Hello all,

So I have been cracking away at my truck for a few months now making improvements, but I am getting to the point where I am going to start sinking money into the engine because shes not the most reliable (hard starting, smokey, alittle sluggish/possibly underpowered, never trusted her enough to push her).

So my question is, I am thinking new injectors, injector pump, new fuel lines. My plan is to stay with the truck either way, whether I need to swap engines or not cause shes got a good body/frame. But what do I have to do before I decide to sink any money into the engine to decide if its worth the effort or if I just get a 7.3 and rebuild?

A side note, I also would like to swap in a junk yard turbo off a late model.

Thoughts?

Thanks Again,
Devin

 

I would do a compression test to see where the engine is at internally.


I'm not sure what the numbers should be for an IDI (Only have done one on a powerstroke), but I know you don't want any more than 15%-20% difference between your cylinders.


The best thing to do is pull out all the glow plugs, and test 1 cyl at a time. Cranking 15-30 seconds at a time, then record your numbers. You will use the glow plug port for your testing. If you have any low numbers, it would indicate wear inside.


Have a battery charger hooked up to keep your batteries up. Also unhook the 12V at the pump to prevent any unwanted starting.

 

the cheap side....
do a leak down test on it.
a compression test only tells you how much pressure each cylinder builds. thats it.
a leak down test will tell you if the cylinders hold the proper pressures.
basically what you do is put the piston at BDC, remove the rocker arm assembly, and through the glow plug hole, apply 100 psi.
with the exhaust, intake off, dipstick, and rad cap removed, this will tell you where leaks occur, if there are any.

the gauges on the leak down tester will tell you the amount of leak down.
then you can make a educated decision on wither to rework, or not.

if youre doing a late model turbo, like a powerstroke turbo, or any turbo for that matter, i would pull the heads, have them cleaned and tested, new guides, and have the valves and seats ground.
this way you know for sure that the top end is good.
i would also grab a torque cam while your at it.

while the heads are off you can inspect the pistons and cylinders.
if they are good, you can get head studs, and new head gaskets.
beware... the rabbit hole goes deeper than your pockets sometimes lol

 

Ok you have my curiosity. Why wouldn't you want to know how much pressure the cylinders build? If the op had cylinders that were lacking in compression, performance would suffer (smoke, low power etc...)

Not trying to be smart, just wondering why this is better.

 

Ok hypothetically to simplify the scenario further. If I had a 7.3 and a 6.9, which one do i rebuild and put back in the truck? Considering ease, cost, availability of parts, and performance?

I'm assuming I will find some degree of failure (as I suspect any vehicle this age would), so I imagine its only a matter of time before I do rebuild whether now or in 2 years. So with some foresight I'd like to make the decision consciously.

Cheers and thanks again,
Devin

 

I'd start with the 7.3. Because 1/2" head studs vs 7/16.
Once you're turboing it, you want the extra clamping force.

That all being said... you can start doing 'performance' mods now, because it will all swap over if/when you rebuild the engine. New injectors and IP? These'll go on any 7.3 or 6.9 engine. If you want performance, go with a RD2-110 from Justin; if you want to run it N/A for a while you can always turn down the fuel screw.

Turbo? Either find a used Banks turbo kit or talk with Justin for a new kit/parts. His turbos are lightyears better than any PSD turbo in terms of spooling and performance.
The banks is /decent/, and a major improvement over /no/ turbo.


Also, as far as performance goes... even a 'weak' engine will be helped by a turbo. Before I rebuilt my engine, it was quite sloppy and weak. That turbo gave me a /lot/ more power once it kicked in(1600+ RPM). The engine, when I tore into it... /multiple/ cracked rings. And it ran until I shut it off to tear it apart.

 

the more information you can gather, the better.
on a low buck build, you can determine the condition of the rings, I & E valves better with a leak down than you can do with a simple compression test.
its pretty much the same amount of work that gives you more data.

for instance, (numbers not to scale) if you do a compression test on 1 cylinder, and you get 280 psi, you know that the cylinder builds decent compression. what else can you gain from doing a compression test?
nothing, you just know that the cylinder builds compression. and even with a slightly bent valve, the engine will still make compression.

with a leak down, it may not tell you the exact compression, but it will tell you if your rings and valves have an issue.
when you fill the cylinder with 100 PSI, the air will either hold, or escape through the path of the least resistance. telling you that you have either a intake valve, exhaust valve or ring issue, and in a head gasket or cracked head failure you will hear the air escaping through the coolant passages.

now a engine with a cracked head will build more compression than a engine with a bent valve, and with the few rotations you do with the compression test you may think things are ok when you have an issue.
but a cracked head issue can be so small that it wont register.

remember youre not at the local dirt track and pulled off into the infeild for a tech and a compression bubble check.

these IDI's are pretty much all of the same compression.
while yes, if you have 10% differences in compression readings, you may call it good, but with the same amount of work, you can tell how good, and what your issues are.

i have been working on engines in cars, trucks, and boats as a hobby for the past 25 years, and i have done way too many compression tests in my day.

i have since then retired my compression tester, and fell in love with my leak down tester.

