Chevy Impala SS Forum banner
21 - 40 of 45 Posts

·
Registered
Joined
·
1,677 Posts
OP had decided that there is a VATS problem.
Yet the VATS lets the starter work.

If the starter and fuel injectors work, and there is no PassKey warning light maybe there is no VATS problem.

Normal no run (starter cranks) start problems first check:
Fuel: pressure and injector function?
Spark: Is there spark?
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #22 ·
OP had decided that there is a VATS problem.
Yet the VATS lets the starter work.

If the starter and fuel injectors work, and there is no PassKey warning light maybe there is no VATS problem.

Normal no run (starter cranks) start problems first check:
Fuel: pressure and injector function?
Spark: Is there spark?
I checked fuel pressure and spark and I have both.
 

·
Registered
Joined
·
1,677 Posts
I checked fuel pressure and spark and I have both.
You started threads about VATS delete.
Your problem is the engine is cranking but not running.

It might save you some time and effort if you post what does work(starter cranks), what is visibly wrong(pass key light blinking or solid on in run), and what you have checked and how.

Do you have a pass key light on after bulb test?

Have you checked for "injector click" or used a noid light to see if the injectors are being activated by the PCM?
 

·
Registered
Joined
·
1,677 Posts
If the injectors are not working the VATS or the wiring to the PCM may be bad. This would not set off a pass key light.. It could also mean blown fuses to the injectors which would be a different problem.
 

·
Registered
1995 Cadillac Fleetwood Brougham
Joined
·
2,033 Posts
OP had decided that there is a VATS problem.
Yet the VATS lets the starter work.

If the starter and fuel injectors work, and there is no PassKey warning light maybe there is no VATS problem.

Normal no run (starter cranks) start problems first check:
Fuel: pressure and injector function?
Spark: Is there spark?
According to sherlock, the starter will still work. The PCM will kill the injectors when it sees the VATS issue, and the car shuts off.

My friend is going through the same thing.
 
  • Like
Reactions: Marky Dissod

·
Registered
Joined
·
13 Posts
Discussion Starter · #26 ·
You started threads about VATS delete.
Your problem is the engine is cranking but not running.

It might save you some time and effort if you post what does work(starter cranks), what is visibly wrong(pass key light blinking or solid on in run), and what you have checked and how.

Do you have a pass key light on after bulb test?

Have you checked for "injector click" or used a noid light to see if the injectors are being activated by the PCM?
Yes starter starts the car, car will run for 3-4 seconds then dies. Pass key light stays on solid even after car is shut off (for about 10 mins then light goes off).
I’ve used a fuel pressure tester and I’m getting fuel, I’ve checked for spark and I’m getting spark, I’ve checked injectors and they are working.
I’ve done the 30 min reset anti theft process a few times and didn’t work.

this whole process started about 6-7 months ago and would only happen once in a while then I would just turn the key to on and wait 10 mins then car would start and drive but as time went on it got more frequent and I would clean my key or wait 10 mins then would run but now car won’t drive at all! Only starts 3-4 seconds then dies. Pass key light comes on (solid)once it dies check gage comes on and check engine light.
 

·
Registered
Joined
·
1,677 Posts
The PCM will kill the injectors when it sees the VATS issue, and the car shuts off.
When the PCM does not get a sine wave it will not activate the injectors. Edit: this is wrong PCM will start engine then shut it off if there is no square wave. This can be wiring and the VATS is working.
The PCM does not "talk" with the VATS it just needs the sine wave.
I’ve checked injectors and they are working.
And you say the starter works. These are the only two things the VATS shuts off.
 

·
Registered
1995 Cadillac Fleetwood Brougham
Joined
·
2,033 Posts
When the PCM does not get a sine wave it will not activate the injectors. This can be wiring and the VATS is working.
The PCM does not "talk" with the VATS it just needs the sine wave.
What?

And you say the starter works. These are the only two things the VATS shuts off.
If the injectors are pulsing then what are we even talking about?
 

·
Registered
Joined
·
1,677 Posts
Pass key light stays on solid even after car is shut off (for about 10 mins then light goes off).
If you mean the pass key light stay on AFTER the key is removed, this is not a problem I have ever read about.
If you leave the key in the run position with the engine not running I can not remember if the pass key light stays on.

