Switch 6.2L idi to V6 TBI or vortec

[MuddiGGEr25]

Ok I know the first thing most people are going to say is, why go from the 6.2l to a v6 and not just a newer diesel or a big block for a 3/4 ton, well, mainly because i dont want to go from getting 14-18mpg on the highway down to 6-8mpg.

I had a s10 blazer v6 TBI loaded to the gills for a funeral 900+ miles from home, and overload springs for the weight and to correct the old springs rolled across the scales that trip around 4,800lbs, and on the way back was about 5,000 lbs, that was with 3.42 axle ratios, 700r4, and 4.3L TBI (1992)

I got a steady 28MPG at 55mph in OD in cruise, after all adjustments and mods. (we were very limited on money so if it got any less mpg then we would not have made it home at all)


Also my inlaws own a 1994 GMC jimmy with the 4.3L vortec (early i believe) he has hauled many a load with it, the largest being a camper trailer loaded between 7,000lbs and 9,000lbs (we kept moving stuff throughout the trip to the other vehicles to help spread the weight off the hitch). We hauled that load in D roughly 200-250 miles, and it had no issues getting up to speed, or holding 50-55mph and even on some of the steeper hills we could hold it, but the pedal was down pretty far. and the jimmy was loaded to the gills with passengers and cargo, he still drives this vehicle but he hauled a few too many loads in OD and needs a rebuild on the trans, but 240K on the engine.

So i am very familiar with what this engine is and is not capable of.


My 1988 V20 suburban weighs 5200-5,500 with just me my wife and a few tools in it, so its just barely heavier than my S10 blazer was and the v20 has 4.10 axles so that would help immensely with the slightly larger weight.

The ratings (from here: http://www.gmtuners.com/gminfo.htm)


Chevy 4.3L 90º V6

1989-91 4.3L TBI V6 vin Z

160hp @ 4000 rpm
230tq @ 2800 rpm
9.3:1 Compression
No balance shaft
1992-95 4.3L CFI V6 vin W Vortec (early)

165-200hp @ 4400 rpm
235-260tq @ 3600 rpm
9.05:1 Compression
Hydraulic roller lifters
Balance Shaft
1992-93 4.3L PFI Intercooled Turbo V6 vin Z (Syclone / Typhoon AWD Truck)

280hp @ 4400 rpm
350tq @ 3600 rpm
8.35:1 Compression
1993-95 4.3L TBI V6 vin Z Vortec (early)

165-170hp @ 4000 rpm
230-235tq @ 2400 rpm
9.05:1 Compression
Hydraulic roller lifters
Balance Shaft

1996-up 4.3L CSFI V6 vin X&W Vortec (late)

175-200hp @ 4400 rpm
240-260tq @ 2800 rpm
9.2:1 Compression
Hydraulic roller lifters
Balance Shaft
 

And here : http://www.dieselplace.com/forum/63-gm-diesel-engines/20-6-2l-diesel-engine/344096-towing-6-2-a-4.html#post3607081

GM 6.2 C-code - 130 HP @ 3600 RPM and 240 TQ @ 2000 RPM
GM 6.2 J-code - 148 HP @ 3600 RPM and 248 TQ @ 2000 RPM

I do know some J codes might have had just slightly higher ratings.

I also know that the 700r4 has steeper 1st and 2nd gear ratios than my TH400

I also know that the TH400 will have more parasitic losses due to its nature and obviously no lockup or OD at this time, nor can afford a rebuild or a 4l80e and controller.

I know my best option would probably be an  earlier S10/Blazer or 1500 with the 4.3l and a manual trans, I would buy an entire parts truck and pull the harness and PCM,

I would consider an 96-01 with OBD2 just because then i could link up to my phone as well for live data, but thats not a breaking point.




I need to know is there a specific flexplate i should look for to mate the 4.3L to the TH400 or would a dual pattern TCI flexplate work?

Does anyone know if there would be issues with the motor mount towers? i know i can change between 305/350/400 using all existing mounts, etc.

Will the oil pan clear ok if the donor is a 4x4 model?

I can get a inline pump rated for the TBI or the higher MPFI/CPI pressures, I can mark the gauge cluster and gas door as well for unleaded no big deal there., and the existing 3/8 fuel line should be sufficient, and the return line should be ok also, i think its 1/4"

Is ther anything else someone knows might be an issue? i searched but all i can find is people going from 2.2L to 4.3L or 4.3 swap to a 350 or 383.



