'92 2.3L running rich, poor mpg: EGR problems?
Hi everyone, new guy here with some problems, hope you can help point me in the right direction. This is gonna be a long post so grab a cold drink.
Backstory: Bought a 1992 Ranger XLT reg cab, 2.3L, 5sp manual. Got it from a guy who had it in a barn for a while and it needed a little work to get running well.
Symptoms: Engine runs OK but rich, fuel mileage around 12-15 mpg. When I got it it had some issues so here's what I've fixed or replaced so far:
New plugs (motorcraft)
New plug wires
New air filter
New fuel filter
New fuel pump (low fuel pressure, wouldn't run under load or at speed)
New fuel sending unit (gauge wasn't working)
New fuel filler neck (usual cracks/leaks when filling tank)
New oxygen sensor
OK, so it runs ok but loads up a bit (rich) at idle but pulls real strong through the rev range, but like I said, it's getting bad mileage. The temperature gauge doesn't work, reads cold even though I have heat in the cab, will probably replace the 2 temp sensors as well.
Anyway, once I put the new oxygen sensor in, it started running really poorly. I think the old one wasn't working at all and it was staying in open loop. So after the new one was installed yesterday it was running ok at idle and great at full throttle but horrible at part throttle. Backfiring, loss of power, seemed like it was running way too lean. Disconnected the oxygen sensor and it runs just fine again, but smells rich (open loop). I read that to test the EGR valve you should apply vacuum to the diaphragm and it should kill the engine. I hooked up my my-t-vac pump and pulled 15 in/hg of vacuum and nothing changed, the engine kept on idling like normal. So is the EGR valve bad and introducing a huge vacuum leak? I also don't notice any vacuum at the line that goes into the EGR valve, whether at idle or higher RPM. That line comes from the EGR sensor/switch on the passenger fenderwell which has good vacuum going into it.
Now, I know the first thing you're gonna say is "is it throwing any codes?". Well remember how I said the previous owner had it in a barn? Well I found a rat's nest in the corner of the engine compartment near the EGR sensor and ECU test terminal plug. At least 4 wires into the test connector and both wires into the EGR sensor/switch are chewed through completely! So needless to say I can't pull any codes until I get a replacement harness at the junkyard. I spliced the EGR sensor wires back together but that didn't help anything. There is NO check engine light on, even while running with the oxygen sensor completely disconnected (or with key on engine off), so I wonder if the bulb even works (in the dash) or if the previous owner disconnected the CEL.
I guess my next course of action is to get a wiring harness and try to get the test terminal working again so I can pull any codes from there. I am pretty sure that the EGR valve isn't working but how can I test it (besides the vacuum trick that didn't work)? Should that EGR sensor/switch be passing vacuum to the EGR valve at idle, or just under load? Will just blocking off the EGR passage into the intake (with a blockoff plate) allow the engine to run OK in closed loop mode, or is it required for the engine to run well and not throw codes?
Hit me up with any other questions you have or ideas for me. I don't wanna just throw money at it by replacing every sensor and valve under the hood, but without being able to pull the codes that's what I feel like I'm doing.
Thanks in advance, guys.