O2 not cycling at idle, lo trim 139%

[unclesam099]

Ok, I have done everything to try to get this thing fixed. Rebuilt my TB, pressure tested w/no leaks, tried adding fuel... NOTHING will get my low trim off of 139%. The other thing is that the car will idle fine for a few seconds (at a 15.x:1 on the WB), but then it'll kinda sputter and immediately drop to a 17.x:1 WB reading.

My O2 will cycle when I'm driving, which is the puzzling part, although it reads lean even with the WB reading 10.x at WOT.

I can't imagine that would be the case with 550s, hotwired 255hp pump, AFPR, MAFT, and SAFC. MAFT set for 530cc injectors, +20% idle on the MAFT will get the O2s to cycle at idle, but that's ridiculous.

The only thing that I haven't replaced is the O2 sensor, but that's barely 25k old.

Is there anything that I might be missing that I should check/replace??

Thanks in advance.

 

[GVR4592]

It's not cycling because it's out of range.

What is your fuel pressure with the vacuum line off? What are the Safc and MAF-T settiings?

 

[unclesam099]

Fuel pressure is 38psi with the vac line off. Running Blow-Thru. Methanol is turned off til I get stuff tuned so I can turn boost up.

SAFC is zeroed out because I'm still trying to baseline the MAFT before I get the RPM points set up.

MAFT is Base 0,A (530 injector size); idle +2, mid +1, WOT 0.

All mods are listed in this sig picture: http://3sforum.com/albums/unclesam099/SigPic.gif

 

[Kevin Jewer]

Given that it cycles when cruising but still reads lean tells me the o2 sensor is dead. The extra heat from cruising wakes it up a bit, from past experiences. Sometimes when this is the case you will also see the voltage rise gradually over a long WOT pull as it gathers some heat and starts to come back.

It's difficult to diagnose these things over the internet though. Luke is also going down a path related to another potential cause, and he could very well be on to something. Good luck

 

[steve]

Check the resistance of the O2 sensor heater and make sure it's gets 12v across it when the ignition is on.

What does the WB read at cruise with the NB is cycling?

I'd guess the O2 is on it's way to dead. I didn't get 25k out of my last one.

Steve

 

[unclesam099]

I will have to check the resistance. WB reads 14.5 - 15.2 or so when cruising. Seems normal to me.

I just did a 3rd gear WOT pull and was 10.x on the WB and .86 - .89v narrowband til I cut it short at 5500 because of knock.

I think that I'll bite the bullet and get a new O2 sensor. It was run for a long time with vac leaks and an open BOV while my brother owned the car and didn't fix anything.

 

[Kevin Jewer]

Those WB readings do seem to support the dead O2 sensor diagnosis. What amazes me is how close AFR is to target without any meaningful feedback from the front o2 sensor. The stock ECU really does do an awesome job (which I have come to realize after switching to the AEM from DSMlink).

 

[GVR4592]

Those WB readings do seem to support the dead O2 sensor diagnosis. What amazes me is how close AFR is to target without any meaningful feedback from the front o2 sensor. The stock ECU really does do an awesome job (which I have come to realize after switching to the AEM from DSMlink).

Not liking the AEM?

 

[Kevin Jewer]

I love it! Well, I won't go that far. I love DSMlink. AEM is awesome though, incredibly powerful, and really is challenging my EFI knowledge, which I like. But it makes me really appreciate how well the stock ECU "just works," and how awesome DSMlink is, especially for people just learning to tune. (If I go to the track friday it will be the first time on race gas, and maybe the nitrous, with the AEM. We'll see if I can match my DSMlink best of 11.52 at 122.

 

[unclesam099]

The cool thing is that my gas mileage really isn't suffering much. I get 30mpg highway and ~24 around the backroads. Not too terrible for a quick little car.

 

[turbo2086]

Try resetting the ECU. Unplug the battery for about 15min. It will set your fuel trims back to 100%. See if you o2 will cycle now, if it does, see how high the fuel trims climb.

What's your other fuel trims look like?

 

[Quasimondo]

Before you replace your O2 sensor, check your base timing. I had a similar issue with my O2 sensor. I replaced it and redid the wiring from the sensor to the harness, only to discover that I had my base timing set for 5* ATDC. I must've either looked at the wrong spot on the crank pulley or never grounded out the timing adjustment pin when I was setting my timing.

 

[unclesam099]

Turbo2086, I have done that many many times now, no help there. Mid is 109% and High is 107%.

Quasimondo, I will have to double check that, but my Palmlogger shows that it's fine.

