Check the evap emissions cannister. If it's plugged, and this can happen, it won't allow the tank to vent which in turn prevents gas from getting to the carb.
Clamping fuel return line fixes all my problems... what the heck? (1 Viewer)
- Thread starter Cole
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Hmm...with the return line clamped, no pressure/vac in the tank....I'll have to think about that one...
Make sure they run it through their computer system for the Service department...the bureaucrats at the front desk won't get you there...
If the mechanic was smart enough to check this, I would work off the assumption that it's not leaking....
Given the symptoms and information you provide, I would be leaning towards a clogged screen (between the needle valve and the inlet to the fuel line at the carb), or a stuck/plugged/clogged needle valve.
And the additional pressure you build by blocking the return line is enough to push fuel by the blockage.
But, I also suspect clogged charcoal cannister like Freep suggests causing some strange anomalies in the fuel delivery throughout the system and lastly, a bad new fuel pump.
Hang on a second, when you installed the new fuel pump, are you sure that you routed the fuel lines correctly? Should be 3: incoming from fuel tank, outgoing to carb and outgoing back to fuel tank...can you confirm that they are correctly routed?
- Thread starter
- #24
My evap emissions canister is crap. Pretty sure it's from 1987. But when I brought it up to the mechanic, he said that should have nothing to do with this problem. I can't remember what his explanation was though. I believe it mainly centered around the fact that the eval canister has nothing to do with a 5psi swing in fuel pressure.
I'm going to see him tomorrow so I'll ask again.
- Thread starter
- #26
I don't know what to do about the clogged charcoal canister. You can't get them anymore. I've seen guys on here putting GM ones on that kinda work and some guys who switch the hoses so it "bypasses" the canister. I just figured it wasn't worth messing with because it couldn't cause problems this extreme. It's just designed to gather fuel evap emissions and then use those emissions once the engine get's warm enough correct?
So, to be safe, get a new OEM fuel pump? Dang. I'll do it.
I'd be really surprised if I didn't route the lines correctly and the mechanic didn't catch it. He's aware I did the fuel pump job myself. But I'll check it in the morning and provide a picture. If that's the case, I will ban myself from the forum.
Just swap the lines going into the charcoal canister. Purge and Tank. The CC is the place were the tank breathes.
To rule out a faulty fuel tank venting system, remove the gas cap entirely and stuff a rag in the filler hole. The gas tank will then be able to breathe in both directions through that rag.
The Fuel Pump (LINK)
is a mechanical diaphragm. When the cam pushes it's lever, the diaphragm inside it pumps fuel. It's internal valving diverts excess pressure to the return line and back to the tank. If the bowl won't fill unless the return line is clamped off, there may be a plug up at the needle valve screen. If, as stated, " cranking does not fill up the bowl" then either the fuel pump is defective or there is a blockage at the needle valve, or sticking float, or needle valve or the pump can't get any gas. One of those.
"Occasional stumble" was not the primary complaint of this thread, hence my thoughts led me to other dark places.....
To rule out a faulty fuel tank venting system, remove the gas cap entirely and stuff a rag in the filler hole. The gas tank will then be able to breathe in both directions through that rag.
The Fuel Pump (LINK)
is a mechanical diaphragm. When the cam pushes it's lever, the diaphragm inside it pumps fuel. It's internal valving diverts excess pressure to the return line and back to the tank. If the bowl won't fill unless the return line is clamped off, there may be a plug up at the needle valve screen. If, as stated, " cranking does not fill up the bowl" then either the fuel pump is defective or there is a blockage at the needle valve, or sticking float, or needle valve or the pump can't get any gas. One of those.
"Occasional stumble" was not the primary complaint of this thread, hence my thoughts led me to other dark places.....
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Yes, it is designed to 'scrub' the gas vapors that accumulate through out the fuel system before they are released into the atmosphere. But if liquid gasoline finds it's way into the cannister, it can compromise the porosity of the charcoal, and the cannister is no longer porous enough to permit the diffusion of gas vapors through it. An ineffective cannister medium means that those gas vapors are trapped at different points throughout the system, like in the gas tank, where they build up pressure (Pressure x Volume = #of molecules x R (gas contant) x Temperature).
