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Long Term Fuel Trim at 92. Renix

my2monkeys

NAXJA Member
My LTFT dropped to 92 from 105 after a new FPR that I figured was leaking thus driving my trim down to subtract fuel.

But checking now after new FPR and fuel pressure gauge reading 31 psi and holding the dang trim stays down to 92.

Any suggestions?

I gotta smog him this month.

Have brand new NTK o2 waiting to go in but im afraid to foul it up with all that fuel.

Or maybe thats my issue?
 
Yep, put the O2 sensor in.
 
less than 128 is removing fuel from engine above the 128 is commanding to add more fuel.

if your running below 128
causes could be
fuel pressure higher than 39psi
dirty air filter
leaky fuel injectors
faulty o2 sensor/circuit
faulty egr valve/circuit

i have mostly replaced everything on my 88 including an entire set of different injectors and im sitting about 110 last i checked.

is your short term staying at 128? im pretty sure if you dont go into closed loop it will never reset the long term trim. and it could take a few days to slowly creep back up.

you can force a reset by disconnecting the battery and see if it dips back down
 
Okay so i changed the O2 sensor and then I put my old fuel injectors back in and then I unhooked the battery.
Now my long-term fuel trim is at 1:28 doesn't change after 50 miles or so, short-term stays below a hundred way down to in the thirties
 
How can the ltft never change from 128 and the stft be way below 75 and left doesn't adjust to compensate.

It goes into closed loop after 1 minute on cold start up.

All sensors read normal
 
LTFT should stay at 128 all the time say at idle. Mine does.

STFT, Short term, will change and thus read below 128 at times. Mine reads about 92 at idle right now.

I think STFT should change a lot during acceleration (increase) and deceleration (decrease)? Have you tested that?

A low STFT might indicate worn injectors with more flow when open than stock new injectors? But I am guessing.

How can the ltft never change from 128 and the stft be way below 75 and left doesn't adjust to compensate.

It goes into closed loop after 1 minute on cold start up.

All sensors read normal
 
short term should bounce above and below 128 when driving as its directly related to the o2 sensor reading. once it hits a threshold and the long term triggers down or up one it resets and starts allover with an offset.

for me a 25 mile trip will usually start getting the long term to change. after about a week it stayed and bounced around depending on driving habits and other variables. weather and fuel quality will also change it. and at least here we have a winter blend of fuel that will alter it some.
 
Thanks for the help guys.

The LTFT is down to 111 and the STFT is going back and forth past 128 as it should.

You boys are spot on once again about it taking a few days to right itself.

So when the LTFT was staying at 128, the Stft had to be way down there to maintain stoic a/f ratio I guess

We'll I hope the LTFT doesn't drop too much more or I'll be back where I started
 
LTFT at 111 would concern me a bit if it stays there. I would like to a know lot more about the blow by blow way they change with driving and at idle and at various ambient temps and engine hardware conditions. The more I learn on these the more I feel like I barely know anything about the fuel trims as far as process control goes. I know the basics, but how is LTFT calculated exactly?

Most folks claim that Renix does not store any data. If ture then LTFT starts at 128 every time the engine is fired up, which I seriously doubt!!!! I have seen imperical evidence that Renix must be storing some long term sensor data, but I can not yet prove it.
 
it keeps the ltft saved and some tps data. it does seem to store KAM faults but im not sure of a method for reading them.

I have been convinced for years it stores some TPS range limit data. So we agree on that.

KAM???? faults.
 
the manual shows it has provisions for KAM faults. aka out of range limits. so a shored or open temp sensor would fault. and injector connections. weather or not you have to send data to the ecu to get it to respond or if its inside of one of the mystery bits in the output stream of the ecu i haven't found yet.
 
the manual shows it has provisions for KAM faults. aka out of range limits. so a shored or open temp sensor would fault. and injector connections. weather or not you have to send data to the ecu to get it to respond or if its inside of one of the mystery bits in the output stream of the ecu i haven't found yet.

Based on my experience, I doubt it stores them when the engine is turned off.

Is KAM Keep Alive Memory? This is what I was asking.
 
Another poster-thread today a guy reported that he spent over $1000 on parts and inspections in California trying to his NOx smog down from huge numbers. He was about to give up. Then replacing the new NTK O2 sensor with a new Bosch O2 sensor dropped his NOx 98%

That reminded me that years ago I read about how to test (at least in part) an O2 sensor on the bench with a torch to drop the O2 level and raise it exposing the sensor to the flame. And using a volt meter to read it. I think the HO sensors produce their own voltage, and the Renix sensors have a changing resistance. They guy on the how too was using it to test multiple junk yard sensors and in a shop environment for servicing vehicles....

The NOx problem story is one where the sensor was not throwing an OBD-I code, but had been biased (something no ECU/PCM can test for with just one O2 sensor), by biased (signal bias error I think is the proper phrase?) I mean it was switching, making the ECU think the ECU was operating at Stoich, but was in fact making the engine run way too lean, and telling the engine everything was OK.

Imagine the sensor things it as at stoich, but is faulty, and is reading a lean condition, but reports the condition as normal, running at stoich, and the sensor detects and reports changes in the O2, but reads say 100PPM of O2 as 200 PPM of O2, that is a 100 PPM bias error.

Short of having a highly calibrated test stand, or a sniffer smog rig, I know of no way to test for that by testing just the sensor.
 
Dang, my new NTK O2 sensor does have a metal insulator instead of ceramic.

Now my LTFT is down to 100 after a week of commuting.

The oil in the air filter has been mitigated by cutting rubes in VC, sealing VC properly, and sealing grommets.

Kinda concerned about not passing smog with a 100 LTFT but I think I'll seafoam it and change plugs after, not sure what to think about the O2 sensor
 
If one had the money and it would be interesting too see the smog numbers as it currently is, then again after disconnecting the battery to reset it all and running right in for the inspection before the LTFT drops.

Congrats on the VC-filter oil fixes. I'd try what I had, as for all you know it might improve the smog numbers?

I forget is LTFT at 100 lean or rich?

Dang, my new NTK O2 sensor does have a metal insulator instead of ceramic.

Now my LTFT is down to 100 after a week of commuting.

The oil in the air filter has been mitigated by cutting rubes in VC, sealing VC properly, and sealing grommets.

Kinda concerned about not passing smog with a 100 LTFT but I think I'll seafoam it and change plugs after, not sure what to think about the O2 sensor
 
Your gonna love this site:

http://www.underhoodservice.com/fuel-trim-diagnosis-and-o2-sensor-performance/

Awesome details, some I forgot, like propane enrichment tests...

Dang, my new NTK O2 sensor does have a metal insulator instead of ceramic.

Now my LTFT is down to 100 after a week of commuting.

The oil in the air filter has been mitigated by cutting rubes in VC, sealing VC properly, and sealing grommets.

Kinda concerned about not passing smog with a 100 LTFT but I think I'll seafoam it and change plugs after, not sure what to think about the O2 sensor
 
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