2002 Yukon XL 2500 / Engine Died / Get a used LQ4 or LQ9

[noodlesandsam2]

So.... Last Tuesday, in NJ, GSP, Exit 157 ish, just a normal airport run, 2002 Yukon XL 6.0 LQ4 174,000 ish miles, Starts losing power - we get to the rest stop, about mile marker 152?, and it dies coasting in to a parking space. Open hood, it smells nasty in there, and I can't get it to start and idle. I can get it to run at about 1500 rpm for 30 seconds. Now there is a bad knock. Most likely it is toast. Do I get a replacement LQ4, look for an LQ9? Any real value to an LQ9, and any retrofit issues ( I know an LQ9 will have been hooked to an 4L65 ( Escalade ), and I have a 4L80, but otherwise? I've never had this happen before in the decades I've been driving ( and no there were no indicators ). Truck is home. I need to make decisions.

 

[Tonyrodz]

LQ4s are more readily available and cheaper then LQ9s. Iirc, LQ9s have the better pistons which gives them a few more ponies. The downside to them is you need to use premium, but the LQ4s allow regular. I guess that'll also matter if you get it tuned too. I'm pretty sure the bell housing for the 4l60 and 4l80 are the same. Hopefully someone more knowledgeable will chime in and correct me if I'm wrong.

 

[Joseph Garcia]

^^^^^x2^^^^^

 

[Marky Dissod]

LQ4 6.0L LS Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More

Find key specs on GM's LQ4 6.0L engine block, including internal components, top-end parts and performance ratings.

www.onallcylinders.com

Chevy LQ4 Engine Specs · Help Center

LQ9 6.0L Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More

From cylinder heads to the camshaft, here's a complete rundown of all the vital engine specs you need for the 6.0L LQ9 LS engine.

www.onallcylinders.com

Chevy LQ9 Engine Specs · Help Center

LQ9 does not require 91 or 93 octane (10.1:1 scr), but that assumes you drive daisy, costs power and torque, and will get you made fun of.
Of course 91 or 93 octane is STRONGLY recommended. Here, read the manual:

If your vehicle has the 6.0L V8 engine (VIN Code N), use premium unleaded gasoline with a posted octane rating of 91 or higher.
You may also use regular unleaded gasoline rated at 87 octane or higher, but your vehicle’s acceleration may be slightly reduced,
and you may notice a slight audible knocking noise, commonly referred to as spark knock.
If the octane is less than 87, you may notice a heavy knocking noise when you drive.
If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you might damage your engine.
If you are using gasoline rated at 87 octane or higher and you hear heavy knocking, your engine needs service.

2006 Chevrolet Silverado Owner's Manual

 

[noodlesandsam2]

thx - LQ9's are flat top. I'm happy with the LQ4 power - I come from a LM7 5.3. I'll stick to LQ4.

 

[West 1]

You could swap in a 4.8, 5.3 or 6.0L that match your trucks model year very easy. Going into the later models like the 6.2 or even newer 5.3l won't match the 2002 computer.
I have had the 6.0 and the 5.3, in some ways I prefer the 5.3L. It does all the work very similar but gets a little better MPG. You would not hang with a 6.0L in a race though!
I would not choose the 5.3 if you have 3.42 gears.

 

[Tonyrodz]

You could swap in a 4.8, 5.3 or 6.0L that match your trucks model year very easy. Going into the later models like the 6.2 or even newer 5.3l won't match the 2002 computer.
I have had the 6.0 and the 5.3, in some ways I prefer the 5.3L. It does all the work very similar but gets a little better MPG. You would not hang with a 6.0L in a race though!
I would not choose the 5.3 if you have 3.42 gears.

I never even considered the rear ratio. Luckily I have 3.73s in mine. I have an LQ9 installed. My 03 originally came with the 4.8.

 

[strutaeng]

Just stick with the LQ4. LQ9s are getting harder to find and command a premium price.

