2000 Grand Marquis Miss fire but no CEL?

[MercMan]

2000 Mercury Grand Marquis. My car runs like it has a miss fire but I do not get any CEL and I don't know what gives? I did try to change all the spark plugs but not all the wires. I wanted to change all the wires until I found out they were individual coil packs at $60 a piece!!
When I was changing the spark plugs, I noticed that there was oil in the coil pack/plug nearest to the oil fill location. I was thinking that it was possibly sloppy maintenance from the oil change place? I found a way to just deal with the feeling of the miss fire and considered it one of those demons that I will never figure out, but it has got to that point now where its just irritating me that I cant figure it out.

Also I believe that I have the crappy plastic coolant cross over tube/intake?? I believe this is so, because one day the miss fire got so bad that it actually threw a code. Turned out it was the rear passenger cylinder (#4 possibly?), so I bought a pack for that cylinder thinking that would fix it. After I started looking at it i noticed that I was leaking coolant from the heater core return. Tried to reinstall the heater core connector, but the threads in the port were stripped out. (I don't know if that description makes any sense.) Long story short, I had to JB weld the heater core connector back into the intake manifold.

So my questions are:
1) Do the grand marquis have a common miss fire problem without engine codes, if so what causes it?
2) Would the crappy plastic intake manifold have anything to do with the oil leaking into the cylinder coil pack near the oil fill?

Any help is greatly appreciated.

[sly]

pull that coil pack and wire and clean the oil off completely if you can. That's probably the source of the misfire. Those things do not like being dirty or wet.

1: yes. it's highly annoying. dirty wires... wet coils... loose wire harnesses (the little clips break off too easy)
2: no oil there... only coolant... so no.

[IPreferDIY]

sly made a great point that I hadn't thought of: make sure everything is clean.

My first guess was that maybe what you think is oil accumulating is actually antifreeze from another part of your intake manifold. My coolant crossover leak was a teardrop leak that you could only see when the engine was warm, but a lot of coolant accumulated in two spark plug wells. If you still have the original intake manifold with the plastic coolant crossover on the front, it's definitely time to change it, especially since the heater core return part has already gone. As much as this may suck to hear, be thankful that you didn't experience a massive coolant leak while driving around.

Another possibility that doesn't seem likely in your case is that the spark plug might be loose. This happened to me well after I had replaced my intake manifold. I had previously had the spark plugs replaced at one of the big chain auto parts and service places, and about 20,000 km later one of the spark plugs was loose enough to allow the fuel mixture to seep past the spark plug and accumulate there. Since you have already replaced your spark plugs, this doesn't seem likely in your case.

Some of the various misfires had been enough to trigger a CEL, but not all of them.

If you're experiencing misfires, there's a good chance that the coil has already been damaged, regardless of the cause of the misfire. When I had a coil issue, I went the cheap route and bought a cheap set on eBay for somewhere around $100CDN including shipping from the U.S. Getting a good deal on a sutable code reader/scan tool would be useful for confirming the location of the misfire. Mine accesses misfire data even in the absence of a CEL.

[MercMan]

Reviving this old thread

First off I want to say, I still could never find the small demon misfire that drove me nuts. However I am re-living a previous nightmare again, so I need some advice.

I began to feel the mis-fire again that was associated with cylinder 4 again (The code I got was P0304). I looked at cylinder 4 and didn't notice any coolant leaking onto the cylinder.

I guess my question is how do I get this heater core return fixed permanently. Does this mean that I have to do the new intake manifold, if so how hard is it to replace on my own? And I saw on other posts that I should get the correct manifold, which one is that? Any help is appreciated.

[IPreferDIY]

I'm not aware of any way to fix the heater core return permanently on your existing manifold. If you do indeed have the plastic coolant crossover, you shouldn't even bother trying again. If you're mechanically inclined, it's not really hard to change the manifold, just tedious and time-consuming. Here's a link from APDTY covering part one of two of their process for a Lincoln Town Car (more-or-less the same as the MGM):

https://www.youtube.com/watch?v=D30hrikOed4

Here's a descriptive version from autoclinix:

http://www.autoclinix.com/Manifold.htm

You might find variations. When I did mine, I basically reviewed various sources and prepared my own checklist. I think someone indicated it could be done without removing the windshield wiper motor etc, but I didn't see how so I removed mine.

I think I got my kit from APDTY, but it looks like they've changed a bit since then. Here's a link showing the parts I got (though not necessarily the same kit):

http://www.ebay.com/itm/NEW-4-6L-Intake-Manifold-w-Gasket-Thermostat-O-Rings-/370456399036?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A2000%7CModel%3AGrand+Marquis&hash=item5640ec0cbc&vxp=mtr

and here's a link showing the current version of what is probably the most commonly-known kit, by Dorman:

http://www.ebay.com/itm/Dorman-615-178-Intake-Manifold-/181582398193?fits=Model%3AGrand+Marquis

(I'm not endorsing sellers or anything. I'm just using links that are convenient.)

It looks like they've changed the thermostat gasket from the internal o-ring type to the external flat type and aren't including the thermostat housing hole spacers or alternator brackets. I have no idea what that's about. Maybe the latter two things are included but just not shown in the photos. (My kit came with two alternator brackets, but you only need the one that matches your alternator.)

Apart from these variations, I think there's only one correct type of manifold, and the gaskets are already embedded in it. I've read about PI vs. NPI manifolds, but I think that only applies to certain other years.

I guess this should be a good start. If you need to know anything else, just ask.