 

[Kevin Jewer]

The logger only tells you what the ECU wants for timing, not what it actually is.

 

[steve]

Kevin, I think you mean that the logger only telly you what the ECU thinks the timing is.
Both the ECU and the datalogger assume that the CAS pulses are correctly synched to 5* BTDC. Since the ECU directly controls the spark timing it can tell you what the advance is but not the actual timing.

Steve

 

[Kevin Jewer]

I'm not sure I see where you are going with this, but that just might be because it's 4am It sounds like we are saying the same thing, so I'll just ramble on in case I wasn't clear.

The value we read at the ECU with the logger is what the ECU wants for ignition timing. The ECU has no idea what the ignition timing actually is. With a 1g CAS the timing has to be synced to the ECU, usually done at the 5 degree "base" (cranking/diagnostic) timing value, to make actual ignition timing match what the ECU is commanding for ignition timing. With the 2g and EVO this is set by the crank trigger plate and is non-adjustable (well, unless you have AEM).

 

[unclesam099]

Alright, I guess I am going to be finding a timing light for rent at Pep Boys so I can get it checked.

 

[steve]

I'm not sure I see where you are going with this, but that just might be because it's 4am It sounds like we are saying the same thing, so I'll just ramble on in case I wasn't clear.

We are.
I'm trying to point out that this is a case where what the ECU wants is what it gets, unlike things such as IPW or ISC steps.
The ECU got exactly the timing advance it wanted value wise just not absolute position wise.
With the IPW the ECU can want more fuel than there is time to spray causing IDC > 100%.

Please excuse the interruption.

Steve

 

[Kevin Jewer]

Gotcha.

 

[unclesam099]

Ok, I checked my timing and it needed to be adjusted. No help there though, still no cycling at idle.

Tested the plug on the car. Only one of the heater wires gets 12v. Should they both get 12v with the ignition on?

I just replaced the O2 sensor - fired it up and it jumps right to 139%. I am sitting now for a few minutes before I smash something and letting the ECU reset. Ok, just got that done and still jumps right to 167%. I get massive knock on WOT pulls even when the WB reads 11.0. Even when adding fuel on the MAFT, (Set for 520 injectors, +3 idle, +2 mid, +1 WOT) there is NO change and 34 counts of knock on a 2nd gear pull.

I'm really getting pissed. What else should I look for other than a new car?

 

[steve]

Tested the plug on the car. Only one of the heater wires gets 12v. Should they both get 12v with the ignition on?

Since you replaced the O2 sensor it's a little late to explain but what I suggested was two tasks, measuring the resistance of the heater and making sure that it was getting 12v.
Only one side gets 12v and the other is grounded but you can hae power and still have a bad heater, that's why you have to check it's resistance too.

Steve

 

[unclesam099]

Is there a way to check the wiring harness to see if I'm losing voltage somewhere? I mean, there has to be SOME reason why I'm running 10.x on the wideband and only seeing .88v on the datalogger...

I don't know electrical stuff very well, sorry if it's a simple question.

 

[steve]

Nothing cares if you are getting 0.88v, 0.84v, or 0.99v. The onlt thing the narrowband O2 sensor has to do is switch around the stoich point.

You can measure the resistance of the wires from under the hood to the ECU and make sure there is no resistance. I'd suggect double charcking your wideband to verift it's readings and then look into why the NB sensor doesn't seem to be cycling.
It's not unusual for MAFT setting to be off but there could be many other causes as well.

Once your sure that the WB is working you can tune the car for both closed and open loop operation. If at idle the WB says your lean the richen the car up or vice versa.

Steve

 

[unclesam099]

Steve, thanks for sticking with me on this thread.

I talked to TurboBob from Full Throttle Tech (a 3S owner as I was in the past) and he said that I should try setting the dip switches for the MAF sensor to the 3.5" GM setting. Apparently, the injector setting size chart does not really apply to blow-thru config. He said to try to give the car what it wants vs. going off of the chart. I did not even consider to do that since I thought that the MAFT settings would be fairly accurate.

Using the 3.5" setting definitely helped and I was running 13.x - 14.x at cruise on the way to work today, low trim is now under 100 and idles with FTO2 sitting at 32.1% and the WB reading 10.x (). So now I have some tuning to do to get this thing under control. However, rolling into boost will give me knock even when rich. I am guessing that it could be too much fuel or too little timing? The knock hits around 2700rpm when flooring it in 3rd gear around 2200rpm, so it's almost immediate. My mid is too low maybe?

Hopefully this thread will help those in the future with MAFT/fuel trim troubleshooting.