I know it will be no speed demon, but the 6.2L is gutless in the first place, I will occasionally tow the mud truck, but since the engine i am putting in has nearly the same TQ as the one removing then I should still be able to tow the same, just still gutless, and downshift on hills, but since the V6 has a higher redline i might be able to creep up the hills slightly faster than the 6.2l, my other goal is to still achieve similar MPG on the highway with the smaller engine. i may or may not pickup a gearvendors OD in the next year or two, it just depends.


Also RPM on the highway will be (55mph) 2400RPM including losses from the TC, which is close to the peak of the V6 of 2400-2800RPM, whereas the 6.2L is pretty stretched at 2400 since peak is at 2000.

Some other benefits to me, maybe not to you, is almost every used vehicle here has autostart just because the temps here in ND and MN get subzero for days on end and people want to warm up thier vehicles, also I gain a newer alternator design that puts out more A then the 10SI, and the lighter weight of the V6 in the front is a benefit to me when taking it off road.



I would be looking to do this swap either in january or feb, depending on how much snowfall we get.


Please no flaming 

[Stewart G Griffin]

This is right up my alley.  As you know, i went from v-8 to 4.3, which, when you think about it is very strange.

Will comment much more asap;  getting sleepy right now.

1) Many (most?) 4.3's in the trucks actually came with TH-400's  (the 85 and 86's at least)

2) Not sure about the flexplate.  i'm thinking that any flexplate that worked with the 6.2 should also work for the 4.3 , but not real sure.

3) Yes, there is an issue with the mount towers.  As in, you can't use v-8 towers for the v-6.

4) Not sure about the 4x4 oil pan.

But much more later.

[Stewart G Griffin]

OK, first off is there anything wrong with the 6.2 other than you feel it's down on power.  Does it otherwise run well?

[MuddiGGEr25]

OK, first off is there anything wrong with the 6.2 other than you feel it's down on power.  Does it otherwise run well?

I dont think its down on "Power" since i know how low its torque output is, i know my modified TBI 350 can and has outpulled it several times. and my 454 with 400+HP was going to go in but i ended up trading off that motorhome.

It does have a fuel leak down issue between the IP and the electric fuel pump i havent found yet but cant deal with that for a few more days since our high temps wont be above 0 for a couple days.

There is a random "rattling" or "knock" at idle, which does not coincide with the engine rythm, like ive heard other 6.2's on youtube, and 6.5 TD's at work, and none of them had this sound, it sounds like a rod or something is wanting to let go, but once past 700rpm or so the sound goes away and it has power towing or alone up to about 70MPH at 3000RPM, but power is non existant after 3000rpm unless i have a tailwind

[Stewart G Griffin]

How are you calculating mpg?   i would think a 6.2 diesel can get better than 18mpg  even in a heavy suburban.

i don't think a 4.3 will get any better mileage than the diesel and if you're unhappy with the diesel's performance, then i really don't think you'll be happy with the 4.3's either.   4.3's do pretty good in s-10's and small blazers because those trucks are about 2000lb's lighter than a suburban and also narrower.

The other thing is, yes 4.3's produce similar peak power numbers as the 6.2.  BUT,   6.2's produce their peak torque at a much lower rpm which is much better for towing.

This is just me, but if i had a 6.2 truck, i would either get a replacement 6.2, most likely from GM and/OR get a banks turbo kit.

[MuddiGGEr25]

How are you calculating mpg?   i would think a 6.2 diesel can get better than 18mpg  even in a heavy suburban.

I am calculating MPG, from the point that the truck sputters out on E and wont start back up (dont worry i have an electric liftpump for priming it), then i put in 1 gallon, and go the the fuel station, put in $20 or $40, and drive until it runs out again, I use the GPS on my phone to track speed and miles, then simply divide them, and 18MPG, is on a excellent day, with either no wind or a tail wind driving 50-55mph but never over and no tools or passengers. I usually see 13-15mph highway, and i dont floor it, and i dont ever go over 60mph EVER (except for testing) because i cant afford that much fuel when the next town is 50-100 miles away, but i also know part of my issue is that i have 4.10 gears, and 265/75R16 tires so im sure thats not helping with my MPG at all

i don't think a 4.3 will get any better mileage than the diesel and if you're unhappy with the diesel's performance, then i really don't think you'll be happy with the 4.3's either.   4.3's do pretty good in s-10's and small blazers because those trucks are about 2000lb's lighter than a suburban and also narrower.


