could vapor lock affect 73 eldorado?

[kkkaiser]

curiously, on two occasions recently,, the 73 has just shut down after about a mile of driving,,

while my gas tank meter doesnt work, i do right down my mileage at the start of a tank, and always pull in at about 200 miles for a fill up, which, i usually calculate at a bout 13mpg,, but recently, i noted at 165 miles,, i would drive, and it would act as if it was out of gas,, so,, thinking that, put about 3-5 gallons in and it would start on up,  i usually use the higher octane,,93 i think,, but when i get to the station, its no were near my usual 17 to 18 gallon fill up number. to account for the 165 miles i had driven,, where i usually go at least 200..

todays example was about a mile of travel, sat at a light for a few minutes, noted some rough idling, drove off the light about 200 yards and it went down.  got gas in it, after about an hour.. and it fired up, 

i think i saw somewhere about this vapor lock in the heat, and it was hot today here in MS.. could this be a potential problem??
am a correct in using the higher octane??

i can get the non ethanol at a couple of stations, here,, should i use that when i can get it.

or does this sound like something else.

Sincerely
Kim

[The Tassie Devil(le)]

Firstly, I would be filling it up with non-ethanol fuel wherever possible.

If your '73 still has the original hoses, then the problem could well be there.   I know that ethanol degrades the old rubber/neoprene lines, and is especially bad on fuel pumps.

Now, as for the grade of fuel, these cars, and Cadillacs after 1970 were designed to run on straight un-leaded fuel, and as the compression ratios are low, don't need the higher stuff.

Vapour Lock occurs when the latent heat of the road is so high that it vapourises the fuel within the lines, and therefore the fuel pump cannot suck vapour.   The lines have to cool down, and the fuel can condense, and return to a liquid form, then it can be sucked by the pump.

One test I would be doing is to install the fuel pressure gauge in the line before it goes into the carby and see what the pressure reading is.   If it is low, then this could be an indication of a bad pump, or blocked lines.

Bruce.

[7gen]

Check your fuel filter.

My vehicle had somewhat similar symptoms. At takeoff, or at the top of a hill, it would buck as if it were running out of gas. Eventually, while passing a semi at night on I-70, it quit altogether with me halfway up the semi in heavy traffic. Managed to get it to the side of the road, waited a half hour, then tried to take off again. It started out, but died. Tried again a half hour later - same. Long story short, the fuel filter was clogged and might have even been the original for all I know (I was driving the car home from my initial purchase).

Each time it was sucking extra gas due to a load on the engine, it quit. The fuel pump was new so I checked the fuel filter and voila! Plugged.

$10 for a new filter and I drove the rest of the way home.

If your car has AC, I believe I read from Scot M. that it has a fuel return line.

[7gen]

Side note - my experience with ethanol has been good, though others have had troubles. Mine is a 76 Eldorado. I use regular grade gas with ethanol and no problems after 5K miles. However, all hoses and lines have been replaced and so have the internals in the carb as well as the fuel pump, tank and sender. Gets 16 mpg on the highway at 65 to 70 mph. Gets no where near that on a two lane with stops and starts.

[jdemerson]

Kim,

      I use to experience vapor lock on my '52, and switching to ethanol-free gasoline a couple of years ago has all but eliminated the problem. That said, vapor lock is not an issue on a 1973 Cadillac.

      In general, look for the simplest most obvious problem first -- e.g., clogged filter or plugged line.

      Although I don't have data to back this up, where possible I'd recommend using ethanol-free gasoline on any car before 1990. The Clean Air Act was signed in 1990 and that required phasing in ethanol use; cars were presumable designed for its use by around then. I've seen first-hand the problems that ethanol can cause on older cars and on small engine equipment even from more recent years. I'm sure others will have opinions on just when ethanol blend stopped being a problem on cars, but I know that if I had a 1973 Cadillac I'd try to get non-ethanol gasoline. For me the price differential is 25 cents per gallon compared to regular grade fuel with ethanol. See:
http://www.pure-gas.org/

John Emerson
1952 Cadillac 6219X Sedan

[TJ Hopland]

I don't think vapor lock while going down the road is a real common problem with these cars especially with the current somewhat mild spring temps.   Peak summer temps with AC, maybe.   Stuck in traffic yes.    Hot restarts yes.

The first step in troubleshooting is to try and figure out if its ignition or fuel.    Ignition pull a plug wire and ideally stick it in a spare spark plug that you are holding to ground and crank it looking for spark.    For fuel some starting fluid is the easiest,  give a shot down the carb and if it pops for a few seconds then you know its lack of fuel. 