The vapor separator that @klinetime574 alluded to and you can see in the image I posted of the fuel line system is supposed give a path for the vapor to flow where liquid gas cannot. If for some reason liquid gas was able to get access the charcoal cannister through that vapor line (like a condition of vac in the system), then the charcoal medium would be compromised...
The good news is that by either swapping lines on the current cannister (so that the fuel system vents directly to atmosphere instead of through the charcoal medium) or by doing the GM install, you can rule that out fairly easily.
I don't know, I guess it depends on what your constraints are on getting this fix done (time, money, principle). Either way, it wouldn't hurt to have a back up (either OEM or if you install the OEM, keep the new aftermarket one as a backup)...if you can afford that type of thing.
You probably got it right...it's just MUD's job to be critical...it's how we treat family...
"once she get's started, she runs perfect except the occasional stumble in 3rd gear"
How much fuel the fuel pump pumps (if a fuel pump could pump fuel...) at cranking speed is FAR below how much fuel it can pump when the engine is running at 2000 RPMs. That might explain why you are not starved of fuel once the engine gets running.
It may be that the aftermarket fuel pump is just, well how do I say this nicely, A PIECE OF CRAP. (maybe not... but maybe so...).
How much fuel the fuel pump pumps (if a fuel pump could pump fuel...) at cranking speed is FAR below how much fuel it can pump when the engine is running at 2000 RPMs. That might explain why you are not starved of fuel once the engine gets running.
It may be that the aftermarket fuel pump is just, well how do I say this nicely, A PIECE OF CRAP. (maybe not... but maybe so...).
oh don't ban yourself, this thread is great. This vehicle creature takes time to learn and one more thing: Don't believe that your mechanic knows all about this rig. Most do not. This web site is peer reviewed and is more correct than most mechanics
dougbert
dougbert
Ok.......This is what I would do. Rule out the easy stuff first:
Make sure tank vent lines are breathing air:
This can be checked easily by removing the gas cap and applying low pressure air (20 psi or so) to the vapor line on the firewall that leads from the TANK port on the charcoal canister. You will be able to hear air and smell gas vapors coming out of the gas filler hole at the back of the car if all is well. If so, then the vapor lines to the tank are clear.
Make sure the fuel is flowing freely from the fuel tank to the fuel filter:
Remove the gas cap.
Remove the fuel hose going into the fuel filter. If necessary, attach a barbed pipe nipple so that you can extend the length of the hose with a longer length of hose.
(I don't recall how long the OEM fuel line is.) What you want to do is get the end of the fuel hose below the bottom of the gas tank.. on the ground. Draw a vacuum on the end of the hose to start a siphon (BUT DON"T SUCK WITH YOUR MOUTH). A cheap hand actuated vacuum pump connected to a brake bleeder works well. If a siphon does not develop and fuel doesn't flow freely out of the hose when it is at ground level.. there is a blockage up stream. Fix.
Make sure the fuel filter is clean.
Test Engine
If no go then….
Deal with the fuel pump:
Remove the fuel pump and test it according to the testing procedure outlined in the factory manual (attached below) or replace it. Personally, I wouldn't want anything to do with an aftermarket fuel pump, so I would replace it on principal and not even bother to test it… but that's just me.
Ensure that the fuel hoses are reconnected back on the pump on the correct nipples.
Test Engine
If no go then….
Remove the carburetor and clean/rebuild it one way or another.
You can do most of it yourself if you feel you are up to dealing with a lot of tiny parts that can be lost unless you are extremely careful. Or send it out to be rebuilt. Or buy a rebuilt one. Buying a rebuilt one is the fastest option but expensive.
Test Engine
If no go then….
Do all the steps again and find out if something was missed.
