Very frustrated with my truck. Misfire above 2000 rpm
 

Hi all. Ned’s some help with this one

When cold my truck performs great. As it warms up though, it develops a misfire when on the throttle and over 2k rpm. I’ve done a lot of troubleshooting but I can’t find the answer

i did the following:

Checked rail pressure. No issue according to the scanner

No check engine light.

I changed bith the crank and cam position sensors

i checked the apps. No issue when cold or warm

i did a cold compression check. All cylinders 400psior above

i replaced the crossover tubes and injectors

im at a loss

it starts perfect and runs 100% below 2k rpm. It’s driving me nuts

i have used spare rail pressure sensor. Rail relief valve and fca. Will try these next.

Any my ideas or advice???

thanks

chay

I checked the valve lash-the intake were maybe a few thou tight, loosened them off.

Also changed the FCA, the rail pressure sensor, and the rail relief valve with spares I had. No change.

Still stumped!

Next up, apps I guess. I hate just changing parts but I have no idea what else to do.

Chay

As it turns out I had two issues with my truck.

The first issue was that it would not go over 2krpm, the first time of the day it was run. It defueled smoothly for this issue. After coming off the throttle, and back on it would run normally.

This was a failed transmission output shaft speed sensor.

At some point, the way the truck acted changed so that when I added throttle after the 2k defuel, above 2krpm it would misfire. Given the same rpm threshold, you can see why I thought the two were related.

The misfire issue persisted after the transmission issue was found.

I failed to mention that I had a self created modified tune using HP Tuners in the truck. I didn't suspect the tune because I had driven it for some time without the issue cropping up, when on the modified tune. Why didn't it crop up? No idea. Anyway, I reset the ecm back to the bone stock 2003 auto program...problem gone. I obviously have some learning to do on the programming side. Ironically the whole point of modifying the program was to get the 2003 ecm to output similar to the 2006 engine that I swapped in the truck. Back to the drawing board!

What an ordeal!!

Chay

Good info,, thanks for posting.

For those that are interested it seems like the tables that exist in the 2003/2004 tables are used differently by the ecm than the 2004.5+ Ecm. I had pretty much the same values as far as I could figure patches from the 2006 ecm. Needless to say they did not work in the 2003

The HP tuners programmer...The software has
se misleading titles. Things like adder tables have been shown to work more like limiter tables in the 03-04. Too much guess and check for me so I left it stock

Chay