Big flatspot on Bluetop 4AGE- but I think I might have an idea

[Lauren]

Hmm, flat spot seems to have come back again.

Error codes:

5 Oxy sensor open circuit
6 RPM signal/no-signal to ecu from distributor ("ne" or "g") after engine has been cranked: distributor/circuit; starter/signal circuit; igniter/igniter circuit; ECU
10 Starter signal (no "sta" signal to ecu until engine speed exceeds 800rpm): vehicle is push started; ignition switch/circuit; ECU. Not a real problem unless it recurs.
11 Switch signals: TPS idle switch off; neutral start switch off (automatic transmission in Drive); A/C switch on; A/C switch/circuit; A/C amplifier; TPS/circuit; neutral start switch/circuit; ECU

Have reset the ECU again to clear the codes. Last time we did this the engine seemed absolutely spot on.

Am guessing this daughter board on the ECU may be the culprit as that's quite a few error codes! Oxy sensor though is worth checking, hope it's okay as know it is likely around £150.

[PW@Woodsport]

I would agree there Lauren, there are too many unconnected codes there to be the symptoms of one fault.

[Lauren]

We'll check the oxy sensor as that's dead easy, once Mark's portable oscilliscope is charged up.

[toxo]

Potential dodgy wiring?

[Lauren]

Yeah good point. Mark has said he is going to check that as well. What a wonderful Fiance I have.

[PW@Woodsport]

You can check O2 operation with a basic multimeter Lauren, just measure the voltage on the signal wire, should be switching between 0.2 and 0.8v as a general rule, no need for a scope just to see if it's working.

[Lauren]

I know, it's just a better way of doing it really as it's easier to see variance in voltage according to Mark. I think Mark likes to get his toys out given the opportunity.

[PW@Woodsport]

I was gonna say, all you need to care about is that it's switching back and forth past lambda 1, the voltages are irrelevant really, but if it's stuck on a single voltage it's screwed, or its heater element is faulty. (4 wire type only)

[Lauren]

Right we've checked it and it's not working. Boo.

But, Mark has found a spare one knocking around in the shed that we can try.

[PW@Woodsport]

Before replacing it make sure the heater circuit supply/earth is working and sensor ground/signal wires are doing their job or no amount of replacement sensors will work.

[Lauren]

It's a one wire Paul. Mark is going to replace the earth wire.

Thanks for your help.

[PW@Woodsport]

Ah if it's a single wire then that is the signal wire and the sensor earths through it's body so unlikely the signal wire is broken.

Only thing to be aware of on single wire sensors is they take a little while to heat up and start switching so it might appear dead if checked immediately after start up.

[Lauren]

Fair point (I admit Mark knows this kind of stuff better than me). We ran it for around 15-20 minutes or so (starting cold) whilst Mark did lots of tests.

Mark said there was a signal, but not one he considered acceptable.

[PW@Woodsport]

In that case it would appear to be bu88ered. I have a brand new spurious single wire sensor you are welcome to if you need it, it's not genuine Toyota but will do the same job, i bought a load of them years ago for LPG conversions and never used them so you can have one if it helps.

Is it the screw in type or two bolt type?

[Lauren]

Thanks for the offer, though luckily Mark has one that is the same part off his old SC. This fortunately turns out to be the same part number as fitted to late AE86's.

It's the bolt in type. Just need to get a new gasket from MrT.

[JMR_AW11]

Because the engine is modded and it has a modded ECU you might want to double check the O2 sensor against an AFR meter.

i.e. maybe the modded ECU can't/won't allow the mixture at idle to get weak enough to let the O2 sensor toggle in closed loop.

However, it's more likely the O2 sensor is simply duff

[PW@Woodsport]

That's a very good shout actually Jeremy, if the sensor is reading at one extremity of its voltage range that would definately point towards that, i guess if it's not switching and stuck on a middle-ish voltage that confirms the sensor has gone, what were the voltage readings Lauren?

[shish]

tbh i had considered that the piggyback might be keeping it in open loop and hence the sensor signal not looking like it should (sluggushly moving within a narrow range)

we have a backup (stock) ecu on the way and a spare sensor, so we should be able to figure out whats what

[Lauren]

Tried the other oxy sensor, got an even lower reading (in the millivolts according to Mark). So maybe that one is worse than the one we took out?

So, Paul, if the offer still stands for an oxy sensor, reckon I'll take you up on it if that's okay?

Cheers.

[PW@Woodsport]

I'll gladly send you a new sensor, however just something to note, not all sensors operate in the 0-1v range, the 3vz-fe V6 Camry sensors operate below 0.1v, is this the sort of reading Mark is seeing? A very low (but switching) reading?