backfiring through air intake

[toxicity61284]

Hi all . i am gettign a backfiring through my airfilter when the car has been started after the engine is cooled off... for the first few minutes the car will backfire and hesitate and wont go over about 20mph .... ive brought it to the dealer in november, where they foudn it being a mass airflow sensor, which fixed the problem up until a month ago, where it is doing the same thing,, i brought it back, they claimed it was now a fuel pressure regulator,, i had it changed, fuel filter changed, and fuel system flushed. still i am getting the same symptoms,,, slowly it is getting worse....

i have a 1994 grand marquis GS with single overhead cam, it has 119,500miles on it.


any suggestions??

thanks

-rick

[Samurai0]

Hi,
I'm not experienced with that year, but my limited experience and knowledge of engines leads me to believe you problem couldbe related to a spent Cam.

Figure this logic:
What does a Cam do? It times/controls the lifting of the fuel & air valve ports.
A great example of an 'overhead cam' is here:
http://auto.howstuffworks.com/engine3.htm

So, if the "orbs" on your overhead cam are worn down, or springs under the "rocker arms" that contol the valves are weak, then that could mean your backfiring (actually is) being 1 or more valves being stuck-open during combustion.

My feeling and knowing that Linc/Merc service departments aren't know to be sharp, especially with 10+ year old cars, they could've been offering a low-cost temporary solution to a minor cam replacement ($75 for cam, 2-3 hours labor @$85/hour).

The fuel regulator on EFI or SEFI engines just regulate the vacuum for sucking the fuel to the injectors.
The MAP sensor (mass airflow) is used to calculate the fuel/air mixture, and power-curve.
This is not a fuel problem.

Since the distributer is gone, and it's distributor-less, it would be a computer timing thing (a worst case scenario).

For 100,000+ miles on a SOHC (single overhead cam) engine, it probably worn cam and springs.

Was this car driven hard?

Later,

[toxicity61284]

Hey thanks for replying,,,

this car was not really driven hard, its a one owner, my mom bought it brand new in 94... i drive it a little harder than her but, i dont think ive driven it hard enough to make it do this all of a sudden,,, it was doing this kind of thing when i first got it, and when they replaced the mass airflow sensor,, that fixed the problem for a short time... thats why i was almost thinking it could be that again,, but i dont know....

so replacing the cams is not that big of a cost??

... another thing some one told me it could be that i need a new EGR valve? does that sound reasonable?


thanks,

-rick

[Samurai0]

Do you have any performance add-ons, or is it stock?

Maybe and EGR valve. You can check the computer codes yourself with an analog multimeter (not digital).
Check and see if you can get the "Haynes Computer Codes Techbook" Inside it'll show you were to stick the probes, and get the codes. Then just look up the problem.

If you don't have a budget, buying parts on a whim shouldn't be a problem.
If you want to, you need 4 things:
1) Permatex gasket sealer (glue)
2) EGR valve position sensor = ~$50
3) EGR Valve = ~$40
4) EGR valve gasket = ~$2


I wish I could see this happen, and hear how the engine sounds. Try jotting down what exactly happens in-order one more time, just to see if something else is wrong.

[toxicity61284]

Thanks your your help,,
I bought a new EGR valve but it is behind a mess of tubing and wiring so my uncle is going to help me change it... what it basically does is this ..

when the engine is cold and hasnt been run in a few hours,, itll start up fine,, but you can smell heavy exhaust smell like its rich.... and if you just put it in gear and go, itll pop through the air filter, and sorta give a jerking motion, like its hesitating as you give it the gas, then slowly after a couple of minutes, itll jerk a little faster then accelerate almost completely normal.... and other than that it runs jsut about fine, only when you are at a dead stop and trying to give it quick acceleration will you notice a very strong lag.... the check engine light also flashes off and on often when im on the highway...

im hoping it is only an EGR problem,, because ive heard replacing the cams is like a 1,000$ job

thanks,

-rick

[Big_Rob]

Hi I have a 2001 grand marquis it has 80000 milestone hasn’t been started in a while it was my grandmothers and I just recently tried to start it and it started but when I took jumper cables off and it shuts off, I come back today and it wouldn’t start so I sprayed starting fluid in the air cleaner and it backfired out of the intake and it still won’t start.