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Vortec: About to start pulling hair....

It knows what cylinders are missing by looking at the crank position sensor. When the crank slows down, the computer knows there's a miss. It can then see when it is happening each revolution and pin point it to a cylinder.
 
I'm not sure about the vortec, but the ls stuff I think even uses some kind of feed back from the coil since it's got a coil for each plug. At least that's whatI rread somewhere once upon a time and at the time, it made sense.
 
When I unplug the MAF and force it into speed-density, does the computer still take input from the O2 sensors into account in the fuel/timing calculations or does it simply rely on a static table of MAP vs TPS vs IAT?
 
Swapped EGR valves with the crew cab and replaced the PCV valve house because of a cracked fitting and no improvement. It actually started missing more and threw an EGR closed performance CEL. I cleared the code and it ran good for a bit then I heated it up pulling load in gear to try to isolate an engine load % the miss happens at and it started running really rough. 12% load in R against the brakes BTW. But it started running really rough at about 18% pulling uphill, which is a new issue and maybe related to the EGR swap.
 
I just did an edit: find for pump/pressure, have you checked fuel pressure?

SOME of what you describe sounds like it might be a pressure issue. I actually had an off-idle stumble that I could NOT tune out when the hose in the fuel tank was split. Also consistently lost power (now thinking back it was exactly like when a carb starts starving for fuel, bucking) at specific MPH/gear points like trying to accelerate in 2nd at 45MPH, and multiple seemingly random problems with idle...rough or surging idle mainly.

I just don't know with the OBD2 stuff though.
 
I replaced the crank position sensor this evening after finding a few threads talking about rough idles and missing with the CPS going bad. No luck, still missing. I found a thread where a guy had replaced the intake gaskets on his 5.7L Vortec and one section had pulled up into the runner causing an internal intake leak. I stopped off the PCV system and checked the crank case pressure with a vacuum gauge. It went positive on the gauge so that's not it either. I then sprayed all around the lower and upper intake sections, the throttle body and injection connector and got no reaction from the engine.

Fuel trims (via Torque) where in the (-12)-(-14) range at idle, but were in the high teens and lower 20's on the interstate under load. No missing under power or when pulling hard but as the throttle eased off after climbing a hill with cruise on, it would miss. Cylinders 1 & 4 as usual... :doah:

I'll buy a fuel pressure gauge this weekend if I'm not working the whole time and check that out.

list:
Delphi MPFI conversion (with new engine)
Spark Plugs (with new engine)
Plug wires (one set with new engine, one set since)
Distributor Cap (since new engine)
Rotor Button (since new engine)
MAP sensor (with new engine)
EGR swapped off CC
MAF swapped off CC
CPS (as of this reply)
 
If compatible, and you have them, I'd just borrow/rent the pressure checker from autozone or other store that will let you use it for free. Depends on the rig, some may not allow the pressure tester setup to be visible while driving, just depends where you tap the pressure and the length of the hose to the gauge.
 
I had rather just buy a fuel pressure gauge and have it if I need it.

I saw today that the vortec engine has problems with the cam gears wearing. It looked fine while out, but I didn't look extremely hard at it. I would think I would have a more constant misfire than I'm having. Any thought?
 
I'm surprised there were issues with the cam gears...GM had been using roller cams in the gen1 since 1986 in the cars, I don't see why a transition to the trucks would have made a difference. None of the Vortec Gen1 motors used a composite distributor housing did they? I am vaguely aware of those existing, but unsure what they were used on.
 
This truck does indeed have the composite distributor housing. And it seems common for them to "knife edge" the cam gear, which I think is just their term for wear thin.
 
Yeah, probably from the housing flexing under load would be my guess as to why they do that. Stupid to try and cut corners, but that's GM sometimes.

I know there is some peculiarity with pulling the Vortec distributor and getting it back in so that the PCM doesn't mess timing up, but shouldn' tbe any more difficult to pull it out and look. At the same time, turning crank back and forth while looking at rotor might show some significant slop if the gear is worn badly. Pretty arbitrary though when just a couple of degrees can make a noticeable difference in how an engine runs.
 
Pulled the distributor and the cam gear is showing the wear that I've read can cause missing issues. Gonna pick up a new one at NAPA tomorrow and give that a shot. :dunno:
 
Skipped working over on this beautiful evening and put the distributor gear in. It idles noticeably better, but I'm still getting the misfire. Did actually get a count on cyl7 this time, but only one. I think I'm going to fix the oil leak and let the wife drive it. If it ever causes a big problem, I'll find it then.
 
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Pulled the fan shroud, fan, pulley and balancer off. It's getting dark so I'll try to pop the seal out tomorrow. Can the balancer seal be replaced on these plastic vortec timing covers? I really don't want to drop the oil pan on this thing. That just don't seem like a good time.
 
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Ok, so other than the miss, the suburban has been doing ok. Sunday night though, it locked itself in first gear after getting off the interstate. Pulled codes (no check engine light illuminated) and it's a shift solenoid "a" code.

Is there anyway to check the solenoid on the truck without a Tech2? The pcm provides the ground, so with the switch on but not running can I simply probe the wire coming back to the pcm at the connector and show voltage if it's good? If that works, I should be able to ground it and head the solenoid thump too, right?
 
Nor am I. Reason I insist on manuals. Not to be a jerk, just my reasoning. Sorry I can't help. Greg Ducato should be the man here, no?
 
I got some info from a buddy back home on checking some places. Haven't looked at it yet because of work. He said checking a bunch of voltages.
 
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