Low and fluctuating fuel pressure

[MY500SS]

The 07 SS seems to have a low and fluctuating fuel pressure.  At start up she runs 18-30 psi.  As she warms up it runs 30-40 psi.  I don't remember seeing the pressure run that low.  I tried changing the fuel filter but that didn't help. I called Kenne Bell but with the current health crisis they are shut down.

  What do you all think? 

[GT500-2007]

I have a similar issue. Was thinking to change out the regulator under the hood thinking it was bad and if that didn’t work change the gauge.

GT

[MY500SS]

18 minutes ago, GT500-2007 said:

I have a similar issue. Was thinking to change out the regulator under the hood thinking it was bad and if that didn’t work change the gauge.

GT

Thanks for the info GT.  Are you running a Kenne Bell Boost-A-Pump?

[GT500-2007]

I believe so.  It is the stock Shelby 725SS build.  I have made no modifications or upgrades.

GT

[MY500SS]

33 minutes ago, GT500-2007 said:

I believe so.  It is the stock Shelby 725SS build.  I have made no modifications or upgrades.

GT

Yep, your Shelby has it.  I'll keep you posted on what I find.

[GT500-2007]

Interesting that I went to start the car today and it only cranks but won’t fire. Haven't run it for about 3 months or so.  A few minutes later I get a strong smell of gas.  I look around and see some gas on the floor on the passenger side of the engine.  I look further to see where it’s coming from and it looks to be seeping from one of the injectors, right where it seats into the block.  Thinking a blocked injector and lack of proper pressure is preventing the engine from firing.  They are the original injectors wondering if this is linked to the fluctuating pressure.  I guess it’s time to install a new set of injectors.

[MY500SS]

34 minutes ago, GT500-2007 said:

Interesting that I went to start the car today and it only cranks but won’t fire. Haven't run it for about 3 months or so.  A few minutes later I get a strong smell of gas.  I look around and see some gas on the floor on the passenger side of the engine.  I look further to see where it’s coming from and it looks to be seeping from one of the injectors, right where it seats into the block.  Thinking a blocked injector and lack of proper pressure is preventing the engine from firing.  They are the original injectors wondering if this is linked to the fluctuating pressure.  I guess it’s time to install a new set of injectors.

Very interesting.  Please keep me posted.

[Robert M]

A thought on checking the actual fuel pressure at the rail, with a second gauge verification.........The Black adaptor block that was install on the right fuel rail that has the Autometer fuel pressure sender screwed into it.........I believe there are a couple of additional 1/8" plug ports on the Black block, a small inexpensive fuel pressure gauge could possibly be screwed into one of those spare ports, if there is room, and a pressure reading could be verified right at the block where the Autometer fuel pressure sending unit is located. I have thought about installimg a small gauge on that fuel block under the hood, but that is as far as I got.........."thought about".......

I believe the actual fuel rail regulator itself is on the top of the Shelby installed block. The Shelby added adaptor block is sandwiched between the oem fuel regulator on top and the fuel rail on the bottom. My Autometer fuel pressure sending unit points forward on the block/adaptor.

R

Edited May 26, 2020 by Robert M

[Robert M]

I did a little bit of searching...................I kind of like this Black................

https://www.ebay.com/itm/Marshall-Gauge-0-100-Psi-Fuel-Oil-Pressure-Midnight-Black-1-5-Liquid-Filled/303560162323?hash=item46ad987c13:g:vj4AAOSw~gRVg7kE

It is a small 1.5" diameter, 1/8 pipe thread for that Black fuel rail adapter block, and it is Black, so it will be able to be seen and read under the hood, but it does not stand out like......."look at me!".

At first I thought I had found an Autometer gauge in the small 1.5" diameter, but maybe not.......or not yet......

R

 

Edited May 26, 2020 by Robert M

[Robert M]

Here is one with a Chrome bezel by Autometer........called Auto Gauge......

https://www.autometer.com/pressure-gauge-0-100-psi-sport-comp.html

^^^I think this can be found with a Black bezel also...

