Corvette Forum : DigitalCorvettes.com Corvette Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
I have a 91 Convertible that runs great. Over the summer I came out of a store and when I went to start the car, I would start momentarily and then die. This happened several times. I waited a few minutes then it started and ran fine. A few months later the same thing happened in my garage. If I gave it gas when I cranked it, it would run until I let off the gas, then immediately die. This is when I learned about VATS. I waited about 15 minutes and it's been fine until this morning.

Same deal, it won't start. The difference is now I've tried it several times today and it still won't start. The security light flashes. The confusion I have is that some report their car won't even crank. Mine will and will briefly catch then die. I'm assuming a VATS failure will disable the injectors. I'm pretty sure it's not the fuel pump - but I haven't actually checked the pressure yet - but I do hear the pump when I turn the ignition on. Any help would be greatly appreciated.
 

·
Registered
Joined
·
1,855 Posts
If I gave it gas when I cranked it, it would run until I let off the gas, then immediately die.
You can't give a EFI engine" gas"; nothing to pump fuel in like on carb
If you crank with foot on accelerator then computer shuts of fuel because it thinks you are trying to clear a flooded engine.( will do the same if the TPS volts are too high when cranking)

If it starts with throttle open generally means engine is rich ( leaking injectors ?) and opening throttle lets more air in to lean it out

The confusion I have is that some report their car won't even crank. Mine will and will briefly catch then die. I'm assuming a VATS failure will disable the injectors.
VATS takes out the injectors and starter but someone could have bypassed the starter enable relay .
It is also possible for only the injector part of the VATS to be faulty.Both would give your crank ; no fire condition


I haven't actually checked the pressure yet - but I do hear the pump when I turn the ignition on.
At this point you are only guessing.
Pump may well be running but not making enough pressure.
Ditto if fuel filter is blocked
Fuel reg may be faulty, bleeding rail pressure back to tank.
Time to do the basic fuel pressure tests to see what area problem lies in.

If fuel pressure is good ,get a noid light and check for injector pulse while cranking.

Check the computer for codes
 

·
I have poor impulse control.
Joined
·
3,813 Posts
If your "Security" light still blinks with the ignition turned "on", then it is a VATS issue. However, there's also a small chance that a VATS issue could be related to a bad ECM.
 

·
Registered
Joined
·
186 Posts
91 Vert

same model and same problem, mine seems to have been the fuel pump. would run on starter fluid for a bit and then die, it was a real PITA since it was intermittent. finally died altogether and discovered the short i was looking for was apparently a dying fuel pump. not to say this is Definitely your trouble but certainly check it out; i could have kept lots of storage time off the books had i been able to narrow it down more quickly. takes about 30min to change fuel pump and i dont normally do much more than brakes and oil changes on my cars.

good luck,

and you are asking the right guys here on DC. grumpy has a lot of "wont start" info to look thru in case you need it. its in one of the main c4 forum posts at the top
 

·
Registered
Joined
·
4 Posts
Discussion Starter #5
vetteoz, I realize you don't hold down the accelerator when you crank a fuel injected vehicle. The engine will catch, that's when if i push on the accelerator it will run. As soon as I let go, it will die. I have fuel pressure at the rail. I don't know how much as I don't have a gauge yet. I was hoping someone would be able to narrow it down before I had to start buying tools.... The security light will flash when I open the door, but will go out after I attempt to crank it. I was leaning toward a VATS issue initially, but now....
 

·
Registered
Joined
·
38 Posts
vetteoz, I realize you don't hold down the accelerator when you crank a fuel injected vehicle. The engine will catch, that's when if i push on the accelerator it will run. As soon as I let go, it will die. I have fuel pressure at the rail. I don't know how much as I don't have a gauge yet. I was hoping someone would be able to narrow it down before I had to start buying tools.... The security light will flash when I open the door, but will go out after I attempt to crank it. I was leaning toward a VATS issue initially, but now....
I would sugest pulling one injector connection at a time and try to start it after each one is off put it back on and try the next one I had a bad injector on my 91 and found the bad one that way as soon as I removed the connection it fired right up and kept running as long as it was disconnected it would run! this is a quick check and no special tools needed for it and works! Hope it helps!
 