I never said i was unhappy with the diesel's performance, i actually find it quite adequate, i know i wont be the first one there and i know i wont win any races, but thats what the other suburban is for.  I have owned 2 s10 blazers with the 4.3L TBI, i drove one for quite a while with the 4.3L vortec (1995), and my father in law has a 1994 gmc jimmy 4.3L Vortec with the spider injection system, I also have used a W/T or two with the 4.3L TBI,  I know plenty well what the 4.3l can do in a blazer lol. as for the 2000lbs lighter, the weight difference is actually not that high, i drove my 1992 S10 blazer (240K on the dash) to illinois for a funeral (1900 mile round trip) and back at 55mph in cruise, i got 28mpg using the OD, and i got 21mpg in 4x4 hi driving back through minneapolis in a white out blizzard at 45-50mph. I weighed it on the scales before i left and we were around 4800lbs with us in it, and on the way back we picked up some stuff and we were 5,000lbs across the scales at the beet plant upon arrival. MY other 3/4 suburban "cliffy" has a 350TBI, TH450, 4x4, and K20 axles with 3 springs up front, 6 rear, and usually has a load of tools in the back, when i haul loads of garbage or scrap last summer, he rolled across the scale every single time after a load at 6100lbs with me in, so thats only 1100lbs heavier than the S10 blazer.



Also, i have hauled various flat trailers, pickup trailers, our old popup, with the 4.3L TBI, usually my total weight at the scale was around 8,000-9,000 inlcuding trailer and its load, so i know the 4.3L is capable of moving my 6,000lb suburban, also (and i have atteched a picture for proof)  my father in law towed a 7,000-9,000lbs trailer 200ish miles with his 1994 s15 vortec, yes we weighed it, yes it was overloaded, yes it was dangerous as heck, but they were homeless and had to move or the trailer would be impounded by the police and they would have lost thier only shelter.  my point being that the trailer and blazer rolled across the scale at just over 15,000lbs before we removed and put 2,000lbs of stuff into other vehicles, and that trailer in the pic is waaaay bigger than my suburban and it pulled fine in 3rd gear even up hills, but it did get warm, and was almost to the floor to get up those steep hills, but the 6.2l has to be floored to get up a steep hill too.


The other thing is, yes 4.3's produce similar peak power numbers as the 6.2.  BUT,   6.2's produce their peak torque at a much lower rpm which is much better for towing.


And im only concerned with torque curves not HP, because im not worried about holding 100mph on the freeway. ]Here are the specific rating for the 4.3l and 6.2l, the 6.2l produces peak tq at 2000RPM while the TBI produces it at 2400-2800, and seeing as i have 4.10's my highway rpms are at 2400 at 55mph and 3000 at 70mph,so the TBi would actually be in its power band at just about any highway speed.


The ratings (from here: http://www.gmtuners.com/gminfo.htm)

Chevy 4.3L 90º V6

1989-91 4.3L TBI V6 vin Z

160hp @ 4000 rpm
230tq @ 2800 rpm
9.3:1 Compression
No balance shaft
1992-95 4.3L CFI V6 vin W Vortec (early)

165-200hp @ 4400 rpm
235-260tq @ 3600 rpm
9.05:1 Compression
Hydraulic roller lifters
Balance Shaft
1992-93 4.3L PFI Intercooled Turbo V6 vin Z (Syclone / Typhoon AWD Truck)

280hp @ 4400 rpm
350tq @ 3600 rpm
8.35:1 Compression
1993-95 4.3L TBI V6 vin Z Vortec (early)

165-170hp @ 4000 rpm
230-235tq @ 2400 rpm
9.05:1 Compression
Hydraulic roller lifters
Balance Shaft

1996-up 4.3L CSFI V6 vin X&W Vortec (late)

175-200hp @ 4400 rpm
240-260tq @ 2800 rpm
9.2:1 Compression
Hydraulic roller lifters
Balance Shaft


And here : http://www.dieselplace.com/forum/63-gm-diesel-en gi...

