Hi team

experiencing a no start condition. Key in, security light comes on and goes out, turn key to start (with clutch pressed)and nothing; temp gauge pegs, wideband cuts out; all normal stuff but no crank

clutch safety (green and purple) link up fine with clutch pressed and bypassing the starter relay (connecting the big green and yellow wires) has it cranking and stumbling for a few seconds then dying (presume no injector pulse)

VATS disabled in bin

stumped! Thoughts really welcome

 

Given this statement; "VATS disabled in bin" I'd think once you got it to crank the starter, and it stumbled for a few seconds, I'm not so sure VATS is your problem. How could it be, since the ECM has effectively been programmed to ignore it?

I'd be inclined to do a noid light check, fuel pressure check, and check the spark for good measure.

 

Thanks Orangebird

just seems odd that it doesn’t crank unless I bypass the relay and then won’t run but for a few seconds. Rinse and repeat. Plug the relay back in and nothing

Fuel pressure is good and can hear the pump prime

but fair and not impossible a few systems have been knocked out here

 

What happens if you disconnect the EST connector and take away ECM spark control?

 

thanks - see the car on weekends (lol, sounds a custody arrangement) and so can play about with it then.

Curious, what's your thinking with pulling the EST connector ULTM8Z?

 

When you say it won't crank unless you bypass the relay are you talking about the starter enable relay inside the driver side kick panel?

 

Exactly. Pull the relay and bridge the outer wires

 

Do you have the proper key with matching resistor pellet?

VATS is a two-part system:

(1) the passkey module verifies the resistor pellet in the key matches spec and then enables the start relay.

(2) the passkey module verifies the resistor pellet in the key matches spec and then passes on a signal to the engine ECM to enable injectors.

Disabling VATS in engine ECM software only impacts fueling. The passkey module still has to be satisfied with the correct resistor pellet to operate the start relay. There are multiple ways around this if needed, but you shouldn't need it if you have the right key in good condition (they do wear out).

 

The reason why I asked is because I don't understand why if you have VATS disabled in the programming on your chip in the ECM then why you also don't have the starter enable relay permanently bypassed too.

Do you have it setup this way so you still get the starter interrupt benefit of the VATS for some theft protection?

 

QwkTrip - yep same keys that have been working for years prior to this issue. Tried both on experiencing the issue. This was also my thought. I'm running EBL and the starter bins contained within and I've seen posts by RBob (RIP) mention that these have VATS default switched off. In Tunerpro I only see one flag for VATS and indeed the box for that flag is not 'checked' - tried checking just in case but no luck.

Airwolfe - as above, VATS is disabled really as a product of using the EBL flash system bins - haven't touched it otherwise

The VATS security light in the gauge cluster illuminates and then goes out after a few second suggesting to me that VATS is functioning insofar as it powers up and recognises the correct resister in my key (light going out).

I'm thinking to probe the VATS wiring as best as I can without pulling the dash to be able to actually get to the VATS module - so that's the ECU side where I would expect some kind of a signal current to fire the injectors, and to the starter relay to switch on the relay - if I understand the VATS system correctly

not discounting OrangeBirds back to the fundamentals approach which I'll have to move to

thanks for the constructive fact finding - appreciate it is challenging on a car thousands of miles away...

 

I think the passkey module operates the security light, so perhaps you will still see it flash even with ECM de-featured. Just a guess.

There are some screenshots in this thread of programming out VATS,

https://www.thirdgen.org/forums/elec...pass-vats.html

 

OK now the people trying to help you have some more information to work with.

I assume you have a Dynamic EFI EBL P4 ECM since your username is GTA1990 and you have your car listed as a 1991 Trans Am with a L31 Vortec engine with LT4 Hot Cam, a T5 manual transmission, and a 3.42 to 1 gear ratio in a 10 bolt rear end with a limited slip differential. I assume you meant 3.42 instead of 3.43. 3.42 was in the GM 10 bolt and 3.45 was in the BW Aussie 9 bolt.

I want to get this question out of the way now. Does your engine still have the original assembly line installed or original replacement GM Rochester Products Multec fuel injectors?

The 1989 to 1992 RP Multec fuel injectors are retroactively defective by design as I like to say. The "Enamel" insulation used on the wire the voice coil is wound with can't stand up to ethanol, methanol, and other chemicals/solvents used in reformulated gasoline, fuel injector cleaners, "HEET" and other products like it for treating water in fuel, or many other things people like to pour into their gas tank. These RP Multec fuel injectors fail intermittently and in weird ways with their impedance measuring all over the place cold, warm. or hot with them dead shorting out to intermittently shorting out. This can cause all kinds or starting, running, or drivability problems and can make the injector driver in the ECM say FU buddy I'm going to sleep until you sort your problems out or pop 1 or both injector fuses in the fuse panel.

