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Member
- Joined
- Mar 27, 2011
- Messages
- 105
- Reaction score
- 23
- Points
- 18
- Location
- Tennessee
- Vehicle Year
- 1992
- Make / Model
- Ford
- Engine Size
- 3.0 Vulcan
- Transmission
- Manual
So I finally found the cause of the power loss I'd posted about and thought I'd post the solution.
Symptom- 92 Ranger 3.0, OBD1. The truck would act like it dropped cylinders right at 2000 rpm and they would kick in around 3000. Before it got this bad, it would buck and jump under a load going up a hill. Flooring it usually made it clearIt felt like fuel starvation, but it has a new fuel pump that had no effect (old one had a bad drain back valve anyway), pressure was fine, and I couldn't find any spark issue.
At 270k miles, I decided to check the cat even though that vacuum didn't really indicate a blockage. I pulled the o2 sensors (still plugged in, just out of the pipes) out to relieve any extra backpressure and it ran like it should so I swapped the cat only for it to fall on its face again just like before.
I've now checked everything obvious. TPS is new, o2 sensors replaced last year as part of a tuneup, maf seems ok and clean, fuel pressure is good, no egr on this one.
I started suspecting the PCM fuel signal and dug through my copy of the Ford Fuel Injection book by Charlie Probst. Highly recommend this book. I read the chapter on the different EEC-IV fuel strategies. Short version- the only sensor differences between part-throttle acceleration and full throttle is part throttle relies on the o2 signal to try to save fuel, and full throttle goes to a static table based of tps and maf. Going back to the truck, I unplugged the o2 sensors and went for a drive. It wasn't perfect, but was better. Did some digging and found reviews of the sensors I bought had some people receive downstream sensors instead of upstream. Ordered/installed 2 new Denso sensors. It now runs like a 3.0 should. It also seems to rev a bit quicker.
The clues were there, but I misinterpreted the o2 sensors out/cat results. The entire problem was two new o2 sensors that were sending what was apparently a bad signal. I suspect an OBD2 system would have set a usable code, but OBD1 didn't. I learned a lot in this quest. Just glad to have it running right again. Hope this helps someone down the road.
Symptom- 92 Ranger 3.0, OBD1. The truck would act like it dropped cylinders right at 2000 rpm and they would kick in around 3000. Before it got this bad, it would buck and jump under a load going up a hill. Flooring it usually made it clearIt felt like fuel starvation, but it has a new fuel pump that had no effect (old one had a bad drain back valve anyway), pressure was fine, and I couldn't find any spark issue.
At 270k miles, I decided to check the cat even though that vacuum didn't really indicate a blockage. I pulled the o2 sensors (still plugged in, just out of the pipes) out to relieve any extra backpressure and it ran like it should so I swapped the cat only for it to fall on its face again just like before.
I've now checked everything obvious. TPS is new, o2 sensors replaced last year as part of a tuneup, maf seems ok and clean, fuel pressure is good, no egr on this one.
I started suspecting the PCM fuel signal and dug through my copy of the Ford Fuel Injection book by Charlie Probst. Highly recommend this book. I read the chapter on the different EEC-IV fuel strategies. Short version- the only sensor differences between part-throttle acceleration and full throttle is part throttle relies on the o2 signal to try to save fuel, and full throttle goes to a static table based of tps and maf. Going back to the truck, I unplugged the o2 sensors and went for a drive. It wasn't perfect, but was better. Did some digging and found reviews of the sensors I bought had some people receive downstream sensors instead of upstream. Ordered/installed 2 new Denso sensors. It now runs like a 3.0 should. It also seems to rev a bit quicker.
The clues were there, but I misinterpreted the o2 sensors out/cat results. The entire problem was two new o2 sensors that were sending what was apparently a bad signal. I suspect an OBD2 system would have set a usable code, but OBD1 didn't. I learned a lot in this quest. Just glad to have it running right again. Hope this helps someone down the road.