R

[MY500SS]

Great idea Robert.......I'll be doing that nest. Thanks.

[Robert M]

5 hours ago, MY500SS said:

Great idea Robert.......I'll be doing that nest. Thanks.

I found this 0-100psi oil filled mechanical gauge that is 1.5", and to me, it would be a perfect "stealth" gauge to add to the side of that fuel block, it also comes with a Red needle if that is the preference, but I like the White numbers - White needle look.......I want it to fully blend in, unless I am using it for a diagnostic tool.......then it is there for me to see....

https://www.ebay.com/itm/Marshall-1-5-Direct-Mount-Liquid-Filled-Fuel-Pressure-Gauge-MSB00100/114037044208?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908131621%26meid%3D17a1b65bb37d42afa24d4d319291769b%26pid%3D100678%26rk%3D1%26rkt%3D15%26mehot%3Dnone%26sd%3D114037044208%26itm%3D114037044208%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DMarshal&_trksid=p2380057.c100678.m3607&_trkparms=pageci%3A5986800a-9f78-11ea-a01a-74dbd180be5d|parentrq%3A5214a2191720a9c94ededd3dff7c36d4|iid%3A1

R

Edited May 26, 2020 by Robert M

[Robert M]

.............and the addition of a 1.5" fuel gauge would get rid of that ugly square head brass plug in the side of the fuel rail adapter block.....

^^^^^^ I had not noticed that brass plug before, I knew the fuel block had extra ports with plugs, but I did not look at the block on my car. I would have replaced that plug long ago with either a Stainless/Polished Allen head 1/8" plug or a Black anodized Allen head 1/8" plug, I have both in my fuel rail stuff, but I had never really looked at mine.....

That fuel rail adapter is made by Metco, the same people who made the Shelby fuel rails. That fuel adapter block is only available in Black currently, from Shelby or from Metco. A few years ago I was do some "few rail searching" on eBay and came across this same fuel rail block in billet aluminum Silver finish, I contacted Metco with the part number shown on the Metco box in the eBay auction........The Metco rep. said yes, that was a Ford fuel rail block that they offered a few years ago along with the Black and then they changed to Black only.  i think he also said the Silver adapter block is Clear Anodized.

R

Edited May 26, 2020 by Robert M

[mhr1961]

Not trying to tell you what to do, but I wouldn’t put a gauge under the hood. If it ever cracks or fails you may have quite a glycerin mess under the hood. If you use a dry gauge those are typically not very vibration tolerant and fail prematurely with rapid cycling.  If you do decide to do so, make sure the gauge is designed to handle the temperature range you would see under your hood. Most dry gauges are designed to operate from about -40F to 150F, and liquid filled gauges are usually about -10F to 150F. The reason that a typical pressure gauge is rated at these temps is because the bourdon tube inside the gauge is typically soldered with a soft solder (lead/tin mixture) that can soften at temps above 150F and the bourdon tube inside can fail. The temps the gauge could/would be exposed to at times will likely far exceed 150F.

         Optimal gauge pressure range selection for best accuracy is 2 times expected normal operating pressure. Two of the biggest enemies of a gauge are temperature and vibration. Besides the obvious need to be readily visible, temperature and vibration issues are why gauges are usually mounted in the cockpit on automobiles and other mobile machinery. If you are insistent on measuring pressure at the fuel rail/fuel block with a permanent mount gauge make sure you get a high quality gauge rated for high temps and vibration. Otherwise just remove the plug and temporarily install your fuel gauge, do a quick check and then put the plug back.

 In regard to the Marshall’s “fuel gauge” you are mentioning above. I wouldn’t use it as a permanent mount. If you go out to the Marshall’s Gauge website and find the gauge you are talking about, then go click on the FAQ just below the picture of the gauge. Here is what you will find:

 MNB 0-100 PSI
Item: MNB00100

What are the temperature limits of my gauge?

