[Mk2] [NA] Poor MPG, maybe running rich and inconsistent idle

[jem]

Is this a dealer part?, do you have a part number?, how much?
Cheers

Was £10 from Unipart

[smig]

Sensor is 89422-35010 £39.91 + vat
Crush washer is 90430-12005 79p + vat

Or pattern sensor from Camskill is £15 + vat

Those parts are all for the turbo, dunno if it's the same for the N/A. Maybe someone else can confirm!

Is this a dealer part?, do you have a part number?, how much?
Cheers

Was £10 from Unipart

Thanks

[jem]

Well I cant say my MPG is any better

[Moo]

When you fitted the K&N induction kit did you reconnect the temperature sensor that came out of the stock airbox? I would have thought you did as you're not getting any ECU error codes but worth checking. Does the K&N have a fitment to accept the temp sensor or do you have it dangling loose somewhere?

[jem]

Yep all connected, and there is a hole in the base of the K&N filter to slip the sensor into, so it's not that.

[daveslater3110]

Hey, sorry to jump in. But you know you were saying about the ECU coolant temp sensor? Well I don't understand what that does and would you mind explaining it to me? I'm also having bad mpg and I've got a code 25 on ecu for a cream crackered oxy sensor. But that being beside the point, this ecu water temp thing caught my attention? I just don't understand how a water temp sensor could have anything to do with mpg? Any advice would be much appreciated. Cheers, Dave.

[toxo]

If you have bad MPG and a code for a broken O2/lambda sensor then that WILL be your problem, they have a DIRECT effect on fuel usage.

The ECU coolant temp sensor only really affects MPG during warmup, but if you only do short journeys in your MR2 and with the cold weather meaning that the engine takes longer to warm up then its effect is lengthened.

The ECU alters the fuel map while the engine warms up, which is where this sensor is key - if it's broken then the ECU thinks the engine is warm all the time, even on the first turn of the key. It also has a few protection circuits that kick in when the coolant isn't up to temperature which cease to function when this sensor misreports.

[daveslater3110]

Oh ok, see what you mean. Thanks for that mate. Ok so change the oxy sensor and I'll be right. Cheers bud. Dave.

[jem]

Well I've had a further look at this today. I don't have a timing light at the moment, but took a punt at setting the timing by ear and then locking the distributor off very slightly retarded from the sweet spot to be on the safe side. The old fashioned way so to speak but admittedly far from accurate

Anyway with the distributor turned fully advanced, where it was previously set, the engine sounds good, but retard it just slightly and it stutters and doesn't rev cleanly. I suspect that if I had a timing light the timing would still be a little retarded (well at least retarded from 10° BTDC), so I can only think my inlet cam is a tooth retarded

I was planing on changing the cambelt this weekend, but I'm not going to get the chance. Going to have to be next weekend.

[RobCrezz]

Dont forget to connect the diagnostics TE1 and E1 with a paperclip or the ECU will change the timing while your trying to set it.

[jem]

Can I ask what is adjustable on the engine management of a REV3 NA. I know of the following two:

Throttle position sensor
Base ignition timing

And also is there a list of ECU sensors anywhare? Again I know of the following on the car:

Inlet air temp
Throttle position
MAP sensor
Coolant temp
O2 sensor
There must be a crank or cam position sensor, or both?

Anything I've missed?

[toxo]

Distributor acts as cam position sensor on inlet cam. Also has at least manifold air temp without which the MAP sensor would be useless.

Also missed:
CAT temp sensor (not sure that goes to ECU)
Knock sensor

[jem]

So the cam position must be working otherwise it wouldn't run. I don't have a cat temp sensor and would assume the knock sensor is not to blame. So it must be some sort of timing issue.

[jem]

Right I bought a timing light today and I've just finished setting the ignition timing. After Sundays attempt at setting it by ear, the base timing was 13° BTDC. It's now spot on 10° BTDC with E1 and TE1 bridged. Just to be sure I disconnected E1 and ET1 reved it a couple of times and then reconnected them and rechecked, and still bang on 10° BTDC. I then reset the ECU and too it for a spin and does feel smoother and more urgent, but I don't know if that placebo effect or not. I suspect the cam timing must be right, I cant see it idling smoothly and pulling strongly, which it does, if it was a tooth out.

One last thing, is there a knock sensor, and if so where is it located on the block/head?

[toxo]

Knock sensor bolts into the block on the inlet side at the top.

However the knock sensors are pretty weak on these cars so they usually blow on the first sign of knock and that flags an ECU code 52.

[jem]

Well changed the cambelt this morning and the cam timing was correct all along so not the cause of my poo MPG.

I think I give up

[jem]

My last tank did 26.3mpg

[Dale_V]

My last tank did 26.3mpg

why the sad face? Thats decent from an na mr2

[jem]

My last tank did 26.3mpg

why the sad face? Thats decent from an na mr2

Is it? My daily commute is 25 miles on national speed limit A roads, and it's normally pretty free flowing. From reading on here most with NA's are getting well over 300 miles to a tank. The best I've got is 270 miles.

[jem]

Changed the thermostat today too. I don't have any doubts it was working as it should as the temp gauge would reach halfway in about five minutes and stay there. Only thing I had noticed is the heaters would blow warmer after giving the car a good thrashing, but that's not to say it didn't blow warm when the car was not being thrashed.