Help! Fuel Pressure Test Video, Need Opinion

[dogfish246]

Here is the Video I took of the fuel pressure. It has become increasingly difficult to start the engine (it will start every time) where it turns over too many times.

Otherwize the car seems to run fine (no high idle, good acceleration, etc)


What do you think is wrong? I have an idea, but would like to verify it!

YouTube - Corvette Fuel Pressure


Thanks:cool

 

[gmjunkie]

Here is the Video I took of the fuel pressure. It has become increasingly difficult to start the engine (it will start every time) where it turns over too many times.

Otherwize the car seems to run fine (no high idle, good acceleration, etc)


What do you think is wrong? I have an idea, but would like to verify it!

YouTube - Corvette Fuel Pressure


Thanks:cool

Man, at turn on that fuel pressure should hold for at least 30-35 minutes even without the key left on before bleeding off much at all!!(2-3 lb) I think you have some leaking injectors!

PS Could also be a cracked or leaking rubber fuel line above the fuel pump in the tank!

 

[dogfish246]

Ok, when I connect my OBDII scanner it runs the fuel pump for a long time without the car running (just in the run position). I think that caused this problem.
I dont know why my scanner does that and I called the company and they said it wasnt their scanner, but the guy sounded like he was just defending the scanner the whole time!

What can I do about leaking injectors and how can I check the rubber fuel line? What is a leaking injector, is it internal, or a gasket on the outside? Does it get fixed or is the injector junk?


Thanks!:cool
What should my next move be?

Uhhh, I had a feelingad!

 

[93Rubie]

What can I do about leaking injectors and how can I check the rubber fuel line? What is a leaking injector, is it internal, or a gasket on the outside? Does it get fixed or is the injector junk?

Uhhh, ok...

Leaking fuel injectors bleed off fuel into your intake manifold, just above your intake valves. To much fuel equals rich, which means can cause to not run right or other things like yours. The injector(s) is junk if it is leaking. If you determine that you have a bad injector(s) replace all of them just b/c if one failed the likely hood of another is increased.

You probably don't have the tools but if you did you could test individual injectors with a injector pulser. Which basically with the use of a Fuel Pressure gauge measures injector flow over a certain period of time. Monitoring pressure drop you can determine if a injector(s) flow like they should or if it is excessive or not enough.

For grins and giggles pull the vaccum line off your fuel pressure regulator and make sure no gasoline drops out of the line.

 

[gmjunkie]

Ok, when I connect my OBDII scanner it runs the fuel pump for a long time without the car running (just in the run position). I think that caused this problem.
I dont know why my scanner does that and I called the company and they said it wasnt their scanner, but the guy sounded like he was just defending the scanner the whole time!

What can I do about leaking injectors and how can I check the rubber fuel line? What is a leaking injector, is it internal, or a gasket on the outside? Does it get fixed or is the injector junk?


Thanks!:cool
What should my next move be?

Uhhh, I had a feelingad!

Fuel line in tank...................................
#7 they call it a pulsation dampener, It's a Thick rubber hose they sometimes crack and leak back into the tank!!

If it's not that,turn the key on 4-5 times and then start pulling injectors!!
You'll see the leaking ones when you pull them out!!:L:L:L

FIC has a great deal on New and Reconditioned injectors,I use them all the time!! Great Guys!!

 

[Hib Halverson]

Most likely, you've got one or more leaking injectors.

What should happen, when you turn the key on/engine off, is the pump comes on and the pressure goes to about what you saw on the gauge. Then, since the ECM senses no tach signal (because it's not running) it cuts off the pump. At that point, the fuel pressure should hold close to it's max reading and it should hold for several minutes before it drops out of the acceptable range listed in the Service Manual.

When it drops that quick, you have a leak, either an injector, (less likely) the FPR or, rarely, the check valve in the pump.

Best bet it to run the fuel pressure tests listed in the FSM.

 

[Robertwav1]

I don't know how a 96 is arranged but I pulled a vacuum line and checked for a raw fuel order caused by a very small crack in the diaphragm of the FPR.

 

[Schrade]

Here is the Video I took of the fuel pressure. It has become increasingly difficult to start the engine (it will start every time) where it turns over too many times.

Otherwize the car seems to run fine (no high idle, good acceleration, etc)


What do you think is wrong? I have an idea, but would like to verify it!

