98 SE runs sweetly after UIM/LIM job (oops-engine codes) - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 10-12-2006, 07:54 AM   #11
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Hey, thanks all!

Yeah, that'* a good idea on the O2 sensor. It does seem like it could be yo-yoing rich/lean/rich/lean etc.

Spark plugs sure look like something ate 'em down. TB area looks like it was spared, but I'll check anyway. Well, I'll get the codes read tomorrow morning at AutoZone. Maybe it wasn't me after all.

I'll post what I get.
Rich/lean toggling is GOOD! This is the behavior you want and is expected from the O2 sensor.
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Old 10-12-2006, 01:34 PM   #12
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ok, I just got back from AutoZone with check engine codes (by the way, it'* 33 degrees out and snow flurries--just thought everyone would like to know that. Glad I decided to leave the 195 degree thermostat alone). They are:

PO121 throttle position sensor performance
PO171 fuel trim system lean

I've put in the exact wording from the forums TechInfo section for year 1998.

I see there'* some threads to follow up on for PO171 especially leaky manifold (or a vacuum hose problem, etc), since I just did that. I also have experience in checking O2 sensor output. MAF was also mentioned. So I have some things to go on for that code.

Didn't pick anything up on PO 121. Hopefully, I just loused that up during reassembly. It should be easy to spot and check, I would think.
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Old 10-12-2006, 02:14 PM   #13
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On the TPS performance..I'd be hookiing up a multimeter to check the full range of motion and see that there are no dead spots.

On the P0171.. if you only found vacuum leaks and manifold issues... oh you missed out on some good info. SanJuan Cruiser and myself experienced battery/corrosion/connection issues that cleared up the P0171, Foghorn found the ground from battery to engine block was his P0171.

First thing I'd do for 0171 is pull the battery cables off the battery and look for corrosion.
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Old 10-12-2006, 02:20 PM   #14
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It'* good that you have the codes. Now you can set out to addressing them.

It'* a good idea to check the O2 sensor anyway, especially if it hasn't been replaced ever or recently. UIM failure has been known to accellerate O2 sensor failure at times.

The P0171 code immediately makes me want to suggest that you take a really close look at your battery cable connections in addition to your vacuum lines. As you read the P0171 threads, you'll see that more than one person found their code to have been caused by corrosion.

As to the vacuum lines, double check to make sure that all hoses are connected to the right places. We had one instance where a member had two vacuum lines swapped after a UIM replace, causing misfire issues.
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Old 10-12-2006, 04:04 PM   #15
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Thanks, Boosty and Lash!

Just got back in from the garage, and did take a look at a large threaded hole in the LIM just left of the #3 injector. I knew about it--it'* to mount a bracket holding a vacuum/electronic doodad. I got the injector rail on too soon and it was in the way.

I probed the hole with a stiff piece of plastic tubing, and yup, it goes right on in to the LIM chamber. Corrected the problem and it did dramatically get rid of the rough idling and the surging (while in drive) at stoplights. Engine light is still on full as before (it would be just too lucky to kill two birds with one stone). No other vacuum problems I could see.

I did pick up on the battery cable and ground corrosion problems in the threads. I'll certainly check for sure. Also, O2 sensor is original, so it gets a check/and or replacement also. Ditto TPS


Thanks!!

(PS We're heading up north to our cabin for awhile (in the truck), so this project will have to go inactive for a while. But I feel alot better about where to go with it now)
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Old 10-12-2006, 11:28 PM   #16
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Well, I'm still here.

Too tired to take the trip due to working on the car. So I'm working on the car .

Checked TPS output: 0.45 volts idle 4.05 volts WOT

Volyage output is smooth up/down up/down etc.

One of the push/pull throttle cable pastic end ferrules kind of fell off in my hand as I was testing above. Don't know that it was a factor, but I did a kludge repair and put it back on.

Cables to battery look great. Battery negative to chassi at chassi a little rough. Loosened and applied dielectric silicone. Alternator wiring good. I give everything I can a loosening, wiggle, and tightening anyway. Can't hurt. All good maintenance.

Left battery cables off for a good while to try to clear codes. Haven't found chassi to engine strap yet. I think I'll just use booster cables here and there to temporarily accomplish that before activating again.

Haven't gotten to O2 sensor yet. We'll see what happens tonight after firing up, and then maybe off to Autozone to see if I got rid of any codes.
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Old 10-13-2006, 02:34 PM   #17
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fired up last night with no extra cables -- still got check engine light

left negative batterry cable off over night. Reattached this morning. Ran booster cable directly from battery negative to alternator strut.

No engine check light
Wow Thanks guys for all your help
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Old 10-13-2006, 02:37 PM   #18
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Quote:
Originally Posted by Slug
Thanks, Boosty and Lash!

Just got back in from the garage, and did take a look at a large threaded hole in the LIM just left of the #3 injector. I knew about it--it'* to mount a bracket holding a vacuum/electronic doodad. I got the injector rail on too soon and it was in the way.
That doo-dad is your evap purge solonoid.
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