help for a poor running truck

[RW]

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This is a copy of a post I recently put up at Pacific Audio. Regulars there are familiar with this story. I am hoping spreading the story around will help me gain additional insight from a wider fountain of knowledge. So here goes. Sorry for the length.

For those who have been following the two year saga of my rough running 99 Sierra 5.3 I have collected some new data. This info might be helpful for those of you out there who are better versed on the inner workings of these trucks than I am. I'll just give you the raw data and accept any comments as to their significance.

(Autotap ver. 1.01)

Operating temperature 194 degrees

Hypertech III installed/stock temp setting and stat

Idle speed - 558-591rpm/desired 575rpm

ignition timing at idle 15-18.5 degrees

ignition timing advance #1 cylinder@idle -15.5 - -17.0 degrees

Steady 1700rpm-cruise control on

ignition timing 23-48 degrees and everywhere in between

O2 sensor@idle B1S1 - 100-850mV

B1S2 - steady 850mV

B2S1 - 82-838mV

B2S2 - 85-100mV

Desired linear EGR Position - 0.0%

Actual 16.1%

EGR Pintle Position Error - -100.0%

No Codes

Runs like s**t

John, Jody, Airdeano, Speeder, Neil, anybody see any significance or connection between these values and how the truck runs? And if they are screwed up what is the likely cause and how do you fix it? I could use some ammo the next time I go talk to the dealer. I got one good email response from an earlier posting suggesting that the computer itself might be bad hence no codes. Does that sound reasonable to you guys? It came from an owner of a 99 Silverado who had had a similar problem. So far the dealers and GM customer service have been zero help in this matter. Nice but worthless. Their motto "No codes, No problem." If I don't get this problem fixed soon I am going to be posting on the Toyota Tundra board. I paid to d**m much for this vehicle to have it run this poorly. Thank in advance.

[Shaners]

RW, First off Welcome...

Have you tried any other dealers?? Or tried to get a rep involved?

I know that the stock computer tries to constantly adjust timing for emmissions reasons, but That seems pretty excessive to me.  I don't have any way to check mine so I can't tell you how much it retards and advances.  Ryan is running the Hypertech and maybe he could get some numbers...  I guess that's up to him.

Your idle is changing about 30 rpm and these trucks idle so low I don't really have a problem with that.

The other thing I have a problem with is the EGR reading.  Your op temp is good and I don't think the EGR reading should be where it's at...   If the EGR is bad the truck will definatly run crappy.  Have you tried to get the dealer to replace the EGR valve?

Also I'm guessing your O2 sensor is changing so much because of the 25* of timing that is coming and going.

There are alot of variables here, and I have never visited Pac Audio, so I'm not at all familiar with your personal situation.  However, seeing the numbers you have posted here I'm very concerned and interested what comes from this.

Please keep us up to date...

Shane

(Edited by Shaners at 8:48 pm on Sep. 3, 2001)

[RW]

I am posted here, PA, LS1 and Pickup.com. I am getting a lot of interesting feedback. The consensus so far is that the EGR is probably bad, the computer may be and the one O2 sensor reading seems to be off. Everyone seems to agree that the 20+ degree timing advance is just not right. I have been fighting this thing for over 2 years now. I have talked to GM's customer service 3 times and have been to 2 different dealers a total of 4 times. I have been now told twice that these trucks are supposed to run this way. I hope not. If they are then I have wasted a lot of money buying a GM product. If the problem ever gets resolved I will post the info on all the above mentioned forums. By sharing info we all get a better product.

[Shaners]

I read your post at another forum and didn't realize the problem was worse at 1/4 tank or less.  One reply to your problem was the gas cap.  That's not a bad guess either...  It says in your manual that a bad seal on the cap will cause the engine to run abnormal.  It can even cause a code in the computer too...

I have also heard of a piece of Carbon getting stuck in the EGR valve.  If that were to happen you would see some of these conditions.