'87 Suburban, help diagnose engine problems (long)

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!)

  1. 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 problem.

  2. 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.

  1. 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* cylinders. 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 answer.

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?

Thanks,

Una

Reply to
Una
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Please follow-up to alt.trucks.chevy alone. Thanks.

Una

Reply to
Una

Una,

There are several mechanics that offer help to those who need it in this group. I am one of them.

One the other hand, I will not offer you any help. Why?,... because of the "idiot mechanic" remark.

You can take the suggestions of a novice, or you could get an honest response here from a mechanic. Which do you choose? I have been insulted. You won't get it from me.

My time is money, but not on this group. I like to solve problems. It's like a crossword puzzle to me. I log-on once a week to try and answer questions free of charge. Hmmm, ....I'm an idiot?

GMdude

P.S. Don't tell your mechanic that he is an idiot, he might just screw you on the repair bill.

Reply to
GMdude

No insult intended. And I do see your point! Some people would use "idiot mechanic" to mean "idiot = mechanic". I don't use it that way, and you may choose not to take it that way. I hope so.

I choose advice from a mechanic who is not an idiot. Same for a physician, or a lawyer, or any other specialist. You would too, I am sure.

FWIW, in my profession diagnosis is an important skill, and I am good at it. So I know I have twice requested, been charged for, and paid for a diagnosis...and not gotten any. (I paid because, well, I learned something. Too bad what I learned was to take my business somewhere else.)

Peace?

Una

Reply to
Una

i would recommend getting a print out of the diagnostics. you did pay for it. as for your speedo, did that occur after a tire change? (tire size affects speedometer accuracy)

black smoke out the pipes does indicate rich mixture which should show up in the diagnostics. i'm not sure if you said you already replaced the cat converter. in a rich mixture, sometimes the cat converter will overheat (i've seen them glow red).

Reply to
127.0.0.1

I would check the fuel pressure for the CEL problem. Might even throw a MAP sensor on it or at least check its vacuum supply carefully. If it has a speedo cable you can put a gear on it to adjust the readout. Does the speedo jump or anything wierd like that? Does it have a cable?Sorry for the top-post but I cant bring my tired finger to scroll anymore :)

Reply to
Scott M

To start with,, I would address the oil leak first. Since you've grown shy of mechanics or technicians, I would probably try an additive, I'm not generally in favor of them but with your situation I'd make an exeption just to determine what's up with the leak. I would start with something like Lucas since it's the only one I can think of that's everywhere & works. Wait for a week or so after you put it in to see how it's working. Before you do this step tho,, you should confirm that it is in fact, an engine oil leak, & not the trans. OK ?? Surely someone close to you could determine the difference. Let us know how you do on this step. I actually had really good success with this situation just recently, and in a BBC motor too, mine turned out to be a really dirty crankcase,,so maybe it's not gonna be all that bad. Cheer up & Good Luck Rich

Reply to
RGH

he, he

He he, there are some smart people in the world after all. I like the way you see it bud, gal, una. Send me an email and tell me what your diagnostic skills are if ever I need them.

Sure thing, Hatt

Reply to
DJ Hatt

Are you a mechanic? I thought it was a lean mixture is why I ask.

Hatt

Reply to
DJ Hatt

did i get it reversed? carbon buildup in the exhaust is caused by lean mixture? i'm not an engine diagnostic tech. (electrical/steering&suspension/brakes/AC/cooling, about 15 years ago)

Reply to
127.0.0.1

Timing must be adjusted for altitude. Which way? I don't remember, but I can tell you this. Get a good consensus before doing it. I know, I know, thats what you are trying to get. Good luck, I really don't think anyone knows anymore.

Might have to do that one twice more. Seriously though, you do have to get the correct one, and few know which one that is. If you find anyone let me know.

Yes, keep changing it until you get all the bad gas out of the tank, then go to Standard or Texaco only. If you can find one. These older vehicles will not run on the shit gas of today.

Be sure you get the right ones. Delco, same ones that were on it originally. Good luck finding someone who knows what they were.

Ouch!

88 were plastic gears in the transfer case, and changing them will not help if you have non standard tires.

Probably bad injectors, or the wiring to them, or the connections. This could be several things, but it was my problem.

