Mongoose350

iTrader: (1)

First, I posted about this in General maitinance over a week ago with no help. So maybe it will be better served here.

Okay, so last week I swapped alt's with a kg3 I've had for about a year. No reason for the swap, I just decided that I'd put it off long enough. After the swap, the car started fine but the alt wasn't charging. No big deal, I put the pos 102amp alt back in until I could get the kg3 tested. After the swap, car wouldn't start.

Now I've checked everything such as relay, connections, grounds and even put in a new starter. Everything has power, the dash lights behave as normal, just no crank. Now it did start with the new starter too, but only three times. Now it's just like it was before with the other starter.

What it does, besides not cranking, is either nothing, or I'll get a click down near the starter as if it gets power for a split second. Also, when I turn the key to accessories I don't hear the fuel pump come on either. However, aside from it not starting, all the dash lights dim or go off when I try to start it as normal.

FYI, it is NOT the Vats, I've had that issue before and it doesn't behave the same, and I've had the Vats bypassed when that happened. Security light goes off after a few seconds as normal. It doesn't flash.

So I've read that it could be the Theft Deterrent Relay (TDR) that is just above the BCM. This will prevent power from going to the starter and fuel pump. I had my courtesy lights and power door locks go out a year ago, so it's time I pull it and fix that connector while I'm at it.

Does this seem like the likely culprit?

WhiteBird00

iTrader: (4)

No, the theft deterrent relay is not involved in starting the car. The relay is connected to the lighting circuit and is used to flash the lights when the alarm is armed or disarmed and when it is tripped.

The VATS system in the BCM is what controls the starter relay and the fuel supply. When starting the car, the VATS system determines if it sees the correct resistance (+/- 10%) through the key resistor pellet and then provides ground to the starter relay coil and sends a fuel enable signal to the PCM to start the fuel pump.

If the car won't crank, try grounding the yellow/black wire at the starter relay. That will allow the relay to trip even if VATS isn't providing the necessary ground, so the engine should crank. If it now cranks but still doesn't start you probably have VATS preventing the fuel enable signal. A tuner can program the PCM to ignore the missing fuel enable signal or perhaps you can fix your VATS bypass.

Mongoose350

iTrader: (1)

One thing I didn't add. The entire time I've owned the car, I have had a similar issue on a much smaller scale. I would turn the key and the same thing would happen, but if I hold it, it will finally crank a random amount of time later. Sometimes as much as 30 secs or so. It's always started before, and it's done this once as it sits. But now unlike before, it doesn't seem willing to do even that.

WhiteBird00

iTrader: (4)

Okay, that doesn't really change the steps to determine if VATS is the problem although I would try replacing the starter relay first because it's quite possible that it has sticking contacts. You can also test the relay with a multimeter or test light. The red wire at the relay should have power at all times. The dark green wire should have power when the ignition is in the start position. Test that the yellow/black wire has ground when the ignition is in the start position or else provide another ground. Then test that power is output on the purple wire when trying to start. If everything else checks out but you have no power output on the purple wire then your relay is bad.

Mongoose350

iTrader: (1)

Will do. Just in case this gives you any ideas, I have replaced the relay itself as well as the starter. I hear the relay clicking when the key is turned. And, just now my buddy tried tuning the vats out and his scanner isn't even reading my car.

**Edit**
Also, this is the same HP Tuners scanner and PC that I used to tune out my rear O2's. It just doesn't pick up anything from my PCM.

Mongoose350

iTrader: (1)

Well, I ended up unhooking the starter and re-hooking it up again, just to be sure. Now I'm getting a click everytime I turn the key. If I hold it in the start position, it will start to click repeatedly but nothing more. Also can smell electrical smell as if it's shorting on something. Thing is, me and a buddy just checked all the wireing from the batt to alt to starter, there's nothing touching and everything is tight. So now I'm lost again....

Hottcamaro86

Whitebird, this is exactly whats going on with my car. Can jump the starter and get it to fire. But wont stay running even with keys in the "on" position. And ive already bypassed the vats. is tuning the PCM the only alternative I have now?

Hottcamaro86

Did you end up ever figuring out your issue?

WhiteBird00

iTrader: (4)

No, tuning the PCM, by itself, cannot eliminate VATS. You can program the PCM to ignore the missing fuel enable signal from the BCM but it can't handle the starter relay.

If both the starter relay fails to trigger and the fuel is not enabled then it is likely that the problem is caused by VATS. If the SECURITY light is on or flashing in the instrument cluster then you can be certain VATS is the problem. Just because you have done a VATS bypass doesn't necessarily mean it's still working. That's where I would check first.

Hottcamaro86

If you have the time to give me some advice I would greatly appreciate it. Im just stumped and don't know what the next step is in process of elimination. I've cleaned my key, replaced my key with correct code, bypassed ignition, verified power from ignition is being sent to starter, jumped starter at relay and been able to get it to fire just not stay running(even with the keys in the "on" position.) checked all of the fuses and made sure all are working. Been trying to read as much as I can for ideas. My next step is looking into theft deterrent relay to try and bypass. good idea or would you suggest I look somewhere else?

WhiteBird00

iTrader: (4)

I don't know what else to tell you. As previously mentioned, the theft deterrent relay has absolutely nothing to do with starting the car so checking it is pointless.

Similarly, if you have already installed a VATS bypass then the ignition cylinder is not connected to VATS anymore and cleaning your key or even replacing it will do nothing since the BCM never sees it. I'm pretty sure there's something wrong with your VATS bypass. That's where you need to start looking.

G8One2

Can you turn the engine over by hand?

Hottcamaro86

Im learning all of this as I go. But the only bypass I did was on the ignition. so I purchased new ignition, plugged new ignition into vats harness, and left original ignition in the column. To my understanding, the new ignition is all the vats system will read and if I have key in new ignition it will always read correct ohms. so then I can just use a regular key in the ignition on the column. So I haven't actually purchased a bypass for the bcm. If I have replaced ignition and replaced key. The only other part to this is the BCM correct? The purple and white wires that make-up the vats harness, where do those wires go? Im guessing the bcm? Im getting ready to purchase BCM bypass today.

Hottcamaro86

I can jump the starter at the relay and get it to fire. But wont stay running.

WhiteBird00

iTrader: (4)

I've never heard of anyone doing a VATS bypass that way although there's no reason it wouldn't work. Most people just spend the dollar or two on resistors and wire them across the VATS wires.

Yes, those wires go from the steering column to the BCM. But unless you are having other problems that are related to the BCM, I wouldn't replace it without some other testing. It would be unusual for the BCM to fail in just the VATS circuit and not anything else like power locks, keyless entry, retained accessory power, courtesy lights or several other circuits.

The first thing to test would be that the BCM sees the key in the bypass ignition switch. First, use a multimeter to measure the resistance of the pellet in the key. Then unplug the blue 32-pin connector from the BCM and measure the resistance between the purple/white wire in position C2 (second from corner of connector between a black wire and an empty terminal) and the white/black wire in position D7 (near the middle of the connector between a yellow wire and a dark blue wire - it's the only white/black wire in the connector). The resistance should be the same. If not, there's something wrong with the wires between the BCM and the bypass ignition switch or the switch itself is bad.