Atlas

In the motorhome world, people refer to tire manufacturer's pressure-weight charts to determine a good PSI for their motorhome tires. What they do is get axle weights for the vehicle at a CAT scale or other scale. Drive on, drive off, the scale spits out a ticket with the weight over each axle. Then, you know the approximate weight per tire on that axle. Then, you refer to the pressure/weight chart published by the manufacturer and set the tire PSI accordingly. Of course, you will want to adjust (and know how much to adjust) when you decide to carry more weight. For everyday unloaded ride, bringing down the PSI within a safe range that still adequately supports the vehicle's weight relative to the construction of the tire can really help with ride quality and under/over-inflated wear issues. I don't see why it would be any different for a pickup. The key is the tire needs to be rated to support the load safely at the PSI you've selected.

National Average back up to $4.04 for gasoline and $5.35 for diesel. https://gasprices.aaa.com

Well, okay then...

The answer you're looking for is the TPMS threshold can only be reprogrammed through an MDI 2 interface with the truck using an advanced scan tool, or, at the dealer. We deal with this all the time in the Jeep world when people upgrade tires and wheels, but, there are cheap aftermarket solutions so we can lower the TPMS threshold ourselves. I don't think one exists yet for the newer GM trucks.

That 2000 Jimmy did well. $22,250 https://bringatrailer.com/listing/2000-gmc-jimmy-4/ I was thinking about jumping in when it was $17k this morning. Had it been a ZR2 2-door Blazer in the same condition I think I'd be driving to Idaho to pick it up. Even though it's the same truck, a Jimmy has never been on my wish list like a 2-door Blazer. Plus 5% buyers fee and 10% tax would have put it at $26k. But now I've got my eyes open!

That Jimmy on BaT did well. $22,250. When it was $17k this morning I thought about jumping in, but with 5% buyers fee and 10% tax on the winning bid that's $26k. Had it been a ZR2 2-door Blazer in the same condition I think I'd be driving to Idaho to pick it up. Working on mine has made realize how much I really do enjoy these. I'd like a *nice* one though if I'm going to keep one around for a while.

From what I understand, a code will not set for knock on an OBDI system. It will set a code for circuit failure (unplugged?) but not that knock is detected. Will test as soon as I have the intake put back together.

That IS the test to rule out the knocking exhaust, but, the spider injector is somewhere orbiting inside the USPS network on the way to being rebuilt. I won't be starting the truck anytime soon It's pulling timing under load/driving as well, but it's much more variable.

Why don't I have a good scanner? I've always wanted one when I've needed one. My latest reading says I don't need to do a relearn on the ckp sensor on a 1995 with OBD 1.5. The relearn is prescribed for the later-model 1995's which shipped with actual OBD II when GM completed the transition in prep for the 1996 MY. I need to confirm that. Did you know forums are disappearing? Knuckleheads on Facebook... it's not the same. It's just not. So, scanners. Again, shooting myself in the foot for having eBayed my Snap On MT2500 "brick" with all the adapters. Not that I couldn't buy another but those are getting quite old, and mine wasn't new enough to work on 2000's vehicles. Damn it (as I'm scanning my email between paragraphs here). Did you know there's a 2000 Jimmy 2-door on BaT that's ending this morning? It's local. I want it. 14k miles. Absolutely beautiful. Back to scanners. MT2500's are old. Solus, now that could be a contender. There's a ~2008 Verus with a system error that's basically new in box for cheap. Hmm...I'm not sure about a scanner that runs an archaic version of windows (95 or CE, I can't tell). I want the ability to reset and rotate TPMS, test individual modules, bleed ABS, electronic parking brake controls for servicing brakes, relearn procedures and other bidirectional controls. Snap On does an MT2600. It's a new model as of last year, marketed as their "entry" scanner. Entry? Only where $1900 gets you through the doorway plus, I'm guessing, $1000/year if you wish to keep it current. So goes scan tools actually designed for production environments. Want decent products with excellent support, you pay for it. Everyone is raving about Autels and TopDons and Foxconns and all these newer brands that are selling the $500 "prosumer" scanners for backyard hacks like me. They're tempting...honestly. Updates are cheaper, base prices are remarkably cheaper... And you get to deal with bugs and translation whoopsies and, well, just don't use it on anything expensive, OK? Having a dealer replace an ECU because it needs to be re-imaged after an adventure in scanning is no joke. But I think most people are getting by OK with these units. eBay on a scratch-and-sniff pro-model oldie, a shiny new TopDon, or??? God dang it, I can't stop looking at this Jimmy. I'm ready! I'll Bring The TRailer! It's beautiful.

It's all a crock of

I will be doing that for sure, but I need to solve who has/ where I can find a bidirectional scan tool that will support OBD 1.5. I'm kicking myself because I ebay'ed a Snap On MT2500 that I didn't think I'd ever need anymore. D'oh!! I'd rather not buy another, so I'll contact a few local shops to see if they have one and how much they'd want to do the procedure. I'd rather have the ability to do it myself... I wish there was a modern tool that could do it all, but I'd have no idea what to buy. The theory with the pulled timing is that it mimics a rich condition. The delayed spark causes incomplete burn and the O2 sensor picks up low oxygen levels. That's interpreted as a rich condition so the PCM pulls fuel and that shows up in the deeply negative fuel trims.

