Couple of thoughts/Questions after having read thru this thread...

1) Besides the black smoke @ WOT the car runs fine?

All the MAF and or MAP (VE) sensors are doing is measuring airflow. These measurements are only measurements. The tuner is going to take information from a wideband O2 and calibrate your MAF and or MAP tables in the tune. The GM Tech II is not going to be able to "see" or change the information in the tuning tables. The stock diagnostic settings in your pcm require multiple failures on subsequent drive cycles in order for the MAF to be in hard failure mode, aka speed density mode (SD) which will set a code-note, most tuners will just turn off the light but, THE CODE HAS TO BE PRESENT. SD operation uses only the MAP sensor for airflow measurement and VE table for proportional fueling. Not all tuners/shops perform calibration on both the MAF and VE tables. If your car is truly in SD operation you will have this code even if you don't have a dashlight-you can go by any autoparts store and use a simple code reader to verify this. The 98 Fbody has a backup VE table for when the MAF goes into hard failure mode. This table has half the resolution of the main VE table-If your car was never tuned in SD (VE table) there should be a very noticeable difference in drivability with the setup you have listed in your signature.

If I were you and I had limited access (time) or funds to a tuning shop for a diagnostic I would start with the mechanical things I could check myself.

PCV system, describe the condition and what style and or mods to it?
Original valve seals from the mods you did in the past?
If you pull the lid off and look down the TB in the intake how does it look down there?

Just a few thoughts,

Doc

 

Hey Doc, since he unplugged his MAF 3 years ago, his tune is soley relying on his VE table,correct? If his VE fueling is not correct then over the 3 year time frame, this could have lead to his blow by per say due to washed out cylinder rings due to being so rich it accumalates the residue on the bumper. I agree he needs to get a tuner to look at his tune to see what is going on.

 

Well, since he isn't getting a check engine light, the dummy tuner must have disabled the codes too, that was nice.

 

Hard to say without knowing what codes if any, are set now. He did say that it runs ok to some extent. With that setup there are only a couple of possibilities...

1) Somebody tuned it w/ HPT's 98 Custom OS to get around the resolution reduction of the stock 98 backup VE table.

2) Somebody spent a lot of time interpolating (filling in) data logged from the backup table and put together (trial and error) a solid enough table for it to run like was described-maybe I'm not getting the whole picture but, 3 years?

It is not cost effective for me to do option #2 and I would prefer realtime capability-so I would have just swapped the pcm for a 99+up setup.

Tunes don't change....car parts wear out/fail.

 

I wish I had a dime for everytime a customer's car was "running rich" or (my fav) "dumping fuel"... and the wideband showed them to be LEAN!

Soot on the bumper and the customer's nose are in fact not a very reliable source of feedback for tuning The soot can be from overly lazy O2's at idle (which begin to switch fine by 1400 or so!).

 

"hunter".....A few years ago I just unplugged my MAF and noticed that there was no change, and no SES light. I did plug it back in. So its been plugged in for the past 3 years.
But before that, from 2002 to about mid 2006 the engine ran perfect, burnt no oil and didn't get any black soot on the bumper. In about mid 2006 is when I noticed some soot and began to wonder what was up.

"DOC"....My SES does work. It has come on before for other things. The last time it came on was about 1 month ago after a very hard run on the highway, but it went off about 5 minutes after I slowed down. I checked it for codes the next day and it was clear. Its also clear now. Even if I unplug my MAF the SES light stays OUT and no codes appear. I tried that brand new MAF last week after resetting the PCM and nothing changed. It ran the same. So I returned it.
Maybe my PCM is partially fried and thats why its not recognizeing the new MAF....???

"Frost"......Its pure black, thats all I can say. Really doesn't smell any different then regular exhaust.
For the first 4-5 years it ran perfect, no smells, no soot, no nothing. RPM's didn't hunt on warm up like it has for the past 3 years or so. Also, even after it settles and I can drive away....then I shut it off for say 10-20 minutes and come back out when its still warm it will hunt all over again before it settles again so I can drive off. Also, even if its all the way warmed up...if I shut it off and immediately restart it, almost always it will hunt all over again for about a minute before it settles. 2 new 02 sensors were put in in January because one failed. No change, everything stayed exactly the same after they went in.

Its crazy........

Maybe some vids of the idle surging will help you figure it out....

.

 

There are too many posibilities that it could be without seeing the tune in the car. For all we know the o2's are turned off as well. It seems just from what you have described that the MAF is most defineately turned off, which is pretty shady of the tuner aspecially since they sold you a MAF sensor your not even using! It sounds to me like it is running a 98 2bar SD OS that has the MAP sensor recalibrated for the stock 1bar MAP sensor and the MAF sensor is turned off completely. Otherwise even if the MAF was failed out it would still show the codes on a OBDII reader unless they made the MAF "no error reported".

So basically you need to have someone pull the tune out with HPTuners and post the file up. That is the only way you will get defineate answers.

 

Yup, ok, well thanks to you and everyone else. I'll get that done and post it up.

I do know the front 02's are working because back sometime in 2006 I had one of my factory 02 sensors from 1998 finally fail, so I replaced that and the car instantly ran perfect again. I just put one in and left the other original 1998 one on the other side in there. Then again in January 2009 (12 months ago) that one started to fail and the engine was running like hell again. Bought two new Densos and the engine ran perfect again. The two rears are tuned out/deleted.

