76 cj modified fuel system question - JeepForum.com
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post #1 of 18 Old 07-03-2020, 07:24 AM Thread Starter
Submariner
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76 cj modified fuel system question

I picked up a 76 CJ that the engine has been swapped from a 258 to a 360. Of Course PO did some fine work but I have a question about what all he has done to modifiy the fuel system.

Removed the Manual fuel pump from the engine to replace it with an electric one. but he also added this to it. What is it and how can you adjust it, If you can?

Seems that the engine is running a little rich. I have a 2 barrel on it right now. Seems that I have some after ignition knock while running with applied throttle. Just tying to make the ole girl run out smooth.

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post #2 of 18 Old 07-03-2020, 07:33 AM
John Strenk
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Thats a fuel pressure regulator.

Looks a lot like a Holley

https://www.holley.com/products/fuel...ed_regulators/

Pick one that matches yours for more info.

Usually there is a screw at the top you adjust the pressure and a locking nut.

iF you want it to run good, get rid of that Prest-o-Dark ignition system.
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post #3 of 18 Old 07-03-2020, 07:59 AM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
Thats a fuel pressure regulator.

Looks a lot like a Holley

https://www.holley.com/products/fuel...ed_regulators/

Pick one that matches yours for more info.

Usually there is a screw at the top you adjust the pressure and a locking nut.

iF you want it to run good, get rid of that Prest-o-Dark ignition system.
How about more info on the ignition system please. Thanks

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post #4 of 18 Old 07-03-2020, 08:07 AM
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That is probably the worst ignition ever fitted to a Jeep. The vacuum capsule has a reputation for cracking and the box of tricks to stop working.

A cheap change is to a Motorcraft style Duraspark II setup. A later distributor with a large distributor cap and a Duraspark module.

Lots of other choices.

Your fuel filter is fine but does your 76 have a tank return line? If so have you got the 3 way filter between regulator and carb? It will run better if fitted.
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post #5 of 18 Old 07-03-2020, 10:04 AM
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Get a Duraspark II distributor and control module for a later year AMC V8. But requires some more wiring.

Or get a HEI setup for the AMC V8. That just needs 1 wire to get working.
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post #6 of 18 Old 07-05-2020, 08:12 AM Thread Starter
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As far as I know, there is no return line to the tank. could poss a problem.

I did put a new distributor, plugs, wires, and coil from napa and parts were motorcraft. used the stock autolite plugs(65?).

Question about the vacumm module? more info please.

Also when I put in the new distributor, I did not hook up a vacuum line to it. Caused all kinds of issues, seems to work well with the mechanical advance. Also only hooked up 2 wires of the 3 for the distirbutor. should i ground the 3rd wire?

Anything else that you can think of that I should change out.

I can post more pictures

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post #7 of 18 Old 07-05-2020, 08:15 AM Thread Starter
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When driving. I noticed that when applying throttle and the VAc gage drops below 10" then it starts to ping/knock, as soon as it gets above 15" it settles out and runs smooth again.

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post #8 of 18 Old 07-05-2020, 11:17 AM
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That Holley fuel regulator is a dead head style. There is no return line to the fuel tank coming from that regulator. Your engine should run fine with this style regulator, provided it is adjusted properly for the carburetor you are running. I don’t see a pressure gauge, so it has probably never been adjusted. Additionally, where yours is mounted, it would be difficult to make an adjustment. They are set at 5-6 PSI from the factory, which is probably correct for most carburetors, but don’t quote me on that. The only carb I have any real experience with is the Q-jet, and the Holley 850 DP. All of my experience is in drag racing, where the initial launch and WOT acceleration is the biggest concern.

I have run one for years on my race car. I have seen this regulator on many street cars, hot rods and drag race cars. It is a very popular low cost regulator that normally comes with the Holley Blue, and Holley Black electric fuel pumps. I have a two pressure gauges on my junk, one at the regulator, and another on the interior where I can monitor it. My Q-jet needed 6.5 PSI. Later I switched to E-85 fuel, and a Holley 850 DP carb, which I run at 7 PSI.

The adjustment screw and lock nut for adjusting the pressure is on top. The fuel feed (in) is at the bottom. You can run two fuel lines, to feed two carbs, one on each side. The adjustment screw requires a 7/32” Allen wrench, the lock nut requires a 5/8” wrench. To adjust Pressure break torque on the lock nut, and turn the screw to adjust. Once you have your pressure set, torque the lock nut.

What fuel pump are you running?
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post #9 of 18 Old 07-05-2020, 11:51 AM
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Quote:
Originally Posted by Submariner View Post
As far as I know, there is no return line to the tank. could poss a problem.

I did put a new distributor, plugs, wires, and coil from napa and parts were motorcraft. used the stock autolite plugs(65?).

Question about the vacumm module? more info please.

Also when I put in the new distributor, I did not hook up a vacuum line to it. Caused all kinds of issues, seems to work well with the mechanical advance. Also only hooked up 2 wires of the 3 for the distirbutor. should i ground the 3rd wire?

