1988 300 efi to carb questions

[Jamesfarmtruck]

Hi, i have a 1988 ford f150 4.9L M50d.
im doing a efi to carb conversion on my truck and so far i have everything figured out, except the fuel.
I heard that the efi system uses around 40-50psi which is too much for the carb.
is there any way to bring it down to its recommended carb psi (which is i think supposedly 7psi?) without using a regulator?
Ive heard you can do something with the pumps in the fuel tank to bring it down but i need more information? Help. Thank you.

 

[sixtseventwo4d]

Your 88 should have a supply pump in the tank. The high-pressure pump is on the frame rail, driver's side. Simply bypass the high-pressure pump and disconnect the electrical to it also (no need in letting it run). You should then check the pressure to make sure the in-tank supply pump is adequate to use; as some get weak over the years and may not do well. Most carb pressure requirements are in the 3-4 psi range.

 

[63 Sprint]

Jamesfarmtruck, welcome aboard!!!

The in tank primary pumps on the 1987 to 1989 trucks work fine.

As sixtseventwo4d mentioned: Start with bypassing the frame mounted high-pressure pump and disconnect the electrical to it.

You will still need a pressure regulator with a return because the in tank pump needs constant fuel circulation. Otherwise the pump will deadhead and fuel pressure will rise above rated pressure and fail. Constant fuel flowing through the pump keeps it cool.

Here is a picture of my regulator setup:


The supply line to the carburetor is kept as short as possible. It’s 16” long and the line is insulated with high temperature insulation.

The regulator is mounted on the bracket that secured EFI plenum to the head.

The Feed and return lines are also insulated with the same insulation. The feed and return are only insulated to the frame mounted fuel filter just under the cab near the bottom of the firewall.

In my case, a low pressure regulator was only needed since I’m only using the in tank primary pump that is rated to about 7 psi.

This setup has been reliable even in the hottest weather over 100+ degrees F. Even if the fuel boils out of the carb. The pump reprimes the fuel system to the carb immediately with no problems. In such hot weather, the only thing that I do to make the truck run normally when sitting for 10 minutes after shutting down is, once restarted, I blipp the throttle twice get fuel back in the carbs fuel circuit and then I’m off driving normally. This whole event that happens in just the hottest days lasts for about ten seconds. I might be able to eliminate this altogether if I use a heat shield and two carb insulating base gaskets.


Another picture to show the mounting location of the regulator. The bracket that secures the upper part of the EFI manifold to the head made installation simple.

The fuel pump relay on the driver side fender well stayed in place. The only thing I had to do was rewire it so the fuel pump would operate properly. I’ll cover this later today it’s very simple.

The inertia switch is still used. I wanted this safety feature to stay. Reason is if the truck ever gets in a bad accident. There is a better chance that the fuel pump shuts off if a driver becomes unconscious, or is unable to turn the ignition switch to off.

 

[63 Sprint]

Here is the pressure regulator and fuel pressure gauge that is being used.

Holley 12-881 Holley Carburetor Bypass Style Fuel Pressure Regulators | Summit Racing

Free Shipping - Holley Carburetor Bypass Style Fuel Pressure Regulators with qualifying orders of $109. Shop Fuel Pressure Regulators at Summit Racing.

www.summitracing.com

Summit Racing SUM-800139 Summit Racing™ Fuel Pressure Gauges | Summit Racing

Free Shipping - Summit Racing™ Fuel Pressure Gauges with qualifying orders of $109. Shop Gauges at Summit Racing.

www.summitracing.com

 

[InlineDave87]

If you dont want to swap distributors you can put a tps mounting bracket onto the carb and swap your sensor from the throttle body to that bracket on the carb. Might have to extend the wiring. Good luck, id like to hear your results as i have heard others say they regret doing the conversion.

 

[Frank]

Hi, i have a 1988 ford f150 4.9L M50d.
im doing a efi to carb conversion on my truck and so far i have everything figured out, except the fuel.
I heard that the efi system uses around 40-50psi which is too much for the carb.
is there any way to bring it down to its recommended carb psi (which is i think supposedly 7psi?) without using a regulator?
Ive heard you can do something with the pumps in the fuel tank to bring it down but i need more information? Help. Thank you.

I converted a '90 to carb. It lost power and economy took a big hit. The main reason is the ignition system swap. The EFI head requires precise timing control, and there is NO aftermarket or Ford centrifugal/vacuum advance distributor that will be right for it all the time.
If you can keep your EFI ignition system, it will greatly enhance the swap to carb. What InlineDave87 suggested above- speaking from experience!-
I highly recommend. It will be some work. You need to keep the intake manifold sensor, throttle position sensor, MAP sensor, Coolant temp sensor and the Knock sensor. . I know mine would be much better, especially economy, if I had kept the factory ignition system with the carb.

 

[Jamesfarmtruck]

I Want to thank all who shared the info on how to best get this conversion done without breaking the bank ..my son and i are pleasantly surprised just how good this truck now runs and drives it has never run this smooth and makes great power. Many people said it would not run as good as the EFI well I’m here to tell you it runs excellent so smooth and quiet and very simple to work on now

 

[63 Sprint]

This is great news. It looks familiar. I see you kept the large EFI fuel filter in place. Great move.

