A question for all:

You know that manual fuel pump that sits at the back of the cylinder head on a TM-TP (1987-1991) carbie? I mean the thing that has an arm that goes under the rocker cover and rests on the camshaft somewhere, and whose outside unit is circular and gold-coloured. Not the one in the fuel tank, but at the cylinder head.

Well you might also know that there's two types of these fuel pumps. The TM has a large gold part, and the TN/TP is a much smaller unit. The arms of course are the same, being a functional component.

My question is, do these differences amount to any difference in fuel efficiency or performance? And would a newer fuel pump be better than an older one (say 20 years even)?

Just wondering because I've made a lot of repairs and upgrades to this 1990 TP sedan but didn't get the fuel economy benefits I was hoping for. Then it occurred to just now that changing the manual fuel pump to a larger TM model (though new) might have been my undoing. The original manual fuel pump has a much smaller body, but I thought that due to the age of it, I should change it out. Now I'm not so sure.

Just thinking I should put the original pump back on but have no idea if this could improve anything? Does anyone have any ideas?

Curioso

the TM with a manual fuel pump low pressure type left on from the later sigma days
some TMs were fitted with electrical intank carby pumps also

All the TPs and TNs I have worked on with carbies had electric intank low pressure pumps
pump pressure
TN TP carby intank electric pump 19-25 kPa 3 psi

On hot days the mechanical pump may vaporise the fuel because of the heat factor
even when fitted with the insulation block

ask your supplier about the mechanical pump pressure difference between the TM and TP

as an example
sigma mechanical pump pressure is 26-36kpa
pumps 1.8 litrs per minute

Thanks chain.

I know this TP does also have an electrical intank fuel pump. So how does the mechanical fuel pump work with it? Or does only one work and the other is a vestigial remnant from previous models without electrical fuel pumps?

Curioso

Determine that both pumps are working and
then make a decision on what you would like to do


The current setup
If both work --the electric pump keeps the manual pump primed
the mechanical pump has an in built non return valve


A trip to a dyno or carby tuning shop (phone around for quotes)
will get the adjustment for the worn carby to its
best possible settings for fuel economy

note to picture
{red arrow }
see if anyone has removed the plug to tamper with the factory settings of the carby

if the plug has been removed --the factory setting is approx
three complete {gentle }turns of its screw from its seat
if you remove the needle jet fully -- blow with air it may have crap on the seat or the needle

Great thanks again.

I think I'll check with Mitsubishi and then the guy who tunes the carby. He last tuned it in July last year (had a six month warranty). Cost $500 to get it totally rebuilt that January, but by winter, it didn't seem to be working so good. Turned out the float in it had busted again, so there was no charge. The guy also mentioned something about the air being different in winter and that his adjustment machine takes the surround air or atmospheric conditions into account.

If Mitsubishi can't help, hopefully he can tell me which manual fuel pump I should be using, if I show both to him. I hope they're familiar enough with these cars to make a sound judgement on that. Then again, it's easy to change with a cold engine - just have to use some Greymax oil and compression resistant sealant where it joins to the head.

Curioso

I checked with the fuel system specialist. Turns out the manual fuel pump I installed to the cylinder head is for cars that don't have an electric fuel pump already in the tank. And that you only need one pump, not two. I showed him the original manual fuel "pump" that came with the TP, and he said that was a fuel cannister - it has no arm to the crankshaft to make it operate like a pump (as did the TM Manual Fuel Pump).


So I reinstalled the fuel cannister with no pump arm and the car runs way better now. More power and I think better fuel consumption. So I guess having two fuel pumps is not a good idea.

Curioso

To the MODS... please close off this thread.