I bought my '88 4cyl Fiero back in October 2019 with rod knock and spun bearings. After finishing my rebuild this last July and I had everything reconnected it started up with flying colors, other than an oil pan leak I noticed after starting. Dropped the engine again and fixed the issue, and then more issues started up.
I'm 95% sure my CAT has blown up one of the initial times I started it up after the rebuild. Either it's still clogged or it's clogged my muffler/somewhere along my exaust, I get a nasty rattle from my cat when idling and when the engine is killed it makes a couple of horrible clunking noises My idle would go from 1000/1250 to roughly 750 or nearly stalling, this issue isn't as prevalent now but still occasionally happens.
Yesterday I noticed my EGR was loose, tightened it. Replaced my old rusty fuel filter, air filter and cleaned my IAC sensor to see if I could solve the idle issue/loss of power. Changing the fuel filter seemed to help with fuel delivery, and my injector appears to be spraying in a clear pattern.
When driving it seems like my fuel pump isn't delivering enough fuel. I have very poor acceleration at around 3000 rpm, and the car is running insanely rich. Just the other day, I used 1/4 tank to drive around 20 miles, so my gas mileage is absolutely tanking. I get backfires often and exhaust pops when revving or accelerating. I've filled up roughly 8 full gas tanks in ~580 miles of driving. Running without an o2 sensor doesn't seem to help (fully removing from exhaust header) but I don't know if my o2 sensor is working, clearing the computer doesn't change any issues.
I have no engine codes, and I'm running no AC if that matters for some reason.
I'm wondering if anyone has had similar issues and what steps I should try next. I've got 3, 3800 series 2 engines that I need to work on and combine parts in order to make one running the engine for a swap and I'm leaning towards giving up on the duke, but I'd rather just fix this issue.
Either my O2 sensor is broken, my cat is clogged causing loss of power, my battery/alternator is bad, some other issue or I have a grounding issue or all of the above. If anyone has some insight that'd be great, thanks.
If your cat is producing internal rattling sounds, it's no good. The catalyst has probably broken up, and it's potentially plugging up the cat... or plugging up the exhaust downstream.
Some basic troubleshooting may be in order...
What is the actual fuel pressure? What are the dry and wet compression numbers for each cylinder?
