Fuel pressure with no fuel.... Possible?

[SchnellSchweitz]

I'm having my first real issues with my newly rebuilt 911 and would love some ideas on what may be wrong.... I'll mail someone a bottle of their favorite beer if they can help me solve my issue. No kidding.

Car details - 3.0L, EFI (bitz racing), MSD 6A


First off... The problem.

The starter is working great, she turns over fine, but won't start. I drove the car to work on Tuesday and tried to drive her to go to lunch, but she wouldn't start. I had to use one of my AAA tows to get her home. Nothing is frozen or seized. Motor turns over fine by hand.

I changed the spark plugs today to see if that would help. Nothing improved. Old plugs looked very good.

The fuel pressure gauge shows perfect fuel pressure. Seems to be holding steady at the specified level. However, I've got a non-functioning fuel tank gauge. If I were out of gas, could air from the fuel pump maintain fuel pressure? In other words, could the pressure gauge show air pressure instead of fuel pressure?

It almost seems like I'm not getting any fuel, but I could be wrong. However, I hear the fuel pump working. When I turn the key to start, I hear it activate for the standard 8 seconds or so and then shut off.

Things I've seen so far. The dizzy had an odd layer of brown dust inside. Not a lot, but enough to mention here. I did experience one loud backfire while trying to start her today. A pretty loud bang and a little black smoke at the tail pipe.

All fuses on in the engine bay and on the fuse holder in the trunk appear to be fine.

I'm a little lost on this one because I've checked all the locations I know to check...

Thanks for you advice in advance.

Eric J.

[Targalid]

Back to basics. Pull a spark plug wire, insert a spark plug, ground it and turn the motor over to check for spark. Pull an injector and check for fuel at the injectors. Fuel, spark and compression are what you need to run the car.

[T77911S]

i know on a CIS car you can be out of gas and have fuel pressure since it may not be enough to open the injectors and bleed down, and the pressure may be marginal for spec.
since your injectors open no matter what the pressure, i would think they would bleed off the pressure. now would i say since my pressure gage says i have pressure, would i rely on that alone as a T/S tool to rule out fuel, no.

when i have a car that wont run, the first and easiest thing to do, as said above, is check for spark.
does it start up after it has cooled down? could be a vapour lock issue.

for cars with electronic injection, my first suspect, especially for random running, is the crank position sensor.

[daniel911T]

I have to agree with the "back to basics approach."

First thing I would do, add a couple gallons of premium. You've got nothing to lose on that one.

Second thing I would do on a CIS motor is check all the vacuum connections. If one of the lines is cracked, has popped off, or is in anyway not completely tight, it will either run poorly, not run, or start very hard. Your repair (at least temoprarily) may be just a piece of duck tape away!

Third, make sure all the wires on the loom are connected. If some of the sensors and stuff are unplugged then the motor will be unable to run at all. Cheap fix if you find a loose wire!

If that does not resolve your issue, then I would look into spark. With all due respect to the earlier post, I would suggest first pulling the coil wire from the distributor cap, and cranking, that will tell you if spark is getting to the dizzy. If you have good spark there, but it still does not start, then try pulling a plug and see if you still get spark. This way you know if the problem is in the trigger/coil/ignition box, or the distributor/plug wires/plugs. I just had a weak coil issue where the coil wire would throw a puny spark, but the plug wouldn't spark at all. That was a tricky one to isolate. I guess I should say that it's good to check both spark out of coil, and spark at plug, just to be sure.

If you have good spark, then try the pulling an injector trick. Turn it over and see what you have.

Another easy fix, but unlikely to be your problem, check/change your fuel filter.

Sadly, if you've done all this and it still hasn't resolved your problem, then you're likely getting into deep fuel injection trouble shooting. Get the Bosch fuel injection book from Haynes, a good multimeter, a 6 pack, and a boatload of patience. A friend with a working car of similar year would also be helpful as a donor of known good parts (sensors, etc...) for testing purposes.

Good luck! (You're going to need it!)

GO BEAVERS!

-Dan


Edit: I just noticed you have an MSD 6a. This makes the ignition testing proceedure easier. You don't need to crank to check spark, just turn the ignition on and ground the white wire to the dizzy. Much easier than finding a helper to crank.

[al lkosmal]

Since you have a Tbitz kit, you still are using the CIS intake manifold and airbox. Do you have a pop off valve? If so, check that it is still sealed. And check the box itself for cracks.
regards,
al

PS: and all the other stuff above

[JP911]

You've listed an MSD 6A, so you are using the bitz kit to control fuel only, correct? Can you describe how you have the MSD wired? Wild guess: something is up with the MSD. Either wiring issues, a blown fuse somewhere, or a failed unit (not unheard of). All the advice so far is spot on, but more details on your setup would be very helpful (including pics).

[na2ub]

I vote for distributor cap / rotor. They can quit delivering spark, even when they still look decent. They are cheap, available at your local auto store, and if you have not changed it recently, it is due for a change anyway. I will take a Russian River Pliney the Elder.

Thanks,
Doug

[SchnellSchweitz]

UPDATE - I checked all the spark plugs and they're all providing proper spark. No issue there.

The next thing I will do, as Daniel says, is add a can of premium gas. What's strange is I only drove 85 miles on what I believed was a full tank of gas AND the fuel pressure gauge is showing plenty of pressure.

