I have a 1996 C4 that did not start in the beginning I replaced fuel pump did a bypass on the vats replaced fuel pump replaced relay new Opti Spark new IAC new throttle position sensor new crank position sensor new battery new ECM now it starts but it shuts right back the hell off I'm so frustrated I I want to catch the car on fire in my driveway and watch it burn it does start but it's just right back off can anyone help me trust me and believe I know a lot so my passion is vets I've helped a lot of people fix their vets from YouTube to Facebook I am just stuck on this I need help and I'm asking please please please please please I do understand that these vets are very finicky but this car has got me so stumped thanks a lot you guys and girls out there

 

What was the first original problem or symptom?
First thing is connect a fuel pressure gauge and watch the pressure while all this is happening. See if it goes to 38 and then to about 35 when started.
Sounds like you have spark.
Was the PCM the exact part number as the original one?
Check all plugs, connectors that were touched or you got near to.
Check all fuses inside the car and the 2 sets of Maxi fuses under the hood.
Make sure the EGR valve is closed and feel right with a finger on the plunger
Check drive to the injectors with a NOID light.
I might connect a scanner and check for any codes just to see what turns up. It's OBD 2 so that's an easy one. Or use on board diagnostics.
Just wondering what you did to bypass VATS. Was it just a resistor in place of the key pellet?

I could add more but enough for now.
Who has been doing the repair work.

 

Le Mans Master no codes coming up I bypass Vats fuel pump relay is there more to vats then just that fuel pump relay everything you said I've done thinking of looking at the CCM?

 

Yes - there is more to VATS than the Starter interlock and the fuel pump.

As you probably know - you can make the fuel pump run by bypassing the oil pump pressure switch.

As pcolt94 said - hook up noid lights in lieu of injectors and see if they are being instructed to open.

If you bypassed VATS with a resistor pellet - and the starter is working - then that's fine - otherwise - I think your bypass may not really be working. if you really want to delete VATS - Consider reprogramming PCM for VATS off !

 

OP's car is a '96. Takes special software and interface, or buying on online tune from someone like PCMFORLESS here in Ohio.

OP, why did you bypass the VATS ?

Just because you got a new Optispark, depending on what you bought doesn't mean it is good. The less expensive ones are notorious for sometimes not working right out of the box. You need to go back to debugging 1 thing at a time, rather than guess and throwing parts at it.

 

Brief description of VATS

The CCM reads the key pellet in the key. If it is not correct the engine will not turn over and the security light will come on solid.

If the CCM reads the resistance is correct it will close the start relay. Then it sends a signal to the PCM. The PCM then turns on a program called FEDS which enables drive to the fuel injectors.

So if the engine turns over with the key in the ignition, it sounds to me like VATS is working and letting you start (turn over) the engine.

Bypassing the fuel relay is done anyway when the engine starts and closes a pressure switch with oil pressure. So bypassing this relay has done nothing and not a good thing to do for safety.

In the end you need to do the manual checks on the engine to see what is not right or working. If it starts and runs I don’t believe an opti would cause this especially since there is no opti codes. You need to look at fuel pressure and injectors and the other items suggested and see what turns up.

And would still like the know is this the original problem or a new one?

 

I have seen lots of posts chasing this type of gremlin. One guy did a follow up and it his solution was wiggling the main connector to the ecm. I would bet you have ground issues, oxidation on connectors or even contact points in the ecm/pcm (whatever the term is for 96) that are loose. If a car starts and then shuts off that is usually a ground or electrical issue. If you have a bad fuel pump, faulty relay etc it won't start in the first place.

 

Everyone has given some great advice in this thread, but I've been thinking about it and wanted to add a thing....



