Lean combustion?

[Tuga2112]

a vacum leak would cause more fuel injection first because the MAP (mass air pressure) sensor would recognise the lower pressure and tell the ECU to enrich the mix to prevent the engine from running lean.
this would be a faster reaction than the fuel regulator which is a mechanical reaction.

it should be visible in the graph of MAP and injector cycle (i believe thats one of the pieces of data availablle) if that happens.

you could in theory test the MAP operation with the key in ignition, engine off. read the value in the computer and suck or blow on the opposite side of the vacum tube, the reading should change..
note the MAP is rated up to 1bar. im not sure if humans can pressurise it too much with our lungs. but i would go easy on it just to avoid damaging it in the process.

[Chas54]

Tuga

I think i know what you're getting at , a vacuum leak would lead to higher pressure (absolute) , Then the ECU would increase fuelling to prevent lean running and this would be faster than the fuel reg. I can see changes in the vacuum on the elanscan traces but trying to match it to the injector duty or width is difficult .

i have tested the MAP with a hand vacuum pump and it responds pretty much as my analogue gauge shows. I have a miniature petrol filter in the MAP line because the original trap was cracked when i got the car . I figured if it was around the same volume as the original any damping effect would be close. At the moment i've removed it as i didn't want it having any affect on my testing.

Ive tightened up all the injector caps terminal grips just to rule these out.

Another test today and set up of the IAC bypass. I have carried out a blocked exhaust test with a vac gauge at 2500revs and it seems OK. I noticed that the O2 sensor doesnt respond initially and the blower casing is around 110c before it starts producing 0.4v. Road test again today and whilst it felt good for the first 5 miles the ECU light came on again at almost the exact same spot on my road trip yesterday. Its got to be a coincidence .
The elanscan trace shows it switching between open and closed loop continuously and then the O2 sensor gives up.


I think im going to try one of the older O2 sensors i have and then if no better swap the injectors back to my cleaned originals . Desperation setting in now

road run after IAC setup.zip

Chas54

[Tuga2112]

when you start fully grasping at straws.

i can give you another way to investigate. which is a known fault in toyotas of the same era.

ECU bulged capacitors. they seems to have all kinds of odd side effects but rarely stop the car from running completely.

[Chas54]

I'll have a look in my ECMs , see if I can spot any capacitors swelling .

Im still think what my next step should be. I'm considering the petrol pump as it would explain the intermittent weak mixture fault I get.

I can't think of a way to monitor the fuel pressure whilst driving. I can do it idling in the garage but it's a bit of a lash up with bits of pipe and jubilee clips ,so not really safe for a road run.


Chas54

[chrism]

Weren't you going to change the oxygen sensor? Easy to do and the response would validate the sensor and alt output if it compares with recent O2 'breakdown' times.

Also I wonder if the fuel is getting through the injectors adequately? Don't things seem to go haywire when the revs are higher? I can't remember if you've renewed the fuel filter - but you changed fuel pump, I think; I presume they're both up to the job?

Edit: And is that combination - with the questionable fuel flow of some RAuto injectors - up to it as well?

[Chas54]

Chrism
Sorry i have maybe caused some confusion .
The dips in revs i was experiencing have disappeared and i suspect the lower coil swap was the rectifying factor. I now have a set of four spark testers .
I changed the O2 sensor to the Walker one i bought. It may have improved things marginally but i still get the sudden drops in voltage and then the sensor stops working . Ive tried directly cabled and soldered connections to the 3 O2 sensor connections with no improvement. I have now rejoined the cables to their respective originals.
I am suspecting something odd with fuelling and i havent changed the petrol filter yet . (last changed it about 5 years ago.) New filter on order. Ive had the petrol pump out the tank and cant see anything wrong but if it was stopping occasionally for a fraction of a second, i thought it might cause my issue. Ive got to check the relay as well just to convince myself thats OK. A compatable petrol pump is around £100 so i am looking at extending my fuel pressure test gauge hose so i can fasten it to the outside of the windscreen and watch the pressure when the event occurs.



My current set of injectors came from the US ebay seller "elinjector" and described as OEM .. I am considering reverting to my cleaned original set . I havent used them since the cleaning as one tends to form a drip when left at pressure.

The other thing that was suggested earlier was that i revert to the old chip and CO pot, ie. no closed loop.. I havent tried this yet but i have the pot refitted and set mid range , just got to get round to trying .

Thanks for comments

chas54

Havent really touched it the past week as my grandsons go kart rebuild landed in my garage-- now finished.

[Chas54]

I should also have said the event doesnt occur at particularly high revs . But on my test route of about 10 miles , the lean sensor fault seems to occur on my return and almost the exact same piece of road.
The road isn’t bumpy so I wondered if it was time duration that was the factor and i wondered about the fuel pump performance dropping off ? I dont know what type of pump it is but if its rotary vane type , i can imagine a sticking vane being heat related .. When the stumbling occurs it does feel like a fuel loss> Not really scientific just a gut feeling.


Chas54