge that wasn't for fuel injected engines and would display pressures in the zero to ten psi range, rather that so high that you can't read what's on the lower end of the scale.

Having gone through multiple mechanical fuel pumps I'm convinced that the currently available stock is sh*t. I've resolved that if my problem comes back I'm going to find a stronger spring for the pump to boost it's pressure. I must say that having the Carter electric pump mounted to the top of the frame rail beside the fuel tank (accessible beneath the panel under the right seat), and with a switch accessible from the driver's seat, makes for a great backup. It may even cure the hot start problems if it's higher pressure will force fuel to the carb through the vapor lock bubbles.

Enough rambling - get a fuel pressure gauge and do some diagnosis!

Generally if it backfires through the intake it's a lean miss (little fuel). If through the exhaust, it's a rich miss (too much fuel or little spark). I don't know why folks put on electric fuel pumps and then plumb them with the mechanical pump, either before of after it. If before it, it could pump fuel into the engine if the mechanical pump diaphragm cracks. Just take off the mechanical pump and block off the hole and call it good (unless it's a show vehicle). Most electric pumps are pusher pumps that need to be at the back and push the fuel forward. Put a good filter between the tank and the pump, wire to a cut-off switch in the cab, and/or install an inertia switch on the firewall (for safety's sake). Plumb the fuel line to the carb with a shorter line and eliminate the one running around the front of the engine. [Yes, this is the set-up on my Series III... And my 3500S]

'99 Disco II
'95 R.R.C. Lwb (Gone...)
'76 Series III Hybrid 109
'70 Rover 3500S

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Originally Posted by mearstrae

I don't know why folks put on electric fuel pumps and then plumb them with the mechanical pump, either before of after it...

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Quote:

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Originally Posted by mearstrae

...Most electric pumps are pusher pumps that need to be at the back and push the fuel forward.

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The Land Rover factory did this very thing on 109's with rear tanks. The electric pump is there because of the limited head the mechanical pump can draw when the Rover is pointing uphill steeply.

I too have stalling issues due to fuel starvation. I installed a new fuel pump, carburetor and fuel filter and the problem still persists. Under heavy load at high RPM it will stop running until I back off the accelerator. I notice very little fuel entering the clear filter. Should I drain the tank, and replace everything from there forward to the fuel pump? So frustrating.