GM 6.2 C-code - 130 HP @ 3600 RPM and 240 TQ @ 2000 RPM
GM 6.2 J-code - 148 HP @ 3600 RPM and 248 TQ @ 2000 RPM

I do know some J codes might have had just slightly higher ratings.






This is just me, but if i had a 6.2 truck, i would either get a replacement 6.2, most likely from GM and/OR get a banks turbo kit.


If i had that kind of money i could just pick up a wrecked 6.5l or 6.6l pickup and swap the engine/trans/tcase in myself, but that is way beyond my budget, since we just lost our house to  storm 5 months ago, i literally just got back to work after surgeries this week and i havent even begun to add up the bills that have piled up in the meantime. I bought this burban for 2 reasons,1 i had already committed to purchasing it before i broke my foot in june, and 2, it is a nice low mile truck for its year and has never seen a salty road in its entire life until this month.  I can get a s10 blazer/jimmy around these parts all rusted out for $200-$400 for the entire thing, and i can have the swap done in less than 3 days, and then turn around and sell the 6.2L, 4l60E, and blazer wheels for more than i paid for the whole thing./b]

I do also know that the 4l60e has different 1st and 2nd gear ratios, and im not expecting O/D at this time, but here are the calculations for my FDR's in each gear with the TH400, and my 4.10 axles.

700r4/4l60/4l60e Ratios: 3.06, 1.62, 1.00, 0.70

TH400 Ratios: 2.48, 1.48, 1.00


Ok so here is the final drive ratios (which is what really matters because trans gear ratios mean nothing if you axle has a 2.47 or other numerically lower gear) after accounting for the axle ratios:

___________________1st___ ____2nd________3rd_______ O/D

3.42 & 700r4, etc____10.4652____5.5404_____3.42______2.394


4.10 & TH400________10.168_____6.068______4.10______N/A


I Also know that all the S10 blazers i owned and my father in laws had the 3.42 axles, because i rotated the wheel to find out before putting different tires on.

I am not trying to sound like an arrogant know it all, i am just trying to show what i have already accomplished with that 4.3l and what i know it is capable of with the proper gearing and axles.  Also I will post a screenshot in the next reply of the factory tow ratings on a 2000 silverado with the 4.3l and various axles, and let me know what you think, bc they dont list a 4.3l and 4.10 axles, but the guy posting has a valid point based on deductive reasoning. the dry weight of a 2000 1500 i can find from people posting on forums ranges from 4,400-5,000lbs with just the basics, i.e. toolbox, spare tire, and driver + fuel, so thats not too far off from my 1988 V20 im trying to put this in, and the 4.3l only weighs around 450lbs fully dressed so i would lose 200lbs up front.


If i do end up doing this ( which is a pretty good bet, since i know the 4.3l waaaaaay better than the 6.2l and were going on a 4000mile round trip honeymoon in march) then i only need it to get up to 55mph at the same rate as the 6.2l and hopefully not consume a whole lot more fuel in the process of holding 55mph. i have driven s10 blazers in D, so my rpms were in the mid 2000's while towing and i still got 14-18 mpg most of the time. depending on trailer, but i know my TH400 wont lock up in 3rd so i will have some losses there.  I am not expecting it to be a speed demon, i only expect it to tow 6,000lbs on mostly flat road at 50-55mph at the most, and be reliable, i have read many many many horror stories of 6.2ls web case cracks, spud bearings, thin cylinder walls, pistons cracking due to heat, etc. and i really really dont want our honeymoon ruined if i can avoid all that with a $300 or less swap

[MuddiGGEr25]

I wouldnt be removing my TBI like you did, but i would look for a 1988-1993 S10/s15 with the 4.3l/700r4 so that it wont have any PCM codes for the trans bc they switched to the 4l60e shortly there after.

[Stewart G Griffin]

Ok, a 4.3 can probably tow all that weight because there is a gm engineer who tows a 3500# racecar with 16' open trailer with one (and with a shortbed at that.)  So, probably over 5000 lbs.    i don't have time to find the link right now.

However, i still vote NOT to do it.   i still think the 6.2 is better for towing and for the truck in general. 

The s-10 blazers, while you had them weighing closer to the suburban are still significantly smaller than the suburban and have a smaller frontal area, so i don't think your mpg will be as high as what you got on those two trips.

i would find out what's wrong with the 6.2. , if it can be repaired, and if so just stick with the 6.2.

