and falling all over itself. There is something wrong with my truck. Every now and then, over the past few days, the CEL light will flash. I now carry my scanner with me, every time its 0300 - random misfire. Today, the light came on steady, same code though. I am thinking its either a low/no spark issue, or a fuel issue. I picked up some plugs, even though I just installed new Delco iridiums 15K ago, pulled the plugs, they all looked fine, so I decided not to waste the 80$. Then I put a spark test light on all the plug wires, and was not too impressed. The spark seems weak then strong, then weak. Its the same on all wires. Had 1/2 a tank of gas, dumped some seafoam in it, thinking that maybe the rails and / or injectors were gummed up, but that didn't change much. The last thing I did was to fill up at a different gas station. Not sure if that did anything or not.

I did search, and the symptoms and resolutions that I've read are so varied, that I am not confident in assuming that I have the same problem, especially when a fuel pump is $350. I want to KNOW thats the issue.

Anyone have any ideas on how to test the coil packs? Maybe they are taking a dump on me?

I would also like to know how to go about testing the fuel pressure on this thing (I haven't done that on any vehicle, so I don't know if there is a lie I can tap, or a port maybe???)

What I do know, is that the vacuum is at 11-12hg (according to the scan tool) at idle (650), my long term fuel trims are at 0.0% and O2 sensor 1 bank two is going crazy between .1xx mv and .8xx mv, while sensor two bank two is seady at .450 mv. Hope this helps.

Current mods are heads, cam, LTs, ORY, Level 2 trans 3000 stall,, blackbear tune, Efans, stock fuel pump, probably stock fuel filter (I haven't changed it in the 50K that I have owned the truck), stock intake/rails/injectors.

Any help is appreciated. Thanks guys.

 

check your Maf sensor and clean it, and also you can check your o2 sensers and clean them. You can clean the o2 sensers, but if they are bad they wont last long with the cleaning. While your cleaning the MAF, might as well clean the throttle body as well. These are cheap things you can do to eliminate some things. Fuel pump could be getting ready to go.

 

How many miles?

New wires cant hurt.

You can get a new walbro 255 pump for 139 from Texas`speed.


I know what your saying though, you dont want to " throw" parts at it.

OH, is your filter inline or the tank? if Inline DEF. change it!



But if you have a lot of miles, a new pump/ wires/ and O2 sensors shure cant hurt and are probably needing replaced anyway.

 

Okay, I will try anything. Personally don't think it will have any effect on the problem, but I know they need to be cleaned.

128K on the bottom end, about 15 - 20K on the top end and plugs (delco iridiums). MSD wires with 10K on them. None of these parts should be the issue, I checked them anyway, and they checked out okay. Plugs look good and the wires are fine...so says the wire tester anyway. As for the walbro 255L intank, is that fairly straight forward or is it a wiring nightmare? I don't really want anything else to worry about with this truck, you know.





I have noticed something new tonight. I was leaning towards just having a tank of bad gas, and that still maybe the problem, but I noticed tonight that my converter just decides to unlock when its not supposed to After I had the trans installed, and got the tune from blackbear, its set to lock at 55mph, and unlock at 50mph. Tonight, I was at 60ish, maybe 61, made absolutely no throttle changes, on a flat road and the converter just unlocked? After that, it wouldn't lock again, I had to shut the car off and restart it, then it would lock at 55. WTF is that about? I think I need a can o'gas and a match.

 

anyone know where I can find a write up on the fuel pump swap with a walbro 255L like the one mentioned above?

 

The swap is EASY! Just takes a little time, no biggie.

Follow the write up by BLACK'RADO , Srry, the link is on my other computer.

 

Still no better or worse after cleaning the TB and MAF. Didn't expect much, but they definitely needed a cleaning. Did the TB bypass while I was there.

Still missing randomly. Its not giving me a code anymore, so I guess thats progress, maybe it is bad gas. Right now, if thats the case, I have a half tanks of crap and a half tank of good stuff, so this will continue to happen until I run it all out. Is there any way to drain the gas without dropping the tank? If so, I'll drain that crap and see if thats the problem. I really need HP tuners.

 

clean your o2 sensors.

 

Unhook the fuel line to your rail and let it drain by using the pump, may take a while 5 sec at a time though LOL.


Probably best to get a siphon pump and empty the tank with it.

 

HOLY HELL, that would take a few minutes.

I think I have found the problem...o2 sensors. I have no idea how to clean them, but for ***** and giggles, I pulled the passenger side. It looks good, kinda like the plugs, signs of running rich. When I put it back it and test drove, I noticed that the stumbling problem was back. Not bad enough to not drive, but screwing with the o2 made a noticeable difference. Will be changing those in the near future. Actually, I think I am juist going to buy them and let a shop do it, the drivers side is frozen in there.

Thanks for all the help guys, I think the reason that I am getting the misfire is the pcm is dumping fuel to protect itself given the bad o2, so much so that its actually missing at part/light throttle. WOT, no misfire, idle, no misfire, part throttle, it drops a cylinder randomly.

I will update with the results.