what size does your door plate say came on the truck and what size is on it now? on my pickup I went from 245/75R16 to 265/75R16, the resulting error was 1 MPH per 20 MPH.
yep
Once a cat is dead, it's dead. being 16 years old doesn't help it either. it will be between the Y pipe and the muffler. it should be the same size more or less than the muffler.
You have an 87 Suburban with a 454. The plugs are sooting up. The ECM is storing lean codes.
IIRC, that engine uses at least one, possibly two air pumps.
If the air pump switching valve(s) are malfunctioning and dumping air (raw O2) into the exhaust manifold when they shouldn't be (closed loop), you'll experience exactly what you're describing. Over fueled to the point where the piston rings no longer seat and the oil becomes so dilluted that the seals begin leaking...
I've seen this many times.
I've seen mechanics tripped up by it many times also.
valve....read it carefully. That problem will make it run rich and it thinks its lean.(Not all emission configs are capable of this problem, only if it has the air injection on the same side as the O2. A bad O2 will cause the CEL to come on, following your simptoms closely.Being that you replaced it twice already, maybe there is something else wrong......Burning enough oil to kill the O2 in a short time maybe? Is the smoke gray? gray=oil black=gas. Dont forget the MAP. check its vacuum source carefully... GL P.S. you really need a good tech to look at it in my opinion..... Ask around....
After reading the replies to your questions. I have some points to ask. Do you know if the ECM has been replaced? The spedo cal is in the ECM ( I think for 87) It sounds like the prev owner changed the ECM to try to fix the MIL condition. Just a thought. get the numbers off the top of the ECM and check it. You may have a bad ground connection somewhere, or just a bad connection. O2 sensors last a while. Oil leak , rear seal. Not really a big deal. With 135k on it, do you know what use the prior owner subjected it to? Heavy towing? stop and go? If it was a heavy service then I'd opt for a New power plant, (maybe trans too) if the Body, interior, and under carraige are in very good shape. Was it ever in an accident?
I'm assuming you mean that at 80 it reads 60, not 40
anyway, the speedometer drive and driven gears can be changed to fix this
you will need to remove driveshaft and take off tail housing to see what gears you have (tooth counts)
let me know what you have, I'll send you the proper ones
at 7000 ft, I've seen a lot of tow vehicles do this, especially up a long grade
the ECM is basing fuel rate on your starting altitude, and as you climb, the mixture becomes richer because the air thins out (3% per 1000 ft)
I see you've changed the O2 sensor twice. get the fuel pressure checked, make sure it's in specification
rear seal needs replaced, which will necessitate dropping transmission
lots of engines are going strong at 135k
these 'mechanics' sound like parts changers to me
your check engine light should be out and stay out (if you authorize the work recommended)
you should be informed what was done (or needs to be done) to get to that point
pay via credit card, if it doesn't pan out, call the c c company and dispute the charge
listen: if it tows 3 k at 7000 ft, it's pretty damned healthy in my book
check fuel pressure
get actual compression figures
oil is cheap, a quart in 1000 miles is not too bad, just keep it full
you cat converter is probably OK, if it runs like you said it does.......... as I recall these have 2 converters, and I've seen the rear one plug up on a couple Sub's.........but it was totally gutless when it did
Whats IIRC mean? The engine itself is essentially an air pump. In fact, thats really all it is if you want to reduce it to its simplest form so it can be repaird. I guess no one wants to, but they'd be a lot better off than applying theoretical rocket science with the all too often dubious, undocumented results, any where evident but for the bank account.
Maybe, maybe not, but I know they have learned to take an abstract level, stroke it, milk it, and bilk it while they wing it, mostly because our ego won't let, or can't let, or don't and won't admit its just junk and we can't accept that. Thereby giving us a new understanding.
The only practical level is to start at the center and work your way out. Not around the outside going in. That would be like patching a bicycle tire, torquing the spokes painstakingly one by one, and expecting all that to fix the burnt out bearing at the center.
Well, you wouldn't have been to two shops if there wasn't a limited supply knowlegde about what to do at one of them at least would you? I don't know whether you read my other posts or not, but as I said, I spent thousands going around the outside of my motor, and listening to every other mechanic call the next a liar. Some one told me they are the least trusted, most complained about profession there is. I always thought that was lawyers, but I could always be wrong.
But not for an 88? There is no speedo cal in my 88. They tell me that didn't come till digital speedos and nothing in those 88 ECM's concerning those driven by a chain of mechanical gearing, cables and the use of magnets in the speedo at the dash to translate the vehicle speed for your eyes.
I wasnt sure, and your correct. It a cable driven speedo. Perhaps the previous owner had a junk yard tranny put in and never put the right speedo gear in.
Ya see, since I'm not looking at this particular vehicle, I have to go off of memory. Being from Wisconsin and winters being what they are here with road salt, most of these shit boxes went to the boneyard years ago.
Duh. Would A.I.R (air injection reactor) have been clearer to you? (doubt it)
That's deep, very, very deep.
Was there theoretical rocket science in my reply? On air pump equiped engines, the air from the pump is diverted to the exhaust manifolds (exhaust ports actually) during cold engine operation to assist in reducing the pollutants after a cold start-up. Once the engine is warmed up sufficiently, or in this case, goes into closed loop fuel control, the air from the air pump is diverted to either the catalytic convertor or to the air cleaner housing (to muffle). It's not a great feat of logic that air being pumped into the exhaust ahead of the O2 sensor(s) when it shouldn't be is going to create a false lean indication to the ECM and the resultant rich mixture command by the ECM.
The real beauty is that it costs absolutely nothing to check to see if this is the cause of the erratic engine operation. Simply disconnect the air pumps temporarily and test drive the vehicle to see if the condition (code 44 with sooted plugs) returns.
Hell I live in the Great White North, with copus amount of salt, and around here we oil spray every year to keep rust at bay. My 89 astro's body is as pristine as the day I bought it and it is now at 350,000 km with original tranny and motor and still running strong and burning no oil.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.