1994 ATX stuttering, CEL, 172, 176, 542, 543 codes

[timmay316]

I just picked up a 1994 ATX. Finished all the 60k work (148k with no 60k work ever done... waaaay to much oil in the plug wells), replaced rod bearings, replaced the exhaust and a few other things. It's running better than when I bought it, but there are a few quirks. When I first got the car, it got 33 mpg or so on a regular basis, the fuel mileage is now down to about 20. When driving (regardless of whether the car is hot or cold, from a stop or rolling down the highway), every once and awhile when I try to accelerate, the car will just stutter. If I let off the pedal and push it again the car catches itself and drives like normal. The stutter isnt like a slipping transmission (or VSS issue I have read about), its much more like a misfire or lack of fuel (engine tries to fire and catch up with itself, but just cant). Also, the CEL was on when I bought the car, went away (thought maybe it was related to the sorely needed 60k), and now comes and goes as I drive every day, usually coming on right after the stuttering issue. I checked the codes, and got 172, 176 both banks reading lean), 542 and 543 (fuel pump secondary circuit malfunction). After doing a lot of searching, I cant seem to find anyone with the same problems as me. I have read that the fuel pump secondary circuit is nothing in most cases, but I have to wonder if its related to both banks being lean? I thought maybe it needed new 02 senors, but since both banks are lean, I have to wonder if the sensors are fine... I would appreciate any input. Thanks!

 

[LOUDSHO92]

You should just replace the O2 sensors and see if that fixes the problem. If the O2s were never replaced then they are on their way out as that is a lot of miles for O2 sensors.

 

[timmay316]

Would bad o2 sensors hurt my fuel mileage that significantly (33 to 20)?

This past Sunday when I checked the engine codes again, on the KOER tests I got a 225 code (knock sensor not sensed during dynamic response test). Never saw this code before when I did the test, could it be a fluke?

 

[Storm-Chaser]

I disagree with changing the oxygen sensors. Throwing a $100 at the problem is a pretty expensive guess. Remember, the oxygen sensors provide feedback to the EEC, which uses this feedback to "adjust" fuel metering to change the air/fuel ratio to maximize fuel efficiency and minimize emissions, which in turn affects the relative composition of the exhaust gases. While a "bad" oxygen sensor can throw codes because it's not adjusting properly; a number of other factors can affect how much fuel is being metered through the injectors (or how accurately the density, temperature, and/or velocity of the incoming air-charge is sensed) and exceed the systems ability to compensate, thus throwing oxygen sensor codes.

I think the bigger questions here are, what in the 60K could cause the sudden change; and, what is the probability that both sensors just happened to fail at the same time?

My first inclination is the catalytic converters. As the cats clog-up, I first noticed a gradual increase in overall engine temperature, followed by progressively worse fuel economy, and then a gradual increase in poor engine performance (progressively poor acceleration and increased missing).

I would also check the fuel pressure at the fuel rail, to verify the condition of the fuel filter and fuel pump.

Would bad o2 sensors hurt my fuel mileage that significantly (33 to 20)?

This past Sunday when I checked the engine codes again, on the KOER tests I got a 225 code (knock sensor not sensed during dynamic response test). Never saw this code before when I did the test, could it be a fluke?

 

[n8rsk8r]

atx and getting 33? Woowzers, get that fixed and let me know what you did to get that MPG!!! I saw high 20's on the highway, around town it was a pig. I have a ford laminated pamphlet for our atx's. It is a troublecode-to-sensor chart. I will see if I can hook my scanner up to the Faptop and get it scanned. I will see if any of the codes you say are popping up are on it and what those could come from. Good luck, I will hit you back tomorrow.

-Nathan

 

[timmay316]

I plan on changing the fuel filter this weekend, I'll check fuel pressure at the rail before and after to see if there is a change.

I dont think the cats are an issue, being as they are no longer there (right after the 60k I fabbed up a "damn-near-equal-length" catless y. I also put on a single resonator and two flowmaster 40's, so even when the car is running like shit, it still puuuurrrrs).

Engine temp hasn't risen compared to what it was before (assuming I can trust the stock gauge).

I think I'll also try cleaning the MAF. Can't hurt anything. I did just recently make a true CAI that places the filter right behind the drivers side foglight, think that would give me any trouble? (although the symptoms were there before I put the intake on).

The other thing is, I dont know if the problem is related to the 60k. Now that I really think about it, the car stuttered before the 60k, but I never got a chance to check the engine codes. I had stupidly assumed that the stuttering was a misfire caused by the 1.5" deep oil in all the plug wells. I did the 60k work, and the car ran better, but the stuttering soon came back. Then I checked the codes, and here I am now lol...

I disagree with changing the oxygen sensors. Throwing a $100 at the problem is a pretty expensive guess. Remember, the oxygen sensors provide feedback to the EEC, which uses this feedback to "adjust" fuel metering to change the air/fuel ratio to maximize fuel efficiency and minimize emissions, which in turn affects the relative composition of the exhaust gases. While a "bad" oxygen sensor can throw codes because it's not adjusting properly; a number of other factors can affect how much fuel is being metered through the injectors (or how accurately the density, temperature, and/or velocity of the incoming air-charge is sensed) and exceed the systems ability to compensate, thus throwing oxygen sensor codes.

