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Discussion Starter #1
I have a 93 Taurus 3.0, which has developed a problem that none of the local mechanics seem to be able to diagnose. It runs very well until it's been at operating temperature for a while. Then, when I stop at a light and take off, it won't accelerate past 5 miles an hour. Give it more gas and it bogs down and backfires. It also seems not to want to downshift, but since it's running so poorly, it's hard to tell. In neutral, it revs fine. After it cools down completely. It's fine again. I put it on the computer and got the following bad codes:

335 EGR feedback signal is/was out of range
171 Oxygen sensor not switching - system was at adaptive limits
172 Oxygen sensor not switching - system is or was lean
175 Oxygen sensor not switching - system was at adaptive limits
176 Oxygen sensor not switching - system is or was lean Left or Front HO2S
181 Fuel system was lean at part throttle Single, Right or Rear HO2S
186 Injector pulse width longer than expected or Mass Air Flow lower than expected
189 Fuel system was lean at part throttle - Left or Front HO2S
326 Pressure Feedback EGR shows low pressure
327 EGR feedback signal is/was low
542 Fuel pump open, bad ground or always on
634 Manual Lever Position (MLP) sensor out of range in PARK

I put in a new fuel pump, filter, and EGR, with no effect whatsoever. I can't test the vacuum, but one mechanic said it's fine.

Does anyone have any ideas on this one? As I say, no one around here seems to be able to figure it out.

Ken
 

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Try having the fuel injectors professionally cleaned.

Do you have an oxygen sensor in each bank, on a '93? Both may have gone bad, but it's unlikely they both went bad at the same time.

Here's my reasoning for cleaning the fuel injectors: The engine has been getting leaner and leaner over time (codes 171, 175 and 186) most likely because of deposits building up on the injector tips. (Could be a fuel pressure problem, too.) Finally, the 'puter couldn't compensate any furthur.

The EEC doesn't pay any attention to the oxygen sensor signals until the engine is at operating temperature. There are a few other things it overlooks until the engine is up to temp, but it's real late as I type this and I'm surprised I've given as lucid an answer to your problem, as I have.

Good luck and keep us posted.
 

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Discussion Starter #3
Well, my local dealer was checking out the car and switched MAFs with another one (temporarily) and the problem went away right away. So now, I need to install a new MAF. Is this a difficult job? The aftermarket parts I priced range from $80 to $95, but I have no idea which is best. Anybody got any info on installing a MAF?

Ken
 

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Use the OEM MAF. They are very specifically calibrated, and using an aftermarket one will throw off your EEC calculations. Get one from a junkyard from the same year (93).

It is not difficult at all. It is on the air intake line, inbetween the filter box and the Throttle Body. usually it is attached to the filter box itself. Just a couple nuts.
 

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Discussion Starter #5
... Installed a new Ford part - as you said, there's nothing to it .... now I'm crossing my fingers that the problem is solved.

Ken
 

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Here's another update. The car is running great now - no sign of the previous problem. But now, the CHECK ENGINE light is coming on a lot. The dealer who discovered that the old problem was caused by a bad MAF also said that there was a bad DPFE code. I had read in a couple threads here that Auto Zone would check the codes free, so I called the closest location to get some info. What they told me was that they can't do Fords older than 96. Does anyone know if this is true of all locations, or if other parts places will check the codes for free? AZ's replacement part is $38, so we're not talking about a major plunge here, but I don't want to throw more money at a problem which may not exist. Any advice?

Ken
 

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Older than 96 ford used the OBDI computer system instead of the OBDII system. THe local Autozone must not have an OBDI scanner. There is a write up on the site as to how to read OBDI codes. Look it up.


The DPFE is a common problem, so replacing it is a pretty safe bet.
 
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