1) If you can get the whole setup for $300, do you think everything's automatically going to be ok?   i got my first 4.3 for $300 and look what happened.  So that's why i decided to get a new(remanufactured) engine and do it right.
a) why not rent a truck for the honeymoon?

2) i did not actually take the tbi off the engine because the one i got was carbed---they used the carb for two years---85,86.

https://www.youtube.com/watch?v=3JvVkpshHwU
https://www.youtube.com/watch?v=kTvAdSf_1vI

[MuddiGGEr25]

Ok, a 4.3 can probably tow all that weight because there is a gm engineer who tows a 3500# racecar with 16' open trailer with one (and with a shortbed at that.)  So, probably over 5000 lbs.    i don't have time to find the link right now.

However, i still vote NOT to do it.   i still think the 6.2 is better for towing and for the truck in general. 

I also agree that the 6.2l might be better suited for towing, but thats not its primary purpose, its primary purpose is going to work, and get groceries 100 miles in any given direction.

The s-10 blazers, while you had them weighing closer to the suburban are still significantly smaller than the suburban and have a smaller frontal area, so i don't think your mpg will be as high as what you got on those two trips.

I know my MPG wont be anywhere near 28 lol, i am only expecting 10-13 when towing, and 14-16 when not towing, I know our 1988 and 1987 astro vans growing up, both with auto's would get 17-19mpg at 55mph, granted im thinking both had OD so i would have to expect a 30% drop by not having the Overdrive. our astro vans weighed 4,800-4,900 when we emptied them for hauling supplies for the house, and with all 5 kids and both parents, and supplies for camping trips (usually 90-150 miles round trip) we would be loaded to 8,000 or more sometimes and we still managed 15mpg, and last time i checked the astro vans were just as tall or taller than suburbans, so the frontal area and wind drag is not really a factor when they used them in larger vehicles.

i would find out what's wrong with the 6.2. , if it can be repaired, and if so just stick with the 6.2.

Again this comes down to money, if i could fix it for under $300-$500 and have a warranty sure, but thats highly unlikely with shop rated of $80-$120/hr, and if i do it myself i wont have warranty

1) If you can get the whole setup for $300, do you think everything's automatically going to be ok?   i got my first 4.3 for $300 and look what happened.  So that's why i decided to get a new(remanufactured) engine and do it right.
a) why not rent a truck for the honeymoon?

That was your first 4.3 for $300, this would be my 8th or 9th, i know these 4.3l's like the back of my hand (depending on the year) and i always pull valve covers if im buying an engine or parts truck and if they dont let me then its a no go for me, i want to watch the rockers move while the engine runs to look for any flat spots in the cam or other issues. I also plug up a live scanner to the engine too, because some people disable the CEL so you dont know if anything is wrong, and i watch the outputs of all the sensors, and the exhaust, i also use a timing light to check the injector spray pattern of any TBI i am buying.

As for renting a truck for 10-14 days (3 days there, 3 days back, the event is 4, and any sightseeing we do) that would rack up into the thousands extremely quickly with the mileage and fuel, and the perday rental, and i cant rent a car from any of those rent a car places because i am 26 and i have bought everything i own with hard earned cash and the only thing on my credit history is a few medical bills from back when i was homeless and couldnt afford them or insurance, so either they say no we cant rent to you, or they say your credit score is really low so we have to jack up the rates to cover our &$%!.  Of course if i could afford a reman engine i would, but thats way out of the picture atleast until a year after my next 2 surgeries

2) i did not actually take the tbi off the engine because the one i got was carbed---they used the carb for two years---85,86.

Sorry it slipped my mind that they had carbs those years, but now that you mentioned it i do remember reading several posts about it in my searches

https://www.youtube.com/watch?v=3JvVkpshHwU
https://www.youtube.com/watch?v=kTvAdSf_1vI

[hatzie]

It should be fairly cheap to fix an overnight prime loss as long as the DB2 injection pump shaft seals are not the source of your air leak.  It'd be using more fuel if they were.

The tank return lines can cause lost prime overnight.  The usual culprit is the return off the Injection pump governor cover but all three or four sections of hose between the Injection pump and the tank can bleed air. 
I'd replace the return line off the pump with SAE J30R9 hose.  Be sure to clamp it with proper diameter Constant Tension Spring Band Clamps or German Fuel Injection Clamps (don't use Ideal worm clamps on fuel hoses). 

