My 87 Chevy Suburban R20 (3/4 ton with all factory towing extras,
gas 454 aka 7.3 L, TBI) has several perplexing engine problems.
I have read in the newsgroup archives, but my head is spinning,
so I need more direct help.
My husband does most of the maintenance on this vehicle, but can't
stand idiot mechanics. So I do that. I have tried to find a good
mechanic (recommendations from other large vehicle owners, etc.),
but so far no luck. In fact, I am getting really bad service (do
they all think women are fair game?) I am in Santa Fe New Mexico.
This vehicle travels at or above 7000 feet altitude, and usually
tows 3500-4000 lbs of horse trailer plus horse and gear.
I bought the vehicle 10 months ago, and have put on 3,000 miles.
Its 5-digit odometer showed 33,000 miles, and the previous owner
(who had it several years and IIRC put on 20,000) asserted it
was 133,000, so my title reads Not Actual Mileage. No idea if
the true mileage is 133,000 or 233,000; wear and tear for an '87
suggests the former. I don't care which; the body has ~0 rust
and is otherwise in very good condition, apart from the usual
deferred minor maintenance. It always starts easily; never
stalls, hesitates or surges. Automatic transmission, replaced
with a rebuilt by the previous owner, shifts well. Now that we
installed a locking gas cap (!), it gets about 7.5 mpg, mostly
towing in mountains at highway speeds. We bought service manuals,
including wiring manual, and DH reads them. Among much other
maintenance, in that 10 months/3,000 miles DH (sometimes with me
helping) has personally:
replaced air filter
replaced PCV valve
changed engine oil and filter (2x)
added 1 quart oil (down 1 quart 1,000 miles after last oil change)
changed transmission oil
flushed cooling system
replaced oxygen sensor (twice)
replaced fuel filter (twice; second time by idiot mechanics)
replaced spark plugs (twice)
replaced spark plug wires (twice; first new set broke a wire!)
replaced distributor rotor and cap
replaced fuel pump and strainer
replaced exhaust manifold gaskets and seals
replaced speedometer (changed to a 6-digit odometer)
Now the problems
1. The speedometer and odometer both are inaccurate, by the same
amount. At 40mph the meter reads 30mph; at 80mph it reads 40mph.
Replacing the speedometer did not fix the problem. Is there a
gear involved? How can I change it for the correct gear? This
is an old problem. (And it means gas mileage is actually about
9mpg, not bad for a tow vehicle!)
2. The vehicle occasionally, nearing the crest of a long, steep
hill, puts out some black exhaust *and/or* begins to lose power.
Not nearly as much as diesel trucks the same size produce on a
regular basis. I don't know if it normally has full power; it
has enough that it can tow a trailer and keep up with traffic,
but I have not driven any comparable vehicle at highway speeds.
I think the black exhaust is tapering off, too; didn't see any
on my last long trip. DH says the exhaust is rich (raw fuel),
but his experience with the vehicle is limited to maintenance
work, so it would be soon after starting the engine. I read the
exhaust is supposed to be rich then. The 1st set of new spark
plugs, in service only 500 miles, were gunked. Engine oil does
not smell of gasoline, and looks okay. This is probably an old
3. The Service Engine Soon light comes on within a few minutes
of starting the engine, and mostly stays on. It sometimes goes
off during trips, usually *after*
climbing a steep hill. On my
last trip, 4 hours each way, the light stayed off several hours
at a time. DH used a paperclip to read the codes; the only
code it gives indicates the O2 sensor complains of a lean mix.
Changing the sensor the first time *may*
have improved mileage,
but hard to say, given that someone may have sucked small
quantities of gas before the night they sucked 6 gallons (when I
started the engine the next morning, the fuel guage *dropped*
This is an old problem.
4. Engine oil is now dripping from the back of the engine,
where it joins the transmission. I think the leak had been slow,
and has recently gotten faster. Up to a week or so ago, there
never was an oil stain under the vehicle (probably the leak is
worse when traveling), but now there is a fresh stain. This may
be a new problem. This might account for the missing 1 quart,
in which case it isn't going through the engine (yay!).
I have now taken the vehicle to 2 mechanics to diagnose the SES
code. Shop #1 charged me for 2 hours of diagnostics and changed
the fuel filter. No other information! The guy at the counter
didn't know who did the work, or what the findings were.
Shop #2, which has the vehicle now, will charge me for 2 hours
diagnostics, and I got a phonecall from the mechanic. He said
the compression test showed low pressure in *some*
My Q: which ones? His A: well, all of them really. My Q: how
about the valve seals and guides? His A: they're okay. And the
problem is the rings (how does he know?), and he recommends I
get a new (not rebuilt) engine. He'll do it for me for $6,000.
This same guy took my service request at the counter and when
I said the vehicle has 135,000+ miles on it he said "well
there's your problem right there; old engine". So perhaps he
thinks diagnostics are a waste of time; he already knows the
So...what kind of information should I get for 2hr diagnostics?
Do I need another engine? If so, do I need a new one? I plan
to keep this vehicle "forever", but even so it is 17 years old.
I have tried to disentangle these problems, but problems 2-4
may all be related. How can I tell? I guess we should fix
problem 4 first, and see if I miss any more oil. And get the
numbers from the compression test(s). About the O2 sensor;
should we replace the catalytic converter?