Hot start misfire

[grim_d]

Ok this one has me stumped completely, and before I start just changing parts willy nilly just wanted to see if anyone can offer any pearls of wisdom.

From cold the car starts fine, drives fine, all is normal as far as I can tell, but If I get the car warmed up and then stop it for a short while, to go into a shop for example, then often when I come back to the car it will badly misfire and will not clear with revs, I have to turn it off and on again, often multiple times, until it starts normally, at which point all is fine and it drives fine.

A bit of throttle when it's misfiring and it stinks of fuel with associated vapour from exhaust so it kind of seems like it's creating a flooding condition but I don't understand why?

I suspected perhaps ECU coolant sensor but it seems to be reporting fine to Nistune unless intermittent. Put new plugs in today as was doing oil and fiter anyway. I have a new dizzy cap, rotor arm and coil there but not sure if it's ignition component related. There are no fault codes.

Any ideas or anyone experienced this?

Cheers.

 

[LeeSmith]

Could be a leaky injector?

 

[grim_d]

Could be, flooding a cylinder, it has been slightly richer at idle than usual but I had put that down to the warmer weather. Think ill have them serviced either way, been meaning to for a while.

Would think that would clear itself without having to restart though?

 

[grim_d]

Pulled the fuel rail off today and pressurised the system, no leaks at all when hot or cold so that rules that out.

As it sods law I couldn't get the car to misbehave today to try and narrow down which cylinder is misfiring.

 

[grim_d]

So have done a lot of tinkering with this, having changed a few bits like ecu temp sensor and some ignition parts without success, all sensors are functioning as normal according to nistune.

I have discovered that is is not a ignition related misfire but rather it overfuels to the point where it misfires and stumbles, I pulled the plugs after an episode and all were fouled with soot, backed up by the amount of fuel coming out the exhaust, cleaned them and it fired up first time no problem.

I noticed the other day that sometimes when I turn the ignition on the radiator fans come on too, at the time I didn't think much of it but today I noticed that the only time it misbehaved was when the fans had come on, the many other times I had tried to start it today had been a success, unfortunately it stumbled and stalled on that occasion rather than maintaining a rough idle. Not such what link there would be there but there does seem to be one.

With that in mind I did the active fan tests and maybe 2 out of the 10 times I ran the test I would get a "check pin failed on this board" error and it would disconnect, I don't know what that means, anybody offer some insight, could I have a intermittent fault with the nistune board?

 

[daddyone]

lambda? I've had a faulty one which only misbehaved when really warm, made the car over fuel for some reason.

 

[BMCC]

At the time the fans are running, should they be running? If you disconnect the Engine Temp Sensor then the fans will run regardless of engine temp. Pull the plug on the sensor and you will see the fans running when the engine is on.

 

[grim_d]

lambda? I've had a faulty one which only misbehaved when really warm, made the car over fuel for some reason.

I am suspicious of the o2 sensor but 1.35v when hot on the o2 gauge in nistune was about 12:1 afr (ish). which is probably about right, it's certainty not wildly off the scale. (Glad I just found out about our cars o2 sensor voltage!)

At the time the fans are running, should they be running? If you disconnect the Engine Temp Sensor then the fans will run regardless of engine temp. Pull the plug on the sensor and you will see the fans running when the engine is on.

I dont think the fans should ever run with just ignition on if everything is working correctly, should they?

When the engine is running they kick on and off as normal and ecu temp sensor is brand new and is working correctly.

I wonder how the ecu handles fueling when it has no data from the temp sensor?

 

[The Doc]

It turns the fans on to protect the engine and goes to a default map running rich with less ign timing....

 

[BMCC]

"It turns the fans on to protect the engine and goes to a default map running rich with less ign timing...."

I am suspicious of the o2 sensor but 1.35v when hot on the o2 gauge in nistune was about 12:1 afr (ish). which is probably about right, it's certainty not wildly off the scale. (Glad I just found out about our cars o2 sensor voltage!)



I dont think the fans should ever run with just ignition on if everything is working correctly, should they?

When the engine is running they kick on and off as normal and ecu temp sensor is brand new and is working correctly.

I wonder how the ecu handles fueling when it has no data from the temp sensor?

That is what I was getting at (message from the Doc), could you have an intermittent wiring or ECU problem?

 

[grim_d]

I could easily, strange thing is that it that when it starts fine, and the fans don't come on at igntion, it idles a bit richer than normal, indicating it's on the default map.

However, after the fans came on at ignition and its stumbled and stalled, indicating a lack of signal from temp sensor, the next restart it was idling at stoich (as it's mapped to).

It's giving me mixed signals but it is looking like a wiring issue, the ecu temp sensor was always reporting to nistune however.