Tricking The Ecm

[12gauge]

I have little to no backpressure so my o2 sensor gives to lean a reading and kicks the ecm(1993 CHEV - OBD1) into limp mode. My 5.7L is getting about 7 mpg. I want to trick the ECM by sending the correct voltage from the o2 sensor (make my own O2 simulator) to fix my problem rather than having to add backpressure. I know there are simulators for sale but nothing for my model year. If you have any ideas on how to do this, I would certainly like to hear them.

My truck originally had only one O2 sensor, it was just below the drivers side manifold(1 wire). The drivers side header now has it in the collector.

[SloNlo_350]

Hmm that would explain why my headers have an O2 bung in them. My O2 is originally behind the cat (95 350). I thought i saw sims before, but then mine has the 3 wire so it may be different. I have very little backpressure as well, but my O2 still sends the correct signal. Have you hooked up a scanner to it (or volt meter) and gotten the exact mV being sent by the O2. Maybe that isnt your problem.

[quaddriver]

Originally Posted by 12gauge

I have little to no backpressure so my o2 sensor gives to lean a reading and kicks the ecm(1993 CHEV - OBD1) into limp mode. My 5.7L is getting about 7 mpg. I want to trick the ECM by sending the correct voltage from the o2 sensor (make my own O2 simulator) to fix my problem rather than having to add backpressure. I know there are simulators for sale but nothing for my model year. If you have any ideas on how to do this, I would certainly like to hear them.

My truck originally had only one O2 sensor, it was just below the drivers side manifold(1 wire). The drivers side header now has it in the collector.

back pressure schmack pressure. the ECM tries to alternate rich/lean/rich/ealn over and over to get the cat to 'switch over' and alternately do HCremoval and NOx removal. hook back up to the scan tool and look for the O2S crosscounts, ifthey are 0 or very very low (they go up appx 1 per second to 256 (1 byte field) then wrap) then you will get the same result.

[JWhite8055]

1995 and earlier models had one o2 sensor in the exaust manifold, which set the ECM based on o2 levels at the manifold.

You will not get a correct o2 reading elsewhere, i.e. in the collector. (unless you have changed the ECM to 1996 or later)

The voltage (generated by chemical reaction in the o2 sensor itself) for this particular setup is either low or high, 0.1 v. to 0.9 v.

Low voltage, (0.1) such as when the engine is warming up sets the ECM to bypass mode.

You can move the o2 sensor to where it belongs, in the exaust manifold, (this simply involves drilling and tapping the manifold (or replacing it with an appropriate one)) that likely will resolve the problem OR if so inclined and adventurous...

You can use a single cell 9 volt battery and a series of resisters to reduce the voltage to 0.1 v output ( ECM engine-warm up-bypass mode) and should include a dual operational timer such as the venerable ic555 and add an onboard CPU to vary the voltage by run-time to simulate operational tempature increase(s) - or bettery yet include a thermistor in the design and vary output votage levels based on thermal resistance, (simulating o2 levels) to optimize fuel ecomomy and reduce pollution.

HTH

[cornfedmf]

you can buy o2 sensor dummies on the internet i did it on my 96 350 after cutting the cats off. no more check engine lights and better fuel economy