Hi I took out my old sending unit from my 84 vet and found out why their was an external fuel pump,the fuel pump wasnt on the sending unit,must of had problem and went to external pump. Well i put in a whole unit with the pump and did away with the external,but now my car will run for about 1min. and shut down like it ran out of fuel,do i need to bleed some air from the system because I changed units,or could it be another problem,Please Help

 

it may be running out of fuel or running rich and shutting off, but that might take several minutes. ("It ain't air!")
if fuel regulator is leaking the vac line will have fuel. check that. if FR is open, it may be sending fuel back to tank. can you check pressure while running?
was the external unit connected with same circuit as original?

***sorry, wasn't thinking clearly. if pressure was the issue it would have been there with external pump. seems to be an electrical issue that the other one didn't have. was it same circuit, spliced in or what? assume you replaced the pulsator ? have heard of them leaking fuel back into tank. any codes set, like 14 or 15?

 

Hi Joe The pressure on the external pump was 7lbs. on the new sending unit with pump I get 0 pressure,all I did was disconnect the lines from the external pump and hooked them together and just bipassed the external,the person I got the unit from said it worked fine before he pulled it out and sold it to me,its got me confused,so the new system must be working somewhat right,everytime I go to start it it starts and runs for awhile if it wasnt getting any gas from the unit it wouldnt start would it. so you dont think its air bound. any help would be appreciated Joe thanks so much. Wayne Joe I forgot to tell you that this CFI system has been converted to a 4bbl. holly carb, dont know if that helps or not.
Joe would it hurt anything to rehook the external and also keep the new unit in the tank just a suggestion.

 

I just realized, from the 7 lbs pressure, that this is an 84!!

all along I was thinking 87. Fuel injection. not familiar with the x fire at all, but know what a Holley is!
anytime you break into the fuel system line you get air, never knew it could be a problem, certainly not with a carb. I guess you have changed fuel filter.

I reckon I would be ready to check for spark as soon as it quits, have to check that eventually, you know? running out of fuel sounds different from no spark.
with the holley, you can remove the fuel check screw and see if it has fuel, even remove the line and crank it. doesn't take a lot of fuel to idle. also, if it was out of fuel the bowl would be empty, or nearly so, and the accellerator pump would be, too.
I assume it has the HEI?

***just re read it. if it was fine before you changed to the internal pump, it is most likely something with the fuel delivery, pump, whatever. does the unit have a pulsator? maybe I mentioned it, but they can leak fuel back to the tank. nothing wrong with an external pump if it works.

 

joe The reason I went to the internal unit is because the pressure should read between 9 and 13lbs. so their was a hesitation in the engine,it wasnt to bad just going easy but when you put your foot into it it really hesitated,i was told because it wasnt getting the proper pressure,also my fuel gauge didnt work but it works now with the new unit,i dont know,what do you think,can i use both the external and the internal units together,this is all greek to me when it comes to carburetors,hope you can help.

 

7 lbs is too low, yes. if the carb was fine before it isn't the problem. read my posts and answer all the questions. example, does it sound like running out of fuel or shutting key off? how can your pressure read 0?

 

Joe When it shuts down it chugs alittle than it revs up and than it shuts down,its not the same as when you turn the key off,as far as a pulsator I dont know,my next step will be to unhook the line and than try to start it to see if the carb is getting fuel as far as the pressure reading 0 i dont know,maybe the needle has gone all the way around and it looks like it reads 0 Im not that familar with engines,just thought i could save a dollar,im 100% disabled vet and disability doesnt go to far and the price they charge at a garage,i cant afford it,wish i could,than i wouldnt be bothering you,i just dont have to many options. Thanks Joe Wayne

 

not a bother, dude. we're all here for a resosn -this forum, I mean. the suffocating sound is no fuel. narrows it down. actual pressure is not needed.

one method is as you say, unhook the line, crank it and fill a jug with fuel. lets you see if there is water or something else. also, fuel filter, if has not been changed in last 50,000, cheapest they have is fine.
the pulstor was maybe not on the 84, but is a metal box on top of the pump, like a small exhaust muffler, which it is. can be replaced with a fuel line, rubber, clamps. don't asume that the lines in tank are open.
you have the fsm, shop manual, or Haynes?

