TBI sensors and running condition issues
#1
12-29-2018, 08:38 PM
TBI sensors and running condition issues
All right fellow members. I am new to blazer forums. Honestly I just registered as a last resort to see if you guys can throw some helpful information my way.
This is a long post but I don’t want to be vague so stick with me if you can..
I have spent the last 2 months spending countless hours of research and google searches to find a solution to my problem. I’m hoping that some of you tech guys will be able to help. Now admins I wasn’t sure where to post so if you must move this feel free.
Now I can find similar issues on other posts but there are some specific symptoms that I feel I need to clarify. Let me just start by giving a run down of what I own. My issues, and what I have done so far.
My vehicle is a 1993 Chevy K1500 Blazer. It has a 5.7L TBI with a 4L60E. Completely stock other than shorty headers, and true duals. Ever since I got the blazer it has run poorly. Idles, but has random misfire, sputters, surges, popping through exhaust, consuming a lot of fuel.
Now before starting anything I checked all vacuum lines and sprayed carb cleaner on the intake and TBI but found nothing..
So I moved to the ignition system thinking that it was related to spark. New acdelco plugs and wires. Completely new distributor. New ignition coil. Set base timing at 0* with spark control unplugged. Problem persists.
After that I looked into possibly a fuel related problem. New sending unit and pump, fuel filter, new lines after the old ones fell apart, even broke down and bought a TBI rebuild kit. TB is clean and fresh. Same issue.
Attempt number three. Sensors... okay so maybe I’m dealing with a bad sensor somewhere.. right? I wasn’t getting any codes from the ecm. But I know my trusty old OBD 1 systems can be misleading. So I bought a new coolant temp sensor, 02, tested the egr. Replaced the map sensor and egr solenoid with known good ones. Swapped out the IAC and TPS. Got another ECM from a running truck of the same year and drivetrain.. No change.
now I feel like I should mention that when I got the truck it didn’t have an 02 sensor at all. Previous owner put the headers on and left out the sensor. So I put one in. Didn’t change anything. What is also odd is that when the 02 is unplugged there’s no service engine light. But if I disconnect any other sensor it turns on.
After everything I did. I tried a compression test. All cylinders average about 150psi. So nothing mechanical wrong with the engine.
so any advice? Something I missed?? The truck only acts up after it runs for a few and enters closed loop mode. So I’m stumped. Money isn’t an issue per say. Just sick of chasing this elusive problem. Any help would be great thanks for reading through my sob story. haha
This is a long post but I don’t want to be vague so stick with me if you can..
I have spent the last 2 months spending countless hours of research and google searches to find a solution to my problem. I’m hoping that some of you tech guys will be able to help. Now admins I wasn’t sure where to post so if you must move this feel free.
Now I can find similar issues on other posts but there are some specific symptoms that I feel I need to clarify. Let me just start by giving a run down of what I own. My issues, and what I have done so far.
My vehicle is a 1993 Chevy K1500 Blazer. It has a 5.7L TBI with a 4L60E. Completely stock other than shorty headers, and true duals. Ever since I got the blazer it has run poorly. Idles, but has random misfire, sputters, surges, popping through exhaust, consuming a lot of fuel.
Now before starting anything I checked all vacuum lines and sprayed carb cleaner on the intake and TBI but found nothing..
So I moved to the ignition system thinking that it was related to spark. New acdelco plugs and wires. Completely new distributor. New ignition coil. Set base timing at 0* with spark control unplugged. Problem persists.
After that I looked into possibly a fuel related problem. New sending unit and pump, fuel filter, new lines after the old ones fell apart, even broke down and bought a TBI rebuild kit. TB is clean and fresh. Same issue.
Attempt number three. Sensors... okay so maybe I’m dealing with a bad sensor somewhere.. right? I wasn’t getting any codes from the ecm. But I know my trusty old OBD 1 systems can be misleading. So I bought a new coolant temp sensor, 02, tested the egr. Replaced the map sensor and egr solenoid with known good ones. Swapped out the IAC and TPS. Got another ECM from a running truck of the same year and drivetrain.. No change.
now I feel like I should mention that when I got the truck it didn’t have an 02 sensor at all. Previous owner put the headers on and left out the sensor. So I put one in. Didn’t change anything. What is also odd is that when the 02 is unplugged there’s no service engine light. But if I disconnect any other sensor it turns on.
