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Ive been looking on here and people reffer to the 6.2 by different letter codes. Id like to know because im starting to stockpile parts and i dont wanna buy parts i cant use. i think i read about injectors being longer or something. I have a 86 blazer with a 6.2 and im trying to buy a 6.2 or 6.5 to put in my older blazer. i almost got one on ebay for 120 buck but i got out bid. does anyone have any 6.2 or 6.5 for cheap. also, what would i need to run a 6.2 on an engine stand. if i get a spare engine id like to do some testing and modifying on the stand b4 i pull my old engine.
 

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theres C code and J code. differences are that the C code has emission equipment built into it (intake manifold), thus restricting some air flow. the J code does not have this problem, its intake manifold is more free flowing. parts are interchangable between these.
 

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blazin6two;1571662; said:
Ive been looking on here and people reffer to the 6.2 by different letter codes. Id like to know because im starting to stockpile parts and i dont wanna buy parts i cant use. i think i read about injectors being longer or something. .
Not all C-codes are same, nor are all J-codes. But, basically - a J-code is allowed to put out a little more horsepower and a little more emissions since it only gets installed in heavier GVW vehicles - usually 3/4 ton and up. All the parts physically interchange - and many are the same. I don't personally believe the J-codes breath better. They do have more wide-open intake-manifolds since some emissons stuff is left out - but the J-codes often also have smaller valves. The idea of smaller valves in a higher power engine was to get the more metal between the valves to avoid cracking. The somewhat restricted intake in the C-codes still has an opening the exceeds the CFM flow needs of the 6.2 diesel engine. C-code injection pumps are set to pump less fuel than Js. And, injectors over the years vary many ways. The first year 1982 - all the injectors were coarse thread and will not fit any other year. The later fine-thread injectors also vary. Different nozzles for C or J code - but I believe the differences are subtle. Also, injectors in vans are shorter than in other vehicles. Late engines, maybe around 1991 - injectors got shortened for all and also the pressure raised.
In regard to other parts interchanging. GM stopped using direct-drive starters in 1988. After that, they are all gear-reduction - but either will fit any year. 1985 the fuel injection pump were improved by eliminating the plastic weight retainer that tended to fall apart. That may be a moot point, since most older pumps that failed should of been updated with the new EID. The glow-plug controllers changed in 1984 - from a thermal two-piece system to a unitized electronic module. Crankshaft pulleys changed around 1985 although they can be swapped back and forth. Up to 1985 they were solid-steel and were hard on belts due to the diesel-pulse-slap at low engine speeds. If could sometimes make a belt jump off - or hit a radiator hose. That's why the upper hose has a metal belt-guard on it. In 1985 and after, a rubber-cushioned pulley was used. It works great but is expensive an only seems to last around 100K miles. In 1988, new body-style trucks with 6.2s got a serpentine belt system. Some later 1 ton trucks also got it. In 1992 - 6.2s got a new crankshaft that mates with a new one-piece rear main seal.
There are other subtle differences, but those are the biggest ones I can think of.
 

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C-code engines (usually engine RPO code LH6) were equipped with an EGR/EPR (Exhaust Gas Recirculation/Exhaust Pressure Regulator) system that helped reduce NOx emissions (a side effect of high combustion temperatures) at idle. The EGR allows a little bit of exhaust to get into the intake which reduces combustion temperature enough to reduce NOx emissions to an acceptable level. The EPR valve increases exhaust backpressure enough so that the EGR works properly (without the EPR there isn't enough backpressure for the EGR to work very well). The system is only active from idle through 8 degrees of throttle (measured at the injection pump throttle shaft). The main problem with this setup is that the EGR valve restricts the intake a bit and (more noticeably) has a tendency to leak exhaust into the intake under heavy load after a lot of use.

J-code engines (As I recall they were engine RPO code LL4) didn't have the EGR/EPR system. They were more powerful than the C-code engines because the air intakes were less restrictive and the injection pump was set up to supply more fuel. This was the HD engine, installed in vehicles with a GVWR of 8500# or higher.

You can convert a C-code to put out similar power to a J-code by adding the J-code intake manifold and turning up the injection pump (you may also need to add a fuel delivery valve out of a J-code pump to get enough fuel - seems to me they were different, but I'm not 100% sure).
 
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