 

Joe Thanks for sticking with me,you seem to know your s--- when it comes to cars,i have the shop manual for my 84,as soon as i get a hand i will try the fuel in a can system and see what happens.i will email you tomarrow when I get this done,thanks again joe,you have been a big help. Wayne Joe I forgot to tell you i took the fuel filter out and hooked the lines together and it still happened.

 

I worked on chevy engines all types in '60's and '70's. still fairly new to c4's. normally filter will not cause a problem till higher rpm, but, was worth a comment.

if you had the fuel pump cover off you would have seen water or residues in the tank. am leaning towards a def pump. someone out there probably has a good idea, but no one has chimed in.

I have to recheck my thinking: if the old pump was low pressure -I recall that mine used to run up to 15 but may be wrong on that- it would cause starvation at high rpm, but not hesitation. savvy? it would simply not pull the rpm. so if the old pump is there you MIGHT consider hooking up to see if this issue goes away. I suspect it will. try to measure the fuel output first.

anyway, gives you something to do with your hands and mind.

 

I'm not sure how the '84 system works because everything changed in '85 and then again in '86, but on the '86 the ECM runs the fuel pump for 2 seconds to prime the fuel system. When you start the car there is an oil pressure switch that supplies power to fuel pump. It sure sounds like that oil pressure switch is bad or the wiring or fuse has problems. The switch is located on the back of the engine near the distributor. It tees off the oil pressure sender.

 

good input, cliff. on the 91 the oil sender switch is backup only. the ecm uses the pump relay to prime, then the relay is on until key is shut off. oil switch can't prime since the engine is not running. the two are in parallel. so, both would have to fail at the same time.

not sure about the 84. easy to check the plug, sicne some models come loose easily.

but...I was not focused on the possibiity of relay issues. I read so many forums I get my thoughts confused.

 

dude, I've thought about it some. the sound you describe shutting down leads us to fuel starvation. maybe you said, but does it restart with 3-5 secs of crank time? then run out of fuel again?

Cliff may be correct on the 84, that the FP relay primes, then the oil sender SWITCH, not the gage you read, supplies voltage to the FP. on early models that switch was on a "t" as he said, driver's side behind distrib. may have a boot connector that is off. Check that. (1)

also, (2) the 84 had fuel return line, I think. what did you do with that, since the carb does not need it?

try to loosen the gas cap in case it is pulling into a vac (3)
remove sight screws in front bowl of carb and watch with a flashlight for fuel in the bowl. if it is out of fuel, bowl will be empty. (4)

you can apply 12 v to terminal G on the aldl if you have some instructions or experience and FP will cycle until it is removed. it sure sounds like the carb bowl is primed and then fp is shut off. YEt- it ran ok with the other pump.

we need Cliff or others who know the 84, and have experience with converting to carb. carbs do not need fuel pressure regulator -at least, early ones did not.

if you get desperate, plug up old one again. as I said, you MIGHT see fuel starvation at RPM but not hesitation.
joe

 

Hi Joe Its me again,what I did this morning was I unhooked the line going to the carb and hooked a hose on it put the hose into a container and turned on the car,gas came out at first,than it stopped,is that normal or should it run steady,what I did next was to pull the sending unit from the gas tank to make sure the pump was working and it was,so the pump is working. The car would start right up and run for about 1 min and shut down,i would wait a few minutes and it would start again than shut down after about 45sec. The carb has been giving me trouble from the start,at low rpm it would run so so as soon as you would come on to it it would sputter and skip like it wasnt getting the right amount of gas,the external was only pumping 7lbs. should have been between 9 and 15 so I got another sending unit,put that in and now it starts and than quits after about 45sec.I hope you understand how Im explaining it,this problem here with the car quiting, started only after I put in the new sending unit.any other tricks I should try or parts i should by,if so just tell me and i will order them today, Thanks Joe Wayne

 

OK,
We all NOW know you are using a Carburetor in place of the X-Fire efi system on your 1984 Corvette.

