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General Low MPG

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General Low MPG

lightweightmick said:
I think it would be a good idea to post resistance readings of the temperature sensor on the manifold. This 'tells' the ECU how much fuel is required - if it's faulty it can read low and result in too much fuel being delivered to the injector.
I had this problem with mine (CLX) drinking fuel and fitting a new sensor (£8-10) cured it.
(y)
Click to expand...

I thought it was the lambda sensor that controls the amount of fuel? How do I go about getting the readings?

CLXCraig said:
Thats really poor. Have you got fuelly set up right?

apart from a fuel leak or a duff sensor somehwere i see no other possibility
Click to expand...

I think fuelly is set up right, I worked it out manually anyway and it was the same. The only thing I can think of is that I was stuck in about 3 miles of traffic on Wednesday which was crawling along the whole way.
 
A cool engine will 'ask' for more fuel - what you describe is like my CLX was after I'd done the head gasket - lumpy running and hesitancy may be down to running too rich (mine was poor starting as well)
Remove connector and measure resistance across the two pins (they quite close together so put probes onto outside of connectors) - thing is, we don't know what it should be, but as mine was newly fitted I can get mine up to temp (till fan cuts in) then measure it and see how they compare.
Ideally it would be good to have readings for the sensor at given temperatures so best test would be to take it out and hang it in a pan of water with a thermometer really, as with the above method (on manifold) we would be relying on both engines cutting cooling fan in at same temp...
I do still have the old faulty one though and another that came with the Inj head I fitted to the 1000s so we could build up a picture as to what it should be maybe.
I could test all 3 and knowing that 1 is faulty see if the other 2 read similar but both diff. to the faulty 1 - if you follow...
as I remember there was quite a noticeable difference in my old one to my new one
 
lightweightmick said:
A cool engine will 'ask' for more fuel - what you describe is like my CLX was after I'd done the head gasket - lumpy running and hesitancy may be down to running too rich (mine was poor starting as well)
Remove connector and measure resistance across the two pins (they quite close together so put probes onto outside of connectors) - thing is, we don't know what it should be, but as mine was newly fitted I can get mine up to temp (till fan cuts in) then measure it and see how they compare.
Ideally it would be good to have readings for the sensor at given temperatures so best test would be to take it out and hang it in a pan of water with a thermometer really, as with the above method (on manifold) we would be relying on both engines cutting cooling fan in at same temp...
I do still have the old faulty one though and another that came with the Inj head I fitted to the 1000s so we could build up a picture as to what it should be maybe.
I could test all 3 and knowing that 1 is faulty see if the other 2 read similar but both diff. to the faulty 1 - if you follow...
as I remember there was quite a noticeable difference in my old one to my new one
Click to expand...

Sounds like this might well be the problem, I'll try and get some readings tomorrow, will probably be with it in the manifold as the haynes manual says I would need to drain the cooling system to remove it and if I'm removing it I may aswell just fit a new one anyway since they are only cheap.

I put some cardboard over one half of the radiator but I dont think it has made that much difference, I'll keep an eye on it anyway.
 
Just brought complete manifold into house - with Digital Multimeter (Caltek) set to 20K (ohms) - I got 8.0 (outside temp 3° but as it was warming up it fell to steadily to 7.48 (now 6.62) - so it's obviously very sensitive...
So if I'm getting 8 at cold yours could well be out... it would be handy if we could set a standard here! I'll go and read the one on the CLX as I know that one's right...
 
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Well, old one from garage measuring 17.2 and falling... could well be colder in garage than outside ambient temp though... seems a big difference though...
One on manifold in hse now reads 4.91
seems to me that if you read yours at ambient of 3° yours could be okay...
best test would be to measure at a known temperature of course :eek:
 
hmm, now my meter is showing low battery symbol...
I'll change it tomorrow and see if we can't make any more progress. If we can establish it's NOT your sensor it's another thing off the list at least.
Have you had time to check the thermostat btw?
 
My mums car says it is 1° but the temp it displays is usually abit low so it is probably more like 2°. If you are getting 5.88 on your know working sensor at 3° then I should really be getting a reading slightly higher than that at 2° if my sensor was working properly.

But then if my sensor thinks it is warmer than it actually is then it wouldn't be overfuelling it would be underfuelling which wouldn't make much sense.

Thanks for all your help on this LWM btw, its much appreciated:worship:
 
Yeah, we can't get too scientific here! :p
Here's my best efforts this am:
(Put another battery in so now not showing low batt on meter)
It's 5° out there and the reading from the sensor before starting car was 5.9 (set to 20k - only reason for this is it won't give a steady reading on next lower setting of 2000 ohms)
Allowed to warm up till fan cut in a second time:
Reading then .28
On rechecking (switched engine off - allowed to cool a few mins - then restarted) took reading after fan had cut in once this time and it read on the lower setting (2000 ohms) 315.
I can't get my head round figs. but is this then:

cold 590
hot 280
less hot 315 ?

...as I say, not very scientific... but we could well be looking for a reading of around 300 ohms for a running engine that's up to temp.

Feel free to comment if you can come up with a better test :eek:

Temperature sensors for the temperature gauge may well be less accurate, but I would think that the manifold sensor would need to register pretty accurately for the ECU
 
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panda1408 said:
Not yet, but I reckon I might aswell just change it if I'm going to take it out, unless there is a way to see if its working without actually taking it out?
Click to expand...

Well you can always feel the top hose - should suddenly start to get warm as thermostat begins to open rather than stay luke warm for ages.
Other thing is to note how soon fan blows warm before temp gauge begins to rise, as the heat should get to the heater matrix before it gets into the top hose - thus showing that the thermostat is staying shut. Demister should start blowing quite warm after about a mile in my experience,
(y)
 
Vernon, are we looking at a difference of between 315-28 then for readings on a hot engine?
As I thought .28 was a big difference I went back to check it - restarted engine and waited till fan cut in once - finding it would then give a reading on the lowest setting (2000)
now i'm going to have to do it all over again... :eek:

meanwhile I've been doing a bit of swatting...

http://c4owners.org/plugins/faq/faq.php?0.cat.10.161

http://www.picoauto.com/tutorials/emissions-components-actuators.html

http://www.asashop.org/autoinc/may98/techtotech.htm

It seems a better test would be to measure the voltage from the sensor... (see end of last article)
(y)
 
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