Some codes and stumbles at low throttle

C

cragus

Registered
Hey y'all

I was driving yesterday, and got ce light and some codes. The car was stumbling really bad at around 1000 rpms, and light throttle. It seems fuel related. The fuel filter is about 1 year old. I pulled the codes by grounding the self-test lead, and the codes I got were:

539 something to do with ac
176 lean condition on left H02S
177 rich condition on left HO2S
524/543 Low pressure fuel pump relay

Anyway, I did a consult with my bro who is a technician, he told me that it is probably something electrical, and to pull the fuel pump relay and replace it with a different one. I was kind of in a hurry this morning, and I didn't have the manual showing which relay was the fuel pump, so I just wiggled 'em all. On the drive the ce light didn't show up. It seemed to stumble a bit, like maybe starving a bit for fuel. What do you folks think? My next move will be to replace the fuel filter, check pressure with a gauge while driving around. And maybe do some diagnostic tests on the relay/fuel pump system electrical area.
 
RE: Some codes and stumbles at low throttle

Get a fuel psi gauge on it. SOunds like a bad fuel pump to me. But that is just what normally what happens to these cars.
 
RE: Some codes and stumbles at low throttle

Cragus Hi
You need to clear those codes , and the next time you have a problem recheck the codes , thats a pretty odd mix of codes. The codes are stored even if the CE light is cleared , some of them could be from long ago , and not pertain to this problem..
You need to clear the stored codes , with a code reader , diconnecting the battery only clears the CE light and the ECM not the stored codes ..
 
RE: Some codes and stumbles at low throttle

Thanks for the help guys, I will be fiddling with it this weekend.
 
RE: Some codes and stumbles at low throttle

Sounds like the same problem I am having. Only my 94 stumbles occassionally. I did get a 176 code too. With 130k miles I knew the O2 sensors were due for changing. Since I changed them I have not got the 176 code but the stumbling continues, but like yours, at low RPM regardless of speed. I changed my fuel filter and all plugs with no results. Car is drivable but stumbling is annoying when it occurs. I own a "parts car" and will begin to swap things out. I could not find anything in the service manual relating to this.

Keep posting and maybe we can nail this one together.....cg11
 
RE: Some codes and stumbles at low throttle

I've been getting o2 codes for a while now.. and I even changed them( granted with aftermarket o2 sensors) but still get the codes. sometimes its 176,175, somtimes its 177 176, its all different. I also get 524 and a few other fuel codes. everything in my fuel system has been changed or cleaned.. new pump new regvulator, filter... so don't jump to any ideas that it is the pump.. or it is the regulator. cause you never know what the hell is causeing it. when I get some money I'm bringing it down to the dealship so they can troubleshoot it. I might fix it but I at least want them to tell me whats wrong.
 
RE: Some codes and stumbles at low throttle

I"m with you guys on this one. Just started. The plugs/wires/ fuel filter have all been changed (fuel filter very recently).

I havent pulled the codes b/c I have a 93 model mark and the autozones don't have code readers for years below 95 (the autozones I've found in my area) and I'm too cheap to buy one for 20$ off ebay.


I wonder if the dealership will read my codes for free? :D
 
RE: Some codes and stumbles at low throttle

I have referred to this TSB before:

---------------------------------------------

Engine - Lean Driveability Symptoms
Article No.
98-23-10

11/23/98

MASS AIR FLOW (MAF) - SENSOR
CONTAMINATION - SERVICE TIP

LINCOLN-MERCURY:
...
1993-98 MARK VIII
...

ISSUE
This TSB article is a diagnostic procedure to address vehicles that exhibit lean driveability symptoms and may or may not have any Diagnostic Trouble Codes (DTCs) stored in memory.

ACTION
Follow the diagnostic procedures described in the following Service Tip. The revised diagnostic procedure is a more accurate means of diagnosing the symptoms.

