So I just dropped my fresh built 383 into my 87 Trans am and I'm now having issues with fuel delivery. I've got a Holley 110 Gph mechanical fuel pump fitting into a 750 CFM carburetor, and I'm getting a lot of vapor lock issues even on the highway while driving. Upon attempting to restart, there doesn't seem to be any fuel getting pulled in from the gas tank. As I was poking around in the engine bay I found this line plugged off next to my fuel line and was wondering if it was a return line that I could plumb in with a regulator in order to eliminate this issue. This is an H Vin Trans Am, so it came with a QuadraJet from the factory. Any help is appreciated, thank you.
In a word, yes.
I had similar issues with fuel delivery once I upped the game, abandoned the mechanical pump and various other changes.
I've lines for fuel that are 3/8" supply, 5/16ths return and a 1/4" vapour return. (Former EFI chassis but it doesn't matter.)
If you've the 2nd line back to the tank you're golden.
I went with Holley's bypass style regulator for carburetors and used the 5/16ths as my bypass return.
The end result is fuel isn't sitting in the lines next to the exhaust when demand is low. It may take some fiddling with the regulator to ensure that the WOT fuel pressure is sufficient and the idle pressure isn't excessive.
One thing worth noting is that you may find that the smaller return line is insufficient as I did. I had to run a length of 3/8" (-6 AN braided hose) as a substitute. This resolved some of the pressure issues I described. I spliced it onto the 5/16ths stub that comes from the tank. The small amount of smaller diameter line didn't seem to make a difference.
that is the factory return line for the factory mechanical fuel pump. no reason it wouldn't work as intended with the correct mech pump installed.
the vin H 87 would also have come with an in-tank 'helper' electric pump. it wasn't strong enough on it's own to work without the mech pump. chances are that your in-tank pump is either no longer working, or no longer connected to power. this would explain your fuel starvation issues-the mech pump won't pull well through a dead in-tank pump.
I would:
1. acquire and install the correct stock replacement fuel pump and plumb it in appropriately
that is the factory return line for the factory mechanical fuel pump. no reason it wouldn't work as intended with the correct mech pump installed.
At 110 GPH, it's far removed from the factory pump.
This is why the restricted size of the return line may prove to be an issue.
As for the in-tank pump, good catch on that provided of course over the course of 30+ years it also isn't long gone.
that is the factory return line for the factory mechanical fuel pump. no reason it wouldn't work as intended with the correct mech pump installed.
the vin H 87 would also have come with an in-tank 'helper' electric pump. it wasn't strong enough on it's own to work without the mech pump. chances are that your in-tank pump is either no longer working, or no longer connected to power. this would explain your fuel starvation issues-the mech pump won't pull well through a dead in-tank pump.
I would:
1. acquire and install the correct stock replacement fuel pump and plumb it in appropriately
2. correct any issues with the in-tank electric.
Wouldn't a stock pump be insufficient to the needs of a 383? It's a relatively high idling engine and I'd hate to end up starving it.
At 110 GPH, it's far removed from the factory pump.
This is why the restricted size of the return line may prove to be an issue.
As for the in-tank pump, good catch on that provided of course over the course of 30+ years it also isn't long gone.
I only ever seen to have a fuel supply issue once the engine actually warms up. I was debating on swapping the 12-327-11 I have installed with a 712-327-11. Was hoping that would sufficiently cover the vapor lock issue.
Warming up is the issue.
As the exhaust gets hot so too will anything close to it. At low fuel demands there's sufficient time for the fuel in the line to warm up significantly.
The return lines reduces that tendency. But you need a specific regulator to accomplish that.
And I doubt a stock pump, with or without a return line will be enough. I started losing capacity somewhere north of the 350 HP mark.
And a cautionary tale for you 383addict.
The increased pressure with the high capacity pump will beat the hell out of your cams fuel pump lobe.
This is how I know...
Warming up is the issue.
As the exhaust gets hot so too will anything close to it. At low fuel demands there's sufficient time for the fuel in the line to warm up significantly.