I think the bigger questions here are, what in the 60K could cause the sudden change; and, what is the probability that both sensors just happened to fail at the same time?

My first inclination is the catalytic converters. As the cats clog-up, I first noticed a gradual increase in overall engine temperature, followed by progressively worse fuel economy, and then a gradual increase in poor engine performance (progressively poor acceleration and increased missing).

I would also check the fuel pressure at the fuel rail, to verify the condition of the fuel filter and fuel pump.

I couldnt believe the fuel mileage either! My old 89 was lucky to get 25, and I was happy with that. The 33 is relative though, that was all highway mileage (I never got a chance to check it with combined city/highway mileage), and I just took a trip up north, so I checked highway mileage again, thats when I saw the 20 mpg. Definitely let me know, I appreciate any input I can get, this car is driving me nuts (although I can live with a few quirks, I bought the car for $450).

atx and getting 33? Woowzers, get that fixed and let me know what you did to get that MPG!!! I saw high 20's on the highway, around town it was a pig. I have a ford laminated pamphlet for our atx's. It is a troublecode-to-sensor chart. I will see if I can hook my scanner up to the Faptop and get it scanned. I will see if any of the codes you say are popping up are on it and what those could come from. Good luck, I will hit you back tomorrow.

-Nathan

 

[LOUDSHO92]

Yes O2s can cause thta much of a drop in milage.

During the y-pipe thingss could of changed with the O2s, though I would check for leaks to make sure everything is good there. Also check the EGR for leaks.

Also make sure all of the vacuum lines are good and intake couplers are good as well.

 

[timmay316]

What would be the easiest way to check for Vacuum leaks?

 

[Storm-Chaser]

Were those codes all Continuous Memory codes? It's possible that they're remanent codes from before the 60K. CM codes are stored for 40-80 cycles from their last occurrence.

If you didn't annotate the codes when you read them, pull the codes again. Note whether they're KOEO, CM, or KOER codes. Then I would clear the codes, drive the car for a few days (enough to run through another tank of gas), pull the codes again and recheck the mileage.

Do one thing at a time - then pull the codes again. Making multiple changes will make it difficult to tell what was the problem, or more difficult if new codes or problems surface.

Matt brings up some good points - check the EGR and vacuum lines, and around the intake couplers for leaks. You can check for leaks by spraying ether or similar flammable spray and note if the rpm increases. You can use less flammable sprays (carb cleaner) and listen for rpm changes.

Also check the grounds and connections for any harnesses you disconnected or moved around to get at things while doing the 60K. Did you clean-up the DIS grounding strap (runs from the left rear of the plenum to the firewall below the passenger side hood strut).

How did you determine/calculate your mileage? Did you use the trip-odometer? The reason I ask, is that the mean of 33 and 20, is 26.5 - which is more typical for most SHOs. Also, have you had your foot in-the-throttle a little more now that it's running better?

I plan on changing the fuel filter this weekend, I'll check fuel pressure at the rail before and after to see if there is a change.

I dont think the cats are an issue, being as they are no longer there (right after the 60k I fabbed up a "damn-near-equal-length" catless y. I also put on a single resonator and two flowmaster 40's, so even when the car is running like shit, it still puuuurrrrs).

Engine temp hasn't risen compared to what it was before (assuming I can trust the stock gauge).

I think I'll also try cleaning the MAF. Can't hurt anything. I did just recently make a true CAI that places the filter right behind the drivers side foglight, think that would give me any trouble? (although the symptoms were there before I put the intake on).

The other thing is, I dont know if the problem is related to the 60k. Now that I really think about it, the car stuttered before the 60k, but I never got a chance to check the engine codes. I had stupidly assumed that the stuttering was a misfire caused by the 1.5" deep oil in all the plug wells. I did the 60k work, and the car ran better, but the stuttering soon came back. Then I checked the codes, and here I am now lol...




I couldnt believe the fuel mileage either! My old 89 was lucky to get 25, and I was happy with that. The 33 is relative though, that was all highway mileage (I never got a chance to check it with combined city/highway mileage), and I just took a trip up north, so I checked highway mileage again, thats when I saw the 20 mpg. Definitely let me know, I appreciate any input I can get, this car is driving me nuts (although I can live with a few quirks, I bought the car for $450).

 

[n8rsk8r]

The info sheet is geared mainly at the atx it's self and the sensors that deal with it's function, not fuel related codes. Sorry man. Good luck though. Keep us posted on what you find out.

 

[timmay316]

Sorry i sort of fell off the face of the earth, but I've been really busy with school and work. Anyway, I wanted to bring some closure to this thread...

First thing I did was change the fuel filter, I figured it was good to do whether it fixed the problem or not. Car seemed to run better, but the occasional CEL and sputtering continued. Couldnt find any intake leaks, and I replaced a few suspect vacuum lines, still no change. Finally I broke down and just replaced both O2 sensors. Bingo! No more CEL, no sputtering/stalling, and the car just feels peppier and all around better. I have yet to check fuel mileage, but I have a feeling that since the car is running better now, the fuel mileage will follow (assuming I can keep myself from wanting to hear the flowmasters and secondaries all the time!). Thanks for the input everybody!

 

[BruceJEubanks]

Maf

I had those same codes try the MAF. Once I change the MAF it fixed the issuse on my 94 MTX