The 3.5mm injector return lines are another source of air leaks.  Get some 3.5mm Braided Jacket German Fuel Return Line.  It doesn't need clamps.  You can get end caps from VW or Mercedes (they used the same Bosch injector bodies) or just use a short section of braided line with a 3.5mm plastic plug.  Get the stuff with MADE IN GERMANY emblazoned on the braided cover.

Check the governor cover for small leaks.  The Stanadyne 27244 governor cover gasket is fairly easy to replace.

The Stanadyne 80 Box filter has a well deserved reputation for leaking like a sieve.  When they seal they work just fine but the base eventually corrodes and leaks.  I replace them with the Stanadyne 100 top loading Fuel Filter manager used on the 1993 and up 6.5L in the T400 CK trucks.  They are available for $125 brand new. The AC Delco part number is 10226035.  https://www.amazon.com/ACDelco-10226035-Professional-Fuel-Filter/dp/B005574T0U

[MuddiGGEr25]

It should be fairly cheap to fix an overnight prime loss as long as the DB2 injection pump shaft seals are not the source of your air leak.  It'd be using more fuel if they were.

The tank return lines can cause lost prime overnight.  The usual culprit is the return off the Injection pump governor cover but all three or four sections of hose between the Injection pump and the tank can bleed air. 
I'd replace the return line off the pump with SAE J30R9 hose.  Be sure to clamp it with proper diameter Constant Tension Spring Band Clamps or German Fuel Injection Clamps (don't use Ideal worm clamps on fuel hoses). 

The 3.5mm injector return lines are another source of air leaks.  Get some 3.5mm Braided Jacket German Fuel Return Line.  It doesn't need clamps.  You can get end caps from VW or Mercedes (they used the same Bosch injector bodies) or just use a short section of braided line with a 3.5mm plastic plug.  Get the stuff with MADE IN GERMANY emblazoned on the braided cover.

Check the governor cover for small leaks.  The Stanadyne 27244 governor cover gasket is fairly easy to replace.

The Stanadyne 80 Box filter has a well deserved reputation for leaking like a sieve.  When they seal they work just fine but the base eventually corrodes and leaks.  I replace them with the Stanadyne 100 top loading Fuel Filter manager used on the 1993 and up 6.5L in the T400 CK trucks.  They are available for $125 brand new. The AC Delco part number is 10226035.  https://www.amazon.com/ACDelco-10226035-Professional-Fuel-Filter/dp/B005574T0U

That all seems easily within what my abilites are, but i will have to record the engine idling, both cold and hot so you guys can hear the random rattle in it, thats my main concern and i cannot afford, nor know how to tear down the 6.2l, and i have heard many bad things about these short stroke diesels, that basically once they want to go, thats it, and your screwed, usually on the side of the road.

Ok let me put the air leak this way.... i start it and drive it around all day, running errands and working with my customers, (about 9 hours, i also run an inverter for tools on some jobsites, i.e. the high idle times and 200-300 miles in a average day) i let it sit anywhere from 3 hours or 10 days (yes it sat for 10 days recently because i needed new batteries), I cycle the key on, wait for glow plug light, once the glow plug light shuts off, it fires IMMEDIATELY, HOWEVER runs out of fuel after 5-10 seconds, i am running an electric lift pump rated 35GPH, 4-7PSI, if i open the bleed valve on the filter housing, 99% of the time i will get air, then spit, then after a few seconds it will pump out all fluid, then i use WD40 to get her fired up again once the filter is primed, then she is golden all day unless i let her cool off, and if the temp guage is at the far left (i.e.~ 100F, then the glow plugs dont light and i have to floor it for it to fire up)


So im thinking its my filter housing because the filter is brand new, and new lines to and from it

[hatzie]

Leaking injectors or injectors with poor atomization will make her knock consistently on the offending cylinder. 
Even tiny air bubbles, if they're constant, can make her knock and surge like she's trying to climb out of the engine bay.

Sounds like you either have a leaking filter base or the hoses on your electric pump are leaking.  Or both.  Again... worm clamps loosen up and lead to leaks.  Make sure the fuel hoses are SAE J30R9, or worst case SAE J30R7, compliant. 
The original  hose formulations don't like Biodiesel blends...  even B5 can melt the hoses and pump seals.