The return lines reduces that tendency. But you need a specific regulator to accomplish that.
And I doubt a stock pump, with or without a return line will be enough. I started losing capacity somewhere north of the 350 HP mark.
Both of the fuel pumps then I listed have an internal regulator that keeps the pressure around 6.5-8 PSI, but the one that I'm looking to install will send any fuel that would exceed that pressure back to the tank. Wouldn't that solve the vapor lock issue? I can't really see an additional pressure regulator solving that issue any better than a pump with a return line built in. From what I understood having a return line on the pump is actually better than having an external one.
The problem with a pump with no return is that it dead heads. While this may keep the pressure in check, it doesn't do much for keeping the fuel cool.
The Holley regulator I posted a link to is specifically designed for a carbed engine so that the pressures are suitable but rather than dead heading, the fuel is kept in circulation through the bypass port.
3 lines. One in from the tank. One out to the carb. The third back to the tank.
I've tried several mechanical pumps with a built in return but none worked as advertised. Carter has a couple of models. One of which has the incorrect capacity listed in various catalogues. Says 110 but in actually it's more like 40.
Post up your choices so far and I'll cross reference with my selections.
The problem with a pump with no return is that it dead heads. While this may keep the pressure in check, it doesn't do much for keeping the fuel cool.
The Holley regulator I posted a link to is specifically designed for a carbed engine so that the pressures are suitable but rather than dead heading, the fuel is kept in circulation through the bypass port.
3 lines. One in from the tank. One out to the carb. The third back to the tank.
I've tried several mechanical pumps with a built in return but none worked as advertised. Carter has a couple of models. One of which has the incorrect capacity listed in various catalogues. Says 110 but in actually it's more like 40.
Post up your choices so far and I'll cross reference with my selections.
The one I was mostly looking at was the Holley 712-327-11 found here https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/fuel_pumps/carbureted_fuel_pumps/carbureted_mechanical_pumps/parts/712-327-11
But, that Carter pump (above) didn't have the jam to take care of my fueling needs as it turns out it's only 40 GPH. But it does have a return line.
I opted for an electric pump with the Holley bypass regulator as posted.
All of that said, in summary, if I were to revisit the mechanical pump again I'd go with the Edelbrock 1721. That worked very well. I'd use a bronze tipped fuel pump push rod with it though. http://www.summitracing.com/int/parts/edl-1721
But, that Carter pump (above) didn't have the jam to take care of my fueling needs as it turns out it's only 40 GPH. But it does have a return line.
I opted for an electric pump with the Holley bypass regulator as posted.
All of that said, in summary, if I were to revisit the mechanical pump again I'd go with the Edelbrock 1721. That worked very well. I'd use a bronze tipped fuel pump push rod with it though. http://www.summitracing.com/int/parts/edl-1721
Plenty of GPH combined with a fully adjustable regulator and a return line.
I believe this will take care of your issues.
.From what i can see, that fuel pump is the Edelbrock equivalent of the one I have currently installed. I can definitely see installing the FPR to maintain the pressure in the lines at the carb and sending the rest back. I think that would solve my issues perfectly.
.From what i can see, that fuel pump is the Edelbrock equivalent of the one I have currently installed. I can definitely see installing the FPR to maintain the pressure in the lines at the carb and sending the rest back. I think that would solve my issues perfectly.
If that is the case (your pump being equal to the Edelbrock) then I'd say the adjustable bypass regulator is your ticket. Keep in mind that the smaller (5/16ths") return line may prove problematic. As I did, you may find that an upgrade to 3/8" may be needed. Holley suggests this with their regulator ( 3/8" in and 3/8" out, IIRC).
If you can do thirdgen a favour, post up with your results and link this thread.