Injector is being sent off today for rebuild and I estimate I'll have it back in 10 days or so. It may not be the injector...of course...now that I've torn down the intake again. But, let's rule out the injector and replace those spider legs that have been almost rubbed through. The truck has always had negative timing and I'm reading "normal" timing at warm idle should be +16 or so. I'm negative 16 to 25 or more, and it's always been like that since I bought it. A light turned on upstairs last night in the old noggin. Rare, I know... This will be wild, if it turns out to be the cause! In 2001, according to the old service documentation, the muffler was replaced. Why? I have no idea, it wouldn't have been rusted through by then. But they did a crappy job. In 2019, another shop replaced it and noted the prior install was poorly done on the work order. "Exhaust system vibrates on crossmember". Except...I guess they just left it be? I believe the husband, the couple who were original owners, had passed by then. Maybe she said it's just not worth it to have the exhaust system fixed and declined repairs. Very few miles were driven between 2019 and 2025. The exhaust system vibrates heavily on the crossmember and you can feel it and REALLY hear it, even today. Not always, but at idle, it gets going pretty good sometimes. What if.... ....What if that's enough to trigger one or both of the knock sensors? Could it be tricking the sensors into sensing knock, so it's pulling timing aggressively? Pulling timing heavily means it's firing after the piston reaches full height which means incomplete burn which means the O2 sensor is sensing a rich condition, which means I've been chasing my tail, and what I thought was an inconsequential problem (janky exhaust) has been THE issue for this truck for 25 solid years? That would be wild. Maybe it IS wild. The service documentation thereafter, for years, shows visits for rough idle, replacing O2's, replacing the cat, replacing plugs and wires, a misfire condition, like they could never solve the issue. The injector has been replaced 4 times in 80k miles, that's just crazy. The secondary theory.... The engine has clearly had a leak at the front seal for a very long time (the greasy trench...). I think the truck changed hands quickly ~2025 because there's Napa receipts from someone I don't recognize in the ownership history. They apparently replaced the timing cover seal, and they did a terrible job. There's RTV smeared all over and the leak I had reduced to a weep by snugging the front oil pan bolts is now a leak again. HOWEVER....I read about replacing the crankshaft position sensor. Any time the ckp sensor is disturbed or timing cover is removed, the truck requires relearning, and that can only be done through a bi-directional scan tool. Skippy with the RTV probably didn't do the relearn procedure is my guess. His scan tool is lost in a pile of RTV goo somewhere. So, it's very possible the sensor has been disturbed and the truck is just running on the old learn data but not setting a code for anything. The distributor has since been replaced and so has the camshaft position sensor, so all bets are off for that thing. In the theme of one step forward, two steps back, I returned the accumulator for the AC. The gal I've been working with at O'Really's has been great. She refunded it under manufacturer's defect and we compared it to the replacement I ordered, and sure enough, the replacement is machined very differently (and a gauge actually fits on it!). Got it home, installed it, started vacuuming it down.... and I couldn't get good vacuum. The high side service port, where I replaced the old GM ball valve suspecting that was a source of the previous leak....well, I've clearly exposed whatever pre-existing crack in the line where the service port is welded, and made it much worse. Blessing in disguise? Except there goes another $25, now I'm waiting for a replacement AC line. In 10-ish days ALL the parts will be here. Rebuilt injector, new exhaust system, new cat, new high pressure AC line. Oh, did I mention the squeaking ISN'T coming from the AC pump? The truck still squeaks when started, and there were words after I started it with the new AC pump installed. But, there was more to replacing the AC pump for just a squeak. A truck with good working AC is something of value, for the comfort alone. I've ordered a new harmonic balancer because, 30 years is a good run for one of those. Rule it out. The squeak may be something more sinister, though. I'm worried about that ckp sensor and if it was shimmed correctly, or if the timing set was installed correctly. The squeak may be coming from UNDER the timing cover. At this point, once I get it put back together, I'm thinking I'll take a 50 mile victory lap and then promptly put it up for sale. This truck is cursed. Betty, from beyond the grave, doesn't want anyone messing with her Blazer. Or maybe she's getting revenge for 30 years of shop visits with that thing.

$5.10 for regular at the Kroger It's been 6 months... is this the "new normal" ?

While waiting for parts I have been working on installing the AC compressor, new accumulator, and orifice tube. Also changed out the high side ball valve (original). The orifice tube that was in there wasn't too bad. Slightly dirty, a little bit of junk, but not blocked. Glad I changed it out. The accumulator, which should have been a 5 minute job, may have just burned $50. Put some PAG in it, wrote the date and mileage on the side, fresh o-rings and gooey'd up the threads and rings with Nylog. Got everything connected and snugged and was going to vacuum down the system, and.... My manifold gauge won't fit on the port. It's not an R12 service port. It LOOKS like an R134 service port but the diameter is a hair too large. There's a sticker on the accumulator that says it's designed to be used with R12 and R134a systems only. So it's not R1234yf. Even if I reduced the diameter slightly with a file, the shoulder on the port is too large so the quick-connect valve won't lock on. I'm stumped. It's going back, and 50/50 on if they'll give me a refund. Also, I did a fuel pressure test.... Key on, the gauge spikes to about 60psi and quickly bleeds off, like 2psi per second. The fuel isn't going into the plenum, no smell, starts fine, so I'm guessing there's a bad check valve in the pump and the fuel is just draining back into the tank. oh, hell. But, it shouldn't be a problem, pump primes just fine and the truck starts right up. It just means I can't really ever use fuel pressure to verify a leak at the injector or intake.