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I currently have a 2003 Blazer with a 4,3 engine, and when I bought it I was told that it has a series 2 engine,


How many different engines were there for these trucks, ?


Can someone tell me the differnces of these engines ?



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Never heard the 4.3L V6 referred to as a "Series 2" only the 3.8L V6 "Buick Engine"

There were Pre-Vortec and Vortec versions of the 4.3L V6 throughout it's history. The 4.3L V6 saw many changes throughout it's long running history. It's based on the 350 V8 with the # 3 and #6 Cylinders removed basically. It came to life for the 1985 model year so it has a LONG history. I think it holds a record for a production engine in the USA, based on how long it's been in production. From, the not so smooth idler carb'd, non-balanced shafted version to my current LU3 version with it's distributor-less ignition system, Multi-port returnless fuel injection and roller rockers/Roller lifters, better ECU's and sensors, etc.. Making it a smooth running more modern feeling engine.


GM made MANY changes on this engine thoughout its history and the versions or as GM calls them RPO's were called: LB1, LB4, LU2, L35. LF6, LG3 and finally the Current and only one produced begin produced the LU3(GM made many changes to the LU3 also and just kept this RPO code rather then changing it). The Turbocharged version was also the LB4 but also included the RPO code ZR9.

Your engine is the LU3 and If I remember correctly the 8th digit of your VIN should be a 'W', this version produced 190 HP @ 4,400rpm and 250 lb-ft torque @ 2,800rpm. in your truck.

If you go to this Wikipedia link it has a bit more detailed information on the 4.3L V6 --> http://en.wikipedia.org/wiki/Chevrolet_90-Degree_V6_engine#4.3L_.28262_CID.29 <--


IMO the 4.3L V6 hands down is the BEST 6 cylinder gas truck engine produced, yea I know It's not perfect and had its teething issues early on. Yeah It may lack the Horsepower at a mare 195 @ 4.600 RPM. Compared to some competitors current truck V6's with 300hp life Ford's 3.7L V6. It's just reliable/dependable, easy to work on/maintain in my truck(lots of room under the hood). Producing 265 Lb-Ft torque @ 2,800 rpm with a relatively flat torque curve too. The competitors V6's are not much better torque wise and at a higher RPM.

The 4.3L is a true work horse engine, It's used in everything from cars, trucks, vans, even powering boats and in industrial applications like: forklifts, pumps, generators, ETC. yeah the other V6's will beat it in a drag race but this engine will be the one hauling them to the junk yard. So it makes up for what it lacks, IMO. Many are glad to see this engine gone for the 2014 model year, but it just goes to show you how great of and engine this is buy how long it survived begin able to pass the ever growing stricter emission and fuel economy standards. Fuel economy is good for me I average a bit over 20 MPG as I drive alot oh hi-way and country roads. Yeah the V8's could do the same MPG wise if driven with the same feather light foot and some say the 4.3L is a gas pig and it can be if you drive it hard. I get great fuel economy in mine and I'm happy!

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Thanks for the Reply I looked at another blazer 2 wheel Drive last night it was a 2000 year model and it looked to have a EGR valve sticking out of the front of the intake or something similar,


do all the 2000 model years have the intake issue of leaking ? and is this the same engine I have now ?


Thanks again

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The round black cylinder looking thing with the wire is the EGR valve, I don't remember the year when GM got rid of the EGR system. I know my 2011 4.3L V6 don't have an EGR system on it. I'm glad cause that;s one less thing to deal with down the line. The 200 Blazer 4.3L is the L35 version. The difference between the LU3 in the 2003 and the L35 in the 2000 is a few things. The Cam is different the LU3 had a 'Quite Cam' the cam lobes were shaped different to stay in contact with the lifter longer and ramp down slowly. This was to help with vibration and reduce the amount of valve train noise. The L35 had the older version of the cam. Net was the Fuel system, The 2000's L35's fuel system: Had six centrally mounted injectors and used poppet valves at each intake port, called the SCPI (Sequential Central Port Injection). The 2003's LU3 had a MPI (Multipoint Fuel-Injection) with six Multec II fuel injectors mounted at each intake port on the lower manifold. Commonly referred to as a "Spider Injector" cause it looked like a spider, the whole injection system in mounted under the plastic upper intake plenum. The 2000 also had the same power output (190hp/250Lb-Ft torque)


