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Dick Hussey's Tech Corner
Fuel Injector Problems 1989 - 1992
Allantés with 4.5 liter engines have potting material used in their fuel injector coils that ethanol in the fuel supply seems to attack. Over time, the coil resistance drops, and the injector ceases to function. The bad coils can also cause an engine computer module problem. Only the 4.5 liter injectors of the 1989 through 1992 Allantés seem to be affected by the
ethanol. The 4.1 liter engine on the 1987 and 1988 Allantés uses a different fuel injector, as does the 1993 Northstar.
When we first started seeing the failures on the 4.5 liter engine fuel injectors a couple of years ago, we replaced just the injector that had failed. As the problem escalated, we made harness adapters so we could quickly check the condition of the injector coils. A good injector coil will have 12.5 ohms resistance. So we started using the arbitrary value of 9 to 10 ohms as a threshold for a minimum acceptable value. Any injector coil less than nine ohms would be replaced.
Tools for the job
After a while, we realized that anything less than 12.5 ohms showed the injector had already started to fail. In one of my
own Allantés, we had installed a set of reconditioned original injectors that were tested and were found to be at 12.5 ohms
resistance. About six months later, running problems started to show up again. We retested and were surprised to find that three of the "good" ones had already failed. At that point, we knew we needed to find other injectors. We now have a
type of new aftermarket injector and also a reconditioned injector we have been using for over a year with zero subsequent failures. This trial and error process, done
in our own Allantés, got us to this point.
What we have learned is that the best solution when you start to have problems is just replace all eight injectors at the same time, or chances are you'll be doing it again. And again. We had one Allanté come in with an injector problem, and we found three different types of injectors in it-pintle type, disc type, and the original ball type injectors. We installed a matched set of eight.
Cleaning the injectors is not a solution. This actually can make matters worse on those that have not failed, as it is not a dirt or clogging issue. The solenoid coil has failed. Running cleaning solvent through the injector will only attack the coil porting material a little more and further weaken the injectors that have already starred to fail. The following guides will help you measure your injectors if you wish to determine their electrical condition and also inform you how to replace them WHEN you need to do so:
MEASURING INJECTOR COIL RESISTANCE TO CHECK CONDITION
1.) Locate the two injector harness plugs by fo llowing the wires out of the injector harness on the driver's side of the engine. One is in front of the distributor and the other is back behind rhe oil filter adapter. (picture 1 and 2)
2.) Remove the retaining clips on the harness connectors, and unclip the connectors.
3.) With a digital vole ohm meter set on the 20 ohm scale, measure and record the resistance for each coil. The harness connecter has 8 sockets: two for each injector.
To determine location, look for small letters on the connector. If you hold the connector with the cab facing down and start at the upper left corner, that is
Pin A. Pins B, C, and D are to the right. Then the sequence reverses in the bottom row. E is below D, and then the sequence is F, G, and finally H. The wiring pairs for each injector are as follows:
Front bank, cylinder #'s 1, 3, 5, and 7
Injector# 1 Pins A and H
Injector# 3 Pins Band G
Injector# 5 Pins C and F
Injector# 7 Pins D and E
The wiring pairs are one above the other
in rhe connector, so all you have to do is
to check the vertical pairs. It is helpful
to have clips on the ohm merer probes
when performing these coil resistance
Rear bank, cylinder #'s 2, 4, 6, and 8
Injector # 2 Pins A and H
Injector# 4 Pins B and G
Injector# 6 Pins D and F
Injector# 8 Pins C and E
You will notice the configuration is not the same in rhis plug as it was in the frontbank harness. The first two cylinders are the same, but the second two are not. The connections are diagonal, not adjacent. Record the values. Typically anything above 8 ohms will perform OK. Anything 2 ohms or below will not fire. Anything below 12.5 ohms has started to fail. One other interesting point is chat if you check the injector fuses, they do not support one bank or the other. Rather, they alternate in rhe firing order, which is 1-8-4-3-6-5-7-2. So, injectors #1, #4, #6, and #7 are on fuse #4 under the ash tray. Injectors #8,
#3, #5, and #2 are on fuse #5. The car will run with one of the injector fuses blown but will have absolutely no power.
REPLACING YOUR FUEL INJECTORS (BEST DONE WITH ENGINE COLD)
1.) Disable the fuel pump by disconnecting the negative battery terminal (or pull Fuse 19 under the ashtray). Relieve the fuel pressure through the Schrader valve fitting on the fuel rail. The best way to do this is with a fuel pressure gauge with built-in release valve and drain tube. If that is not
available, it is possible to do this with a small screwdriver and a rag to soak up the small amount of gasoline that will escape if the rail is still under pressure.
2.) Remove the air box cover. Disconnect the air inlet duct at the throttle body and remove both items together.
3.) Remove the crossbar that runs berween the strut towers over the top of the engine by removing the recaining nut at each end.
4.) Using a 1/2" drive ratchet inserted into the tensioner pulley's slot, lift up to release the tension on the belt, then remove the serpentine belt by sliding it off. Picture 3
5.) Remove 5 bolts holding the power steering pump mounting bracket so the pump can be lifted slightly. There is no need to disconnect any hoses or pipes. Picture 4
6.) Disconnect the rwo harness connectors over on the driver side of the engine. Pictures 1 and 2
7.) Disconnect both fuel lines at the fuel rail near the throttle body. The size of Eight new injectors installed on foe/ rail the threaded line is 13mm. The rwo Torx screws are size T25. Once the rwo Torx screws have been removed, CAREFULLY pry up the rear line out of the fuel rail.
8.) Disconnect the cruise control servo cable, the MAP sensor connector, the PCV valve, the MAT sensor from the back of the intake plenum, the ISC motor connector, the TPS connector, and the vacuum connector from the top of the throttle body.
9.) Remove the bolt holding the dipstick to the back of the throttle body, and the rwo bolts on the support bracket on the back of the intake plenum.
10.) Remove 4 nuts holding the intake plenum to the lower intake. Lift off the upper intake and tie it to the left hood support with a bungee cord. Enough slack exists in the throttle body coolant hoses and the accelerator linkage to do this without disconnecting them. Pictures 5 and 6
11.) Place a rag or other cover over the exposed holes in the lower intake to prevent anything from falling down inside.
12.) Remove the four bolts holding the fuel rail down onto the lower intake manifold.
13.) Carefully pry up the fuel rail assembly as a unit - as you are lifting it guide out the wiring harness connectors
14.) Tip the fuel rail upside down on a work table. Press in the center of the wire clip holding the connector onto each injector, and remove the connectors. Picture 7
15.) Remove the retaining clips and remove the injectors to be changed. Then reverse the steps above to install the new injectors. Picture 8
A few points for reassembly:
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