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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I did a search but didnt really find the info I was looking for. So here's the car:
85 Sport Coupe
Originally a 2.8L mpfi v6, now a 350 punch .040 over, new rotating assembly, stock heads ported and polished, flat tappet COMP Thumpr cam, 1.7 roller rockers, RPM Air gap intake, edelbrock 1406 (unfortunately), Holley blue fuel pump 105gph, 700r4 with the run of the mill goodies, stock 10 bolt.
I've been having the pretty regularly occurring problem over vapor locking due to dead heading the pump. I've already plumbed everything from the carb to the return line but I'm about to tackle the supply line @ thebengine bay>regulator and also relocate the pump back to where the stock fuel filter is.
My questions are: I want to put the pump where the filter is but also keep the filter three-what are the fittings I will need to make this work? The pumps female inlet/outlet look slightly bigger that the stock Male fittings. I tested it with a Male fitting that fit the pump and tried to thread it into the fuel filter to fit check but could only get 2 threads in before it stopped. Fuel filter I used is a microguard 33481 (fram p#G3727) specific to the year of my car.
2nd question: fitting sizes and best fuel line material from supply line under hood to regulator?
Pics included for reference. Fuel Filter inlet/outlet Male fitting that matches fuel pump Female reciever on pump Male fitting on supply line under hood.
I got it all plumbed up burning having an issue with loosing fuel pressure/starving for fuel at higher rpms while driving (anything past 3k honestly). It doesnt do it in park but only while moving (under a load). I plumbed in the return line into the factory return line as so=
Pump>>⅜ line>>bypass regulator>>filter>>carb.
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Return line to tank ¼ line
I've increased and decreased throughout it whole range and it still starves on hard acceleration or higher rpms. Should I add a restriction to the return line to restrict the flow and stabilize the fuel system? And if so what should I use and where in the system should it be placed?
What regulator are you using?
For the record, I'm running a Holley Blue pump in the stock filter location. The regulator is mounted on the frame rail near where the stock mechanical fuel pump would be. At one time I was using a twin feed regulator rather than a true by-pass style regulator and that had to change. After the swap what I found was using the 1/4" return line (formerly for the evap canister) wasn't enough of a return and the restriction caused all sorts of problems. I could stabilize the fuel pressure at idle but it would out of whack at WOT. Adjusting for WOT (I have a cowl mounted fuel pressure gauge) and the idle fuel pressure was messed up. I had to bump up the return to 3/8". Problems solved.
I had to give up on the 12-803 and get the 12-803BP. And when using the BP version, the return line has to better than the 1/4" that you (and I are/were using). Otherwise, fuel pressure is all over the place depending on the demand. I found that with the two port version, 12-803 (designed for two carbs), could be adjusted for a nice even idle pressure when using the 2nd outlet for a return, The problem was that the idle fuel requirements and the WOT requirements are so different that the two port couldn't do the job. A similar sort of thing happened when I tried using the small return line with the BP regulator. At WOT, the small return line worked OK and would provide about 6 PSI . But once idling, pressure would spike and flood the carb. Conversely, if I adjusted the pressure to be satisfactory at idle, WOT pressure would drop below 1 PSI. I used a length of -6AN braided fuel line for the return. After that , everything was a-ok.
You used the -6AN for the entire length of the return all the way to the tank? I have the stock fuel lines still in the car from when it was a mpfi 2.8, the supply is ⅜ and the return is a ¼. I have ⅜ line running from the stock fuel line to the regulator the to a filter then to the carb and have ⅜ line running from the other port on the regulator to the return, where it of course is reduced down to ¼ @ the stock return line. My fp gauge died on me so now I have no clue what the pressure is. I have the screw about half in and locked down. I plan on getting an oil filled gauge, hopefully itll last longer. I have 2 of these regulators, wouldnitnbe worth the trouble to try and choke down the return line with the other? Possibly almost fully closed to keep it from starving the carb while dialing in the main reg to even out the pressure? I plan on doing it right but I gotta get this thing back on the road, I'm putting wayyy too many miles on our suv.
You used the -6AN for the entire length of the return all the way to the tank? I have the stock fuel lines still in the car from when it was a mpfi 2.8, the supply is ⅜ and the return is a ¼. I have ⅜ line running from the stock fuel line to the regulator the to a filter then to the carb and have ⅜ line running from the other port on the regulator to the return, where it of course is reduced down to ¼ @ the stock return line. My fp gauge died on me so now I have no clue what the pressure is. I have the screw about half in and locked down. I plan on getting an oil filled gauge, hopefully itll last longer. I have 2 of these regulators, wouldnitnbe worth the trouble to try and choke down the return line with the other? Possibly almost fully closed to keep it from starving the carb while dialing in the main reg to even out the pressure? I plan on doing it right but I gotta get this thing back on the road, I'm putting wayyy too many miles on our suv.
