Difficulty starting petrol engine after stopping

Hi,

We've started having difficultly starting the petrol engine (2RZ-E) once it's properly warmed up. If you stop and start it straight away, then it's fine - but if it's left for 5-30 minutes then it won't fire. It will turn over fine and the battery is new and in good condition.

It will crank but no audible sign of ignition. If you crank a few times and leave it a minute or two, then it fires up fine. Other than that , it drives perfectly well.

I did change a failed O2 exhaust sensor recently. It was not doing this before that.

Also, I'm in the UK and the weather has been warming up - around 20 deg C.

Thanks

Disclaimer.. I'm no expert on these engines or how all the electronics work but could it be flooded ? When it won't start take out a spark plug and have a look, it might be that after a while resting the "choke" resets but it's not needed and too much fuel goes in at the beginning. I had a strimmer that did this and it was a pain in the *%$@ !

Hi - thanks, but its not flooded (other than occasionally flooding it when trying to start). Normally, it will start instantly, but in this situation it's not igniting, It needs to be left for a while.

Saying that, since posting the original post, it's getting worse. It's taking longer to recover before it start again - and when it's running just below normal running temperature, it's started to stagger and nearly stall. Also, there's a slight smell of petrol when it's parked and warm (not running). I think it's time to take it to a local garage.

Took it to a garage and they replaced the distributor cap and rotor as they were burnt. I've also found out that the fan clutch is on the way out. However, it's still doing this. I've since got hold of a TOYOBD1 diagnostics reader that runs against the OBD1 port in test mode.

I've noticed an odd thing - but I'm not sure if it's the issue or the readings are just playing up.

The diagnostics display shows the ECT temperature in Celsius. When the van is running fine - the values are usually normal - and the van runs around 88-95 C. Very occasionally, it will drop for a few seconds and then rise again - especially when warming up. Down to the 40s. But the van behaves fine.

What I've noticed is that when it won't start are leaving it 30 mins from warm - it will show around 70C but on cranking, it drops to -16C (!) But only when cranking. When I stop it jumps straight back to 70C.

On the occasion is did start, the temp stayed at -16C and the engine was trying to stall and was slow to react to the gas pedal.

I'm hoping this indicates a failing temp sensor, but the way it is behaving is very odd - hopefully not the ECU. When the engine is cold again, it works fine.

Any thoughts?

Thanks

I'm no expert but if the temperature sensor is telling the engine to mix the fuel for the wrong temperature that might explain a lot.

I wouldn't have thought that an engine temperature can drop suddenly either so something's not right If when the engine is cold it's fine maybe it's because the sensor then becomes accurate ( like the clock that's stopped telling the right time twice a day ) but when it's hot it's telling it that it's colder than it is and messing up the mix. Dropping from 70 to 40 degrees might not alter the fuel mix as they're both similar, not cold and not hot, the warming up phase.

If the temperature drops when cranking then maybe that's because of the extra drain on the battery and less power going to the sensor so it might not be an issue and just normal. But if it goes to -16 on other occasions then that might mean that -16 is the lowest possible reading so the sensor is not doing anything, it's sort of turned off, which tells the engine it's super cold outside and it messes up the mix.

You might just have a loose connection.

There's a whole heap of stuff about your engine/ troubleshooting and testing components in this.. https://www.workshopservicemanual.com/m0072151-toyota-hiace-h100-1989-2004.html you just have to navigate it to find the relevant parts but there are ways to test your sensor.

Thanks,

I got it to running temp and then left it for 40 minutes to cool down to 70C. It wouldn't start as expected - with the OBD1 diags showing -16C again. I then disconnected the sensor and it would start (though took a second to 'catch' rather than the normal instant start). I repeatedly disconnected and reconnected the sensor and the above was repeatable.

So it looks like the temperature sensor circuit is related. Also, the disconnecting/reconnecting and repeatability suggests it's not a loose connection. But I'm a bit confused with the sensor resistance dropping/closing/opening when cranking. You would think that would indicate an issue with the wiring or ECU?

I drove to get the new sensor with the TOYODB1 in 'graph' mode and could see the temp also dropping occasionally for a split second while it was warming up. It also went the other way once and hit 220C. At these low points, the fuel trim jumped to max too, which suggested the ECU was reacting to the change.

I installed the new sensor and it seems to have worked, I only did it yesterday, but I took it for a good drive to get it warm and left it an hour - it started normally. I tried a few more times as it cooled and it didn't fail. Fingers crossed.

One thing I did notice with the new sensor, is that the engine does run hot most of the time - the old sensor would sit around 95C on the TOYOBD1 but now it sits nearer 103C. Now, it could be the tolerance of the sensor, it's not a Toyota sensor but a 'Blue Print' OEM brand one. And the temp sender for the gauge sits in the middle (I know, I know). But I know the fan clutch is on the way out so next will be that (when it arrives!) and a new gauge temp sensor as I'm now getting obsessed about the engine temp. Also, I might flush the coolant and replace the thermostat while I'm at it.

Just for completeness, with the new temp sensor, here's a trace as it warms up from cold - you can see the fuel trim (orange) drop as it gets warmer (also, I assume, the O2 exhaust sensor is hot enough to work too). The temperature line is pink.




And here it's up to 97C - the mix (cyan) jumps between rich and lean as the ECU alters the fuel feed to keep it in the middle.



These photos where while the van was stationary - so the graph is sitting quite steady. The petrol SC doesn't have any diagnostics coming from the transmission, maybe the diesel does - then you could add ratio details and it would display speed, MPG etc. too.