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Discussion Starter · #1 ·
7 PSI for my fuel pressure!!!

Hi All,

I just registered a 7psi of fuel line pressure for my EFI system. It took a couple of hours to get the gauge in-line and once I fired up the engine, I at first thought I had no pressure.

I spoke with Gil earlier and he told me it should be between 33-43 psi. I revved up the motor and initially, the pressure dropped to around 3.5psi and then as I'm holding the revs up a bit, the pressure returned to 7psi. Never any higher.

It seems like I need a new fuel pump. But my I can't seem to make any sense of the fact that as I open the throttle, my fuel pressure actually goes down. Why is that? Or is this just another indication that my fuel pump is bad?

I've done a search on this subject and didn't find anything relevant. But I did find a lot of discussion on surge tanks. I have experienced fuel starvation numerous times and would be interested in knowing if there is an off the shelf tank that someone here has found that works well on our GTs. I'm going to do a search on readily available surge tanks and hope to find something that can just work.

Thanks for any info you might provide,

Manny
 

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Fuel Pump

Manny:

If you are using the stock fuel pump, I don't believe you are going to get much more than that. I believe that you need an electric pump with the capacity to deliver the pressures Gil mentioned. You didn't indicate the type of fuel pump you were using, but I am suspecting stock. Probably need to convert to electric.

Bob :)
 

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Manny, you need to have the pressure Gil stated. It take that pressure to get the fuel atomized into the combustion chamber. A surge tank is a good idea, but, in order for one to work correctly it needs to be vented and/or overflow back to the fuel tank. Check out my recent Willit? thread posts, I've got pics of what I'm using for the V-6 with Sequential Fuel Injection. I've got a low pressure filter between the tank and an electric feeder pump at the rear of the car. The feeder pump fills the surge tank which overflow back to the fuel tank. The surge tank feed a high pressure electric fuel pump, which bleeds off fuel in excess of 70psi. That bleed fuel also goes back to the gas tank. From the high pressure fuel pump, I've got a 100 psi filter, I don't want bits and pieces of the fuel pump going to the fuel rail if it breaks apart. Then the fuel goes to the fuel rail where a pressure regulator on the rail bleeds off pressure in excess of 50 psi. That bleed fuel also goes back to the gas tank. I put an extra fitting in the filler neck of the gas tank for the overflow and bleed fuel to go back into the tank. If you want, I can draw up a schematic to show how I did all this stuff. But what you can do is go to your local auto parts store, check out their fuel pump books and get a pump that puts out 40-50 psi and a feeder pump that will keep your surge tank full as your high pressure pump feeds the fuel injectors. The reason your pressure drops now, is because you don't have enuff pressure to begin with and as your engine accelerates the injectors are opening faster that the pump can keep up with as the EFI sense a throttle opening and enriches the fuel mixture. Once a stable RPM is reached the pump then catches up, but it's still not enuff pressure or volume for proper fuel atomization so you go into fuel starvation. Not a good thing. Anything else you need to know or have any more questions, lemmee know.
 

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Hunch ...

I have a feeling that you are measuring the fuel pressure in the fuel return line and not in the injector rail. I don't think a Bosch FI system will run with fuel pressure that low at the injectors - I know my Isuzu system which is based on the Bosch type, just cuts out if fuel pressure drops below 33 psi.
Found that out in traffic when the fuel pump finaly failed.
 

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Discussion Starter · #5 ·
TealCarver,

It's an electric pump for an EFI system.

Ron,

Thanks for the offer. I'll read thru your Willit thread more closely. I've only scanned thru it looking for specifically what I was dealing with.

Jim,

I hooked into the fuel line just before the metal marshmallow (for lack of a technical term). Is this the return or the supply line? I'll take a look again in a little while.

