98 Grand Marquis ran perfect until it went boom

[gradymotorco]

My father in law's 1998 Mercury Grand Marquis has always been a great running car, and he has taken excellent care of it since purchasing it new. It only has 140k miles on it, so I was very surprised when he called and told me that it had made a boom noise when he cranked it the other day and now it runs very rough, with a loping idle and backfiring through the intake and the exhaust. Oil pressure is still good according to the idiot light. Any ideas?

 

[OVERKILL]

It may have launched a plug.

 

[gradymotorco]

Well come to think of it he said it still had the factory plugs in it...

 

[TrevorS]

There goes the "excellent care" theory!

 

[Roadkingnc]

The plastic intake exploded

 

[kyxtremetuber]

Want to bet that the plastic chain guide let go and it jumped time

 

[gradymotorco]

I was thinking intake as well, but usually when I have seen that happen there's coolant everywhere. I could see the plug theory or a broken chain guide being it because it acts like the timing is off.

 

[silverrat]

Originally Posted By: TrevorS
There goes the "excellent care" theory!


I'm sure he armor all'd his tires every week and oil changes every 3 months. That's usually what people mean when they say they take care of cars without actually doing maintenance,

 

[mene]

Another vote for timing chain

 

[JimPghPA]

Well the checking of a bad sparkplug is a heck of a lot easier thing to check for compared to an internal part like the timing chain guide. So logically one should check the plug idea first.

 

[SwampSurvivor]

Intake manifold explosion

 

[supton]

Seems like a quick look under the hood will rule out some obvious things. I have a hard time believing it has window'd the block with a rod; I have to believe that this repair should cost far less than a new car.

 

[TFB1]

Originally Posted By: supton
Seems like a quick look under the hood will rule out some obvious things. I have a hard time believing it has window'd the block with a rod; I have to believe that this repair should cost far less than a new car.


Agreed...

If it was running without issue, unless he was holding it at WOT chances it's launched a rod are almost zero & none...

This is like asking the doctor "why is there a pain in my leg?" and not mentioning the hole from your girl friends husband's 38...

 

[RF Overlord]

140,000 miles is just getting broken in for a Ford 4.6 modular motor. Many taxis have double and triple that mileage on the original engines.

Also, '98s are not known for the flying spark plug issue, but they ARE known for cracked intake manifolds.

 

[Bror Jace]

Small-block Fords in the 80s and 90s had issues with their oil pumps failing suddenly. Did they fix that with the 4.6L series of engines?

 

[bdcardinal]

Originally Posted By: Bror Jace
Small-block Fords in the 80s and 90s had issues with their oil pumps failing suddenly. Did they fix that with the 4.6L series of engines?


Yup, the modular motors have oil pumps run directly on the front of the crank.

 

[OVERKILL]

Originally Posted By: Bror Jace
Small-block Fords in the 80s and 90s had issues with their oil pumps failing suddenly. Did they fix that with the 4.6L series of engines?


Not that I have ever heard of. They had issues with the oil pump drive shafts snapping though because people would run too heavy of oil in them.

This was often exasperated by the guys fitting HV oil pumps to them and then running 20w-50.

 

[Falcon_LS]

Timing chain guides were only an issue on 2000-2003 vehicles. I'm thinking more spark plug shot out.

 

[TFB1]

Originally Posted By: RF Overlord

Also, '98s are not known for the flying spark plug issue, but they ARE known for cracked intake manifolds.


Yeah that plastic POS is leaking on my 61K mi '98... Is different than general, leaks where bung is molded in for temp sensor...

 

[Falcon_LS]

Mine's an early production '01 and the thermostat housing had a slight crack in it. Replaced it with an OE Ford unit nevertheless, it lasted 130,000 miles!