Hi guys,

Today(Saturday), I decided to see if I couldn't improve my engine performance by tuning my injectors.
My engine's had a bit of a lope, especially at idle, and recently lost a bit of power. As one of my crummily-rebuilt injectors had already failed on my, I figured that some others were probably on their way.

I also didn't have the money to get a /proper/ set from R&D, so... Time to hack it!

What you'll need to do this:
1. A couple of spare injectors, for parts(shims especially)

2. Injector pressure tester. I've got the $150 Indian one off Ebay; note that the gauge on it seems to be a little off, so I'm not sure about my numbers. For relative measurements, however, it will do fine.

3. Digital Multimeter with .1 mV-level precision at least. I used my $5 Harbor Freight one; seemed to work fine.

4. 0-1" Micrometer. Digital or analog. Harbor freight one should do fine.

5. 12-pt 15MM socket, torque wrench set to 55 ft-lbs for the nozzle cap nuts.

6. 5/8" wrench for the injector lines

7. 1" socket and long ratchet or breaker bar for the injectors themselves.

8. Roll of paper towels(this is a messy job)

9. Time. Make sure to budget yourself a good day for testing.

10. A working set of glow plugs, all the same model.

11. Piece of plywood to put on top of the engine: In my case, at least, reaching to the back of the engine to check glow plug voltage is hard standing in front, so I sat on top of the engine while doing this(right over the fan). In order to do this, I put a piece of plywood over top of the fan. The front of my plywood was on the radiator, the back on top of the alternator and AC mount. You may have to figure something different out.


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Now, the first thing to do is warm your truck up. Take a short drive, get it up to temperature. Shut the engine off.
You will likely need to pull your air cleaner, to give you room to get to the GP connectors.
Unplug all your GPs.

Get your multimeter and plywood out. Start the engine, and get setup on top of the engine.
Put your multimeter in the lowest mV setting it has(in my case, 200mV with a 0.1mV precision).
Climb on top of the engine, and check from the GP terminal to ground on each GP in turn. At low idle(650RPM), I was getting from -15mV to -20mV, with my plugs.
I used the top of the fuel filter housing as my ground, and it seemed to be consistent. Remember that your multimeter won't draw any current to speak of, so resistance is less of an issue.
What values you get depend on your setup, and don't matter exactly.
What matters is the differences in value. If all of your GPs are within 1 mV of each other, I'd say they are good.
I found a range of values: 3 at -19-20mV, several in the -17-18mV range, and a couple in the -15-16mV range.
Obviously, this isn't good. The voltages correspond to cylinder temperatures - low values = low temps, high values = high temps. If all are close, it means all your injectors are firing consistently. If not, it's why your engine is running rough at idle.

What I found was that high values = low pop pressures and leaks, low values = high pop pressures.

Now, pull your highest(or furthest out) injector. Test it's pressure. It'll probably read something quite a bit different than it should be(1800-1900). If not, perhaps /everything/ is off, and you can either match to those, or re-shim them all.

Once you've figured where you are at, figure out how much more(or less) shimming you'll need. It's approximately 40PSI to .001 shim.

Take the injector apart, in a nice, clean work area. Clean all of your parts as best you can. Lint-free cloth and such would be best, but I used paper towels...which worked OK. Here's a diagram of the parts: https://www.ford-trucks.com/forums/m...010-153554.jpg

Now, measure all of the shims in it. Sometimes they stick in the housing, and you need to take a little hook or pokey-thing and knock them loose(I used a 3.5" long philips screw). A good hard tap on your surface may also work. Be careful not to lose the shims.

Take your shims and come up with a new set that is the new spacing you want.

Put the injector back together, tighten the nut by hand. It should turn freely until you have only about 3 threads visible. If there are many more, you did something wrong.
Now, tighten the nut to 55 ft-lbs, and test it. If you got it where you wanted it, great. If not, pull it apart and adjust some more. I found that it varied more than I would like, but it usually only took a few tries to get it where I wanted it.

Reinstall the injector. Make sure to use plenty of grease of vaseline to reinstall the injector cap.
(You are *supposed* to use new brass crush washers when you do this, but I just cranked it down hard and called it good. Once you get everything perfect, then use a good set of washers, but now you'll be pulling and reinstalling them quite a bit getting them to match. )

Start the engine, run it for a minute or so to allow the injector to get fuel and run for a little while.

Test the GPs again. See if it worked, you didn't go far enough, you went too far, etc.

Rinse and repeat.


Personally, I managed to get all but one to be within one mV of each other, and they ended up in the -17.5-18.5mV range. The final one, I didn't have enough time to get it tweaked, but it was at -15.6mV(i.e. retarded). When I get a chance, I'll fix that one too.

Even at this point, it's a bit quieter at cruising speed(and, most importantly, doesn't sound like I've got knocking rods). Also has a bit more power.


Good luck, guys!

 

Thanks for the write up on this. I'm pretty sure my injectors could use an overhaul as well.

One question. What is the significance of using the GPs as opposed to just pulling the injectors and pop testing/shimming them to match?

Thanks
Robby

 

Great little write-up!

 

#4 stainless flat washers that have been lightly sanded also work well for shims. They vary in thickness from 28 thousandths to 36 thousandths with most about 32 (at least the batch I got).

Nice write up!

 

what about the variable of the gp,s . did they all test the same cold/hot before tuning?

 

This is a very good question. I thought about this for days, and finally came up with this:
If you are dealing with good quality injectors, an accurate pop tester etc? There should be no advantage to testing using the GPs.
However, if you only want to tune a few injectors(to save time), or figure out what's going on? GPs are invaluable.
On the 5th, when I did this, I found out how useful it was: After installing 3 adjusted injectors, my engine sounded great. I revved it up, and suddenly one cyl stopped firing.
Tested my GPs, and found out which injector it was that had died, pulled just that one, and found that the bottom had come loose due to improper torquing.
Much easier than pulling *all* the GPs.


No. And this is exactly why I was doing the tuning. They were measuring very different readings, and the engine was rough at idle(see for what it sounded like).
The closer they are, the better things sound, and the more power you have.

 

That's a great way of measuring consistency between the cylinders.

 

Thanks for the follow up. This is very helpful info.

Robby

 

I'll have to give this a shot. I know I have a bad injector for sure, but it'll still be interesting to check out.