On the ignition side there are several things at this age.  First thing if its points try a new set.  90% of what is available today seems to be crap.  More than one time I have had them occasionally stick open. 

On the fuel side.  Did your carb get a good going through?    The Quadrajets have the jets in the floor of the bowl so crud floating around can land in different places at different times.

If its all original there is a screen in the fuel inlet of the carb that in theory only gets serviced when the whole carb gets serviced.   The main fuel filter is in the bottom of the fuel pump.  I say if it was original because you could get an earlier or later fuel pump that doesn't have the internal filter so there could be no filter at all. 

On a new to me car I always install a clear inline fuel filter somewhere.   Usually the easiest place is in the piece of hose between the hard line from the frame to the pump.   It may take some extra hose to keep the bends nice and smooth but that is fine as long as you secure it and keep it out of harms way.   This filter will give you an idea of what is in the tank.    IF you run a few tanks through it and the filter looks new that tank is likely alright and you can put it all back stock.   IF the filter fills up with crud you will need to get the tank cleaned out. 

There are short pieces of rubber fuel line at the back of the car between the tank and the hard lines along the frame.   Most people seem to forget about these.   At this age they will be rock hard so they can crack easily and or shed internal bits.   Its not the most comfortable area to work in but they can be replaced without dropping the tank.   73 and up its 3 pieces maybe a little over a foot long.  5/16, 1/4, and 3/8.    72 may have been the same 71? had a much different setup back there with some wacky venting thing they were trying out. 

[7gen]

I probably said it wrong because I'm not real knowledgeable - the issue for me was what TJ is calling the screen just before the fuel line enters the carb. It was a paper media that got clogged up, probably from bits of the tank, which I ended up replacing anyways. I called it a fuel filter and I suppose it is but not the main filter, it seems. Sorry.

[Scot Minesinger]

I drove a 1972 Eldorado during summer 95'F no problems with ethanol gas last year.  Everyone blames that gas, but never had a problem using pump gas in 25 Cadillacs driven over the last four years ranging from 1966 thru 1982.  No question you suffer an issue, probably very difficult to diagnose on this forum.  Need more info, such as why engine quit - either fuel or spark - be sure.

[TJ Hopland]

I don't know why Cadillac put the fuel filter in the fuel pump some years.    I think all the other GM's did it in the carb.    It may be worth checking to see if there is one in your fuel pump also.  If its got one its under a big nut that has the hard line up to the carb in it. 

I think there is 4 different fuel pumps you can get to fit these engines plus a few variants without the return line.   One looks like a typical fuel pump nothing special at all.   The other 3 the canister part is larger like an oil filter.  There is a large version with and without the internal filter then there is yet another version where the canister is smaller but still larger than usual and no internal filter.    They will all interchange except for length issues with the hard line.    I think the 'normal' one was very early and those used a inline filter.  Early 70's was the large one with the filter.   Mid 70's was the large no filter.   Late 70's was the smaller no filter.   I think the 368 may have gone back to the normal looking one.

When they had the external filter the one in the carb was just a semi fine screen.  There was never a paper or stone one in the carb from the factory in the years that had the paper one in the fuel pump.    I don't think those screens come in the kits and I think all the other GM's had a filter there so over the years I suppose people or re builders just started sticking filters there.   Performance people often talk about how restrictive those filters are so having 2 in a system could maybe be an issue for a stock person. 

["Cadillac Kid" Greg Surfas 15364]

Kim,
The first thing you said was that your fuel gage is not working.  It is possible that your "fuel starvation" issue lies in the fuel tank's sending unit/fuel pick up.  If for no other reason if this were mine I would drop the fueltank,check the pick up and pickup filter, check the operation of the sending unit and re install the tank using new hoses.
If the problem continues you will have eliminated the tank/sender as its cause and perhaps solved.your fuel gage issue at the same time.
Greg Surfas

[dochawk]

I don't know why Cadillac put the fuel filter in the fuel pump some years.    I think all the other GM's did it in the carb.    It may be worth checking to see if there is one in your fuel pump also.  If its got one its under a big nut that has the hard line up to the carb in it. 

My '72 Eldorado has the filter in the pump (which I had to buy a huge socket to get off), *and* one going to the carb.  Someone who knows this era well insisted that there was no such thing in the pump, and offered to bet $100, but I wasn't going to take money from someone who stopped to help me in a parking lot . . .

And I'm going to add a clear one on the way out of the tank . . .

[The Tassie Devil(le)]

Mine had one in the pump, and another in the Carby.

Now just the pump.

Bruce.

[kkkaiser]

I will have to give it a go,, see what pops up,,,thanks for the help