That's what the mechanic said. But, here are the numbers:
We have now located discussion of compression testing in *3* Chevy maintenance manuals. They all say the same thing: don't worry about bad piston rings until the dry numbers are less than 70% of the wet numbers. These numbers are 84% or better.
Manuals also say the nominal compression in this engine (454) is 150.
Una
I had a similar problem (instantaneous rich and lean conditions) and after trying to find the problem myself, I took it to a garage. The first and second garages couldn't locate the problem so I finally took it to the dealer. It took the mechanic exactly 30 minuts to pinpoint the problem - a worn shaft on the TBI. It seems that the wear in the shaft (or housing) was allowing the TPS to be thrown out of kelter for short periods of time, screwing up the computer. You might want to check on this.
****************************************** I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it. ~ Thomas Jefferson ~"Una" wrote
And this is a problem, technicians not really knowing what "normal" specs are, and often attempting to use compression numbers to sell engines. Sad thing is that you probably would have the same problem with the new engine. In my opinion, wet and dry compression readings are not a good way of diagnosing cylinder and ring problems. Leakdown testing is probably the best, but even then....I usually use these methods to just confirm that 'yes'.....that cylinder is dead.
Even the dry readings that you have...as long as the highest and lowest cylinder are within 25% of each other, it's considered fairly normal.
Ian
This is an interim update. We still haven't solved all problems, but I think we are much closer to doing so. Some problems we discovered were due to spark plug wires. The first replacement set DH installed melted (a big block engine will do that, if you don't know to buy wires that will hold up to the heat). Then, the second "idiot mechanic" who looked at the engine neglected to re-attach one spark plug wire. I knew the engine was "off" when I got it back but I did not see why; DH saw the unattached wire as soon as I got the truck home from the shop.
Taking the throttle body apart, DH found extreme wear, to the point that the valves tended to stick and when closed could not prevent flow. That alone could explain most problems with the engine, and also explained the chronically "sticky" gas pedal. DH replaced the TB core and all gazillion gaskets; soon after, the truck started to stall when coming to a stop or near stop, and would not start again easily. Taking the TB apart again, we found the new gaskets were leaking. So, DH installed a second new set of gaskets. Now, for the first time since we bought the truck one year ago, the engine runs very smooth and idles slow. The service engine soon (SES) light still comes on as soon as the engine reaches normal running temperature, but now that may be due to a fouled O2 sensor. (The only code ever pulled off the computer is the 02 sensor complaining about a lean fuel mix; reading the sensor directly shows it was seeing alternately too rich and too lean fuel mixes, that mix way out of whack.) The current sensor is only a few months old, but the constant fuel flooding from the worn-out TB may have fouled it already. So, the next step is a new O2 sensor. If that doesn't do it, then a visit to a good (non-idiot) mechanic with diagnostic equipment to monitor readouts while the engine runs.
By the way, we also discovered that a previous owner removed the engine thermostat, which DH promptly replaced, grumbling about "yahoos". When we first bought the truck, the engine could not reach its normal running temperature; the missing thermostat was the reason why. Did some idiot remove it in an attempt to "fix" the chronic SES light and "lean fuel mix" error code from the O2 sensor?
Old problems remaining from September:
New problem:
[...]
That's a code 44, FWIW.
I guess it was more than they wanted or were able to take on, but they chose not to say so. Because they were not up front with me, they will get no more of my business.
This shop at least took a stab at the problem but they did not get far with it. Instead they tried swap-parts-until-it-goes- away, beginning with just about the most expensive part. Pass.
More than a year later, I found Shop #3, and Shop #3 fixed the SES code 44. A previous owner had the transmission replaced, in which job the wiring harness got pinched. So the computer was getting garbage data from the O2 sensor. The fix: patch the wiring harness. Cost: $180.
Of course, to *find* the source of the problem took hours of work, during which many other problems were found and fixed (mostly leaks: vacuum lines, gaskets, fuel injector), so the total cost came to $1800, but that is money well spent! Shop #3's compression test showed a nominal 140 (outstanding!) on all cylinders. So I don't need that $6,000 new engine block.
This truck suffers rubber rot (no surprise given its age and the climate here in New Mexico) so a lot of money is going into replacing the gazillion hoses and tubes under the hood, as well as all door seals...and the tires...and and and. But still it is a good deal, financially. New, a 3/4 ton Suburban with the functional extras this one has would cost $40,000. And because depreciation has run its course, I feel comfortable driving it where few people would risk driving an expensive newer truck.
Una
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