Intermittent miss??

[danielhv]

Not sure how to completely describe this...

Drove the mustang to work the other day, and on the way home, the temps were a little high for my comfort (around 230F). Then all of a sudden, the A/F gauge showed lean while under slow acceleration. If I gave it more gas, it'd richen up, but still lacked power and ran like shit. The car sounds like a cylinder isn't firing... I pulled over, let it cool down, but it still did the same thing. Then all of a sudden while I was sitting at a red light, it went away. Car richened up, and was smooth again. I chalked it up to a fluke.

Then, today took it out to run to Starbucks, and got on it on the service road headed home. Once I got out of it, same issue as above (except temps were normal).

Where do I start? I checked the plug wires, checked the injector plugs....

I'm running the autolite 24's gapped at .030 (per Andy @ Prime-Tuning) if that matters.

Car runs great 90% of the time... but when it gets in this "mood", it sucks.

[black2002ls]

It may be a long shot but check the injector harness for bad spots in the wire. I chased an intermittent dead miss on my s-10 for a LONG time. Every shop I took it to said it was a blown head gasket. Finally found someone willing to spend some time diagnosing it properly. It turned out to be a bad spot in the harness.

Sometimes it would run just fine, others, it would not fire on cylinder 3 AT ALL. Bumps or hard acceleration would cause the wire to either make or lose contact/continuity.

Is it throwing a code so you can see which cylinder or if it is s random cylinder misfire?

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

[91CoupeMike]

Fuel pump ?

[91CoupeMike]

Describe rich/lean condition also.

My car also tuned my Andy, will idle at 14.5-15:1 afr. and drives at 13-14:1, wot is 12.6-12.8:1. On decel in gear it can spike to 16:1 but that's normal.

[91CoupeMike]

Afr is the same as when it was stock with a wide band. Except it idles better now, new IAT.

[danielhv]

It may be a long shot but check the injector harness for bad spots in the wire. I chased an intermittent dead miss on my s-10 for a LONG time. Every shop I took it to said it was a blown head gasket. Finally found someone willing to spend some time diagnosing it properly. It turned out to be a bad spot in the harness.

Sometimes it would run just fine, others, it would not fire on cylinder 3 AT ALL. Bumps or hard acceleration would cause the wire to either make or lose contact/continuity.

Is it throwing a code so you can see which cylinder or if it is s random cylinder misfire?

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

I'll check. I don't have a CEL, so its a pain in the ass on these cars. Counting blinks and shit... how gay.

I will say the injectors were bought used. Of course everyone says they have low miles, so who knows. They are the Bosch "Mean Green" 42lb ers.

[danielhv]

Describe rich/lean condition also.

My car also tuned my Andy, will idle at 14.5-15:1 afr. and drives at 13-14:1, wot is 12.6-12.8:1. On decel in gear it can spike to 16:1 but that's normal.

Idle is around 18, crusing is around 14 - 15, smooth acceleration is around 15 - 16, WOT is 11.4 - 11.8.

When the issue is going on, my smooth acceleration value is around 20 - 22.

[danielhv]

Fuel pump ?

It's a new Walbro 255.

[91CoupeMike]

Which bank is your wide band on?

Sounds like the lean is just picking up the misfire, mine pegged my gauge at 18 when I melted a plug and had a dead hole.

Best way to find which one is dead is to see which header primary is colder than the rest., or hotter if its a lean miss.

[danielhv]

Which bank is your wide band on?

Sounds like the lean is just picking up the misfire, mine pegged my gauge at 18 when I melted a plug and had a dead hole.

Best way to find which one is dead is to see which header primary is colder than the rest., or hotter if its a lean miss.

Its in the drivers side of the H pipe before the "H", and after the O2 sensor. I'll have to track down an infrared thermometer to determine which one is cooler / hotter. Think my dad has one so we shall see.

[danielhv]

Ran the KOEO and KOER test today...

KOEO: 15, 31, 84, 95
KOER: 12, 31

Havent ran the cylinder balance test yet... it got too late.

Looked up the codes, but I'm not 100% solid on what exactly they mean, or if any of them would cause my symptoms.

Thoughts?

[91CoupeMike]

https://Www.canobd2.com

[danielhv]

Www.canobd2.com

15 = EEC (PCM) Read Only Memory (ROM) test failed
31 = (Cars ONLY): EVP or PFE circuit below minimum voltage
84 = (Cars ONLY): EGR vacuum regulator circuit failure
95 = Fuel pump secondary circuit fault

12 = RPM at idle out of range/high
31 = (Cars ONLY): EVP or PFE circuit below minimum voltage

The only one that I would suspect would cause my symptoms is 95... but I dunno wtf it means. Fuel pump is running fine as far as I can tell...

[danielhv]

95 could be from my kill switch. It is tied into the fuel pump power wire...

[Coupe81]

Check your grounds.