Who is going to do do the work? A quick oil pan removal will likely tell you how bad your engine is or if it's even rebuildable. Also, most places that sell used engines will require a core back.

I would recommend a new gasket set for the used engine at the minimum.

Edit: if your donor engine comes with a 3 hole flexplate, swap over your 6 hole flexplate along with the little spacer.

 

[noodlesandsam2]

Ok - Sticking with LQ4 -

Not sure on who is doing the work. It sounds awful when I can get it to fire. If I was getting a Jasper, or such I can see a core charge. I can get a LQ4 from a local dismantaler for about $1500 ( around 100K miles - not sure on the truth of that ). Thanks for the flexplate hint - I'll watch for that. I had a 5.3 ( 2001 1/2 ton ), and I'll spring for the 6.0, I'm ok with the gas hit, It has more punch, and I have found the 4L80 to be different from the 4L60. Not sure I would like it with that combo.

 

[Marky Dissod]

I'd comparison shop LQ4s vs truck-L76s / LY6s / L96s / LC8s, but I find it very easy to convert a Gen4 V8 to work like a Gen3; some of you may not.

Either way, I'd swap 243/799 heads onto whatever 6.0L I got - again, I find it very easy to tune for a small increase in scr; some of you may not.

 

[noodlesandsam2]

Thanks for the feedback. I've got a few things to figure out. This happened on the Garden State Parkway ( NJ ). I felt the loss in power, we were middle lane, doing 60/65 with traffic. When the Service Engine light started blinking, I put an OBD scanner on, and saw P300 - multiple misfire - Water Temp, Oil Pressure never went odd - 45 PSI Oil, Water at normal 210 ish ( just under 1/2 way ). It went for another 3 miles, made it to the rest stop, and that was it. I have confirmed that there is 0 Fuel pressure at the test port, it just dribbles out a bit of gas. It will almost fire. It is December in NY, Butt cold. It's going to a shop ( friend ), and we are going to start with the Fuel pump. Maybe Crank and Cam Sensor too? Will let you know how this ends.

 

[strutaeng]

Huh?! You deduced your engine is blown on the fist post...

...but you say you have 0 psi fuel pressure?! Post #11

Definitely have to get the truck properly diagnosed before you can start thinking about engine replacement...

 

[Marky Dissod]

have confirmed that there is 0 Fuel pressure at the test port, it just dribbles out a bit of gas. It will almost fire.

Unfortunately you need to be specific about HOW you confirmed 0PSI. If the pcm THINKS there is zero fuel pressure (or oil pressure),
then it does not matter if the pcm is wrong or tricked, it makes an @$$ out of you by protecting the engine from a zero pressure situation that is not actually true.

That was just an example. You may actually have 0PSI at the fuel rail, but WHY? is my point.

 

[Fless]

The PCM doesn't monitor a fuel pressure PID in these -- no sensor for that. As the OP stated, the fuel pressure at the rail is low or non-existent.

To the OP: if you change either the crank or cam sensors, please use GM OE or AC Delco. And do a CASE relearn afterward.

 

[noodlesandsam2]

I tested at the Schrader valve with a tester I rented - Zip. I sent it to a shop run by a friend to confirm, and then do that nasty job, if it is indeed dead. Yes, OE or Delco only - for sensors. ( and likely the pump )

 

[noodlesandsam2]

Huh?! You deduced your engine is blown on the fist post...

...but you say you have 0 psi fuel pressure?! Post #11

Definitely have to get the truck properly diagnosed before you can start thinking about engine replacement...

Yeah, It still maybe dead, but I have been known to jump to the worst possible scenario. It sounded awful when trying to start before getting towed home. I have to determine baseline of gas and crank sensor.

 

[noodlesandsam2]

Time for a new/used LQ4 - it went to the shop, it ran for 10 min - with misfires. Then seized... So my worst case scenario is the scenario. The journey continues.