After everything I did. I tried a compression test. All cylinders average about 150psi. So nothing mechanical wrong with the engine.
so any advice? Something I missed?? The truck only acts up after it runs for a few and enters closed loop mode. So I’m stumped. Money isn’t an issue per say. Just sick of chasing this elusive problem. Any help would be great thanks for reading through my sob story. haha
#2
12-30-2018, 04:34 AM
Hmm first 5 cents of thoughts:
When reading through your post the very first thing that came to my mind was - Full dual pipes = no cat = most probably no O2 sensor.
This could create the symptoms or part of the symptoms. From your write up - a nice one BTW - I would start by:
Check why the SES light does "not come on" despite the truck running without an O2 sensor. Do you have to pass emissions or would that SES light cause you trouble? I would start looking into the signal path of the O2 sensor to see if the previous owner has been tinkering with that input. I'd see if the lines (wires) running to the ECU are continuous and the signal is not altered somewhere in between. Putting a resistor into the line comes to my mind to cheat the ECU.
If a correct O2 signal is not received it could explain a lot of the symptoms.
When doing all the sensors have you also checked and made sure all the vacuum lines are tight and the system does not loose vacuum too quickly? The joints and the grommets on the TBI are a known issue to rot and brake. Sometimes the grommets develop invisible cracks which still pull air and upset the vacuum signal.
When reading through your post the very first thing that came to my mind was - Full dual pipes = no cat = most probably no O2 sensor.
This could create the symptoms or part of the symptoms. From your write up - a nice one BTW - I would start by:
Check why the SES light does "not come on" despite the truck running without an O2 sensor. Do you have to pass emissions or would that SES light cause you trouble? I would start looking into the signal path of the O2 sensor to see if the previous owner has been tinkering with that input. I'd see if the lines (wires) running to the ECU are continuous and the signal is not altered somewhere in between. Putting a resistor into the line comes to my mind to cheat the ECU.
If a correct O2 signal is not received it could explain a lot of the symptoms.
When doing all the sensors have you also checked and made sure all the vacuum lines are tight and the system does not loose vacuum too quickly? The joints and the grommets on the TBI are a known issue to rot and brake. Sometimes the grommets develop invisible cracks which still pull air and upset the vacuum signal.
#3
12-30-2018, 04:45 AM
This may help. IMHO the 1995 has a similar setup to the 1993. What changes is the ECU which is OBDII after 1995. Still it may be used as a guideline on where to look and what to look for.
https://workshop-manuals.com/chevrol...ion/page_3043/
Try looking for a copy of the Driveability & Symptoms, Electrical Wiring Manuals in these years the complete set of manuals for our Blazers is normally three (3).
The Service and Repair manual
The Electrical and diagnostic manual
The components service manual
Such as this:
https://www.faxonautoliterature.com/...al-P14186.aspx
They can be found on e-bay or other platforms. Sometimes rockauto features them as reprints. It may be necessary to figure out which other vehicle of the same year has the same engine setup and look if a manual is available.
The Chilton or Haines are not suitable for this kind of troubleshooting, while the factory manuals have all the data and ranges, plus the diagrams and wiring diagrams in them.
https://workshop-manuals.com/chevrol...ion/page_3043/
Try looking for a copy of the Driveability & Symptoms, Electrical Wiring Manuals in these years the complete set of manuals for our Blazers is normally three (3).
The Service and Repair manual
The Electrical and diagnostic manual
The components service manual
Such as this:
https://www.faxonautoliterature.com/...al-P14186.aspx
They can be found on e-bay or other platforms. Sometimes rockauto features them as reprints. It may be necessary to figure out which other vehicle of the same year has the same engine setup and look if a manual is available.
