thesuperbad234

Hey guys, I have a 1995 f150 with the 5.0, mazda manual 5 speed and 4 wheel drive. My check engine light will randomly come on, and then shut back off. And often times come on and repeat the whole process again with random timing.. It only happens after around 10 minutes of driving once the truck is warmed up. Sometimes it'll turn on and then right off, sometimes it'll take 2 minutes to turn off, sometimes 5, sometimes never. I ran the codes and it gave me a 172, HEGO sensor reading lean. But if the sensor was bad wouldnt the check engine light always be on???? HELP!!!!!

Just call me Sean

iTrader: (1)

It says it's reading lean, not it's bad.

thesuperbad234

I'm aware of that much. What could be causing this to happen, though? It just randomly comes on and off as I drive. I've never experienced anything like it before.

Just call me Sean

iTrader: (1)

Failing fuel pump could do it.

Warlockk

A leaking EGR could do it also.

John231

I have the same problem with my 93 with a 5.8 except my code is 173, any ideas what might be the culprit or solution to this.

thesuperbad234

I'll check my EGR.. Can't believe I didn't think of that. Would that cause it to come on and off while driving? And I don't think it's my fuel pump. It does it on both tanks, and there's no other symptoms.

Warlockk

The computer tests is very slow compared to a modern car. It must catch the error usually 2 times in a row to set the light. Often with an intermittent problem like a leak or loose wire it won't catch the error every time so if it goes a few cycles with no error it turns the light off. Also EGR is only supposed to operate during light demand cruise at operating temperature. So there are only a few times in a drive cycle they it will activate.

thesuperbad234

Okay. Where should I start to fix it then?

Warlockk

Well you are looking for something that makes the system read lean. If there are no other symptoms it must be a small issue. EGR may be likely because it turns on when you aren't using power so you may not notice any problems. Visually inspect the system. Look for broken lines or hoses. Then measure the sensor, and test the system with a vacuum gauge and a multi meter. A shop manual has step by step instructions or we have done several write ups on it in the forum ( mostly Aktech ). Just hit a quick search.