Add One-way valve to keep fuel at the carb? '86 Burb 454

[suburble]

Guys and Gals-

I'd appreciate some input, especially if anyone has tried this...

I'm having what I think are heat soak issues causing me to stall out after extended driving at low speed / stop-and-go, and start-up and idle issues after being parked hot. I just changed out the mechanical fuel pump and thought for a while I had gotten past this. Fuel pressure also seems to be erratic when hot, wavering between 1-3psi hot (when it's not stalling out) vs. 5-7 psi cold.

The key observation is that the fuel appears to be draining back through the pump or evaporating, not quite sure which. Also seems like the pump is not keeping fuel in the line when idling. I've got a clear filter right up by the front of the intake, and I can see it's dry when the problems are happening, and I can see good fuel flow at other times when it's running right.

I've bought a one-way check valve to put in the fuel line, but I'm trying to understand the problem a little better before I try it out. Certainly not seeing any leaks... Although I do get a strong fuel smell after a few minutes parked hot.

Before I try the check valve, I've bought a phenolic spacer and a cooler t-stat that I plan to install but I'm not convinced this will fix the issue. (I'm running a 195F right now, but temp is holding steady at around 200).

Other potentially helpful info- I am running an Edelbrock 750cfm electric choke carb. Choke is definitely open. I've vacuum tuned for best idle with the engine warm (not hot) and have hot idle set to about 800rpm.

Could heat soak be causing the fuel bowl to pressurize, pushing fuel back down the line with enough pressure to open the bypass in the pump?

Has anyone else had this issue with the Edelbrock carbs?

Is the check valve a bad idea?

Thanks,
-Josh

 

[HotRodPC]

I've never heard of an Eddy Carb having issues losing fuel like Quadrajets do with leaking well plugs. That's a bunch of heat soak to be emptying the fuel bowls on an Eddy Carb. For some reason, I just don't think that's your issue.

My first thought was going to be fuel pump, then you've mentioned you just replaced the fuel pump. 1-3 psi fuel pressure is the problem IMO. That's only going to happen for 2 reasons if I'm thinking correctly. Either you've got a defective fuel pump, or you mentioned it's a mechanical fuel pump, so either your fuel pump rod has worn and to short which is rarely heard of, or your cam lobe that operates the fuel pump has wore down and you're not getting a full push on the mechanical fuel pump arm. That's my thoughts and things you might want to consider. That 1-3 psi is what sticks in my head. Should be in the 4-7psi range.

Hopefully some other ideas will surface from some other heads.

 

[1987 GMC Jimmy]

HRPC is right. That fuel pressure isn't what I'd call nominal. You mentioned the strong smell of fuel, which I take to mean fuel vapors. Are you running factory evaporative emissions, or have you done a canister delete? If you have the canister and whatever else goes with that still on it, a fuel cap and canister filter replacement plus an inspection of the vacuum lines associated with that system may be in order. I understand that may not help, but fuel tank venting is an overlooked, however important, component. I think the best way to test to test the pushrod/eccentric theory is to pull the pushrod and see if something doesn't look right with it. You could also try a little carb friendly electric fuel pump as an alternative to that.

 

[suburble]

I've never heard of an Eddy Carb having issues losing fuel like Quadrajets do with leaking well plugs. That's a bunch of heat soak to be emptying the fuel bowls on an Eddy Carb. For some reason, I just don't think that's your issue.

My first thought was going to be fuel pump, then you've mentioned you just replaced the fuel pump. 1-3 psi fuel pressure is the problem IMO. That's only going to happen for 2 reasons if I'm thinking correctly. Either you've got a defective fuel pump, or you mentioned it's a mechanical fuel pump, so either your fuel pump rod has worn and to short which is rarely heard of, or your cam lobe that operates the fuel pump has wore down and you're not getting a full push on the mechanical fuel pump arm. That's my thoughts and things you might want to consider. That 1-3 psi is what sticks in my head. Should be in the 4-7psi range.

