Before I buy an injector

A friend of mine has an early '99 (7/98) 7.3 with 310k miles. He bought it with about 280k miles and no known service history. He has always had a hard starting issue and now the truck is running rough, like it is missing.

The missing started about 4 months ago and he had it towed to a shop which diagnosed it with a bad IDM, the IDM was replaced and the truck ran good for about 2 months. Now it is back to a miss.

I finally broke down and had him bring me the truck. I don't normally work on his vehicles because he doesn't care for them. He buys high mileage vehicles drives them till he thinks they cost him to much and then sells them.

Anyway, all 8 glow plugs were bad, there is the hard starting problem.

Did a buzz test using the Car Gauge app. It says #1 injector high side open but it was actually the #2 injector (front driver's side) injector that screamed to high heaven, very loud.

All injectors measure 3.5 ohms except the #2 injector (front driver's side) which measured 4.5 ohms. This was using a new wiring harness.

So I am certain it is the #2 injector. Can just the solenoid be replaced or should he just bite the bullet, spend the $140 and get another injector?

Let me correct something. When I start the buzz test and all injectors buzz at once, that is when the #2 injector is very loud. When it is buzzed individually it sounds fine.

Car Gauge returns cylinder #1 high to low side open.

#2 injector with a brand new harness still returns 4.5 ohms where the others show 3.5 ohms

I had 2 bad solenoids that ohmed out to 7.5 on my old injectors. I just swapped out the solenoids from a core set I had. All was fine.

Try swapping solenoids from an adjacent injector and see if the problems follows that solenoid. Real easy to swap them out.

Billy T.
[email protected]

Also make sure the armature plate isn't loose and slapping around. You'll see it when the solenoid is off.

gnxtc2 said:

I had 2 bad solenoids that ohmed out to 7.5 on my old injectors. I just swapped out the solenoids from a core set I had. All was fine.

Try swapping solenoids from an adjacent injector and see if the problems follows that solenoid. Real easy to swap them out.

Billy T.
[email protected]

Click to expand...

Swapped the solenoids from 3 to 1 and 1 still reported back as high to low side open. The wiring ohms out at 3.5 ohms at the 42 pin connector.

The IDM is marked Reman Auto Electronics https://www.remanautoelectronics.com/product/Ford-7-3L-Diesel-Injection-Driver-Module-IDM

I'm thinking that may be the issue

Did you check the harness that goes over the driver side valve cover for any chaffing?

Billy T.
[email protected]

No chafing anywhere I can find.

I ohmed all the way back to the IDM plug. Getting ~7 ohms on all injectors.

At this point I can't imagine it being anything other than the IDM

PsRumors said:

Swapped the solenoids from 3 to 1 and 1 still reported back as high to low side open. The wiring ohms out at 3.5 ohms at the 42 pin connector.

I'm thinking that may be the issue

Click to expand...

My very first post here was cylinder #2 High to low open. Only thing that fixed it was swapping in a reman injector...

So you have 3.5ohms at each injector, the same at the 42pin connector but it increases to 7 on each one at the IDM?
Is this testing the wiring at the IDM connector? Sure your not testing across two injectors?
A single strand of wire can give a good continuity as it isn't carrying a load. The same wire will show a voltage drop(if it carries any at all).
Need to understand how/where the test is being performed that increases the resistance in your diagnostics.
If you switched injectors and it is still a #2 problem then the problem is in the wire harness somewhere.
Make sure you have a really good meter that has a 200ohm scale as you will need this sensitivity to find the problem.
Any increase in ohm's(test the leads together first, always) is suspect.

I suspect a loose terminal going to the #2inj.

Hope this helps

To recap,

Buzz test is returning #1 High to low side open
Replaced UVCH on both sides as the ohm readings were upwards of 10 ohms across some injectors
At each connection back to the 42 pin connector I now get `3.5 ohms
At the plug that plugs directly into the IDM ohms reading jumps to `7
Switched the #3 solenoid with the #1 solenoid and still have the #1 high low open issue

The multimeter I am using is nothing special but does have the 200 ohm range. I don't necessarily trust the meter but look for consistency. At the plug at the IDM I am getting `7 ohms across each injector.

It's not the injector. It's the harness between the IDM and the 42 pin connector, if anything.

It is twice as far from the IDM to the injectors as it is from the 42 pin connector to the injectors. It appears that the resistance doubled when it went twice as far.

Do a rough guess, get a piece of wire the same gauge for approximately the same length, see if it has the same resistance.

I'd unplug at the 42pin and the IDM. Check your resistance on the ground circuit, i seriously suspect it. Look for even the slightest resistance increase.

One stand of wire out of a bundle of say 25 will show good continuity but won't carry a load.

With the harness disconnected if nothing shows in resistance try running power thru each wire(harness MUST be disconnected at 42pin and IDM.

Look for a voltage drop, even the slightest drop can indicate the culprit wire.

Truck is repaired, was in fact the #1 injector.

I checked, double checked and triple checked the harness, at the 42 pin connector ohms across the injectors was ~3.5 ohms, as soon as you went to the connector at the IDM the ohms reading jumped to ~7. From the 42 pin connector to the IDM connector the readings was ~2 ohms so I assume the 42 pin connector itself is responsible for about 2 ohms of resistance.

Fact of the matter, the ohms readings stayed consistent across each wire / each injector which leads me to believe the harness was all good. Replaced the injector and all is well.

So what in the injector, other than the solenoid, can make the solenoid fail a buzz test?

Did you try swapping solenoids?

Billy T.
[email protected]

gnxtc2 said:

Did you try swapping solenoids?

Billy T.
[email protected]

Click to expand...

I did and the issue didn't follow the solenoid...

if the armature was loose on the poppet, the solenoid would pick up the armature plate but not be able to move the valve. I had one like that and it would not buzz.

Understood, thanks.