F7R problem NEW !! :-)

[Schakal]

williams f7r engine , no catalytic converter or power steering .
2" stainless steel exhaust system .
engine runs great and pulls like a train .
but sometimes it will idle like this in the video from cold,
once the water temperature is over the first line on the gauge
everything is fine.

does it for the first 5 minutes from cold .
when driving i can feel the power is going down slowly but as
soon as i dip the clutch pedal revs go up to normal . so it has got
something to do with the engine being under load !! ??


http://www.youtube.com/watch?v=cDkwpG3oSsM

[Rob@Backyardracing]

faulty lamber sensor..

[Schakal]

faulty lamber sensor..

are you sure on this mate ? have you had the same problem ?
most people reckon lambda readings dont affect fuelling
untill engine is warm !!

if it is the lambda ,should it make any difference if i disconnect the leccy plug to it ?

[Rob@Backyardracing]

sorry i was ment to put a ? mark after that post...I have a valver with the exact same fault, i havnt fixed it yet, but i scratched around some old posts on the valver sites and most peeps say its this at fault.. the temp sensor tho was my first thought to mind?? but then you would think it would struggle to hot start then..

[markey b]

is the speedo cable connected up via the plug at the top to the ecu?

[markey b]

scrap that actually, car isn't moving on the vid!

[Matt@CodeRedMotorsports]

Have you buggered about with the 'idle screw' in the throttle body or the tps? 'cos they are set from factory......
Try cleaning out the idle control valve as it costs nothing first.....
If the speedo cable is unplugged they idle high.
If the 02 sensor wiring is present, it means phase 2.... If that's not connected it goes open loop so, relies on programme only and cannot control fuelling, mind you these things are open loop on warm up and after 4/5000 rpm......

[Tony Walker]

Lambda sensors warm up very quickly and enter closed loop before water temps are anywhere near warm. different for different makes models of car but i'd say no more than a minute before the precat sensor starts working, even quicker if you raise the revs.

[Matt@CodeRedMotorsports]

Agree with that. Yep 100%
But.... We are talking about an early 90's single sensor system here.

[Tony Walker]

doh, not worked on one in a long time, presumed it'd be 3 wire heated at least. nm, prob take a fair few mins to warm up then

[Matt@CodeRedMotorsports]

My memory isn't too good either!!!
I think it is a 3 wire heated sensor, but the early programming isn't too good.

[Tony Walker]

dont worry bout it, i work on all makes/models remembering whats where and sensor values is impossible. It does seem like the heater element has failed on the sensor and is taking the "5 mins" to warm up then works correctly. Without scoping the sensor its difficult to tell, you could try probing the sensor see if you have a 12v feed and less than .5 volt drop on the two white heater wires.

[Tony Walker]

If its easy enough to do its worth taking the sensor out and giving it a blast with a compressed air line and maybe a little brake cleaner, non silicone based cleaner. Doesnt work all that often but on your own car its worth a go. They do get clogged up sometimes.

[Matt@CodeRedMotorsports]

Years ago when 02 sensors were quite expensive, we used to bench test them, heat them up with a blow torch and record the voltage, about .8 of a volt if my memory is correct... Then in the cooling phase the voltage should drop quite steadily.

[Tony Walker]

Yeah up to temp they should cycle pretty much 0.1-0.8v

Im sure its the oxygen content difference that provides the voltage so that 0.1 is lean and up to 0.8 is rich, thats on a 4 wire but im sure its the same for 3.
So up to temp surrounded by oxygen it should read 0 but maybe it was your blow torch "using" the oxygen while burning that created the difference? did you just heat the element and not the other side of the sensor?

[Schakal]

thanks for all the replies guys

the problem has disappeared again
what i have done was to get some redex in the tank and give the engine a
good high revved driving .

my theory now is ;
i accidentally overfilled the engine oil (went 1/2 inch over max mark )
a few weeks ago , when i checked the oil level again 2 days ago ,it was just under
max . so i assume that excess oil has been burnt in cylinders and probably covered
lambda sensor as they exited . causing this problem somehow .
since than i gave it a booting with redex and lambda is sort of cleaned up of oil .
does that make sense ?

also could someone in the know explain to me what "open" and "close" loop
exactly mean ?

[Tony Walker]

oil destroys lambda sensors pretty quickly.
Open loop is while the lambda sensor is warming up not in use. Closed loop applies as soon s the sensor is up to temperature, the loop is the sensor detecting rich/lean mixture then adjusting the fueling for the next cycle then detecting the opposite, thats why sensors cycle from rich to lean when working correctly because... thats what the engine is doing, cycling very quickly from lean to rich to create as close to stoicheometric burn as possible, this is the loop thats constantly monitored. systems go open loop when warm only on full throttle and some when cruising down in gear(injectors switch off on most modern systems) there are allways execptions tho, and depends what year vehicles too.

[Schakal]

Open loop is while the lambda sensor is warming up not in use. Closed loop applies as soon s the sensor is up to temperature, the loop is the sensor detecting rich/lean mixture then adjusting the fueling for the next cycle then detecting the opposite, thats why sensors cycle from rich to lean when working correctly because... thats what the engine is doing, cycling very quickly from lean to rich to create as close to stoicheometric burn as possible, this is the loop thats constantly monitored. systems go open loop when warm only on full throttle and some when cruising down in gear(injectors switch off on most modern systems) there are allways execptions tho, and depends what year vehicles too.

i am sorry , i have no idea what you are saying there ^^^
any chance of explaining this a little more basic ?

are you saying lambda sensor cant affect the fuelling untill it
gets to a certain temp ? if this is a fact ,lambda sensor cant be causing this
problem on my car ,could it ?

[Nick k]

i am sorry , i have no idea what you are saying there ^^^
any chance of explaining this a little more basic ?

are you saying lambda sensor cant affect the fuelling untill it
gets to a certain temp ? if this is a fact ,lambda sensor cant be causing this
problem on my car ,could it ?

Yea lamba reading are not used by engine ecu until and certain temperature is reached. So from cold the engine ecu is not looking at the lamba sensor.

I have had this fault on a F7P with different things causing it,

1, was a sticking idle speed valve
2, Doggy plug on idle speed valve
3, Knackered ecu ( something to do with the 5th/cold injector)

worth a 2 minute look at idle speed valve.

[Schakal]

Yea lamba reading are not used by engine ecu until and certain temperature is reached. So from cold the engine ecu is not looking at the lamba sensor.

I have had this fault on a F7P with different things causing it,

1, was a sticking idle speed valve
2, Doggy plug on idle speed valve
3, Knackered ecu ( something to do with the 5th/cold injector)

worth a 2 minute look at idle speed valve.

so it cant be lambda at all but giving it a good thrashing seems to have
fixed the problem for now

nick , i have changed the icv with 3 different ones ,all cleaned lubed up .
its not the icv .

[Tony Walker]

It runs fine once its warmed up after about 5 mins is the main point im going off. With this in mind, it sounds to me like the lambda sensor heater has failed and is taking along time to warm up, once up to temp fueling is fine.
Its by no means a 100% answer just something id personally check in the diagnostic process.
Easy enough to test the heater is working and test the heater element resistance(roughly)