Hi guys,

Alright, I did a search and I read through a bunch of threads but I didn't really see what I was looking for. My question is:

My 1998 C5 has a fuel return line with a fuel pressure regulator mounted on the fuel rail. (apparently only 97 & 98 C5's are configured this way) I am experiencing weird engine starting issues. The engine always eventually starts, but sometimes it starts right away, sometimes it cranks and starts after a few seconds, sometimes it cranks and will not start until I stop cranking and then try it again, at which time it fires right away on the second try. There is no pattern to this.... it's completely random.

I began to think maybe it was the fuel check valve in the pump module..... then I started to think maybe I had a leaky injector(s) and it was dumping fuel pressure into a cylinder(s) when I turn off the engine.

I connected my scan tool and I wanted to run a fuel injector balance test but I didn't get that far because as soon as I went to test the first injector I lost all fuel rail pressure as soon as the pump shut off. The rail pressure goes immediately to zero in about one second

So, in my mind, it's either a REALLY leaky injector(s) dumping all fuel pressure into a cylinder(s) or it's the fuel pump check valve, right?

But then I started to wonder about the fuel pressure regulator. What if that is not working properly and just allowing all the fuel to run back on the return line?

One of the things I read on this site was very interesting. The 1997 and 98 fuel pressure regulators do not work like most FPR's. The small tube that runs to the air intake snorkel is a VENT line, not a vacuum line. This is what I read here in another thread on this site:

So, now do I have a REALLY leaky injector, a bad check valve in the fuel pump module, OR do I have a bad fuel pressure regulator?

I know how to see if I have any leaky injectors..... I can pull the fuel rails up and off the intake while everything is still connected and cycle the key on/off one or two times and watch for leaking fuel.

But how can I determine between a bad fuel check valve, or a bad regulator? Without just loading the parts cannon?

Any ideas?

Thanks.

 

To check for a bad check valve if you have a Mityvac with a 3/8th inch male fuel line fitting attach it and using pressure apply 15 psi to the fuel line going back towards the check valve…pressure should hold for 1 minute…this is a 100% foolproof method so you don’t have to drop the fuel tank for nothing.

 

I just came from Amazon where I ordered a bunch more fuel system test fittings to go along with my existing test kit. I like your idea pictured above. I will have enough pieces to put together something like you posted but it may look a bit different. lol.

Do you know if the fuel check valve on a 1998 is built into the pump module itself, or is it an external check valve that is built into the fuel line outside of the tank? (like I've seen pictured in other threads for later C5's)

Thanks for your reply!

 

It is external.

 

I see that part number is no longer available. That sucks. Looks like I would need to either modify the original with a new check valve installed..... OR, just install my own check valve somewhere in the fuel line going to the front of the car. Maybe even right at the fuel rail where the fuel line quick disconnect is? Either way, I need to wait until my extra test fittings get here tomorrow and then I can officially diagnose exactly where the problem is. I will cross this bridge if/when I get there.

Thanks again for all the info you have provided.

 

Since that line is plastic you’ll probably not be able modify it..if it were rubber yes !!…I’ve heard of others using some type of external check valve.

 

My car is doing the same thing. What is the purpose of the check valve hose in the complicated fuel system?

 

To keep fuel in the fuel rail so it doesn’t drain back into the tank which will result in extended cranks before starting…if you have a fuel pressure gauge fuel pressure should not drop when the pump is shut off…this can also be a leaking injector or a few other things.

 

I was just going to cut the plastic tubing on either side of the existing check valve and stick one of these in there. In theory it should be pretty simple.... but I haven't seen it with my own eyes yet.

It's just a push lock plastic check valve designed to work with nylon and plastic tubing.

I will let you know how it works out.

 

I wouldn't be comfortable using that on a fuel line.

 

Why.... everything else in the fuel system is plastic or nylon. This is no different.

It's at the back of the car. If it drips then I move to plan B.

I'd rather buy the correct part but they don't exist.

 

Actually, I just noticed the seat materiel in that check valve is not comparable with gasoline so I will need to go another route. Probably a stainless Check of some sort....

 

If you google fuel injection check valve a number of options come up, including Lingenfelter, Jegs, and Summit. Might be a pain to figure out fittings, but should be workable.

 

Yep, I've seen a bunch of those.... and I will probably end up with one of them but like you said..... figuring out the correct fittings to attach to the plastic fuel line will be the hardest part. I think I've already figured it out but I want to verify it's the check vavle that is bad before I order anything. The test fittings that I ordered arrived late today so that is tomorrow's project. I will post back here with whatever parts and pieces that I come up with.

 

Yes please! I doubt I’m the only one contemplating whether to take similar action.

 

There's a large and a small fuel line connected to the engine. If the large line is the fuel supply is that where the check valve goes to stop fuel from going back to the pump?

 

Yes.

 

Okay, this is what I came up with....

This is the Carter fuel pump check valve from Amazon (actually this is the Delphi check valve shown because it had a better picture but I bought the Carter version. Same thing)
The check valve has 1/4 NPT (national pipe thread) on either end. I am assuming the plastic fuel feed line back near the fuel tank is 3/8" like it is up near the engine. In order to make this work I also ordered two 1/4 male NPT to D.O.T. rated 3/8" compression fitting adapters to connect back to the factory fuel line on the car. These are the D.O.T. rated compression fittings and are used on big truck air systems every day. These are not the same as the compression fittings that you can buy at Home Depot.... although those would probably work, too.

Pictured below is the fuel pump check valve:




I also ordered two of these D.O.T. rated adapters to connect the check valve on the factory plastic fuel line on the car.



The difference between the D.O.T. rated compression fittings and the hardware store compression fittings can be seen below. Notice the internal tube sleeve is permanently attached to the body of the compression fitting. (bottom) Unlike the type that come from the hardware store (top) that comes with an internal sleeve but it's not attached to the body of the fitting. (the ferrule is stuck inside the compression nut, it's there) You can also buy compression fittings from the hardware store that do NOT have an internal sleeve but those are not designed to be used on plastic line, metal tubing only. These are fittings from my stash here at home. I was hoping that I would have the correct fittings but I had to order some.




Again, my plan is to cut the plastic line on either side of the factory check valve and then insert this check valve into it's place. I have not laid my eyes on the factory check valve, I have only seen a drawing of where it's located. I am removing the rear tires later today to put on new tires and install new brakes. While I'm in there, I also plan to tackle this check valve problem. If getting to the factory check valve location looks like a pain in the ***, then I will try to install my new check valve somewhere else in the main fuel supply line that runs to to the front of the car. I will try to keep it as close the the factory location but yet in a spot that is easy to work in. I think it will be fine. We'll see if all this stuff works like I think it should.

And yes, I know these 1/4" fittings are technically a bit of a restriction but it's only a few inches of total length, it's not like the entire length of the car is being restricted. It will be fine, trust me. The car is 100% stock.

 

Have you actually diagnosed the check valve to see if that is indeed your issue ???

 

Yep. I just did that this morning. It holds absolutely ZERO pressure.