SERVICE TIP

MASS AIR FLOW (MAF) DISCUSSION

MAF sensors can get contaminated from a variety of sources: dirt, oil, silicon, spider webs, potting compound from the sensor itself, etc. When a MAF sensor gets contaminated, it skews the transfer function such that the sensor over-estimates air flow at idle (causes the fuel system to go rich) and under-estimates air flow at high air flows (causes fuel system to go lean). This means Long Term Fuel Trims will learn lean (negative) corrections at idle and learn rich (positive) corrections at higher air flows.

If vehicle is driven at Wide Open Throttle (WOT) or high loads, the fuel system normally goes open loop rich to provide maximum power. If the MAF sensor is contaminated, the fuel system will actually be lean because of under-estimated air flow. During open loop fuel operation, the vehicle applies Long Term Fuel Trim corrections that have been learned during closed loop operation. These corrections are often lean corrections learned at lower air flows. This combination of under-estimated air flow and lean fuel trim corrections can result in spark knock/detonation and lack of power concerns at WOT and high loads.

One of the indicators for diagnosing this condition is barometric pressure. Barometric pressure (BARO) is inferred by the Powertrain Control Module (PCM) software at part throttle and WOT (there is no actual BARO sensor on MAF-equipped vehicles, except for the 3.8L Supercharged engine). At high air flows, a contaminated MAF sensor will under-estimate air flow coming into the engine, hence the PCM infers that the vehicle is operating at a higher altitude. The BARO reading is stored in Keep Alive Memory (KAM) after it is updated. Other indicators are Long Term Fuel Trim and MAF voltage at idle.

NOTE THE FOLLOWING PROCEDURE MAY ALSO BE USED TO DIAGNOSE VEHICLES THAT DO NOT HAVE FUEL SYSTEM/HO2S SENSOR DTCS.

Symptoms

^ Lack of Power

^ Spark Knock/Detonation

^ Buck/Jerk

^ Hesitation/Surge on Acceleration

^ Malfunction Indicator Lamp (MIL) Illuminated -

DTCs P0171, P0172, P0174, P0175 may be stored in memory


OBDII DTCs

^ P0171, P0174 (Fuel system lean, Bank 1 or 2)

^ P0172, P0175, (Fuel system rich, Bank 1 or 2)

^ P1130, P1131, P1132, (HO2S11 lack of switching, Bank 1)

^ P1150, P1151, P1152, (HO2S21 lack of switching, Bank 2)


OBDI DTCs

^ 181, 189 (Fuel system lean, Bank 1 or 2)

^ 179, 188 (Fuel system rich, Bank 1 or 2)

^ 171, 172, 173 (HO2S11 lack of switching, Bank 1)

^ 175, 176, 177 (HO2S21 lack of switching, Bank 2)

^ 184, 185 (MAF higher/lower than expected)

^ 186, 187 (Injector pulse width higher/lower than expected)

---------------------------------------

The above is from AllData. I hope this helps as it seems to fit the modus operandi.:)
 
RE: Some codes and stumbles at low throttle

Yup.. its clocked at 3. I usedto get rpm surges then I talked to geno who mentioned the clocking. now I don't get any surges
 
RE: Some codes and stumbles at low throttle

So you are saying you get the DTCs but no drivability issues?
 
RE: Some codes and stumbles at low throttle

I changed my MAF with a good one from a perfectly running 94 Mark VIII, car still bucks. This tells me that the problem lies elsewhere. My gut feeling tells me the problem lies in the fuel system or coil pack(s)......

One more thing, I did repair a vacuum leak on the left rear runner rail and the stumbing is not as severe. Check for leaks.....

What is the frequency and driving conditions of the stumbling? How many miles are on your vehicle?
 
RE: Some codes and stumbles at low throttle

So you are saying you get the DTCs but no drivability issues?
Click to expand...

its weird my car seems to drive fine. but if I'm driving for like 20 minutes or so on the hwy I get chk engine lights, which come and go.but that doesn't happen all the time. if I turn off my o/d my car has more rpms, so it happenes more frequently. but if I get off and go to a side road, or stop at a light my car runs rough and the last time seemed like it would stall out but it didn't. sometimes when I just lightly kepe my foot on the gas after this happenes I feel slight hesitations. I always seem to get different codes, like sometimes I've gotten 215, 214, 224 121( not at the same time) but if I clear the codes they don't come back. the ones that keep comming back are my 02's and something with my fuel circuit its way too confusing for me thats why I wanna bring it to the dealrship. if they can figure out whats wrong, I can most likely fix it myself and save money as long as its nothing major.
 
