2008 Yukon dying.

[j91z28d1]

your scanner is fine, a tech 2 while good for 300$ isn't really supported anymore. you probably have something better in your hands. unless you have like mine the odd ball hybrid one, the aftermarket scanners don't really support it. but I'm sure you're fine.


odd your trims go negative from a leak. if I remember right, when I forget to plug in the fresh air side of the pvc to the valve cover. my trims go rich, needing more fuel based off the o2 sensors saying it's lean because of the extra unmeters air getting after the maf.

anyways keep us updates on what you find

 

[Fless]

odd your trims go negative from a leak. if I remember right, when I forget to plug in the fresh air side of the pvc to the valve cover. my trims go rich, needing more fuel based off the o2 sensors saying it's lean because of the extra unmeters air getting after the maf.

While I understand what you're saying, it's probably more accurate to say that with a vacuum leak the trims go positive (not "rich"), adding fuel.

 

[j91z28d1]

yes. I definitely didn't word correctly. trims go postive as they add fuel for the extra air.

thanks.

 

[Fless]

After much research I'm making the decision, intake gaskets are leaking unmetered are in causing the negative LTFT fuel trims.

A lean condition will cause positive (+) fuel trims -- the PCM is adding fuel to compensate for too much oxygen and too little fuel, as determined by the O2 sensors.

Check the trims (both LT and ST) at idle and at a higher RPM like @strutaeng suggested in Post #18. Add each bank's STFTs & LTFTs together and get the total trim for each bank at both RPMs.

Generally speaking, total trims that are within -10 to +10 are "okay," with trims between -5 and +5 being excellent. The PCM strives for zero but should always be adjusting based on what the O2 sensors are reporting.

EDIT: this is just something to check and rule out, but what is the scanner reporting for ethanol content of the fuel? Compare that to what is being put in the tank.

 

[rdezs]

Unmetered air then....if nothing located with flammable spray, vacuum check the power brake booster. Often overlooked.

 

[SpareParts]

Nothing located with carb cleaner. I really can't check the bottom side very well at all. I did clamp off the brake booster line. No change.

I explained to the owner the situation. He said with 250K change the intake gaskets and considers it preventive maintenance if nothing else. Next month he wants the timing chain changed as preventative maintenance.
Anyway, you guys have no idea how much conflicting info is out there on this subject. Some respected websites say it is absolute possible for a vacuum leak to cause - fuel trims. Others never mention the cause. Almost no fallow up either.

Smelling the exhaust, it is not rich and it does not burn your eye's and no unburnt fuel smell.

And to Strutaeng's post. I did mention when the engine is put under a load the LTFT moves to like -1 or 2, when coasting they go back to -14 or a little more.

This Yukon had a pretty severe lack of maintenance before my friend bought it so he is doing a lot of catch up at 250K.

The engine is actually in great shape though. New plugs, wires, 2nd oil change i have done, No strange noises and cold OP is 60PSI and hot is 30PSI.

 

[SpareParts]

Ohya, the Flex fuel sensor is at 0 percent. He runs non ethanol premium.

 

[Fless]

I'm not sure why you'd get lean codes with negative LTFTs but we'd need to see the combined trims (ST & LT added, each bank, and ideally at hot idle and at 2k rpm). I may have missed it but what specific codes are presenting as active?

Somewhat negative fuel trims are indicative of a little too much fuel or not enough air. Typical causes are a malfunctioning purge valve (allowing carbon canister vapors to over-fuel the intake), plugged air filter, flooded evap carbon canister, leaky injectors, too much fuel pressure, etc. A purge and seal test might indicate an issue with the evap system, but there could also be fuel in the oil or excess vapors in the intake.

One wacky injector could be wreaking havoc, and I'm very curious about the specific condition and what you find to be the cause. Keep posting info.

 

[Fless]

I'm not sure why you'd get lean codes with negative LTFTs but we'd need to see the combined trims (ST & LT added, each bank, and ideally at hot idle and at 2k rpm). I may have missed it but what specific codes are presenting as active?

Somewhat negative fuel trims are indicative of a little too much fuel or not enough air. Typical causes are a malfunctioning purge valve (allowing carbon canister vapors to over-fuel the intake), plugged air filter, flooded evap carbon canister, leaky injectors, too much fuel pressure, etc. A purge and seal test might indicate an issue with the evap system, but there could also be fuel in the oil or excess vapors in the intake.

