Petrol Smell, Stalling .. But Quick Otherwise

[kyepan 291]

Hiya,

 

 

On the warm up cycle, towards the end I mean, its fast as fook (i don't thrash it from cold) , but once warm it seems to be running rich, and overfuelling, stalls pulling up to lights if I slow down too quick. and when i get out after turning it off it pongs of go go juice.

 

for what its worth i've changed the temp sensor about a year ago, and also it's got a very new dizzy cap and fairly new leads on it.. have cleaned the breathers fairly recently and taken it on some good long thrashy runs.

 

help as i'm a bit stumped.

 

It's also getting terrible MPG...

 

J

[GLPoomobile 958]

I'm only advising this as it sounds similar to my recent experience, but maybe duff AFM

 

My problem started with the car stalling in traffic - everyone time you engaged the clutch as you came to halt the revs would drop down to about 500rpm and it would either stall or they'd bounce up to 1500rpm, then come down again, and it would ping pong back and forth before stalling.

 

The next time I went to use the car a few days later it wouldn't idle, sounded like it was only firing on 3, but revved OK once you got past 2000rpm. I found it was overfueling as the plugs were wet.

 

When I eventually narrowed it down to the AFM I found the flap was stuck fully open, hence it was overfueling at idle and wouldn't run. I cleaned it up and got the flap moving but the tension was way down so it still wasn't working brilliantly.

 

I have no idea how my flap could just suddenly lose it's tension like that

 

EDIT - guess it's worth double checking the temp sensor and wiring, but I've always been of the opinion that they either work or they don't, and if the car is starting OK then it's unlikely to be that.

Edited August 6, 2007 by GLPoomobile

[GLPoomobile 958]

Another thing that may support the faulty AFM theory, if my logic is correct, is this:

 

The ECU only takes readings from the AFM for fueling up to 4000rpm. Above 4000rpm, with the flap wide open, the fueling is all based upon the parameters set in the ECU. This is all 2nd hand info that I remember reading on here a while ago, so I reserve the right to be completely wrong with this info

 

But if the above is true, it would explain why the car feels quick when you are nailing it, as above 4k the AFM is redundant. But under less load, if the AFM flap is faulty then the fuelling will be out.

[kyepan 291]

Another thing that may support the faulty AFM theory, if my logic is correct, is this:

 

The ECU only takes readings from the AFM for fueling up to 4000rpm. Above 4000rpm, with the flap wide open, the fueling is all based upon the parameters set in the ECU. This is all 2nd hand info that I remember reading on here a while ago, so I reserve the right to be completely wrong with this info

 

But if the above is true, it would explain why the car feels quick when you are nailing it, as above 4k the AFM is redundant. But under less load, if the AFM flap is faulty then the fuelling will be out.

Thanks Pooh

 

Now that makes sense... because its bansai up in the top range, but it lacks the low down grunt, when warm, when cold its pulls strong from bugger all.

 

Can it be retracked? or is it a replacement jobby? how much did you pay for it?

 

might also be the exaust not leaking quite as much when cold.. must fix that too.

[welshpug 1,622]

you can do the following tests on an Airflow meter ( AFM ) -

 

terminals 5 9 E 7 8 on AFM

terminals 18A and M18 on AFM plug

 

connect voltmeter between wire 18A and earth, disconnect ignition control unit and operate the starter motor, check that 9 volts is obtained.

 

connect ohmmeter between M18 and earth should be no more than 1 ohm.

 

check that the afm flap moves freely, clean if neccessary.

 

connect and Ohmmeter between terminal 5 and 8 of AFM, readign of 340 to 450 Ohms should be obtianed.

 

repeat for 9 +8, reading should be between 160 and 300 Ohms.

 

connect 5 and 7, and move the AFM flap, readings should be between 60 and 1000 Ohms.

 

give that a go

 

(will endeavour to take better quality pics!)

[welshpug 1,622]

EDIT! i'm an arse! this is for an 8V jetronic AFM, and Boobies had got my 405 Haynes manual cos I left it in Silky's 4bie at pugfest DOH!

[kyepan 291]

thats bloody briliant, thanks loads welshpug, i've got a 405 manual! will have a look:) never realised they had that info in them!!!

Edited August 6, 2007 by kyepan

[welshpug 1,622]

yeah I dotn think an Mi16 AFm will be much different, the functions are the same, but some resistances may be different.

