'98 3800 seriesII, P0171, scan data stream, what do you think?

[TexasJohn55]

idle after road test.pdfHey guys, I need some ideas. '98 Olds 88. Inspection time, light comes on randomly, runs great and good mileage. I ran live data scan after clearing code, not driven enough afterward to reset Readiness states. First file is at hot idle, second and third files are with throttle cracked open a little, in driveway. I don't know how to arrange them side by side for easier reading. I am going to set it to trigger a snapshot when the code sets and get that data on here also. I am using a hand held scanner and that is all the info that it displays to monitor. If you have time to look at data and give suggestions,, I appreciate it. Thanks

By the way, my friends '95 that was missing.......I put inline spark flasher on wires and coil was bad for #2 and 5, #5 showed random miss and 2 fired a few times and quit, plugs showed that also by color,new coil fixed it right up. TexasJohnSteady fast idle.pdf

Well I just drove it to get snapshot by DTC trigger, of course it won't set code now. It did 3 times and I would reset it. Now when I need to, it won't set. So I recorded data under steady driving conditions,and 02 monitor test at idle.

Steady fast idle 2.pdf

Hot idle data.pdf

data at 50mph.pdf

on board monitor test.pdf

02 monitor test.pdf

Edited June 4, 2013 by TexasJohn55 (see edit history)

[Guest Mc_Reatta]

What are the two tests it fails in file #1, IDs 0C and 0D near the end?

IAT temps 100 F or greater are way high but not sure it's a problem.

[padgett]

I see 130-140F IAT after a hot soak all of the time. Drops fast on WOT.

P0171 seems to be either the O2 sensor or the MAF.

[TexasJohn55]

What are the two tests it fails in file #1, IDs 0C and 0D near the end?

IAT temps 100 F or greater are way high but not sure it's a problem.

I don't have a clue, my scanner book says that stuff is identified by the OEM. My IAT reads ambient on cold engine.

[TexasJohn55]

I see 130-140F IAT after a hot soak all of the time. Drops fast on WOT.

P0171 seems to be either the O2 sensor or the MAF.

Glad you brought that up about the MAF, I was removing the intake boot off the throttle body one day and punched the airstream honeycomb. The sensor was not damaged, just a small area of the honeycomb. Problem of setting P0171 does seem to have become more of a problem since that incident. John

EDIT: The only pattern I can see while monitoring is that the STFT approaches maximum, 25% at times on base idle but trim % decreases as rpm is increased. Seems to be most prevalent at idle, returning to normal trim numbers while driving. Setting code today was predictable, came back every time on startup or idling after clearing with scanner. NOW it won't ???????? Probably will set as soon as wife drives it tomorrow.

Edited June 4, 2013 by TexasJohn55 (see edit history)

[Guest crazytrain2]

John,

Link to a good write up on how the MAF could be the underlying cause of your P0171 DTC. Sometimes you can tap on it with the butt end of a screwdriver and if it causes engine to stumble then it's bad. Not 100% accurate test though (as I recently found out ...lol)

Understanding Mass Air Flow Issues: Counterman

[TexasJohn55]

I tried to upload copy of my scanner manual, failed. It says the 02 monitor test retrieves info previously stored by ECM. The Onboard monitor test was vague as whether it was on demand or not.

[TexasJohn55]

crazytrain2, That is a good article, Thank You.

[TexasJohn55]

Thanks guys, I believe you have me pointed the right direction. If you see anything else in the data, please let me know. I'm gonna revisit that MAF. John

[TexasJohn55]

cruise at 65 scan.pdf UPDATE: Light wouldn't come back on today, drove it 40 mi round trip to Dallas with scanner ready to trigger, no light. So I checked Readiness Monitors, Evap and Calalyst still not ready but it passes emissions inspection. What are the parameters for Catalyst Monitor to reset? No hurry now, got a sticker on it. The data at cruise looks good to me, whattaya think?