One wacky injector could be wreaking havoc, and I'm very curious about the specific condition and what you find to be the cause. Keep posting info.

I'll add over-reporting MAF sensor to that list.

 

[SpareParts]

Not going to know anything till probably Wednesday. He took it last night and will drop it off Monday night.

 

[alpha_omega]

New Purge valve and evap vent valve within a month of the fuel pump, Canister appeared fine. New GM oil pressure sending unit about 8 months ago.
Im going to wait on the fuel pump (for now) It is controlled by the FPCM and maybe the one time i saw it dip down to 15PSI for a second something told the FPCM to do that.
I have had a gauge on it yesterday and all morning today driving around and it has not done it again. The FP varies a little around 54PSI idling or wot.

Looking further i found the oil fill tube O ring not sealing at the valve cover so fixed that.
After changing the MAP sensor it now tests ok. I don't know if changing the map sensor had anything to do with it but it started giving a TPS code. Removed and cleaned TB did the relearn procedure and still got the TPS code.
Swapped it out with a spare i had here and did another reset. All good now no more codes after driving it a little more.

The MAS is showing about 4.7 g/s idling around 575 rpm. From what i know that should be over 5 g/s

The HOT, LTFT is around -14 (varies a little)idling and when giving it heavy throttle driving it moves to 0 + - a little.

There was a TSB for the oil filler cap and fill tube o-rings.

Injector o-rings are another source of vacuum leaks. Are they original? Just like the oil pick up tube o-ring, as well as the ones on the oil filler cap and the dipstick.... They are a maintenance item once you get some miles on.

How often are the o-rings on the injectors supposed to be replaced? 150k? 200k?

 

[Tonyrodz]

There was a TSB for the oil filler cap and fill tube o-rings.


How often are the o-rings on the injectors supposed to be replaced? 150k? 200k?

I never even thought of that as a maintenance item. Does make sense tho.

 

[alpha_omega]

I never even thought of that as a maintenance item. Does make sense tho.

Makes me miss cleaning carbs the old fashioned way. Time to get the GNX out for a ride and smile.

 

[Tonyrodz]

Makes me miss cleaning carbs the old fashioned way. Time to get the GNX out for a ride and smile.

You have a GNX? What number? Pics!!

 

[alpha_omega]

You have a GNX? What number? Pics!!

Are we having this conversation again? Go check your emails. I swear we’ve talked about this three or four times. You’re not getting that old are you T?

 

[Tonyrodz]

Are we having this conversation again? Go check your emails. I swear we’ve talked about this three or four times. You’re not getting that old are you T?

Lol, I must be! Too many hits to the head I guess.

 

[alpha_omega]

Hits from the ****.

 

[alpha_omega]

b 0 ng? Thats a bad word?

Edit: @Tonyrodz I need an adult!

 

[jfoj]

Makes me miss cleaning carbs the old fashioned way. Time to get the GNX out for a ride and smile.

I was working in Michigan when the GNX came out. Saw GNX #001 in the Buick HQ garage. The Buick GM was driving it to work for a while. This was the first GNX I saw possibly before they even ended up on the dealers hands. Looks like GM kept #001 for itself, but I did get to see it actually daily driven to work for a short time.

Inside GNX #001 - 1987 Buick Regal GNX

In the summer of 2008, Group Art Director Brendan Moran and I leftGM High-Tech’soffice for Detroit. We’d spent the prior months planning a special “GM Confident

www.motortrend.com

At the time I had a 1987 Black Regal T Type which was the "poor mans" Grand National but probably a bit rarer than a GN and actually lighter. Actually ordered it new. I had contacts in Buick Engineering and was able to get a PROM that increased the boost to around 16+ PSI and removed the top speed limiter and probably had tweaks to the fuel and ignition timing maps. Actually made copies of the PROM for a number of friends that had similar models.

As I recall the car would run upper 12's or right about 13 seconds 1/4 mile times in street trim. Not a GNX, but a respectable G body that could be driven daily and on highway trips. Probably should have kept it, but like anything sometimes life gets in the way of some things.

 

[Marky Dissod]

Probably should have kept it, but like anything, sometimes life gets in the way of some things.

Anything that gets in the way of Buick's turbo'd 231 makes life a lil bit sadder.