Thanks guys,

Manny
 

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Stock fuel pump pressure . . .

tealcarver said:
Manny:

If you are using the stock fuel pump, I don't believe you are going to get much more than that. I believe that you need an electric pump with the capacity to deliver the pressures Gil mentioned. You didn't indicate the type of fuel pump you were using, but I am suspecting stock. Probably need to convert to electric.

Bob :)
Sorry, but stock fuel pump delivers 3.5 psi at most! Solex, Weber, Dell'Orto carbs require low pressure/high volume. Much higher pressures than this will cause all sorts of problems with these carbs!
 

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FI regulator connections

gtzero said:
TealCarver,

It's an electric pump for an EFI system.

Ron,

Thanks for the offer. I'll read thru your Willit thread more closely. I've only scanned thru it looking for specifically what I was dealing with.

Jim,

I hooked into the fuel line just before the metal marshmallow (for lack of a technical term). Is this the return or the supply line? I'll take a look again in a little while.

Thanks guys,

Manny
FI regulator connections explained below.
 

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Fuel Pressure

Let me ask some background questions. What did you take the EFI system from that you are using? Is it the Manta/Ascona Bosch L-Jetronic? If so, Gil is 100% correct. At idle you should have about 40-44 psi of pressure at the fuel rail. This measurement is easily taken by placing a 3/8 inch tee fitting on the cold start feed line that fits on the the cold start injector at the rear of the intake manifold.

If, on the other hand, you have the LE-Jetronic with no cold start valve, you must obtain the input fuel pressure from the high pressure side of the fuel system going to the fuel rail.

I've experienced over pressure of 100 PSI based on the return line being blocked. You'd know it if that were present. You'd have fuel coming out everywhere. Not good! I don't think that system would operate if you only had 7 PSI on the rail.

Where is it plumbed in and how did it take 2 hours?

Good luck with that.
 

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FI system fuel pressures . . .

David McCollam said:
Let me ask some background questions. What did you take the EFI system from that you are using? Is it the Manta/Ascona Bosch L-Jetronic? If so, Gil is 100% correct. At idle you should have about 40-44 psi of pressure at the fuel rail. This measurement is easily taken by placing a 3/8 inch tee fitting on the cold start feed line that fits on the the cold start injector at the rear of the intake manifold.

If, on the other hand, you have the LE-Jetronic with no cold start valve, you must obtain the input fuel pressure from the high pressure side of the fuel system going to the fuel rail.

I've experienced over pressure of 100 PSI based on the return line being blocked. You'd know it if that were present. You'd have fuel coming out everywhere. Not good! I don't think that system would operate if you only had 7 PSI on the rail.

Where is it plumbed in and how did it take 2 hours?

Good luck with that.
Actually, you will see lowest system pressure, ~34psi, due to highest vacuum being applied to the FPR and bleeding off some pressure, ~9psi, from maximum, ~43psi. Fuel pressure requirements are least at idle, greatest at WOT.
 

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Discussion Starter · #10 ·
26-38 Psi

OK, here's where I'm at now.

What I have is the LE system from what I've gathered from all of your replies. No cold start injector. It took me 2 hours because I have very limited space in my garage and even more limited space in and around the intake manifold. Or maybe I'm just not aware of a quicker way. But basically, I had to take all the connections off of the fuel rail to re-connect the fuel pressure gauge. Now it is in the correct position to get the correct readings.

When I fired up the engine, I saw 30 PSI. It gradually dropped to 28 within a few seconds. Then I revved the engine a bit and the highest that it registered was 38 psi. As I continued revving the engine, I noticed that the lowest pressure was now 26 psi. It would sometimes rise a bit to settle at 28 psi. Then I'd rev the engine again and back down to 26 psi.

When I hold the throttle open, not WOT, then pressure reading initially goes up to a maximum of 38 psi depending on how quickly I open the throttle and then drops down to around 33 psi with the throttle opened to a steady position.

Does this sound more like a clogged filter than a bad fuel pump? Or maybe both?

Thanks,

Manny
 

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Discussion Starter · #11 ·
Reason for all this...

