1990 Merc Col Park 5.0 "Check Engine" on. Runs rough.

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1990 Mercury Grand Marquis Colony Park 5.0.

This problem came on suddenly one morning.
Running very rough.
Using excessive fuel.
"Check Engine" light on most of the time.
Occasionally the "Check Engine" light goes off for a while,
and the engine smoothes out during these brief periods.
Sometimes you can smell raw gas.

We've changed the timing chain, distributor, fuel filter, plugs, and
plug wires.
Also checked for vacuum leaks.
I've been told that it could be the MAF sensor, or the EGR.
I'm replacing them tomorrow.
If those don't work,
can you advise me where else to look?

Thanks.

posted by  JackBlanchard

Before you go dumping more money into parts you may not need Autozone does free engine annalysis, go there, get is checked, replace the parts it needs. :2cents:

posted by  srober32

not to try to be argumentative ... and curious too but this AUTOZONE you speak of, do they only scan? or do they actually test the sensors and wires related to the code they scan for? cuz free diagnostics would be huge profit loss and frankly BS if ya ask me.

posted by  BanffAutoSpa_ap

Yes I agree, and I am pretty sure they only pull codes on the car and test the sensors, not the wiring. I guess they do it in the hopes that people will buy the part from them, and if you look at the huge mark up on auto parts the cost is realy kind of not an issue. But you are right, the wiring could be bad as well, I just hate to see people wasting money on new parts they may not need.

posted by  srober32

yeah thats what i thought and what do they say after you buy the part and it doesn't fix the problem, just like millions of lincoln owners with 4.6 v8 who have a lean o2 code after highway drive, they'll sell you 30 oxygen sensors b4 you realize they know diddly squat about cars, do they reimburse the part if it doesn't fix the problem or do they tell you to go frig yourself. having free code scan can be handy for DIY'ers but it can sure screw some poor old woman out of alot of money too, cmon like WTF!

posted by  BanffAutoSpa_ap

Today we replaced the EGR and MAP.

In the past week we replaced these:
timing chain,
distributor,
fuel filter,
plugs, and
plug wires.
Also checked for vacuum leaks.

Here was the original problem.
(We still have it.)
Running very rough.
Using excessive fuel.
"Check Engine" light on most of the time.
Occasionally the "Check Engine" light goes off for a while,
and the engine smoothes out during these brief periods.
Sometimes you can smell a little raw gas.
.

posted by  JackBlanchard

well what codes do you get?

posted by  BanffAutoSpa_ap

one or all you oxygen sensors are bad cause's the engine to go into limp mode(check engine light) bad oxygen sensor play a big part in the engines management of air/fuel mix if the sensor lie's to the computer that theres to much o2 in the exhaust the injectors stay open longer dumping in more fuel flooding engine and extra gas leave's into you tail pipe smell raw fuel the o2 sensors are in the exhuast pipe before the converters

posted by  osborste

well let's for fun just say it was a dead hole(no compression) won't burn the fuel therefore the o2 will read a rich mixture and try to compensate for it maybe making it run like a bag of shit.... now would you still say it's a bad o2? thats what i thought.

posted by  BanffAutoSpa_ap

ya that would be possible but then it would run rough all the time he say's it will clear up at times and the engine light goes out

posted by  osborste

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