·
Registered
Joined
·
1,855 Posts
I had a bad injector on my 91 and found the bad one that way as soon as I removed the connection it fired right up
:thumbsup:
One bad injector will shut the whole injector bank down.
Can put a DVM on each injectors terminals and see if all are in the correct range ( 16 Ohms )
 

·
Registered
Joined
·
89 Posts
I'm in the bad fuel pump camp. Check your fuel pressure. Also as a quick test, get a mallet and hit your fuel tank 4-5 times then try to start it. If it starts and runs, you confirmed the pump is bad.
 

·
Registered
Joined
·
38 Posts
There's a red wire hanging out of the harness under the computer box that is a test wire for the fuel pump just put a hot wire from the battery to it and the fuel pump will work or not easier than banging on it!
 

·
Registered
Joined
·
89 Posts
Granted that the test lead is easier for seeing if the pump cycles. My mallet suggestion was more so a tip for getting the car home if you're stuck on the side of the road.
 

·
Registered
Joined
·
21 Posts
I don't think it's your vats because on my 86 when I would go to turn the key i would get nothing at all only inside lights would come on, i found out i needed the vats module thing from ecklers and 15 dollars later it was starting fine. so if your started and then died that's prob not what it is but then again mine is a 86 so maybe they changed things?
 

·
Registered
Joined
·
1,855 Posts
I don't think it's your vats
As I noted in post # 2
VATS has two parts ; injectors and starter.
It is possible for the injector side only to be faulty ( unlikely but has been reported before )
 

·
Registered
Joined
·
4 Posts
Discussion Starter #13
I'd like to thank everyone for their help. I tried everything I could and fought with it several hours everyday for a week.... I had no hair left to pull out so I called a trusted garage. The garage owner came and got it today, I'll let you know how it turns out.
 

·
Super Moderator
Joined
·
8,519 Posts

·
Registered
Joined
·
12 Posts
you've been given a good deal of mostly good and useful advise,but Id point out no ones mentioned the
sensor(s) next to the distributor, base occasionally one of these starts acting up intermittently causing the fuel pump or ECM to stop working




http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401

http://members.shaw.ca/corvette86/FuelSystemDiagnosis.pdf

Bingo! If it fires and kills then it is getting fuel pressure, bu low oil pressure or a failed switch will kill it every time. :thumbsup:
 

·
Registered
Joined
·
1,855 Posts
Bingo! If it fires and kills then it is getting fuel pressure, bu low oil pressure or a failed switch will kill it every time.
How so?
Once the ECM gets the ref pulses from the dist if fires the fuel pump relay back up in parallel with the oil pressure switch to run the fuel pump
If the ECM doesn't get the dist ref signal and see the OP switch come on line while cranking it won't pulse the injectors so you would have no fire with a faulty OP switch
OP switch input to ECM is only functional when engine is cranking so if switch was intermittent it would not shut engine off AFTER it had fired

DC won't let you post links to other Vette sites so here is a cut and paste from L98 startup

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run.
The distributor will send a string of pulses to the ECM) in response to the engine being rotated by the starter. These pulses continue as long as the engine turns and if they are not present, the engine will not run.
ECM Reaction:

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors

The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch. (If the fuel pump relay fails, you can still normally get the car to start and run unless you can’t make at least 4 PSI oil pressure. This is a “limp home mode” feature put in place to allow for a fuel pump relay failure).


 

·
Super Moderator
Joined
·
8,519 Posts
Ive seen several corvettes with similar issues that cleared up after replacing those sensors, Im reasonably sure the sensor INCORRECTLY and INTERMITTENTLY, indicate the oil pressure momentarily drops to ZERO causing the problem, but what IM sure of is that replacing the sensors cure the issue ocasionally
 

·
Registered
Joined
·
547 Posts
Hey guys, it turned out to be the air idle control sensor..... what a nightmare, lol.
Was was wrong with it? Did you put a new one in and then make sure the minimum idle is set right? When you took this out, did you remove the TB and the IAC housing and clean it thoroughly?
 
1 - 19 of 19 Posts
Top