Hello, I have a 2004 Chevy Silverado 1500 v6 4.3. I was getting codes for vacuum leak and engine misfire, I installed a new evap purge canister and it solved the vacuum issue, I’ve replaced the fuel filter, the spider injection under the throttle body, it is running better but still misfires on occasion, has effected the gas mileage, and hesitates mostly switching from 1-2 gear or 15-25 mph. I was a hoping for any ideas what I should do next. I have considered changing the throttle position sensor and MAP sensor but I don’t want to keep throwing parts at it if anyone can give me any advice. Thank you for your time and I can answer any questions you might have. Hope to hear from someone soon.

 

post your miles please.
If you still have misfiring then use a diagnostic tool to get a cylinder misfire count, fuel trims and other live data.
Shift hesitation is the transmission wearing out.

 

Here is a recommendation for an inexpensive (under $25) OBD II code reader/live data scanner setup that will allow you to monitor multiple engine functions simultaneously and save the data to an Excel-like spreadsheet for offline analysis on a regular PC. This setup is for Android devices:

Veepeak OBDII Dongle for Android


For the app that many of us use on the android platform, it is Torque Pro, available from the Google Play store and it has a one time licensing fee of about $5.00. You definitely want to go with the Pro version of the app instead of the free version because it allows one to do infinitely more. This combination will allow you to simultaneously monitor several different engine systems - Short & Long Term Fuel Trims, MAP output, Throttle Position, cylinder misfires, engine coolant temp, etc. Plus, you can choose to store the data in an Excel type file for later data analysis. Oh yeah, and you can set it up for multiple vehicles, each with it's own profile (and things to monitor).

The above was written for use on another automotive forum where several of use use this setup quite successfully.

Good Luck!

 

It has 208k miles. I have a scan tool, nothing fancy I believe it’s a obd 2. There is no code for any particular cylinder misfiring. It just says random misfire detected before I fixed the vacuum leak issue. It would have an error for lean on bank one but since making those repairs, I’ve had no more errors other than the random misfire.

 

I don’t believe the transmission is wearing out, I changed the transmission fluid, filter, and the 1-2 shift and 3-4 shift solenoid while I had the pan removed. No metal shaving or anything found and the fluid looked pretty good for the age of the truck and not knowing when it was done last. I of course am not sure as I’m posting here for help but it’s not something that happens every time. Once I’m past the 20-28 mph the rpm seem to stay where I’m used to and it doesn’t shift hard or anything. I can also let off the gas some when I’m approaching 20 mph and I don’t experience the high rpm’s. Of course I know I shouldn’t have to do that. The spider injection was completely covered in carbon as well as the throttle body housing. I cleaned it thoroughly before installing the new injection body.

 

Would the transmission wearing out cause it to misfire? It just seems to me as I have corrected some of the fuel and vacuum issues the hesitation has gradually returned closer to normal I was used to, as to why I was hoping to be on the right track figuring out the issues. I read that the TPS sensor and Idle are control valve both connected at the throttle body can cause hesitation as well. I appreciate the responses and I apologize if my responses are not posting how they should this is the first forum or any site I’ve posted on.

 

Some years ago I replaced the spider on a 4.3 and had a miss. I had put the wrong injector in the wrong hole. It was easy enough to fix, hardest part was disconnecting the fuel lines. Guess I was thinking it was a batch fired system.

 

individual cylinder misfire counters are live data, not trouble codes. So are fuel trims.
even though you may not have trouble codes, this information helps the troubleshooting process and gives you a direction to go instead of changing random parts.



no

 

I have triple checked that I got all the injectors in the correct position. I went to the junk yard and found a TPS sensor new on a crashed truck. I have not installed it yet. Just wanted to see the feedback before any additional repairs. Driving this morning the rpm’s are a lot closer to what I am used to although when I have my work trailer on the truck the issue is still very evident. Truck goes to about 3500-4000 rpm’s before shifting 1-2 or 2-3 gear.

 

As mountainmanjoe said, you really need to look at the misfire count data for each cylinder. Misfire counts are viewed as live data and not as a DTC.

Without diagnosing your problem you will simply be throwing money down the toilet.