Tuesday, May 4, 2021

MGB - Fuel Pump 2 Step

Picking up where we left off with Oliver, the 1978 MGB, we had completed the ignition swap out and we were ready to start the engine and set the timing. Until the battery went flat.

To Start Or Not To Start
should be an image from AutoZone
AutoZone product picture
At this point, I was ready to test-start it. Or, so I thought. Last Fall, I thought Oliver's battery was going bad. It later turned out to be the clock sucking all the juice while left sitting for weeks (see MGB Battery Monitoring). Before I learned that, however, I swapped the battery out for the battery from the donorZed. At this point in my electronic ignition install, I discovered that the donorZed battery actually was bad. I mean bad. Like, I would put it on the charger overnight and then I could put a voltmeter on it and watch it discharge down to 0. Fortunately, I had left Oliver's prior battery on the trickle-charger, because I guess I was not 100% convinced it was bad. So, I swapped his old battery back in. I turned the key, heard the fuel pump click once, and then heard nothing. In the past, I have had this happen when the fuel pressure had not let off since it was last running. Since the engine had not run since October, that was unlikely. Perhaps the inertia switch got nervous and is preventing the fuel pump? Well, then I would not have heard the one click. Still, I pushed the reset button. No change. Then, I jumpered around the inertia switch, running the wire disconnects through a 3A bladed fuse instead of the inertia switch. Same single click.

Fuel Not Pumping
what arrived
I concluded that the fuel pump, which had not been behaving consistently (sometimes just not working at start up), needed replacing. I slid under Oliver's backend and recalled that the original fuel pump had been replaced by the prior owner for what looks like a universal pump. I can't judge. Quite the contrary, I was not going to invest in a $200US+ original MG fuel pump on the assumption that the fuel pump is the problem either. So, I ordered a Spectra fuel pump from AutoZone for $48US delivered next-day-ish. This pump meets or exceeds the requirements for pressure (3.8psi) and delivery volume (18gph) for an otherwise stock MG engine. I sourced the requirements from this page on the MG Experience. The Spectra offers 2.5 to 5 pounds of pressure and 21gph, has reviews on Azn from MG owners saying they work great and even AutoZone shows these are a direct replacement for the Midget.

It is possible to over-power your carb with too much pressure, so that's one for the back of the mind while trying to diagnose what's going on with the fuel flow through combustion. I may introduce a pressure regulator, but one could argue that adding a cheap pressure regulator on top of a cheap fuel pump starts approaching the cost of a good stock-style replacement pump. While that's very true, I am not running a stock carb either. The prior owner installed a SK Racing (now known as OER) side-draft carb, which seems like a combination of the Mikuni PHH and the Weber DCOE, but this blog post has some great information about them. My knowledge of carbs is extremely limited, so I am accepting this as a learning opportunity.

Fuel Pump 2-Step
Holley Mity Mite
The pump that arrived was not as pictured. Lovely. This one was equipped with a 3/8" barb on one end and a 3/8" NPT female on the other. Into the 3/8" NPT, the consumer was expected to thread in the included mini-filter that has a 3/8" barb on the end. While I am sure a filter is needed, that one they included is tiny and virtually irreplaceable. Perhaps these pumps don't last past a fuel filter change. Since the pictures and the spec's I could see did not match, I was not going to go forward with it; I already have more than enough mysteries with the fuel system. I returned it unopened and got a Holley 12-434 Mighty Mite Electric Fuel Pump. These top-out at 4psi, push 28gph and actually ship with 5/16" hose barbs. Between the delays from CoViD and possible delays from that cargo ship that was blocking the Suez Canal for a week, the arrival of the fuel pump was not exactly immediate. Still, through the power of split-posts, it arrived in time to keep this blog active.
Fuel Pump Swap
The pump arrived mid-week, so I started my Saturday planning for the fuel pump swap. Over breakfast, I prepped the wires and assembled the pump and pre-filter. While the Spectra above also delivered with a filter like this, I know that Holley supports replacement pre-filters (I verified on their website). Either way, I figure I have one of those in-line clear filters just upstream of the pump, so I don't expect it to require service too terribly often. For the wire prep, I attached a male wire disconnect to the ground (black) wire and a male disconnect to the positive (red) wire.

ready for install
So, with the pump in one piece, and wire disconnects attached to the wires, I slid under the rear end of Oliver, bringing a collection of tools, a drain pan and a flashlight with me. I closed off the fuel supply from the tank with a small pair of vice-grips. I then moved from that hose forward through the fuel pump, disconnecting hoses and draining the contents into the pan. I only got as far as the pump before I didn't need to drain anymore. Clearly that old pump was not working anymore.

The MityMite is actually larger and heavier than the universal pump I had removed. So, I needed to adjust some fuel line lengths, but otherwise things just fit together. I reused the bolt hole which was holding the old pump to the front edge of the trunk, for example.Once all together, I wired the black wire to the grounding wire that was previously attached to the ground tab on the universal pump. Into the female disconnect coming from the pump, I put one blade from a 3Amp fuse. I put the other blade into the female disconnect which is ultimately wired to the inertia switch. I worked the disconnects with a pair of pliers to get the fuse to stay firmly in place. I wrapped the disconnects and the fuse with electrical tape. Last, I spooled up the extra wire and zip-tied it to the pump pre-filter so the connections would not shake loose.

Pump Test Fire
With everything as I thought it should be, I removed the vice grips and my tools from underneath. I turned the key to "RUN" and the pump fired right up. I left the key in "RUN" and checked the fuel lines for leaks. None appeared, so I concluded the pump was fine. Hoping for the best, I returned to the driver seat and tried to start the engine. Oliver would not start, but the engine would turn. That's a start. I removed a spark plug and I could smell gas on the tip, so We now have fuel and electricity. Next, we need to get electricity to the plug... at the right time.

Recall from my last post that my initial effort to find TDC were wrong, and that I needed to pull the valve cover to figure out true TDC? Well, I did that here. Still, even with true TDC found, Oliver would not start. I did figure it out, but that's my next post.

Thanks, as always, for following along--

No comments: