Injector Ohms

[olddog]

I suspect I may have an injector coil breaking down and shorting out when hot. I took the following measurements with the engine at normal operating temp. It was running fine when shut off. The column that says "coil" is measured across the injector coils two pins in ohms. The 3rd column "coil to ground" was measure with the meter red lead to valve cover stud and black lead to injector coil. I got the same reading to either side of coil. This column is in Meg Ohms.

Now what amazed me is that if I put the black meter lead to the stud and the red meter lead to the injector coil I get a reading about 6 Meg Ohms higher than the other way. Typically I never pay no mind when measuring ohms. It is not an el cheapo meter. This is a Fluke 70 III digital multi meter.


cylinder .. coil ...... coil - gnd
1 ......... 12.6 ......... 3.5
2 ......... 13.0 ......... 8.3
3 ......... 12.8 ......... 5.5
4 ......... 12.7 ......... 8.5
5 ......... 13.1 ......... 8.2
6 ......... 13.0 ......... 14.2
7 ......... 13.0 ......... 9.3
8 ......... 12.9 ......... 8.1


I went back out and re-check the ground to coil measurement, maybe 30 minutes after I took the first readings. Then the #6 injector reads open from the coil to gound and the rest are reading 15-25 Meg Ohms.

Your thoughts?

[RICK LAKE]

olddog Those 3 injectors are in question. You could burnt out the injector drivers in the ECU depending on what system you have, Batch fire (4) or sequiential fire, (8) There is a basic test to charge the injector and check amp draw on each. This works for GM not shore about others. Rick L.

[trularin]

Most drive systems have a current limiter so the ECU will not burn out. Trouble is, not all have a current limiter.

Those very high resistance readings can be anything from poor connection to ground to the meter itself.

Very high readings like 25 MOhm are what we would consider open. They can change just by letting the meter sit and let the battery wear down a little more.

Just my $0.02

[olddog]

Originally Posted by RICK LAKE

olddog Those 3 injectors are in question. You could burnt out the injector drivers in the ECU depending on what system you have, Batch fire (4) or sequiential fire, (8) There is a basic test to charge the injector and check amp draw on each. This works for GM not shore about others. Rick L.

It's sequiential. It is a 89-93 ford EEC4 ECU.

I assume the injectors are 12 VDC. Can anyone confirm that?

If I can find an old wire harness, I can put an amp meter in the line and plug them in one at a time to see what the current draw is. I could also put a clamp on amp meter on them (engine running), but with the pulsing I'm not sure it would be accurate. Perhaps it would be relative to each other.

[olddog]

I just checked them cold. Half are 12.0 the other half is 12.1 ohms. All read open to ground.

12 ohms is what GM injectors are supposed to read. Ford injectors are supposed to be high impedance injectors. I was expecting more than 12. Anyone know what the resistance is supposed to be on a Ford injector?

[RICK LAKE]

olddog Try and find one of the companies that cleans and flows the injectors to match each other. There is a 5-7% fudge factor for high to low injectors on most. Mine where matched back in 97 buy a pirvate guy who has passed on. Try over on the 5.0 club for this. The ohms reading will change when ampage is applied to them. The test we have is a 30 second pulse test for the coil inside. The other way is a flow check into beckers and read the CC after 30 seconds with a steady fluid source for the readings. 45 psi. I will look and see if I can find a company for cleaning. Rick L.

[olddog]

Thanks RIck.

I have found one source (rcommended by a friend who uses them). They do not attempt to match the injector flows. By the time you pay shipping it will approach $150. I can buy new injectors for $280 - $330 depending on size.

I have 36 lb/hr now. My 347 might make 400-450 hp at the crank on an engine dyno, if tuned to perfection, but we all know it isn't going to get there in the car. Bottom line I think 32 lb/hr is plenty big enough and 30 lb/hr might be enough. So do I want to buy a new set.

Also I couldn't see a battery cable sized ground going to the engine. I have to get under it and make certain, but I don't think there is an adaquate ground on the engine. I'm wondering if the ground may be causing some of my problems. I want to get a good ground on it and see if that makes a differance.

Anyone ever clean there own injectors?

[RICK LAKE]

olddog I run 50 lb injectors in my 452 motor. I have many problems with fitting the blower drive under the hood back in 1999. After 2 belts jumping, I gave up on this for a while. With a good fuel regulator that is vacuum controlled and steady supply fuel lines, I could have run 96 pounders. My 50's are running at 68% duty cycle at 6,000 rpms in the 452 motor. I now have a 482 motor with high compression and same setup, they are up to 73% duty cycle. Could a run a small injector, yes but here is the rub, if you get larger inijectors they have IMO 2 advantages. 1 they don't every over heat from being open in the 90% duty cycle which over time kills both the drivers in the ECU and the coils in the injectors. 2 This also gives you room to play with down the road and not have to change your injection system. If your ECU can handle 36 or 42 pounders I would go with them.
Cleaning injectors, the correct way is to pull them apart and sonic tank them, install new screens and flow test them. The down side is the coil test is not 100% accurate. If you have a scharder valve in your fuel line and the fuel pump has a one way valve, you can get this done. I can't answer for Ford but at GM we have a cleaner call TEC top engine clean. You add 4 oz into a small tank and fill with gas. Pressure the system and run the tank dry. We have very good luck with this. You can only do this ONCE. It will eat rubber hose and some plastics. This is way the fuel system should be caped for the return side.
It is in the long run cheaper to buy a new set of injectors, but you will have to do a little programing on the ECU again unless you stay with the same size injectors. The ECU should be able to adjust for the 5-7% differents between old and new. Just remember that injectors are not like a carb. The smaller injector is not always better depending on motor and rpm range. Spray patterns is also key. Emmissions and GPM are the differents. Also do you have a narrow or wide band O2 sensor in the car?
For grounds, I have a total of 3. 2 main grounds to the motor and chassis and a #12 gauage wire going to the ground of the ECU directly. These are inside the car and are clean and dry. My battery is in the trunk. I run heavy cables to the front of the car. Rick L.

[olddog]

Narrow band O2 sensors, located in a single pipe on each side. I will try to get a good ground from battery to engine this weekend.

I'm thinking about pulling the injectors and attempting to clean them my self. I will check locally to see if I can get the plastic tips and o-rings. I'm sure that sending them to shop would do better, but I may be able to do a good enough job.

[RICK LAKE]

olddog There is NOTHING for you to clean. It's internal. the only way is to hook a pressure cleaner to the rail and run the car this way. The other end of the injector is pretty much self cleaned. The fuel power washes the pintle end. Unless you have the little screans for the inlets, they break when trying to remove them. They are not reusable. With out those screens large partical get into the injectors and shut them down or get stuck and the injector can't close. You get a leak down problem that washes the cylinder down and will in a short time wipe out the bearings in the motor. Gas and oil don't mix. I have seen this more than once. No, it's was not me. $2,600 to rebuild short block. Rick L.

[trularin]

For single lead sensors, we like to use Copslip ( probably didn't spell it right ). It is an antiseze that has small copper balls in it and when conpressed between threads, aids in conductivity. IT IS NOT a fix all. but I have seen some changes in readings between the sensor and ground by using it.

If you are challenged with a sensor that seems to be giving you problems, maybe a little of this would help.

Riock is right about the screens.

Hope this helps.