Help! Is this normal? 94' 6.2 Conversion Suburban

[dkhajavi]

I am just finishing a conversion on my 94' GMC Suburban 2500 4X4 to a rebuilt 6.2. I have spent thousands more than intended after my good used 6.2 engine turned out to have a cracked block. But now I have a freshly overhauled 6.2 in the truck and a TCI trans computer to control the 4L80. She has new pistons, bearings, heads, etc. Top to bottom overhaul.

The truck is running but not fully completed with A/C working and such but starts and runs fine (I am using a manual glow plug set-up). I have the largest GM radiator used in Suburbans which is bigger than the unit used on the 6.2 or 6.5 units. She also has twin 16" electric fans and and an electronic controller. The exhaust is stock 454.

The big problem is that she has so little power that I cant climb any decent hills. I have to use the 4X4 low range to get over hills I could jump over with the stock gas 454. I expected a difference in HP from the 454 but figured the TQ would be similar and since I am not looking for speed I would be OK.

I did not change the stall converter but have been told that the 454 is slow close in it's power curve that it should be just fine with the 6.2 ltr. The gearing is very tall which is normal for the 454s which I thought would be a good pairing for the 6.2 ltr.

When floored she puts out a good amount of smoke like she is going to pull great but there is nothing there. She drives around but like she has a 15,000 lb trailer behind her all the time.

I am not 100% sure the mechanic that set up the engine was OK so that is one concern I have. Another is whether or not the transmission controller is set up right or not. One big difference is that when the tranny shifts it is much firmer than before which I thought would help matters not worsen them. If I am getting smoke at full throttle I should be making power right? Do I need to go to lower gears? To add insult to injury I want to tow a heavy trailer! Any thoughts guys?

[john8662]

Smoke = Unburnt fuel.

What hills are you talking about climing? Mountain passes or out wheeling?

That rig is pretty heavy, it really is, I have one and it had a 6.5TD in that did ok, but had 4.10 gears in it.

What gears are you running currently?

Your choices will be 3.42, 3.73, or 4.10.

For pulling with a N/A 6.2 I'd vote for 4.10 gears.

What do you have for tires? The factory 245/75R16's?

Bigger won't help you in the power department.

J

[dkhajavi]

I need to check what gears I have but I would guess either the 3.73 or 4.10s. I am running 285/75/16s on her. So you think I need to re-gear her huh? I guess if I'm going to do it I can go even lower too? Speeds where I live are not very high (60 MPH at best) but I do want economy too. Propane injection?

[93GMCSierra]

Sounds to me like you have too much unburnt fuel I would check to make sure you have enough air, possibly go with a turbo.

[dkhajavi]

What about propane injection setup for just full throttle use (so all the time basically)? I have a complete box full of valves, regulators and all the goodies to run it.

[DmaxMaverick]

What about propane injection setup for just full throttle use (so all the time basically)? I have a complete box full of valves, regulators and all the goodies to run it.

You don't have enough oxygen to burn the fuel now. Adding another fuel won't give you any more power. It (propane) will likely take up valuable space in the combustion chamber now used by O2, reducing power. NOX, on the other hand...... Without a method of increasing O2 available to the cylinder, more fuel is not the answer.

Your issue sounds like a timing or fuel delivery problem. While larger tires and/or tall gears will take away from your power, you shouldn't have to use 4 low to travel up a grade. You need to have a close look at your fuel system and injection timing. What color is your smoke?

[Peter J. Bierman]

Getting your timing too advanced will couse the blacksmoke but not the power to go with it, check the fuel lift pressure, it might couse the timing problem.

Peter

[dkhajavi]

The smoke is grey/black and only when full throttle. I also have a Land Rover Defender with a 300tdi 2.5 ltr Diesel and if I compare the two I would say that based on the size of the engine, that the smoke level is about right to a little to high for a factory setting. Not super excessive for sure and could be increased (visualy) for more power. This is all very subjective, I know.

