Car Only Runs Well with MAP Sensor Unplugged

[dapinky]

There are 2 sensors here which seem to have issues (one or the other, or possibly both!)...

... The MAP sensor - when you replaced it, what item did you fit? There are numerous items which look the same, and are a direct 'plug in' replacement (and others than need plugs re-wiring), BUT not all of them will give the correct electrical impulse to the ECU. The Sensor needs to be a 2-bar unit (assuming that you have the OE turbo and don't run it beyond 1 bar boost). If it is a 3-bar unit, then it is designed to work with a different turbo set-up (up to 2 bar boost), and in the Elan will only put out 2/3 of the electrical impulse that the ECU expects for a given manifold pressure.

... the O2 sensor - needs to convert the gas levels in the exhaust to an electrical impulse to the ECU, and in the Elan it is a heated system which requires a 12V feed to the heater part, which comes from the alternator .

It is often quick and easy to replace an O2 sensor to see if that changes things, after that, it may need alternator work (as a US based owner, it is easy to get a complete unit from Rockauto to save messing around with replacement of individual components, but the parts are also available if you want to do it that way).

[chrism]

Just a thought that I tried:

To check heater circuit continuity inside the sensor probe, disconnect the O2 sensor m/plug and try connecting your ohm-meter across the two heater wire ends - the white wires - to see if there's a high resistance or a break there. My new Bosch 15701 resistance is about 3ohms when cold, the used Denso 13ohms. I don't think they should be higher than ~20ohms or so.

That's about all you can do if 12V is getting there and the black earth lead is continuous to earth.

If for some reason it's a very high resistance then I suppose this'll 'use up' the heater current and the sensor filament won't get hot enough to work?

I understand your idea that it 'should' run with the O2 sensor disconnected: I know mine defaulted to the mix pot cos it was originally built with one - but does your FED have one of these to fall back on? I dunno; should your ecu have a default air:fuel ratio if the O2 sensor breaks? Would this be built into the 1499 map? Someone might know...

[RonR]

My Bosch also measures 3 Ohms which means that unless the resistance increases as it heats up (Unlikely, but not impossible), at 12 Volts the heater must draw around 4 Amps --> 48 Watts, somewhat more that the ~2 Watt Battery Light - so it's no wonder that the M100 Alternator Regulator needed to be beefier that the norm!

Chris - The lower the resistance the more current is drawn - at 13 Ohms your Denso would draw around 1 Amp - 12 Watts or so, it will probably take longer to warm up than the Bosch, but as long as it reaches 360C it should work OK.

BTW It looks like the 1499 prom doesn't take the CO Pot into account, it defaults to the middle value of the available range i.e. Range 0-255, 1499 code uses 128. This sort-of makes sense as the California version of the Closed loop prom uses ECU pin B12 to connect the EGR Temperature sensor, the same pin as the CO Pot is connected to on Open loop cars.

Edit: ... Which means that using an Open-loop prom on a California car could give "Unpredictable results"!

[chrism]

Yep, absolutely right RonR.

Before the de-pin the new expensive UK-sourced Denso took upwards of 5mins to start firing properly and now that it's 'sorted' the new 3ohm RAuto Walker sensor takes ~2min to reach the same level of activity. (I'd put the new sensor in thinking it would solve my problem before I found out that it'd depinned so I left it there; glad cos I reckon it's 'better' than the old one...)

I suppose eventually if the exhaust gases get the sensor filament hot enough it could go 'closed loop' without a heater current until it all cooled down again?

And when mine defaulted back to 'open loop' the a:f ratio stayed constant at 14.5:1 which wasn't sufficient for me to immediately notice a drop in performance. I assumed, wrongly, that this value was what my adj pot had been set to before the conversion.

Edit:- so I reckon that your 'open loop' Californian might run - albeit with higher emissions and greater fuel consumption? Which might mean mozayyani97 is suffering from something else as well?