Help needed on C5 (probably C6 too) fuel line to inlet manifold connection and also on/off valves.

[Yellowshark]

During diagnostics of my recent backfire problem I noticed that my fuel pressure was not quite right. The FSM spec is low 50s to 62 psi with a drop in the first minute of the pressure test of no more than 5psi. Whilst I was registering a healthy 58psi I was dropping 6psi. I am finding it difficult to get excited about that, but maybe it is could get worse and go phut when I am 400 miles from home an so I probably out to look further.

So it seems to that an early test is to test the pressure at the inlet manifold which will either place the problem at the rear of the car or at the front with the fuel rail and injectors.

The FSM solution is to fit a GM tool which connects in between the fuel line and the inlet manifold and lets you turn off or on the fuel supply. BUT whilst I have found this tool on ebay it is 150-200 USD (plus freight/customs) which is just too expensive for what would probably be a one of use.
An alternative is Amazon which has plenty of plastic on/off valves for £20 but all seem to be used with lawnmowers etc. and my brain is telling me they will not work with the C5 fuel pressure.

One solution that occurs to me is to unhitch the fuel line from the inlet manifold and fit my pressure gauge into the fuel line but I have never worked on a fuel system before (apart from carburettors on the old cars) , know nothing about these quick connectors that are used on the C5 and no idea at the moment if I have a suitable connector in my pressure gauge box that would allow to do that.

So has anyone had to confront this on their C5/C6 and what did you do?

 

[Oneball]

Just fitting the gauge into the fuel line won’t let you stop the supply.

I’m assuming you’re attaching the gauge to a schrader fitting on the fuel rail?

Can you not just clamp the fuel hose?

 

[oelarse]

You need this tool to disconnect the fuelline from the rail.

But I think you need somthing like this to shut of the fuelsupplyline in order to verify if the injectors are leaking or the checkvalve on fuelsupply line

Fuel Line Shut Off Adapter

 

[FIVE RED]

Without checking I'm wondering if the connection is the same type as used on the fuel filter?
I bought one of these when I changed my filter, worked perfectly, if so then a cheap but reliable solution.

OEM Fuel Line Disconnect Tool | eBay

Find many great new & used options and get the best deals for OEM Fuel Line Disconnect Tool at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

 

[oelarse]

Yes , I think you can use this tool ( I have this tool also) . Here is a photo from when I replaced my fuel filter three years ago and the connector on the fuel filter looks very similar to the fuel feed line coupling in the engineroom

 

[Custom exotics]

Has ur vette only 1 fuel line if so and if you havnt done so change rhe fuel filtet on the late c5s and c6s the fuel filter has the return line out back to tank and controls fuel presure alone the whole fuel line to engine (filter has 3 pipes inlet outlet and return this could be cause of ur fuel presure loss if ir car has 2 lines to engine then it regulates fuel presure at rail again the regulatorcould be faulty as for checking pressure manually as said in earlier post there should be a valve on the fuel rail to screw a gauge to looks like a bike tyre valve but should only tell you what the computer/diadnostic real time data is telling you i would be suprised if the car would stay running if the fuel pressure dropped to 6psi for anymore than a split second thats hardly enough to keep a carbed car running feel feel to call us on 01279441133 if you need anymore help

 

[Yellowshark]

Hi guys, well I certainly was not expecting so much quality information so quickly, just brilliant thank you so much. OK let me go through your responses.

Hi Oneball – I suspect you may be misunderstanding what it is I am trying to do. Having fitted the fuel gauge to the fuel rail Schrader valve I have identified a pressure drop outside of the Corvette specification. So now I want to identify the pressure drop at the fuel line connection to the fuel rail. This will tell me if the problem is from the fuel filter backwards (there may be something before the filter) or if the problem is the fuel rail/injectors. I should add that I have had the car from new which now has a mileage of 160,000 so parts are getting old. I have never done nor had any work done on the fuel system.

So my desire is not to fit the gauge into the fuel line, it is remove the fuel line from the rail and terminate the line with the pressure gauge, pressurise the system and see if continues or stops leaking.

Now as you say maybe I could just clamp the fuel hose. It strikes me that there may just not be enough time between pressurising the system and getting the clamp closed down before the pressure loss occurs. I guess there is one way to find out! I suppose an alternative is to run the engine and then tighten the clamp until the engine stalls.



Hi oelarse – firstly thanks for the great photos. It is all clear to me now how the connection works . I have a new fuel filter sitting in front of me and the connection is exactly the same and given it is the same fuel line fitting into both it will be the same sizing too.

And thanks for the link to the Kent Moore shut off adaptor, lol looks remarkably similar to the GM tool but half the price. Mind you with freight and VAT there is still going to be little change from £100, so whilst I suspect I may need to go there, there are a couple of things for me to try before admitting defeat.



Hi olearse/FIVE RED – thanks for the details on the connection tool. I have seen these on Amazon so it is good these cheaper tools(compared to the GM tool) will do the job - ordering will be my first job tomorrow!



If anything more occurs to guys just keep the thoughts coming!

 

[Yellowshark]

Hi Custom Exoctics thanks for your comments. Lol it is not quite as bad at that, the pressure is dropping by 6psi not to 6psi. And this only on the pressure test not when the engine is running. I.e. with engine running the fuel pressure runs constantly at 58psi which is the pressure shown in the pressure test, but with the engine off the pressure test shows that the pressure goes up to 58psi and then quickly drops to 52psi, whereas Corvette specify a maximum drop of 5psi in the first minute. As I said whether or not I should get overly excited about this is probably debatable.

I have a middle C5 (2001) which fortunately and unlike the later models has the filter located exterior to the fuel tanks. It is a combined fuel filter and pressure regulator with an inlet line from the petrol tank, a return line to the petrol tank for any unused fuel and a single fuel line to the engine compartment which itself has no regulator.

I do have a new filter/regulator sitting in front of me so I will push that up the priority list – lol any excuse to get out of swapping over the final cylinder 5 and 7 spark plugs!!

 

[Yellowshark]

>>>snip

Hi oelarse – firstly thanks for the great photos. It is all clear to me now how the connection works . I have a new fuel filter sitting in front of me and the connection is exactly the same and given it is the same fuel line fitting into both it will be the same sizing too.

And thanks for the link to the Kent Moore shut off adaptor, lol looks remarkably similar to the GM tool but half the price. Mind you with freight and VAT there is still going to be little change from £100, so whilst I suspect I may need to go there, there are a couple of things for me to try before admitting defeat.



Hi olearse/FIVE RED – thanks for the details on the connection tool. I have seen these on Amazon so it is good these cheaper tools(compared to the GM tool) will do the job - ordering will be my first job tomorrow!



If anything more occurs to guys just keep the thoughts coming! <<<<snip

Hi guys just to let you know that firstly the fuel line disconnect tool arrived yesterday and it fits snugly into the new air filter I have ready so all looks good there. Secondly I have the Kent Moore shut off adaptor on its way over the Atlantic so with the new tool I should be able to fit that in about a week and check which part of the fuel system the pressure is dropping from. I have an MOT and annual service coming up so I may well wait and get my garage to fit the filter for me. It takes me almost as long to get the rear up and fully secured as it does for the NHS to build a Covid field hospital these days. It is hardly worth the effort for what should be a simple job for them with a lift. And I need to get my annual show and shine done too.