 

will be interesting to find out what they are.

[kyepan 291]

perhaps someone can do the test with a known good one, or a new one.

[jim21070 2]

perhaps someone can do the test with a known good one, or a new one.

 

I can test a known good 1.6 one later today.

 

There is a thermister in the AFM to measure air temperature. This could be playing up and causing the problem.

 

Excellent test procedure Welshpug I like to refine it a bit futher using a small 9V battery across the AFM and reading the changing voltage on an old-fashioned multimeter with a moving hand. You see a much greater rate of change than doing a simple ohms check and can see very clearly any discontinuities or breaks in the track.

 

I'll post up how to do it later.

[jim21070 2]

I've tested a 1.6 AFM using my voltmeter method. This is how:

 

Connect a 9V battery (PP9 or similar) between Pin 5 (+ve) and pin 8 (-ve) and connect an analogue voltmeter between pin 8 and pin 7 (the AFM Potentiometer wiper).

 

With the flap fully closed you should see 7V on the meter. Gently push the flap fully open and the meter needle should fall gracefully from 7V with the flap fully closed right down to 0.25V with the flap fully open.

 

You are looking for a nice smooth fall in voltage with no jumps or sudden major changes in reading. If you do, this indicates a need for a clean of the potentiometer track and/or retrack of the AFM. You can only use an analogue voltmeter for this. A digital one will not show the smooth change in voltage you're looking for. A digital with a "fake Analogue" bar display may be OK but nothing beats a real old-school meter with a real hand on it

 

The Air Temperature Thermistor appears between pins 5 and E and has a resistance of around 500 ohms.

 

I stress the reading above applies to a 1.6 AFM. A 1.9 8V and an Mi16 AFM may well give differing readings but the basic test procedure remains valid.

[GLPoomobile 958]

I'm going to nip over to Machinemart tomorrow and pick up a Multimeter, and get an analogue one at the same time since they are only a few quid, so then I'll be able to test a known working Mi AFM and then I'll post the results. I also have my old Mi AFM that I re-tensioned the flap using Damir's guide for a 1.9 8v AFM, but I know that it is not correct as it now has a lot more tension than the known working one. So I'll test this too to see what the readings come up as.

 

Jim - how do I identify which pin is which, as you have mentioned pin numbers, but how do they correspond on the AFM socket?

[jim21070 2]

Excellent That'll add nicely to the collection of figures. Also note the resistance of the Air Temperature Sensor Thermistor between pins 5 and E

 

Jim - how do I identify which pin is which, as you have mentioned pin numbers, but how do they correspond on the AFM socket?

 

The pin numbers are cast into the socket moulding just above the socket. From the top (air inlet end) they go 5 9 E 7 8

 

Pleased to see you're getting an analogue meter. Much more use on a car than a swanky digital job in my opinion. They're easier to use as the needle can be seen at a glance and trends are easy to follow. High accuracy, typical of a digital meter, is not required.

 

For me, being old-school, a moving needle means there is some real volts, amps or ohms behind it making it move!

[kyepan 291]

I'm going to try and have a go at this at the weekend too.

[GLPoomobile 958]

Sorry to be such a complete spod, but I'm not sure how to use the multimeter for this test. I've set it to 10V DC. But on the gauge there are different ranges and I don't know which to read.

 

From the top there is:

ACDC - reading 0 to 250 with each mark being 25V

then 0 to 50, in increments of 1

then AC10V, 0 to 10, in increments of 0.4 as far as I can tell

[jim21070 2]

That is a very bizarre set of scales

 

Is there not one that reads from 0 to 10 or 0 to 100 or even 0 to 1? Almost every meter on the planet has at least one decade scale...

 

Pop the meter, on the 10V DC range, across a 9V battery and see what it reads. On one scale or another, it should read just over 9V if healthy.

 

It is common to have a separate scale for AC volts as measuring AC is not straightforward to measure like DC.

 

Can you post up a picture of it please GLP?

 

EDIT: You could try the 0 to 50 scale and double what it reads. Trouble is, inaccuracies creep in doing this.

Edited August 12, 2007 by jim21070

[GLPoomobile 958]

This is the one Jim

 

Clarke Multimeter

[welshpug 1,622]

aaah! I want one of them! how much was it?

 

you want the knob 1 click anti clockwise from what it is on the pic IIRC, been so long since I used one of those.

