I have a 1990 Vert with almost 12,000 miles on it. Had it just 2-1/2 months and have the dreaded Multech injectors. These are my COLD readings;
Front Driver Front Pass
16.1 15.7
12.5 14.4
15.3 16.0
15.9 16.2

Should I be concerned about the 12.5 and 14.4 only readings? Never had to worry about this when I had my 88 Formula 350. Getting ready to take a early retirement next May so I want to act on a possible problem now and not later. Need your opinions!!!!!!!!

 

Uncle Bill: The spec for Multec resistance is 16.5 +/-.3 ohms. Since some of your readings are below this, you injectors are beginning to fail. As the resistance is reduced, that injector will inject less fuel into its cylinder. This will cause rough idle and loss of power. You will have to decide if you want to "fix it now or fix it later"

 

Thanks Sam Lam: one more question....why are the readings so different between Cold and Hot..just got some HOT readings....
13.5.......11.1
9.6.........13.8
9.9.........12.7
13.0........17.1
Totally lost on this subject as I never had to deal with injectore before.

 

Mine (89) were all over the board like that. Put in new injectors, what a difference. There are a few very good threads on the procedure.

 

You definetly need new injectors all around. Go with #24 injectors and an AFPR. Good set, go with Bosch. Cheap set, go with Ford.

 

not trying to bogart this thread but should the injector readings go up from cold to hot or down?

Mine al seemed to go up from 15.9-16 to 17 - 17.4.

Thanks for any info

 

As heat rises resistance falls, which is normal. Regarding your readings, I'm with Sam....time to replace your injectors.

 

so what would make the resistance go up as heat rises? Makes no sence to me.

 

Uncle Bill: You have two issues going on with the injector readings you have given.

Issue 1 - NORMAL condition - Injector # 8 was 16.2 ohms when cold and 17.1 ohms when hot. The injector contains a coil of copper wire and the resistance of copper wire is directly related to its temperature. As the temp of the wire goes up......so does the resistance. Normal condition!

Issue2 - The Multec injector has a unique design such that the gasoline passes over/thru the turns of copper wire in the injector coil. I think this was done as a GM cost reduction since the fuel tends to cool the wire in the injector coil. The wire used to wind the injector coil is coated with a special enamel, which is an insulator. It appears the formulation of the special enamel was not sufficient for todays additives and the use of new fuel injector cleaners. The enamel (on the surface of the wire) breaks down, has open or bare areas and then shorts to any adjacent coil wire that also has an open or bare spot. On the question of why the injector resistance decreased (not normal) when hot......remember, that copper wire expands when heated.....the coil is expanding and additional contact is made with more adjacent wires......and the resistance is REDUCED. In reality, you now have less "effective" turns of copper wire to operate the injector. This condition is seen on injectors 1, 2, 3, 4, 5, 6 and 7. These injectors will deliver LESS fuel to their respective cylinders as compared to a good injector. The ECM will take its O2 readings on cylinders 1, 3, 5 and 7. This info will be used to calculate the fuel delivered by the passenger side cylinders......the ECM "assumes" all injectors are in good working order.

The good news is that you have one good injector. The bad news is that you have seven that are in the process of gradual failure over time.

I hope this makes sense. I strongly recommend you stay with 22 lb/hr injectors in you car. The 24 lb/hr injectors do not always work due to differences in car engines.

 

I agree with Sam on the #22 lb injectors, I was talked into #24 lb injectors and my car ran rich.#22 lb should be about right. If you have an adjustable fuel pressure regulator you can get away with higher lb. injectors. WW