For the record there's a few others here that have travelled this route before. Except for me though, I can't say how they all fared.
an accepted rule of thumb is 10 hp per gph. so 110 gph may be overkill. like Five7 said, that's HUGE
the carter replacement is rated at 40 gph. combined with the in-tank helper pump the system (when properly functioning) likely flows more than that. this can easily be checked by timing flow into container.
if your in-tank pump is dead you're dropping the tank anyway. then it's time to consider an appropriate in-tank replacement along with regulator and do away with your mech pump altogether.
bottom line. your vapor lock issues are likely (99.99% certainty) caused by lack of return flow to the tank. the fuel lines run right by the exhaust and return flow is required to keep them cool.
fix your in-tank pump issue. you'll never get adequate flow through it if it's dead.
were it me, assuming I got the in-tank pump working, I'd invest in an appropriately sized upgrade to the mech pump WITH return. plumb it in correctly and enjoy trouble free miles until the next problem crept up.
Keep in mind that the 110 GPH is free flow. Like what you'd get with the discussed metering into a bucket.
Add 15' of twisty 3/8" hard line and your actual output will be off the mark by a measurable amount.
If the idea of 10 HP per gallon is true, then the Carter at 40 GPH should have handled my under 400 HP.
It didn't.
And by a wide margin at WOT.
My stock fuel lines have plenty of 90's and other bends. Add to that the fact that the fuel also has to overcome the forces from acceleration and you can see where 110 GPH isn't all that huge.
meter it into a bucket from the fuel pump outlet at the motor. this takes into account head loss within the system. (at least the head loss up to the point of discharge-expect some additional loss through the carb filter, needle/seat, etc.)
not sure how you could do it otherwise.
the pump ratings, being a single number, are only one point on the pump curve. and likely not a very conservative estimate.
the actual flow rate would be determined by the intersection of the system head and pump curves. we could calculate the system curve but our numbers would only be as good as our assumptions. still don't have a pump curve though, as I don't expect you'll get one from the manufacturer(s).
only way to know is to measure it.
yes I have to agree that without seeing the pump curve, I can't say that 110 gph is HUGE.
meter it into a bucket from the fuel pump outlet at the motor. this takes into account head loss within the system.
not sure how you could do it otherwise.
only way to know is to measure it.
yes I have to agree that without seeing the pump curve, I can't say that 110 gph is HUGE.
This is true and something I considered after that post.
But, that said, I think what it really demonstrates is the advertised rating isn't something you can live or die by.
Some intimate knowledge of the system in the particular vehicle has to be known otherwise, yes, you'd have to measure and reverse engineer what's really needed. Possibly at the expense of another pump or reworking the system for better efficiency.
All of that said, I'd go for the greater GPH if that's the decision that has to be made. There's really no loss with having more capacity. Unless you're deadheading the pump in which case I would say the excess makes the situation worse.
actually we CAN measure the system head curve...it's simply the fuel pressure nearest the carb inlet.
forgive me, it's early on a holiday, by the fire with the pets commanding attention
some pumps provide a rating at a specific pressure. although I didn't find a curve for the Carter M6626 (as an example anyway) the flow rating is listed as 'minimum' which leads me to believe that it's at the higher end of the expected system head.
another point of discussion could be that the fuel flow for factory motors was required to support the 'gross' hp rating- the power the motor must produce to overcome the losses that downgrade output to 'net'. ehh
regardless I stand by my opinion that the OP won't fix his vapor lock issue without proper fuel return and ensuring he's not drawing through a dead in-tank pump
you've been around these forums near as long as I have.
some may consider that to be a long time.
I certainly do.
One thing I've learned is that regarding 3rd gens specifically, there are many here that know these details (such as the in-tank pump) that I don't concern myself with.
To me, my Camaro is simply a platform (and an attractive one that I always thought from the get go in 1981 when I saw my first) and it's a base for a hot rod.
Twenty years ago when my 86 IROC gave up the 305, it was a wholesale change of the fundamentals. Computer gone. EFI gone. Etc.
Fast forward to today and my approach might be different but the minutae will be something I'll leave to those who have that interest.
