Engine running with no AFM?
#1
Engine running with no AFM?
Today while putting everything back together from removing my front cover, I got a little over-anxious to see if it would fire back up ( if I had the timing on, check for any oil/coolant leaks, etc..) and I started the car without the AFM on. The car started, idled, and reved. Although it idles and revved very poorly, spuddering, etc.. it did hold an idle on its own, and did rev. Now this is my 1st S5 car, so it may be different, but I know none of my other S4s would even start with the AFM not plugged in. I thought the ECU used the AFM position to trigger the injectors..
#7
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Originally Posted by Rxmfn7
I thought the ECU used the AFM position to trigger the injectors..
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#8
The biggest difference between the S4 and S5 that I can see causing this is the addition of a full range TPS.
On the S4, once the TPS has gone wide open, the ECU really has no way of telling what the engine's doing. It could use the manifold pressure sensor combined with the engine RPM (FD style), but if it had the ability to do that, why use an AFM in the first place?
With the S5, the full range TPS could be used to approximate AFM values (through some sort of conversion function). It won't be *good*, and will fall apart at higher power output, but in a low power range it's obviously good enough to keep the engine running.
-=Russ=-
On the S4, once the TPS has gone wide open, the ECU really has no way of telling what the engine's doing. It could use the manifold pressure sensor combined with the engine RPM (FD style), but if it had the ability to do that, why use an AFM in the first place?
With the S5, the full range TPS could be used to approximate AFM values (through some sort of conversion function). It won't be *good*, and will fall apart at higher power output, but in a low power range it's obviously good enough to keep the engine running.
-=Russ=-
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Doesn't the ECU control the fuel pump relay on the s5, and on the s4 it's the switch in the AFM? IIRC that's why a s4 would never start is because the fuel pump would only run during cranking and then stop.
#11
... yea, and that minor issue of "fuel flow."
What happens if you jumper the fuel pump test connector & try to start a S4 without an AFM?
I'm going to have to try that tomorrow.
-=Russ=-
What happens if you jumper the fuel pump test connector & try to start a S4 without an AFM?
I'm going to have to try that tomorrow.
-=Russ=-
#12
Originally Posted by SonicRaT
Doesn't the ECU control the fuel pump relay on the s5, and on the s4 it's the switch in the AFM? IIRC that's why a s4 would never start is because the fuel pump would only run during cranking and then stop.
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I found some info on how Toyota ECU's control the fuel pump, and it would be a logical assumption that the S5 ECU does this the same way.
Instead of using a switch in the AFM, the fuel pump relay (aka circuit opening relay) is controlled directly by the ECU instead. It closes the relay any time it receives a cranking signal from the ignition key or there is an "Ne" signal coming from the CAS, indicating the engine is turning. If the engine stops turning, the signal from the CAS stops and the ECU opens the circuit opening relay, killing the pump.
It seems the S5 ECU can run the engine poorly at low load without an airflow signal. The same is probably true for S4's, if you jumpered the fuel pump check connector to bypass the AFM safety switch.
Instead of using a switch in the AFM, the fuel pump relay (aka circuit opening relay) is controlled directly by the ECU instead. It closes the relay any time it receives a cranking signal from the ignition key or there is an "Ne" signal coming from the CAS, indicating the engine is turning. If the engine stops turning, the signal from the CAS stops and the ECU opens the circuit opening relay, killing the pump.
It seems the S5 ECU can run the engine poorly at low load without an airflow signal. The same is probably true for S4's, if you jumpered the fuel pump check connector to bypass the AFM safety switch.
Last edited by NZConvertible; 01-18-05 at 05:40 AM.
#14
Originally Posted by Syonyk
... yea, and that minor issue of "fuel flow."
What happens if you jumper the fuel pump test connector & try to start a S4 without an AFM?
I'm going to have to try that tomorrow.
-=Russ=-
What happens if you jumper the fuel pump test connector & try to start a S4 without an AFM?
I'm going to have to try that tomorrow.
-=Russ=-
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