Problem on the 'limp' home yesterday.

[Lou Merrell]

Is there a relearn process or something after the MPFI upgrade? Truck runs good with misfire and hard start when hot issues fixed but fuel trims still whacked.

 

[Lou Merrell]

This was a ride around the block.

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[stutaeng]

No relearn. Those fuel trims look good.

So no misfires? And no "crank-no-start when hot"? I think that's what I understood you said?

They'll likely improve slightly after you drive a bit more...

 

[Supercharged111]

It's never a bad time for checking CMPRET, assuming that hasn't been a complicated recently.

 

[Lou Merrell]

No relearn. Those fuel trims look good.

So no misfires? And no "crank-no-start when hot"? I think that's what I understood you said?

They'll likely improve slightly after you drive a bit more...

So far your right. A few misfires but nothing like before. I'll still seek to address that. This was the ride to get gas this morning:

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[Supercharged111]

Ideally bank 2 will eventually start to cut fuel like bank 1. Go for a longer drive and see what you get.

 

[Lou Merrell]

I'll be driving 18 miles to work tonight.

 

[Lou Merrell]

Well crap.
Just before I got to work I got a p0154 and p0300 and truck running like crap again.
Would a clogged converter cause the misfire?
Would a carbon fouled bank 2 02 sensor be the issue since the old pressure regulator was dumping gas?

 

[df2x4]

With the history of trouble codes that your truck has had recently (bank 2 sensor 1 no activity + bank 2 sensor 2 low voltage), I suspect there may be something up with your bank 2 oxygen sensors or wiring. The first sensor on each bank controls fuel trims, so the "no activity" condition on bank 2 sensor 1 is most likely contributing to your misfires and the truck running poorly.

 

[Schurkey]

If the engine misfires, the O2 sensor--if it's working--will report a false "lean" condition. The computer responds by enrichening the mixture. Which may--or may not--make the misfire worse. Which drives the O2 sensor signal farther "lean". Which makes the computer enrichen the mixture even more.

Fix the misfire, which then fixes the fueling. But all this assumes that the O2 sensor works properly, and apparently at least one of yours aren't.

When it's me, vehicles get fresh O2 sensors unless I'm satisfied (can prove) that they work properly. One of my vehicles had a sensor that "seemed" to work right--good response at low speed. But at highway speed, it reported false lean, driving the fuel trims way rich. In this case, it wasn't misfire-related. I spend two years on-and-off trying to track down the problem. Eventually, I crammed in a $13 O2 sensor and fixed it.

Do you REALLY have a P0300? Some (many) scan tools fail to report the TRUE code, falling back on generic codes instead of vehicle- or manufacturer-specific codes. Does your scan tool have the ability to display individual-cylinder misfire codes? What are the misfire counts for each cylinder?