Long time viewer, but first time poster. I've looked and researched and can't seem to find anything about my odd issue.

I pretty much gave it a full tune-up about 5k miles ago. Put on a new cap/rotor, new plugs and wires, and a new coil pack. It ran like a new one for the most part after that.

In the last few weeks I've had a nagging intermitant "miss" (not sure that you'd call it a miss because it's not sluggish) and it seems to happen when I turn (mostly to the left) where the tachometer jumps maybe 400-500 RPMs and pretty much looses power. Most of the time if you let off of the gas it will "settle" back down and run smoothly with normal power. Sometimes if you try to accelerate through this the tachometer will just bump 2-300 rpms as you are driving (almost like it's trying to shift up and rev) and then when you come to an idle the truck will shake and shimmy like it's going to stall. I've had it stall on me once, and it fired right back up but the RPM's went to 2500 and stayed there at idle. I shut it back off and started it right back up and it started up normally and smoothly and drove it with no problems.

This is very intermitant. Sometimes it will happen, sometimes I'll drive it and it will not. Seems to happen after the engine is warm, or maybe after I've driven it and then it's sat for a few minutes while runnning into a place of business.

I do have service engine soon light. I have a code reader, but it's a cheap one and not a diagnostics machine. The codes that I am getting are p0440 and p0446. I usually only get 1 at a time, and they will go off sometimes for a day and then come back it will be the other one. I know these both typically mean leaks at venting system for the fuel, but I haven't had these particular codes cause me any mechanical difficulties.

Any help or direction would be appreciated since I really have no codes to draw from and now I'd be throughing money into parts and sensors with no idea of what the cause is. I've thought maybe it was a vacuum leak, but I don't really hear any hissing, but I haven't truely inspected all of the hoses to make sure. I've checked a few and those I've checked appear to be ok.

 

I've seen that my original post has been viewed 104 times with no responses, so I assume this isn't something that has happened to anyone else.

I was talking with my Father-in-law yesterday and telling him what is going on, as soon as I told him that it seemed to happen when I turned left he asked me, "is it your fuel pump?" I've read several other threads here and was sort of wondering if that might be the issue. I need to do a leakdown test on my fuel rail, and I may have time to do that tonight. Just wondering if anyone might think this could be the problem

 

as usual with these do a fuel pressure test and leakdown. Take a Vacuum pressure reading and isnpect the intake plenum for leaks as well (these dont show up as low vac but mess up the MAF sensor).

 

I did the leak down test last night. When I turned the key on it went to 58 PSI, and then I turned the key off. I went back exactly 10 minutes later and it was 32 PSI, went back 10 minutes later and it was 24 PSI, went back 20 minutes later and it was 12 PSI. Seems like it's not holding pressure and that I have a bad fuel pump. I may still have a small VAC leak somewhere, but I'm assuming that at least the fuel pump has an issue. Now, I've had a fuel pump go bad before where it wouldn't start, but would run, but I've never had a fuel pump seemingly "fail intermittently". What is the cause of this, if there's really an answer for this?

 

might be fuel pump, might be injectors. the leakdown is not in spec but "shouldn't" casue too much drivability with that leakdown rate. Focus on vac leaks first, its a cheaper fix.

 

Took the blazer to the mechanic since I was at a loss of where to begin with no codes, no apparent vacuum leaks, and seeming like it was electrical I figured it would be cheaper to pay the diagnostics fee than to throw money at parts. Turns out the crank sensor needed replace. Had them do it so they could do the relearn and make sure the timing was ok. Drove it home and to work this morning and no issues. All inidications it's fixed, and now I'm just waiting for the next problem to crop up