Where are you guys plumbing into the cylinder to perform a compression test? Is there an adapter to test through the injector port?

Tried compression testing trough the glow plug holes, but the rocker arms need to be disconnected......which depending on where the piston is located on the stoke and the valves closed, you get all kinds of results. One day it just started having major over fueling problems with no power and I've been eliminating different things (just got the injectors flow tested...no problems).

 

I am actually going to do a short write up on my travails trying to do a compression test. First, it is done through the glow plug hole. Others will tell you how to do it, etc., because I haven't gotten that far.

1fixitman or BigAl will hopefully tell you how to make the adapter and what to do. You need a diesel compression gauge because the high diesel pressures will blow out a regular gas compression gauge.

The Harbor Freight 12 piece diesel gauge set doesn't work because the adapter won't fit (returned to H.F.). And hooking something else up to the H.F. gauge is a problem because it uses BPT (British Pipe Threads) rather than NPT (U.S. National Pipe Threads).

So, I bought a Mityvac MVA5605 Glow Plug Adapter from Tooltopia.com (RMA return request pending) and the Star TU-15P gauge from beachaudio.com (RMA return request also pending). These two fit together perfectly and the Star TU-15P gauge appears well made.

The Mityvac cross-threads apparently because the hex bolt near the fuel boss which goes into the glow plug hole hits the rocker arm. I drop in a used glow plug and can thread it in easily with two fingers. I try the same with the Mityvac and it will bite no more than one-half thread. I bought a 10mm x 1.0 die thinking that the chrome on the threads was the problem and I could clean them up a little, but no dice - it will not thread in without force which I will not do.



So, I just ordered the Snap-on EEPV314A adapter. Check it out. It looks like a glow plug. The hex nut next to the fuel boss is small like a glow plug.



But I can tell from the picture that it will not fit into the Star TU-15P diesel compression gauge, at least without an adapter (possibly from Parker Hanifin). So, I may be buying a Snap-on diesel compression gauge (ouch!).

Good luck, let us (or at least me) know how you solve this problem.

Edit: Some companies sell an injector-looking adapter, but my guess is that you wouldn't want to use it, because your new or tested injectors have new o-rings and new copper washers on them and to do a compression test might require you to install them and then remove them one by one to do the compression test? (I am not sure about that.) And people on this forum have said that you should consider injector o-rings and coppers a one-time-only-use-item. So, I decided to reinstall my injectors with new o-rings and coppers, spin the engine to get the oil out of the cylinders to prevent hydrolocking with a remote starter switch (mis-named because you use it rather than the key so that the engine will NOT start and you don't fry your UVCH as I learned from Franko72), and leave all the glow plugs out, and do your compression test through the glow plug holes with a glow plug adapter.

 

With the right fittings and gauge, where do you go from there. I have never done a compression check and have ordered the gauge and fitting. Do you remove all the glowplugs before starting or remove 'em one at the time and put each one back as you do the compression for that cylinder?

 

pull all the GP's dont have the injectors running and turn it over.

i use an adapter as Tim but a different brand cant think of the name, i got mine of ebay cheap.

 

BigAlsPSD, SkySkiJason and many others have helped me, so hopefully they will chime in here and correct what I get wrong or add to what I miss.

Warm up engine to operating temperature.

After removing the valve covers, unclip the wires to each injector by flipping the retaining wire and pulling out the electrical plug for all of the injectors. Pull the glow plug electrical connections for all of the glow plugs up and off.

Plug your battery into a battery charger.

Use a 10mm thin wall deep socket (1/4" drive is usually thin enough) and carefully pull out all the glow plugs straight out so as not to knock off a burned-out tip of a glow plug. You will need a 12" long piece of 1/8" fuel line tubing to spin out the glow plugs quickly and to pull them up and out. You will cut off about 3/4" of the hose for each glow plug, because the inside gets greasy and doesn't hold onto the glow plug well unless unused.

Do not remove the injectors.

