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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. -
An ultra wealthy man had the most beautiful daughter. But, there was a problem. Everything she touched would melt in her hands. No matter what, Metal, Wood, Stone. Anything she touched would melt. She could not feed herself. Because of this, men were afraid of her. Nobody would dare marry her. Her father was despaired. What could he do to help his daughter? He consulted doctors, scientists and anybody who could solve this problem. Finally one of them said, "If your daughter touches one thing that does not melt in her hands, she will be cured." He was overjoyed and came up with a plan. The next day, he held a competition. Any man who could bring his daughter an object that would not melt in her hands would be given billions of dollars to marry her. Three extremely intelligent and handsome young men took up the challenge. The first brought a very heavy steel rod, But alas, when the she touched it, it completely melted in a matter of seconds. He sadly went away. The second brought a beautiful diamond, knowing diamonds were one of the hardest substance in the world and would not melt. But alas, once she held it in her hand, it melted. He too was sent away disappointed. So now, there was one left He was very nervous & sweating. He approached the daughter & said, “put your hand in my pants pocket and feel what is in there." She did exactly what he asked. She felt something very hard. She held it in her hand, squeezing it as hard as she could. It did not melt & remained extremely hard. Her father was overjoyed. Everybody was overjoyed. She was finally cured. Nothing never, ever melted in her hand again. They married and they both lived happily ever after, raising a wonderful family. Question: What was in the the groom’s pants pocket??? Answer below ↓ M&Ms of course! They melt in your mouth, not in your hand. What on earth were you thinking? -
By asilverblazer · Posted
There's a bunch of tea leaves that you've read, but in any case the delayed timing is unusual. Not sure how that relates to the rich at idle vs. 'normal' while driving. If you're in this deep, might be worth investigating, and re-learning the sensor. What have you got to lose? Plus, it properly fixes the timing cover leak. -
By asilverblazer · Posted
The only problem I have seen this cause is longer crank times. -
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.
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