YouTube - Corvette Fuel Pressure


Thanks:cool

This story ends at :15 (static pressure test). Pressure drop to '0' psi as 2-second prime duration ends means a weak diaphragm spring in FPR, ot a ruptured bladder in FPR, or multiple injector failure (doubtful, because of how fast it drops to '0').

If there is a check valve in the fuel feed line (I do not know if so, or if not), it might have failed.

To check the 'check valve' function, disconnect and cap the line BEFORE the FPR, then retest.

Ruptured bladder will show by gasoline in the FPR vacuum hose. Disconnect it and smell it.

Weak bladder spring is less likely, since pressure goes to '0' psi.

Post results.

 

[gmjunkie]

This story ends at :15 (static pressure test). Pressure drop to '0' psi as 2-second prime duration ends means a weak diaphragm spring in FPR, ot a ruptured bladder in FPR, or multiple injector failure (doubtful, because of how fast it drops to '0').

If there is a check valve in the fuel feed line (I do not know if so, or if not), it might have failed.

To check the 'check valve' function, disconnect and cap the line BEFORE the FPR, then retest.

Ruptured bladder will show by gasoline in the FPR vacuum hose. Disconnect it and smell it.

Weak bladder spring is less likely, since pressure goes to '0' psi.

Post results.

There is a check valve in the pump as Hib stated above!

 

[Schrade]

There is a check valve in the pump as Hib stated above!

Thanks! I guess I 'guessed' well then... And of course, the test would be good too. (I don't read too many 'other' posts, besides op post; just not too much that contributes - guess I should correct the bad info tho').

I know there's a rollover valve, but I hadn't seen the regular valve in schematics.

 

[Schrade]

Here is the Video I took of the fuel pressure. It has become increasingly difficult to start the engine (it will start every time) where it turns over too many times.

Otherwize the car seems to run fine (no high idle, good acceleration, etc)


What do you think is wrong? I have an idea, but would like to verify it!

YouTube - Corvette Fuel Pressure


Thanks:cool

Good diagnostic work! Now, finish and shoot the tests COMPLETELY, and you can turn this into cash - promise. Or get CAC to make a sticky HERE. This will make 25k hits / year promise, if done right. PLUS, when you sell the car, you have photo-doc, dated SPEC maintenance, which means MORE $.

Now, you want to get 30,000 hits on your vid??? I'll guarantee it YUP. You could probably turn this into cash too, if you get your own domain, and do a FULLY DETAILED fuel pressure diagnostic. I should have done it with my headlight sticky at CF, instead of posting it there - it would have thrown off at least couple of hundred bucks with page sponsors... 11,000 hits, 4,000 AFTER I deleted pics in 01/09 after bannage . GIJoe even told me to do that, but I was lazy... Be lazy, get no cash.

Do the vid again, and do the complete static and dynamic tests for fuel pressure.



Static Test:

Make sure to get AUDIO of the pump doing the 2-second prime duration.

Include bleed-down time in the video (of course now, you have a problem, so make that part of the 'before and after' readings).

Include ohmeter checks of injectors, or link to Jon/FIC's vids at CF (THAT was MY idea too, to Jon (ask him), and to the forum admins too (ask them).

Show static test with line capped, NOT PINCHED, at FPR, to show check valve function. Pinching damages stuff, and doesn't guarantee a flow 'hold'.

Show the static test with the vacuum line-to-FPR pulled, to show ruptured bladder part of the test.



Dynamic test:

Show pressure at idle with vacuum line ON FPR, then show pressure at idle with vacuum line OFF of FPR. This confirms that regulator is responding to vacuum, which is allowed to FURTHER pull the FPR diaphragm out (or in), to modify fuel pressure. It also shows something else which I forget at the moment, but can find out if necessary.

Show hammer down test (all the way down). Tape the guage to the windshield, like you have it now, get on the road, and drop hammer. This test shows FPR responding to vacuum change under max load, for ACCELERATION ENRICHMENT test. There's a spec pressure for this test - in second gear, @WOT.

If you have FSM, you can include shots of specs for comparison of your actual readings with reference readings.


EVERYONE - BOOKMARK THIS POST!

