Once again, have you checked your spark plug wires? If they are sending the spark to ground, that would cause a rich condition to be read on the O2 sensor. It would also result in a sluggish acceleration. If the wires aren't getting the spark completely to your spark plugs every fire order, then you will be getting unburned fuel into the exhaust. Do the simple stuff first.
Tbi 350 has no power on the road
- Thread starter Mitchell93
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If the spark is shunted to ground, the cylinder misfires. Misfire results in false-LEAN signal from the O2 sensor.
The O2 sensor does not sense fuel in the exhaust, it senses the free oxygen that did not combine with the fuel when the cylinder misfired. With the false-lean signal to the computer, the computer goes into "rich-command" where more fuel is delivered to the engine.
i've said this before on other threads, but a good way to check your ignition is open the hood at night in a very dark place. excellent way to see if you have spark where you're not suppose to. i dont know if you installed the plugs or not but it is easy to crack them and will cause a miss.
Lots of good info. Looking at the last four pics I see 15 deg of spark advance st 44 mph? Am I reading this correctly? It’s difficult to sync the pids with separate pics. Are you able to export the scans to a delimited format and post (CSV,CDF etc). Not sure if you already looked at the EGR system as a whole. I see your idle is at 650 in Park. It’s within spec, but I usually see 725 to 850. Just want to be sure you don’t have any vacuum leaks that would impact vacuum-related sensors/components (MAP, EGR..). Many good suggestions already posted for ignition in general and you did pull the plugs. Did you pull all the plugs? If so, do they look any different between the two banks? Again it would be nice to see the scanned data stacked to scale to gather any general trends or outliers. Attached are a couple of examples of working the data outside the DAQ scanner. I’m confident you will figure this out.
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So don't check the spark plug wires. Got it.
Obviously not. You've completely misinterpreted what I was saying.
If the O2 sensor was reporting a rich condition, the computer would try to compensate by going into lean-command.
When the O2 sensor reports false-lean, the computer tries to compensate by going into rich-command.
Misfire results in rich-command, extra HC in the exhaust stream, overheated catalyst, poor power, terrible fuel economy, cylinder wear from washing the oil off the cylinder walls with raw gasoline, and oil contamination.
Mitchell93
Newbie
I will be checking my cams lift this weekend, I'm not a complete noob to this, I went to college for automotive technology, and worked at a dealership for 3 years, that was 9 years ago. now I'm a linemen working on the road, bought the modis is 2018 when I flagged down a random snapon dealer to warranty my ratchet. Honestly only used the scope, maybe one time for a wheel speed sensor, if I'm able to save and upload the graphs, I have no idea how that's done, will do some googling and maybe be able to get good data logs for you guys.
Btw I've ruled out misfire with my "cylinder deactivation load test"
I've sprayed carb cleaner all over to try and find a intake leak, found none
The data is shown 15 degrees advance at 44 mph yes
I've pulled plugs 3 weeks ago and they all looked the same, a bit black, they got cleaned and gapped b4 they went back in
I'd like to add, the more and more I think of this, I've feel like I've covered everything, except mechanical, the cam makes logical sense in my mind, and not a thing I've done or the previous owner has done has made a bit of difference. Maybe if I was older and had more experience with the sbc, diagnosing mechanical issues would be easier. I do appreciate everyone's input, and I thank you for the ideas, except the ls swop idea, that's not going to happen, lol
Btw I've ruled out misfire with my "cylinder deactivation load test"
I've sprayed carb cleaner all over to try and find a intake leak, found none
The data is shown 15 degrees advance at 44 mph yes
I've pulled plugs 3 weeks ago and they all looked the same, a bit black, they got cleaned and gapped b4 they went back in
I'd like to add, the more and more I think of this, I've feel like I've covered everything, except mechanical, the cam makes logical sense in my mind, and not a thing I've done or the previous owner has done has made a bit of difference. Maybe if I was older and had more experience with the sbc, diagnosing mechanical issues would be easier. I do appreciate everyone's input, and I thank you for the ideas, except the ls swop idea, that's not going to happen, lol
If you go back to the OP's original post, he has a 1991 with a TBI. There are no individual injectors at the cylinders. Additionally, I'm pretty sure he has only one O2 sensor in that exhaust system. In a TBI system, and I'm sure as you know, a misfired cylinder will still inject and then exhaust the very same fuel/air mixture into the cylinder as every other cylinder is receiving. A cylinder that does not fire will exhaust a rich fuel/air mixture.
The OP said in one of his posts that he was smelling what he thought was a gas smell from the exhaust. That was the point of checking the plug wires, which, if I remember correctly has yet to be done, although I have not gone back to every post to find that out for sure. My point was to simply check the simple stuff first, especially after having a very similar condition with my own 1994 TBI that was solved with new wires.
Lastly, I don't claim to know more about this than you do, and I am not the one trying to solve the problem for me. The comment was for the OP's benefit only. Until he absolutely rules out the plug wires as the culprit, we all know how these frustrations and waste of money on parts and test equipment can go.
Mitchell93
Newbie
The plug wires are no my issue, the previous owner put brad new ones on, and I threw a set on I yanked from a 95 I have in the weeds, no difference, I also power braked it, to make it run like ****, and did a cylinder deactivation test, to find out that I am not chasing a missfire, it's fireing on all 8 under load and at idleIf you go back to the OP's original post, he has a 1991 with a TBI. There are no individual injectors at the cylinders. Additionally, I'm pretty sure he has only one O2 sensor in that exhaust system. In a TBI system, and I'm sure as you know, a misfired cylinder will still inject and then exhaust the very same fuel/air mixture into the cylinder as every other cylinder is receiving. A cylinder that does not fire will exhaust a rich fuel/air mixture.
The OP said in one of his posts that he was smelling what he thought was a gas smell from the exhaust. That was the point of checking the plug wires, which, if I remember correctly has yet to be done, although I have not gone back to every post to find that out for sure. My point was to simply check the simple stuff first, especially after having a very similar condition with my own 1994 TBI that was solved with new wires.
Lastly, I don't claim to know more about this than you do, and I am not the one trying to solve the problem for me. The comment was for the OP's benefit only. Until he absolutely rules out the plug wires as the culprit, we all know how these frustrations and waste of money on parts and test equipment can go.
have you verified the injector plugs are on the correct sides? have you verified both injectors have 12Vdc all the time and that the other ecm side isn't grounded full time? i have an automotive meter that i can check this with. I would also put a stock distributor in. i have not had good luck with new or reman distributors since COVID. you said you had a '95 that you pulled wires off of.
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