Please help with double cold start, crazy trims on idle and O2 sensors showing 0V...

[Piotr Piech]

I belive I need some help before I start the global change of everything in my 2000 SOHC Ex 2 gen, 112 000 mi on it. Runs great while everyday driving but I have noticed some strange issues. When cold (in the morning), it rarely starts at the first time. Secod time ignition starts the engine but it does not work smooth. Idle RPM goes around 1200-1500 for a while (P on trans), then it comes down after a minute or so (or when I switch to N on trans). Looks like a cold start makes a problem for the engine to start a smooth run. No issues while driving.

To add a problem, LT fuel trims on idle go crazy (around 28%), they go fine (around 5-6%) while driving. Short term trims while driving (around 2000-2500 rpm) go like on the attached screen.

And last but not least, O2 sensors on bank one sensor 2 and bank two sensor 2 show 0V all the time. Both of the sensors one (the upstream I guess) work as shown on the pic, with the peak voltage around 0,78V or so. Are these trims and idle problems beacouse of the faulty (?) O2 sensors? The MAF seems to work fine, the intake manifold gaskets were changed with ne ones around 15 000 miles or so. Spark plugs as well.

The funny thing, there is no engine light or any trouble codes showing the faulty O2 sensors or lean / rich mixture. Even with so crazy fuel trims.

I have been looking for some replacement O2 sensors but cannot figure out the right ones. Are the upstream ones the same as the downstream? I plan to get the BOSH ones from Rock Auto - 13117 Actual OE Oxygen Sensor but I cannot figure out if that one fits only upstream sensor or can be applied as well as the donwstream? There is another one: BOSCH 15716 {#13127, 15718} Bosch Engineered Oxygen Sensor and it showes as the downstream one... little crazy...

I think that changing all the O2 sensors just beacouse of the mileage is a good idea. Hope it helps with these crazy trims as well, what do you think?

Any help with these issues would be great. I plan a long family trip soon and would be great to have the Ex 110% up and running

Thanks!
Piotr

 

[XploderPhil]

Don't overthink those cold start PID readings. The computer can care less what the O2 sensors are doing, infact the PCM is really only looking at a couple of important values on start up, engine cooling temp, intake air temperature, calculated baro pressure, MAF.

This time of year it's possible that you are dealing with summer/winter fuel blend change over. On a cold day with summer blend it's harder to start and the other way, warm day with winter blend. Again don't over think the starting unless it involves long cracking times.

If the converter's are working the rear O2 usually read close to 0.

 

[C420sailor]

Check your fuel pressure in the morning before you start. Bet it is damn near zero.

 

[Piotr Piech]

Check your fuel pressure in the morning before you start. Bet it is damn near zero.

That is possible as well. You think of fuel pump that might be a cause of these trims and other issues? Never did that before so a quick, few steps "how to" would be a great thing to know. Should I remove the fuel filter? Or check the pressure anywhere else? Let me just give a few tips so that I can figure it out.

 

[Piotr Piech]

If the converter's are working the rear O2 usually read close to 0.

Did not know tjat. Strange is that 0V is no matter of the gear, speed or throttle... all the time these two sensors show 0V and do not want to move any way from there...

BTW, what is the recommended mileage to change the O2 sensors? Should these be changed periodically or only when a trouble code appear on the computer?

 

[XploderPhil]

Personally I've never change an O2 sensor unless it was bad or getting lazy