Quick background, picked up a 1990 camaro convertible with 305 TBI. Came with stock motor and tranny but the previous owner was in the process of removing the engine and trans before I bought it. There was no engine wiring harness or computer. I got a replacement TBI harness and 305 tbi computer and replaced all of the missing sensors with oem sensors. The fuel pump was replaced by previous owner as evident by the complete hack job done to replace the pump. The vats system is bypassed with the started relay being jumped, i do not have a resister bypassing the PASS module. The steering column was changed with a new key and ignition and I have the PASS module for the column I put in but did not change out the one that was in the car.

The good:
The car will crank and starter engages as well as fuel pump primes

The Weird:
occasionally the injectors will fire and the car will try to idle but dies almost immediately. If i try to keep it running by opening the throttle blades, it might stay running for another couple seconds but still surges and dies. The injectors spray sporadically with the engine surge and then it dies. I have tried to play with timing at the distributor to get it to idle but no success.

The Bad:
The injectors do not want to fire all the time, like now for instance if i try to start the car it just cranks with no fuel from the injectors.

My question to everyone is
Where should I start my diagnosis.

 

Will it start with the prom removed ? What ecm 1228746 ?

 

Yes it is ecm 1228746 and Holy $*** after checking the prom inside the computer ( I didnt even think to check it) I noticed it is some hypertech chip, PN 122 361 SN 548 982. That seems to be the proper hyper tech chip for the TBI units, but I pulled the prom and wouldn't you know, the damn thing fired right up and idled. I didn't let it run long but it fired right up with no surging or idle issue or stalling. I guess now I need to find a stock TBI chip and see what it does with the stock prom.

Unfortunately, I think it might have a knock but I will have to diagnose that another day when i have time and let it run a little more.

 

Sounds like you actually have a vats issue, a few ways to bypass a hz modulator, chip programmed without vats or get a 1227747 305 automatic truck ecm with chip. It’s plug and play .

 

Can I change out the modulator with the correct one to fix the problem?

 

You can attempt to fix the passkey module and correct resistor or send a 30hz to the ecm with this

 

That is your problem. You don't have the VATS bypassed. You just have the starter enable relay bypassed.

It works like this. You stick the key in the ignition and turn it all the way forward, the PASSkey module reads the value from the resistor pellet on the key and if the resistance value matches the PASSkey module enables the starter enable relay, the car cranks and starts, if the ECM doesn't see a frequency signal on the VATS pin within a few seconds it kills the fuel injector driver and the car dies.

There are several ways you can fix this depending on if you want to bypass the VATS and have no security or if you want a fully functioning VATS security system.

Do you have the VATS key that went with the steering column you removed from the car?

 

Do those vats bypass modules work?

 

Yes they work. I have used the exact same one Tuned Performance linked to you on Amazon. Even though it says PASSkey II and LT1 and LS1 it also works with PASSkey and TBI and TPI.

 

Yes I have the the key and the passkey module that came with the steering column. The key is #2 on the resistance values in the VATS chart measuring about 524 ohms. I have a resistor i could place in line off of the ignition (the orange wire). I can only assume the module i got with the steering column is the correct one though.

 

I meant do you have the ignition key that came with the column that was in the car that matches the PASSkey module that came in the car and is in the car now.

 

Yes to my knowledge it is the original key that came with the column and the pass key module for that key. Can I test the module to confirm? The module that came with the column is currently on my bench.

 

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

 

Your car came with a PASSkey module installed installed in it and is still in it, you changed out the column for another column and key and you have the PASSkey module that matches your newer column. Do you have the ignition key that came with the column that was in the car when you got it before you swapped columns?

 

If you got time you can get this but have to wait until the passkey times out between testing each resistor.

https://www.ebay.com/itm/19644480154...mis&media=COPY

 

Negative, I do not have the original key that came with the original column.

 

I bought a bunch of resistors, do they have to match the resistance exactly to the key "chip" I have a 510 ohm and 560 ohm and my key measures at 542.

But i think i see the issue, I would need to know what the ohms are for the pass key in the car currently, correct?

 

There is some difference in resistance that will work see chart

 

OK. If you did you could just measure the pellet resistor and get the value needed for the bypass resistor.

Do you have a set of the 15 bypass resistors?


VATS Bypass Resistors

 

560 of the module is 2 should work

 

I have the various resistors to be able to bypass the system. I would need to trial and error though waiting 3 minutes between each try because i dont know what the passkey module resistance is and i dont have the original key for the one in the car.

 

Yes the pellet resistor in the key you have has to match the PASSkey module you have. It's a B*tch to swap PASSkey modules. They are hard to get to. If it was easy to get to then wouldn't provide much security. A PASSkey module can't be recoded either. New they are blank, first key installed they are hardcoded to that key's pellet resistor range.

You can disconnect the the orange wiring that goes to the ignition cylinder from the connector and wiring that goes to the PASSkey module under the column. Your ignition key will now just be a dumb key. Start with the first of the 15 resistor values on the chart and connect each resistor one at a time to the connector going to the PASSkey module waiting 4 minutes between values until you find the correct one so your car starts and stays running.

 

Thank you, I will try the route of trying the various resistors in the orange wire and that should fix the issue.

 

Did you have any luck getting your car to run?

 

Yes, I ended up buying that GM VATS bypass module and hooking it up. Car starts up and idles now, but I have to set timing and adjust the idle because its idling probably around 2k. I'll check the IAC and TPS and maybe adjust the idle screw and see if I can get that settled , but for now I am happy it starts and runs on its own.

 

Interesting.
We have the whole dash out currently and now the car won't start, or starts just like the OP says.
It was running and driving just fine before the dash came out due to a PO and his dremel to make speakers fit...

The VATS has had the resistors soldered in line as we tested them the other day at 680 ohms on the key and the resistors in the line.

When we go back out there this week to try and get it going again, I will be referencing this thread to see if that is our issue.

Awesome work by the PO to fit his crappy speakers in the dash....


Old dash removed and it feels kinda nekkid in there now...


Fresh from the junkyard dash ready to install.

The new dash is somewhat installed now, but we stopped moving forward when the car suddenly stopped starting.
That is where we are currently.

 

Have to check to make sure the soldered in resistor is not dislodged or damaged. You can try removing the chip from the ECM and see if that changes anything for you.

 

Junior went out at lunch and found that he had unplugged the VATS from the harness.
But this thread is what lead us to look for that little black box.
Car starts right up now with it plugged in, imagine that.

He was going to pull the chip to see if that was the thing as well, but didn't need to go that far this time...

I still ordered the little 30hz modulator gizmo for the car though.
There is also a 1989 305 powered truck in the local junkyard we may go and requisition the computer and chip from as well.

Good thread!