SkinnyZ gave the correct answer, but here are a couple of things you might try before abandoning the 12-803 Holley regulator.
The second picture would be correct for your needs using a true bypass regulator.
If you are using a Holley carb, then the third pic is what you want to do. Notice the BP regulator is AFTER the carb (no restriction to the carb). You will need the dual feed fuel log type of supply line to the carb.
In the fourth pic, you can try to cheat the return line circuit by installing a "T" as far back towards the fuel tank as possible. As SkinnyZ said, the lines must be 3/8".
The second pic is exactly how I have it ran currently. But like he stated, I too can get it to idle wonderfully but WOT or even higher rpms such as shifting out of 1st starves it for fuel, itll buck and sputter and I have to get out of it for a few seconds to let the fuel system catch up. I deadhead this car for 3 years before vapor lock became a problem but I recently discovered where the stock fuel filter is (I know shame on me lol) and changed it, it was full of black trash and gunk so I may set it back up to deadhead and see if that remedies it. This is so aggravating.
You have two options and it relates to what I experienced. Keep the standard regulator and dead head it. Or get the BP regulator and up-size the return line. As I didn't have the original 5/16ths return available (I also started with a 2.8L EFI platform but had no intention of an electric pump when the project started so I stripped back some of the stuff I didn't think I'd need), I tired the 1/4" inch I mentioned but it wasn't large enough to allow the by-pass to to work properly.
As for the vapour lock, I also experienced that which put me on this fuel system upgrade.I'd be out about to the 1/8th stripe when at the track, then the car would nose over for a split second and then pick back up again.Originally I went for a bypass style mechanical pump but I couldn't find one with sufficient capacity to meet the engine needs. Or if it did have the required output, my installation was out of whack (more on that later) I know they're out there, but anything I tried was a failure. Enter the Holley Blue pump.
It's installed as per the picture below:
Interestingly, looking over the pictures that NoEmissions posted, I may have had success with one of the mechanical bypass pumps had I hooked it up as illustrated below: I hadn't the vaguest notion that such an arrangement would work.
Perhaps that'll be something I re-visit one day. Thanks No Emissions!
I recently discovered where the stock fuel filter is and changed it, it was full of black trash and gunk so I may set it back up to deadhead and see if that remedies it.
I thought the PO had scrapped it since a lot of this car has been molested, I had looked for it before but since it was coated with road dust and grime from a bad trans leak from one point, I didnt see it. It wasnt until the car was completely immobile and I had starting tearing everything apart to fix it did I get under it and actually find it lol
Once the new filter is installed and you've reverted back to the deadheaded fuel delivery system, you may that you're back to square one. Square one worked for me for a number of years until my fuel requirements outpaced what the OEM system could offer. Keep in mind here that my OEM system consisted of a mechanical fuel pump. That was it.
Good luck and keep us posted. These threads are great. Especially when there's a conclusion.
Interestingly, looking over the pictures that NoEmissions posted, I may have had success with one of the mechanical bypass pumps had I hooked it up as illustrated below: I hadn't the vaguest notion that such an arrangement would work.
Perhaps that'll be something I re-visit one day. Thanks No Emissions!
Thanks Skinny Z. I will also most likely be trying something like the above in the future, because like you, I also ran into the problem of the car nosing over for a split second and then picking back up again. I was making quarter mile test runs on the highway (using a G-Tech) and at the top of 2nd gear (700R4) the engine would just go flat, as if someone turned the ignition key off. Foot still to the floor while the car would sputter for a few seconds and then pick back up. Finished the run with (obviously) a terrible time, but at 107 mph. I tried different plumbing configurations, larger mechanical fuel pumps, adding the 12-803 regulator, restricting the return line, etc. I even flow tested every aspect of the fuel delivery system. No kinks in my lines anywhere. As it turns out, the stock system is a 19 gal/hr restriction from the tank to the pump. In the end, I put a small electric FP close to the tank to give the fuel a push up to the block mounted mechanical. A Band-Aid, but it worked. I never did actually solve the problem, though.
Well just for sh*ts and giggles I put my spare regulator in the return line and closed it completely. It seemed to help a little bit but nothing nominally better. Deadheading the pump just vapor locked it as before all this plumbing fiasco began. I have yet to reinstall the pump in place of the stick filter in lieu of having time to do so, so maybe that will help. I'm afraid that I'll end up having to drop the tank and change the sock and clean out the tank to fix it. So aggravating.
