84 Corvette ECM fuel shut off
04-22-2014, 01:34 PM
#1
Burning Brakes
Thread Starter
84 Corvette ECM fuel shut off
I'm reposting this problem with a new heading to get specifically to 84 owners, because my car idles and runs great, except that sometimes it stalls when I go down through the gears -not every time, but intermittently.
I had never heard of this and maybe it didn't go to production, but on page 38 of the 84 Corvette sales brochure it states;
"When you're cruising down the highway, ECM provides a set of instructions to the TBI and transmission overdrive to enhance fuel economy. And, when you are decelerating, the TBI gets waste reducing fuel cut off signal which totally shuts down the engine (without your sensing it) until a programed lower RPM level is reached".
If that is the case and something isn't performing correctly, my thought is that at the lower rpm it sometimes doesn't get the resume fuel message.
So here are my post questions;
1) I changed the chip to a Hypertech chip about 3 years ago, but don't remember this being an issue then -but wondered if it could be going bad?
2) Or could the ECM be acting up?
3) Or wondered if there is some sort of valve in the TBI that gets the signal to shut off the fuel and that part is going bad.
I had never heard of this and maybe it didn't go to production, but on page 38 of the 84 Corvette sales brochure it states;
"When you're cruising down the highway, ECM provides a set of instructions to the TBI and transmission overdrive to enhance fuel economy. And, when you are decelerating, the TBI gets waste reducing fuel cut off signal which totally shuts down the engine (without your sensing it) until a programed lower RPM level is reached".
If that is the case and something isn't performing correctly, my thought is that at the lower rpm it sometimes doesn't get the resume fuel message.
So here are my post questions;
1) I changed the chip to a Hypertech chip about 3 years ago, but don't remember this being an issue then -but wondered if it could be going bad?
2) Or could the ECM be acting up?
3) Or wondered if there is some sort of valve in the TBI that gets the signal to shut off the fuel and that part is going bad.
04-22-2014, 07:47 PM
#2
Instructor
Member Since: Aug 2002
Location: Kingsville Ontario
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Check the oil pressure switch it sends a signal to the ECM, so when there is no oil pressure it will shut down the fuel pump. Plus, have you checked your fuel pump, I had a split in the rubber hose from the pump that caused this problem for me.
04-22-2014, 08:05 PM
#3
04-23-2014, 02:08 AM
#4
Race Director
on page 38 of the 84 Corvette sales brochure it states;
"When you're cruising down the highway, ECM provides a set of instructions to the TBI and transmission overdrive to enhance fuel economy. And, when you are decelerating, the TBI gets waste reducing fuel cut off signal which totally shuts down the engine (without your sensing it) until a programed lower RPM level is reached".
"When you're cruising down the highway, ECM provides a set of instructions to the TBI and transmission overdrive to enhance fuel economy. And, when you are decelerating, the TBI gets waste reducing fuel cut off signal which totally shuts down the engine (without your sensing it) until a programed lower RPM level is reached".
You might have problems with your TBI calibration. I assume there is something equivalent to the minimum idle adjustment for TBI systems. The throttle bodies might not be matched correctly. Check the FSM and go through the whole setup procedure.
04-23-2014, 02:12 AM
#5
Race Director
I have unplugged my oil pressure switch while the engine was running and it continued to run just fine.
04-23-2014, 08:54 AM
#6
Burning Brakes
Thread Starter
That is called DFCO (Deceleration Fuel CutOff). The ECM stops firing the injectors, so it is true that the engine is actually shut off for a short time. It restarts when the RPM drops to the programmed value.
You might have problems with your TBI calibration. I assume there is something equivalent to the minimum idle adjustment for TBI systems. The throttle bodies might not be matched correctly. Check the FSM and go through the whole setup procedure.
You might have problems with your TBI calibration. I assume there is something equivalent to the minimum idle adjustment for TBI systems. The throttle bodies might not be matched correctly. Check the FSM and go through the whole setup procedure.
DFCO is a weird thing and now that I am aware of it, I do notice that as I down shift and the engine is slowing the car down, it does feel like it is off and then has a slight surge/ start sensation as the RPMs get below maybe 1200 rpms.
One thing is that the stall is intermittent and seems to be most often when the engine is warmer.