When it comes to issues with the 2000 model year: Yes the intake issue could happen and I know it can bee hard to see with the very tight engine bay with the 4.3L shoehorned in there. -If it's leaking externally you could check the back side of the engine for any signs of leaking, look for coolant traces on the trans bell-housing and trailing along the engine to the sides, Same with the front of the engine. If the oil hadn't been changed in a while, pull the dipstick and check for "milky" looking oil. Also you can check the bottom side of the oil fill cap and look for any grayish/brownish cruddy buildup. This could be a sign of an internal leak. The oil cap check is not the best due too if the truck was used for short trips allot. You will get the same build up cause the engine will not get hot enough long enough to burn out the moisture build up inside of the engines crankcase. Also check for low coolant, these can be hard cause if the person selling, changed the oil, washed the engine really well could have washed away any signs.

If the truck has a far amount of mileage on it the intakes might have been changed already. I have seen 4.3's go over 150,000 miles with no intake leaks and if repaired with the new updated gasket kit and done right!! i.e gasket surfaces pred'd(cleaned) and all the bolts torqued to spec. You most likely will not face this issues again.

The other thing is with the SCPI the fuel injector unit is known to develop fuel leaks over time. One place is at the FPR(Fuel Pressure Regulator) which is mounted to the SCPI's injector unit body under the upper intake plenum, same goes with the fuel line that lead from injector to the poppet valve. Poppets to can become plugged with carbon or even debree from the fuel too over time. Especially if the owner used poor quality fuel and never changed the fuel filter. If the SCPI unit is leaking bad enough you usually get poor running, bad MPG, SES light. I check for a bad SCPI if suspect by removing the air intake tube from the throttle body. Open the throttle valve and use my small led flash light and my small mechanics mirror(if needed) and peer inside the intake. On the EGR 4.3 especially the inside of the intakes are dirty covered in soot and blowby from the PCV system. Fuel is a good cleaning solvent so it will clean the area when its leaking. So if I see a really wet intake and a nice clean spot you know the SCPI is leaking. The small mirror I use if I need to peer into the back of the intake. You can by a updated replacement injector unit with a modern MPI like the LU3's have. No more issues for a LONG time with the MPI's unless the truck is neglected(like poor quality fuel and not changing fuel filter)


These are the two most common issues with the 4.3;s that I know about and have seen, other stuff pops up hear and there, like sensors etc. but that's no different than any other engine. THe fuel injector unit is an easy change, the intake is more involved but can be done if your mechanically inclined and have the proper tools and torque specs. All these issues I know were solved for the newer 4.3L's the only issues I had with mine and I have nearly 60,000 miles on my 2011 Silverado 4.3L V6 is with the TPS(throttle position sensor) failed on mine. GM used this same sensor on a lot of different engines. I have the electronic throttle and no throttle cable on my engine.


Sorry it took a bit to replay, having internet issues at my house last night.

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  • 1 year later...
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Hey All,

Old member here now back in the game.

I am in Fla. looking for a 4x4 s-10/sonoma and scored a 03 s-10

4x4 x-cab.  Its clean as as a whistle inside and out and no rust like all

the trucks back home in NY! 

 Tough to find a 4x4 down here that aint been all cobbed up!

Its a one owner truck with 165k on it!

Fresh rebuilt tranny, good tires, full power and cold a/c!

Grandpa bought a new full size chevy.

Needs some steering work as the steering is sorta loose.

4x4 quiet and works good,  no shimmies and no shakes either.

Paid a measly $2000 for it!

A nice rust free truck back home in NY cost twice that much!

I guess we will see is she makes it back to NY with no issues!





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On 3/9/2015 at 6:10 PM, [email protected] said:

I have a 2003 GMC Sonoma and I have the X (X in the vin not the W) with Multi Port Fuel Injection vs the previous years single port fuel injection.

I have a 2001 GMC Sonoma 2wd 3dr pick up that I'm in the process of replacing the v6 4.3 engine cause it was ran dry on oil by previous owner so its toast!! But I have a 4.3 thats in a 95 full size chevy truck and idk if it'll go into my sonoma without making any changes or not? Can I use it? And also would like to ask what years did they make the same type of v6 thats compatible with the 01 gmc sonoma?

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