It was time for an 02 Sensor!

[91BroncoPickup]

Ya' think? Running a bad mixture for about 6 months, steadily worse, but also kinda intermittent results...

Anywho... Just pulled it and SHEESH!

Here's hoping this is as easy as it looks... If you've followed at all, you know I've replaced everything from fuel pump, filter, pressure regulator, injectors, TPS, EGR, EVR, IAC and more .. about ready to call it all a day if this can't get it running right. Pic attached.

Any tips on brand to replace with? This was a Bosch, which I hear is the best.

 

[Tiha]

I have run bosch without issue. I know some guys complain. I never had an issue

 

[Jimbo26]

Thats definitely carbon-dated.

 

[lynchsg]

Wonder what the Cat looks like?

 

[91BroncoPickup]

Thats definitely carbon-dated.

Yep.

PROBLEM.. put in the new one (I had a shoulder surgery, hence the delay) and...

NOW IT RUNS WORSE!!!

 

[91BroncoPickup]

Wonder what the Cat looks like?

Me too... But now I'm stumped as to why it runs worse. Still bogs upon acceleration at HWY speeds.. Heaven forbid I use cruise control. Ugh!!

 

[91BroncoPickup]

I have run bosch without issue. I know some guys complain. I never had an issue

I did get that brand - did not solve issue

 

[lynchsg]

I mentioned the catalytic converter before. I had major issues similar to yours in a Durango and it ended up being an old plugged up converter. Don’t know how old yours is. I put new O2 sensors in even a new ECU, among other things and it still ran terrible until I changed the converter.

 

[Gary202]

Knock sensor?

 

[L\Bronco]

Me too... But now I'm stumped as to why it runs worse. Still bogs upon acceleration at HWY speeds.. Heaven forbid I use cruise control. Ugh!!

Hey 91Bronco
Couple quick checks. Drive it with the O2 sensor unplugged. It will be in open loop control, If it runs better, check the sensor ground, (on a 91 it should be an orange wire bolted to the rear of one of the heads, if memory serves)
If it doesn't change, check the vacuum line to the Map sensor, along with the sensor itself.
Plus a restricted cat is definitely on the table. A quick check there is measure manifold vacuum at idle, then at 2000-2500rpm, both in neutral. The vac reading should be 18-20 in/hg at idle and 1-2” stronger at 2 grand. If it goes down, pull the exh away at an easy spot and check again. If its better, plugged cat.
Hope that wasnt too much at once.
Good luck,
Cheers

 

[lynchsg]

One other thing on new sensors out of the box. When I was going through my Durango fiasco, I installed a new crank sensor- what a pain. Out of the box 2 wires were swapped in the plug connector. I didn’t realize it and the engine wouldn’t start until I checked the old connector to the new.

 

[91BroncoPickup]

So... I did the ECM capacitor refresh...

When I opened it up, the capacitors were NOT the OEM!! And they were the incorrect values!! (Pic with 3 incorrect caps outside the case, and new correct ones soldered-in.)

All shifting is smoother. Accelerator responds as it should, and I finally have a feeling of a benefit from the new multi-port fuel injectors I put in 8 months ago!!

I actually averaged 16.2 MPG on the Highway!!!

Just for giggles because it was the only aspect I've not replaced, I ordered a brand new fuel tank, vent valve and vent hose w/filter, and a new locking gas cap. (Why? I did finally figure out I have had some pinholes in the tank, and that's also been screwing up fuel pressure.)

Also, I have an adjustable fuel pressure regulator with a hair gauge I'm installing.

See pics below!!

 

[L\Bronco]

Nice find, congrats!
Cheers

 

[Jimbo26]

Debugging- always a process of elimination.
Sometimes it takes brain surgery.

 

[91BroncoPickup]

Happy to report that today I drove it 120 miles round trip at HWY speeds up to 81 mph, and even on cruise control, with ZERO issues!!!

 

[91BroncoPickup]

Knock sensor?

It ran better without it before the ECM repair, but that's been resolved. Removing it was a good band-aid under 45 mph. Good insight!

 

[Tiha]

That is awesome news. I myself have never had an ecm failure. But everyday it seems I run into more and more people that do.

Even worse, someone else didn't correct fix it before you. That is the worst.


Nice work.

 

[goodO1boydws]

Glad to hear that you're running well now.

(I can relate to replacing the tank.)
By 20 years of age, in most climates, replacing a tank is almost "preventive maintenance" (even if it isn't leaking) as it almost certainly would have interior rust. Especially so if your vehicle had ever sat for a verrrrrry long time-with a mostly or only a partly full tank, from gas gone bad+condensation, (its particularly likely with ethanol in the gas).

I wonder how much the improvement in mpg is from no longer losing gas from those pinholes?

 

[91BroncoPickup]

Glad to hear that you're running well now.

(I can relate to replacing the tank.)
By 20 years of age, in most climates, replacing a tank is almost "preventive maintenance" (even if it isn't leaking) as it almost certainly would have interior rust. Especially so if your vehicle had ever sat for a verrrrrry long time-with a mostly or only a partly full tank, from gas gone bad+condensation, (its particularly likely with ethanol in the gas).

I wonder how much the improvement in mpg is from no longer losing gas from those pinholes?

I will update with that information for sure! The tank is supposed to be here by tomorrow, but not sure how soon I'll swap it... I just had to fill it up full because I have to drive 60 miles away in the morning.

But I will update this thread!

 

[goodO1boydws]

Looking forward to it.

If your ride IS a '91, It may well have been built in '90, and that was fairly early in the widespread adoption of ethanol-laced gas as the "standard" regular gas so I'd double check to see if "gasohol" at 10% of the mix being ethanol was its intended fuel, or if non-ethanol gasoline was. (Trucks/light trucks/SUV's likely had a slower roll-out on the switch.)

For those younger folks, "regular gas" was 89 octane for many years, back when there was no ethanol blended gas. NOW 10% gasohol is almost universally "regular gas" (in the USA) and it is usually rated at 87 octane. In some areas non-ethanol 89 octane and higher octane-rated "pure" gas is still available, but the highest octane formulas are becoming harder to find every year. Now 94 octane gasohol is considered "top premium" gas. I remember when you could easily get 103 octane "pure" Sunoco pump gas at an ordinary gas station.

In parts of the country (in the Mid-West esp.) E15 is getting to be more common now, and pre-2001 or so vehicles aren't as pleased with THAT as when running E10. Fuel mileage is often measurably poorer on E15 than on lower blends or on no-ethanol gas, as any mix of ethanol blend gas has a lower BTU content than gas with less ethanol in it, or with none.

Interestingly, pure ethanol DOES have a higher octane rating than gasoline, so in certain situations, an ethanol blend gas can potentially offset its inherently lower fuel efficiency/BTU content/lower power yield when an engine is close to the start of pre-ignition, as its knock sensor wouldn't cause the ECU to back off the engine timing quite as early as it would have if it were running on regular gas. So its possible that you might reach higher rpm or a greater peak torque level on ethanol blends in that situation.