I started My 1986 Daimler Double Six after a year’s rest in the barn and while it did run, it was hard to start and ran poorly, had little power, and would surge at idle. I had changed the fuel filter a year ago because of similar symptoms. The old filter had rusty gas in the inlet, and it seemed to run OK after the filter change so I thought that had taken care of the problem.
I removed the fuel filter again and to check it and this time the inlet and outlet gas was clean so I put a hose on the pipe that runs to the filter and ran the fuel pump from an external battery and the flow was in spits and spurts so I thought the lines from the tanks might be clogged. It did fill and overflow the right tank while it was running so there may be a return valve problem too.
Today I removed the fuel pump and changeover valve and put the pump on a length of hose connected to the tank line to pump out the left tank (which didn’t have much fuel in it after filling the right tank) and than connected the pump to the right tank line and pumped a few gallons out of it until the flow turned from a solid looking flow to a slightly bubbly one. I put a gage on the pump outlet line, deadheaded, to see what pressure it could produce. It went up to 80 PSI and then 100 PSI, but when it got that high it sprayed fuel from the pump case at the negative terminal.
There were no leaks from the pump or any lines in the boot before I removed the pump and changeover valve, so did I do permanent damage to the pump by deadheading it? I will check further, but so far the lines from both tanks appeared to be clear, so I am not understanding why the pump had produced spits and spurts and apparently inadequate pressure for the engine to run as it should.

Edit: I just tried running the pump deadheaded again and this time it did not spray gas from the pump body, (and it was at the negative terminal before, not the positive terminal). It produced a bit over 100 PSI this time without leaking.

 

I never had one apart for examination but it's a fair bet the the pump case has some o-rings or similar to seal it from the areas of the pump that actually carry gasoline. The seals are likely dead from old age. AFAIC I wouldn't trust the pump to remain leak free. No way, no how. I'd replace it, personally.

If your tanks are rusty...and they probably are.....you can clean them. There are various approaches on that task, none of them particularly pleasurable.

Or as an alternative....

Add additional filters between the tanks and the changeover valve to capture any particles before they damage the valve or (hopefully) new fuel pump. If the tanks have a lot of rust these filters might need changing a few times before all the rust is eliminated. A pal of mine used this approach and it worked for him.

Cheers
DD

 

+heaps.

That rust from old fuel at the Inlet of the old filter indicates rust IN the pump rollers and their cage will also be a factor.

The o/ring seals have simply died.

Maybe a flush of the supply (RH) fuel line to the rail would be smart.

"Spitting" fuel out of the pump outlet is usually the rollers jamming due to contamination.

 

Thanks for the replies. I discovered that the changeover valve was stuck in one position and un-stuck it and I used the pump to empty both tanks at the tank lines and the gas came out clean so I put everything back and it still would either not start or barely run. I put a fuel pressure gauge on a T in the line after the filter in the boot and had 40 PSI after several key-on primes, but the engine would still barely run if at all and stalled easily.

Looking back in my notes, the last time I had a barely running engine with no power, I changed coils, GM ignition module, and any number of things without success, but what eventually worked was replacing the ECU with a 16 CU unit from a breaker yard in England. A short time later found a 6 CU unit on eBay (way less expensive) and had put it in to try it and thought it was a bit smoother so I had left it in; That was 11 years ago.

So today I pulled the 6 CU ECU and replaced it with the expensive English breaker yard 16 CU ECU and had a running engine again. I had cleaned the ECU spades and the connector and also wire brushed the ground ring connector, so I also cleaned the 6 CU spades and tried it again and the engine ran with it too but the idle was a little low so I re-installed the 16 CU and will keep the 6 CU as a spare. Running fuel pressure was 38 PSI.

Seems I had two unrelated problems in the stuck changeover valve and a bad connection to the ECU; at least I hope those were the only problems now that it is running again. Time to give it a good bath.

 

I did that on my 87 XJ6 as a preventive measure; had not added tank line filters to the DD6 yet. So far the pump has not leaked again and the flow at the tank returns is a good solid stream now that I un-stuck the changeover valve which apparently emptied the left tank and overflowed the right tank. I also had poor connections to the ECU in addition to an empty left tank. Hope it is sorted out now, though Time will tell, but I plan to start/drive it way more often to keep it happy.

 

I am with Doug. I just could not trust that pump. Spraying fuel under pressure in the boot location circa electrics just is not worth the risk to property or even life.


Because of my past profession, I am very sensitive about fire....


Carl