Are you sure you have power to the newly replaced in tank fuel pump ?

Verify with the gas door removed again with a 12 volt test light.
Tap into or backprobe the 16 gauge GRAY power wire for the electric fuel pump motor.
Other end of the test light connect to body ground or a long test lead back to the battery ground cable in the engine compartment.

If the test light goes off after 1 minute with the car shutting off,
Suspect the Fuel pump relay, bad terminal connections, bad fusible link, ect.

If the test light stays on,
defective fuel pump allready?
Possible.

More than likely the float(s) in the carburetor you are using are set wrong,
Or the Viton fuel inlet needle & seat(s) assembly are worn out.
Or the fuel inlet needle & seat are sticking.
No gasoline getting in to replenish the fuel bowls constant.
Or the engine is flooding over & the engine shuts down because the air to fuel ratio becomes too rich.

A huge vacuum leak somewhere in the induction system plays havoc with carbs just like EFI also.

I have retorqued carbs down to 8 ft/lbs on the intake manifold & all was A- OK once again.

Next the engine shuts down,
with the air cleaner off,
Grab the throttle arm & open fully at a fast rate & see if you are getting a full shot of gasoline into the Venturies or not.

No gasoline shot,
No fuel in the carb float bowls.
Engine shuts off of course.

Keep looking & troubleshooting.
Problem(s) is there in front of you.
Your job to find & correct.

BR

 

Holley Red painted external performance fuel pump is best match with a Holley 4160 vacuum secondary or 4150 series double pumper street driven with 400 HP(flywheel) or less....
On a budget less than $100.

Internally regulated that pump to 7 psi.

Holley Blue pumps work too,
Need to use an external regulator.

Set fuel pressure with engine running to 6 to 6.5psi with a good fuel pressure gauge like an AUTOMETER.
Those tiny 1 inch gauges from summit or ebay are garbage & cannot be relied upon.
If you have one,
remove it at throw it as hard as you can like a baseball.
You will thank me later on.

Mallory best carb fuel pump 110 or 140 comp series on the street- strip I have found.
Quite too.
They Purrr like a kitten pumping gasoline at all times.

 

if you read the posts by BR, you now have someone who has experience with your combination. look back through my last, questions1-4 or so, try to answer those so I have more information. as BR said, the soultion is in front of you.

I asume you cranked the engine until fuel stopped? fuel should run as long as engine is cranking/running.

from what BR says I would simply put the external back on. the problem may have been the Holley, which is easy to fix.

if you do that, try to test for fuel delivery again. if your ecm is like later models, FP will prime for 2 secs with key on, but will remain on as long as engine is cranking. IF the FP relay is kicking out, whatever, the oil switch as Cliff mentioned will be in the circuit so it will run as normal.

SOOOO- check the oil sender switch connector as I mentioned -now, or before you go further. IN CASE the fp relay is part of the current problem.

 

Troubleshoot together as a team.

I don't know all.

Most but not all.

 

same here. same everywhere! I can mange my 91 pretty well, but if someone put a carb on it before, I would be clueless on how and what still works.

never heard of a fp relay verified as kicking itself out consistently after a minute. even if it did the oil switch would supply the FP.

so, fuel check showed fuel shuts off. instinct/logic says fp is leaking, pulsator whatever, or elect supply shuts off, or restriction in line.

would either of us mess with it if the external pump worked? as for the Holley, I tuned many of the 4150 models in the 60's, pretty easy to fix. more I learn more I think that the carb may have been part of or all of the initial problem.

saludos, joe

 

I joined C4 because I wanted to learn more about EFI tuning & exact operating systems they use.
Still really clueless because I never purchased a MOATES system yet to date.
On my list.
Want to retune my 87 vert before I drop my 410ci in.
Then EFI is going bye bye with that motor.
Till I earn a small pile of $$$ again for a nice aftermarket EFI system.

If I buy a Moates,
I can drive Gregg from Kansas crazy with all my questions.
He will want to beat me again.

LOL