1988 v6. 3 cylinders not working. Inj2 fuse blown. Electrical problem? (Page 4/4)
Patrick SEP 30, 04:44 PM

quote
Originally posted by danahart:

I guess my plan was to see if it is the injector first by pulling the distributor wires one at a time for a quick sec while the car is idling and see if it changes the idle any. I figure if the injector isn't working, that should be pretty obvious by doing that. Let me know if that is a bad idea.



Any time a plug wire is "pulled" while the engine is running is a bad idea. It can damage the coil, as those thousands of volts desperately want to go somewhere. It's much better to use a grounded probe at the distributor to kill one plug at a time. Prior to that though, double-check that you simply haven't got the plug wires going to the wrong plugs. It happens more often than you might think.
danahart OCT 01, 03:41 PM
I'll doublecheck but I wrote the numbers on the plugs in paint pen before I pulled them as I was afraid of that happening. They go in order around I assumed. But I'll doublecheck.

Can you describe what you mean by using a grounded probe to kill one plug at a time?


quote
Originally posted by Patrick:

Any time a plug wire is "pulled" while the engine is running is a bad idea. It can damage the coil, as those thousands of volts desperately want to go somewhere. It's much better to use a grounded probe at the distributor to kill one plug at a time. Prior to that though, double-check that you simply haven't got the plug wires going to the wrong plugs. It happens more often than you might think.



Patrick OCT 01, 04:15 PM

quote
Originally posted by danahart:

Can you describe what you mean by using a grounded probe to kill one plug at a time?



High voltage from the coil will seek the easiest path to ground. Normally it's by jumping the gap between the center and ground electrode of the spark plug(s).

One way to supply an easier path for this voltage is to provide a direct path to ground using a pointed metal probe (could perhaps use a small Philips screwdriver) with a wire connected from it to the engine block. With the rubber boots pulled up out of the way of all spark plug wires plugged into the distributor, the pointed metal probe is simply positioned as far in as possible into the edge of each hole in the distributor cap where the spark plug cables are inserted. Even if the probe doesn't actually touch anything metal inside each hole, the voltage will usually be able to jump the gap, as it's easier for the voltage to jump a gap in atmospheric pressure as opposed to the high pressure within the combustion chamber. When the high voltage seeks out ground in this manner, the associated spark plug has been effectively disabled.

I suggest using a metal probe with an insulated handle, but in theory this isn't necessary... as it should be easier for the voltage to travel down the wire to the engine block than through you to ground.

If the probe isn't able to get close enough to allow the high voltage to jump to it from the terminals in the distributor cap, the spark plug cables may need to be pulled up a bit out of the holes in the cap.

I've used this procedure going back to the early 70's with small/big block Chevies.

[This message has been edited by Patrick (edited 10-01-2024).]

danahart OCT 12, 02:50 PM
Update.

Ok. Work finally let up a bit and I had time this weekend to investigate my issue.

Issue fixed. I was pulling the cables off the distributor cap and noticed that one came off way too easily. So I replugged them all back in correctly and fired it up - problem gone. Stupid but I'm glad it was something so simple and I found it before taking anything apart.

Thank you all for your help with this issue. Now I move onto the next problem on my list of Fiero to-do issues....
zkhennings OCT 29, 10:30 AM
Glad you found your issue, for the future, unplugging the injector wiring harness and probing the Inj 2 power line with a multimeter to ground (while the car is off) is an easy way of letting you know if the short is in the wiring harness, you would get some kind of reading if there was a spot where it was shorting out. Since yours ended up being an injector it would have read O.L. on the multimeter indicating there is no connection between that wire and ground. Moving the harness around while taking a reading with the multimeter will somewhat simulate what is happens when the engine moves around under load and decel. Your problem was happening at near peak torque while going uphill, that is exactly when the motor will be at maximum displacement and could have been moving the harness around for a bare area to short out.

And the reason that putting a larger fuse in can cause a fire is because the wire is only rated for so much current at 12v. The fuse is typically sized to prevent the wire from ever reaching that rated current. Put a larger fuse in and suddenly you can be melting the jacket off the wire, short out, and starting a fire.

If you were ever inclined, it is not very expensive to send your injectors out to have them cleaned and measured to see how well they are flow balanced with one another. There are DIY ways to get a good approximation yourself but will require you to make some sort of jig to run the injectors outside of the car.
Raydar OCT 29, 10:52 AM
Good show!
And thanks for coming back and letting us know what you found.

I'm happy that you got it sorted.