General guidelines for a silicone filled mechanical pressure gauge with brass internals:

• Min Ambient Temp: -60F
• Max Ambient Temp: 200F*
• Max Process Temp: 150F*

*It is generally accepted that the maximum temperature inside the sensing element of a brass internals gauge should not exceed 150F. This temperature limit is based on the fact that a lead tin solder (soft solder) is commonly used to seal the tip and socket on a bourdon tube type gauge with brass internals. At higher temperatures these joints may loose their strength and fail.

Not trying to rain on anyone’s parade. Just providing info that may save you some headache. Good Luck on your project.

 

 

 

 

[Robert M]

2 hours ago, mhr1961 said:

Not trying to tell you what to do, but I wouldn’t put a gauge under the hood. If it ever cracks or fails you may have quite a glycerin mess under the hood. If you use a dry gauge those are typically not very vibration tolerant and fail prematurely with rapid cycling.  If you do decide to do so, make sure the gauge is designed to handle the temperature range you would see under your hood. Most dry gauges are designed to operate from about -40F to 150F, and liquid filled gauges are usually about -10F to 150F. The reason that a typical pressure gauge is rated at these temps is because the bourdon tube inside the gauge is typically soldered with a soft solder (lead/tin mixture) that can soften at temps above 150F and the bourdon tube inside can fail. The temps the gauge could/would be exposed to at times will likely far exceed 150F.

         Optimal gauge pressure range selection for best accuracy is 2 times expected normal operating pressure. Two of the biggest enemies of a gauge are temperature and vibration. Besides the obvious need to be readily visible, temperature and vibration issues are why gauges are usually mounted in the cockpit on automobiles and other mobile machinery. If you are insistent on measuring pressure at the fuel rail/fuel block with a permanent mount gauge make sure you get a high quality gauge rated for high temps and vibration. Otherwise just remove the plug and temporarily install your fuel gauge, do a quick check and then put the plug back.

 In regard to the Marshall’s “fuel gauge” you are mentioning above. I wouldn’t use it as a permanent mount. If you go out to the Marshall’s Gauge website and find the gauge you are talking about, then go click on the FAQ just below the picture of the gauge. Here is what you will find:

 MNB 0-100 PSI
Item: MNB00100

What are the temperature limits of my gauge?

General guidelines for a silicone filled mechanical pressure gauge with brass internals:

• Min Ambient Temp: -60F
• Max Ambient Temp: 200F*
• Max Process Temp: 150F*

*It is generally accepted that the maximum temperature inside the sensing element of a brass internals gauge should not exceed 150F. This temperature limit is based on the fact that a lead tin solder (soft solder) is commonly used to seal the tip and socket on a bourdon tube type gauge with brass internals. At higher temperatures these joints may loose their strength and fail.

Not trying to rain on anyone’s parade. Just providing info that may save you some headache. Good Luck on your project.

 

 

 

 

^^^^^^Thank you for that info. I definitely retract my suggestion on putting a gauge permanently under the hood with those temp. specs.  I will continue forward with a cleaner looking plug in that adapter and be happy with that.

Thank you very much for the deeper insight into the under hood gauge mounting, I was just getting ready to order one, now I will hold off. I was thinking I had seen guys that run Nitrous with a small gauge under the hood and that is what made me think of it, but I may have been mistaken OR they have a trouble ready to happen.

 

R

Edited May 26, 2020 by Robert M

[Robert M]

.........And then you put "under hood fuel pressure gauge" in Google, and this one comes up in Amazon and when you scroll further down and read the description it definitely states for mounting under the hood....BUT....I don't see any temp. specs for the gauge................and I certainly would not consider putting anything "Glow Shift" under the hood of my Super Snake.....

https://www.amazon.com/GlowShift-Liquid-Filled-Mechanical-Pressure/dp/B07895TP2Q

They may get around it by claiming it is a test tool for install during trouble shooting, but I do not see that anywhere.....

R

Edited May 26, 2020 by Robert M

[Robert M]

So now down a different path with FueLab, to see what they offer after reading the copy and paste below.......

