Techie question MPG down

[tinytim]

Hi all,

A bit on the technical side but an answer could benifit us all if my suspisions are correct. Here goes, the full story.

By the way it's an open floor, ANY ideas, fire them in.

I dropped my engine to do the clutch and timing belt. No major problems and I changed the Gbox oil as well.
I also changed the cat complete with the temp sensor and the other sensor, which I am guessing is the Lamda sensor?

My MPG went from 50+ to 35/36:confused:

I've whipped the cat off and there are fuel, water dropletts on the cat intake end. (The water I can understand although rather surprised so close to the exh manifold but the last run before I did this was a short one) The fuel:confused: Its a definate petrol smell.

I put an AVO across the 4 terminals of the Lamda? and get an open circuit across everything in both directions (polarity) except the black wires (which do not earth to the cat body). This is on both sensors.

On the "new" (suspect) cat I get a reading of 11.3 Ohms initially, which flicks to 13.2 after about 0.5 seconds. (The flick in the reading could be my AVO but it is s definate reading the same every time).

On the "old" (good) cat I get 11 Ohms flicking to 12.9 again consistant readings with both figures.

Has anyone got, or can anyone get the correct figures (has anyone got a new one they could test). If these little beggers are breaking down it could explain the difference in fuel consumption we are getting. I intend to put the old cat back on and see what happens but it's in a bit of a state. (Top seal gone, 1 stud sheared and an un-removable, broken heat sensor). I am in the unfortunate position of having a 93 model so I need the cat for the MOT:(

OTHER INFO
Both cat matrix' are clean and clear.
Car seems less willing to get up and go but will still rev and get to speed (using a whole lot more fuel)

Any ideas on anything I may have done wrong with the timing belt most welcome but I get no engine warning light or anything obvious at idle.

Again it's an open floor ANY ideas, fire them in.

[Steve_M]

You disconnected the battery and lost the ecu long term memory could be a cause. it will return with running time.

[Midship]

Hi Tim

I think you could be on to something there with the idea that the O2 sensor is breaking down or sending inaccurate readings, I too am getting 30 something MPG, im guessing its running very rich given the strong smell of petrol at idle.

Chapter 6-21in the workshop manual seems to detail a procedure for testing the O2 sensors however my Japanese isn’t the best! Maybe OZ could give it a read?

I have knocked the centre out of my cat which means a better noise and prob a few extra horses but I regret doing it now because of the dramatic increase in fuel consumption.

Its defo worth getting to the bottom of this problem alright, petrol price are on the up!

[john m]

Mine also does about 30 mpg and always has, I was amazed when I hear you guys talking of 50 mpg. I too get a strong smell of petrol and get some backfiring on over run, its a nice cracking sound but it has to be damaging the exhaust. I am due a service soon and was going to ask them to retard the fuel mix a little. If the O2 sensor contributes to the ratio of fuel to air mix then that could be my problem too. I am getting no fault signals from the ecu so I was hoping nothing was wrong other than the need for a service.

[tinytim]

Thanks for the quick replies (I'm not the only one taking a day off:D )

Well the exhaust is back together and even from just a quick start up and a few throttle blips I feel I've solved the problem.

I'm going to fill up and we'll see how it goes.

Any chance over the next week or so you guys could take a resistance reading. Not the easiest plug to get to but if ou're in there anyway it may be useful. I'll blast an e-mail to Oz and see what the Master can come up with.

Cheers guys
Tim

[barkley]

without going and checking my car how many wires are on the oxy sensor 2,3or 4 i can give you a reading for all of them ..also motor factor sensors at £40ish will do to replace them with

[tinytim]

Hi Barkley,
There are 4 wires, 1 green, 1 white and 2 black. There is a web of plastic inside the plug, if you check the terminals across this rather than the pairs on each side you should get an open circuit on one set (green white)and a low resistance on the other (black black). My readings were in Ohms not K or M. ( I also got O/C green black and white black)
Having given the car a blast to the fuel pump and back I feel it's back to what it was with regards to get up and go but I'll see how it goes on this tank of fuel and post back on here.