Okay so update. I've decided that the best route would probably be to junk the tank, I know it has rust in it and I can get this fuel cell for $50 that should fit well into the stock tank area. It comes with the sending unit, -10 AN fittings and I can just cut and weld on the filler neck. Hardest part is deciding what to do with the fuel lines. I'm positive the stock supply line is large enough but what should I do for the return? Should I even worry about it? The inlet and outlet fittings on the cell are one the front wall at the bottom so they'll be easily accessible. I'd like to stay hard lined as much as possible.
What do you have remaining from the original EFI fuel lines? The 5/16ths may provide an adequate return.
Literally everything from where the hard lines end under the hood on the LH frame rail all the way to the back, although idk what's going on in the tank, whether or not the stock pump is there or if it's a complete hack job.
I used the original EFI 3/8" supply hard line. I cut in a coarse filter between the tank and the pump. The pump is mounted in the original fuel filter location. I adapted from the LH frame rail and hardlined across the crossmember. Then to the regulator, fine filter and eventually the carb.
As I mentioned, I didn't have the 5/16ths return line so I used the 1/4" vapour line which proved too small. I think Holley recommends the same size for supply and return. So I ended up with a length of -6 braided line to the 5/16th stub still on the tank. Works 100% without issue. It may be that the 5/16ths would do the same and would have tried that first. That would have kept the all steel arrangement too.
And as mentioned by NoEmissions with this setup, I no longer have the vapour lock issues.
I suppose you could consider the short length of 5/16th line right at the tank a restriction but other than that, it's wide open 3/8" braided line.
I recommend getting a fuel pressure gauge with sufficient length of hose so you can view it from behind the wheel (outside the cabin of course). Infinitely helpful.
I have a relay centre on the firewall between the master cylinder and the RH fender and that's where I put a generic 30 amp relay. From there I ran two #12 gauge wires to the fuel pump. I zip tied them to the fuel rails. For the switching/control side of the relay I picked off a ignition tab in the fuse block so when I turn the key to on, the relay fires (small gauge 18). For the power/pump side of the relay, I've an in-line fuse from the battery. Both grounds (switching and pump) are to a local good chassis ground.
Well I have it all mocked, besides the actual return regulator, waiting for it to come in, I deadheaded the everything, temporarily disconnecting the return line and plugging it off at the regulator. I tested it to see if it would hold fuel pressure and my glass filter completely drained backwards back into the feed line. Any insight?
Well I have it all mocked, besides the actual return regulator, waiting for it to come in, I deadheaded the everything, temporarily disconnecting the return line and plugging it off at the regulator. I tested it to see if it would hold fuel pressure and my glass filter completely drained backwards back into the feed line. Any insight?
Is that to say with the engine running the filter was full but when you shut down, the filter drained?
No, I just key-on tested it to see if it would pressure up and to check for leaks. Used to, back when I used to deadhead the pump before vapor lock became an issue, it would always completely fill the filter up so this time around I wanted to see if it would do the same but instead, what gas was sitting in the filter back fed when I turned the key on and never filled back up. This only happened once I took the return off, it was fine before.
No, I just key-on tastes it to see if it would pressure up and to check for leaks. Used to, back when I used to deadhead the pump before vapor lock became an issue, it would always completely fill the filter up so this time around u wanted to see if it would do the same but instead, what gas was sitting in the filter back fed when I turned the key on and never filled back up. This only happened once I took the return off, it was fine before.
That's really strange. Are the IN and OUT of the FP hooked up correctly?
That's really strange. Are the IN and OUT of the FP hooked up correctly?
As far as I know and I checked multiple times but come to think of it, I did hear a gurgling/bubbling noise in the tank once I cut the pump on. For all I know, although i checked like 5 times before committing to a mounting spot, it's probably backwards and sucking my line dry
I'll be on it tomorrow after work, I did want to ask though, where'd you mount your pump? I put mine directly under the driver side backseat pan as close into the fuel filter area as I could, but it just seems so low. I'm thinking about moving it further back and up some on the incline toward the tank...
It's all soft line until I can get a routing and setup working that I can commit to so I'm trying to nail this thing before I use up all my rubber fuel line test fitting everything lol
As far as I know and I checked multiple times but come to think of it, I did hear a gurgling/bubbling noise in the tank once I cut the pump on. For all I know, although i checked like 5 times before committing to a mounting spot, it's probably backwards and sucking my line dry
I'll be on it tomorrow after work, I did want to ask though, where'd you mount your pump? I put mine directly under the driver side backseat pan as close into the fuel filter area as I could, but it just seems so low. I'm thinking about moving it further back and up some on the incline toward the tank...
I mounted a small pusher pump to aid the block-mounted mechanical under the car on what would be the back seat rests (above the hump).
I've placed my pump where the original fuel filter was. As a pre -filter, I've a billet piece between the pump and the tank tied to the vertical portion of the "frame". So far, no ill effects from having the pump in that position.
This is before the rubber line was replaced with braided steel and the up-sized return line was added.
