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Old 11-18-2007, 06:13 PM   #1
ATXVette85
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Question 1985 Start Problem: runs 4 sec and dies

Friends,

I am humbled by this issue and need to ask for help. I don't want to resort to a shop or just simply replacing stuff randomly in desperation.

Here's the details:

1) 1985 / Auto / 107K miles /
2) Engine died while traveling at 50 mph on even road. No prior signs of trouble or abnormality before failure.
3) The fuel system will now prime the engine to 38 psi, start and run for approx 4 seconds.
4) When the engine dies the fuel pressure drops to zero simultaneously.
5) I have replaced the fuel filter, fuel pump and filter, fuel pressure relay and connector pigtail, oil pressure sending unit, and MFC. Nothing changed the symptoms.
6) Oddly, no trouble code is being issued. Computer displays the 12 code and nothing further.

I read the write up thread listed by the Grumpy Corvette guy. .....Really good info, the answer may be right in front of me, but I have not solved it yet.

I understand 1985 was the only year to use a burn-off module. Does anyone know how to test one of these on the car? I recently purchased a used module off ebay, but would like to test the original before I remove it from the car.

Is there something else I should be checking at this point that would cause this problem?

Thanks,

Lance
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Old 11-18-2007, 11:08 PM   #2
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I just battled a stalling issue , - ended up being worn parts. plugs, cap rotor, coil and igniton control module. after replacing I had eazier start up, and no stalling.

its weird that your fuel preasure is 0 when the car dies. maby it dies from lack of fuel? like the fuel pump stops, and then car dies imedietly following?

how are you checking fuel preasure? is guage hooked to the rails the whole time car is running? - and how long does it take your fuel pump to prime up to 30+ psi ?

could your fuel preasure regulator be blocking fuel at the rails, causing most of the fuel to feed back to the tank instead of going to the engine?

just some diffrent ideas. hope you get this fixed.
I was pulling my hair out over my car last week.

edit - did you replace the small piece of rubber between the fuel line and the fuel pump? I have heard that that piece can go bad / swell up and develop holes and end up leaking gas right back in to the tank instead of pumping it to the engine. - was yours looking ok?
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84 crossfire - new top end - mild cam - k&n filter - shift kit - x piped true dual exaust, no cats, flowmasters - smog equipment removed. = pretty fast for a crossfire
Old 11-19-2007, 06:18 AM   #3
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Brian,

Thanks for reply. I have a fuel pressure guage on the rails during prime, start, and run sequence. When I engauge the engine ignition, the fuel primes the rails immediately. The engine will then start effortlessly, run for 3-4 seconds and die. As it dies the fuel pressure is declining to zero. I believe something is telling the fuel pump to stop running. So yes, I believe the engine stops due to lack of fuel delivery. Fuel flow to the engine appears to be sufficient and unrestricted. In addition, the engine has new distributor, rotor, and the spark plugs are burning perfectly.

Thanks,

Lance
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Old 11-19-2007, 07:26 AM   #4
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the first thing Id check is the oil pressure is reaching and maintaining at over about 10 psi with a separate gauge, the fuel pressure cuts off if the oil pressure drops below about 5-6 psi (yeah I know it says 4 psi BUT that's in an ideal world, in some cases it takes up to 9 psi with a sticky switch)

remember this part
"When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

Fuel Rail Pressurization:

When you first turn the key to the “on” position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.test by attaching a fuel pressure gauge to the fuel rail at the shrader valve, on TPI and LT1 engines its located on the pass side fuel rail
(IF IT WON,T MAINTAIN THE FUEL RAIL PRESSURE FOR SEVERAL MINUTES AFTER THE ENGINE SHUTS OFF,THE FUEL PRESSURE REGULATOR IS SUSPECTED OF BEING DEFECTIVE, OR ONE OR MORE OF THE INJECTORS MAY BE STUCK OPEN

Initial Crank Action:

If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver’s side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time). "


btw those oil pressure switchs are a known source of problems, they get deffective, intermittently,at times, they get oil leaks and they just start doing crappy connections at times, ID replace it even if its supposed to be newly replaced, or at a minimum Id get out a V.O.M. and check its opperation durring the start/run procedure, but thats a p.i.t.a. Id replace it and check the connections and wireing.


If thats not the cause Id be looking at the fuel pressure regulator diaphram it may be leaking and need replacing, better still install a adjustable fp regulator, the pump itself may be defective, allowing the fuel to flow in reverse once it stops, you might have a injector thats leaking (constantly stuck open)


this should help also

http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
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" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"
Old 11-27-2007, 07:37 PM   #5
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Thumbs up! Thank you!

Gumpyvette, thanks for the tips. Your comments allowed me to get the car operating. Is there a Grumpyvette T-shirt I can buy somewhere?


Here's some strange details if you have a few minutes to ponder:

I started by replacing the oil pressure sensor (again).

When I engauged the power the fuel pump failed to initially prime the fuel rails. I reverified all my connections and found them to be good, I then connected my battery charger assuming that perhaps I had a slightly low battery.

Upon re-engauging the power, the pump primed the fuel system as expected. When the ignition engauged the motor started and I turned the charger off. The engine immediately lost fuel pressure and died.

I repeated the start process listed above again but allowed the engine to run for 20-30 seconds with the remote battery charger boosting the system. The engine continued to run with out issue.

I disengauged the charger and the car has operated normally and within spec ever since.


Thanks again,

Lance
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Old 11-27-2007, 08:11 PM   #6
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always glad to help out a fellow corvette owner
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" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"
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