RESOLVED: The BWD Ignitor/original coil combo was weak in some way, as after replacing those with a pair from the junkyard it fired right up. Swartlkk was right.

I also replaced the distributor with a newer one from the junkyard, as mine had play between the gear and the shaft -but that wasn't the issue. The coil/ignitor did it.

Thanks for all the help.


Original post:

So the blazer was running fine, only a slight hesitation/stumble/misfire at 2000 RPM. No big deal.

The motor is newly rebuilt. I've replaced the cap and rotor plus plug wires to deal with the 2000 rpm weirdness, but to no avail. I did the ignitor when I was diagnosing the no-start upon rebuild -turned out to be the timing, but anyway, that's new too. All of these components were BWD, AC Delcos were hard to come by.

Then out of nowhere, when the truck was driving fine, it stumbled, sputtered, and wouldn't rev past 500 or 600 rpm. I coasted it into a gas station, and it started a few times, but hard and ran VERY rough when it did. The motor shook violently if I tried to rev it past idle, and eventually it wouldn't start anymore.

I tested the fuel pressure, and here are the results:
Key on, fuel pump on: 58/59 psi
key on, fuel pump off at end of pump run: drops immediately to 51 psi, doesn't drop beyond that within the 10 minute window.

My diagnosis: inconclusive, but probably not fuel. I smell gas at tailpipe, not heavily, but it's there. Are those numbers indicative of a fuel problem? They numbers are the same as they were before this issue, so unless they're out of spec I doubt they're the only culprit.


The coil could also be a problem, but I do have spark. I pulled a plug and held it against the ac pump mount while it my wife turned the engine over. Blue/purple spark.

Not the coil?

 

Fuel pump. 99% sure. Do the test at the fuel filter,if it does the same thing its the pump,if not,its the fpr. has to hold above 55 psi for 10 min. Its either the check it valve in the pump,or the regulator in the intake is leaking.

 

Good point, however it's a brand new MFI spider, so the fpr should be good. Same with the filter, maybe 200 miles on both. The truck did sit for months, though, and this is the second tank through so I'm aware it could be gummed up.

I just put a cat on it Thursday and it died on Monday, so I doubt that's plugged but anything is possible.

The codes I pulled were 0300 (oh goodie, generic misfire) and 0140 and 0141, o2 sensors.

Does that change anything?

 

Sounds like the pump still. if its misfiring,it could be from not getting fuel etc etc. Check the pump,if is bad (which im pretty much sure of it) dont cheap out and buy a aftermarket pump. these will not last in our blazers. Buy only a delphi or ac delco.

 

The P0140/P0141 codes are B1S2 (down-stream pre-cat) codes which have nothing to do with the operation of the engine.

I suspect your choice of ignition components is the likely source. If possible, return the aftermarket components & buy AC Delco. Many members have chased their tails replacing components on a whim only to find out that the $40 cap/rotor set they bought from 'XYZ Aftermarket Co.' didn't work out of the box and they wasted their time & money on everything else along the way.

Have you tried misting down the ignition system components at night to see if you have any spark leaks out of the wires? Or pulled the cap to check for signs of cross-fire inside (carbon buildup)?

 

Kyle, I'll go check for those. Does the fuel system seem suspect to you? For $400, I can't decide to do the pump/sender or not.

What chain stores can I get AC Delco/Delphi components through? Dealer only? Rock auto only has the one pump without the sender, and I'm not sure which part number I need.

Thanks, guys.

I should restate. What places stock acdelco parts? Is that dealer only? And I realize I may not need the fuel pump, just trying to price this all out.

 

Considering that your fuel pressure is within spec, no, I don't. Unless you monitor the fuel pressure during the problem and see something different, I think looking deeper into the fuel system would only waste your time & money.

As far as AC Delco retailers, the easiest place to find that out is ACDelco.com. Advance Autoparts is one of the larger chain stores that carry AC Delco & Delphi parts. Whether their stocked or not is a different story. Probably not something you'll be lucky enough to find on their shelf. I think it would be the same situation at the dealership.

You shouldn't need to change the whole sender (lines & all) unless you bend, break, or otherwise damage it during the disassembly. they are sold separately. You can replace the fuel level sending unit separately from the sending unit assembly just like you can the fuel pump if you need a little extra peace of mind.

For part numbers, you can take a look at the part catalog portion of ACDelco.com.

 

Perfect, thanks. I still have all of the original parts, so I suppose it's time to try them again.

UPDATE:

Replacing the cap, rotor, and plug wires with the ones originally on the truck didn't change anything. They were, however, aftermarket ones as well, so I've gone back to the new set.

Verified that I have purple/blue spark at each plug, on its respective wire. Re-deadtimed it, wasn't off any. I suppose the coil could be at fault, is that a safe assumption? I'm hesitant to blame this on ignition, as I'm getting spark on each cylinder.

Plugging in the ACDelco ignitor didn't change anything.

I am reminded, however, that I noticed something funny ignition system diagnosis when I couldn't get the truck to start up initially (turned out to be timing):
And now that ignition and fuel seem to check out, this (and the coil, I guess) are all I have left in the ignition system to investigate/verify working.

The diagnostics link above is for a no spark condition, so I'm wondering if getting no flashing on test 3 and flashing on test 4 is a valid test in a SPARK PRESENT condition.

Spraying starting fluid into the TB (MAF disconnected) didn't change anything. I did not pull the fuel pump fuse/relay as I'm not sure where it is, so I'm not 100% done testing fuel.

Resolved. See first post for conclusion.