From memory the pass key bulb test is 5 seconds then it should go out.
If the VATS system thinks there is a key issue the pass key light will light solid or blink.(if the engine is already running)
When the Light is on solid at start up it may or may not prevent the starter and injectors from working.

If the starter cranks BUT the injectors do not work programming the VATS to disabled should let the injectors function.

If I am not understanding something point it out. But it seems you have miss reported something. Spark fuel pressure and injectors should mean a running engine. Edit: this is wrong PCM will start engine then shut it off if there is no square wave.

If you crank long enough you should smell raw gas at the tail pipe if the injectors are actually opening.

We do not know if you are a master mechanic or if this is the first time you have lifted your car's hood. So please do not be offended If I ask again how do you know you have spark and injector signals.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #30 ·
If you mean the pass key light stay on AFTER the key is removed, this is not a problem I have ever read about.
If you leave the key in the run position with the engine not running I can not remember if the pass key light stays on.

From memory the pass key bulb test is 5 seconds then it should go out.
If the VATS system thinks there is a key issue the pass key light will light solid or blink.(if the engine is already running)
When the Light is on solid at start up it may or may not prevent the starter and injectors from working.

If the starter cranks BUT the injectors do not work programming the VATS to disabled should let the injectors function.

If I am not understanding something point it out. But it seems you have miss reported something. Spark fuel pressure and injectors should mean a running engine.

If you crank long enough you should smell raw gas at the tail pipe if the injectors are actually opening.

We do not know if you are a master mechanic or if this is the first time you have lifted your car's hood. So please do not be offended If I ask again how do you know you have spark and injector signals.
Ok when the car runs for the 3-4 seconds the injectors give off a pulsating noise stating they’re running. I’ve used a fuel pressure tester and it was within limits. Now yes when the car dies after the 3-4 seconds of course the injectors are not working. With spark I’ve checked almost each wire with a spark tester and there’s spark. Yes there’s a raw gas smell while it’s running for that lil bit.

so as soon as I turn the car to run the pass key light comes on and it’s a solid light that light will stay on for a few mins before turning off again but when I go to start the car again it’s the same thing over and over again.

so where exactly do those 4 wires run to that are going into the anti theft relay? Because at least one of the wires should be a hot wire correct? I’ve tested all 4 and none of themhave Any voltage.

I really appreciate the feedback and input because it’s driving me crazy!
 

·
Registered
Joined
·
1,677 Posts
200929

Try searching the web with "LT1 VATS sine wave"

Hm, I don't think you're right, dude. I have an EFI system and VATS is supposed to send 55Hz squarevawe signal to my ECM. If my module is really fried (as opposed to my ignition lock being dirty and not sending the right resistance anymore), I'd have to not only jumper the starter relay, but also generate that signal using a 555 or something like it.

When the vehicle's EPROM cannot be reprogrammed to "turn off" passkey, the vehicle's Passkey module or a clone must be used. An ECM programmed with the Passkey option requires a 30 or 50 hz 50% duty cycle square wave in order to enable the fuel injector outputs. The signal is only needed during cranking to get the engine started.

You want to be between 30Hz - 50Hz, and as close to 50% duty cycle as possible (on and off time are equal)

The VATS has evolved but for many years GM used a 30-55 hertz signal. A simulator was not something the average "break the ignition with a hammer and start with a screwdriver" thief would use. It takes a few minutes to patch in.

If power or ground to the PCM would work more cars would have been stolen.
 

·
Registered
Joined
·
1,677 Posts
The relay ONLY affects the starter. Your starter Cranks. Why check it?
In the 1994 ALL power is switched by the ignition switch so no voltage is present at the relay UNLESS you are cranking the starter.
See the PDF
So If you have to check first use a screwdriver to touch the relay case then put your ear to the handle..You may be able to feel the relay click or hear the relay. If the relay clicks when you turn the key from run to start the coil is getting power.
If you remove the relay and are able to make contact with pin 30 then turn the key from run to start there should be +12volts.
If you remove the relay and are able to make contact with pin 85 then turn the key from run to start there should be +12volts.

Font Parallel Rectangle Number Slope


The starter cranks so either your VATS is activating the relay and the relay has power, OR this circuit has been bypassed. It does not matter which because your starter cranks.

