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Discussion Starter · #1 ·
My '05 with the 4.6 started missing a couple of months ago. This is my 3rd car in this platform, and I knew the first steps were going to be replacing coils and plugs. Both done, still missing on same cylinder.
Tried running injector cleaner through it, no change. Bought a new injector for cylinder #4, and while removing it, the top O ring disappeared. Never saw it again. Decided to finish replacing that injector, and clean the other injectors, also replacing the O rings on them. No change.
Swapped out the new coil for another one I had sitting around, miss went away. For about a week. Came back even worse than it was before, so changed the plug on that cylinder again. Once again, no dice.
I've swapped coils from other cylinders to #4, swapped injectors around, and tested the voltage to the coil. All appears to be good, 12 volts where it should have it, and the coil fires if I take it off the plug.
Only things I can think of are 1. vacuum leak (although from what I've read, that usually causes issues with the vent doors kicking over to defrost) or 2. compression test.
If anyone else has ideas, let me know, because I'm leaning toward giving the car to the local Sheriff's department and letting them practice their range maneuvers with it.
 

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2000 grand marquis ls with handling package, magnaflow mufflers,dual exhaust, 3.55 rear axle
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Since you have tried different coils and injectors without success, I think a compression check would be the next logical step. It could have a bad valve or just be worn out if it is a really high mile engine.
 

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Discussion Starter · #3 ·
Certainly not high mileage, at least not from my experience with this engine. 116,000 as opposed to the last two 4.6 engines I had, which went over 200k easily. But that sounds like what I've got to do next. I love this platform; built sturdy, lots of parts cross over between a lot of other models, and the ride is great. I wouldn't look forward to an engine swap, though...
 

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2000 grand marquis ls with handling package, magnaflow mufflers,dual exhaust, 3.55 rear axle
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Certainly not high mileage, at least not from my experience with this engine. 116,000 as opposed to the last two 4.6 engines I had, which went over 200k easily. But that sounds like what I've got to do next. I love this platform; built sturdy, lots of parts cross over between a lot of other models, and the ride is great. I wouldn't look forward to an engine swap, though...
I agree, 116,000 is nothing for that engine. I thought there was a possibility that it had over 300,000 miles. That would only be 20,000 per year.
 

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Discussion Starter · #6 ·
Done the coil replacement, as well as FI replacement. Also checked wiring to the coil and FI. I suppose it's possible to still have a vacuum leak with the under dash heater/ac controls working, so it's down to that and compression.
 

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Discussion Starter · #7 ·
I checked the compression today; 50 PSI on cylinder 4. That would explain the problem, since it should have more like 150. So it's to be continued until I can get in there and find out what's leaking by.
 

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2000 grand marquis ls with handling package, magnaflow mufflers,dual exhaust, 3.55 rear axle
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I checked the compression today; 50 PSI on cylinder 4. That would explain the problem, since it should have more like 150. So it's to be continued until I can get in there and find out what's leaking by.
Thanks for the update. Let us know how it turns out.
 

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Discussion Starter · #9 ·
Well, I haven't yet had it apart, but right now I can say there's no water in the oil, or vice versa. There doesn't seem to be any appreciable blow-by (I've been told you'll get at least some oil blowing out the filler cap if you watch it). My local mechanic says it's probably not a head gasket, as this engine tends to blow from one cylinder into the adjacent one, so I'd have 4 and 3 both leaking.
That seems to narrow it down to the valve train. As I recall, these have roller cams, as do most newer vehicles. Is the lifter actually a hydraulic or mechanical one? I could see the possibility of a burnt valve, or a broken spring, but a keeper shouldn't be the issue as the valve would most likely hit the piston. Perhaps a very badly carbon fouled valve, or even a flat cam lobe (assuming the flat lobe is on the intake side, it would keep the cylinder from pulling in air).
No matter what, the head has to come off, and right now I don't have the space to do that myself, or the money to pay someone else. Fingers crossed that I get some extra work soon to cover this.
 

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Discussion Starter · #10 ·
The plot thickens... I decided to pull plug 4 and start the engine up. I let it idle for several minutes, then revved it a couple of times without that plug. Shut it down, reinstalled the plug, and I've got a whole lot of power back. It's still missing on #4, but it almost runs normally.
I have a suspicion I may have blown something out of the cylinder, and so my next step is to run the compression test again. Maybe something got in there that was blocking a valve? Whatever it is, I'll say it's not normal behavior.
 

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I doubt is because these are interference engines so a valve hung open would most likely have had a run in with a piston. I would suggest buying a vacuum gauge and hooking it up to a vacuum line and performing some tests with it. Its old school but it works and it’s easy.




