Engine hesitation ***Need help***

[Philbo]

Hi everyone,
So I performed a 5 speed swap on my 1999 3.4l. It went fine and the truck ran great for at least a week with the auto ECU. Then I figured the immobiliser on my manual ECU and swapped this one. The truck ran fine for another couple of days then starts to hesitate @ low rev and more than 1/3 of throttle. Runs pretty smooth over 2000rpm. I reswapped the automatic ECU and no luck, stays the same so I dont think the ECU is related.
-I changed my MAF and my TPS with no success.
-I look for a vaccum leak (visual and with propane), no luck.
-No CEL in the dash. If I check the pending codes I have #5missfire (not surprise since the truck jerks at every take off.
-Seems to be running a little smoother when cold

Not sure what to look for now to avoid changing every sensor of the car.

Any path to follow or ideas?

Thanks in advance folks!

Phil

 

[tgreenwood75]

If you're getting a code for a misfire on Cyl5, I would start by pulling that plug, check the plug, coil, wire. Could just be something up with only that cylinder that feels like it smooths out at higher rpms because the other cylinders can keep up? Perhaps when colder it idles higher so it is less noticeable if you feel it more at lower rpm?

 

[ocbruin]

Scotty on youtube has a great diagnostic for misfires. You should be able to swap the coils, read the code and see the misfire "move" if that is really the problem.