OK thank you to all that's helping me with my project. So far I got good news that my truck might be a real ss. Now I have a TBI backfiring problemS with no check engine light. So when I start my truck she runs perfect no problems at all. Very responsive and sounds amazing. When she warms up to running temperature she feels sluggish when I accelerate and then when I let off the gas her RPM drops down then increases and stays. My rpm gauge don't work so what I'm trying to say is that when I rev her after warmup the RPM drops down to around 400 then inclines to a normal RMP maybe around 550. The part that's troubling me is that I replaced the thermostat, DISTRIBUTOR CAP MODULE, CAP AND ROTOR, SPARK PLUGS, WIRES, ENGINE COOLANT CONTROL SENSOR, ALL the vacuum lines and rebuilt the TBI the injectors look to be working ok. Egr valve works ok. No check engine light and I was thinking the IAC VALVE BUT any help would be very very helpful. I'm at a loss with this truck. This only happened when she warms up, she kinda hesitates when you rev then after that I get TBI backfiring. Thank you all for helping me.

 

If you could get a scanner that reads live data, you could check for O2 sensor voltage. That might give you some information. I don't know if yo have a mass air flow sensor, but maybe if you do, it needs to be cleaned.

 

Sorry I didn't mention it but it's a 1993 454 SS. Do a bad O2 sensor wouldn't throw a code on a OBD1 and I don't think there's a mass air flow sensor.

 

I didn't know it is OBD1. I don't think they show a check engine light. Maybe they do. You have to use a paper clip to retrieve the codes.

https://www.obd-codes.com/faq/read-g...codes-free.php

https://www.obd-codes.com/trouble_co...igit-codes.php

 

No my truck ifa OBD1 and I do have a scanner that reads OBD1 and no code. I was just wondering if a bad O2 sensor will cause it to run the way it does when it warms up without any coff.

 

You can take them out and test them. How many miles are on the sensor?

They do get sluggish and have a service life. Kind of like spark-plugs.

It looks like a code 61 might get thrown if it is bad. Since you aren't showing that, maybe it is fine.

Again, if your scanner reads live data, you can monitor the O2 sensor for voltage changes. The numbers should respond quickly to changing engine fuel use, like blipping the throttle.

If it is a heated-type O2 sensor, maybe the hearter part of the sensor isn't working, so the sensor is offline because of it.

 

If you think it's iac, try unplugging it after the engine is close to operating temperature.

 

There is an O2 code on a 93. You can check codes by jumping two of the pins in the OBD1 connector and counting flashes of check engine light. I don't remember what - but https://www.chevytalk.org/fusionbb/s...php?tid/273660 has info.

I have a 93 5.7L C1500 suburban and have had various drivability problems over the years - it's old, 200k+ miles. Spark retard is controlled by computer and a lot of things go into what the computer uses to set spark timing. There is a very good free/donate software for reading codes and monitoring data from sensors, etc. - TunerPro. You'll need a connector to USB - easiest/best is to get one from Moates. It's been helpful to me to find what's sensor or thing is causing the problems. TunerPro is used by people tuning their TBIs so it's much more than data monitoring and a big community of support.

I recently had a backfiring + poor idling + intermittent stalling/sluggish - basically crap running. In my case, replacing fuel filter and knock sensor did it. I don't know if both or one, I did both at same time. TunerPro showed I had had a knock sensor failure but when I cleared it - it never came back. I had read that low fuel pressure/clogged fuel filter could cause drivability problems as you have throttle had more open position than normal to get enough fuel and computer thinks you're trying to accel hard when you really aren't - or something like that. Regardless, one or both fixed my problems.

 

Thank you all I am going to try the fuel filter and give you all a update thank you so much for your help.