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The plot thickens... I decided to pull plug 4 and start the engine up. I let it idle for several minutes, then revved it a couple of times without that plug. Shut it down, reinstalled the plug, and I've got a whole lot of power back. It's still missing on #4, but it almost runs normally.
I have a suspicion I may have blown something out of the cylinder, and so my next step is to run the compression test again. Maybe something got in there that was blocking a valve? Whatever it is, I'll say it's not normal behavior.
Ingenious. I just wonder if you should unplug the fuel injector for that cylinder while the plug is out to keep from spraying gas vapors out through the hole. Perhaps a few full throttle accelerations (up to the speed limit) might blow some carbon deposits out. Keep us updated
 

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Ingenious. I just wonder if you should unplug the fuel injector for that cylinder while the plug is out to keep from spraying gas vapors out through the hole. Perhaps a few full throttle accelerations (up to the speed limit) might blow some carbon deposits out. Keep us updated
Just to clarify. When I suggested full throttle accelerations, I meant with the plug in.
 

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Discussion Starter · #15 ·
Well, it keeps getting more interesting. I took the car back to the guy whose compression tester I'd borrowed, and checked the compression on 4 again. Still 50 PSI. So I hooked it up to #1 and got.... 50 PSI. #1 hasn't been missing, hasn't missed a beat. So now I'm starting to suspect his compression tester has issues.
I then took a look at the plugs for both of those cylinders; #4 had been beaten up so much that the insulator was loose. Something has to have been inside that cylinder at some point, and parts of it may still be there. After replacing the spark plug, it's time to run it a bit with the plug pulled and injector unplugged again. It's still got that miss on 4, but now I've got reason to question whether it's actually got low compression, given the identical reading on cylinder 1. I could believe 2 cylinders having low compression, but these have THE SAME READING. I find that difficult to believe. Not impossible, but not very likely.
 

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Well, it keeps getting more interesting. I took the car back to the guy whose compression tester I'd borrowed, and checked the compression on 4 again. Still 50 PSI. So I hooked it up to #1 and got.... 50 PSI. #1 hasn't been missing, hasn't missed a beat. So now I'm starting to suspect his compression tester has issues.
I then took a look at the plugs for both of those cylinders; #4 had been beaten up so much that the insulator was loose. Something has to have been inside that cylinder at some point, and parts of it may still be there. After replacing the spark plug, it's time to run it a bit with the plug pulled and injector unplugged again. It's still got that miss on 4, but now I've got reason to question whether it's actually got low compression, given the identical reading on cylinder 1. I could believe 2 cylinders having low compression, but these have THE SAME READING. I find that difficult to believe. Not impossible, but not very likely.
I would check the compression with a different tester. If it comes back normal you have been on a wild goose chase. If it comes back low you have a serious problem. Are there any strange noises coming from that area of the engine?
I read all your posts again. You said at one point you changed a coil and the miss went away for a week. That would point toward and electrical problem.
 

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Discussion Starter · #17 ·
Yes, I've even checked voltage to the coils and fuel injectors. The owner of the compression tester said it was supposed to hold at the highest reading, like most I've seen do, but this one seems to have quit doing so, which is another reason not to trust compression readings off that device. I did briefly have a knock/rattle at a cold start, but that's gone away, and that raises even more questions. If the car had been low on oil, I might believe a knock at startup from that, but this oil isn't even dirty, and I'm running synthetic. The fact that the knock has gone away makes me think something got into cylinder 4 and could have damaged a valve like it damaged the spark plug, or it at least left some residue that's just not cleaning out easily.
 

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Yes, I've even checked voltage to the coils and fuel injectors. The owner of the compression tester said it was supposed to hold at the highest reading, like most I've seen do, but this one seems to have quit doing so, which is another reason not to trust compression readings off that device. I did briefly have a knock/rattle at a cold start, but that's gone away, and that raises even more questions. If the car had been low on oil, I might believe a knock at startup from that, but this oil isn't even dirty, and I'm running synthetic. The fact that the knock has gone away makes me think something got into cylinder 4 and could have damaged a valve like it damaged the spark plug, or it at least left some residue that's just not cleaning out easily.
I guess if another small part of the valve broke off it could damage the plug and them fly out the exhaust. It would be a miracle if it did not do other internal damage.
 

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Discussion Starter · #19 ·
Could be part of a valve or something else; I'm going to swap coils around again tomorrow in the hopes the miss goes away, and in the hopes that the compression tester I used is wrong. If not, then I've got more work to do.
 
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