Sent from my SM-P605V using Tapatalk

[MuddiGGEr25]

Leaking injectors or injectors with poor atomization will make her knock consistently on the offending cylinder. 
Even tiny air bubbles, if they're constant, can make her knock and surge like she's trying to climb out of the engine bay.

no surging whatsoever and the knock is completely random no matter engine rpm, seems to emenate from the center, but it is definitely NOT consistent, sometimes its kinda steady knock i.e. once per second, but then a moment later the knock it completely erratic, BUT the engine speed has NOT changed. 


Sounds like you either have a leaking filter base or the hoses on your electric pump are leaking.  Or both.  Again... worm clamps loosen up and lead to leaks.  Make sure the fuel hoses are SAE J30R9, or worst case SAE J30R7, compliant. 
The original  hose formulations don't like Biodiesel blends...  even B5 can melt the hoses and pump seals.

No biodiesel here at all, and the PO was the original owner, and they said no biodiesel either, and it was run in cali from 1988 till 2009 but didnt have to be smog tested due to the GVWR of 8,600, i am using worm clamps until i have a check, but in my defense i have used worm clamps since I was 11 and put 10-30K a year on some of those vehicles, ( all low pressure tbi or carb) and never had a fuel leakage issue while i owned them, not to say 10 years later, or 100K more miles there might not be a problem

Sent from my SM-P605V using Tapatalk

[hatzie]

Leaking injectors or injectors with poor atomization will make her knock consistently on the offending cylinder. 
Even tiny air bubbles, if they're constant, can make her knock and surge like she's trying to climb out of the engine bay.

no surging whatsoever and the knock is completely random no matter engine rpm, seems to emenate from the center, but it is definitely NOT consistent, sometimes its kinda steady knock i.e. once per second, but then a moment later the knock it completely erratic, BUT the engine speed has NOT changed. 


Sounds like you either have a leaking filter base or the hoses on your electric pump are leaking.  Or both.  Again... worm clamps loosen up and lead to leaks.  Make sure the fuel hoses are SAE J30R9, or worst case SAE J30R7, compliant. 
The original  hose formulations don't like Biodiesel blends...  even B5 can melt the hoses and pump seals.

No biodiesel here at all, and the PO was the original owner, and they said no biodiesel either, and it was run in cali from 1988 till 2009 but didnt have to be smog tested due to the GVWR of 8,600, i am using worm clamps until i have a check, but in my defense i have used worm clamps since I was 11 and put 10-30K a year on some of those vehicles, ( all low pressure tbi or carb) and never had a fuel leakage issue while i owned them, not to say 10 years later, or 100K more miles there might not be a problem

Sent from my SM-P605V using Tapatalk

It could still be minute amounts of air or injectors that are not all they could be anymore.  The random nature of the knocking would point toward air bubbles rather than injectors that are in need of attention but neither is out of the question.  I typically test the spray patterns and balance the pop pressures of injectors on a new to me engine.  The spray pattern actually has to get pretty nasty before the 6.x engines start to actually exhibit symptoms.

Don't dose your fuel with 2cycle oil or ATF.  There are several studies that show it's not a good idea.  The Zinc in the oil will coke up the injector nozzles.

Good that it hasn't seen biodiesel.  Commercially produced Biodiesel is not "washed" the way the guys that carefully home-brew in batches do.  I've found alcohol and soap in some less expensive bio blends.  Even clean properly washed biodiesel can rattle loose a lot of the crud from the last thirty plus years and melt, or at least soften, the old 1980's and early 1990's vintage hoses and the DB2 injection pump internals.  I found this out the hard way on a 1983 C10 6.2L diesel.  You can harden the fuel system for Biodiesel but it's tedious and the Injection pump seals have to be updated with the tolerant parts.

I've had inconsistent results, even in the short term, with worm clamps on hoses under 1/2" to 5/8" or so.  The constant tension clamps on 3/8", 5/16", & 1/4" fuel hose are actually much easier to work with and they stay uniformly tight as the hoses expand and contract.

Did you or the PO remove the mechanical fuel pump from the fuel lines when the electric pump was installed? 

[MuddiGGEr25]

yes the mechanical fuel pump is entirely bypassed. i dont think i am even using the return line at all( i think there is a fuel return line at the old pump... not sure now)  i dont know how to do any of those things you just listed sadly, and probably dont have access to the equipment now that i dont work at an actual shop anymore.