You say your injectors are working so The VATS is sending a pulsed (square wave) to the PCM. Edit: this is wrong PCM will start engine then shut it off if there is no square wave. This could be checked with a frequency meter or oscilloscope.
 

·
Registered
Joined
·
1,677 Posts
200931


I should have said square wave. You would see the square wave image on pin A3 of the VATS going to A 25 of the PCM if you looked at a FSM..
 

·
Registered
Joined
·
1,677 Posts
This could be a bad spark timing due to the OPTI. It could be a bad PCM temperature sensor making the fuel mix too rich. Please do not just throw parts at it. There are ways to test most problems. Intermittent problems are very hard, as you can get good data but the problem only lasted a second.

This is not a easy problem.

Get a scanner, or get a cable, and Eehack for a laptop to check for codes and to look at live data. Maybe you need someone to scope the OPTI, ICM, or coil. Any of those could mess up the spark you need to keep running.

If the PCM gets the square wave from the VATS during crank and the engine starts that is enough. It is like the new cars with a fob and push to start button. After the car has started you can walk away with the fob. For safety reasons the engine will not stop. This is what has happened when the pass key blinks after the engine is running. It detects a fault but the PCM never knows about the pass key problem so the engine remains running.
 

·
Registered
Joined
·
1,677 Posts
To add to the list of guesses a stuck injector will flood you out.
There are 4 injectors per fuse. Are all eight injectors running.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #36 ·
To add to the list of guesses a stuck injector will flood you out.
There are 4 injectors per fuse. Are all eight injectors running.
That I’m not 100% sure I’ll double check all the injectors because I’m pretty sure I didn’t check all of them but most.
I’ll also mention that it runs for 3-4 sec then right before it dies it revs real quick.
 

·
Registered
Joined
·
1,677 Posts
I’ll also mention that it runs for 3-4 sec then right before it dies it revs real quick.
I have been surfing the web. The guys marketing VATS simulators do mention engine shut down in the first three seconds but they list their product for 1980-2000 products.
The LT1 sites suggest the square wave is needed at start up and no mention of three seconds.
Yes there’s a raw gas smell while it’s running for that lil bit.
What I am thinking is there would not be a gas smell if the PCM shut off the injectors. Spark but no fuel.

Does it start quickly or is the engine cranking long before starting?

You might be able to see the square wave by using a voltmeter. One probe to battery+ the other to the dark blue wire on A3 of the VATS. In theory you should see some sort of voltage during crank and run. Cheap digital meters might not see this pulsing signal.

If you had a scanner we would look at IAC(idle air control) numbers.

Have you tried opening the throttle slightly before starting it? If the idle circuit is stuck or plugged the engine might stay running if the throttle was slightly open.

I am still not clear on your pass key bulb indicator. Below are quotes from the FSM.

When you turn the key to run it should turn on for 5 seconds then turn off. It should stay off until the key is turned to off.

The FSM says if VATS is in "active shut down mode" the pass key bulb will be lit for 3 minutes or till key off.

A bad key will blink the bulb and " the engine will not start"

If the resistor key circuit fails while the engine is running the pass key bulb will light any time the ignition is in run and the VATS will allow the engine to be restarted any time until "the fault is corrected" So the bulb would stay on as long as key is in run. The engine would start every time even though the pass key is lit.. This is what you asked about in the other thread.

I have found wrong information in the FSM, usually typos or they cut and pasted information from another manual. I have seen a lot of conflicting information about VATS on the forums but a lot of it agrees with the FSM so this is what I refer to.
 

·
Registered
Joined
·
1,677 Posts
According to sherlock, the starter will still work. The PCM will kill the injectors when it sees the VATS issue, and the car shuts off.
If the injectors are pulsing then what are we even talking about?
The problem with "the VATS issue" is it is not one issue. It can be one of many OR more than one issue at the same time.
It could be a VATS module melt down, bad PCM, a bad broken, shorted, open, coroded wire, keys or contacts.


I went through the FSM last night and need to clarify some things. I and others may have been re-posting information that does not agree with the FSM.


First the easiest check of VATS is the key pass light. If it goes off after 5 seconds VATS thinks the key is good and allows the theft relay to energize and outputs a square wave(GM says pulse width modulated wave form PWM)

The injectors working at start up DOES NOT guarantee that the PCM is getting a VATS PWM signal.
If there is no PWM signal the FSM says DTC 46 will set and the engine will STALL 1.7 seconds after starting.
Since engine "starting" is software defined, stalling in 3-4 seconds could be VATS.
Several other parts of the FSM just say the PCM "will not provide fuel to the engine" This is where most of us got the idea "if the engine starts the VATS is working" BUT only the DCT 46 section says stall after 1.7 seconds.