Fuel filter mounted vertically (hard to tell from the picture angle) between the pump and the tank.
Well I moved the pump a further back and a little higher so that it would be in danger of being hit by debris or anything in the road. The system is pressuring up enough to send fuel to the filter but still not filling it up like it should. I didnt get a chance to put the return back on since one of my fittings decided to develop an unstoppable leak. I'm about ready to sell this car, nothing I do seems to help anything and even the simplest of tasks always end up being a wholesale size can of worms. I'm tired.
Well I moved the pump a further back and a little higher so that it would be in danger of being hit by debris or anything in the road. The system is pressuring up enough to send fuel to the filter but still not filling it up like it should. I didnt get a chance to put the return back on since one of my fittings decided to develop an unstoppable leak. I'm about ready to sell this car, nothing I do seems to help anything and even the simplest of tasks always end up being a wholesale size can of worms. I'm tired.
I'll address the discouraging tone of your reply rather than the technical side.
Is this Camaro of yours a hobby? If it is, put it in perspective and realize that it's not life and death and that setbacks are all part of it. I've had several snags with the continued development of mine and have simply packed it away into storage while I muster up the resources, both of time and money, to get it back on track (no pun intended). In the meantime, while I very much miss the late summer evening cruises or bettering my previous personal bests at the track, I've let it go while I pursue what's important at the moment. That I bought a money pit of a house (intentionally) may help you understand somewhat my current situation.
If it is your daily driver, I can offer my sympathies. It's really not cut out to be that when it's a work in progress as you've described. I have driven mine as everyday transportation but that's after getting everything ironed out in one of it's many iterations or another. Then I break it. And the process repeats.
Not trying be preachy or anything. Just offering a little moral support while you get this project of yours sorted out.
Good luck and keep posting.
It's been my daily from 2013-2016. The torque converter went bad and warped the flexplate, I sat it up with intentions of fixing it that fall but sat for 3 years before I replaced them. Now I'm in the process if buttoning up a few odds and ends but things like this that should be simple and up being a month or 2 ordeals. I've been waiting to put plates and insurance on it but everytime I think I have it fixed-things like this pop up. It ran fine before any of this with my original deadhead setup but was very susceptible to vapor lock during the summer. So I figured while I had it down, I would plumb in a return and move the pump where it should've been to begin with (it was under the hood where the washer reservoir used to be) according to everyone and everything I've read. I'm thinking it may have an air bubble in it. Deadhead systems dont like air bubbles because they cant purge them as easily but I cant claim to be an expert because this is whipping me lol.
Don't get discouraged. What you are experiencing IS one of the problems with these cars. When I put mine back on the road, I'm going to have to go through the same also. Just take a break. You must realize these cars are far from new (30+ years old) and are going to have their share of problems. And YES, they pop up at the worst times. We all go through it - that's life. When you get it sorted, you will feel better.
Well I slept on it and I'm pretty sure it's an air bubble. After soaking both my arms in gas and smashing my hand last night, my mood wasnt exactly car friendly lol
Back when I had just the pump and regulator here under the hood, when changing the filter or anything that involved opening the fuel line up, it would do the same thing until I cracked open the line and bled their out so hopefully sometime this week, I can try that and hopefully it'll work.
Would it be worth the trouble of wiring the pump to the original fp relay and if so, anyone know which wire off the top of their head would go to the pump?
Well I slept on it and I'm pretty sure it's an air bubble. After soaking both my arms in gas and smashing my hand last night, my mood wasnt exactly car friendly lol
Back when I had just the pump and regulator here under the hood, when changing the filter or anything that involved opening the fuel line up, it would do the same thing until I cracked open the line and bled their out so hopefully sometime this week, I can try that and hopefully it'll work.
I'm surprised that the Holley pump even works in that location because electric fuel pumps are better at PUSHING the fuel and it has a lo-n-g way to PULL fuel from the tank where it is in that picture.
Yea I know, crazy thing is, I ran it like that for years, only reason i ever had to change the pump was because the little electrical board on top of the pump developed a short. Now I just have to replace a fitting and I'm waiting for my new regulator and pressure gauge to come in and hopefully this fuel pressure ordeal will be over with.
Long story short, the BP reg is a must have, moving the pump to the rear is also essential, and you may have better luck with a carter sytle pump. Good luck and hope it goes better for you.
Well after I got everything plumbed, leak free and ready to go, I went to start it and it shot a load of fuel into the engine, flooded it and most likely hydro locked it and burnt the *24th* starter up. I'm done. In the weeds it goes until I can LS swap it.
Use a Holley "RED" pump instead of "BLUE". The RED pump has a built in fuel pressure regulator and only puts out 5-7 psi. Perfect for a carb setup. I've used them on several cars.
07-04-2019, 07:53 PM
lmao 
