1986 2.5L to 3.4L: Amateur Hour

[coheed]

Make sure whatever you're using to bypass the VATS is sending the correct signal and that the PCM is seeing it. If you don't have scan9495 on a computer and an ALDL cable, I would get one. Scan9495 will show if the PCM is throwing a code for the VATS, and it's easier to use than most modern code scanners in my opinion. I had 2 different bypass modules hooked up to mine, and for whatever reason the PCM wouldn't recognize the 55Hz signal that was coming out of the bypass modules. And without that the injectors won't fire. Noid lights would also tell you pretty quick if its VATS not pulsing the injectors. Eventually I spent the money on Tunercats and disabled VATS completely in the PCM, along with editing some other things.

[FigurativeGarbage]

Thanks, Coheed. Yes, the noid flashes a bit. Yesterday I found that my PCM ground wires (C1 and C17) were not connected. I got one hiccup. I can still test voltage levels at cranking. I have suspected VATS (by Timers) could be the issue. I recall you ground it to change the Hz, and I am using the default setting. Agree I should get a scanner.

[FigurativeGarbage]

Reviewing my notes, the PCM I ordered years ago was actually for a 94-95 automatic, not a manual. Unclear if that matters, as I gave the seller a manual Camaro VIN for coding.

I had the Timers VATS bypass set to 30Hz. I set it to the more common 50Hz. Still nothing. I can try the two other functions on that system, but your comment makes me doubtful it will help. On your suggestion, I've downloaded the Scan9495. I ordered a jumperless ALDL connection and matching wire mount, but it take a week or so for them to ship. Once I see what's happening, I'll see if I need to escalate to deleting the VATS or otherwise tuning.

[coheed]

Depending on the program they use to write the new VIN in the PCM, it may just be changing what a scanner would show as the VIN when hooked up and nothing else. The auto has a park/neutral safety switch and the manual has a clutch safety that are both tied to the VATS starter relay. Depending on how you bypassed that relay you may have already bypassed those. In theory an auto PCM would still start an engine with no 4l60 hooked up to it, so long as the safety switch is bypassed and it's getting the right signal for the VATS (and fuel/spark/timing are good). Most people seem to have great luck with the VATS bypass modules, so maybe it was a fluke of my wiring in the truck. It ran with the module in the Camaro, it was just terribly inconsistent when everything was in the truck.

 

Do you still have the VATS module attached to the wiring? And do you still have the ignition cylinder from the Camaro in the wiring harness? If you have both you could try wiring in resistors of the same value as the pellet in the Camaro key if you know that value.

 

Also, have you tried some starting fluid? If it runs on ether I'd bet money it's a VATS issue. 

[FigurativeGarbage]

Great ideas. Hadn't thought about the safety switch. I still have the VATS attached, just in case I can avoid tuning. I don't have a Camaro ignition cylinder. I've looked at a number of sources and this engine seems very hard to pin down whether it is 30Hz or 50hz. I don't have a reference key to measure resistance. The diagnostic connectors arrive Saturday per FedEx, so I'll just wait and see what the scanner says.

Got an adjustable throttle cable from BMC installed yesterday. Crawling towards victory.

[Gojira94]

On 9/12/2026 at 2:14 AM, FigurativeGarbage said:

the PCM I ordered years ago was actually for a 94-95 automatic, not a manual. Unclear if that matters

 

You said you'd rather avoid tuning if possible, but there is a flag in the V8 and V6 F-Body calibrations that enables or disables all configured parameters for auto trans. This screen shot is from TunerPro RT, showing a factory calibration for a '94 LT1/ auto. With TunerPro, the L32 V6 datastream definitions (.adx) for logging are easy to find, but the .bin definition files (.xdf) are a bit harder to come by. TunerCat is a good product, I wouldn't hesitate to recommend it if you decided to pursue some edits in your PCM calibration to solve some issues. Point being you can do things that would remove some headaches.

 

Edited 5 hours ago by Gojira94
edited for clarification

[FigurativeGarbage]

Thanks, Gojira. I have some things to work with just from an initial scan tonight. I don't see a VATS issue if I am reading the data correctly. But I do see low battery voltage while cranking (7V to 8.5V per a multimeter and the computer). I'll have O'Reilly's check and charge the battery, then I'll check again. It could be the starter is pulling too much power (misaligned?). There is an injector fault indicator, which might be wiring. I see a MAPS error, but I think that causes the PMC to use a default number and it would still fire. The MAPS connector is damaged, so I'm not very surprised. I have a spare MAPS if it's not the connector.
 

[coheed]

If there's an issue with VATS you would have an error show up in the DTC tab that's titled something to do with Passkey. If no DTC, then your VATS bypass is working fine. But, if there is a VATS issue it will also throw an injector fault on that main screen.