I have two cylinders that aren't running. I have a strong spark and more than enough compression.

I put a stethescope (sp?) up to the good injectors and can clearly hear them firing. But the injectors in the cylinders that aren't firing, there is no ticking at all. So they're not firing.

I hooked up a test light and the electrical connectors to the injectors are getting power.

Both injectors failed at the same time, and it was not a gradual thing. Drove in the morning, parked, started he up again and ran really rough.

What could cause two injectors to fail at the same time? Grounds are fine.. all connectors are fine.. I'm running out of ideas.

Thanks!

 

Clogged? Take them all out and clean them or bring them to be cleaned. Maybe there was an internal failure with 2 somehow. Weirder things have happened I'm sure.

 

are you getting the proper pulse at the injectors? power alone wont fire a injector, it sure seems strange to me that all the sudden two injectors would fail, theres gotta be something else going on there, check for proper injector pulse at the plug, compare it to some good injectors, i bet youll find no pulse.

 

I don't have a stethescope to try mine out, but believe I may have a similar problem with cylinder/injector #1. The cyilinder stays cold and I know spark and fuel are getting to it. Please keep us posted on what you figure out!

 

Check all of your fuses and relays for the injectors if you haven't done that yet.

 

Fuses are next on my list... I'm also looking for anything that relates the two injectors together. I know on my Mazda truck, two injectors are grounded by the same ground. So that kinda of thing would cause them both to fail at once.

After that I'm going to just take them out and clean them up.

white/blackss: What is "proper pulse"? How do I check for it? Does it have something to do with the power, or the timing? Thanks!

 

theres a tool, actually its a light that plugs into the suspected bad injector and when the engine is running you can look at the light and see if its pulsing.

if the light ( tool ) is pulsing then you know that you are getting a good signal to that injector. if its not pulsing but either staying on or not lighting at all then you can start trying to figure out why. it makes chasing a bad injector easier because you dont have to rely on a stethascope witch isnt reliable in the first place for testing injectors.

remember all injectors dont make alot of noise when they fire, so the problem might be in the wiring or even the injector driver whitch is probably in the ecm. do you have a haynes manual? i think it would help you out alot, mine does.

 

You might want to mention which two specific cylinders you are talking about. Your eninge has sequential injection. Each injector has a "driver" in the PCM, that supplies a ground to fire each individual injector. No injectors are "paired" an the driver/ground side. They are fed from only two different fuses on the +12V side, 4 injectors to each fuse.

If the injector isn't firing, its not getting +12V (easy to check... its the pink wire to each injector. Onefuse supplies #1, 4, 6, 7, the other fuse supplies #2, 3, 5, 8). Or it isn't getting a ground.... bad wire or bad driver in the PCM. If either of these events occurs, you will get a DTC code in the PCM, because the PCM can tell that the circuit isn't being completed. Do you have any codes? Have you scanned it?

If you really have two injectors that aren't firing, you should also be getting a misfire code for the specific cylinders that are misfiring. The misfire count per cylinder can be viewed with a scanner. Again... is the SES light flashing for misfires? Do you have any misfire code? Have you had it scanned?

The other causes would be a faulty coil in the injector (again, would show as a DTC due to circuit fault), or some mechanical problem preventing the ball from lifting off the seat.

Might also be a problem of the injector being plugged up, but it would still be "firing".... the electrical circuit would still be OK.

If you can isolate the problem injector, its possible to swap it with another injector and see if the problem follows the injector (faulty injector) or stays where it was (faulty wiring or PCM driver).

 

injuneer,

i'm having a similar problem with my car. 2 cylinders seem to misfire after a hard drive.

i've swapped around the injectors (as well as checked all the plugs/wires/coils). the injector move didn't change which cylinders miss. it stays constant on 5 and 7.

other than a misfire code for each cylinder (or multiple random) what codes would be triggered if it were something in the PCM?

after the holidays i'm taking it to the dealer to see if tey can figure it out. but any info you can give me would be great.

 

In OBD-I the injector circuit failure is DTC 18. In OBD-II is is P0200. I don't know that there is a code for an internal error in the PCM, or if that would simply show up as the same P0200. That code gets set when the PCM detects a control cirsuit voltage near "0" for 5 seconds. It continuously monitors the voltage.

 

Fuses and Relays are Ok because he:
into the injector's connector it's called a Noid light, pull the fuel pump fuse, start the engine, and allow the engine to use up the remaining fuel in the lines then install the Noid light, crank, and check for light pulses. This may not be possible with OBD2. The injector pulse is longer during a no start which makes it easier to see the pulse, with the engine running the pulse is so fast that all you'll see is a steady light which doesn't indicate that the driver is actual firing. Some Digital Volt Ohm Meters can detect pulse frequencies.

If you have a DVOM you can check the injector coil's resistance it should be around 14-16 ohms if it's significantly higher the other injectors will draw less current an spray patterns will suffer, or if lower the other injectors will draw too much current and over-heat; the bad injectors must be replaced because they affect the good injectors and damage them over time.

No need to swap injectors it's easier to just swap connectors unless there's some reason that prevents you from swapping connectors.

Engine electrical connectors in general are prone to vibration failure which causes corrosion to build up between the mating pins. Disconnecting and reconnecting may cure the problem for a while. Apply an electrical lubricant as preventive maintenance, and check for broken locking connector tabs, missing, or damaged rubber seals, and retaining clips.

As Injuneer stated regardless of cause OBDII should have logged
the misfire after 2 consecutive misfires during a driving cycle.)

To perform an OBDII Driving cycle do the following:

Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.

Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.

Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

 

You have to be careful with that one. With sequential injection and OBD-II misfire detection, swapping injector wires will work if you are looking at a "non run" condition... e.g. using the noid light at cold start, as you described. But if you are looking at the misfire count by cylinder in a running engine, the irregularity from out of phase injectors can show up as misfires.