What would cause the Inj. Pulse Width to drop to 0.6 under load?

[cartman003]

This is a somewhat follow up post to my first post. My previous post was too vague, so here is a more direct way of asking what I need answered.

I have a 99 Z28, ATI SC, 38# inj., with an erradict Injector Flow Rate issue. The Injector Flow Rate will fall to 0.6 every 7-10 seconds.

The sample scanner file is performed at light load. If no load is placed on the vehicle it can not overcome the surge and turn off.

I have tried a stock file, a stock file with new injector flow rate to accomodate the 38# injectors, OL, SD, disconnected MAF, checked for misfire, verified fuel pressure by hooking up a gauge.

Can anyone give me a clue as to what would cause the injector pulse width to drop and come back up every 7-10 secs.

[WS6FirebirdTA00]

are you on a stock OS or a 2/3 bar?

looks like you have an issue with the 5v reference circuit, that can be causing some issues there.

[cartman003]

are you on a stock OS or a 2/3 bar?

looks like you have an issue with the 5v reference circuit, that can be causing some issues there.

This is a stock OS. The 5v Reference circuit is one of the DTC's. My understanding about that is that ECU will send a 5v reference to each sensor; but I thought that was done just once or only at startup.

How can I isolate the problem and fix it?

[WS6FirebirdTA00]

The is what gives the signal to the sensors (like the TPS, could possibly be injectors but I am not sure on that).

I think this is built in to the computer, might want to swap computers with a buddy to see if it goes away.

[cartman003]

Thanks WS6FirebirdT00; the injectors are new and where recently installed with the ATI kit. I think the strangest part for me is that both banks drop at the exact same time. How often in your experience does an ECU go bad?

I found this about the 5v reference:

http://extreme-check-engine-light-co...ur-gm-engines/

[WS6FirebirdTA00]

it's not typical, but it happens. I know someone else had a similar issue with that recently, but I need to remember what the fix was.

[cartman003]

Really!? How long ago? Was it on a Camaro as well? We are thinking it just might be a bad ground. So we are in the process of double checking all ground connections.

[cartman003]

Thanks to EC_Tune and suggesting to turn off the VATS the strange behavior has stopped.

Thanks Doug!

Now the question becomes how would you reconfigure the VATS to properly function?

[WS6FirebirdTA00]

hmm, weird.

[EC_Tune]

If it's a key/lock issue you may have to replace the key/lock in the car.
If it's a BCM issue then it may requre a new BCM (not cheap).

[s57_s2k]

I have got the same problem , VATS is off. but I noticed Idle Adapt (STIT) does not go to zero when revving the engine . I am guessing a wiring problem.