I use a bump switch (also called a remote starter switch) from Napa connected to the starter so that I can spin the motor for the test without electrifying the UVCH ("Under Valve Cover Harness") to the injectors and glow plugs.

It is important that the harness is not energized! I think it was Franko72 who burned out his harness when it arc'd to a close piece of metal. We all learned from him. You should also disconnect the plug from the CPS (Cam Position Sensor) on the crank pulley (easily accessed on your back under the front of the vehicle) or you can disconnect the 42-pin connector which is in the valley between the valve covers just to make sure that the harness is not energized.

Spin the engine a few "puffs" (i.e., cycles) to push any debris and fluid out of the cylinders.

Then install the glow plug adapter. You will need to align the flat side of the nut against the rocker arm to push the adapter down into the glow plug hole. It was tight slide for cylinder #8 for me but easier on the others. Use the 1/8" fuel line to spin the adapter into the hole. Do not cross thread. The glow plug adapter must be seated (in fact it has a small o-ring on the bottom, don't lose it or pull out the adapter of the glow plug hole at an angle and leave the o-ring in the glow plug hole!). Tighten the glow plug adapter slightly by hand with a 7/16" open end wrench (i.e., 5 Nm ?) just enough to compress the o-ring a little to get a good seat.

Hook up adapter to compression gauge and spin for 12 "puffs." Write result down. Then repeat again for same cylinder.

Then do the same for each of the other cylinders.

Print out the cylinder number order diagram so you can write your results next to each cylinder:



Replace the glow plugs with new MOTORCRAFT (not Autolite!!!) glow plugs part no. ZD-11 F4TZ-12A342-BA

I think that is it.

Then post your results and the people here will help you interpret them.

 

i would try cold and warm motor it can change the readings.

 

That is exactly what I have been looking for during my dozens of of thread searches. Admin should make this a "sticky" for newbies like myself. I appreciate your post, and by the way, I usually try to abstain from thread hijacking but just had to ask the question.
Thanks again,
Willie

 

Here's a printable PDF, with the tester, parts numbers, and adapters. It really needs refined to show the testing procedure better, but it's what I have available at the moment.

7.3_Compression_Testing.pdf

 

I'm not sure how I missed this thread... opps.

I ordered one of those a while back, it was around xmas last year. I didn't even have a 7.3 then... but thats kind of irrelevant now. My adapter came with a standard 1/4" air compressor fitting on both the adapter and tool. And when I say standard, you can remove it and have a 1/4" threaded pipe on the Snap-on adapter to attach the correct fitting for your tool.

 

BigAl: Thanks for the pdf. It should be attached to any sticky. I was just too much of a weenie to build my own adapter especially after buying the Mityvac adapter to find that it would not fit.

Is there anything you would add or subtract from my description of the testing procedure?

I wouldn't mind putting together a sticky (I will have to write it up anyway or I will forget what I did by the time I get around to testing the passenger side cylinders).

But I have no pride of authorship. (I learned a long time ago that I wasn't the brightest bulb on the tree.) I just want what I write to be right.

So, everybody's input would be appreciated.

 

I don't see any issue with your procedures personally, they seem thorough enough. I would only add, the unplugging of the CPS, or 42 pin connector to ensure you aren't firing. I know that you used a starting switch, but if you were to use the key the user needs to remove the firing capabilities.

 

Got ya! I know that the CPS is next to the crank pulley and how to unplug it. But I don't know where the 42-pin connector is. Also do all of the 7.3's have a 42-pin connector?

 

The 42 pin is the main motor wiring harness, on the trucks it's atop the DS valve cover. Not sure on the vans, but assume it's the same location, although I have a van motor currently in my truck, and there was no provision for the bracket, I had to swap it over from the truck motor. The connector unbolts with a 10MM socket.

Also the GP's you need a 10MM rather than the 8.

 

Excellent, thanks again!

 

This a good tread with some great info. Because if I find I have a bad glow plug before I replace all of them I was wanting to do a compression test to check the health of my engine.