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3 cylinders misfire simultaneously

Hello everyone,

I have been struggling a lot with my 94’ ford probe GT. I’ll try to be as clear as possible in my explanation.

It’s been 4 months I have a cylinder bank 2 misfiring which means that 3 cylinders always misfire.

Here is the list of the stuff I replaced and checked:

  • new fuel pump
  • new gas filter
  • new injectors
  • new ECU.

From what I saw I have sparks on each spark plug. I have no possibility to check error codes as it’s a 94 obd1 system and it doesn’t work, so I’m kind of blind in this story.

The next step will probably be to change the distributor as it also includes one if the 2 crankshaft sensors in this engine.

I am really lost here, can anyone help me?

Thank you

First things to check on misfires are SUFFICIENT spark, fuel and compression. Before you spend money on parts, you should probably do a compression or leak down test.

Thanks for the quick reply.

How can I know if I have sufficient sparks? Bear in mind that the 3 other cylinders fire perfectly.

What compression are we talking about here, cylinder or fuel compression? If it is cylinder wouldn’t it be strange to have all 3 cylinders having such a low compression that none of them would fire? Regarding fuel compression I have 3 bars which is what’s recommended for this engine.

What do you mean by leak down test?

Spark should be a nice blue accross electrodes. Seeing that you replaced fuel pump and filter I would assume you have fuel pressure. But would be a bonus to see it with a gage. A leak down test is a fancy compression test. Although it may seem unlikely that there is no compression in all 3 cylinders, it is a quick test to eliminate that possibility before putting money into it. It is a 94. A bad head gasket can cause low compression between 2 neighboring cylinders. If you have fuel delivery and compression, you can then go back to spark and see if you might be able to determine if you misjudged sufficient spark. For cheap at the parts store you can find a spark tester that allows you to check spark with an adjustable gap between the electrodes.

The most likely possible single non catastrophic failure that would cause a misfire on one side of a V-6 engine would be the common injector triggering. A broken wire of damaged connection would seem likely. If the trigger circuit were shorted the injectors on that back would be dumping fuel and if the power to the injectors were shorted a fuse would be blown and the entire fuel system would be disabled.

FWIW I’m shooting from the hip based on experience with domestic Fords of that vintage and it seems that car is somewhat European based.

1 Like

The Ford Probe was built on the Mazda G platform.

Tester

Thanks for your inputs, guys.

@tcmichnorth From what I tested, I have that nice blue across electrodes but I’ll give it another look.

@Rod_Knox it might be a european based model as I am living in Europe but it is still a KLDE Mazda engine, could it change a thing? I just linked the wire graph so that you can understand better how this circuit is made. It doesn’t seem I have any blown fuse.

Does it help you?

That schematic indicates sequential injection which will not drop a bank of injectors when a single wire or circuit fails. Ignore my SWAG.

in other words? :sweat_smile:

Well that’s kind. Others here might be more appropriate and reply DUUUUUUH!

And to give myself some possibility of being redeemed it is possible that a vacuum leak, possibly even a leaking EGR valve will cause one bank to misfire but such a misfire would fade as RPMs increased. And the Ford EEC!!! system can be diagnosed with a proper scan tool.

Right but as you said, I still have cylinders misfires at high RPMs. Ford EEC scantool is pretty expensive and I suspect the diagnosis plug not to work. I tried to jump a wire as mentioned in the technical book to see the Morse code through the check engine light but I get no errors at all which is very unlikely lol. Thank you for your help!