Lambda reoccuring fault- running out of ideas p3

[chaos19810]

I've been having an issue with a low rev or when cold hesitation with some exhaust popping, once on boost warmed up and about 2000 rpm the engine runs well and your,d never Know there was a problem.

First though was ignition parts so I've change the coil, leads, dizzy, rota and spark plugs. Next was a boost leak so I checked all the pipes and changes the BOV as it was letting air escape and low revs. This improved it but its still there just not as bad.

So I've just checked the code and had code 21 so lambda sensor, So I cleared the codes and checked again and the code was still there before I turned the engine over. So I disconnected the battery pumped the brake and left it off for 30mins and reconnected it and the code was still before I turned the engine over?

So can a lambda fault cause the low rev hesitation and the popping in the exhaust?

[fingers99]

I'd do a compression test. The cold/low revs hesitation thing can be an early sign of the head gasket going. In turn, the chemicals in coolant don't do lamdas any favours.

That the fault doesn't clear might point you in a different direction, though. Wiring fault?

[chaos19810]

I hope not I'll be a very unhappy bunny if its the head gasket, hopefully a new sensor will sort it?

[shinny]

If the code is coming up immediately I'd put my money on the sensor being at fault. Low revs / off-boost performance will suffer badly with a dodgy lambda.

[chaos19810]

It is coming up immediately as soon as I turn the key, and before the engine starts no matter often I reset the ecu, off boost is where the problem is. I'm hoping it gets here ASAP so I can tick it off the job list

[Kinsy]

Maybe check you've plugged it in? Didn't you just do an engine conversion? If it's logging the code straightaway then there's either a wiring problem or the sensor's not plugged in!

Lambdas operate between idle and about 3,000rpm on the 3SGE- over that and you're on the ECU fuel maps - so yes it will definitely give you better running at 2,000rpm!

[chaos19810]

I have just done a rev3 tubby conversion, my first thought was that it wasn't plugged so I checked and someone had used a connector block that had melted so I soldered the wires it into place and still no joy, when then engine was first put it I checked the codes after running it for a few days and all was fine. So im hoping a new lambda will clear it up. I didn't know the lambda only operated up to 3000rpm.

[shinny]

The lambda is used for closed loop running - ie. when the engine is trying to achieve stoich (AFR of 14.7) it uses the lambda sensor as an essential part of the feedback loop to determine how much fuel to put in. If the lambda is reading incorrectly (or not at all) then the engine will either over or under fuel, giving you poor performance. Once you rev high enough and come on boost the ECU switches to an open loop mode where it just uses the air flow information (calculated from the MAT and MAP sensors alone) to determine fuelling. That's why the car can go fine on boost but struggle at lower revs.

That said, I had a duff lambda when I had my like-for-like engine swap done and it ran the engine very lean in closed loop mode, making the car hesitate massively. However it never threw a code. If your car is throwing the code, I would also check out the wiring if you can.

[chaos19810]

Do you know where the wiring connects to the ecu, or what the wires are called on the pin out diagram and I'll check them with a multimeter

[shinny]

It's from an earlier ECU so don't take the pin numbers as gospel (in fact assume they're wrong), but the pins you're looking for are OX (oxygen) and HT (heater): http://shinny.co.uk/toyota/MR2_SW_1993_ ... g3sgte.pdf
Page 62, bottom left-ish

The code could easily be thrown if you've not connected up the heater circuit correctly, as that will mean the lambda takes longer to warm up and give good readings and the ECU will know something is wrong, hence throwing the code.

[chaos19810]

The code could easily be thrown if you've not connected up the heater circuit correctly, as that will mean the lambda takes longer to warm up and give good readings and the ECU will know something is wrong, hence throwing the code.

Assume that a idiot knows more that I do, I'm not sure what you mean? Or even how to check it

Sorry

[chaos19810]

http://shinny.co.uk/toyota/MR2_SW_1993_ ... g3sgte.pdf
Page 62, bottom left

Anyone help me understand this?

[_Al_]

Have you got the 4-wire lambda? If so my money is on the heater coil, as you say the problem goes away when the car gets warm.

My car struggles when cold in winter and the resistance tests show the heater side to be out of spec. Fine once warmed up.

[chaos19810]

I need to get myself a multimeter, and start checking it mines not in a good state!