On the pic (if it comes up) check across the bottom pair

[barkley]

pin 3 and 4 the black black ones should be 10 to 40 ohms according to 4 wire oxy sensor on autodata

[tinytim]

Is that the working range?
More to the point does anyone know how the blighter works. 4 wires suggests to me that it's not a simple variable resistor like the temp sensor but I have no idea how it does it's stuff. Time for a google I think.

[barkley]

yes that is the range as for how it works in greater detail cant help ya

[tinytim]

Well I can definately say changing it has done something. I took it for a longer blast and gunned it. Whilst it still reved through, the engine warning light came on at 7000rpm. I dropped back and switched the ignition off then on again and all was fine until I gunned it through 7000 when the light came on again. It now idles at 1000-1050 whaere as I had set it spot on to 1200 with the other sensor and had no warning light ever.
I'll reset the idle tomorrow.

[Paul w]

Could it be a wheatstone bridge type sensor? These tend to use 4 wires. (i'm not that familiar with car sensors, but in industry this type is often used for gas, temp or flow sensing)

I think you can attach two other wires to the 'corners' and measure the current drawn. (its been about 12 years since i had anything to do with them!)

PW

[Adam]

Originally posted by tinytim
Whilst it still reved through, the engine warning light came on at 7000rpm. I dropped back and switched the ignition off then on again and all was fine until I gunned it through 7000 when the light came on again. It now idles at 1000-1050 whaere as I had set it spot on to 1200 with the other sensor and had no warning light ever.


The same thing has been happening to me in the last few weeks. I haven't had a chance to check the codes yet.

[Midship]

Just wondering if your timing was done correctly? a beat I done some work on had that problem and was sorted by doing the timing- just a thought

[tinytim]

There is no flashing, the light comes on with the ignition then goes out after a few seconds as normal. It drives fine until I take it past the 7000rpm mark. It wasn't doing this with the other O2 sensor on but then I treeked the dizzy to give 1200rpm at idle when I did the timing belt.
All I did yesterday was change the cat complete with sensors. (The cat that is on now is the one we did in Fishguard). The car runs better (has more willingness) but at 7000 the light comes on and stays on until I switch the ign off. It also idles at 1000-1050 when warm so I'm gussing I just need to put the dizzy back to where it was.
I may get a strobe and do the whole lot just to be sure.

Paul,
Is there any chance of a "common jobs" page. 1st post on each thread is how to do the job and subsequent posts can be tips, where to get substitute bits etc.
Can I suggest:
1 Timing
2 Timing belt
3 Radio clock setting
4 Brake pad changes
I know all the info is on the pages but it can be a pain searching (especially when looking for ECU, cos it's only 3 letters long:D )

Anyway, just a thought.

[Paul w]

Mmmm, probably a good idea a 'How to..' thread with sticky guides.

I can start the threads but it would be up to you lot to fill them in!

PW

[tinytim]

That works for me. It'll be a cut and paste for the most part but at least we'llonly have to find the info once:D

[ozsamurai]

Sorry to join the thread late..... I'll take this up w/ Honda techs soon, see if they have any ideas 4 ya!


Cheers

Oz

[tinytim]

Cheers Oz, I hadn't got round to e-mailing you yet:suicide:

Well I started with a diagnostic and got Oxy sensor and No 1 position sensor. No real surprises there, I'm pretty sure I started it with the oxy sensor disconnected and I'd tweaked the dizzy.

Reset the ecu warmed her up (no warning lights came on) switched off, bridged the diagnostics and checked the timing. It was a good way of, I could only just see the timing mark in the rear of the window:awwww:
Reset that at 1200, switched off, removed the bridge and started. She now runs at a steady 1200.

I whipped the plugs out,,,definately been running rich, rather a lot of carbon.

I'll let you know on the fuel consumption but it's looking good. I'm still of the opinion it's the oxy sensor failing to flick to a lean mix but from what I've found so far I'll need to get an osciliscope to check it???
Oz i hope you can come up with a static check, I've been told you can heat the Oxy sensor and it should produce a voltage, can you confirm this ?