Some have asked why you bypassed VATS? I agree and wonder how you did it?
When I first got my '92, it too, "did not start in the beginning" -like yours. I didn't know how VATS worked back then, so I bypassed the start interrupt relay, just to get it cranking so I could diagnose it better -or so I thought. I ended up causing myself a bunch of extra grief, from that clever move. BUT after doing that, the symptom was identical to what you're describing; it would "start, then shut right back the hell off". "Ra-ra-VROOoommm...dead." Over and over and over. If I pumped the gas pedal wildly, I could keep it running (barely/poorly).

The problem with my car was that it had the wrong key; VATS -or the BCM wasn't seeing the correct resistance value from the key, so it had disabled the injectors and starter, of course. I'd bypassed the start interrupt relay so then it would crank, and I guess the ECM shoots some fuel to start it regardless....I also guess that the TPS causes the injectors to shoot "pump shot" fuel regardless too....since pumping the gass pedal would keep it running. But ultimately, the injectors would stop firing and it would die.
SO....how did you bypass VATS and why? Is it possible that you (orsomeone previously) bypassed the start interrupt relay? When the key is on, and you're not trying to start it, what is the "Security" light in the IP doing? And finally, when it won't stay running, what's missing; spark or fuel? Those are really easy/quick checks that can tell us a lot.

 

Actually - IMHO a '96 is easier to reprogram - you can do it through the ODBII plug with the Jet "tuner". No pulling the PROM and sending it away.

 

As pcolt94 mentioned, check the fuel pressure.

 

Long story read the thread honey thanks a lot for reaching out though

 

So what was the 'fix'?

 

Someone changed the CCM it was another shop that didn't know what they were doing the key is vats 2 the CCM is vats 13 it started right up running like a champ I seem that u had the same problem so pretty much what it boils down to is some swapped it and the computer did not see the right resistance from the key your friend Tom got a hold of me and I already fixed it I want to thank you for reaching out to me first VATS IS A B*tch I don't know what the hell GM was thinking from a horse and carriage C3 to a space shuttle C4 LOL I hope you enjoy your weekend thank you very much again for reaching out to me God bless you honey

 

Damn. I threw that one out there, but though it pretty unlikely. That was the deal with my car too. CCM change...prev owner drove it home from the dealers, then "it wouldn't start" and that's how I bought it. I think the owner grabbed the old keys one day and it wouldn't start. Only thing that I can think of that makes any sense.

Glad it's running again.

 

Thanks sweetheart I appreciate U reaching out seems like we had it 📌 pointed I want to add u as a friend on here can u tell me how to do that?? I might need ya in the future or vice versa Pcolt94 told me about u but I already had it figured out I'm a pretty smart woman Pcolt94 said u r one of the smartest people on the Forum I've been helping people on YouTube & Facebook and they track me down now I'm helping on here

 

IDK how to make friends on here...just ask most any of the other members and I'm sure that they'll confirm!

You should post up some pics of your shop! I'd love to see it. Here are a couple of mine....

 

Hoy ****!!! That's triple bad ***!!!

 

This is very interesting thread about the VATS being the culprit.

I have a 96 LT4 car. I made some minor upgrades to the motor when I rebuilt it.

I called the guy at PCM for less and he sent me a reprogrammed PCM. He set it for the cam per the cam sheet. Set it for 30# injectors, set the fans at 195. Turned off the skip shift. Turned off the lower O2 sensors. If I decide to bite the bullet on some headers I wont have to mess with the rear O2 bung. He never said anything about the VATS. I got the PCM plugged it it and the car runs great. I know he didn't turn it off because it was still working, the flashing etc. Fast Forward 1 year. I had to replace the starter actuator in my column because the old one decided to break. This was another new repair for me and took a while. I pulled the column to get easier access. I had to have the ignition switch out, I can't believe how small the VATS wire is, so I decided to bypass the VATS. I checked my key, 8K ohms, ordered the bypass module from Ecklers. Installed it and the car starts and runs as normal. Is the VATS info not housed in the PCM on the 96?

Thank you

 

Did you have to find a VATS 13 key?

 

VATS is w/in the BCM.