The engine is pretty loud (rattles) at idle and has a pretty significant vibration compared to the 454 gas engine. I am not hearing a mechanical problem as the vibrations and rattles are very rythmic and seem to match my other diesel just much louder. Right off idle it is much better on both counts. The injectors are all new and I dont perceive the above issues as a clogged or dirty injector.

If the timing is off would this effect the smoothness only or can it also effect the power? I assume the cam can be off too?

The exhaust is about 2.5" X2 then into one 3" which is enough right?

[Peter J. Bierman]

Much rattle indicates advanced timing and can be the course for the lack off power.
It kinda sounds like the TDI engine.
I think you shoud check the timing.
It will never be a racecar but youmight expect normalpower from this engine and climb pretty steap hills in 4X2 hi.

Peter

[DmaxMaverick]

What fuel lift pump are you using? I hope you aren't using the original in tank pump (from the 454 gasser). If so, the pressure is way too high, and can cause the problems you describe. Fuel pressure should be 4-7 PSI, and never above 10 PSI. Minimum pressure is anything above zero at full load. An OEM mechanical Diesel lift pump will do the best job. If you have both in place, I'm not sure what the result would be. Some in tank electric pumps allow little or no pass-through, which would be a significant restriction. Put a gage on it and verify your fuel pressure at idle and full throttle under load (hard acceleration).

The engine shouldn't rattle too bad at idle. If it is, it could be too advanced. Retarded timing is usually a quiet engine.

An air intake restriction will also cause gray/black smoke.

[dkhajavi]

I bet they left the original pump. I hope the put it in with a return and a regualtor at lease. I assume that is OK?? If the pressure is 4-7 PSI we are good, however we get there right?

I also think you guys are on the mark with the advanced timing. So they next issue is whether I should trust this to an 'expert' or do it myself. The concern I have is that the way we ent through two blocks and different heads etc... I am scared that the timing pointer is not right. Can I do it by ear as I have read others do?

[80Sierra]

I may not be right, since I am still fairly new to these diesels, but there is a little line scribed into the aluminum timing cover, and a corresponding line scribed into the injection pump.

My understanding is that you want the line to be about two line widths to the right hand side of the line when you look down at it. Anything more than that, and your too advanced... Moving the timing involves loosening the three bolts that hold the IP on, and carefully rotating it until it is lined up where you want it, then tightening the IP back up.

[DmaxMaverick]

Yes. 4-7 PSI, however you get there is fine. Your description of the problem can also be caused by no lift pump operation. The IP has a transfer pump built in, but it will only draw so much fuel. Put a gage on it and get right to the horse's mouth. Also, trace your fuel supply line and verify what you have the injection pump attached to.

[BARRAZA]

It may be helpful to check the timing, but a 6.2 will feel like a slug compared to a 454 because it is!! As much as we all like these diesels, a non turbo 6.2 is probably down 150 ft lb of torque compared to a 454, and as much as 200 HP. You will definitely notice it, but you will feel better at fillup time.

[dkhajavi]

Barraza, thank you for your post. This really goes back to the heart of my post. I am tying to get to the bottom of what can end up being a very subjective question. Is my 6.2 performing as is to be expected or not. If it is well then it is and I need to look into other options such as another member recommended, lower rear end ratios, or turbo charging.

I am a part owner and manager of the worlds first carbon neutral airline, Nature Air in Costa Rica. We did this initially purely becasue being a small outfit in an environmentaly conciencus country like Costa Rica, thought we could. Well we have, and as such we are allways looking both as a company and as as individualy to stay on the walk that we talk. What was a crazy idea has turned out to be a marketing windfall as we have been honored accross the world for our pioneering efforts. We have made far more from this than we have spent in time and money. The reason I go into this is that I no longer feel comfortable sitting behind my managers desk having driven to work in a 7.4 ltr Suburban getting less than 10 MPG. I also did not feel comfortable scrapping the truck when she had so much more life in her to consume so much in new resourses to make a new one. So when I looked into repowering here I stayed away from the 6.5 becasue of the difference in economy though I knew there would be a perfromance drop.