[Guest crazytrain2]

John,

From my vast (half vast is more like it..lol) experience with MAF sensors going bad (I'm now on my 4th one). If you supect it might be going bad it may not be a bad idea to pick one up from someone here, through Ebay or at a junk yard. They seem to be able to sneak up on you and Bam, next thing you know engine is bucking like a bronco on the highway. If you have to buy it at a FLAPS you end up paying for it AND a new throttle body, typically>$125. If you get just the MAF you're probably <$40. Part number should be molded into the face of the sensor just above where the plug is probably something like AFH50M-03A. I'll appologize in advance if your series II MAF is altogether different, I'm assuming it's consistent with the (pre)series I. Also another link below for wide variety of DIY engine diagnostics (including GM 3.8L series II MAF test) BTW-gotta love your emphasis on Pontiac with 8-track!........lol

http://troubleshootmyvehicle.com/

Edited June 4, 2013 by crazytrain2
forgot to insert link (see edit history)

[TexasJohn55]

ct2, My concern is with the honeycomb upsetting the airstream, it is not integral to the sensor but does not look to be replaceable in the airhorn, MAF is in the airstream behind it. Yeah I'm a junkyard fan, would go there first. Car is currently running w/no light on. It has always run good, no stumble or anything with good mpg, 27-28 on highway at 70-75. Can't complain, I have another year to deal with it if it becomes a nuisance. John

[KDirk]

Honeycomb can be removed, it is held in with a snap ring (well, at least on the 88 and 91 Reattas it is) so if you find a throttle body at the junk yard you could use just the honeycomb from it if you want to keep your existing throttle body for some reason. I removed the one on my 88 to clean a lot of carbon out of the throttle body without getting it all over the honeycomb filter.

KDirk

[DAVES89]

'89 and '90 Honeycomb held in that way as well. Simple to remove, I didn't even use a snap ring pliers. I also remove the MAF sensor and then clean the throttle body w/carb cleaner, reinstall the MAF sensor and honeycomb.

[TexasJohn55]

Well it has been a year and time for inspection sticker. Car has been running flawlessly and still gets good mileage. Random P0171 didn't bother me, knowing it was running lean at idle and short term fuel trim at near zero while at speed so I never replaced any components last year.

I have been doing some more data stream study. Snapshot of code indicates it sets at idle with high fuel trim numbers. Monitoring data stream shows high +trim at low idle and progressively improves with rpm to zero out at 2000 or above. If vacuum line is pulled at idle, fuel trim maxes out at 26%, returns to lower trim numbers with lines hooked back up. I tried wafting a propane torch all around intake manifold and throttle body while idling and got no response on fuel trim or O2 sensor voltage change. It idles at 800+- with 9.2 to 10" MAP. Reads 29.5 MAP engine off. MAF reads .430+- at idle and tapping on it causes no change in response.

I have done some more research and found that a vacuum leak is most likely cause with these kind of readings. It was also suggested that low fuel pressure could sometimes cause it. I have checked fuel pressure in last 6 mos and it was ok.

This year it has also set a P0137 for low voltage on rear O2 sensor, I may have a bad connection or sensor there but it did not reset after erasing it yet.

I posted here because of this forums intimate knowledge of the 3800. I really didn't want to rehash everything because I have not replaced the MAF sensor yet, it seems reliable and consistent.

Has anyone personally experienced this on an OBD2 Vehicle???.................................Thanks, John

[zoltanb]

I would replace all the vacuum lines than look at the intake manifold gaskets if the are seeping oil or water. If it is it also sucks air it in the intake.

[Guest Dan Gibbs]

I bought my '97 LeSabre in August of 2012 with 97,500 miles on it and it had only a few codes set, P0301 random misfire and P0171 Lean to Bank 1. I cleared the codes with my Actron CP9190 and only occasionally would the P0301 reappear - that turned out last fall to be a failing Crank Position sensor. The other code, P0171 plagued me constantly and would never go away for a day. This last December as soon as the temps fell below 20degF, the car would be near impossible to start. New plugs, wires, new fuel pressure regulator (check and replace), clean MAF, clean IAC - nothing made it better, Struggled with the problem for the rest of the month and finally found my fuel pressure guage - checked the pressure and found it to be 22psi (supposed to be 47-55psi on 3800 Series II). To save another paragraph on denial, I finally had to have the car towed to a shop and had the fuel pump replaced. I haven't seen the P0171 again and it sure is nice to have that SES light out.