[ozsamurai]

Static testing is quite difficult and really not conclusive for the O2 sensor, you can run voltage through it to check heater resistance values with a tester, maybe check for operation (voltage variation) by spraying propane gas, but all the experts say its best to just throw it on the car and do the test. For static testing you'd have to rig a bench probably just for it. Of course the resistance value for each model is different, and no one here knows the Beat's as its a little old... sorry!

Oz

[tinytim]

What's the test on the car?
Neither of the sensors I've had fitted gave a fault through the ECU (until I started up with the sensor disconnected).

From what I've managed to find out on the net the sensor produces a voltage of between 0.1 and 0.9v from a comparison of O2 in the exhaust and in the air. (Some have heaters in order to get to work quicker, I take it the Beat has a heater)
The voltage produced forms a signal to the ECU which adjusts the fuel pulse width according to the signal voltage. The fuel air mixture flicks between lean and rich giving a mean average of correct fueling.
The sensor fails in 2 main ways:
1. It gets coated with dirt from the exhaust gasses(particularly if the car is burning oil). This will tend to reduce the measured O2 in the exhaust so the ECU will reduce fuel giving an unrequired lean mix. This is hot and will damage the valves and cat as well as increase overall wear to the cylinder bore. I'm not sure how the Beat ECU reacts to this but apparently if the measured difference in O2 becomes TOO great (unrealistic) the ECU will read an error and disregard the signal giving an uncompensated, rich mixturre. (I guess this is a fail safe to prevent the above list of damage)

2. Over time the voltage produced drops off as the sensor ages. This gives the effect of sending an overall lean fuel signal to the ECU ALL the time. The ECU compensates by throwing in more fuel this increases the carbon buildup on the sensor, see note 1.

So eventually a fault will show up through the ECU BUT with one or two problems first! All in all this little sensor can, if not working right, cause all sorts of problems, many of which I've seen experienced on these boards. I guess the next question is how much are they and is there a special tool for getting them out?

[Midship]

Very expensive ive heard! its possible that one from another car could suit... hopefully! there’s is a special tool for removal.. I bought it some time back.. Never used it and cant remember where I put it! I must have a look for it. If you have trouble finding one, you’re welcome to borrow mine!

[tinytim]

Cheers michael,
You're right on the expensive bit £250 won't include the postage :eek:
Thanks for the offer of the loan (if you can find it:D ) I'll see what I can do but it depends on how tight the thing is. No rush though she seems to be working fine at the moment.

[john m]

It might be worth buying a good fuel additive to try clean the sensor, if petrol is pasing through the exhaust valves then so will the cleaning additive. I will try it at the weekend and see if the petrol smell goes away.

[barkley]

erm im missing something what is 250 squids and and the socket for it is about a tenner from draper

[Midship]

It would appear from the parts manual that a replacement sensor is about 250 euro....

I paid 150 euro for something that costs 9100 yen (in the manual), the replacement sensor is quoted at 15500 (in the manual) which turns out to be 255 euro so im presuming thats where the figure came from...

The O2 socket is cheap alright, at the end of the day its only a socket, i found the issue not be the cost but rather finding where to get one, Dublin isn’t the best place to find little tools like that! :rolleyes:

[barkley]

well i will double check tomorrow but im quite sure that after market sensor will do the job and these can be got from the motor factors at a cost of arround pounds 2,3, and 4 wire sensors i have fitted in the past make and model was never required just the number of wires weather the sensor was heated or not ....i will check in the morning and let you know tomorrow......

[Jennifer]

In all seriousness now what kinda MPG are you lot achieving? one of the reasons Im getitng one is because when I was a month or so ago I was sold on the fact that most of you lot got 40mpg+

Jen

PS drove my 1st beat this morning I still got a big grin!!

[tinytim]

Hi Jen,
Well I'm now hovering on the 1/2 tank mark having done 195 km.
That's 120 miles on "roughly" 2.5 gallons so 48mpg.
I'll be putting the duff O2 sensor back on next week just to ensure it was that causing the problem but I'm pretty sure it was.
Tim

[Jennifer]

sounding extremly good to me so far. Plus I remember someone saying it only cost £20 to fill up which is great