One thing I'll say is that thirdgen is an invaluable resource for anyone, including me, who is into the platform.
regardless I stand by my opinion that the OP won't fix his vapor lock issue without proper fuel return and ensuring he's not drawing through a dead in-tank pump
I did route a return line to the tank and it helped to mitigate some of the issues, but I'm still locking on the intake on the pump side. I think it's time to give up on an "easy option" and finally just drop the tank to replace the fuel pump. I was hoping to do this relatively cheap and quickly as this is supposed to be my daily driver. Any advice on dropping the tank?
Dropping the tank becomes a pain in the *** if you have to cut the exhaust off as I did. I made the cut at the arch over the rear axle then welded back together.
The rest is shocks to allow the axle to swing as low as possible. I don't recall what all else gets in the way.
Personally, next time I revisit this tank, it'll be through a hole I cut in the floor for a proper access panel.
Quick question: Can you monitor fuel pressure from behind the steering wheel? I've got my gauge rigged up under my cowl hood and can observe it while driving. Very helpful.
Dropping the tank becomes a pain in the *** if you have to cut the exhaust off as I did. I made the cut at the arch over the rear axle then welded back together.
The rest is shocks to allow the axle to swing as low as possible. I don't recall what all else gets in the way.
Personally, next time I revisit this tank, it'll be through a hole I cut in the floor for a proper access panel.
Quick question: Can you monitor fuel pressure from behind the steering wheel? I've got my gauge rigged up under my cowl hood and can observe it while driving. Very helpful.
I might just end up cutting an access panel and sealing it back up later. Just need to be careful not to nick the lines. I have my fuel pressure gauge under the air cleaner so it's easier to tune.
I might just end up cutting an access panel and sealing it back up later. Just need to be careful not to nick the lines. I have my fuel pressure gauge under the air cleaner so it's easier to tune.
I can relate to the access panel. There are some nice examples here at thirdgen.
As for your gauge. Under the hood is fine but seeing what happens at WOT can be a real revelation. I've observed idle pressure nice and steady at 6 PSI which dropped to less than 1 when I've pinned it.
Then there's the recovery.
It's these observations that forced me into rethinking the whole setup.
That, and the mangled cam pump lobe I posted.
I can relate to the access panel. There are some nice examples here at thirdgen.
As for your gauge, under the hood is fine but seeing what happens at WOT can be a real revelation. I've observed idle pressure nice and steady at 6 PSI which dropped to less than 1 when I've pinned it. Then there's the recovery. It's these observations that forced me into rethinking the whole setup. That, and the mangled cam pump lobe I posted.
Would it be impossible to swap a fuel sender from a pre 87 carbureted engine? I really don't want to have to deal with electronics if I don't have to.
Would it be impossible to swap a fuel sender from a pre 87 carbureted engine? I really don't want to have to deal with electronics if I don't have to.
When I changed over from EFI to carb on my 86 IROC (305 TPI) I also changed out the entire in tank assembly for a carbed version.
So, gone was the pump and associated wiring. IIRC, I still had the 3 lines. 3/8, 5/16 and 1/4 plus the vent.
My factory fuel gauge worked as it should. Which is something I can't say with my since swapped in aftermarket gauge.
When I changed over from EFI to carb on my 86 IROC (305 TPI) I also changed out the entire in tank assembly for a carbed version.
So, gone was the pump and associated wiring. IIRC, I still had the 3 lines. 3/8, 5/16 and 1/4 plus the vent.
My factory fuel gauge worked as it should. Which is something I can't say with my since swapped in aftermarket gauge.
Would I be able to just swap the sender instead of the entire tank? Was hoping to avoid the hassle of dropping the tank.
Would I be able to just swap the sender instead of the entire tank? Was hoping to avoid the hassle of dropping the tank.
That's what I did but dropped the tank to do it.
With an access panel, you should be able to accomplish the same provided the opening is large enough. You have to get in there an knock off the retaining ring. It takes a little extra real estate to do this.
Check out 427seven's build page. He has a sterling example of how it should be done.
That's what I did but dropped the tank to do it.
With an access panel, you should be able to accomplish the same provided the opening is large enough. You have to get in there an knock off the retaining ring. It takes a little extra real estate to do this.
