Hello all, Registered today to get help with what mechanics can't find. My name is dan and I have a 91 Ranger super cab 4.0l. The ck engine light has been coming on. Mechanic #1 said o2 sensor, he replaced. light off about 4 days and back on. I took it back, he said faulty 02 sensor, replaced for free. 4 days on again. went to mechanic #2. bad 02 sensor, told him just replaced twice. he said other things show that code, he would just have to start replacing things. can't afford guess work. I replaced PVC valve Light out 2 days. Replaced all vac lines I could and checked one I couldn't. I have no egr valve. I have had thi truck for ten years and have only had to replace belt and fuel pump. It starts and runs fine, I go about 5.6 miles and the light comes on. if I turn it off and restart, the light doesn't come back on for several miles.
Anyone have any ideas.

 

could be a catalytic converter...that sounds like your catalytic converter is going bad...how many miles are on it?

 

125,000 miles on it. I also forgot to say I replaced the mass airflow sensor. I always thought when the converter went bad, there was a bad smell from the exhaust and milage suffered along with idle problems.

 

your problem reminds me of my exemption exams SAE questions for the ministry.... mechanic A says,"...... mechanic B says "...... who is correct??? mechanic A? mechanic B? both? neither?

 

that is not always the case...sometimes you will get a smell but other times it will just go without any warning ive seen it happen

 

omg... i hated those lol

 

What is the code it is throwing and is it always the same?

 

I don't know the code number but both mechanics said the code was the 02 sensor. All the auto stores wont read anything that is not a 96 or newer so I can't run to autozone and have it checked. I do know it was two different computers that read it. One was a snap on with a program called Vresus? The other was as big as the bed of my truck. they brought leads to enginge compartment to hook up. It had two screens about chest high.

 

sounds like your leaking coolant in to your combustion chamber
the excess vapours are coating the oxygen sensor ( it cannot read the exhaust vapours )

thus triggering the CEL

 

Is there any way to test or check that.

 

pull a spark plug and look for whitish deposits on the electrodes

 

Here's where we are. I took it yesterday to the garage that works on our company vehicles. I know mechanic # 3, he said codes are for 02 sensor. but he pulled some vac lines to prove the sensor was working. said computer said it was running rich. he ck'd fuel pressure and it was out of range, running high. he wants to change the fuel pressure regulator. What should this pressure be. I can get a loan a tool and ck myself. He also say mass air flow sensor was not working. I just replaced. I did notice that with engine running I can unplug this and replug with no change to engine idle. Is this normal.