___________________________________________________________________

It should be noted that under hood heat can affect the accuracy of liquid-filled gauges. The gauge housing is sealed to hold in the liquid. Temperature changes causes expansion of the liquid fill and can create pressure build-up in the gauge case, which causes an error in the gauge reading. For this reason Fuelab offers non-liquid filled fuel pressure gauges.

As previously discussed, permanent direct mount fuel pressure gauges are intended to be a reference tool. When tuning a vehicle it is best to verify fuel pressure with a high quality external fuel pressure gauge. This type of gauge is temporarily connected, is more precise than permanent mount gauges, and can also be used to cross check the permanent fuel pressure gauge for accuracy.

___________________________________________________________________

^^^^^ But maybe it is still indicating the underhood gauge to be used as a temp. tool?

R

 

Edited May 26, 2020 by Robert M

[Robert M]

I'm going to call Fuelab about this one tomorrow.......

https://fuelab.com/product/71501-efi-fuel-pressure-gauge/

R

[mhr1961]

Always glad to help a fellow Shelby Enthusiast. Good Job on the further research you did on your gauge issue.

Yes that “plug” on the fuel block looks like a standard Parker Fitting #221P-2, Square Head Pipe plug. It’s about the cheapest pipe plug available.

A Parker #219P-2 Countersunk Hex Head Plug-Brass would definitely look nicer. You can buy them online for about $49 cents

If you want to get  fancy you can use a Parker # 2 PHH-SS Countersunk –Hex Head Plug Stainless Steel- Those Run about $5 to $10 online.

Don’t buy cheap Chinese made fittings at Home Depot or Lowes, in many cases they are made with softer brass content and/or they may not be annealed to proper hardness r thread specs are not held to good tolerance.

By the way, from the picture of the fuel block it looks like you could install a a Parker  45 degree Street Elbow 1/8" npt Male to 1/8" npt Female fitting and turn it to where the Elbow points up a bit so you can more easily see your “test” gauge and then when you take out your gauge just use the stainless plug mentioned above.

[MY500SS]

Great stuff guys, thanks.  I'm going to make up a test gauge that can easily be removed.

 

[mhr1961]

BTW, forgot to mention in an earlier post. Holley makes some Quick Disconnect Fittings for Fuel Pressure Testing. Here is the link.

https://www.holley.com/products/plumbing_an_fittings_and_hose/adapters/carburetor_-_power_steering_-_fuel_pump_-_fuel_injection_adapters/quick_connects/

Post up some pictures and a write up when you come up with a solution. Good Luck!.

[Robert M]

Ok, I just talked to Tech Support at Fuelab. He said that under hood heat does not affect the gauge shown below, and in fact 95-98% of their customers have this gauge permanently mounted to a fuel regulator (either their regulator or other) under their hood, and many in race conditions. He said that the internal connections and structure of this gauge are made to withstand under hood heat and vibration. He did mention that since this gauge is not liquid filled, the gauge may fluctuate by about a pound because it does not have the liquid for dampening the needle movement.

https://fuelab.com/product/71501-efi-fuel-pressure-gauge/

^^^This exact gauge can be bought for about $3 less on eBay with free shipping........put Fuelab 71501 in the eBay search.

Here it is on eBay......

https://www.ebay.com/itm/Fuelab-71501-1-5-0-120-Psi-EFI-Fuel-Pressure-Gauge/362888664471?epid=4022586063&hash=item547dd99597:g:Tr0AAOSwsFheJh~~

It can also be purchased with the BARS/PSI scale under 71511.

I see this gauge listed on quite a few diesel sites........speaking of vibration!!!................

R

Edited May 27, 2020 by Robert M

[Robert M]

13 hours ago, mhr1961 said:

Always glad to help a fellow Shelby Enthusiast. Good Job on the further research you did on your gauge issue.

Yes that “plug” on the fuel block looks like a standard Parker Fitting #221P-2, Square Head Pipe plug. It’s about the cheapest pipe plug available.

A Parker #219P-2 Countersunk Hex Head Plug-Brass would definitely look nicer. You can buy them online for about $49 cents

If you want to get  fancy you can use a Parker # 2 PHH-SS Countersunk –Hex Head Plug Stainless Steel- Those Run about $5 to $10 online.

