nicholasbartleet

Ive been having some issues with my car on cold start for some time and posted many threads to try and resolve it. I think i'm getting close now.

I am noticing that i am getting very high negative short and long term fuel trim readings.

Short term readings are ranging from 0 to -16 long term is averaging -8

Does this sound like the evap system is purging too much fuel vapour into the system or

Does it sound like the spark is not powerfull enough to detonate properly. (Battery voltage is reading 12.3Volts when off and 14.5Volts when on which seems low.

The car has had new plugs last week becuase it has obviously been running rich and the plugs keep getting fouled. They are the correct plugs and they and they are gapped properly.

Any help would be much appreciated.

s2konroids

-16 seems a bit strange normal is probably - or + 5%, though those 2 figure combined dont. It does take time(a few weeks) to learn though LTFT wise.

When are you monitoring on cold startup/coasting etc???

First off on cold startup, airpump comes on to heat CAT up, to get into closed loop quicker for emmisions so it will run lean when it gets warmed up it will go into closed loop then the LTFT can be modified.

Negative is normal'ish i cant remember mine i 'think' it was around -2/3%, are you monitoring with an OBD2 logger? IIRC with LTFT/STFT it can adjust as much 25%. STFT dicatates LTFT over time and obviosuly 0 is no correction, actually they will flucatuate a wee bit during a normal day its normal. If the short term going across 0% then the long terms will not change. I cant put my finger on it but 'i think' honda run at particular readings, STFT+LTFT are used by Honda not a req of OBD2.

Now your o2 sensor need to be in good working knick, it is pretty important amongst other things?

I'd check and you';ve probably already checked so but here goes, from what you said about it running rich.

IIRC negative STFT should could mean the following...monitor the o2 sensor if its read is more 0.5V it means you have oxygen, more oxygen is needed so it reduces the amount of fuel now the ECU will thinks its running rich thus reduces the amount of fuel (a (if your o2 sensor is working fine) too much air or not enoguh fuel, so id check injectors, MAP sensor its maybe worth monitoring the o2 sensor, and looking for vac leaks etc.

Have you monitored your STFT during a drive if you gently acclerate monitor your STFT, trend aiflow and revs as they increas. If the STFT climbs rapidly, there is a lean place.

Can you not go on a dyno or at least get access to a wideband o2 sensor might give you a clue, as it will give your AFR and rev ranges where it flucatuates this may prove to help you further.

IIRC the evap take evpaorated fuel and burns in engine, Is there a filter inside the evap???

This leads me tuning, when in WOT it will be looking at LTFT but with my VAFC2 i dont do any adjustment on partial throttle where it learns plus WOT is set at 81% different from stock, so it only read not adjust LTFT hence AFR is the same.

Its all very complicated! and web diagnosis is difficult. I'm still learning myself.

Good luck, where are you located? we could monitor if you'd travel to the lakes?.

Cheers

AJ

nicholasbartleet

Thankyou for your reply. I have just monitored it again. I am using an OBD2 Autel Datastreaming code reader and i am getting some unusual and seemingly very erratic results. All of these readings are taken when the car is fully warmed up and while driving.

1. The Fuel System fluctuates from OPEN LOOP to CLOSED LOOP continually while driving.
2. The Short term Fuel trim reads between -15 and -20 on idle and when the throttle is pressed it momentarily returns to around 0 before shooting back into the high negatived. While driving the readings are almost always negative, but very random as they flick around leaping from -3 to -15 to -7 etc.
3. The Long Term Fuel trim reads -8
4. The 02 Bank 1 Sensor 1 Reading is just as erratic. It fluctuated randomly from 0.1 to 0.8
5. The 02 Bank 1 Sensor 2 Reading is fairly consistent at around 0.8

To recap, the 02 Sensor 1 is erratic. The engine is flicking from open to closed loop continually and the ST fuel trim reads randomly in the (negative) figures, favouring between -7 and -15 most of the time. All of these readings seem very random.

m1bjr

FWIW I agree with the above - in that O2 sensors always seem to degrade and the voltage shift will cause over fuelling.
Hence the neg trim, so I would try the O2 sensor first.
Chech the physical connectors under the car - one is quite exposed near the gearbox.
Oh- and earth connections.

(Assuming the very obvious like blocked inlet tract or air filter is okay!)

nicholasbartleet

Thanks for the advice. I shall track down a new 02 sensor.
The reason i have never considered it, is because the rough running has always been on cold start when the 02 sensors arn't even working. It seems to be running rich in open loop which is strange if it is an 02 sensor issue isn't it?

s2konroids

The o2 sensor fails lean thus making the car run rich, rich is colder thus is safer but obviosuly uses more fuel.

Its supposed jump between lean and rich 0.2v to 0.8v as you say, it should flucature very quickly a pattern should occur buit not necessary 100% smooth. IF you put your foot down flat to the floor (this is WOT) it should stay steady voltage wise.

If its going from closed to open loop that because your going past 50% throttle position then taking foot off and on arent you? (which puts in closed loop).

So from what you say i dont suspect a problem your o2 sensor, the problem i found out when i wrote my program to monitor/graph all these things is the response time may not reflect the actual realtime trend (so its a bit behind thus dissorted slightly) but you can get the jist.

Tell tale signs of duff o2 sensor are rough idling, hestiation etc etc.

nicholasbartleet

thanks that really helps. So the 02 sensor is probably not at fault and you think these readings seem fairly normal. At least that is one more think i can rule out.

I think i should check all of my ground connections next.

s2konroids

What is the problem at cold startup, i bet it runs fine normally???

nicholasbartleet

Yes, it runs fine normally although it does have a funny rev drop when you drop the clutch at traffic lights and it sounds like it might stall and then recovers.

The cold start issue is:

1. A strong fuel smell
2. Clicking from the timing chain
3. The engine boggs and the revs shoot down and back up repeatedly.

Once its warm, its fine for the rest of the day. Its not a VAC problem or IAC. This is what it sounds like:

http://www.pixelloft.com/car.mp3

veehexx

going on purely the "clicking from timing chain", i'd say TCT..... or maybe low oil level