Hello,
I have a 99 Blazer that won't rev up and has a hard start condition. Right before it decided it's new redline was 1800 rpm, I had filled the tank AND then driven it about 20 miles to pick up dog food. Going up a slightly steep grade from a stop, it decided to say emphatically say NO, conked out and wouldn't start for quite awhile. It sounds like the exhaust is backed up or at a minimum, there's a leak on the passenger side exhaust collector. Hard to describe other than a two step launch control set at 1800rpm except it's constipated... Finally got it towed back to the house and I've replaced the fuel filter, checked the air filter, tested a new coil (no difference). Here's the kicker, it's not throwing any codes. Last code it threw was months before for an inefficient emissions system (can't remember the code, just the descriptor) and it cleared. I had been idling the truck on break with the heat on so I didn't think much of it. On to the fuel system diagnostics Sticky I found here: Didn't have a fuel injection tester kit so I bought one off Amazon for $25 instead of $50 at Harbor Freight so the numbers could be off a little but here's what I got:
Service port pressure: 59psi with pump active immediate drop to 56psi and still at 56psi after 10 minute timed leak down test (I don't know what to make of that since it 'failed' max pressure but not leakdown)
Max pressure at the fuel filter outlet: 69-70psi steady with the pump relay bypassed. Leakdown after 10minutes timed 50psi. Disclaimer: I didn't have the correct 5/8" ****** adapter for the Amazon pressure gauge so it was highly 'improvised' and I had fittings blowing off hose clamps multiple times. If I have to retest I will but it'll be awhile before I take another $10 in gasoline shower. I ended up ruining the K&N fuel filter clips getting the hose on there but I already had a spare (new) AC Delco Fuel filter on standby and installed it (with no change in symptoms).
From the Sticky, it seems I have a leak in the gas tank but what exactly does that mean? I replaced the fuel pump, fuel filter, plugs, cap, rotor, wires all about 6 years ago (AC Delco except for MSD wires and the K&N fuel filter). Is it the 5-6 year old AC Delco fuel pump or should I be looking elsewhere?

 

While the fuel pressure leaking down may be a problem, it doesn't sound like it's THE problem. I would pull out an O2 sensor before the cat and go for a quick test drive to see if it improves. If it does, then it sounds like you have a plugged cat.

 

Well, other than sounding like a sneaked in a V8 swap, no improvement. It smelled rich before pulling the 02 and even more so with it out. Where do I go from here?
Edit for quick recap of current diagnostics:
Service port pressure: 59psi with pump active immediate drop to 56psi and still at 56psi after 10 minute timed leak down test (I don't know what to make of that since it 'failed' max pressure but not leakdown)
Max pressure at the fuel filter outlet: 69-70psi steady with the pump relay bypassed.
Leakdown after 10minutes timed 50psi. Disclaimer: I didn't have the correct 5/8" ****** adapter for the Amazon pressure gauge so it was highly 'improvised' and I had fittings blowing off hose clamps multiple times. If I have to retest I will but it'll be awhile before I take another $10 in gasoline shower. I ended up ruining the K&N fuel filter clips getting the hose on there but I already had a spare (new) AC Delco Fuel filter on standby and installed it (with no change in symptoms).
From the Sticky, it seems I have a leak in the gas tank but what exactly does that mean? I replaced the fuel pump, fuel filter, plugs, cap, rotor, wires all about 6 years ago (AC Delco except for MSD wires and the K&N fuel filter). Is it the 5-6 year old AC Delco fuel pump or should I be looking elsewhere?

 

Did you happen to check the fuel pressure while you were driving, under load? If it doesn't drop off dramatically under load, your fuel system is probably ok. Do you have a scanner that displays live data? Maybe check the MAF readings under load. I had a bad MAF sensor in mine that didn't set any codes but, once it warmed up, gave me similar symptoms to what you're describing. When I watched it on the scanner, it "topped out" at about 50 grams per second, which is like 1/3 throttle. So, at WOT, it was only getting enough gas for the airflow that was being reported. Needless to say, it had a nasty bog at anything over about 1/3 throttle. I'm not saying this is your problem, but it's something you can look at pretty easily.

 

Well, it's not drivable as it sits really. It's a struggle to move it from one side of the house to the other. As far as I know, there really isn't any published data on what the fuel pressure is supposed to be under load but for giggles I did test it while idling at the test port and it was around 50psi, when attempting to rev it, it would drop as rpm increased until it started bucking/bogging whatever you want to call it and it seems to spike as it bogs, returns when it catches. As an extra fun thing I just found, if I try to 'ride it out' to see if it will smooth out at upper rpm's (it doesn't make it that far), I choked it out enough for it to completely stall out where it: Dieseled out and blew a blue/black (not positive which was the more dominant color) smoke back through the throttle body, intake, and the MAF. I had the filter box off so I could look and see if there was anything obvious on the MAF but it looked okay without any discolorations. Fuel trims at idle seem to be okay (I do have a livestreaming OBDII scanner) staying +/- 3% but I have no idea what they should be at an attempted 1000-1200rpm. I also see that the LTFT at the downstream O2 sensor is sitting at 99.8%. but also have no idea if that's a good/normal/bad thing.

 

Short and longterm fuel trim for B1&B2 are looking good here right? The timing was fluctuating between 10.5 and 23 degrees as the engine rpms were going up and down.

Voltage on the post cat O2 is 0.91V which I think means rich correct? Both B1&B2 were around the 0.5v at the time with reasonable +/- 2% short and long term trim.

So, do I remove the rear O2 and see if idle clears up or should I skip that and see what unbolting the cat does? Or am I really jumping the gun and barking up the wrong tree with the cat entirely? I know I'm being impatient but the wife want to buy another 10k vehicle and sell this (that otherwise is in damn good shape) for next to nothing. My labor rebuilding brake system, hubs, transmission, heater core, vac and A/C system over the years appears to be free in her mind. I still think it's a great little SUV.

 

Well, dropping the cat didn't change anything. Still bogging under 2k and won't Rev higher. Rear O2 is probably doing its job because short term fuel trim went positive on first one bank and shortly thereafter the other followed suit. Aside from wanting a V8 swap now, I'm getting down to the swap out cap, rotor and plugs (and pray) portion unless someone out there has something else.

 

For as much of a resolution as I have at this point: The rotor had spark blowing through the bottom. Everything looked good from up top but it just goes to show that sometimes you chase fuel when it's air or spark (and in this case also cam timing since the cam retard is -5 when spec is +/-2 degrees). But it runs!