I used the Suburban today to tow somewhere, and on the way back through Glorieta Pass and later on the flat the engine sounded wrong (stuttering?), had poor power, and sometimes exhausted thin black smoke.
I followed up with both shops. Shop #1 say they read the codes off the computer, and told me the mechanic's name. I still have to talk to him, to find out what else he did in the 2 hours he looked at it. At Shop #2 I talked at length to the mechanic who did the work (not the guy who called to sell me a new engine). His findings:
The O2 sensor is detecting huge instantaneous fluctuations in the exhaust, from extremely rich to extremely lean and back again. This looks like oil is confusing the O2 sensor, which gives the TBI instructions to adjust the air/fuel mix. And there is a lot of soot in the tailpipes. So there may be some usage of engine oil, but when there is, it is being masked by excess fuel, hence when there is visible exhaust it is black (not blue).
Compression test finds poor compression and suggests rings are bad:
Left Right dry wet dry wet
119 142 129 149 Front
123 139 131 151
127 141 131 144
127 141 131 149 Rear
The replacement engine Shop #2 recommends is a factory new engine, not a rebuilt one, plus several other factory new parts, to qualify for a 50,000 mile warranty on the engine. Reason to get a factory new engine: 454 being particularly difficult to rebuild well.
Prior owners. The one we bought the Surburban from had not had it long. He is into NASCAR (Dale Erhart? #3 stickers on the windows) and had been messing with the Suburban for a couple of years. DH found the engine(?) thermostat was not present, causing the cooling system to work overtime and the engine not to reach normal running temperature. The seller probably used the Suburban mostly to commute to work, maybe
5 miles each way. There was mention of towing a trailer, but I doubt he towed much because the trailer brake controller that was installed did not work right. When we bought it, the odometer was NAM; the seller asserted the true mileage was 130,000, but he also bought it NAM, so he doesn't know. It could be 230,000. I can't say which, from the condition.
The owner before that had the Sub repainted, from red to white. Looking at the panels, including the insides, there is some evidence of collisions in two places, prior to the paint job. But both collisions were minor. The R front fender is a replacement; its original color was white, not red. But the R door, front bumper, grill and lights all are original. The R rear fender has a dent under the bumper and the rear bumper is a replacement, but the gate etc. are original. Otherwise, the body is in really good condition. According to the guy who sold the Sub to me, this owner bought it as a fix-up project but didn't do much more than repaint it. I know nothing about who owned it in the ~13 years before that.
The interior is all original; the front bench seat now has holes in the upholstery under the driver, but is otherwise good. We plan to upgrade to bucket seats anyway; bench seats are a whiplash hazard in a crash. The headliner is separating from its backing, and the plastic sleeves on the seatbelts are mostly dead. The dash is sun-cracked (most older vehicles in New Mexico have this damage). The rest is fine.
Okay, I have many new things to investigate, but cannot get to them for a few days.
Una