Don’t buy cheap Chinese made fittings at Home Depot or Lowes, in many cases they are made with softer brass content and/or they may not be annealed to proper hardness r thread specs are not held to good tolerance.

By the way, from the picture of the fuel block it looks like you could install a a Parker  45 degree Street Elbow 1/8" npt Male to 1/8" npt Female fitting and turn it to where the Elbow points up a bit so you can more easily see your “test” gauge and then when you take out your gauge just use the stainless plug mentioned above.

^^^^^^Thanks for that information, yes, I had not noticed the "hardware store" brass plug until we got into this discussion.

After talking to the Fuelab tech support this morning, I am going to try that Back gauge that they offer. My car has not been started for quite a while (but it has been on a Battery Tender), so I may be able to take that plug out without fuel spewing out under pressure..............

R

[MY500SS]

20 hours ago, Robert M said:

^^^^^^Thanks for that information, yes, I had not noticed the "hardware store" brass plug until we got into this discussion.

After talking to the Fuelab tech support this morning, I am going to try that Back gauge that they offer. My car has not been started for quite a while (but it has been on a Battery Tender), so I may be able to take that plug out without fuel spewing out under pressure..............

R

Going to do the same.

[Robert M]

5 hours ago, MY500SS said:

Going to do the same.

I also contacted Marshall, to see if they had a "Dry" 1.5  0-100psi gauge that was Black case, Black face with White needle and numbering, they do not.

 

R

Edited May 28, 2020 by Robert M

[Secondo]

Hi Dan, good to see you here.

Your GT500 has Ford GT-style dual fuel pumps. If you are running a boost-a-pump, check wiring to them (under the rear seat) and fuses. I've seen melted wiring at the pumps when running a boost-a-pump. One of the pumps may not be functioning. 

[twobjshelbys]

1 hour ago, Secondo said:

Hi Dan, good to see you here.

Your GT500 has Ford GT-style dual fuel pumps. If you are running a boost-a-pump, check wiring to them (under the rear seat) and fuses. I've seen melted wiring at the pumps when running a boost-a-pump. One of the pumps may not be functioning. 

Correct.  But at least on the GT the monitoring system is very good at detecting a bad pump and throwing a check engine condition.  If you have the boost-a-pump system I would look there first. 

Edited May 28, 2020 by twobjshelbys

[mhr1961]

6 hours ago, Robert M said:

I also contacted Marshall, to see if they had a "Dry" 1.5  0-100psi gauge that was Black case, Black face with White needle and numbering, they do not.

 

R

Robert,

You do realize that the Fuel Lab gauge is also made by Marshall? Look at the bottom of the guage, its says Marshall. many large gauge companies private label for smaller companies.

Here is perhaps a better choice. Summit Racing Part#153009. This one appears to be a dry fill fuel pressure gauge, chrome bezel and housing, 1/8 npt center back mount. Black face/white letters and a red indicator.

here is the linky:   https://www.summitracing.com/parts/vdo-153009

I would also call them and ask for the temperature rating, and ask whether the gauge had a clear plastic face, or glass face. For the price point it is at I would think it is probably glass. If plastic I would pass on it because if you get fuel or oil on it then it will likely cloud up. It also has a restrictor (orifice built in to the gauge to dampen pulsation).

Edited May 28, 2020 by mhr1961

[MY500SS]

21 hours ago, Secondo said:

Hi Dan, good to see you here.

Your GT500 has Ford GT-style dual fuel pumps. If you are running a boost-a-pump, check wiring to them (under the rear seat) and fuses. I've seen melted wiring at the pumps when running a boost-a-pump. One of the pumps may not be functioning. 

Thanks man, I'll look at that.

[MY500SS]

19 hours ago, twobjshelbys said:

Correct.  But at least on the GT the monitoring system is very good at detecting a bad pump and throwing a check engine condition.  If you have the boost-a-pump system I would look there first. 

Hopefully Kenne Bell opens back up soon so I can get ideas from them as well.