Perhaps (hopefully) I've been fooled twice on this one and it's just empty.

If that doesn't work.... I'm thinking of checking the injectors. I will use Daniel's method.

GO HOKIES!!! How'd you know I was a Beaver Daniel?

Thanks for everyone's help. I'm reading every post for info.

[Joe Bob]

Well if you have spark......give it a shot of ether/quick start. If it coughs or tries to start, it's a fuel delivery issue. Also it will help draw fuel up the lines if you are low on fuel....

[daniel911T]

Originally Posted by SchnellSchweitz

How'd you know I was a Beaver Daniel?

Thanks for everyone's help. I'm reading every post for info.

I had no idea, I just noticed that you live in the Portlandish area. I'm a Beaver, so I figured you'd either be an evil Duck fan, then I would have demonstrated the clear superiority of OSU; or a Beaver fan, then we would have something in common. Third option, you could be a fan of some strange school called the "hokies" whatever that is, then there would be no harm done.

Joe Bob's idea is very good. It is really beginning to sound like you may have a fuel issue. If it simply isn't running, rather than running poorly, start looking for things that would effect the whole system, rather than little stuff like o2 sensors etc...

Good luck! (Go Beaves!)

-Dan

[ischmitz]

As others said, check for spark and fuel. If you have spark squirt fuel into the air cleaner. If it runs for a couple of seconsds you know spark and timing are O.K. and you are missing fuel.

I don't know the details of the Tbiz kit but this is a Megasquirt, right. And Megasquirt allows to run a laptop with Megatune and see the fuel injector length in real-time. That'll help sorting out engine speed and TDC sensor signal issues.

And yes, a making sure there is gas in the tank doesn't sound like a bad idea......

Cheers,
Ingo

[SchnellSchweitz]

UPDATE - Ok.... we have ignition with a small shot of starter fluid so it just isn't getting fuel. I put 4 gallons of supreme in today so I am pretty sure there is fuel in the line.

Next up.... removing the injectors and checking/cleaning them.

Eric J.

[SchnellSchweitz]

Injectors removed and cleaned. Now I am losing pressure and the car is having difficulties turning over.

Not sure if it's a fuel pump issue yet. Anybody have a way to test the fuel pump. I can hear it come on for the standard 8 seconds or so when I turn the key to the run position. The pressure builds right up. But almost immediately it drops to 20 lbs and then straight to 0.

[1990C4S]

Shouldn't the check valve hold the fuel pressure on that car?

[SchnellSchweitz]

Ok... I found where the fuel is going. My number one cylinder is leaking fuel into the exhaust. I'm getting a pool of gas under the car when I try to turn it over.

Is this the sign of a bent valve??? Fuel is only leaking into the exhaust manifold. I can tell it's cylinder number one because the manifold bolts are letting a little pass.

I opened the valve covers (top and bottom) and nothing looked wrong. All the rockers looked solid and could not be pushed unnaturally in.

Any ideas???

[Mo_Gearhead]

QUOTES: "Injectors removed and cleaned. Now I am losing pressure and the car is having difficulties turning over".... "number one cylinder is leaking fuel into the exhaust."
__________________

If the injector is defective/faulty it may be allowing fuel to run into the cylinder. If fuel is leaking out of the exhaust you could be on the verge of "hydraulic lock". I would NOT continue trying to crank an engine that has so much fuel in a cylinder that it's pouring out the exhaust!

Physics 101 - you can't compress a liquid.

[SchnellSchweitz]

I have a hunch that's exactly what I've got - a hydrolock from a bad injector.


I'm going to replace that injector, but how do I go about unlocking the system. Can I drain the fuel someway?

[1990C4S]

You don't likely have any residual fuel pressure if the injector is leaking. Just remove the injector(s) and out them into a jar. Turn the fuel pump on and see if it leaks.

Search 'injector flow test'.

[SchnellSchweitz]

Ok... I removed the #1 fuel injector and cleaned it again. It did seem to still be letting fuel go through, but I think after a second cleaning I've got 'er so she'll hold pressure.

I also used my mytee vac to pull residual gas from the #1 cylinder bung. It pulled about 1/6 of a cup of gas out.

I also changed my fuel filter and will be reassembling everything this afternoon for another wack at 'er. We shall see.... My plan is to see if the motor will turn by hand before hooking everything up again. Hopefully I didn't bend something in my #1 head/cylinder by the hydrolock.


1990C4S - My fuel pressure was dropping to 20 lbs and then to zero in a matter of seconds so the injector cleaning is a great idea. Thanks!!!

Mo_Gearhead - I believe the hydrolock was a correct diagnosis at this point. Everything seems to be pointing to this.

Wish me luck. I will have another report soon.

[lucittm]

To answer your original question... Yes, your fuel pressure gauge may show full system pressure but you may have no flow. This could occur if there are any check valves in the fuel circuit as I suspect there are in the pump fittings and these one way valves would maintain system pressure if the tank level was below the pickup point depending upon where the fuel pressure sensor is located. As soon as the injectors open the pressure should decrease, but not by much because it is the fuel flow that opens the injectors on the CIS cars. On an EFI system there are other considerations, but you still need flow to have the injectors "fire".
You really should get your tank level sender and/or fuel level gauge fixed.

Mark