patrowan

I posted info tbi 86-89 AFM mods so I'll post something regarding the Titania O2 sensor used in those cars. In all my searches everything says the Titania O2 is a resistance device, which i'm sure to most ECM's it is. The O2 sensors 86-89 tbi nissans differ from the normal titania O2 in that it has 2 plugs one plug has 3 conductors (basically for the heater) 12V,gnd,gnd, the other plug is one conductor, signal. This signal is 1V when rich and close to 0V when lean. I had made up a little circuit to convert the aux output from the Innovate WBO2 to resistance so I could change the closed loop mixture from the default 14.7 to something leaner. When I tried to hook it up I learned this so I just hooked the aux2 to the ECM and reset the voltage to 1V when rich and 0V when lean. I had a scrap plug from an old harness so I unpluged the signal plug and pluged in the aux2, and everything worked as if it was stock. I then moved the switch point from 14.7 to 16.0 and now when in closed loop (which is just about all the time) I run between 15.4 and 16.2. I haven't tried leaner yet. I think i'll drive awhile this way and see if I notice any mpg difference. I have not notice any difference in driveablity. If i see a difference I'll try going leaner. I haven't tried it (I don't have a resistance O2) but I belief you can take a 20K ohm resistor from the signal wire to gnd (rich condition) and then switch in a 1K ohm resistor across the 20K (2 in parallel) for the lean condition. Using the aux output of the WBO2. To do the switching you can use reed switch relay with 5V input. This isn't perfect, but the reed switch are rated at a billion cycles under no load and 5-6 million under rated load (350ma). The load across the contacts is only a couple milliamps, so life should be in the range of a couple 100 million cycles.

First Post, so a little history I don't own a PF, I have a 68 521 PU that I put a vg30 and AT from a 88 PU in. That was in 1988 about 450,000 ago. I came to this forum because there was more info on the tbi then anywhere else. There really isn't much anywhere which is why I posting. I've been thru 2 import engines and a couple trans rebuilds. The last time I rebuilt the engine because I couldn't find any short snout imports. That brings me to the first reason I started messing with tbi which has never given me any problems. When I rebuilt the engine it seems that the little bit of increase in displacement caused a problem with the AFM (This is what Nissan calls it, and I think in the case of the tbi it's more accurate than MAF. Since it really doesn't measure all the air going the engine.). The signal from the AFM would peak at 4.5V at about 4000 rpm and the engine would just stop reving any higher. By playing with the throttle I could work it up to 4500 and then it would take off to above 5500 were I stopped. I lived with this for quite some time since it didn't really affect my daily driving, but I finally decided to do something about it. I bought a Innovate WBO2 (I picked that brand because of the programable outputs although I didn't have any plans to use them) so I could get some idea what was happening when I started modifing. The first thing I did was try closing off the slots where air enters the AFM, this had the effect of leaning out the idler mixture and full throttle mixture (anywhere it wasn't in closed loop). I could readjust idler mixture with the pot that's on the ECM on 86-89 tbis. The full throttle was at 10.9 afm before, and went to 11.3 after (still more than rich enough). Now the 4.5V peak happened at 4500 and the engine rev smoothly up to 5500. That was with about 3/4 of each slot closed off (I just used silicone rubber to close the slots). That really wasn't very accurate, it worked and it was easy any quick to do. I decided to be more accurate, so I cut the signal wire going going to the ECM a put pot series and a resistor to ground. This forms a voltage divider and lets you lower the voltage signal. By lowering the voltage you lean the engine, just like closing the slots. I set the pot to 0 ohms ( divider circuit has no effect on signal) and measured the at idle. I removed the silcone and the voltage went up about .3V, then I adjusted the pot till I got same voltage as when the silicone was in. I played with going even lower in voltage, but you can't go to much lower before you run out idle mixture adj. and full throttle mixture gets into the 13's. I hope this helps anybody messing with tbi, doing what I did will not get much if any increase in mpg because the engines spends most of the time in closed loop where the O2 controls mixture. I was going to address the O2 mod., but i'll do another post (this is more than long enough)