Hey all, new to the forum here and I need a little help. I have a 1994 Mazda B2300 with the 2.3l. Manual everything, probably the most analog vehicle of 1994. Its a ranger in a Mazda costume. It recently broke its timing belt which has been replaced and all seemed well at first. It runs perfectly at start up and will run great for the first few miles up the road. But after it builds some heat in the engine the trouble starts. It will lose almost all power, like it's only running on 2 cylinders or something and it sputters and idles terrible. But all the while it's doing this it will intermittently come back to full power and act perfectly normal for a couple minutes and then return to running rough. It will continue to cycle like that until it's parked cooled down and it will then run great until it's warm again. Any ideas?

 

Welcome to the forum

All Engine computers have 2 basic operating modes, Open Loop and Closed Loop
This is because a cold gasoline engine needs to be Choked, and O2 sensors need to be heated up above 600degF to work

In Open Loop the computer has air/fuel mix tables in memory, for engine size, so computer doesn't need to calculate air/fuel mix "on the fly",i.e. at XXXX RPM air/fuel and spark timing = XX/XX and 25deg BTDC
And if coolant temp = 100degF then add 10% more fuel, the Choke part, and keep idle above 1,000rpm

Once coolant temp exceeds 140degF the computer will "look at" voltage coming from O2 sensor
If O2 is outputting voltage the computer will go to Closed Loop
Closed loop means the computer is now calculating air/fuel mix "on the fly" based on RPM, air weight(MAF), air temp(IAT), engine load, and throttle position, it then looks at O2 voltage(feedback) to see if its calculations are correct
So in "Closed Loop": calculation >> feedback >> calculation >> feedback >> ect......................its a "closed loop"

O2 sensors use a chemical reaction to detect Oxygen in the exhaust, and they run low on chemicals after 100k miles or 12 years
So if you don't know the age of the O2 then change it, may or may not be the issue but computer has no "comparison" for the O2, like it does for other sensors, O2 is "The word of God" as far as computer knows, there is no "back up plan"

If you KNOW O2 sensor is good then the running issue after warm up can be addressed further
As said most sensors have comparisons the computer can use so computer will set codes for that
If no codes the could be computer issue

1994 was last year of the EEC-IV 60-wire OBD1 computer in Rangers/B-series
They have 3 barrel capacitors that will wear out after 20+ years, under $5 to replace them
Also good to check computer and to unplug its 60 wire connector and plug it back in, that cleans the contacts, sensors all work at under 5volts so even slightly dirty contacts can change the the voltage enough to cause issues, O2 sensors are under 1 volt

1994 was also the last year of the ICM in 2.3l, ICM = ignition control module, it runs the spark system
These were know issues as they got older, they run HOT, which is why they are located behind the fan, but after years of use they can cause running issues after they warm up
Hard to diagnose these because testing them when cold can/will show they are OK, its not until they get HOT when faults show up, very much like coils/coil packs in that respect

 

So I do not know the age or condition of the o2 sensor and I am going to go forward with replacing it. I decided just to check timing and it wS 20deg btdc. The manual I have doesn't even list what it is supposed to be set at.

 

It just feels strange because the truck was running totally fine before it broke its belt on the highway

 

Yes, that's the way things happen
Was running great yesterday, now its not

Could it be related to broken timing belt, maybe
Did you replace crank sensor?
Always a good idea to do that, so could be the issue if you didn't and new crank sensor may be faulty if you did, lol
Also need the tool to space the crank sensor "wheel" so it doesn't rub the sensor, did you do that, and did you check it after?

Could also be "bad gas" have you got gasoline recently?