Hopefully some other ideas will surface from some other heads.

Mechanical fuel pump is actually the 2nd replacement in less than 2,000 miles. Previous pump I took off because of this same issue, thinking it must have a bad diaphram or relief spring. Pushrod is new, and I did look through the access hole as best I could and didn't see any signs of abnormal wear on the drive eccentric at the cam, but it wasn't too easy to see.

It's developing good pressure, around 5-7psi, when the engine is cold / warm.

I suppose I really can't rule out the "got 2 bad fuel pumps in a row" theory.

Thanks,
-Josh

 

[suburble]

HRPC is right. That fuel pressure isn't what I'd call nominal. You mentioned the strong smell of fuel, which I take to mean fuel vapors. Are you running factory evaporative emissions, or have you done a canister delete? If you have the canister and whatever else goes with that still on it, a fuel cap and canister filter replacement plus an inspection of the vacuum lines associated with that system may be in order. I understand that may not help, but fuel tank venting is an overlooked, however important, component. I think the best way to test to test the pushrod/eccentric theory is to pull the pushrod and see if something doesn't look right with it. You could also try a little carb friendly electric fuel pump as an alternative to that.

Still have the factory Evap system, but everything is in good working order, all new (fuel rated) soft lines throughout the system including the vent hoses at the Evap cannister and tank.

I pulled the pushrod and replaced with new last fuel pump change, removed and inspected it (and the cam eccentric as best I could see it) this time and everything looked fine.

Again, the frustrating thing is that it seems to work just fine at lower temps, plenty of fuel visible in the clear filter. At high operating temp there is very little to NO fuel visible in the filter except the occasional spurt.

It is 100% a fuel delivery / keeping fuel at the carb issue, mainly trying to figure out if there is anything I'm overlooking that would make putting a check valve in the fuel line a bad idea.

Thanks,
-Josh

 

[donnieray]

Ive been going through the same issues, although I have a 5-7 psi fuel pressure reading even when the filter appears empty or half full or full. Ive did several things that helped but the less than full filter still happens. This is on two trucks, a 86 C10, fresh 355, new Edelbrock 600 and Edelbrock intake, new rubber lines rerouted away from the engine, new gas caps, new strainer/ fuel pick up, 84 k10, 350, same carb and intake and same everything else, I added heat shields on this one where the fuel line seemed close to the dual exhaust under the cab. It is better after all the work on both trucks but still not 100%. The C10 don't starve when I put my foot in it like it used to and the K10 used to go through periods of starving on hiway runs, not always but once in a while and that has went away. My next move will be electric fuel pumps and when Im satisfied I will trash the clear filters and use the metal ones. Ive got to throw this in, Ive just recently purchased a 85 K10, 350 with Holley 600, Weiand intake, stock fuel pump, old lines, old strainer/pick up old everthing and put a clear filter on it and the damn thing fills up on start up and stays full until shut down. yep. Keep me posted on any progress you make. Good luck.

 

[HotRodPC]

OK, so it sounds like you're been around the block with this for awhile and it's time to start back at the very bare basics and quit the tunnel vision you have of being a fuel problem. You're frustrated and not thinking from the basics. I see you've had the problem on 2 trucks now, 2 different carbs, more than 2 fuel pumps blah blah blah, SOOOOOOOOOOOOOOO, when are you going to give up on it being a fuel issue??? It's NOT a Fuel Issue.

You've transfered the same dizzy to both trucks haven't you???? Yep, You have !!! NOT A FUEL PROBLEM.

I'm going to say 95% chance you have either a bad coil or Electronic Ignition Module. If it's not that, then maybe you don't have a full 12 volts (13.2-13.8) volts in run mode. WASH YOUR BRAIN of it's frustration and start from scratch and the basic troubleshooting.

