Major misfire problems.

[crzy8mnky]

2002 5.3l L59 flex fuel into a 98 k1500

Got everything hooked up and the the truck runs, however it runs like crap. I have a P0200 and P0300, which is injector circuit and random misfires. So far I have hooked up a noid light and the injectors are pulsing. I have verified the wiring for the coils, the injector wiring was not changed except for swapping a few of the wires around. I checked a few of the coils and plugs by grounding against the block and spark was present. I have EFI live and I have misfires on every cylinder, along with 0mv on bank 1 sensor 1 02 sensor, however no codes for that. Fuel pressure at the rail is 40 PSI.

Before doing this swap there were no codes and no issues with my truck, and I was running the same computer. The 0411 that I am using came with the L59, so I flashed it with the original stock tune when I did the swap.

I'm thinking that the fuel pressure regulator is bad, since fuel pressure should be around 48-54 PSI, but what other issues could be causing misfires on every cylinder?

Edit: All fixed now. The PCM pins for 6 and 8 were pushed back into each other and shorting out. Once that was fixed everything was running correctly. It was discovered by taking a multimeter and checking the frequency of the injector pulses, 6 and 8 were showing a higher frequency than the other cylinders.

[George C]

if using stock tune for injectors you need much higher base fuel pressure. stock GMs see 58 for most part and that could be causing your issues since your injectors are scaled for the lower psi

[crzy8mnky]

The injectors are the stock flex fuel injectors, which run 33lbs at 48 PSI. I'm using the stock tune, so I don't think this is the issue.

So I replaced the regulator and it still showed 40 PSI. Sometimes it will go up to 50 though, and when I pinch the return line I can control the pressure. However, none of this has made a difference in curing the misfires. I pulled the injectors and send them to be ultrasonically cleaned, since I don't know their history. If this doesn't fix the issue then I'm out of ideas.

[George C]

if you are at 40psi and tune is stock then the scaling is off

you either need to scale injectors for 40psi or figure out how to raise pressure

[crzy8mnky]

I was able to raise the pressure by crimping the return fuel line and it made no difference.

[George C]

I was able to raise the pressure by crimping the return fuel line and it made no difference.

crimping the line now restricts volume....motors need to see a certain psi and a certain volume

[crzy8mnky]

It was the return line, not feed. Regardless, it did not seem to make a difference as the truck ran poorly no matter what the pressure was at.

[George C]

restricting any line will cause issues but either way any time i seen your issues it was purely a fuel delivery issue

[crzy8mnky]

That's what I'm thinking, especially since both O2 sensors are showing lean. Hopefully getting the injectors cleaned will take care of it The weird thing with the rail pressure is that immediately when I turn the key it will jump to 50, and then the pump will shut off and it will drop to 40. And when it's running it will go anywhere from 37 to 50. The first regulator was a brand new AC Delco part and this new one is a BWD and the same thing occurs.

[crzy8mnky]

I got the injectors cleaned and placed back into the truck, no change. I am misfiring the most on 1-4, with a few misfires on 5 and 7, and very few on 6 and 8. I have 12 volts on pink, and there is about .7 ohms of resistance on the ground wire on 7 of them, the 8th one if 1.7 ohms. Noid light flashed on all 8. Still have the p0200 and p0300 codes with a lean condition on bank 1. One thing I noted is that when I unplug the MAF the truck seems to be running better, although it seems that the MAF being disconnected means that the misfire counter on EFI does not work, however both O2 sensors are around 800-900 mv. I'm using the original MAF. I'm pretty much out of ideas so any ideas are appreciated.