Intermittent check engine

[Farang]

UPDATE: UPDATE:

Code 335: Differential pressure feedback EGR sensor. Sensor output less than or greater than expected during Key On Engine Off Test.

After driving my 94 Mazda B4000 4.0L V6 Automatic (113k miles) around for a bit, maybe a half hour (either highway or city), I sometimes have the check engine light come on for a minute or so during city driving. I've had it happen at about 35mph once but usually seem to be at lower speeds when it turns on. It turns off to quickly for me to hook the computer diagnostic dealy up to it.

One issue I read with this was a dirty thermostat, was wondering if it is also an issue that the engine never gets passed 1/4th of the way on the temperature gauge even after 30+ miles of driving.

No obvious signs of anything wrong when the light comes on.

 

[ZetaEpyon]

The codes should still be logged, even if the light has gone off.

 

[CrackRabbit]

It could be any number of things, codes should be stored even if the light had gone off.
That is the first place to start.

 

[Vette73]

The temp gauge sucks in these. I have a 94 B4000 as well and my Therm was stuck open yet after replacing the gauge barely moves any more then it did before.

Does it do it more/less with the AC on? Have you cleaned the MAF sensor yet? Cleaned the EGR valve? and have you replaced the front 2 O2 sensors?


I am leaning toward EGR maybe. But hard to say without a engine code.

 

[Farang]

Marlin where is the OBD code reader outlet?

 

[Vette73]

Originally posted by: Farang
Marlin where is the OBD code reader outlet?

For most fords its under the hood. It is OBD1, NOT 2 so there are 2 plugs you will need to attach to the scanner.

just get a basic Ford scanner that goes up to 94. I have not got one yet as when i did my major 100k+ tuneup it fixed my light.

 

[Farang]

Damn, I have a OBDII reader here at home. I'll have to wait then. Do the parts shops not lend these out for free anymore?

 

[Vette73]

Originally posted by: Farang
Damn, I have a OBDII reader here at home. I'll have to wait then. Do the parts shops not lend these out for free anymore?

I think autozone use to have a OBD1 scanner but most did not know how to use it well so i don;t think they still have them. They are very cheap like less then $20 at eBay now.

 

[Farang]

To answer your questions I haven't touched anything, will update when I get my hands on a reader.

 

[drum]

I've had a spark plug and wire replacement take care of that. You should check those anyway at that age.

 

[Farang]

UPDATE:

Code 335: Differential pressure feedback EGR sensor. Sensor output less than or greater than expected during Key On Engine Off Test.

 

[hoope11]

It's pretty common for the EGR pressure sensor to fail. At 73k miles, I'm about the replace the one on my 2001 Ford Focus for the 4th time.

As the sensor begins to fail, you might notice a few symptoms:
* extra cranking on start-up
* rough idle
* hesitation @ partial throttle (early on, it might feel like you're driving into a strong headwind)

The sensor should be a sub $100 part, and is generally easy to replace.

If the sensor is OK, it could also be the EGR valve itself, or some crud in the system somewhere.

 

[Farang]

I do get about 5-7 chugs when I crank the engine to get it to start and it seems a bit too much. Hesitation: maybe but I'm just getting used to auto and I thought that was just how they drove. Rough idle: not really, but the engine is maybe the quietest I've ever heard so it is hard to tell.

Is there an easy way to check for clogs before I spend the $75 on a new sensor?

 

[Squisher]

Originally posted by: hoope11
...If the sensor is OK, it could also be the EGR valve itself, or some crud in the system somewhere.

I should probably be the last person giving advice in this forum, but it says "Key on, engine off" so nothing mechanical could be the issue unless it was a position sensor and something was stuck in the wrong position. This is a pressure sensor that is being checked when no pressure is present and it's giving a false reading. I would think this is a slam dunk, it is the sensor.