DTC 46 is set BUT the PCM does not lite the MIL(check engine light) You need a code reader to find DTC 46.Some people call a set code with no MIL light a "soft code" or "hidden code"

FSM test is to check for FWM signal by setting a meter to Hertz and checking for a 40-60 Hz signal between PCM pin A25 and ground.
If you do not have Hz try battery+ to PCM A25 in DC or AC mode.
If you do not have Hz try ground to PCM A25 in DC or AC mode.
This covers what the FSM suggests IF the key pass bulb lights for a 5 second bulb test then goes off.



If the resistor key circuit fails while the engine is running the pass key bulb will light.
After this happens:
Any time the ignition is in run the VATS will allow the engine to be restarted(starter and PWM)

Until "the fault is corrected" So the bulb would stay on as long as key is in run.
The engine would start every time even though the pass key is lit..
I assume no DTC 46 as the VATS keeps sending PWM.

This mode could leave you stranded. If VATS "thinks" the fault has been fixed it will check the key resistor inputs and if they are "wrong" (open, short, or wrong Measured resistance) there will be a no crank no start. The pass key will light and the VATS will do a 3 minute :"time out" where the VATS does nothing EVEN if the key resistor inputs get the correct signal.



Key resistance input wrong. The common reason for the "VATS resistor bypass" modification.
Dirty key pellet, worn or damaged key pellet, wrong key pellet, bad pellet contacts in the ignition lock cylinder, and any wiring problem between the cylinder and the VATS.
The key pass light will light and for 3 minutes the key resistor input will not work, and the starter will not crank.
A malfunctioning VATS module can provide the same problem. If the correct resistance is connected to the VATS and it still lights the key pass bulb, no starter crank, does a "time out" and sets a PCM DTC 46 it may be the VATS module and not the key resistance circuit.

[email protected] What you seem to be experiencing is a VATS malfunction IF:
The key pass light stays lit for more than 5 seconds.
You retrieve a DCT 46 from the PCM
You use a multi meter or scope to check for PWM at A25 of the PCM and it is not there.

Since your starter cranks you could "program VATS out" of the PCM as a quick test. The same cable would let you check all "PCM codes" If you do not bypass the "Theft Deterrent Relay" as part of a permanent VATS bypass the VATS module could still "lock out" the starter


I apologize for saying "If the injectors are working it is not a VATS problem" Several parts of the manual just say the PCM "will not provide fuel to the engine" There is only one place where the manual mentions "engine will STALL 1.7 seconds after starting". This information is found nowhere in the pass key diagnostic section, The stalling information is only on the DTC 46 page and nowhere else I looked.
 

·
Registered
1995 Cadillac Fleetwood Brougham
Joined
·
2,033 Posts
I could have chosen my words better the first time, but I think it's important to clarify that the starter cranking does not rule out a VATS issue. That was the primary point of my post.

Like you said, there are multiple VATS conditions that can be triggered.
 

·
Premium Member
Joined
·
709 Posts
Ok when the car runs for the 3-4 seconds the injectors give off a pulsating noise stating they’re running. I’ve used a fuel pressure tester and it was within limits. Now yes when the car dies after the 3-4 seconds of course the injectors are not working. With spark I’ve checked almost each wire with a spark tester and there’s spark. Yes there’s a raw gas smell while it’s running for that lil bit.

so as soon as I turn the car to run the pass key light comes on and it’s a solid light that light will stay on for a few mins before turning off again but when I go to start the car again it’s the same thing over and over again.

so where exactly do those 4 wires run to that are going into the anti theft relay? Because at least one of the wires should be a hot wire correct? I’ve tested all 4 and none of themhave Any voltage.

I really appreciate the feedback and input because it’s driving me crazy!
This may be a long shot,but look closely at the grounds bolted to the icm/ignition coil mounting stud at front driver cyl head.The VATS grounds there.These eyelet grounds are notorious for corroding and or breaking off the eyelet lug,if never attended to.
Jim
 
21 - 40 of 45 Posts
Top