Check out 427seven's build page. He has a sterling example of how it should be done.
Awesome, the only reason I ask is because I remember seeing a forum post a couple years ago saying that the size of the sender hole between the old and new carb pickups are different.
Awesome, the only reason I ask is because I remember seeing a forum post a couple years ago saying that the size of the sender hole between the old and new carb pickups are different.
The difference between new and old I can't comment on as I went from something pre 87 (as it was from a carbed car) to my 86 (even though that was EFI).
I'd say that if you're doing the same (more or less) you're good to go.
Often I go through the listings at Rock Auto and look for any changes that might have occurred through the years. It can be very informative. Especially if you're buying something previously enjoyed.
The difference between new and old I can't comment on as I went from something pre 87 (as it was from a carbed car) to my 86 (even though that was EFI).
I'd say that if you're doing the same (more or less) you're good to go.
Often I go through the listings at Rock Auto and look for any changes that might have occurred through the years. It can be very informative. Especially if you're buying something previously enjoyed.
I have a guy willing to sell me a used sending unit for a hundred bucks. Removing the helper pump shouldn't cause too many drivability issues, will it?
I have a guy willing to sell me a used sending unit for a hundred bucks. Removing the helper pump shouldn't cause too many drivability issues, will it?
I've never had a helper pump in all of my years driving this carbureted Camaro.
It wasn't until two things happened: The first was that I outraced the capacity of the stock mechanical pump.
Then I upgraded to the 110 GPH Edelbrock pump which was excellent until it took out the pump lobe.
After that I was forced to go electric and have been ever since.
If I were to do it again (I may be repeating myself) I'd go with the Edelbrock pump (or equivalent), the Holley bypass regulator and either a bronze tipped or roller tipped fuel pump push rod. And check it regularly.
Maybe get pictures of the used unit with a ruler laid across it and compare it to your own (seeing as you're going into the tank anyway).
Of course a new thread with the question asked specifically may get a better response.
the in-tank pump was installed on L69s and the 87 LG4 to cure the vapor lock problem. prior to that there were dealer installed fixes that included installation of the in-tank pumps.
the problem is exacerbated by the proximity of the fuel lines to the right side exhaust, which can be made worse with the installation of headers which are closer to the fuel lines.
find the fuel pump relay and jump it out with the supply line disconnected from the mech pump. verify its operation before dropping the tank. chances are the wiring has been farkled with at some point.
you'll need to remove the retaining ring from the top of the tank to remove the unit. the tank is the same so either a pump unit or non-pump sending unit will fit.
I'm not in favor of cutting the access panel, not so much because of the cut panel, but because you have to cut and splice the metal fuel lines from the sending unit where you can't easily tell they may be leaking. there are ways around that with the proper fittings, but most just use flexible fuel line with clamps.
a new sending unit starts at around $70 on rock auto if you need one.
Is your charcoal canister still in place and functional? Or is it capped off? If so, then your tank can't breathe - as in let air in so that fuel can flow out. The more fuel you draw out, the more the tank is put under a vacuum, up until the fuel is unable to overcome the vacuum trying to keep it in the tank. Quick test, open your gas cap when the "vapor lock" issue happens and check for an inrush of air.
Is your charcoal canister still in place and functional? Or is it capped off? If so, then your tank can't breathe - as in let air in so that fuel can flow out. The more fuel you draw out, the more the tank is put under a vacuum, up until the fuel is unable to overcome the vacuum trying to keep it in the tank. Quick test, open your gas cap when the "vapor lock" issue happens and check for an inrush of air.
I actually have the answer for this one! The charcoal canister was not in the car when I bought it. That's the black canister with the vacuum lines coming out of in on the front driver side of the vehicle, right? That's where I keep a spare quart of oil since it's empty lol
If I have my facts straight, there'll be a hard line from the canister to the tank. 1/4" steel.
If that's what you're using for a return from the bypass regulator, you'll probably have some pressure issues. At least I did. I was using the 5/16ths for the EFI return and it wasn't enough. Ended up with another 3/8" to the back.
