Lambda sensor

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stevo82

Member +
Is there a way to test the lambda sensor, and to test whether the signal reaches the ecu? I'm boosting around 0.8 bar and when the engine is at normal operating temp(if I've been driving around for a long time) theres a lot of misfiring and hesitation. When the car isnt very hot or the weather is wet or cold the problem isnt that bad. Tested resistances of coolant temp sensor, seems to be fine. My fuel pressure is at around 3 bar (modified standard fpr). I'm not hitting fuel cut and from what I've been reading around here it could be overfueling as there is quite a bit of blackish smoke on hard acceleration, especially when it misfires/cuts out. It happens only on full throttle, I can stop it from happening by lifting off a bit, but keeping boost at full, or close to full, not sure.

Would very much appreciate any help! Thanks!
 
dac69er

dac69er

Super Moderator
it wont be the lambda.

why are you running 3 bar fuel pressure? how as it been modified?
if its overfuelling it will misfire.

are you sure your ignition components are spot on? that is the most common cause for misfires at high loads on boost.
 
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stevo82

Member +
A tuner told me to run 3 bar for 0.8 to 0.9 bar boost until we can set it up on the rr (need to buy a rrfpr, have a fcd, want to run 1 bar). The same tuner just put a bolt into the fpr which you turn to adjust the pressure. So its no longer rising rate, its at a constant 3 bar. I replaced my leads and plugs but the problem persists. Any idea why it gets worse at higher temp? I'm attaching a wire to the lambda sensor to test its voltage with a multimeter while driving to see what it does.
 
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stevo82

Member +
Maybe, but he's the only one with a dyno around here ( it costs around 55 GBP per run so I'm waiting to get the rrfpr before I go). I hooked up my multimeter to the lambda sensor. The voltages are mostly between 0.5v and 0.8v and goes to 0.9v and a bit over when I'm gunning it. I read that lambda = 1 (good afr) should be around 0.45v, ranging between 0.2v and 0.75v, so it looks like I'm running quite rich. I'm gonna adjust the fuel pressure to about 2.8 bar later and see what it does.
 
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stevo82

Member +
Last night I was driving around for about an hour and when I put my foot down the car just started bogging down and backfiring! I'm trying to figure out what can be causing my problem. Here are the things I know:

1) When I havent been driving the car long, only couple of minutes, it doesnt hessitate or misfire when I put my foot down, so I'm thinking the problem starts when it warms up a lot. It seems that the longer I'm driving around the worse the problem gets (probably up to a point)

2) When its warm, backfiring and bogging down when I put my foot down, i can keep it from doing this by only depressing the throttle by a small amount once it has started boosting, it still feels like its pulling quite well but the throttle is maybe one fifth open and its still boosting nicely!

3) The check engine light doesnt come on so its not fuel cut, I have a HKS fuel cut defencer (keeping it on 12 till I get my fueling done), but I dit put it on setting 9 just to check if it makes a difference ( boosting 0.9 bar ), but it doesnt.

4) I dont know what the resistance values of the intake air temp sensor and coolant temp sensor are, but I did measure them on hot and cold and there is a substancial difference, making me think they work.

5) I connected a multimeter to the lambda sensor and the values range from 0.3v to 0.95v, and as I understand 0v is lean and 1v is rich and the range should be between 0.3 and 0.7. But the values change very fast.

6) My fuel pressure ranges between 2.6 and 2.9 bar.

Does anyone have any ideas on what could be the problem? I would really appreciate the input! Thanks!
 
weeJohn

weeJohn

Lifer
Your problems do sound fuelling related, engine bay temps go up after driving about and intake air is thinned out because of that and that can cause a weak mixture. The multimeter on a normal Llambda sensor is really only good for a guide, you really need a wideband sensor to set it up right, your tuner will not doubt sort that out.

But also, when things heat up they expand and this can cause gaps to open. I would check the dizzy cap and rotor arm, and the ignition lead connections for signs of burning, showing a poor connection.
 
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stevo82

Member +
Ok so the problem is finally sorted, I just changed the spark plug gaps from the standard 1mm to 0.7mm, now I have no more problems! Thanks to all!
 
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