Check Engine Light On


#1

I have 99 Merc. Grnd. Marq., code 0174 know showing up on the scanner, I also had 0171. I have done a vacum test and holding 21.5 Hg, I have changed all rubber vacum hoses even if they did not need changed. I even changed the gromet for the PVC Vale on the right valve cover. Checked the injectors and all are clicking. I had changed spark plugs earlier and show a normal firing color. I had changed the fuel filter(last week) and MAF sensor a month ago. do I need to change the MAF sensor again. Lost?


#2

its common to both banks,PCV hose ,intake leak at the split plenum,these could be the cause,even though the vac reading is ok.

is the PCV valve a bobo model or the OEM model?

good luck.


#3

You have a V6 engine which is showing a lean condition on both cylinder banks with DTCs P0171 and P0174.
We need to know what a LEAN condition is before we can determine what has caused it. What is it? A lean condition is when there is more air in the air/fuel mixture than the ideal A/F ratio of 14.7 parts air to 1 part of fuel.
A lean condition may not be an excess of air, it may be a deficit of fuel. Fuel can be less than it should be because, the fuel flow is less than commanded by the engine computer; the command may be for too little; there may be a fuel flow restriction; the fuel pressure may be less than specified.
Check fuel pressure. Use a Throttle Body Spray Cleaner to clean the throttle plate and throttle bore. You should consider a professional “fuel system cleaning” to clean the fuel injectors, intake tract, and cylinders. It should cost under $100.
If you have one of the more comprehensive scan tools, as contrasted to a “code reader”, you could look at the MAF flow, and STFT (Short Term Fuel Trim) and LTFT (Long Term Fuel Trim).
There is other stuff to check; but the DTC charts for the “fuel control” system are your best bet. You can get the DTC Charts at places like www.alldata.com.


#4

There is a Technical Service Bulletin, dated 10-15-2001, Article No. 01-20-5 “Driveability-DTC P0171 and/or DTC P0174-Detecting Vacuum Leaks”. It instructs you to use a Rotunda Smoke Machine to do a smoke test on the intake and engine. Not everyone has a Rotunda Smoke Machine; so, I have an alternate method that may work: acquire smoke bombs from a novelty store, use the smoke bomb (your choice of colors) to do the test. The specified “smoke” pressure is only 1/2 psi, so a smoke bomb should be enough. Try it. It can’t hurt. Might yield usable results.


#5

It’s a 4.6L V8. The forward oxygen sensor is generating the “too lean” code. Replace the sensor.


#6

which one? caddyman

fore there are two.

take a guess?

thanks


#7

original and working and I cleaned it.


#8

I HAVE A 4.6 LITRE V8, 75 K miles.


#9

More info on howto use the smoke bomb?


#10

I had changed it right before Xmas? I changed all four, the conectors where a pain - unscrewing the sensors was no problem.( used a candle on the threading after I ran the engine for 2 minutes - unscrewing was effortless… The right front manifold O2 sensor was less time consomming hat the drivers side the one just in front of the cats where a piece of cake


#11

never had thoes codes come up?


#12

No V6’s on a Grand Marquis!
It a 4.6L V8.


#13

We see people all the time who try to change enough parts to solve a problem. It seems that we can never persuade them that their “method” is very expensive and is unlikely to fix it. They continue to push for that one “sure-fire part”. It never comes.
This problem needs another, less expensive, more thorough approach to solve it. Are you willing to try a different approach.? If not, you need to take it to a shop.


#14

what is the different approach