.

 

So, here's a video of a start after it has warmed up. I stopped to get gas for about 5 minutes. Started it back up and you can see how the rpm's start jumping around, then a short drive home. You can see how it drives fine once I take off. And then after I pull into the driveway it idles fine and runs normal. Only if I shut it down, then restart it does it hunt again for a little bit, then its fine.
(after I shut the engine off thats the end of the video, I forgot to turn the camera off)

link good for 7 days: big *** file, had to use yousendit.
https://www.yousendit.com/download/S...cG84Q1NGa1E9PQ

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The idle hunting is part of the tune and the only way to fix it is to tune the idle. Alot of places don't take the time to pay attension to details like idle parameters and driveability.

 

But remember, it never did that for the first 4-5 years. The engine was 100% picture perfect since the day I picked it up till about 4-5 years in when this wierd stuff started and the MAF was left out of the loop and my bumper started tuirning black.

Strange. I'll get it checked soon.

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Hello LS6427,

Some thoughts here for you.
When un-plugging a maf-sensor the car as agreed, goes into back-up mode (SD).
It then runs from the PCM Low Octane table. Normally because of the different ignition advance values between the two tables (Hi & Lo) anyone should notice the difference in response and behaviour on the road.

If you aren't it either means you may have concrete sox (!) or the two tables in your PCM are identical; which is more likely.
Some tuners do this, copy and paste the Hi Octane Table into the Lo Octane table.
Trying different maf-sensors won't necessarily show an obvious change as the PCM has a Maf-sensor calibration table that is set at the time it was tuned and any maf connected will reference to that.
Regardless of this, even in SD mode the fuel trims will work as you could assume they weren't dis-abled when it was tuned and there's no reason they should have been if it was maf-tuned.
Also even if the VE table had been adjusted (richer) once you are at the Closed Loop Operating Temp, the car will, when cruising maintain 14.7:1 as you mentioned they were operating okay (with the trims working at a high negative value probably).

Which means the smoke may only be from the time it is in Open Loop and using the OL table as reference & with the LT trims being at the negative value mentioned. As during warm-up to CL they have not started to adjust yet. This period would be from actual start to around five minutes after.
The mention of your rpm jumping around could be the rich symptoms described. The Commanded Fuel When In Open Loop table also being set rich.

But,
There could also be an oil consumption issue; I don't remember reading if you mentioned how much oil you are using(?)
Though 100k plus shouldn't be an issue if it's had regular changes. As you mention it didn't use much oil for the first 4-5 years(?)

There may also be a fuel injector issue; they may need a clean if they have done high miles, or it's possible the IFR tables aren't quite right.

Just some ideas as food for thought.

 

WHAT!!!!!

Just kidding thanks for the detailed info. I'm thinking I have a ton of blow-by with 130,000+ miles. I was talking to my builder on Thursday about it all and he says I'm wasting my time trying to fix a tuning issue with so many miles on a 4.125" stroke with these old "short" LS1 sleeves. He thinks my cylinders are way out of round at this point. I would just expect white/bluish colored oil smoke when I go WOT instead of pure black from being rich. Since it runs so good otherwise, I'm just gonna ride it out till I build something new.

Thanks.

.

 

You got 130k on a stroker! In my 5.0 days I was considering doing a 347 my engine builder told me if I was easy on it and took care of it, it might go 15k!

 

Yup, 132K. I guess I should just be grateful and rebuild it or build a new one when I'm ready. But this thing is nowhere near ready to quit. I think I'm gonna pull it, bore it further to 4.125" and have a 441ci. Then buy some LS7 heads, LS7 intake, new 4.125" pistons, new bearings and gaskets and slap it back together.

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Has 130k miles and was tuned in 2002 -which the only tuning software was LS1 Edit and the cars been driving good this long? I'd say don't even mess with the tune at all.

I'd say your problem is valve seals and worn out valve guides from the mileage ussing that Cam.

 

Heads were completely rebuilt in 2006. I'd assume I'd get a nice trail of white/blue smoke when I went WOT if it was valve seals though, right?

.

 

It is possible to have blow by which will show signs in the PCV system. You won't necessarily get oil smoke (blue smoke) with weak rings. But what you will get with weak rings is less compression which starts messing with your airflow. If the car is tuned SD which from what you have said it really seems to be the case and the rings arent sealing as good as they used to due to them being weak then it is very possible for it to be richening itself up. SD tunes are based on calculating airflow via VE (volumetric efficiency) which takes your RPM and MAP readings and looks up the VE on a table. When the engine was first tuned it was new and was sealed up great which netted the VE that is in the tune. It's possible the motor isn't pulling in as much air because the rings are allowing pressure by the rings which in turn has effectively lowered the airflow or the VE because the engine isn't pulling in as much air as it used to. The PCM doesnt know that because it's calculating the airflow by a set VE table in the tune that was created when it was fresh.

I don't know if this is your case but it's just a thought to elaborate on. I've not ever kept a car or a motor long enough to know from experience if this happens or not.

 

I think you're right, lotsa blow-by simply because the sucker has 130,000+ miles and a long stroke (4.125") in the old style short LS1 sleeves.

I can't ask for better longevity than that out of a forged 427ci at almost 500 RWHP. I've got a new engine in the works anyway, since it runs great still I'll just keep driving it and not mess with it.

Thanks for all the input....by everyone.

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