Periodic checks on the screw type hose clamps are recommended. I changed to crimp on clamps a while back. Special crimp pliers are used. They work very well. Changed over to crimp hose clamps on most of my equipment. Still do periodic checkups.

 

[InlineDave87]

Might i recommend putting an oil catch can too? Keep the fuel going into your engine clean. Also a carb cheater might help too. Congrats on making it work.

 

[Oldtimeford6]

I am curious about the accelerator cable. I have a 96 and want to convert it back to rid myself of all the other sensors acting up anytime they want and sticking me on the road with no one around. I want to get an 85 intake with carb and try to go back with points. I ran trucks many many years with that set up and then i get this 96 and nothing but troubles on it. What cable did you use?

 

[63 Sprint]

I am curious about the accelerator cable. I have a 96 and want to convert it back to rid myself of all the other sensors acting up anytime they want and sticking me on the road with no one around. I want to get an 85 intake with carb and try to go back with points. I ran trucks many many years with that set up and then i get this 96 and nothing but troubles on it. What cable did you use?

Oldtimeford6,
Welcome aboard!

Below is a link that has information that might be of interest.

https://fordsix.com/threads/good-fuel-economy-mild-performance-gains-can-be-achieved-on-a-stock-internal-4-9-efi-engine-converted-to-carburetor.86418/#post-705694

If you have any questions, send me a PM.

 

[sixtseventwo4d]

I am curious about the accelerator cable. I have a 96 and want to convert it back to rid myself of all the other sensors acting up anytime they want and sticking me on the road with no one around. I want to get an 85 intake with carb and try to go back with points. I ran trucks many many years with that set up and then i get this 96 and nothing but troubles on it. What cable did you use?

Is yours auto or standard?

 

[Oldtimeford6]

Oldtimeford6,
Welcome aboard!

Below is a link that has information that might be of interest.

https://fordsix.com/threads/good-fuel-economy-mild-performance-gains-can-be-achieved-on-a-stock-internal-4-9-efi-engine-converted-to-carburetor.86418/#post-705694

If you have any questions, send me a PM.

Thanks, so far i have an old 60's one barrel on my 70s-80s intake. same exhaust all on my efi 90 model converted, point ignition. I think the one wire alternator avoids a lot of problems with regualtion in the wiring. I wanted to convert to a two barrell intake but digs in the pocket some unless i can find one i can assume to afford. I have the mechanical fuel pump and an electric one for back up if ever down in the boonies with no way out, same with the electronics, i dumped them so far on my 79 super cab. I got this 96 six now and i got a tremendous amount of sensor and wiring problems i am trying to run down. It starts, goes dead, starts again, shakes a little and drops out again over and over. I took the pump out today and tomorrow i check it direct with a gauge to see how much it is kicking. If bad, that resolves the upline problems. If not, i have to go from scratch running from the filter to the pressure sensor and the other what nots to check out, crank sensor, aic, throttle, etc. vaccum is well and good and the funny part was that i could choke the breather tube and it would run with slight choke, let go and it would die. I cannot understand what it is doing by this.

 

[ka4wog]

View attachment 20429I Want to thank all who shared the info on how to best get this conversion done without breaking the bank ..my son and i are pleasantly surprised just how good this truck now runs and drives it has never run this smooth and makes great power. Many people said it would not run as good as the EFI well I’m here to tell you it runs excellent so smooth and quiet and very simple to work on now

I saw you used HEI in your conversion, just curious if you had it recurved or what you did to make it work.

 

[Frank]

I saw you used HEI in your conversion, just curious if you had it recurved or what you did to make it work.

He may not answer, has been off the sight for over a year. As we've addressed on your thread, the HEI has too much timing advance for the Ford EFI head, period. HEI is a Chevy distributor originally. The Chevy takes 40+* of timing, the EFI Ford low 30's max, and frequently in the 20's. There is no mechanical distributor set up for an EFI conversion, the timing curve is different than any carbureted engine, including the carb-head 300.
HEI, or Ford points distributor or Ford DS2 distributor- all will have too much timing for the EFI head. You can recurve it yourself or have it professionally done.
On my conversion, I started with a HEI distributor. I didn't know then what I'm sharing with you here. I knew the engine was sluggish, but when I discovered the reason, I was shocked, and thankful I didn't blow a head gasket or burn a piston. The timing was so far over advanced the engine didn't even ping. Required removing 15* from the total advance.

 

[63 Sprint]

ka4wog,
It hasn’t been mentioned in a while. Some aftermarket HEI mechanical advance flyweights and linkage wear out very quickly and could start malfunctioning.

If you don’t have the experience and proper equipment to properly recurve a distributor, it’s best to have someone that has the equipment, knowledge and expertise. Otherwise you could wind up with a damaged engine.

Many times detonation cannot be heard. And people wonder what happened when their engine suffered internal damage.

With the EFI 4.9 conversion. It’s critical to get the timing right. This was mentioned earlier in your thread. Members with good knowledge gave you proper advice. The best thing you can do is follow their advice.

It’s been mentioned that the HEI distributor is not a wise move. It’s best to buy a DuraSpark II. And, for now, there are ways to save money on the ignition controller if you don’t want spent the money on an MSD6A ignition control box right now.

Then plug wires. This is what I would recommend:

The impedance on these wires are only 40 to 50 ohms per foot.