Fuel pump question on 79 carb

[bobcity]

I'm still working on getting my engine running again and discovered that the mechanial fuel pump that the shop manual discribes has been replaced. I had assumed that it had an electrical pump all along didn't know it was once mechanical.

Is it common to swap them out for electric?

When you turn the key to on, the pump starts and keeps on clicking until you shut off key. Is that normal?

To diagnose for a problem should I check the pump pressure and if so what should it be?

Thanks.

[So Cal Mark]

your pump will run whenever the key is on. Those pumps only need to produce about 3lbs of pressure, the volume is more important. If you remove the hose from the carb and place it in a coffee can, turn the key on and there should be a steady stream of fuel

[mbouse]

Is it common to swap them out for electric?

When you turn the key to on, the pump starts and keeps on clicking until you shut off key. Is that normal?
Thanks.

i agree with the 3 psi pressure reading.

no it is not normal or common to swap a mechanical pump for an electrical pump, and yes when it is not done properly the user may hear the pump running when it does not need to since there is no sensor to shut it off when desired pressure has been obtained. your particular vehicle was not wired to accept an electric pump. 1974 was the only non-fuel injected year that Spiders came from the factory with electric fuel pumps.




1978 Fiat Spider with over 90,000 original miles on the original mechanical fuel pump
1980 Fiat Spider with over 120,000 original miles on #2 of 2 mechanical fuel pumps...and at least 50,000 miles on mechanical pump #2

[manoa matt]

I'll have to disagree with Mike, in that most of the fiats I've seen in the past few years have undergone the mechanical to electrical conversion. There are several reasons for this, The mechanical fuel pump location makes repalacing it somewhat difficult. Its far easier to drop an electrical pump in the trunk, than to articulate your second elbow to change out the pump. Finding new pumps, and not "NOS" pumps is getting harder to find without breaking the bank, as the electric pumps are aviailable at almost any parts store.

In general the belief is that the mechanical pumps are more reliable. This is true to a certain extent in that a mechanical pump will give indications that it is failing, while the electric pump may just quit suddenly. "NOS" pumps should be avoided due to the fact that the pump diaphrams have a shelf life, and its anybody's guess how long the pump sat on the shelf and under what conditions. These pumps usually fail shortly after installation because the diaphram is dry rotted. One of the most important reasons to consider switching to an electrical pump is that the gas delivery circuit is separated from the crankcase and engine. Original or NOS, when the mechanical pumps begin to fail tiny pinholes and tears develop in the pump diaphram. This allows gasoline to mix in the crankcase and dilute the engine oil. If left unnoticed for a length of time the diluted oil can lead to bearing failures in the lower half, or worse yet the vapors could ignite or explode. The indications of a failing mechanical pump will be an increase in the oil level, dilution of the oil, and a gasoline smell in the oil. Regardless whether its a mechanical or electric pump small amounts of gasoline will eventually make its way into the oil from blowby, if the piston rings are worn.

The main disadvantage of the mechanical to electric conversion is the electric pumps are frequently installed in the wrong location or wired incorrectly. As Mike stated other than the FI cars and 1974 cars, all other cars lack the needed wiring and relays to opperate the pump without it running all the time with the key in the on position. If you are patient and carefull the 74 wiring diagram should provide sufficient information to correctly wire up the electric pump to any other car.

The clicking and humming of the pump is usually heard because the pump is mounted directly to the unibody, for grounding purposes, thus transmitting vibrations throughout the car. Some guys have isolated the pump from the body with rubber spacers or mounts, this will greatly quiet the humming and clicking noises, but a secondary ground strap is required to ground the pump if it does not have two wires.

[mbouse]

we will agree to disagree, right Matt? i will usually argue in the favor of NOT deviating drastically from stock, or original equipment; after all, Fiat spent a large sum-0-cash to design that mechanical pump. and there are many of us still using that design, faithfully.

i will concede that low pressure electric fuel pumps are not made of gold, but according to my files, nearly 2x the price (IAP catalogue) of the mechanical replacement pumps for the 1979-80 carbureted vehicle. specifically $26.95 verses $45.95.

and, thanks matt for elaborating on my comments about improper wiring. this, above all, is my major complaint about previous owners when they deviate from original styled equipment. Improperly following through with all of the proper installation.


BOBCITY - - - you won't hurt anything by keeping that electric fuel pump. but, you might wanna check to see if the previous owner installed a blanking plate to the side of your engine block when he removed the failed mechanical pump.

