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Discussion Starter #1
Hey all, '96 MT RS, stock as stock can be. Had a timing belt done recently that was overtightened and made a whirr noise like a supercharger. Did get that corrected, timing belt no longer makes any noise. But not long after the timing belt job, I was driving home and suddenly I lost a cylinder completely. Was cylinder 3. Limped it home and on the way it went back to running again, albeit odd. It's never run right since, and the misfire didn't stay on cylinder 3 either. So far I've replaced the distributor (with a Dragon Fire; distributor had been replaced with a MOSTPLUS earlier this year), the fuel filter, all 4 fuel injectors (old ones had grime around the lower donut but otherwise looked fine), and all four spark plugs. No change to operation with any of these swaps. O2 sensors are relatively new, they were both replaced this year after I lost a catalytic converter to a dead distributor.

Since it's OBD2a I went ahead and logged a drive to work, and found that at idle the engine runs so rich that it knocks the computer out of closed loop after it tries to pull almost 50% fuel. But when it goes open loop due to WOT, the O2 reads mega lean--like 0V mega lean. I can't say what the exhaust smells like at WOT, but at idle it does indeed smell pig rich and my fuel economy has been garbage ever since this problem started. Ignition timing is spot on according to the marks on the crank pulley, and while at first I did suspect the timing belt had jumped a tooth, it's in time as well (checked when it was retensioned). I've checked all the vacuum lines and the hoses are all intact and connected where they're supposed to be. I've tried spraying starter fluid along the common failure points (intake manifold gasket, MAP and TPS gaskets, vacuum ports, brake booster, fuel injector ports) and it didn't affect the engine one iota, so it doesn't appear to be related to engine vacuum. Did a compression test and got 180 all across. For the heck of it I did pull the ECU and crack it open, but it looks brand new inside. No signs of bad capacitors or anything like that, no water ingress. ECU doesn't throw any codes either other than when a full-on misfire condition occurs.

Kind of at my wit's end with this. Dunno what could make it pig rich at idle and lean at WOT and happen suddenly that I haven't already replaced.
 

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Thats a lot to read, but I think it's a timing issue. Possibly a distributor issue (incorrect install or bad) or maybe even the camshaft sensor?
 

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Discussion Starter #3
Two completely different distributors (one about 5 months old, one literally brand new) installed the same way, timed up with a timing light correctly, and performed utterly the same. I find it hard to believe it could be distributor.

Apologies for the wall of text but I had to make sure I covered everything I had already tried so that we don’t go in circles.
 

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Discussion Starter #4 (Edited)
Update: Bought a jumper harness and plugged my dad's automatic '95 ECU into my car. Same exact thing, plus a surging idle due to the automatic transmission stuff. So it's not ECU either.

Bought a valve cover gasket, will be pulling the valve cover and checking mechanical timing next. The shop that installed the belt and then later fixed the belt tension told me the timing was still correct, but I can't trust that now, so I will be inspecting it myself.

Update: Timing belt timing was spot on. With both cams at matching (both UP arrows up, both cam notches point at each other, dowel pin holes line up) the crank pulley indicator shows TDC.

Rechecked Ignition timing and confirmed it is also spot on (middle of the three advance marks at operating temp with the service connector jumped).

Checked compression hot. Got 210, 200, 205, 210 from cylinder 1 to cylinder 4.
 

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Discussion Starter #5
Update: Ordered a new FPR, turned out to be the wrong part (return bung was too big for return hose), but I had a B16A2 in the garage so I ripped the FPR off that, put on the new o-ring, and fired it up. Did the exact same thing it did before.

So now I've replaced everything in the fuel system except the pump and lines, neither of which would cause too much fuel to get into the combustion chamber. I've replaced everything in the ignition system except the plug wires, which all tested at 6.6kohm or less and as such should be perfectly fine. Just for the **** of it I'll take the plug wires off my dad's car and try those since his car runs fine, but I doubt it'll change anything.

At this point I really am out of ideas. Any help would be appreciated.
 

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Discussion Starter #6
Update. Swapped the wires off my dad's Integra to no effect. Noticed that if I open the throttle and try to start it it starts a little easier than if I try to start it with the throttle closed. Not much, but certainly faster. Also while it's idling, if you just barely touch the throttle plate it will try to die. If you actually open the plate it'll sputter a second then rev up, but just barely tapping the throttle--even repeatedly--will make it sputter out and desperately try to shut off.

I'm at my wit's end with this.
 
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