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Posted by: DC_neun_vierzehn Oct 23 2021, 09:36 PM

My '73 2.0 w/ fuel injection started backfiring a couple of days ago and seems to have gotten progressively worse in the last couple of days. It's not constant. Seems to worsen as engine warms up. I've owned the car since April and it ran fine when I purchased it.

Where should I start with trouble shooting?

Disclaimer - my mechanic/engine skills are very limited.

Thanks in advance.

Posted by: BeatNavy Oct 24 2021, 07:02 AM

Could be a number of causes that are fuel or ignition-related. Is it a popping that sounds like it's coming from the exhaust, particularly on deceleration? If so, my first bet would be that you're running too lean. Running lean can be caused by fuel obstruction somewhere (filter, lines, clogged injectors) or low fuel pressure or several other things. But it could be ignition / timing related, too.

One test you could try would be to temporarily disconnect the ambient temp (T1) sensor. It's a two wire connection on top of the manifold near the TPS. That will artificially enrichen the mixture a bit and may give you a clue if it's running lean.

I'd also just start looking around the engine bay for loose or disconnected wires / hoses, such as injector plugs, trigger points, spark plug wires, etc.

More info would be helpful, too. Does it run fine when you're NOT hearing the issue? Good power, etc.?

EDIT: Another possibility could be an exhaust leak somewhere. You can get popping, especially on decel, if you have a poor connection from HE's to muffler, for example.

Posted by: DC_neun_vierzehn Dec 7 2021, 11:22 PM

To close the loop on this one in case anyone searches for these symptoms and wants to know what it could be ...

My mechanic detected exhaust leak (loose exhaust manifold studs and one of them was actually missing). The missing stud had stripped threads in the head, but the other loose studs just needed new studs and washers to seal. The stud that had stripped head thread was able to be at least temporarily sealed ... for how long we'll find out. He said they will need to drop in an insert to properly fix, but I may just wait to permanently address if/when I do a motor rebuild.

So for now ... the exhaust leaks were addressed and the random/occasional backfiring has been fixed. She's running strong again!

Thanks all for the input.

Posted by: Cairo94507 Dec 8 2021, 07:34 AM

Thanks very much for circling back to let us know what the issue was. Glad it was simple fix.