I would say if it does this, you probably do not have a bad camshaft, but its worth investigation before spending all the money for stuff on the outside of the engine.

It will be back.

DH says the exhaust is rich (raw fuel),

If its TBI, look at the top of the injectors. is there any corrosion?

Yes, but not black smoke.

The 1st set of new spark

Yep, consider the cam shaft again, main bearings too.

So? lean mix, rich mix, you decide. It don't mean shit.

Its an old rig, why would you expect any difference? Its not going to be fixed by all the outside stuff you want to try.

Rear main seal.

I think the leak had been slow,

Find someone who is a reliable rebuilder, and not over 60. Good luck. Check long and hard on this. I mean very long and hard.

Typical

The guy at the counter

Typical

Ha, ha ha. Get a second and third opinion, and don't give them a dime, get an estimate, then decide.

My Q: how

Yep.

He's full of shit.

And the

He don't, but he knows you don't. Blue smoke would be rings cause its burning oil at startup. Now don't go and change to blue smoke from black just to placate me, or yourself.

and he recommends I

He recommends this, because with a new engine, you will get a reman engine. Maybe a 30 day warranty or 1,000 mile if you are lucky. If you can find someone who knows thier ass from a hole in the ground, and I doubt it, present company excluded unless you bad mouth me. IF, and I say IF you can find someone to rebuild it, using a rebuild kit from Sioux City, Ia., and knows their shit, you will get a 12 mo., 12,000 mile warranty at least.

He'll do it for me for $6,000.

Wow! Only 4K too much. not bad.

Yeah, don't you know, we through them away at 100K. Jeesh. Not cost effective, but it is in his case for 6K.

So perhaps he

Diagnostics are a waste of time in this business, unless you know your shit and he don't.

10 minutes worth of bullshit.

Probably.

If so, do I need a new one? I plan

Then spend the money, but not with this guy.

You can't really, unless you want to become your own auto mechanic. Which you may have to do if you expect to get what you want. Or pay the man, and get half that.

I guess we should fix

Umm, wait.

and see if I miss any more oil. And get the

Makes no difference unless compared to original specs.

About the O2 sensor;

Not yet, no. See if you can find a rebuild man, but get customer's who have used him before you decide to do so. I just went through all this very crap you are talking about, and I spent 4K before I got to the rebuild. Fixing shit on the outside will not fix the inside stuff, but who can do it? Its a dying art. Its not cost effective anymore. It will be in a year or two after deflation straigtens everything out again. You can get gas 350's for a dime a dozen now, gets some horsey's in it with a cam if you want. Now I don't know if this will swap in, w/the tranny but don't believe what everybody says on this either. Every mechanic I ever talked to in the last 20 years is a bullshit artist. You get the bullshit detectors out if you talk to enough of them. and they all accuse the other of lying. Unless perhaps they happen to work together, but even then its debateable. These guys have went by the wayside in our throwaway society.

Its just something to look into. You may not have to go with a 454, and get as much power, with better mileage. Depends on what you pull, our tranny, and lots of other things I don't yet know any thing about, etc..

Hatt

Reply to
DJ Hatt

because of

insulted.

problems. It's

answer

Gaurandamnteed! Cause now he knows someone else knows too?

Hatt

Reply to
DJ Hatt

Hi!

Got something to hide?

The OP didn't say "idiot = mechanic", as she has already mentioned to you! Quite honestly, there are people in this world who proclaim to be mechanics that I would not want within 10 miles of my vehicle. I am no expert, but I can tell when people don't have a clue as to what they are doing.

Conversely, there are many very good automotive mechanics in this world...and you may well be one of them...or you may not. I'm not a really good mechanic, but with my own vehicles I will sit down and learn about it or turn things over to someone more qualified before I really mess it up.

You have been insulted, huh? Why, if you're not an idiot mechanic is that the case?

It's Usenet, you'll learn fast how unwise that truly is.

The OP didn't say or mean that YOU specifically are an idiot, unless you happen to be one of her mechanics of choice.

Pay the bill first and do be polite, but do tell them what you think of their service. It is the only way you could reasonably expect an improvement in service if you come back.

William

Reply to
William R. Walsh

I will try to get one.