I couldn't find a evap canister that I wanted to pay for so I thought long and hard and replaced the whole thing with a fuel filter, just to keep wee beasties and such from crawling up the hose. There's a vent out the bottom of the stock one that goes to a hardline which in turn vents in the frame rail. I just took the vent line from the tank, put a fuel filter in it and ran it into that hardline. Frees up a lot of real estate on the pass side engine compartment, too. BTW I live in a no-smog-test place.
Where along the fuel line was the fuel pressure gauge installed when you took this measurement?
Don't install the tank breather like that.
If the tank is filled to the top it can force gasoline into the vent lines when it expands while driving and start a siphon. Gas will pour out of that low breather you set up until the gas in the tank is below the vent lines in the tank.
If you want to just vent the tank to the atmosphere, the breather line in the engine compartment has to be as high as the bottom of the hood. Even then, it can/will gurgle a bit of gas out the end.
The best solution is to keep the charcoal canister and swap the vent lines. If you don't like the look of it, paint it. Most likely it is just the check valve inside the canister that has become plugged up. The procedure how to test the CC can be found in the emissions manual (easy).
How you have the tank venting set up now is the worst possible solution.
If the tank is filled to the top it can force gasoline into the vent lines when it expands while driving and start a siphon. Gas will pour out of that low breather you set up until the gas in the tank is below the vent lines in the tank.
If you want to just vent the tank to the atmosphere, the breather line in the engine compartment has to be as high as the bottom of the hood. Even then, it can/will gurgle a bit of gas out the end.
The best solution is to keep the charcoal canister and swap the vent lines. If you don't like the look of it, paint it. Most likely it is just the check valve inside the canister that has become plugged up. The procedure how to test the CC can be found in the emissions manual (easy).
How you have the tank venting set up now is the worst possible solution.
LAMBCRUSHER
SILVER Star
this^^^ and adjust the valves; bypass egr and see if stumble goes away...AAAAND this>
there was another thread some time ago about crazy fuel problems....ended up being the spacer on the fuel pump was left off.
On face value you have what appears to be a fuel issue..assuming all things are correctly installed. I would point to the fuel pump, unless maybe there might be trash/crap in the fuel tank or fuel lines. The note about fuel pressure does not ring a bell to me that would lend it itself to the carb...what controls fuel pressure but the pump.....other than that where is there a regulator type device in the fuel system?
float in the carb is worth confirming its operations/// needle and seat.
On face value you have what appears to be a fuel issue..assuming all things are correctly installed. I would point to the fuel pump, unless maybe there might be trash/crap in the fuel tank or fuel lines. The note about fuel pressure does not ring a bell to me that would lend it itself to the carb...what controls fuel pressure but the pump.....other than that where is there a regulator type device in the fuel system?
float in the carb is worth confirming its operations/// needle and seat.
LAMBCRUSHER
SILVER Star
a restriction of the needle and seat could cause pressure to go toward tank if the restriction were large enough...not sure how that splains the bowl drying out overnight, but...could be why no fuel enters when cranking unless return line is plugged...a cracked bowl or siphon can also drain the bowl...I think it's rebuild time, myself. problem with carbs is they suck...
I had similar issues and decided to replace the fuel pump with aftermarket. Problems went away for a few months but slowly a bunch of new fuel related issues happened. Ran fine around town but pinching the return fuel line was the only way to get over mountain passes and I'd get vapor lock or something if I parked for a few minutes when it was hot - Then I'd have to wait a couple hours before I could get it started again. After much frustration, and trying just about everything else I could think of, I installed an OEM fuel pump and haven't had a problem since.
I had issues with my gasser. After replacing all my vacuum lines, she wouldn't hold idle anymore. I did everything, from resurfacing the manifolds to replacing and cleaning the egr systems etc. 6 month of fiddling and guess what. I sea foamed the damn thing and low and behold. Everything was fixed. If your carb is gunked I say get her nice and hot and with the truck running and possibly at higher rpm, disconnect the fuel line going into the fuel pump and let it suck a bottle of sea foam through. If your carb is gunked, this will clear everything. My truck ran and started perfect after that.