I live in a country where the best highway has a 55 MPH limit so speed is not an issue here. The problem is getting over the hills. So is it reasonable to believe that a 94' Suburban 2500 4X4 w/ 4L80 and a properly running 6.2 ltr should be able to get over a steep hill in 4X2 or not? Subjectivly of course

[93GMCSierra]

I am no expert but I believe it should not have nearly the power loss you think it does, something is not right with it. as to the 6.5 option, I dont know exactly on them either but I have a 93 6.5 2500 4x4 all mechanical and got 19-21 miles per gallon on the highway at 65 mph this has a turbo and it has plenty of power it can out pull the 454.

[BARRAZA]

I am tying to get to the bottom of what can end up being a very subjective question. Is my 6.2 performing as is to be expected or not. If it is well then it is and I need to look into other options such as another member recommended, lower rear end ratios, or turbo charging.

The reason I go into this is that I no longer feel comfortable sitting behind my managers desk having driven to work in a 7.4 ltr Suburban getting less than 10 MPG. I also did not feel comfortable scrapping the truck when she had so much more life in her to consume so much in new resourses to make a new one. So when I looked into repowering here I stayed away from the 6.5 becasue of the difference in economy though I knew there would be a perfromance drop.

I live in a country where the best highway has a 55 MPH limit so speed is not an issue here. The problem is getting over the hills. So is it reasonable to believe that a 94' Suburban 2500 4X4 w/ 4L80 and a properly running 6.2 ltr should be able to get over a steep hill in 4X2 or not? Subjectivly of course

Depends on what you are calling a steep hill, I dont think any paved hill should require low range, if you are needing that, something is wrong. I have heard people talk about pulling lots of weight with a nonturbo 6.2, but mine was a slug at 10000 lbs gross. The bottom line is that these engines are weak. I know it ruffles feathers around here to admit it, and I like mine anyway. If you are looking for 454 power, a 6.2 is not the place to find it. Mine is a military j code, and it only has 155hp, I think the non j code engines were 130 hp. Another way of looking at it is that for the year I just looked up, 130hp is about 60% of the hp the 350 cu in gas motor had. That is ok hp in a half ton 2wd short bed truck. In your 3/4 ton,4x4 suburban, dont get in too big of a hurry. Your question doesn't have to be purely subjective, if it seems to be running ok, get a stop watch(or a sundial), and time it from 0-60 and over a quarter mile. My 5/4 ton cucv 4wd pickup was accurately timed at 0-60 in 14.2, 1/4 mile is 19.9 @ 72 mph. These numbers were at about 6200 lbs. Definitely not a rocket, and unlikely to be confused with a 454, but it has good compression, a new injection pump, and new injectors. It is a point of reference, check yours and get back to us.

[ccatlett1984]

what did you change over stock to get your truck to go ovr 70mph, a stock M1008 will not go near that fast.

[dkhajavi]

I did a little investigation today and found the following:

The conversion shop is using a mechanical lift pump (looks stock on the side of the block). I was going to check the pressure but could not find my 'T' to plumb in my pressure guage, so that will have to go to another day. I am now wondering if he removed the original in tank electric pump or not. My worry now is whether or not it would cause a restriction being there and off vs being removed? So looks like I get to drop the tank (one of my favorite things to do!).

I could not find any tags on the rear end and decided it was due for a rear end oil change anyway. So after pulling the rear cover and doing some counting I have a 11/41 or 3.73 rear end. I looked in Summit Racing and they have gear sets for $150 each. I am not sure these are the same for the front, but I am considering a mid 4s rear end if I cant get more out of the engine.

The hidden issue is that I have a 30' Enclosed trailer that I need to pull. No major hills to go over but I am very concerned. The truck is fully set-up to tow with airbags, big brakes, mirror extensions etc... I have to get over hills without the trailer before I can hitch her up (if ever)!

[BARRAZA]

what did you change over stock to get your truck to go ovr 70mph, a stock M1008 will not go near that fast.

That was after changing the gears. With the 4.56's it did 67 in the quarter with 38" tires