It's very common on a bad coil, it works when it's cold, it gets hot, BOOM, no spark. Cools off, Starts right back up til it gets hot again. Coils don't go bad often, but when they do, that's how they go and sometimes they'll die and be done but in MOST cases, when bad, Cool they run, get warm, they quit. Though not common for a Ignition Module to go that way, I've seen it happen once or twice IIRC.

I've seen where a guy converted a standard points coil to HEI. It ran just like you say, starts and runs, gets warm shuts off. Cool down it ran, warmed up, shuts off. Problem was, he didn't change the fact points ignition only gets 6v in RUN mode of the ignition switch, HEI needs 12V for both Cranking and Running, not just Cranking.

Check your running voltage to your dizzy wire FIRST.

 

[HotRodPC]

BTW, the above post is for both of you. Good Luck guys. I'm sure at least one of you is going to find it's NOT a Fuel problem.

 

[HotRodPC]

And just for ***** and giggles, lemme give you younger guys who never dealt with Points ignition a little education. And I'll tell you how I fixed up my buddy long ago on his 6V problem. Did you ever think your starter has anything whatsoever with getting spark to the coil??? Why would it? Well, back in the day, the starter had EVERYTHING to do with getting power to the coil. Remember I said, Points dizzy gets 12V while cranking the engine to get it to start? Then the voltage is reduced to 6V after the engine starts. If you'd put 12 volts to a points dizzy, you'd fry your points in short order.

So here's how the voltage was commony cut down to 6v. Ever notice on a Starter Solenoid the 2 smaller lugs on each side of the big lug are marked R and S? As a rule of thumb, you want to remember them as Run and Start. Start side was your Starter activation from the ignition switch to make the engine crank. The R is actually RESISTOR. A RESISTOR that cut the voltage in half. So if you had 13 volts, now you have 6.5 volts. The R wire was the one that went to your coil when you had points so you didn't fry your points in RUN mode. So if anyone ever says the R means RUN or RESISTOR, they're both right in a sense, but RUN is just rule of thump as a tool to remember which one is your Coil wire, but it is a RESISTOR in fact.

The other way to cut voltage in half was using as Ballast Resistor. Commonly done by Dodge on the older points dizzy, but many guys who wired their cars and trucks, just used a hot wire off the ignition and ran it through a ballast resistor and avoided wiring to the starter R side all together. You'd also hear of guys doing to hot wire their car to get home if they had an electrical problem. Go right off the battery to the coil through a $2 ballast resistor.

So for my buddy who converted to HEI from Points, we disconnected the R wire at the dizzy, did a little re-wiring and he got 12V to the coil at all times, problem solved.

 

[HotRodPC]

Still have the factory Evap system, but everything is in good working order, all new (fuel rated) soft lines throughout the system including the vent hoses at the Evap cannister and tank.

I pulled the pushrod and replaced with new last fuel pump change, removed and inspected it (and the cam eccentric as best I could see it) this time and everything looked fine.

Again, the frustrating thing is that it seems to work just fine at lower temps, plenty of fuel visible in the clear filter. At high operating temp there is very little to NO fuel visible in the filter except the occasional spurt.

It is 100% a fuel delivery / keeping fuel at the carb issue, mainly trying to figure out if there is anything I'm overlooking that would make putting a check valve in the fuel line a bad idea.

Thanks,
-Josh

And you won't even get close to see that cam lobe for the fuel pump. When you say eccentric, that's actually an egg shaped circle that usually bolts onto the front of the timing gear and the fuel pump arm is operated off of it like Pontiac, Olds and Buick did. Chevy uses an actual lobe on the camshaft. It can wear down but there is no way to see it without pulling the cam to the best of my knowledge unless you have a tiny cam that will fit up in there. If the engine wasn't in a vehicle you can look up in there with the plate off and a flashlight but I'd say it's hard to see. About the only way to check that, is to hold your finger over the rod pushing it up to the lobe and have someone bump the key a few times and feel the travel. If you're not feeling much travel, the lobe is wore down. If the lobe is wore down, then you have 2 options, replace the cam, or go electric fuel pump and most will go electric fuel pump if the valve lobes are all good in the engine.