[MercMan]

This might be a stupid question. What is the difference between PI and NPI? And how do I tell if I have one or the other?

[Ziggy]

MercMan: Clicky. This thread is worth a read.

[IPreferDIY]

My understanding is that PI is "performance improved" and NPI is "non-performance improved". AFAIK, the Grand Marquis did not get PI's until 2001. The differences are basically the shape of the intake ports (teardrop on NPI vs. squarish on PI) and a larger plastic part on the PI intake. Here's a link with some images:

https://www.google.ca/search?q=ford+pi+vs+npi&num=20&newwindow=1&es_sm=93&tbm=isch&tbo=u&source=univ&sa=X&ei=iH1zVJOaBtalyATwkoDoBA&ved=0CFgQsAQ&biw=1152&bih=626

Apparently, you could use a PI intake manifold on an NPI engine if you do some modifications such as changing the heater tube and adding gobs of RTV in certain places, but if you just want to get your car running the way it was, it's probably not worth the aggravation.

With respect to the heater tube, those are notorious for developing holes, so replacing the intake provides a good excuse for inspecting the heater tube and replacing if necessary. I just resorted to coating my tube with rust inhibitor. One benefit of using the NPI intake is that you can periodically put more rust inhibitor on the front part of the heater tube by taking the alternator off and sticking your hand in there. If mine ever fails, I will probably just route some heater hose around the outside of the engine. Either that or upgrade to PI heads.

Another thing to check is your fuel injectors. I found a rust spot on one of the o-rings in the fuel rail that likely would have progressed to a failure point. It cleaned up nice, so hopefully it will never become an issue. (I know everyone says change the o-rings no matter what, but mine looked fine so I didn't bother. No problems so far.)

[MercMan]

Since my car is a 2000 would it benefit me to replace my intake manifold if it is NPI? Are the NPI intakes still plastic, and are these the Dorman manifolds that people are talking about? Thanks for the replies.

[IPreferDIY]

If your intake manifold does not have the aluminum part on the front, then you really do need to replace it. Here's a link that goes into the problem:

http://www.agcoauto.com/content/news/p2_articleid/185

Dorman is just one brand. I think Ford sells an OEM upgraded intake manifold, but it's probably a lot more expensive. The air channels are still plastic, but they have an aluminum part on the front for the coolant to get from one side to the other.

I don't know if replacing the intake manifold will finally clear up the misfire problem, but you really do need to replace the intake manifold to stop existing coolant leaks and prevent future ones.

[MercMan]

Thanks a ton IPreferDIY. All your posts have been very informative and are pointing me in the right direction. It looks like I am going to have to replace that intake manifold afterall then. I just checked it and it is one of the plastic cross-over types. I think that I am going to go with the Dorman 615-178 for the manifold, and Bosch 97116 for the water pump.

After looking around some, it appears that I should be going with the Dorman 626-223 for the Heater Hose assembly that sits right underneath the intake manifold.

[IPreferDIY]

Glad to help. All your part numbers look right to me. I'm cheap, so I never bothered replacing the heater tube or water pump, but it sounds like good insurance. Since you're doing that, you might want to get new fuel injector o-rings too.

You should contact Dorman and ask them what's up with the flat gasket for the thermostat housing, the lack of spacers for the thermostat housing holes, and the lack of alternator brackets. As I noted above, my kit came with an o-ring, the spacers, and two alternator brackets. Maybe Dorman is currently assuming people will be upgrading their thermostat housing. I suppose it's possible they redesigned their manifold so that you can now use the original alternator bracket, but they also might have started expecting people to buy a new one separately.

BTW, how many miles do you have on your car?

[MercMan]

I will try and give someone a call about the parts that come in the kit. I am thinking about buying it on Amazon since I am a Prime member and should be able to get it fairly soon. http://www.amazon.com/dp/B000C17G4U/...=INZEAX597ZQVW
I checked the link and some pictures are showing the spacers and alternator bracket, but then there is some mis-leading information in the QA portion. Some people asked if there was an alternator bracket and there is conflicting information. Do you think that it would be difficult to "Modify" the original alternator bracket?

Also I have about 122,000 miles on the car, I bought it from an old couple that only had 60K on it and I have been driving the snot out of it. I would say that the problems were almost encountered 20K into the purchase, I have just been ignoring it.

[MercMan]

I will try and give someone a call about the parts that come in the kit. I am thinking about buying it on Amazon since I am a Prime member and should be able to get it fairly soon. http://www.amazon.com/dp/B000C17G4U/...=INZEAX597ZQVW
I checked the link and some pictures are showing the spacers and alternator bracket, but then there is some mis-leading information in the QA portion. Some people asked if there was an alternator bracket and there is conflicting information. Do you think that it would be difficult to "Modify" the original alternator bracket?

Also I have about 122,000 miles on the car, I bought it from an old couple that only had 60K on it and I have been driving the snot out of it. I would say that the problems were almost encountered 20K into the purchase, I have just been ignoring it.

[MercMan]

My apologies for the double post earlier. I just went ahead and bought everything that I could pick up locally at the Auto Parts store. Turns out they were having a good black friday special, unfortunately I could not buy the heater hose assembly underneath the intake manifold. Now what I am wondering is if I tackle this chore myself, or should I take it in.

The majority of the places are quoting me around 550-600 in labor, and thats if I bring in my own parts. They were quoting me over 1K for parts and labor. My question is how hard is this to replace? Just time consuming, or should it actually require a mechanic to replace it?