Chuck84TA

Suspecting a vapor lock issue, is it possible that a new fuel
Pump would rectify that issue? If so, would a high performance pump be the way to go to eliminate vapor lock? Or do you need to rip out all of the other fuel system components?

Chuck

Chuck84TA

Just so it's been covered,
I have a rebuilt carb no leaks, new plugs, wires, dizzy, rotor, timing set

Chuck84TA

And I use 93 octane

Rich1

fuel filter or IAC

five7kid

iTrader: (14)

Check to see if your car has the in-tank electric pump along with the engine mounted mechanical pump. If it does, then check to make sure the in-tank is operating.

They added the in-tank pump for the very purpose of eliminating vapor lock. Thing is, if the electric stops working (and they often do), then the vapor lock problem gets worse than it would be without the in-tank electric.

I drove mine for several years with only an engine mounted mechanical with no vapor lock problems. But, my fuel line was routed a little different than the factory (because my car came from the factory with a V6, and when I swapped in a V8, I didn't run the line the same way they did).

naf

iTrader: (7)

The fuel lines running along the right frame rail, inches away from the exhaust, are the issue. The stock mechanical pump alone should keep enough fuel constantly flowing while the motor's running to prevent any issues while driving. The problem can develop from a hot soak while the motor's shut off and the fuel boils in the lines. Then the block mounted pump can't pull enough fuel through on re-start and the engine can starve. The secondary pusher pump in the tank can overcome this issue and was installed on L69s and 87 LG4s. Some other models supposedly got it as a dealer remedy.

Is this what you're experiencing and are you running the stock return style mechanical pump?

Chuck84TA

The cars fuel system (from what I can tell) is completely original. I notice that the engine hesitates during WOT acceleration after warming up for about 10 minutes. There is a definite decrease in performance after the car is warmed up.

After a tune-up (new plugs,wires dizzy,rotor) Timing set, new remfg. q-jet carburetor, new magnaflow exhaust, and yes, I diosconnected the battery so the ECM can reset itself, I cannot think of anything else. So when I read the "Vapor Lock Bulletin" in the Tech Board I thought I found the answer.

Chuck

naf

iTrader: (7)

Not vapor lock. Let's look elsewhere.

ChrisC

Have you checked your fuel pressure/timing? I would do these tests before trying anything else to save some guess work.

naf

iTrader: (7)

Can you be more descriptive? Is it running out of fuel, in that it cuts out but will pick back up with less throttle? Is it a bog type hesitation: stumbles at first then picks up and runs?

Chuck84TA

Ignition timing has been checked and adjusted. Fuel pressure has not been checked, how do you do that?

Chuck84TA

I would say that its more of a bogging issue. It only occurs when the engine is warm and when I have full WOT at around 3000-3500 rpm. The engine runs very well when cold.

ChrisC

It couldn't hurt to check fuel pressure while the car is warmed up and the problem is occuring. You can get a vacuum/fuel pressure tester that will test up to 10psi, for like $30. They sell more expensive ones that test up to a higher PSI but the less expensive one will be more than adequate for your set up. Are you still running a computer controlled carb and distributor?

Chuck84TA

Its still the E4ME CCC. Stock distributor, as far as I know...

ChrisC

I would try to make the problem happen and check the fuel pressure during just to rule it out of the equation. Look for any interruptions in a steady psi reading and don't be afraid to give it heavy throttle while testing to re create the actual scenario. This may sound stupid, but do you have an engine light on/have you ever used a code scanner on the car before?

naf

iTrader: (7)

Like said above, verify that the in-tank pump is working. You can jump the relay and with the 3/8" hose disconnected from the mechanical pump it should flow fuel. The relay should be near the brake booster, may look similar to the fan relay.

You 'might' have a fuel boiling issue, in that heated fuel can boil in the fuel bowl after passing the needle/seat causing some fuel starvation. This should not happen if both the in-tank and mech pump are functioning properly. Another check is to remove the smaller, rubber return line from the fender mounted hard line and verify that adequate return fuel is flowing with the engine idling. (I've filled my lawn mower fuel can several times using this method-I'm too lazy to run down to fill a gallon jug).

Fuel constantly flowing through the system keeps the fuel and the hardlines near the exhaust cool.

ChrisC

https://www.thirdgen.org/forums/tpi/...ump-relay.html