I've screamed, yelled, cussed, pulled my hair out, and chased my tail in circles as many times as I ever intend to do and I vowed to never do it again. I won't even begin to troubleshoot or diagnose starting, running, or drivability problems if the engine still has them installed in real life on cars I can lay eyes and hands on and for sure ain't going to do it over the internet across the ocean. These RP Multec MFers are the Devil and an exorcism should be performed on them by shitcanning them straight to the trash can and replacing them with the correct size 100% bolt in drop in Delphi replacement injectors for the RP Multecs. They ain't cheap but they are worth every penny.

If your Pass-Key VATS seems to be working properly but you car won't crank unless the starter enable relay is bypassed then your starter enable relay could be defective or it's not being energized by the PASS-Key module. The PASS-Key module could have partially failed in a way that it is no longer energizing the starter enable relay or the connections and wiring between the two have failed.

You say that the starter bins that come with your EBL have VATS disabled by default and you have checked and verified this with TunerPro. I don't know anything about that but there are plenty of guys here that do know all about it. If this is so then with the starter enable relay bypassed or with the PASS-Key system working enough to energize a working starter enable relay the engine should crank over, start, and run.

 

This is my understanding of how the PASS-Key VATS works on our 3rd gens. I haven't studied this system to the ends of the Earth and I might have a few things a little off that others here with far more knowledge can correct.

PASS-Key VATS doesn't do anything to the fuel pump or ignition system. PASS-Key VATS won't kill an engine that has started and is running.

You put your "PASS-Key" ignition key into the ignition lock cylinder, you turn the key forward to Key On/Engine Off but not all the way forward to Crank, the ECM turns on the fuel pump relay for 2 seconds to prime the system, you turn the key forward to Crank, the PASS-Key module looks to see the correct resistance range on its input wires, if it likes what it sees then it energizes the starter enable relay and sends a 30Hz square wave signal to the VATS terminal on the ECM, the starter cranks the engine over and the ECM has turned on the fuel pump relay and turned on the injector driver and is firing the injectors, if the ECM doesn't see the 30Hz square wave signal on its VATS terminal it quits firing the injector driver in the ECM which quits firing the injectors. The engine doesn't start and you release the key from the crank position and the ECM turns off the fuel pump relay.

Now the stuff about turning the Security light on the dash and what the light is doing and setting trouble codes in the ECM for VATS I don't know for sure how that all works. I believe the PASS-Key module sends the 30Hz square wave signal to the VATS terminal on the ECM all the time that the engine is running and if for some reason the ECM quits seeing that 30Hz square wave signal it sets a trouble code but it doesn't kill the engine.

PASSS-Key modules are blank when brand new. The first time it is used it picks one of the 15 resistance values that best matches the resistance it reads from the pellet resistor on the ignition key. There is a target resistance value and a range below and above that value that is acceptable. It is now programmed and hardcoded to that target value and acceptable resistance range. It can not be reprogrammed to another resistance value.

You can replace a failed PASS-Key module with a brand new one or you can replace it with a used one if you have the matching key for it. You can figure out the correct resistance for it by buying the 15 resistor VATS kit and testing them 1 at a time until it works but you have to wait at least 3 minutes between testing one to the next one even if that next one is the correct value.

90% plus of the problems with PASS-Key VATS is the pellet resistor in the ignition key, the contacts in the ignition lock cylinder, and the wiring that runs down the steering column. The contacts on the pellet resistor and in the ignition lock cylinder get dirty and it quits working. They can be cleaned and the system work again. The insulation on the wiring running down the steering column gets chaffed or the wires break.

 

Just curious, where would you get a new PASS key module?

 

Same place you get any other old rare discontinued NOS GM part at.

 

Thanks Airwolfe

bosch replacement injectors from southbay and yep the car and modifications are as you have summarised

it not cranking (without the start relay bypassed) and the injectors not firing, has me thinking it must be the VATS. I should add that the ECU looks to be online going from the EBL software

Have an ordered a VATS bypass which should be with me by late next week. Perhaps with VATS disabled in the ECU it still needs a signal (agnostic of the Hz) from the vats to fire the injectors?

 

With VATS disabled in the computer you can bypass the starter enable relay and throw the entire PASS-Key system away. With VATS disabled it doesn't need to see the 30Hz square wave signal.

 

I don't understand what you mean here. It's late and I'm tired too so that is a factor.

If you hadn't mentioned VATS is disabled in the bin in your first post then high on my list would have been PASS-Key VATS problem.

 

Loose language by me. The EBL system includes software for providing realtime monitoring of data observed by the ECU via a laptop

Key on the EBL software is seeing a signal from the ECU and presenting usual readings for the parameters the software displays.

essentially me saying the ECU seems to be active and functioning correctly

 

The only reason the start relay exists is to give VATS a way to interrupt the starter. If the whole problem here comes down to the relay not actuating, then maybe consider bypassing it. All the methods of bypass are shown in the link I gave you earlier.

That seems more logical than putting a bunch of time and money into repairing a VATS system that you wanted to disable in the first place?

 

As above it’s both a no crank and what I presume also to be injectors not firing condition (car starts with relay bypassed and stalls out quickly thereafter)

Experiencing both of these issues simultaneously without one or the other before is leading me suspect the vats is playing up