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Kirkham Motorsports

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  #1 (permalink)  
Old 05-22-2022, 03:25 AM
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Default Fuel Pump? Relay? Inconsistent Starting

Hello,

I'm having and inconsistent issue starting my the cobra with a Rousch 427R. The car has just over 800 miles on it and recently I've had an issue where the car doesn't start consistently. It cranks and everything is fine in regards to the starter but it just does not fire up. I believe that have narrowed it down to something in the fuel system (pump?, relay? ). I have noticed on a cold start that I do not always hear the fuel pump "humming" for those first few seconds as it would normally pressurize. Mine does not have a separate fuel pump switch and it's wired to the ignition key. When I don't hear that humming I know it wont start and sure enough it doesn't. I have fuel injection/throttle body setup with an intank fuel pump. I have pulled the fuel pump relay and inspected. I am going to replace it for the heck of it but I don't think that is the root cause. I thought maybe the fuel pump was\is the issue but being so new I suspect that is not the issue. I inspected the top of the tank and confirmed the wiring to the fuel pump was not loose or anything. I even went as far as tapping the top of the tank\fuel pump lightly with a hammer to see if something was\is sticking. On a couple "weird" occasions I pulled the gas cap off and tried starting it and it actually worked? The last few times that trick has not worked so don't think its a vapor lock or related to that. Stumped....
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Old 05-23-2022, 07:05 AM
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check your fuel pump ground. I had ground issues as well as a bad ignition switch
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Old 05-23-2022, 07:34 AM
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You didn't mention what type/brand EFI you installed.

You mentioned you normally hear the fuel pump humm a few seconds after key-on which would describe a returnless system. Typically relies on a pressure switch.
Do you have pressure gauge on the fuel rail?

Try cracking a line at the fuel rail to see if you already have pressure there. (have a rag under the fitting be ready to grab the fitting with the rag to catch any spray.)

Sometimes an intank pump can hi-side and produce too much fuel and flood your plugs. You might pull one to check.

A set of piercing probes are handy for checking power and ground in active circuits. https://www.amazon.com/Goupchn-Insul...316302&sr=8-11
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Old 05-23-2022, 10:36 AM
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I have an oil pressure cutout switch on my car.. The engine will crank until the oil pressure comes up and then the switch will set the fuel pump relay. The switch should be located at the oil pressure takeoff point on the block. So when there is no fuel pressure it will not start....until you've cranked the oil pressure up. Also if you run out of oil the motor will stop.. If you crash and stall the fuel pump will stop as soon as the oil pressure drops.
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Old 05-23-2022, 12:52 PM
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The probability is 100% that whoever installed your engine and EFI system did not install a PPRV. PPRV stands for "positive pressure relief valve." Basically, it's a check valve that goes between the fuel pump(s) and the injectors that prevents fuel drainback to the tank giving you quicker start-ups after the car has been sitting.

If you ever pushed the relief stem on an OEM EFI Schrader valve you will likely remember the squirt of gas that is emitted. The pressure that produced that squirt of gas does the same thing at the injectors at startup, initially fueling the cylinders for a quick start. If you do not use a PPRV then you need to do a key on but do not start the engine until the fuel pump(s) slows down, indicating the entire fuel delivery line is full.

You can find PPRVs from almost all AN hardware suppliers. They are just one-way check valves. The trick is getting one that is essentially invisible to the fuel pump's delivery process — i.e. low opening pressure, high flow and a good seal.

The best I've found so far comes from the Australian AN supplier, Speedflow. This is a link to the valve I use, click here => Speedflow USA 610-10-BLK. They are not inexpensive but they do work and they provide a low, blow open pressure (around 3 to 5 psi) along with good sealing and fuel system back flow prevention performance.

The valve should be installed in the fuel system feed line as physically close to your fuel pump as possible The PPRV is supposed to help you prevent/mitigate the drainage of fuel in the fuel line back to the tank. The closer to the injectors you place it, the less effective it is. The closer to the tank (but after the fuel pump) you place it, the more effective it is.

Detroit uses in-tank fuel pumps and integrates its PPRVs into the fuel system right after the fuel pump, inside the fuel tank. The closer you can get to mimicking the OEM plumbing model, the closer you will get to OEM-style start-ups.


p.s. My fuel system uses a -10AN feed line. For a n/a application of around 7 liters, you can easily get by with -8 hardware instead of -10.

p.p.s. The other 100% you don't have it bet, I would make, is that the fuel system designer/installer did not install a Schrader valve on your fuel rails. It is a good bet that there is a ⅛" NPT port on one or both of your fuel rails that has a pipe plug installed in it instead of a Schrader valve. Take out the plug and put in a Schrader valve.
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Last edited by eschaider; 05-23-2022 at 09:20 PM.. Reason: Added Postscripts
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Old 05-24-2022, 07:13 PM
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Thanks guys for all the great info. I have some more investigation to do based on your suggestions. I have a Fitech EFI system and no return. I do not have a fuel pressure gauge inline.
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Old 05-24-2022, 08:06 PM
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I'd take a look at the FITech website support tab for instructions on your EFI. If you have an in-tank pump or even external hi-pressure EFI pump it needs a return line so the pump is not being deadheaded (not good at all for the pump banging its head against a brick wall)
Example of the FITech I used to run:
https://secureservercdn.net/198.71.2...ns-8.14.20.pdf
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Old 05-25-2022, 01:39 AM
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Quote:
Originally Posted by thedome View Post
Thanks guys for all the great info. I have some more investigation to do based on your suggestions. I have a Fitech EFI system and no return. I do not have a fuel pressure gauge inline.
Is your system then a returnless system?
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