How this car could run so well once it started still boggles my mind, but it was the fuel pump at 105.000 miles causing the P0171 due to low fuel pressure from the dying pump.

Dan G

[TexasJohn55]

OK,OK, I will recheck my fuel pressure. Odd thing is that it is worse running lean at idle, increase in rpm produces a corresponding decrease in fuel trim in the driveway or on the highway. That is why a vacuum leak made sense. I will report back after fuel pressure check.

[TexasJohn55]

cruise at 65 scan.pdf Here is some more data stream from last year @ 65 mph, looks good to me. I don't know if it would be good reference for someone fighting a problem on series2 3800's. Remember, it runs lean at idle.

[Guest Dan Gibbs]

Hey John

Here's another test that's free to perform. How to test for a failing/leaking fuel pressure regulator. The basic jist is the fuel press reg leaks fuel through it's diaphragm in to the intake manifold via the vacuum line causing the car to flood somewhat and then causing the ECM to lean out the ST/LT fuel trims.

In retrospect, I should have seen that my fuel press reg wasn't the problem because my fuel trims were high at 16 or above - meaning my engine was starving for fuel and leaving the injectors on longer. IIRC, good fuel trims are 0-10. above 10 is not enough fuel delivery, negative numbers are too much fuel.

Here's the Youtube video by ScannerDanner:

Dan

P.S. this was for my 1997 LeSabre 3800 Series II

[TexasJohn55]

I put guages on it today, hope my guages are accurate. I checked vacuum first, was 15" on warm engine start up, after 3 or 4 minutes idling it had creeped up to 17.5 -18". Hmm, either the idle air bleed or the crankcase evacuating from PCV? Anyway, not real concerned about that.

Hooked up fuel pressure guage to schrader, keyed on, bumped to 45 psi and after 2-3 seconds it snapped back to 40 psi and held steady. Cranked it up and it idled on 36 psi, jumped to 45 when vacuum line pulled off regulator.

I hooked up my OBD2 scanner and monitored idle STFT readings. Had 22.7 +-2 idling on 36 psi. Pulled vacuum hose off regulator and capped line, had STFT avg of 16.4% +-2 at 45 psi fuel pressure.

Obviously, higher fuel pressures will bring my STFT numbers closer to desired. I have left vacuum reference line off the regulator for now to see if it will reset lean code of P0171.

I have seen fuel pressure specs listed as 40-47 and 47-55 psi, so whose spec is correct?I don't have genuine GM literature to reference. Are my fuel pressure readings enough or do I chase vacuum leaks, R & I intake manifold, etc?

I will report back after driving enough to reset all readiness monitors.

[Guest Dan Gibbs]

Hey John

I called Autozone when I was t-shooting my problems back in December and they told me 47-55psi so that's what I'm going by - I don't have the factory manuals for my '97 LeSabre yet either so I can't look up for ya.

The way you're describing things is telling my gut that maybe you do indeed have a vacuum leak. I looked at so many different videos and forum info back in December and I'm trying to remember what would relate to your problem.

I will reiterate that my fuel pump problem only showed up in earnest when it got really cold here in mid-michigan the first week of December which to my experience always brings out the weak pumps on starting even though the car runs great once it's started. I may have gotten away with a failing pump quite a while longer in places where the temperature doesn't go lower than 20degF.

One thing that has popped up consistently in the last few years in relation to the 3800 Series II is the plastic intake manifold that warps and also will eventually develop cracks in it due to a heatpipe that runs thought it. Also if you haven't heard, these Series II motors came with sh***y intake manifold gaskets that deform and eventually leak coolant into the cylinders. With any luck maybe your car was repaired and retrofitted with better gaskets. Mine hasn't been yet as far as I know.

Anyway, the tips I kept reading about vacuum leaks was to use WD-40 or something to spray around the intake and various hoses and listen for increased RPM. WD-40 may be wrong, but I don't want to recommend anything I can't remember for sure.

