Read this if you have engine missing problems, IMPORTANT!!!

Sneakysportsman · 08-13-2007, 05:43 PM

Ladies and gentleman this is important, VERY,

I have made a thread about engine missing problems, I haven't had a good response, is not important. But thanks to all who have looked and let this problem cross their mind.

I have a 1995 Chevy 4X4, it has a custom built small block that I myself did and all the research on to be able to use all the factory wiring and emissions on to possibly be fuel efficient. Fuel efficient? THATS ****!!!
The motor put out an impressive amount of HP on the Dyno, 406 to be exact and 412 ft. lbs of tourque. But with all do respect that was with a Holley 750 Carb. Nevertheless the motor is still impressive with the 750cfm TBI unit.
Instantly the motor starting missing, in the cruising speed, it ran perfect at idle and with wide open throttle. It was hideous and very embarrasing with 4 clys missing at different times. I changed every odvious things that would cause this miss. Basically I wasted a lot of money. You name it I changed it. I read the AC Delco book and did everything it said. It didn't solve the problem.
I know, I know, What was the problem? you ask.
The very last thing that any one might think, but with 196,600 mile on the original body it should have one of the first.
The O2 sensor is fouled giving the ECM a false reading. I found it when my air/fuel meter showed that the engine was running rich and the spark plugs were showing Very lean. I have unplugged the sensor and it runs as smooth as a babies @$$. You get it.
At the end of this thread have your O2 sensor checked if you are having missing and performance Problems.

72'CaminoKid · 08-13-2007, 06:01 PM

is it running right now even with the o2 sensors unplugged? my dads 96 has a similar problem with bad o2's. and we cant figure out why they keep goin bad.

Sneakysportsman · 08-13-2007, 08:24 PM

I have to be careful on this and not misslead,
My engine is custom built with a custom ECM program. It has custom set parameters that it runs by, depending on actual numbers when it turns cooler I may have to adjust them, this is where the O2 kicks in the most. Cooler air is more dense so the O2 reads lean and adds fuel same for warmer temps. Yes it runs perfect, with the service light on of course, I will have to get that circuit by-passed or replace the sensor. The function of the O2 is fuel economy and fuel mixture. In 96 Gm had 3 phases of O2 sensors, 305's had 2 or 3 sensors, always had a sensor behind the catalytic conterter, some 350 had upwards of 4 sensors depending on model. Some Z71 were a basic half ton truck, some were considered a HD or 5/8 ton model that produced more hp and torque, that utilized 4 sensors.
Low compression will foul out a sensor just like a spark plug. Oil consumption, poor grade of fuel, clogged air filter. things that will "trick" a sensor, Manifold or header gasket leaks, AIR injection systems that leak. Possibilities are endless. They could be shorting or grounding out. You could be getting an over-voltage to the sensor that will burn them out.

72'CaminoKid · 08-13-2007, 08:38 PM

got ya. thanks

crabtruck · 08-13-2007, 08:39 PM

I agree on the kinds of things that could make them not work, or not send a signal that the compter likes.
IMO I doubt they could be harmed by over voltage because the computer shouldn't be able to source enough
to harm the sensor without cooking itself - have you seen an actual case of this? Honest question.
Curious when folks change out a bad sensor and blame something else, if they ever miss defective sensors.
Just my personal thing, I'm not satisfied when I find what's wrong. I want to know why so I don't have to fix it again.

Sneakysportsman · 08-13-2007, 08:44 PM

Over voltage is not impossible, If like me, an air fuel meter can rerout voltage. The ECM can do it, or an overlying wire that gets to hot from a shorting can do it. It is possible, but I can't imagine the odds. Some sensors use a wire type heating element to read the gasses. Over voltage will burn this wire like a overvoltage light bulb.

crabtruck · 08-13-2007, 08:55 PM

Agreed the crazy stuff can (and probably will) get you. Just thought it would be tough for the ECM to pull off without also dying.

Sneakysportsman · 08-13-2007, 09:22 PM

The most obvious chance of an overvoltage is when jumping a computer controlled vehile off. Your not supposed to jump a computer controlled vehicle off, If you have to you supposed to:
1. Have ignition completely off.
2. Crank Vehicle, DO NOT DISCONNECT JUMPERCABLES.
3. Run vehicle for a few minutes, letting it charge the battery. Shut it off completely and disconnect Cables.
4. Try and recrank vehicle, if it cranks drive to parts house and get a new battery. If it doesnt crank rejump it and as a last resort disconnect the cable.