I started loosing power while driving. It felt like fuel starvation. Everything looked fine as far as my gauges but I'd play with the throttle and it would do nothing. Just basically coasting. Then suddenly, it would start running correctly.

The other morning, as I started the car, I noticed she sounded a little different. A bit "flat". As I backed out of the garage, she started cutting out. I'd play with the throttle and got some intermittent response. And then as I tried to proceed down my street, the engine died. I restarted the engine right away. No difficulties in restarting but again, it was all I could do to keep the engine running and limp back into the garage.

This is when I started checking thru my fuel system. I disconnected the fuel line at the back of the car and gas flowed readily. So I don't think there's any obstructions in the tank. And now I'm checking my fuel pressure.

Manny
 

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gtzero said:
OK, here's where I'm at now.

What I have is the LE system from what I've gathered from all of your replies. No cold start injector. It took me 2 hours because I have very limited space in my garage and even more limited space in and around the intake manifold. Or maybe I'm just not aware of a quicker way. But basically, I had to take all the connections off of the fuel rail to re-connect the fuel pressure gauge. Now it is in the correct position to get the correct readings.

When I fired up the engine, I saw 30 PSI. It gradually dropped to 28 within a few seconds. Then I revved the engine a bit and the highest that it registered was 38 psi. As I continued revving the engine, I noticed that the lowest pressure was now 26 psi. It would sometimes rise a bit to settle at 28 psi. Then I'd rev the engine again and back down to 26 psi.

When I hold the throttle open, not WOT, then pressure reading initially goes up to a maximum of 38 psi depending on how quickly I open the throttle and then drops down to around 33 psi with the throttle opened to a steady position.

Does this sound more like a clogged filter than a bad fuel pump? Or maybe both?

Thanks,

Manny
Change fuel filter and hopefully pump will not yet have been damaged by it. Another very likely cause is inside-tank strainer (very fine copper mesh) being clogged up with minute rust particles from tank. Common problem with FI cars left setting for long periods of time. REALLY messes up pump intake volume at tank!
 

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Classic Symptoms ...

Manny, Your car is showing the classic symptoms of FI fuel starvation. There are three main possible causes:
1) Blocked fuel filters. Check the sock filter in the tank (search for "Sock Filter in Fuel Tank" thread). If you remove the filter inside the tank then you will need a high capacity fuel filter in the line from the tank and BEFORE the high pressure FI fuel pump - they hate rust particles!
There is usually another high pressure fuel filter AFTER the FI fuel pump to make sure no bits and pieces get into the fuel rail and injectors - they like rust particles even less! Check that all fuel filters are free flowing and not blocked.
2) A tired fuel pump. FI fuel pumps deteriorate quickly if left dry for any length of time and are rapidly destroyed by pumping any paricles of rust or even thread seal tape. Most auto repair shops can now days check the output of a FI fuel pump to see if it is OK.
3) Fuel pressure regulator set too low or jammed partially open with ... wait for it ...... rust particles.
HTH
 

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Discussion Starter · #14 ·
GTJIM said:
Manny, Your car is showing the classic symptoms of FI fuel starvation. There are three main possible causes:
1) Blocked fuel filters. Check the sock filter in the tank (search for "Sock Filter in Fuel Tank" thread). If you remove the filter inside the tank then you will need a high capacity fuel filter in the line from the tank and BEFORE the high pressure FI fuel pump - they hate rust particles!
There is usually another high pressure fuel filter AFTER the FI fuel pump to make sure no bits and pieces get into the fuel rail and injectors - they like rust particles even less! Check that all fuel filters are free flowing and not blocked.
2) A tired fuel pump. FI fuel pumps deteriorate quickly if left dry for any length of time and are rapidly destroyed by pumping any paricles of rust or even thread seal tape. Most auto repair shops can now days check the output of a FI fuel pump to see if it is OK.
3) Fuel pressure regulator set too low or jammed partially open with ... wait for it ...... rust particles.
HTH
I mentioned earlier that I checked the tank by taking the hose off at the rear of the car and fuel flowed like a water faucet. No obstruction.

