Doug's Dirty Dozen
We get asked all the time, “What injector do you service the most of?" Anyone that has been in any of our classes can answer that question without hesitation. As a matter of fact, the answer has not changed since we’ve been doing injectors. But do you know why? Do you know what other vehicles have injector problems? Let's take a look at what we see as high failure rate injectors and why they fail. Some of the injectors mentioned may be on the list because of the volume of vehicles sold, others may be because of the age. Some injectors fail do to engine design. Regardless of the reason, it is always nice to know you could have an injector problem.
So, the number one failing injector as we see it is found on…
1. Application: GM 2.8L, 3.1L vin”T” and 3.3L up to 1993.
Type: This is the original design Multec.
Symptom: It is prone to electrically shorting out. We have heard a couple of reasons, too much bronze
mixed in with the coil windings and the winding wires are not shielded where
they come off the bobbin to the terminals. Which ever the case may be, they
short out.
Resistance: The minimum resistance of this injector is 12 ohms. We usually see then 12 – 13 ohms at
room temperature.
Recommendation: Our fix is to replace them with a Bosch DRI (Deposit Resistant Injector).
2. Application: GM 3100 “M” 1994-2000
Type: This is the second design of the Multec injector. It is a little shorter and has an
enlarged discharge area. GM refers to this injector as a “Stamped Spray Tip".
Symptom: We don’t see a lot of these short out electrically but we do find that some fail
testing at low pulse width commands, which is an indication of the winding
breaking down. The enlarged discharge area makes the injector prone to carbon
build up at that end, reducing the amount of fuel flow.
Second Design Multec on left
Recommendation: Reconditioned injectors work great! An intake cleaning should be performed at time of injector replacement.
3. Application: Cadillac 4.9L “B” 1991-93
Type: Here is another original design Multec.
Symptom: It also shorts out!
Resistance: Minimum resistance of this injector is 16 ohms.
Recommendation: Our fix is to replace them with a Bosch DRI (Deposit Resistant Injector).
EXTRA: The same injector (with a different casting number) is also used on the 5.0L “F” engines
that were in the Camaro and Firebirds.
4. Application: GM 3.4L “E & S”, 3.8L “K & L” 1993-2000
Type: This is another Stamped Spray Tip design.
Symptom: It also is prone to clogging at the discharge end and not functioning properly at low pulse width commands.
Resistance: The minimum resistance of this injector is 11.8 ohms at room temperature.
Recommendation: Reconditioned injectors work great! An intake cleaning is should be performed at time of
injector replacement.
EXTRA: There is also a TSB regarding the symptoms that these engines may have. Bulletin # 99-06-04-005B
5. Application: GM 7.4L “J” 1996-2001
Type: Here again we have a Stamped Tip Multec injector.
Symptom: We don’t see them short out and very few of them show any sign of contamination at the discharge end. They just leak! If you watch the injectors
after shut down you will see droplets form at the bottom and then they drip. This causes a hard starting and will give off a raw fuel
smell.
Resistance: The minimum resistance of this injector is 11.8 ohms at room temperature.
Recommendation: Our fix is to replace them with a Bosch DRI (Deposit Resistant Injector).
6. Application: Ford 4.6L “F & W”, 5.0L “F, N & T” 5.4L “L” and 5.8L “H & R” 1993 - 2002
Type: Bosch
Symptom: This is a durable injector but it likes to be well maintained. Most of them become restricted
because of fuel contamination. Sometimes the pintle caps are missing. The caps are important and new ones need to be placed back on the injector before
installation.
Resistance: 14.0 – 16.0 ohms at room temperature.
Recommendation: Reconditioned injectors work great! Take a fuel sample and let it sit overnight to make sure
there is no major contamination problem exists.
7. Application: Ford 5.0L “E & N” and 5.8L “H & R” 1985 - 1992
Type: Bosch, first generation.
Symptom: These injectors have been around for a while and have served well, unfortunately they have a
tendency to leak externally. An internal o-ring failure will cause them to leak
where the plastic top portion meets the metal body. Some may even leak into the
electrical connector area. This may be seen with a visual inspection, look for
the paint being removed from fuel leaking.
