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Listening on 141.850 mHz!
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829 Posts
Discussion Starter #1
Yes, this may be another poor idle thread, but I can’t seem to find the cause of it. And yes, I did exhaustive searches in these forums on this topic.

About 3 days ago I got a “service engine soon” light in my 97 Limited Edition. A rough idle and constant pinging accompanied the light. I took it to Auto Zone and their code reader indicated codes P171 and P174, 2 instances of each in both banks. That translated to oxygen sensors. Last year I changed the 2 sensors that are upstream before the cats. This time I changed the sensors downstream after the cat with the same aftermarket Bosch 13127 sensors that I used last year for the fronts. For good measure I cleaned the MAF sensor, EGR valve, and IAC as well. I did the #15 fuse pull and cleared the computer. Still had the slight rough idle so I decided to change plugs, the fuel filter, and the PCV valve. I got the plugs at Auto Zone and told them I needed the correct Motorcraft plugs for a 97 Thunderbird with the 4.6 engine. I was given some AWSF32M plugs. When I pulled the old plugs they seemed to have normal wear, some more than others, and they have been in there for at least 35,000 miles. The 32M plugs looked a little different, pointier tips. I installed them and then took the test drive. The pinging worsened, accompanied by hesitation, backfire, complete loss of power and stalling. I limped it back home then called a mechanic friend who told me to remove the 32M plugs and get other ones. I looked at the sticker on my car and it suggests AWSF-32PP plugs. The plugs I took out of my car were 4 AWSF-32P plugs and 4 AWSF-32PG plugs. At Auto Zone they took my plugs back but didn’t have any other type of Motorcraft plugs for me, definitely not the 32PP ones I needed. I went to another auto parts store and they didn’t have the 32PP or the 32PG plugs but they had plenty of 32P and 32M plugs. I went to the local Ford dealership and they said that the 32PP plugs were superceded by the 32M plugs. The parts guy told me that the 32M were the correct replacement for my car, but I told him of my bad experience with these plugs just about an hour before. No one else around had any 32PP plugs so I went back to the 2nd auto parts place and got 8 of the 32P plugs and put them in. It performs only slightly better and I have the same pinging but a little bit more power. I got a light back and took it to Auto Zone where I got 2 more codes: P1131 and P1151, still indicating oxygen sensors.

I checked everything out and nothing seems wrong. No vacuum leaks, new fuel filter. I also put in some fuel injector cleaner yesterday. It runs the same regardless of whether the MAF is plugged in or not. I pulled it to take a look and it’s still sparkling clean. So I’m sure I can rule out the MAF. Could it be these 32P plugs? I started to get pinging, hesitation, rough idle and stalling with the old plugs and this thing used to run like a top. This problem came up all of a sudden and I am out of ideas. Does anyone have any?

I just got my car back from the bump shop so I’m eager to drive it around. I have a thread about my story down in the Miscellaneous section titled “My wife CRASHED my 97 Limited Editon”.
 

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W&S Motorsports
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161 Posts
Sounds like you may want to check out the MAF. What are the MAF voltages at idle and when cruzin? The fact that you can pull the connector off and the engine runs well sorta may mean that the EEC-V has had a look at the MAF voltage and had a good puke and decided to run off the default tables (sorta SD like). It should have posted a code for the MAF failure tho.
 

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Listening on 141.850 mHz!
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829 Posts
Discussion Starter #3
It hasn't thrown a code for the MAF yet, but it still runs rough regardless of whether the MAF is connected or not. What voltage should the MAF be and what setting do I put my voltmeter at? I have one I picked up at Radio Shack last year.
 

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W&S Motorsports
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161 Posts
Check between R (hot in start and run) and BK/W (power ground) for vehicle power around 12V. At idle MAF should read around 0.8V between T/LB (sensor return) and LB/R (MAF sensor ). It will be anywhere between 0.8V and around 4V if you are N/A and how far your foot is in the tank.
You can also use an AutoTap to read the voltage that the EEC-V sees which is the preferred method as it tells you what the EEC is seeing in that it checks the MAF wiring and the MAF and also it is a little more convenient to measure the MAFs output especially if the car is moving.
 

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2,894 Posts
Winston, I had the same issues with my 3.8L. RichardM advised the transfer function could be off because of the K&N. I swapped it out and it didn't really help. I had a close look at the MAF, and one wire was slightly off, bent slightly away from the other. My voltages were 14.4 & .68 @ 800 rpm.

I straightened the wire gently and I do not now get the brief CEL that I was getting when warming up before looking at the MAF wire. The pinging is still slight with occasional hesitation when cold. Lots of power.

It seems that the more time passes, the less I get the issues now.
 

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Listening on 141.850 mHz!
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829 Posts
Discussion Starter #6
Well it's all cleared up now!

The answer was literally in my hands the whole time! I finally got the RIGHT plugs for it, not exactly the Motorcraft AWSF-32PP but the Autolite equivalent: APP746. The parts guy at the store I bought them at said that Motorcraft and Autolite were basically the same and that the current concensus is that "they have the same mothers but different fathers". In any case these plugs are what I needed and as to my rough idle, pinging, hesitation, stalling and all that other mother jazz, it's gone. What caused it? Like I said the answer was in my hands all the time, mainly when I was changing out the plugs: SPARK PLUG FRIGGIN WIRES!!!!

I limped it over to my mechanic friend, the one who told me to ditch the AWSF-32M plugs, and he gave it a quick listen then asked me what the symptoms were. He said that sensors were not the problem, it was definitely wires. It was missing big time and he was positive that a wire or so wasn't carrying the whole spark anymore. He suggested I buy the 8mm Motorcraft wires and spend an hour changing each, one-by-one. Well I bought them, changed them out, and the rough idle is gone, all the hesitation and pinging is gone, and I have gobs and gobs of power.

Something so moronically simple as plug wires and I didn't even think of it, I totally ignored it. Woe is me I guess.

Thanks guys for your advice!
 

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Never count on plug wires to last more than 50k miles.... then replace them.... plugs and wires have caused more mystery problems than anything else in these DIS systems.... true, plugs are "supposed" to last forever in these cars but "supposed ' is why these items are overlooked at great expense and frustration, time and again. I learned long ago to toss the wires at 50 k and do plugs every 25 k, if not sooner. I will pull them occasionally as a diagnostic aid, andof course , its cheap insurance to replace them... LOL
 
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