The Chilton or Haines are not suitable for this kind of troubleshooting, while the factory manuals have all the data and ranges, plus the diagrams and wiring diagrams in them.
Last edited by error_401; 12-30-2018 at 04:48 AM.
#4
12-30-2018, 12:35 PM
I agree about the O2 sensor. It's only used in closed loop, so that would explain why it runs ok in open loop. If the ECM gets incorrect information from the O2 sensor, it can command the mixture to be too rich, causing the symptoms you describe. If you have a scanner, you can check the O2 sensor activity and fuel trim (called block learn and integrator back then, for long term and short term). The lack of catalytic converters (assuming you don't have them) won't make any difference because OBD1 doesn't use a downstream O2 sensor.
#5
12-31-2018, 02:56 PM
Very nice. That sort of confirms what I was thinking. Where I live my Blazer is not required to have emissions or an inspection. The exhaust setup I have is just shorty headers, downpipe. Then glasspacks. No cats. Honestly I hate the setup and I am going to switch to chambered mufflers. That is assuming I can get it to run correctly. I believe you guys are onto something with the o2 sensor circuit. As far as I can find out the o2 signal comes from the ECU as a single wire coming from D7 on the ecm connector. So how could I tell what’s happening between the ecu and sensor. Resistance check at the ecu side? If so what should I be looking for for ohms? Sorry for so many questions. I’m lost when it come to electrical. Turning wrenches is one thing. But electricity is my bane.
#6
12-31-2018, 02:59 PM
This may help. IMHO the 1995 has a similar setup to the 1993. What changes is the ECU which is OBDII after 1995. Still it may be used as a guideline on where to look and what to look for.
https://workshop-manuals.com/chevrol...ion/page_3043/
Try looking for a copy of the Driveability & Symptoms, Electrical Wiring Manuals in these years the complete set of manuals for our Blazers is normally three (3).
The Service and Repair manual
The Electrical and diagnostic manual
The components service manual
Such as this:
https://www.faxonautoliterature.com/...al-P14186.aspx
They can be found on e-bay or other platforms. Sometimes rockauto features them as reprints. It may be necessary to figure out which other vehicle of the same year has the same engine setup and look if a manual is available.
The Chilton or Haines are not suitable for this kind of troubleshooting, while the factory manuals have all the data and ranges, plus the diagrams and wiring diagrams in them.
https://workshop-manuals.com/chevrol...ion/page_3043/
Try looking for a copy of the Driveability & Symptoms, Electrical Wiring Manuals in these years the complete set of manuals for our Blazers is normally three (3).
The Service and Repair manual
The Electrical and diagnostic manual
The components service manual
Such as this:
https://www.faxonautoliterature.com/...al-P14186.aspx
They can be found on e-bay or other platforms. Sometimes rockauto features them as reprints. It may be necessary to figure out which other vehicle of the same year has the same engine setup and look if a manual is available.
The Chilton or Haines are not suitable for this kind of troubleshooting, while the factory manuals have all the data and ranges, plus the diagrams and wiring diagrams in them.
#7
12-31-2018, 03:07 PM
You want to check the sensor circuit for voltage while it's operating, not resistance. The voltage should range from zero to one volt, and switch fairly frequently from high to low (<.5v to >.5v)
The easiest way to check it is with a scanner if you have one.
The easiest way to check it is with a scanner if you have one.
#8
12-31-2018, 03:40 PM
Alright. I don’t have a scanner. But with the engine cold and off. Ignition on it’s reading 0.2v at the o2.
#9
12-31-2018, 03:45 PM
I’ll check tomorrow while it’s running and let you know what it says. Too dark to mess with it right now. But I’m hoping this is it. For now. What effects the voltage the ecu sends to the o2?
#10
12-31-2018, 03:53 PM
The sensor is like a battery that sends a voltage to the ECU, based on how much oxygen is in the exhaust. Lots of O2 means lean mixture, no O2 means rich mixture. The ECU continually leans or richens the mixture based in feedback from the sensor. It should go back and forth between rich and lean, but stay pretty close to stoichiometric.