IIRC, the PCV valve is hidden of sorts....it's located underneath the Manifold Absolute Pressure sensor on the front left of the intake area. I found info on it's location either from pics on a web forum of from a youtube video....sorry, memory sucks.

I'm probably not helpin much, but just trying anyway...I was very frustrated last December

Dan

[TexasJohn55]

Dan,

My fuel pressure was 14 psi above yours so maybe not so critical. I have left vacuum off the regulator and test drove 30 miles mixed. It has not reset 3 of the readiness monitors: catalyst, evap system and heated O2. I recorded data stream while driving and at idle, my STFT numbers are considerably better, down to 5 or 6 at idle hot. Looks like when monitors reset I can get an inspection.

About that PCV valve!! Yes I decided to replace it. BEWARE! My MAP sensor had "grown" to the fitting, despite being as gentle as possible twisting back and forth, the sensor seperated and came off in two pieces! I would not have persisted except the 5/8 hex under the sensor had to be accessible to twist out the PCV hold-down fitting. I tried patching it back together but no dice, it read 3.2 under all conditions. New sensor was $57,xx with tax.

I will post new data later with it running on 45 psi.

John

[harry yarnell]

I've had a Cadillac Northstar with a chronic code 171. Turns out to be a vacuum leak in the HVAC vacuum line to the vacuum tank.

[TexasJohn55]

Thanks Harry,

I CANNOT UPLOAD ANY ATTACHMENTS!! It goes thru the motions, Add files, browse computer, select another to add, shows file names in boxes, CLICK UPLOAD, whirlygig goes round and round then stops, NO FILES ADDED.........???? I even tried deleting some of stored attachments, it showed they are gone, then next time I brought up attachments, they are still there, ??????? Am I the only one having trouble? I will search threads so we don't have to clutter this thread with irrelevant BS.

[Machiner 55]

TJ55,

I don't know if this will help but, sometimes if the photo files are too large the system won't load them.

Try resizing the images (smaller) then try uploading them again.

John F.

[TexasJohn55]

TJ55,

I don't know if this will help but, sometimes if the photo files are too large the system won't load them.

Try resizing the images (smaller) then try uploading them again.

John F.

Yeah, I always resize to appx 60 KB before attempting upload.

[TexasJohn55]

I still cannot upload attachments!

After replacing PCV valve and removing vacuum from fuel regulator and boosting pressure from 36 psi at idle to 45 psi at all times, my STFT numbers are 3-5 at hot idle and it passed emissions with no codes. P0171 gone for now. I may later try hooking back vacuum line to regulator and see if problem returns. The one unknown is whether the PCV valve had any effect on it running lean. It did rattle and appeared ok.

The new MAP sensor reads a little lower than the original I tore up, 29.2 ambient instead of 29.6 or 29.8. Weather change can affect that. I don't anticipate that little difference is a factor on tuning. Car seems to drive the same at 45 or 36 psi, really cannot tell any difference.

Still don't know what was the definitive cause of P0171 running lean at idle. I will update thread if I learn anything worth passing along.

Thanks for the help and future comments on subject are welcome.............John

[TexasJohn55]

Well, I thought it was time for an update on the running lean code P0171. If you recall, I had mentioned that the honeycomb screen in the intake was damaged. There was a lot of comments about the MAF sensor and also maybe intake leaks. Came time for another inspection and the code was showing up regularly. I removed the intake boot and sure enough, the screen was held in with a thin snapring. I removed the screen and noticed that the damage was directly inline with the channel to the MAF sensor. I straightened the honeycomb as best I could and rotated the screen so the damage was away from the MAF channel. Long story short, that fixed it. The code has not reset since appx 2 mos ago.

 

Thank you all for your input, I have learned alot from this.

 

PS: those MAF sensors are not cheap so I decided mine might work after fixing the cause of the upset airstream to the MAF.

[TexasJohn55]

Time for an update. Still running good, Moral of the story: Engine will not run right and MAF CANNOT READ CORRECTLY IF THE HONEYCOMB SCREEN IS MISSING OR DAMAGED OR UPSETS THE LAMINAR AIR FLOW ACROSS THE SENSOR.

Edited November 14, 2015 by TexasJohn55 (see edit history)