[manoa matt]

I'll agree, that we can aggree, to disagree, about agreeing, As I am also in favor of mostly stock components and currently running with a new mechanical pump. However my winter project will be a 2L block in my 1800 with dual 40's... which kind of makes me have to put on an electric pump and regulator.

[Tappy]

well this was an interesting post especially because i've started reading last post first

I'll agree, that we can aggree, to disagree, about agreeing,

i've had an 2l idf setup and i did have the mechanical pump still installed. Never thought of the fact that a faulty diaphram could cause damage This might be a lead in why my previeus engine seized. However becouse i'm again on the lookout for an engine ( i found one jippy) i might be a good idea to change out the mechanical fuellpump also
I have to admid that mechanical pump are far cheaper then the electrical ones. @ the local fiat 124 shop (martin willems)
1322 fuellpump1400 29.50€
1323 1600/1800 28.50€
1799 1800 USA elektrisch 100.00€
41972 2000 carb. 25.00€
1324 2000 ie elektrisch 220.00€

I'f i would have to make a choise between electrical and mechanical i would take the mechanical , if only because there never could be any electrical problem and no vibration noises

[mdrburchette]

However my winter project will be a 2L block in my 1800 with dual 40's... which kind of makes me have to put on an electric pump and regulator.

Matt, no reason to go with an electric pump for the IDFs unless you want to. Both my 71 and 72 Fiats w/idfs have mechanical pumps. I just added a fuel pressure regulator and have no problems with fuel starvation at high rpms or hard driving.

[danaspider]

Oh what the heck, I will jump in on this. No one is wrong, but... My 79 has a elctric fuel pump, and if yours is mounted in the engine bay and hard against the body it will thump.... That is until the pressure is built up, then it should quiet down. You will hear the thunping when the engine has been off for a while or the engine compartment is very hot. So if you have an after market add one, do the right thing and move it to the trunk, down by the fuel tank and mount it on rubber isolators.

Now why did some change from mechanical to electric. For the most part it was a very simple reason. When the Fiats came to the USA with emmission junk added the engine compartment got really hot. A common problem from the heat was that when you shut the engine down the heat was hot enough to "boil" the gas out of the carb and the fuel line causing vapor lock preventing starting. Is this my theory on the thing, well no. I first saw this on my 73 Spider in 1975. Had the problem and an old Fiat mechanic gave me the solution. Worked great.

Then foolish me bought a brand new 79 Brava (131) and had the same problem, but the dealer took it back and added the "factory" pump in the engine compartment. The 81 brava I then bought (yes I have been a fiat beleiver for many years) had the "factory pump" from the start.

So if you are having a problem when the car is hot and parked for an hour or so and then will not start, could be the vapor lock.

Now that is when the thumping is good. If it is thumping there is probably no pressure, when it quiets down it is ready to start.

[So Cal Mark]

Mike makes a point with his price comparison between the pumps, and that is precisely one reason Fiat used mechanical pumps. All mfrs compromise between what's best and how much it costs. No production car is built with the best parts or theories. The bottom line plays an important role in the final design of any car, and if the engineers believe a mechanical pump will suffice at half the cost you can bet that's how the car will be equipped.
So, is original always best? Not in a heartbeat, but it is original. Mikes' theory would result in parts that never wear out since they would be built from the best materials with no cost restrictions. There isn't a production car in the world built like that.
My theory is that if I can improve on the original design, I'll do it. NAPA advertises that their replacement parts are better than the originals; improved design and materials

[mbouse]

Mark,

I theorize that your theory is great so long as you intend to make the theoretical modifications completely... and not do a half job like the original poster indicates the installer did to his car.

if you are gonna switch from mechanical to electric....make sure you do ALL of the wiring correctly.

[Jim DeShon]

My 77' has had an electric in it for many years. The reason I changed mine out was it was slow starting in the mornings. In our hot climate, the fuel would boil the float bowl dry after the engine was shut down when I came home from work [a 75 mile drive]. The electric was good because it would fill the carb. without cranking in the morning. It is located under the car right now but I am thinking about moving it because I have lowered the car and it's pretty crowded under there now. I also installed a switch on the dash to shut it off for security reasons because I used to park it a lot with the top down. ...J.D.

[mbouse]

now, THAT, is a good reason to install an electric pump where a mechanical pump was original equipment.

SECURITY!

[So Cal Mark]

I'm looking fwd to wireless pumps!

[Tappy]

I'm looking fwd to wireless pumps!

like the mechanical ?