Tires and speedometer problems both came with the vehicle. The speedometer is off by about 20%, and I think the tires are larger than the standard. So they're wrong in a consistent manner (a larger tire would travel farther with each revolution than the speedometer is set to record per revolution), but the tires are not that big. Circumference = 2*pi*radius = pi*diameter, so if circumference were 20% larger, the radius and diameter would be too. 20% is 1/5 larger; that would be a huge tire.

Black = unburned fuel, blue = burned oil?

Not yet. Newsgroup archives tell me that's probably something we should do at this point. Would the catalytic converter be fried once, dead permanently; or intermittent? Is it above or below the O2 sensor, in the exhaust stream?

Una

Reply to
Una

As a matter of policy I don't complain about things people don't understand and/or cannot fix. And I think both shops are reasonably straight. I got recommendations for both from people who are picky customers. But clearly neither mechanic understands diagnosis on an abstract level, nor has learned engine diagnosis per se on a practical level. Also FWIW, we have had both shops do other work, so far mostly okay (Shop #1 put the wrong type of struts on my commuting car; DH re-did the job himself).

Una

Reply to
Una

Would an additive plug a leak large enough to produce a *drip*? Not sure I'd want that much gunk in the engine.

Does replacing the rear seal involve lifting the engine? (Wow, the things I don't know, that I never imagined I would want to know, but now I do.)

The transmission fluid (not oil, DH says) level is not dropping; the engine oil is. Does that answer the question, or do I need more information than this?

Una

Reply to
Una

DH and I discussed the lean/rich business at length, and this is the upshot. The error code indicates the O2 sensor reports a lean mix, i.e., too much O2. The exhaust smells rich, i.e., unburned gas. There are 2x2 = 4 possible combinations here:

Little O2 and all gas burned is the ideal, right?

Little O2 and unburned gas at the exhaust would mean there is too much gas going into the system but combustion is complete to the point the O2 is all used up.

Too much O2 and all gas burned means too little gas going into the system but combustion is complete.

Too much O2 and unburned gas (our situation) means combustion is not complete. The question is why?

Do I understand this lean/rich business correctly?

Wouldn't fouled spark plugs contribute to the poor combustion?

Una

Reply to
Una

I am a scientist, in a very esoteric specialty of no immediate use to anyone. But one of the immediately useful things I do is offer advice, particularly help with diagnosis of problems, on rec.equestrian.

Una

Reply to
Una

Will do that. If DH has already done that, we'll do it again. But...what would you expect to find, if fuel pressure is the problem? Low pressure, high pressure, erratic pressure, what?

The speedometer unit connects to a cable, which drives the gears which ratchet the digits on the odometer. Is that the cable you mean? The speedometer does not do anything strange, apart from understating the actual speed and distance traveled.

Scroll! How tedious. You might try a newsreader that has a smarter viewer, so you don't have to scroll.

Una

Reply to
Una

We did this with the vehicles we brought to New Mexico from sea level. That fixed the stalling problem my econo car was having.

But the Suburban we bought in New Mexico from a local. DH wrote in its service log "checked timing", but not what he found. We should write more down, so we can follow problems better. Looking back, I see I wrote several comments about the SES/CEL light going off now and then, going back to the first month we had it. Is that a good sign, when the light goes off?

Una wrote:

The correct O2 sensor!? Tell me more.

Next time, I'm going to take the filter apart and *see* what it pulled out of the gas.

Can't do much about brand of gas I use; choices are limited. Should I not be using the lowest octane at the pump, 86?

Hm...

This I helped with, and it was *days* of work but rather fun. It sure is nice to have room to move around under a vehicle. The gas tank is the 40 gallon model, a heavy sucker to drop and raise again. We did it together by hand with some jacks and other supports to assist.

There is no black smoke soon after starting the engine, only on occasion on long steep climbs.

Because there are some references in the newsgroup archives to a bad O2 sensor contributing to poor mileage. So, that doesn't apply in an old vehicle?

That's our take too. Does this call for a rebuild? Same Q I asked in another post; does fixing the rear main seal involve lifting the engine out of the vehicle?

DH has been researching the rebuild option. We're not against spending money; we just want the job done right. (So picky!)

Una

Reply to
Una

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