With that being said, the lobe is either wore or it's not and it's not going to make a difference at all hot or cold. It'll be the same at 20 below Zero, and at 220 degrees.

 

[1987 GMC Jimmy]

The HEI coil is really easy to test. I'll attach a video. You can take the ignition control module to an auto parts store and have them test it.

xc_hide_links_from_guests_guests_error_hide_media

 

[HotRodPC]

Yep and BTW just so you know... Because you have spark doesn't mean an HEI Ignition Module is good either. It may have spark but the timing of that spark can be all out of kilter within the module and your truck will stall or not start. So we're not going to fall for, "But I have spark" and go along with that the module still may not be at fault. This is why we DIAGNOSE things, and don't be parts changers. Parts Changer is only acceptable when it was time or about time to change that anyway, and it could be considered routine maintenance so that it's not a waste of time and money.

 

[Honky Kong jr]

pretty much if you run HEI keep a module in the glovebox and the tools to replace it.

 

[HotRodPC]

pretty much if you run HEI keep a module in the glovebox and the tools to replace it.

I normally do because they give absolutely no warning at all when they go. They work or they don't. Normally, they don't go out while driving down the road. The vehicle simply won't start next time you go out to drive it. And you may or may not have spark when they go. But they can go out while driving too, it's just rare.

 

[suburble]

OK, so it sounds like you're been around the block with this for awhile and it's time to start back at the very bare basics and quit the tunnel vision you have of being a fuel problem. You're frustrated and not thinking from the basics. I see you've had the problem on 2 trucks now, 2 different carbs, more than 2 fuel pumps blah blah blah, SOOOOOOOOOOOOOOO, when are you going to give up on it being a fuel issue??? It's NOT a Fuel Issue.

You've transfered the same dizzy to both trucks haven't you???? Yep, You have !!! NOT A FUEL PROBLEM.

I'm going to say 95% chance you have either a bad coil or Electronic Ignition Module. If it's not that, then maybe you don't have a full 12 volts (13.2-13.8) volts in run mode. WASH YOUR BRAIN of it's frustration and start from scratch and the basic troubleshooting.

It's very common on a bad coil, it works when it's cold, it gets hot, BOOM, no spark. Cools off, Starts right back up til it gets hot again. Coils don't go bad often, but when they do, that's how they go and sometimes they'll die and be done but in MOST cases, when bad, Cool they run, get warm, they quit. Though not common for a Ignition Module to go that way, I've seen it happen once or twice IIRC.

I've seen where a guy converted a standard points coil to HEI. It ran just like you say, starts and runs, gets warm shuts off. Cool down it ran, warmed up, shuts off. Problem was, he didn't change the fact points ignition only gets 6v in RUN mode of the ignition switch, HEI needs 12V for both Cranking and Running, not just Cranking.

Check your running voltage to your dizzy wire FIRST.

Good advice on checking the RUN voltage, simple check and I will do it tomorrow morning.

I'll give up on it being a fuel issue when I can see good fuel flow in the filter when the problem happens. For now, when it first starts acting up, the filter is almost empty /completely empty. Rev it bit, flow picks back up a bit, problem behavior goes away. Let it idle down, fuel level falls in the filter, problem comes back.

Edit- let it go longer and the stumbling gets worse, and the fuel level in the filter drops to zero and it dies a few seconds later.


Also backed up the diagnosis by spraying some starter fluid (while on a test drive) and some fuel from a spray bottle (home) down the carb throat and it perked right back up.

I'm gonna put on the phenolic spacer and change out to a lower t-stat first. Both seem like good bets for Arizona in the summer regardless of the issue at hand.

Again, I will ask my main question: Does anyone have a reason NOT to put a check valve between the carb and the pump to fight possible drain-back issues as a quick trouble-shooting measure?

Thanks,
-Josh