RE: Some codes and stumbles at low throttle

Greenmachine, I get the exact same hesitations as you described and under the same driving conditions. My check engine has not come on since I changed the O2 sensors, but the stumbling still remains, but less frequent and less severe. I am curious with what the dealer finds?? I only got one code, 176 (lean at left bank).

I will check for new codes this weekend and post them (if any) in my next message.
 
RE: Some codes and stumbles at low throttle

A few things:

Pull your codes for free. To do this find the test plug thing on the drivers side fenderwell, take a paper clip and stick it into the hole in the black plastic that has one peach colored wire going into it. Now, pull out the bigger plug from its cover, it should have three sockets in a row, and two in a row. Hold it so the two sockets are on top like this:

+ 0
+ + +

The 0 is the hole where you are sticking the other end of the paper clip. (You are essentially grounding the peach colored wire known as the STI self-test indicator) Now go in the car turn the key to on, don't start the car. Your ce light should flicker, then start blinking. It will blink a few times repeatedly, pause and blink some more.

The car is giving you the codes, you just have to count how many times it blinks between pauses. I just count and write it on a big piece of paper. You have to let it run through the blinks a few times to get them all. It should do three sets of blinks (this is your three digit code), then pause for a longer time, then two long blinks, then it will start a new code.

To clear your codes, disconnect the paper clip while the codes are blinking.

MY CAR:

I cleared my codes and the ce light has not come back on. My worst problem is the stumble at low throttle, so I don't think that TSB is going to help. I did buy a fuel pressure gauge to test my pressure as I drive around, but the hose needs to be lengthened before I can set it up.

My brother (a ford tech) has me leaning towards an electrical problem on all of this, and I think he might be onto something. He gave me a dvd with the service info and was showing me how to check all the circuits and run tests. If any of the wires between the control modules are messed up they could be causing these problems. Also, the relays can go bad. I am going to get a volt/ohmmeter soon, and try to test the circuits that are involved. (this is probably the route the dealership would take) If you have a cd or dvd the circuits and test procedures should be on there, but they can be tough to decipher for the amateur.
 
RE: Some codes and stumbles at low throttle

The fuel pump relay is the relay closest to the firewall. I swap mine with the one next to it. (they appear to be all the same relays on my 94). I drive my car for a day now with no stumbling. Give it a go, it don't cost anything and maybe your bro is right.....
 
RE: Some codes and stumbles at low throttle

I'm going to try this tommorrow. be careful tho, the next relay is the abs. the third one is the horn, so that might be a better one to swap with
 
RE: Some codes and stumbles at low throttle

Yeah, the middle relay is for the horn. My fuel pressure readings seemed pretty normal. About 32-33 idling. 40 at WOT.

I went ahead and changed the filter, and seemed to gain some off-the line, low end power. Definitely a bit more responsive. This was right after a bottle of syntec once a year cleaner too. I haven't switched out any relays yet. I think what I am feeling may be just the waffly torque converter lockup, passing through 40 in overdrive at really light throttle. Still no more codes.

The stumble seems to have been reduced after the filter change. My car does seem sensitive to changes there. (I previously changed it about a year ago.)

P.S. I am at 158k on my 1993.
 
RE: Some codes and stumbles at low throttle

After a day or two of driving my 94, the stumbling is a little better after the relay swap but still exists. I am with you on the "waffly torque converter". The stumbling appears to happen at around 40mph or when the RPMs are at 1000 and in a higher gear. This stumbling may just be the nature of the beast. When I go to 1/2 to 3/4 throttle and the engine downshifts performance is fine with no stumbling.

I wonder if others 93-94 owners experience the same??

Still no codes here and I also changed my fuel filter and the car is more responsive too.
 
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