All of this keeps sudden voltage surges from damaging the circuits in the computer. The computer will tell you if it has been jumped off with a code of An injector with a direct ground, or something of the sort. Or the MIL not coming on when the ignition is turned on.
These are the direct steps from Bosch OBD-1 ECM. I have replaced these ECM's from "jumpings"

crabtruck · 08-13-2007, 09:55 PM

LOL not fair bringing in a friend's truck to get over voltage

08-13-2007, 05:43 PM	#1
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 296	Read this if you have engine missing problems, IMPORTANT!!! Ladies and gentleman this is important, VERY, I have made a thread about engine missing problems, I haven't had a good response, is not important. But thanks to all who have looked and let this problem cross their mind. I have a 1995 Chevy 4X4, it has a custom built small block that I myself did and all the research on to be able to use all the factory wiring and emissions on to possibly be fuel efficient. Fuel efficient? THATS ****!!! The motor put out an impressive amount of HP on the Dyno, 406 to be exact and 412 ft. lbs of tourque. But with all do respect that was with a Holley 750 Carb. Nevertheless the motor is still impressive with the 750cfm TBI unit. Instantly the motor starting missing, in the cruising speed, it ran perfect at idle and with wide open throttle. It was hideous and very embarrasing with 4 clys missing at different times. I changed every odvious things that would cause this miss. Basically I wasted a lot of money. You name it I changed it. I read the AC Delco book and did everything it said. It didn't solve the problem. I know, I know, What was the problem? you ask. The very last thing that any one might think, but with 196,600 mile on the original body it should have one of the first. The O2 sensor is fouled giving the ECM a false reading. I found it when my air/fuel meter showed that the engine was running rich and the spark plugs were showing Very lean. I have unplugged the sensor and it runs as smooth as a babies @$$. You get it. At the end of this thread have your O2 sensor checked if you are having missing and performance Problems.

08-13-2007, 06:01 PM	#2
72'CaminoKid Senior Member Join Date: Jun 2005 Posts: 2,756	is it running right now even with the o2 sensors unplugged? my dads 96 has a similar problem with bad o2's. and we cant figure out why they keep goin bad. __________________ 99 suburban xlt 96 silverado 91 wrangler (my baby ) 08 Honday shadow 750 (my mistress)

08-13-2007, 08:38 PM	#4
72'CaminoKid Senior Member Join Date: Jun 2005 Posts: 2,756	got ya. thanks __________________ 99 suburban xlt 96 silverado 91 wrangler (my baby ) 08 Honday shadow 750 (my mistress)

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08-13-2007, 08:24 PM	#3
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 296	I have to be careful on this and not misslead, My engine is custom built with a custom ECM program. It has custom set parameters that it runs by, depending on actual numbers when it turns cooler I may have to adjust them, this is where the O2 kicks in the most. Cooler air is more dense so the O2 reads lean and adds fuel same for warmer temps. Yes it runs perfect, with the service light on of course, I will have to get that circuit by-passed or replace the sensor. The function of the O2 is fuel economy and fuel mixture. In 96 Gm had 3 phases of O2 sensors, 305's had 2 or 3 sensors, always had a sensor behind the catalytic conterter, some 350 had upwards of 4 sensors depending on model. Some Z71 were a basic half ton truck, some were considered a HD or 5/8 ton model that produced more hp and torque, that utilized 4 sensors. Low compression will foul out a sensor just like a spark plug. Oil consumption, poor grade of fuel, clogged air filter. things that will "trick" a sensor, Manifold or header gasket leaks, AIR injection systems that leak. Possibilities are endless. They could be shorting or grounding out. You could be getting an over-voltage to the sensor that will burn them out.

08-13-2007, 08:39 PM	#5
crabtruck Senior Member Join Date: Jul 2007 Location: on your 9 Posts: 3,364	I agree on the kinds of things that could make them not work, or not send a signal that the compter likes. IMO I doubt they could be harmed by over voltage because the computer shouldn't be able to source enough to harm the sensor without cooking itself - have you seen an actual case of this? Honest question. Curious when folks change out a bad sensor and blame something else, if they ever miss defective sensors. Just my personal thing, I'm not satisfied when I find what's wrong. I want to know why so I don't have to fix it again.

08-13-2007, 08:44 PM	#6
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 296	Over voltage is not impossible, If like me, an air fuel meter can rerout voltage. The ECM can do it, or an overlying wire that gets to hot from a shorting can do it. It is possible, but I can't imagine the odds. Some sensors use a wire type heating element to read the gasses. Over voltage will burn this wire like a overvoltage light bulb.

08-13-2007, 08:55 PM	#7
crabtruck Senior Member Join Date: Jul 2007 Location: on your 9 Posts: 3,364	Agreed the crazy stuff can (and probably will) get you. Just thought it would be tough for the ECM to pull off without also dying.

08-13-2007, 09:22 PM	#8
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 296	The most obvious chance of an overvoltage is when jumping a computer controlled vehile off. Your not supposed to jump a computer controlled vehicle off, If you have to you supposed to: 1. Have ignition completely off. 2. Crank Vehicle, DO NOT DISCONNECT JUMPERCABLES. 3. Run vehicle for a few minutes, letting it charge the battery. Shut it off completely and disconnect Cables. 4. Try and recrank vehicle, if it cranks drive to parts house and get a new battery. If it doesnt crank rejump it and as a last resort disconnect the cable. All of this keeps sudden voltage surges from damaging the circuits in the computer. The computer will tell you if it has been jumped off with a code of An injector with a direct ground, or something of the sort. Or the MIL not coming on when the ignition is turned on. These are the direct steps from Bosch OBD-1 ECM. I have replaced these ECM's from "jumpings"

08-13-2007, 09:55 PM	#9
crabtruck Senior Member Join Date: Jul 2007 Location: on your 9 Posts: 3,364	LOL not fair bringing in a friend's truck to get over voltage