hybridspecies

Hi again,


My 94 2WD MT 22RE Pickup backfired twice today. The first time I was cruising along at about 40mph on city streets and the backfire was so loud it left my ears ringing. The second time a couple of hours later not so loud, but noticeable. The truck seems to be running well otherwise and there aren't any DTCs or CEL. The throttle responds nicely at idle, but is maybe a little "soft" under load, but nothing that prevents me from easily doing up to 90 mph on the freeways without laboring the engine.


The Truck has a little over 220K miles and the exhaust system is original and stock including catalyst and muffler. The only thing I've changed is the pre-cat O2 which I replaced with a Denso sensor about 6 months ago. I also recently (2 weeks ago) adjusted timing from about 4.5 btdc to 5.5 btdc, which made a noticeable difference in engine performance much to my surprise. Can any of these be the cause of the backfire? I live in CA and have never failed smog testing (although the last couple of times I came close) so I would not suspect the catalyst off hand of creating excessive backpressure, but it is kind of old plus I notice a fair amount of condensation dripping from the exhaust each morning for a few minutes after starting the truck. It's not green so I'm pretty sure it's just condensation (the oil is clean too), but could that be rusting out the catalyst or the muffler? I'm not sure if the Toyota catalysts use a metal or ceramic substrate either so that might not even be an issue if it's ceramic. The exteriors of both look fine as well.


Any ideas on what might be causing the backfire? Thanks.

hybridspecies

Ideas anyone on how to diagnose the problem? Thanks.

Gevo

Have you noticed drop in your mpg?

hybridspecies

Yes Gevo, a little.

Gevo

I don't really know what's happening here. First, check your timing. If something in the timing system is bad it may cause backfiring. If your timing is good, check your injectors for leaks. I was having backfiring problems due to to much fuel being sprayed by injectors.

I'm sure someone else will chime in soon.

hybridspecies

Timing is close to where it's supposed to be 5.5 instead of 5 btdc. Injectors were replaced not too long ago with rebuilt Toyota's that were supposed to be flow tested and matched, but how would I go about testing to see if one or more is leaking? I don't spell gasoline under the hood or our of the exhaust. Could the cold start injector be leaking instead?

hybridspecies

Can anyone recommend a Back Pressure Tester that will work on my truck? My O2s are the flange type (held on with two bolts instead of threaded into the tailpipe) and most of the Back Pressure Testers I've seen are meant to be screwed into the O2 socket. Thanks.