Atlas

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.

Fully warm, coolant temp >194, closed loop. Run time can be anywhere from just reached operating temperature to having driven 30+ miles. The O2 chart (which is a feature I just discovered after reading) for the bad idle seems to be "most" of the time. For the little time I've been watching it (scanning and driving! watchout!) I can't seem to isolate any cause or condition yet. It definitely idles rougher sometimes than others and so far what I've seen is the rougher idles are always rich. But not enough to set a CEL. In other news I replaced the starter solenoid. Everything on this truck is such a PITA. Starter "snout" is mangled up with the torque converter inspection cover which is tangled up with hard cooling lines and the driveshaft. But I got 'er done without too much swearing...I just go into everything now knowing it's going to be a frustrating mess. The starter solenoid replacement kicks off the next round of work: AC, injector rebuild, cat, exhaust. I'm just going to do it all. But first: I don't know what my fuel pressures are. I can't definitively say the issue is the injector without first verifying fuel pressures and any leakdown. I "rented" a test kit ($199.99 at O'Really's ...intentional misspelling). They don't "rent" tools anymore, they charge you for the tool and then you return it when you're done. No joke. It is listed as a rental on the receipt but the guy told me there's no difference between renting and buying now, you just return it when you're done and they refund the credit card. Mmmkay, whatever. I will rule out fuel pressure issues (too much), and any leaking (that's how I'll know the problem is inside the intake). I think someone said the return line could be plugged or not flowing and that could cause high fuel pressure (and too much fuel being pushed through injectors). I'll cross that bridge if I get high readings. As of now I'm ready to tear off the intake cover, extract the injector, and have it sent off to be rebuilt just so I can rule that out.

So, do I go elbow-deep on this thing or list it for sale and play dumb? Seems to "runs good." I'm about $1200 away from having: -a rebuilt injector ($300) -a new cat ($250) -a new cat back exhaust (OE style) ($300) -a new AC compressor ($200) -AC refrigerant charge ($150) In theory, this should rectify the obvious detracting issues from its value and operability. Cold AC with a non-squeaking AC pulley both sounds and feels good. An exhaust that isn't cut/hacked in 17 different places and doesn't vibrate on a crossmember would make it sound and feel less janky. A working cat would help the stink, and will save the earth, but *if and only if* the fuel system is working properly, which would also address the intermittent "rich" CEL. Heard a good one... CEL for "Rich condition" means you haven't spent enough money on the truck lately, and it's letting you know. Rebuilding the injector would seem to be the most important part. Replacing the cat would be secondary. I don't think mine is plugged or overly restricted, but it might be a little restricted? I have no good way to tell other than seat of the pants feel. I hate the smell. The current theory is I have a rich idle problem: A bad fuel pressure regulator, or a leaking injector(s) being the highest probabilities. I already replaced the FPR but that doesn't mean its replacement isn't also bad. It was a new part from Dorman, but the packaging looked like it had been sitting on a shelf for 20 years. This is the (single) upstream O2 sensor shown at idle. I'm getting a lot of "rich" it seems. Sometimes it stays high like that and doesn't drop down. That makes me think it's processing injector leaks or a partially stuck open injector. Other times it looks like this. Nice oscillations between rich and lean, which is what I think it should be. Under load and at speed, the oscillations are nice and tight and uniform looking, high and low. Fuel trims suggest the PCM is compensating pretty hard at idle to pull fuel out. But it's not enough to trip a CEL. Something about slowing to a stop: brake vaccum booster, EGR, or the EVAP purge is delayed, or there's pooled fuel in the intake again that's draining into a cylinder is enough to set the CEL. Of course, in two days of driving, it hasn't set. I was hoping to actually look at the freeze-frame data when it sets. IAT is high because it's idling on an 83 degree day here.

I'm not sure I agree with "extreme" low speed, high torque sentiment here with regards to the prescribed use of low range. How about...whenever it's needed? A 2.72:1 transfer case and whatever differential gears these Silverados have (3.42's, maybe?) aren't producing "extremely" low crawl speeds. Or insanely high torque multiplication. Even with the 1st gear in these newer transmissions. But it does provide mechanical advantage and potentially better control at slower speeds. And with extra weight or towing, I think it adds mechanical sympathy for the truck as well. Plus, traction control and the other assists generally turn off when you shift into low range. Those aren't needed here, they'll work against you if you need wheel spin. In high range you'll need to figure out how to turn off the various modes those assists provide. Depending on the vehicle, those things don't all automatically turn off or turn completely off. While I agree that a farmer might have some great practical experience, a recommendation to "always" using one gear isn't very informed advice. If the farmer had said WHY and could explain the physics behind his prescriptive "always" I'd definitely listen. The way he's described here makes it sounds like he could either be uninformed or is telling everyone what worked for him, not necessarily that there could be a more advantageous way about things.

I'd have a hard time selling it like this, I think. The CEL is very occasional but I can imagine someone buying this thinking it's going to get them from A to B and then it gives them trouble a few days later. I still need to fix the starter...that's just embarrassing. The front oil weep/leak...well, it's an old vehicle. I'd fix that if it didn't literally involve dropping the front axle or unmounting the engine and lifting it up several inches for access. It can leak for now.

Any joy with this truck seems to be short-lived. The CEL for P0172 ("bank 1" too rich) is now "intermittent". I'm not sure where to check, or re-check, and my energy to keep chasing problems with junk is wearing thin. The P0172 seems to set as I'm coming to a stop, completely off the throttle, when fully warm. At least, that's what it's done the 3? times it's set. Everything appears normal on the scanner EXCEPT long term fuel trim. There's only one bank on this vehicle because it's an OBD 1.5 with only one upstream O2 sensor. At idle, it's around -16.4% and will dip to -18% occasionally at idle or off-throttle. LTFT approaches 0 when throttle is held at 2500rpm. Short term appears normal, much closer to zero all the time. The LTFT tells me the engine is running rich at idle but compensating at higher load. But, why? The EVAP purge valve doesn't appear to be leaking/sucking fuel vapor continuously. Is it sticking just as I come to a stop and the engine is choking on fuel vapor and sets the P0172? But that doesn't explain the persistently negative LTFT. Disconnecting the purge valve doesn't seem to make any difference. I suppose that leaves another dang issue with the fuel injector. A leaking fuel pressure regulator, a new leak in the spider, or a leaking fuel injector/poppet valve I didn't see, or a small crack in one of the spider legs. The vacuum line leading to the fuel pressure regulator doesn't have raw fuel in it. It doesn't even smell like fuel when it's pulled off, not until you suck air through it, then you can tell it leads to a fuel component. I'd consider that normal? Nothing is signaling this is a FPR issue from the outside, at least. The oil smells like fuel but it's not building volume. I've noticed most oil in most engines smells like fuel to some degree so it's hard to say if the smell is an issue or not. Or if the engine just still smells like fuel because the crankcase was full of it a few hundred miles ago. But it's been changed twice since that original issue of the leaking fuel line dumping fuel into the intake. Patience is running very thin. Every win seems to be accompanied by two steps backwards, or another issue that leads to removing at least the top half of the intake manifold. Enough! LOL

Give it a shot. Come back and tell us all about your visit.

The use of absolutes like "always" to describe gear selection, and giving free advice at a boat ramp sounds like a recipe for disaster. It's a boat ramp, not a farm, for starters. IMO gear selection should depend on the obstacle. If low range is working and this is a slower speed, controlled ordeal, I'd keep using that.