Anything else that you can think of that I should change out.

I can post more pictures
What two of the three?
Did you set the timing on the engine?
Maybe your base timing is way off. Hooking the vacuum advance and you initial timing being too far advanced will give you problems.


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post #10 of 18 Old 07-06-2020, 07:51 PM
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These (and all threads by JH) is worth a read;

https://www.jeepforum.com/forum/f8/t.../#post13151502

https://www.jeepforum.com/forum/f8/i...jeeps-1302352/

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post #11 of 18 Old 07-06-2020, 10:12 PM
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So you are running a Prestolite module with a Motorcraft style later distributor without the vacuum being hooked up?

But did the Prestolite module not supply a true Hall effect trigger with 12 volts? As far as I am aware this is not the type of trigger used in the Duraspark distributor. The Prestolite trigger was an earlier technology, the industry moved to a variable reluctor type trigger that is very common .

In fact the 12V trigger was one of the weaknesses of the Prestolite system, it had to be set up in a certain way and could ground, wiping out the module.

I have not heard of someone using a Duraspark trigger with a Prestolite module. Are you sure your module is compatible with the trigger in the new distributor?

I just ask as I have no idea what shape signal curve they both would produce and whether they are the same and whether running the Motorcraft sensor at 12V is going to cause a problem.

If you have running problems, it may be because you have the two systems mixed together.

My previous comment about the vacuum module was concerning the vacuum advance capsule on the side of a Prestolite distributor. Sounds like you have replaced it.

You may consider changing out to a Duraspark or HEI module (both work with the Motorcraft trigger, both about the same cost, you can get factory wiring harness for the Duraspark) or even CDI and hooking the vacuum up to manifold vacuum. As long as you have 8 to 10 degrees static timing this should work fine, but the timing marks should be verified.

You also need that tank return installed, I would put in the stock 3 way filter after the regulator and plumb it from there.

The third wire is black and is a ground. In a Duraspark it is the main ground for the module but I suspect it has a secondary purpose as a shield for thr sensor wires. I would defo have it connected at the distributor, even if you do not connect it to the Prestolite module.

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post #12 of 18 Old 07-11-2020, 07:10 AM Thread Starter
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When I turn on the jeep., the electric fuel pump is making some wierd load noises. Is that due to no fuel return line? I am going to look for some diagram on how to get a return line hooked up and install it.

What are advantage of a electric fuel pump over the old engine operated fuel pump?

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post #13 of 18 Old 07-11-2020, 07:31 AM
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What type of fuel pump have you got? Where is it mounted?

The carb will not like more than 6psi, prefers less. This could be why a FPR has been fitted, the pump is over specced.

The best electrical type IMHO is the Denso and Facet types, they are solenoid positive displacement and consist of two check valves and a shuttle that is electrically induced to move back and forth. You can hear them rapidly clicking on startup, slowing down as the pressure builds to around 5-6psi. My last purchase of a Denso was $12, I doubt the Made in Japan sticker is original. Much copied and used on many lawnmowers these are adequate for a Jeep.

The worst is a centrifugal turbine type, such as a Bosch 044 which is $140+. They put out over 50psi but are poor at sucking fuel, they are meant for fuel injection but are often fitted by PO. A FPR is needed to reduce the pressure to 6psi. They make a whirring and humming sound and need to be mounted in a rubber sleeve. Waste of time.

A mechanical fuel pump is less than $30. They can last 30 years before failing. They deliver a fluctuating 6psi. A 3 way filter to the tank return blends out these fluctuations. Tehy do not require an electrical supply or special mounting or an FPR. They are silent. This is the best pump on a Jeep.

I have just converted my J20 back to mechanical, a Carter model that cost $28. The noisy POS pump on the frame is gone. It is soooo good now.

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post #14 of 18 Old 07-11-2020, 08:38 AM
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There are a few different ways to control fuel pressure and in most cases the mechanical fuel pump they designed with you system is just fine. But I'm not fond of an electrical pump and the regulator you are using.

The reason the car manufactures use the rail type regulators (bypass) for the electric pumps is that it keeps the pump running cooler. Lets say your electric pump is rated at 10 psig @ 1 gallon a minute fuel flow (i'm just tossing numbers here) and you fuel system requires 6 PSIG. The rail type will bleed off the excess pressure and return it to the fuel tank via the return line. This allows the pump to maintain a steady flow rate and helps to keep the pump cool.

On a down stream type regulator like what you have (bottom picture) , given the same pump specs, the regulator is only going to allow enough flow to maintain the downstream pressure so the pump is dead headed against the regulator which causes and excessive load on the pump, its pumping but has no where to go.

There are regulator made for your application, they are normally called bypass regulators, middle picture. Holley 12-881 is just one of many.
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post #15 of 18 Old 07-11-2020, 12:34 PM
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Would that even do any pressure regulation hooked up the last way?


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