I have the setup you described in #1. I'm planning on replacing the filters since it's been 10yrs.

I'll also have the pump tested.

As for #3, how do you "set" the pressure regulator? As far as I can see, there's no place for adjustment.

Thanks,

Manny
 

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gtzero said:
As for #3, how do you "set" the pressure regulator? As far as I can see, there's no place for adjustment. Thanks, Manny
You are right - the stock L, LE and LH fuel pressure regulators are not adjustable. Most add-on ones are adjustible as increasing the fuel pressure is one way to increase the fuel flow through the injectors if the system is running lean after engine modifications.
 

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Clogged in tank filter.

Your symptoms are indicative of a clogged in-tank fuel filter. This I know from personal experience. Have you converted a carburated car to fuel injection? If so, did you use the original fuel pick up and line outlet from the tank? This may have worked properly for a low demand fuel pump on a carburated car, but will not support the flow requirement of an FI system.

The fuel tank outlet on the '75 cars and those in the Manta/Ascona B series were slightly larger. Additionally, the pickup was configured to have a constant supply of fuel through the return line and a tank bottom pickup.
However, I am relatively certain that your problem is a clogged in-tank fuel strainer.

Pull the fuel pickup, remove the sock/strainer and make sure the line is clean. You'll need a prefilter before the pump and a good high pressure/high flow main filter after the pump. Also, it might not be a bad idea to remove the fuel tank and have it cleaned and sealed to prevent additional sediment problems in the future.

Good luck.
 

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Discussion Starter · #17 ·
David McCollam said:
Your symptoms are indicative of a clogged in-tank fuel filter. This I know from personal experience. Have you converted a carburated car to fuel injection? If so, did you use the original fuel pick up and line outlet from the tank? This may have worked properly for a low demand fuel pump on a carburated car, but will not support the flow requirement of an FI system.

The fuel tank outlet on the '75 cars and those in the Manta/Ascona B series were slightly larger. Additionally, the pickup was configured to have a constant supply of fuel through the return line and a tank bottom pickup.
However, I am relatively certain that your problem is a clogged in-tank fuel strainer.

Pull the fuel pickup, remove the sock/strainer and make sure the line is clean. You'll need a prefilter before the pump and a good high pressure/high flow main filter after the pump. Also, it might not be a bad idea to remove the fuel tank and have it cleaned and sealed to prevent additional sediment problems in the future.

Good luck.
Hi Dave,

My car was converted from carb to FI by Gil Wesson of OGTS. I feel pretty confident that he did it the right way. But I'll ask him to be sure.

Thanks,

Manny
 

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Hesitation problems.

Hey Manny!,

If Gil and Dennis did the work, it's most probably correctly installed; however, this does not eliminate the potential for the clogging at the sock. This is especially true if the car is not run frequently, or the tank wasn't removed and cleaned. I've gone through all this myself and know first hand. It's a pain and can drive you crazy.

Take it easy.
 

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Sock

After my 75 Manta sat the varnish in the tank clogged the fuel pick up filter (sock). Once the entire pick up tube/ sending unit combo is removed from the tank, the sock can be easily pulled off the pick up tube. I could never get mine clean enough. I had to replace it ....

HTH
 

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Discussion Starter · #20 ·
Well, it seems like I will be systematically replacing parts until the issue is resolved. I spoke with Gil on the phone and he very confidently said he thinks it's the pressure regulator. So I'm going to replace that as my next test. Since it is the easiest to get at for me at the moment.

Although the fuel filters are just as easy, that's next on the list if the regulator doesn't fix the problem.

I'll save removing the sock as the last resort since that requires the most amount of work and time.

Thanks all for your help,

Manny
 
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