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Old 12-30-2006, 11:01 PM   #1
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Default A/F Ratiometer stuck...

I did a bit of searching, but couldn't find anything relative to this problem - My sig line shows my setup (1990 - TD04, 16 lbs peak, stock FP, stock ECU, RX7 AFM, 440cc injectors, Vishnu fuel rail).

Before I start tearing everything apart and replacing things, I thought I'd seek some opinions. The car ran like a scalded dog until recently, when my A/F ratiometer, which used to sweep at a regular interval, started staying stuck in dead stoich. The car then started to run richer than usual and my fuel mileage took a dump to 16 MPG and worse (from 20 MPG). The really bad problem was a terrible bogging from 4200 - 5500, where the car ran super rich, but the A/F ratiometer just stayed stuck in stoich. I assumed that my single-wire O2 sensor went bad, so I bought a Bosch unit. I couldn't fit the damn thing into the O2 sensor bung on the RM DP, because the GReddy manifold is in the way. I pulled the O2 sensor from my 1993 and swapped it in and I got some minor response from the guage, but it still stays stuck in stoich as soon as I accelerate.

I plan to pull the RM DP, so I can install the new O2 sensor. I also plan to install my new Walbro 255lph/HP pump and a fuel pressure gauge. My plugs are a few months old (NGK BKR7E-11) and I have the thick Magnecore wires.

I guess the $64-question is what could be causing the A/F ratiometer to read flat, or dead stoich? It only moves if I am at idle and blip the throttle. Is it still a bad O2 sensor? Can I expect normal behaviour when I replace the O2 sensor with the new one?
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Old 12-31-2006, 12:00 AM   #2
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The only thing stoich on your gauge is telling you is your AFR is somwhere below 11:1 or above 17:1. Tuning with a NBo2 is nearly impossible...it's going to be hard to pinpoint the problem. Your NBo2 voltage outputs have no linear relationship between the AFR and the sensor's volt output.



this is why people spend the money on WBo2s...you can see exactly what's going on.
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Old 12-31-2006, 12:46 AM   #3
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Your relationship between nb and wb is very wrong. A typical nb will output 14.0:1 (1.0v) and 15.4:1(.1v). Your own graph contradicts you.

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Old 12-31-2006, 01:13 AM   #4
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Hammerhead,

I am going to work under the assumption that the nb sensor you swapped into the turbo car (if I interpreted your post correctly, you put a known good used sensor in the turbo car) is a good sensor. I'm wondering if your ecu didn't go into no o2 limp home. Before proceeding, I'd remove power from the battery, cycle the headlight switch on and off, then reconnect the battery. See if that doesn't clear your codes and get you going again.

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Old 12-31-2006, 01:18 AM   #5
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Great idea, Ben! I forgot about limp home mode, the same thing occurs in the Rovers under certain conditions. I'll give it a try tomorrow morning!
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Old 12-31-2006, 03:06 PM   #6
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I took the NB graph straight from an Autometer .pdf

http://www.autometer.com/hp/instruct...tions/837j.pdf
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Old 12-31-2006, 03:14 PM   #7
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The graph is correct. Your conclusions are not. Look at the green lines I added in. At 11:1 the nb is producing ~1V and at 17:1 is producing ~.1V.

If your conclusions were correct, the ecu wouldn't be able to control mix inbetween 11:1 & 17:1. We all know the ecu switches around 14.5:1 and 15.5:1 (or thereabout). The whole purpose of the nb is to allow precision around stoich.


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Old 12-31-2006, 03:36 PM   #8
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Regardless of whatever voltages I messed up on, a stock narrowband O2 sensor can't tell the difference between a little lean versus VERY lean; The voltage difference between 15.5:1 and 13.8:1.
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Old 12-31-2006, 04:19 PM   #9
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Quote:
Originally Posted by braineack View Post
Regardless of whatever voltages I messed up on, a stock narrowband O2 sensor can't tell the difference between a little lean versus VERY lean
OK, I'll go with that. But the earlier statement that the NB will show stoich from 11:1 to 17:1 was what I had issues with.

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Old 12-31-2006, 04:54 PM   #10
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yeah i screwed that one up.
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Old 01-02-2007, 12:53 PM   #11
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This is probably covered in another post somewhere, but can I go to a wideband O2 sensor easily?
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Old 01-02-2007, 02:01 PM   #12
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Yeah, and get a megasquirt to go with it. I'm sure it's running ridiculously rich all over, except at high boost.
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Old 01-02-2007, 02:22 PM   #13
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I'm trying to keep it as near stock as possible without adding piggybacks, etc. It's a fun project (for me) to see how far I can tune (and how much power I can generate with) this car without additional engine management.
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Old 01-02-2007, 02:32 PM   #14
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Yeah, that's what andyfloyd did on here. He used AFPR though. how much power does it make?
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Old 01-02-2007, 02:38 PM   #15
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that's what I was doing....and now im giving up and going MS.
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Old 01-02-2007, 03:48 PM   #16
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At one point, this exact kit it made 238 hp - 255 lb/ft with 560cc injectors. I dyno'd @ about 190 HP @ 16 lbs (DynoDynamics), but as soon as I hit peak boost, it dropped dramatically (my dyno sheets are in the dyno thread). If I could maintain boost, I would be well into the 200s.

I have since added a helper spring to keep the wastgate from dumping boost and it definitely retains it longer. I have to replace my crappy 2.5" RM DP, put in the brand new O2 sensor and swap the tranny before I can truly tune and dyno again.
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Old 01-02-2007, 04:49 PM   #17
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Ah, yeah, it seems a lot of people like doing that. I don't really see the attraction, but it's cool I guess. I like my power with good mileage on the side.
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