[jim21070 2]

It all makes sense now. The movment (meter itself) is not big enough for any more scales.

 

Set it on the 10V range for the AFM tests and pretend the 0 to 50 scale is 0 to 5 and double the reading indicated to get the true reading. It'll be more than adequate to see an AFM pot swinging nicely.

 

For general automotive work, use the 50V range.

 

I guess it was priced very economically?

Edited August 12, 2007 by jim21070

[GLPoomobile 958]

Errr yeah. Less than a fiver

 

But I bought a middle of the range digital one for nearer 20 quid at the same time which I'll use for most jobs. Only bought the analogue one for this AFM test so wouldn't have bothered if it had been much more expensive.

[kyepan 291]

Hi guys,

 

Thanks for all the feedback, wanted to be sure the problem was cured, so waited for todays nasty wet weather to give the car the ultimate test, and i'm pleased to say the AFM is fixed, and was definitly to blame.

 

Yesterday dad and I struggled to get any sensical readings from the volt meter / resistance meter. Please correct me if i am wrong but as you open the flap should the response be linear or logorithmic, as ours was most definitly logarithmic, It's not really worth posting up any figures because we got infinite resistance across the first and last pins, then much less than 7v when using a new 9v battery.

 

anyhow, I previously retracked it (a week ago), and dad wanted to check the armature and take readings straight from the carbon... we opened it up again and began taking readings, once again they were not right at all. the voltage was very low.

 

and then a bit of a break through, putting my ear to the track i could hear the arm making contact with the first part of the track but not much after. So i basically bent the arm down a bit to get a better contact...Little did i know this fixed the issue.

 

So, two things to remember when retracking an MI-16 AFM, if you move the board, screw it down as tight as possible, and make sure the arm is making good positive contact with the carbon, if not bend it down very slightly, but be gentle.

 

Secondly, if the contact is bad, having your AFM with the black box bit face down means the arm is working against gravity to touch the carbon... this may not help either.

 

The car's behaviour around idle is now markedly different, instead of rev's plumiting, they are more logarithmic braking quickly and settling gently from 2k downwards to a rock solid 1k when cold and 900 when warm. Also there is no smell of fuel when stopping the engine and at other times. It's not even thought about stalling once. I don't know if you can with your ears, but i swear it sounds like its running leaner, also sub 4000 rpm power is improved, especially when warm.

 

Happy justin..

 

Go retrack your AFM's guys,

 

J

[kyepan 291]

its still much better but is stalling again... perhaps its moisture ingress into the connector block on the afm, will clean and use some moisture dispersant.

[kyepan 291]

just out of interest, what readings should the igintion amp give when hot and cold?

[kyepan 291]

finally got round to testing the afm and air temp sensor and water temp sensor today, eveything seemed to check out. Must admit the caps program is a complete god send, very easy to follow even for a complete electrical novice such as myself.

 

Water temp sensor:

Supply voltage ok

resistance when warm spot on for about 80 degrees (280 ohms) and rising nicely as it cooled about 20 mins later to(560 ohms). Need to check it from cold.

 

AFM

Supply voltage ok

Earth was a bit high 0.29 rather than 0.25

Signal voltage on the No2 wire was also within the required tolerances, at ignition off, idle, 2k, 3k, blip, and rose smootly.

 

Air temp sensor (ambient temp about 5-10 degrees at time of test)

Supply voltage ok

Signal Voltage ok for about 20 degrees (under bonnet temperature when standing and warm engine)

resistance also ok for that temp.

 

so it would seem its not the AFM ATS or Water temp sensor (subject to cold start tests)

 

Next i'm going to probe the ECU end to check whats getting back to the brain .. to rule out wiring issues.

 

and also check the TPS as that looked.. grubby.

 

cheers

 

J

[Doof 11]

Mine was exactly the same and i went over to Skip Brown the other week. Apparently my dizzy was completely shot and was giving 20 degrees advance at idle and was generally all over the place in terms of the advance curve.

 

He managed to sort the idle out slightly, it doesn't stall nearly as much and wavers much less. He said he could only tune it for either the low end or the high end because of the dizzy. I opted for the low end because of the amount i have to drive to work now and its much better behaved although lacking quite a bit up the top of the rev range.

 

I'd be inclined to have an RR tuneup, 50 quid and i know what the problem is!