Intermittent Check Engine Light?

[SHOnOFF]

My Check Engine Light just came on the other day (in the 94 ATX with 94,700 miles) for the first time since I bought the car 3 years ago. It came on once and then went off and that was it for that day. Next time out, it cycled on and off at least 7-8 times. Now it does it constantly whenever I'm driving. I thought I had a theory about when it came on, but it doesn't always hold true. But anyway, it "SEEMED" to come on whenever I would accelerate from a stop and then let off the gas when I reached "crusing speed." When I would let off the gas, THAT'S when it would seem to come on. Anybody have any ideas what it could be?
I have 2 theories but I'm sure some of you guys have already had experience with this so I'll defer to your opinions. (But I think it might be either my fuel pump or the oxygen sensors.) Please give me any advice/suggestions you can offer. Thanks in advance!

 

[SHO--ripper]

Check the codes. If you think it's the fuel pump check the schrader valve on the fuel rail. Check to see if there is the correct amount of pressure.

 

[SHOnOFF]

I was afraid of that (answer). Because that's the problem...the CE light doesn't really stay on long enough for me to get out of the car, pop the hood, and try to pull the codes. Correct me if I'm wrong, but I believe the CE Light actually has to be on when you're pulling the codes in order for it to tell you what code the light is giving. And therein lies the problem. That's why I was wondering if anyone else has had a similar situation happen to them followed by a dead fuel pump or oxygen sensor replacement shortly thereafter. I'll try to check the codes sometime this week, if the light will stay on long enough for me to do it. Thanks.

-Brian

SHO--ripper:
Check the codes. If you think it's the fuel pump check the schrader valve on the fuel rail. Check to see if there is the correct amount of pressure.

 

[LaTechSHO]

you are wrong...most codes will be stored in your computer's memory


Louis

 

[Mr Anonymous]

Refer to the links in my sig. to learn how to read the codes. If the CEL fires while you're driving, a code (or codes) should have been stored as mentioned.

Just a guess, but with the behavior you describe I suspect you'll find a TPS code and possibly and EGR code, both of which are likely due to clogged EGR nostrils in the intake.

In any case, starting with the codes is the first thing to do before spending a penny on any guesses.

 

[SHOZ123]

My '93 has the engine light that goes on and off. Only code I get is a low speed fuel pump problem.

Although I replaced my O2s in December I think that is the problem.

 

[Off Road SHO]

I aggree with SHOOOOO. Both of my 95ATX's exhibited the same problem and both were cured by a good EGR Nostril cleaning. Wire open the throttle plate and use a bent coathanger or bent piece of brake tubing.

Tom

 

[SHOnOFF]

Ok, I just finished pulling the codes and here's the verdict. I did the KOEO test.

Hard faults: 551
Memory codes: 172

I checked to see what they are and here's the corresponding problems.

551 = IAS Circuit Failure
172 = HEGO Sensor indicates system lean (RH)

Now...#1, what the heck is the IAS Circuit? What's going on there? And #2, is the HEGO sensor just another name for the Oxygen sensor? And if so, which one is it (front or back)? Any advice here would be great. I don't want to have to take it somewhere if I don't have to. Thank you in advance again, guys.

-Brian

 

[Billy P]

I'm having this exact same problem. The only difference is my car does exhibit a little shudder at idle every-now-and-again. I am ordering new O2's because I am almost at 100g's on the odemeter. Should I do something with my EGR? I am willing to spend the money - I am in love with this car. I don't have a code-reader anymore and do not have access to one.

 

[SHOZ123]

Mine still does this. After the engine is out of cold loop the SES light will come on and go off. Never any code bu the low speed fuel pump one.

I do have a cylinder that is running very lean. I presume the injector is clogged or in some other way bad. This is what I think is wrong with mine.

 

[wood_e]

I get the same CE light (172) after running my car hard sometimes, it goes away. The O2s probably aren't reading as well as they used to. I just haven't had the time to replace them.

 

[sdpatt]

[Edit] I knew that, but brain farted. Thanks for correcting.

The IAS is the the secondary butterfly valve solenoid on the center of the rear intake plenum. Is it plugged in?

The 172 code is the rear or right bank oxygen sensor not working properly. Since only one sensor is showing this condition, it is more likely that the sensor is faulting rather than the engine control system actually causing a lean condition. You should probably replace both oxygen sensors as they should be replaced about as often as the spark plugs: every 60,000 miles. Use the Bosch 15716 available from AutoZone for $49.00. The rear sensor on the ATX is a PITA to access and requires a O2 sensor socket (borrow from AutoZone), a U-joint and about 9" of extensions. Reach the electrical connector by laying on the top of the engine and reaching between the engine and the firewall with one hand.

<small>[ September 10, 2003, 03:29 PM: Message edited by: sdpatt ]</small>

 

[projectSHO89]

SHOnOFF:


551 = IAS Circuit Failure
[edited]

Now...#1, what the heck is the IAS Circuit? What's going on there?
-Brian

IAS = Intake Air Solenoid (1992 and prior), not the Idle Air Control valve. Different critters.
For 1993 and on service documentation, the IAS is properly called the IMRC (Intake Manifold Runner Control).

About the 551 code: What it is and how to troubleshoot it.

Steve

<small>[ September 10, 2003, 03:18 PM: Message edited by: projectSHO89 ]</small>

 

[sho 'nuff]

I just ran into this over weekend on my drive back from the SHOcago meet. I talked to Mikey about it from the side of the highway to make sure it wasn't anything that was going to disable my engine if I continued to drive home. He was helpful and so was having his list of codes printed off(thanks MoKan SHO thumb ) Anyways it looks like I am in the same case as the guy's post you just refered to. I have secondaries at WOT and I can clearly see them move into a closed position when I turn on the engine. Weird. shrug