Ignition issue, misfiring, tach fluctuations, ticking sound

Topic: Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed (Read 1540 times) previous topic - next topic

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

March 06, 2017, 06:26:11 PM

I’ve got an ’87 5.0, all stock (when I refer to the tach it’s in the stock digital dash).

For weeks I’ve been dealing with what feels like constant partial misfires, becoming more severe with more load. With increased throttle, but not enough for a downshift, it seems like total misses, especially when going up a hill. This happens at all RPMs, and the tach fluctuates a few hundered RPM and reads noticeably higher than it should – especially at higher RPMs. There’s an audible ticking sound that increases with RPM when this happens, too.

Sometimes after starting the car cold, everything runs fine for the first 3 to 15 minutes of driving. Sometimes it happens with the first cold start of the day.

I haven’t changed the plugs and wires in about 3 years, but replaced the TFI module less than a year ago. When that happened, I got trouble codes for missing PIP signal and bad TFI module. This time, I have not gotten any codes other than the 34 that I’ve had for years for the EGR sensor.

Because of the tach flux and ticking sound when this happens, I visually looked for a spark jumping to a ground from the plug and coil wires, but didn’t see any. Any tips?

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

Reply #1 – March 06, 2017, 07:29:38 PM

Plugs and plug wires could be bad. How old is the ignition coil?

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

Reply #2 – March 06, 2017, 07:33:04 PM

Quote from: SlaughterDog;459597

Because of the tach flux and ticking sound when this happens, I visually looked for a spark jumping to a ground from the plug and coil wires, but didn’t see any. Any tips?

Did you look after dark?

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

Reply #3 – March 06, 2017, 07:58:49 PM

I’ll check again in total darkness for the spark jump. The ignition coil is over a decade old too. The sound does seem to come from the driver side, but hard to isolate to the coil. Perhaps bad cap or rotor?

If it was just bad plugs and wires, why would that cause the tach to wiggle and read high?

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

Reply #4 – March 06, 2017, 08:23:45 PM

Bad plugs and/or wires can cause a misfire, which will cause the tachometer to bounce. I've seen it happen on several occasions.

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

Reply #5 – March 08, 2017, 12:49:46 AM

I changed the cap and rotor (since they were way too old) and now, the car runs for a minute or sometimes more before dying and refusing to start for a few minutes. I did get a new error code from memory: 18 loss of ignition signal. This happened as soon as I changed the cap and rotor.

It’s worth mentioning that several months ago the water pump went out and sprayed coolant all over the TFI module and connectors.

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

Reply #6 – March 08, 2017, 01:48:52 AM

http://sbftech.com/index.php/topic,588.0.html

Stop guessing and fix it. 10-20 mins worth of work and your done.

Btw, I hose my engine down at the car wash 2-3 times a month, never hurt anything.

Ignition issue, misfiring, tach fluctuations, ticking sound – diagnostic help needed

Reply #7 – March 18, 2017, 09:59:34 PM

I took it to a shop for diagnostics, since I don’t trust myself to accurately test with a multimeter. They narrowed it down to either the ignition module or the pickup sensor in the dizzy. I just now replaced the ICM and the tach reads accurately and it doesn’t die, yet now there’s sputtering under load. Giving more throttle at low RPMs causes it, and with it floored it starts struggling to climb past about 4k. My guess was bad spark plugs or wires (I haven’t changed them in 3 years and drive a lot), but when I checked codes, the KOEO results were fine but the KOER results are weird. It varies every time I test. The blips for cylinder count are either missing, or too few. I tried a cylinder balance test and it showed 99 twice. WTF?