 

I am thinking I am going to stay with the 6.9 based on economics and situation.

I need a reliable truck now and would still even if I decided to buy a second motor to rebuild because I need to be able to get the donor truck/engine etc.

I already own the motor, and I am going to invest in the IP and new injectors, and who knows what else to get the truck reliable so when the time comes a rebuild of this engine is going to make more sense financially because I would have already invested $1000 on parts that may not be transferable.

Plus from what I read they are pretty much the same engine, performance wise I expect the gain to be minimal from 6.9 to 7.3. Also the 6.9 I have heard to be better for rebuilding because of the thicker walls and not being affected by cavitation.

In other words if it provides to be a reliable truck for a few awhile and I see it going down hill I will be able to plan ahead.

Thoughts?
Devin

 

If you get a pump and injectors now and decide to replace or rebuild the engine those parts can swap right onto the new unit. So no going backwards there. A bad fuel system ,glow plug system can really aggravate a person, sooo, fix these things first, some miles with a good fuel system and then a leakdown or comp test will be more accurate as the excess fuel washing the rings will give a bad reading on an otherwise decent engine. These are tough units, dont be afraid to push it after a "tune up"

 

Based on rockauto I looked at a 85 6.9, a 90 7.3, and a 94 turbo 7.3 and rockauto lists an ip2 pump for my engine, but an ip3 or ip4 for a 7.3, and an ip6 for a turbo 7.3. Not sure what the difference is but they are all standyne DB2 pumps.

Devin

 

Thank you for the explanation, makes sense. I learned something today.

 

I would definitely NOT get fuel injection parts from ANYONE but Conestoga diesel, R&D, or Type4. PERIOD. Way to many complaints and risk.

 

Thanks SP. And as he said, DO NOT buy from any parts store. You will have nothing but problems.
Pm me for more info if you like.

 

Can anyone make a comment on the different pumps? Also whats the deal with the performance pumps like the RD2 I have heard of? I am more interested in efficiency rather than raw power though so not sure if this falls in this category.

Thanks Again,
Devin

 

With a diesel like this, effectively your foot controls how much fuel is injected. More throttle = more fuel. Less throttle = less fuel.
Diesels always run lean; in ours, it's simply a matter of the pump reducing the fuel until the engine RPM is stable compared to throttle input. I.E. you will always be at the 'leanest' setting needed to maintain that RPM under the given load.

If you push the throttle hard and start getting black smoke, that's too rich. It means you are putting too much fuel in.

The difference in the various "stock" pump models is basically what the fuel "limit" is set to - that is, with your foot to the floor, how much fuel is injected.
This can be adjusted easily on any DB2 pump, up to how much it can put out.
Most stock DB2s are rated somewhere around 80CCs of fuel, max. Justin has improved custom pumps which put out 90, 110, and above. If you keep your throttle touch light, there's no difference in fueling between these. If you push hard on the throttle, well, you'll get more fuel from the higher rated pumps.

All the fuel in the world, however, is useless unless you can burn it. This requires more air. The stock pumps have /more/ than enough for a N/A diesel. However, the HP you get out of it is pitiful.
Add 15 PSI of boost to your engine, and you can about /double/ the HP out. If you aren't /using/ that extra power, your efficiency is about the same. If you /are/ using it, however, you will be burning more fuel. But that's the price you pay for going up a hill at 60 that you would have had to go up at 40.


Just as a personal anecdote, I've been tracking fillup-to-fillup fuel economy numbers on my truck for the last 3 years.
Unloaded, I get about 16 MPG. This didn't really change when I added my turbo, when I rebuilt my motor, when I added my RD2-110 IP, or my new R&D injectors. It may have been <0.5mpg higher back before the mods, but I can't be sure.
That being said, I do push this truck a lot more. It's just so /fun/ to rev it up and lay into it when getting onto the road that I do it a lot. Even so, I'm still in the same range.

Under load, things are lower. I've had a trip average of 10MPG when I towed a ~4,000lb trailer empty one way at 60MPH and with ~12,000lbs of hay on it(16,000lbs total) at 40MPH back.
This was recently, with all the mods. I don't think that's bad at all.

Effectively, these power mods aren't taking away from economy. In these engines, what's good for power tends to be good for economy as well; as long as you aren't throwing smoke out the back, you are burning efficiently(well, timing also matters quite a bit).