Resistance: 14.0 – 16.0 ohms at room temperature.
Recommendation: Reconditioned injectors work great! We throw out any of these injectors that show signs of
the paint being ate away.
EXTRA: This same style injector was used on early GM 3.8L “3 & C” engines. Check for leakers on them too.
8. Application: Cadillac 4.5L “3” 1990
Type: Another original design Multec.
Symptom: It shorts out!
Resistance: Minimum resistance of this injector is 16 ohms at room temperature.
Recommendation: Our fix is to replace them with a Bosch DRI (Deposit Resistant Injector).
9. Application: Jeep 4.0L “L & M” 1987 – 1990
Type: Bendix, Deka or Siemens
Symptom: They leak externally. An internal o-ring failure will cause them to leak where the
plastic top portion meets the metal body. Some may even leak into the
electrical connector area. This may be seen with a visual inspection, look for
the paint being removed from fuel leaking.
Resistance: This injector should read 14.5 – 16.5 ohms at room temperature.
Recommendation: Our fix is to replace them with a Bosch DRI (Deposit Resistant Injector).
EXTRA: Other vehicles under the Chrysler, Dodge and Jeep name use this style of injector. Check them for external leaks also.
10. Application: GM 3.1L “M & J”, 3.4L “E” and 3.8L “K”
Type: Multec II
Symptom: It also is prone to clogging at the discharge end. It is very likely that if you have a misfire
code (even a random misfire code) you have at least one of these injector not delivering enough fuel. We have seen as little as 5% reduction in fuel flow
cause a misfire.
Resistance: The minimum resistance of this injector is 11.8 ohms at room temperature.
Recommendation: Reconditioned injectors work great! An intake cleaning should be performed at time of
injector replacement.
EXTRA: The Multec II injector also was produced in a shorter version. These injectors are widely used on GM vehicles.
They all have a tendency to carbon up at the discharge end and reduce fuel flow.
11. Application: GM Central Sequential Fuel Injection Unit (CSFI) 4.3L “W”, 5.0L “M” and 5.7L “R” 1996 – 2002
Type: Poppet valve at the end of each tube with an individual injector for each tube in a metering body.
Symptom: The poppet valves are known to stick, causing a misfire. The injectors may leak fuel into the
wiring harness cavity of the metering body (which can lead to fuel following the wiring to the PCM). The pressure regulator may also leak fuel causing a
rich mixture.
Resistance: The minimum resistance of this injector is 11.8 ohms at room temperature.
Recommendation: Replace the original poppet style unit with the NEWER mini injector style. This unit
uses a mini injector at the end of each tube. There are plastic injector protectors attached to each injector that fits into the intake ports protecting
the injectors from carbon and sticking. The unit is a direct replacement. Always replace the upper plenum gasket when replacing this unit.
EXTRA: Fuel pressure is very critical on the CSFI systems. One of the first checks made should be fuel pressure. Pressure should
be 58 psi or above KOEO and idle pressure should be 54 psi or above. If pressure is below these specs further testing of the fuel pump should
performed. The system should also hold pressure when the pump stops running.
12. Application: GM Central Port Injection Unit (CPI) 4.3L “W” 1991 – 1995
Type: Poppet valve at the end of each tube with only one injector in the metering body to feed them.
Symptom: The poppet valves are known to stick causing a misfire. The pressure regulator is prone to
leaking as is the fuel supply and return lines that are located under the upper
plenum.
Resistance: The injector is low impedance and should be 1.4 ohms at room temperature.
Recommendation: Reconditioned LTS units work GREAT especially when they have our upgraded
pressure regulator installed in them. When servicing these systems it is best
to replace the CPI unit and the supply and return lines. 
EXTRA: Fuel pressure is very critical on the CPI systems. One of the first checks made should be fuel pressure. Pressure should
be 58 psi or above KOEO and idle pressure should be 54 psi or above. If pressure is below these specs further testing of the fuel pump should
performed. The system should also hold pressure when the pump stops running. LTS offers a service kit that includes the CPI unit, S&R lines, upper
plenum gasket and a carbon trap (screen type) gasket for the EGR valve.