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Only half the injectors are working on a 8 cylinder ford E350

hey guys have a 1994 E350 ford van front on a winnebago. Parked it last winter at the mother in laws got mice inside of motor compartment. Hard starting so changed plugs, wires, cap, rotor ,coil, gas tank hose, idle air control valve,vacumn lines, injector plug ends on two, checked and set timing, starts right up but has problem of rough idle swapped plugs around to check with old ones plenty of spark but the weird thing is it is a 8 cylinder motor the two cylinders in the front and the two in back run fine the four in the middle do not get fuel pulled the plugs sprayed gas in the cylinder and put plugs back in and they fire. how do I only get fuel to the four outside cylinders, what could cause this? IS THIS A SENSOR, and if so would it cause only half to work maybe there is a wire on some sensor that they could have chewed and that I missed. It is a 1994 E350 ford van on a winnebago chassie. Fuel injected with 77ooo miles. Ran fine until this even had the original tune up parts and ran well.

Any help would be greatly appreciated I am at my wits end and the family is very dissapointed having to sleep in a tent on our vacations.

thank you


Without a schematic handy I can’t say for sure, but as far as I know most Fords have power provided to their injectors in 4 injector sets. This means 2 fuses, one for 4 injectors and a second fuse for the other 4.

If 12 volts is not provided to the injectors that are not working then odds are the fuse is blown. Hope that helps.

94 E350 uses multiport injection system (Bank fire) not sequential fuel injection. Very simply, 4 injectors fire at the same time, then the other 4, then back to the original 4 and so on. Cylinders 2,3,6 and 7 share the same injector driver circuit. (PCM supplies the ground trigger for these four injectors together) All injectors are fed constant 12v (Batt voltage) with ignition switch on. (Red wire going to injectors) You should see a white wire at the injectors for cyls 2,3,6,7. (This is the switched ground going to the pcm. If you ground this, white wire) the injectors should cycle… I would advise against doing this often or consistently…If fuel system is pressurized and injectors are allowed to spray you could easy hydrolock the engine. If cylinders are full of fuel during a crank attempt, you may find a connecting rod laying in the oil pan if in doubt, remove the spark plugs before cranking to purge fuel… watch ignition cables during cranking as well. fuel plug plus spark means fire… Just work safe)

Items to keep in mind,

1)Never pluggin or disconnect a pcm with the ignition on… Cycle key off then unplug or plug in, then key on…
2) Never jam/force anything into electrical terminals.
3) Never purge fuel from lines, injection system or cylinders with live ignition system… yes this is common sense, but many a vehicle have burned to the ground just because of a quick oversight

Time to dig in, First you should inspect The pcm connector for corrosion damage at pin 59 of the pcm. Do not force anything into the connector terminals, (AKA volt ohm meter leads) they can be easily damaged… If terminals are damaged/corroded, new terminals can be obtained from local ford dealer. If ok, inspect connector 121 at the front of the engine, this is where the engine harness meets the body/pcm harness, just forward to the passenger side of the distributor. Inspect for corrosion or otherwise damaged connector or electrical terminal. If tuneup was recently performed just before the driveability problem arose it may be possible the terminal has pulled back into connector hard shell from rough handling or just the connector getting brittle. If no damage or corrosion is noted, reconnect connector 121. (again just to the passenger side of the distributor) Perform a good visual inspection on the harness… Look for any wire chafe locations (rub thru)

You can perform the next batch of tests in which ever logical order you would like…
1)You will need to verify circuit integrity from the pcm to the injectors themselves. This can be done with a volt ohm meter. With the PCM unplugged and connector 121 connected, Unplug injectors 2,3,6,7 (easier said than done, be gentle with connectors, they will be brittle) Use an ohm meter and check the circuit resistance from the white wire of at either injector 2,3,6,7 to pin 59 of the PCM… (Again DO NOT stab the electrical wiring insulation or the terminal ends… Straightened paper clips work nice. Just touch the ends of the electrical terminals, Forcing meter leads in will damage pins. You should see good continuity. Less that 5 ohms… Realistically it should be less than 1 ohm. If not disconnect connector 121, and measure from the white wire terminal of 121 to the pcm pin 59. Is resistance below 5 ohms. If yes than measure from conn 121 to injector 2/3/6/7. repair the open as required. If you do not have a DVOM (volt ohm meter) you can ground the white wire at the pcm, Ignition key on… Do the injectors cycle?? (remember to purge cylinders of fuel before cranking) If not find the high resistance or the open.

  1. You will also need to verify the operation of the PCM injector driver… The ground switching… This can be done by having a low current test lamp from the positive batt terminal to the the white wire at the injector connector (injectors 2,3,6,7 unplugged)Fire the engine and look for pulse/illumination… It should fail… you can then move up the line to connector 121… (White wire) does the lamp illuminate? if so the open is between conn 121 and the injectors if not you will need to continue upstream to the pcm connector. Validation at connector 121 or pcm connector will require Back probing… This is easily done with small t pin (available at staples or office max). Simply (And gently) slide t pin into the back side of the appropriate wire terminal at the connectors. (Back side/wire side of the connectors) pins should go in gently. This method of probing Gives a decent means of wire verification without stabbing thru the insulation without haivng to buy a bunch of expensive flex probes… Obviously any insulation breaches will give corrosion a place to start.

The tests can continue more indepth from here… start out with the easy and logical first.

DO NOT replace the pcm or any other engine management component until circuit 556 (white wire) is verified OK. If circuit is Ok but no ground trigger is present on the white wire, it is possible PCM failure may be present. Keep in mind, a short to power on the white wire will damage destroy the driver within the pcm… Good luck.