 

[dogfish246]

OK, I took the vacuum hose off the FPR and it has a faint (very little) smell of gas. I really have to get my nose in the hose to smell it. Is there a better way to test the FPR to see if it has failed? I would hate to take the fuel rail with the injectors out to see if they are leaking so I started with the FPR...

Thanks Guys!

 

[Schrade]

OK, I took the vacuum hose off the FPR and it has a faint (very little) smell of gas. I really have to get my nose in the hose to smell it. Is there a better way to test the FPR to see if it has failed? I would hate to take the fuel rail with the injectors out to see if they are leaking so I started with the FPR...

Thanks Guys!

There should be NO gas smell. The diaphragm separates the liquid fuel from the vacuum source, which is behind the bladder. The vacuum assists the tensioner spring in keeping up with fuel delivery, by responding to vacuum change.

You don't have to pull the rail and injectors to test the FPR. You do have to disconnect the return line, and cap it SECURELY.

It's the smaller of the 2 lines see pic. You do need a small plastic tool to unlock the fuel line connector about $7 as Advance / Zone.

 

[Towu4free]

when my car had a similar issue i put a new pump in , bypassed the dampner (with a hose) and turned out my regulator was bad, they're really easy to install and not to pricey, google up coupons for your fav parts store and then go get you one, i think itll run you abou 50 bucks.... good luck bud

 

[dogfish246]

I was refering to pulling the fuel rail and injectors to test the injectors for leaks, but thanks for the photos. I need to get that kit to take the fuel lines off. Did you have something special to block off the fuel?

The test would be block off the return line and see if the fuel pressure regulator leaks (fuel pressure drop) with the key in the run position? If the pressure does drop, how can I tell if its an injector or a FPR?

Also, I broke the stupid little clips for the throttle cable which secures it to the fuel rail coverad They were brittle I guess.

Your area around the injectors is real clean! How did you do that?

 

[Schrade]

I was refering to pulling the fuel rail and injectors to test the injectors for leaks, but thanks for the photos. I need to get that kit to take the fuel lines off. Did you have something special to block off the fuel?

The test would be block off the return line and see if the fuel pressure regulator leaks (fuel pressure drop) with the key in the run position? If the pressure does drop, how can I tell if its an injector or a FPR?

Also, I broke the stupid little clips for the throttle cable which secures it to the fuel rail coverad They were brittle I guess.

Your area around the injectors is real clean! How did you do that?

edit:
DUH. FPR leak will show gas coming out of the vacuum port on the FPR. Disconnect the vacuum line (bottom pic) and watch. Carefully...

No special tool to cap the line. Best thing a little vacuum port cap, and a clamp to hold it on.

To distinguish injector leak from FPR leak, FIRST disconnect ALSO the FPR, and cap the end of the fuel rail with the FPR OUT. Get bleeddown time, do it again with the FPR place, and the return line capped. Note the difference in bleeddown time.

That's easier (but not as definitive) than pulling the rail with injectors as an assembly, and watching what comes out of the injectors...

I can't remember how much line is exposed from the rail INTO the FPR...

 

[92BlackVette]

Your area around the injectors is real clean! How did you do that?

It's probably a garage queen.

 

[dogfish246]

OK, I will do these tests soon! Shes my daily driver so I need a weekend I dont need to go anywhere (never happens, but gotta find time):L!

 

[dogfish246]

OK!!! Here is the deal, I took off the back gas tank lid and looked at the fuel lines. Then, I got someone to turn the car to the run position to prime the pump and right after the pump shut I crimped the fuel line and the pressure stayed up!!! What does this mean?

Im guessing its not an injector leak or FPR pronblem after this test.

 

[Schrade]

OK!!! Here is the deal, I took off the back gas tank lid and looked at the fuel lines. Then, I got someone to turn the car to the run position to prime the pump and right after the pump shut I crimped the fuel line and the pressure stayed up!!! What does this mean?

Im guessing its not an injector leak or FPR pronblem after this test.

Well, that seems to indicate a faulty check valve in the fuel feed line, BEHIND the crimp, and AFTER the pump itself. I don't know if it's integral with the pump itself, or in line AFTER the pump (and before the crimp)...

Yup - that seems to take the rap off of the injectors and the FPR too. Exactly how long did the pressure hold tho'? Were you able to measure it by time?