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Glenn, Senior Master Ford Tech
Category: Ford
Satisfied Customers: 1746
Experience:  26 years exp with Ford Products, ASE Master Auto & Truck + advanced engine perf L1/L2 Gas & Diesel
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2003 Ford Crown Victoria police: random misfire..cylinders..igntion

Customer Question

I have a 2003 Ford Crown Victoria police car. It has a random misfire when it's warm (lately it's saying cylinders 5 & 7). We have tested the plugs and igntion COPs and they are fine. The fuel pressure is normal as well. When the car is cold, it runs flawlessly for about 5 minutes, then it starts missing out. The oil pressure is normal and there is not a hint of smoke from the exhaust. Oil & coolant are not mixing. It also has a loud squeeling noise (Like a belt slipping) coming from the #7 cylinder area, the camshaft bearings have been checked and are fine. Finally, a compression test was done and all were normal except for the #7 which was low (Don't know how low, mechanic just says low). The squeel is most noticeable when you are first accelerating. Any ideas on what we should look for next? I know these are notorious for intake manifold problems, but dont' know if that would cause the low compression or squeeling. Thanks.
Submitted: 7 years ago.
Category: Ford
Expert:  ford/lincoln tech replied 7 years ago.

easyist way to chech and make sure what cyl is missing is to pull coils from plugs when running if you pull coil and does not effect running is cyl missing just because coil tested ok doesn't really guarantee ok they go out when hot may test ok cold you could try spraying brake clean or carb cleaner to check for vac leak once determine which cyl missing you can swap coils with other cyl see if miss moves, if doesn't is not spark concern pos injector concern

Customer: replied 7 years ago.
Well, we are fairly certain the misfire is not spark related. The #5 and #7 coils are both making the plugs spark. Just a hunch, but I'm guessing the high pitched squeeling noise coming from the #7 cylinder area may be causing the misfire. We have sprayed carb cleaner all over the top of the engine and it made no difference. I will say this, the engine is very sensitive to moisture, I pressure washed the engine a few weeks ago and the car would almost not run, even if it rains it runs worse. Have you ever seen a cracked intake manifold cause low compression on one cylinder and /or a squeeling noise?
Expert:  ford/lincoln tech replied 7 years ago.

if intake was cracked you would think something would show up when spraying with carb cleaner and would not cause low compression would still be pulling air into cyl

if you had injector sticking could wash down cyl poss cause slightly low comp are plugs on missing cyl wet could be valve concern /carbon built up on valve have seen that

may not make sense but if you remove check valve from comp guage hose and take eng running compression needle will fluicate if needle stops moving at times could be valve sticking compression is built in cyl should build comp even if intake is off because it is still pulling air in

i once had older crown civ with bottom of intake blown off and vech still ran crappy but ran could hardly believe it

Customer: replied 7 years ago.
Relist: Answer quality.
Expert:  Glenn replied 7 years ago.

hello there,


A problem with intake would NOT cause low compression. You must have proper compression before proceeding [you already said you have low compression on #7 and a misfire on that cylinder] What are the compression readings?

Ignore it running correctly cold, this would be do to the pcm increasing fuel pulse width [more fuel] during warm up.

A cylinder leakage test would be the next diagnostic step to determine if its valve train or rings. Also do a wet compression test. Pull the valve cover and inspect the rockers for a problem on #7

Customer: replied 7 years ago.
Thank you for your reply. The leakdown test will be our next step. like I said it doesn't smoke a bit so I have trouble believing it is the rings, my mechanic said he look in the spark plug hole and it "Looks like the piston is broken" which makes me a bit nervous about my mechanic, I guess it might be possible. One thing I did not mention, he did a fuel pressure test, the spec is 30-45psi and his gauge was showing a constant 30 psi while driving, however, the computer was showing 41 psi the whole time. Will that make a difference?
Expert:  Glenn replied 7 years ago.
No the computer reading is always a little higher, this is normal.
Customer: replied 7 years ago.
Thank you for your time, I understand this is a complex situation, I was just hoping there would be something we haven't tried yet. I'm not concerned about the compression now because the mechanic said it was still within spec. My main concern is the misfire. We have narrowed it down to the PCM (Hopefully). We went for a drive today with a diagnostic monitor hooked up. The car ran perfect until it warmed up then missed badly. It set a whole new set of codes (Ignition Circuit Malfunction for 7 of the 8 cylinders) and the Cylinder head temp sensor was only reading 53 degrees when it was fully warmed up. The fuel trim was showing -0.0% at a stop light, the mechanic said the fuel was being shut off completely and when we tried to go the car would not move but was still idling. Then as if a switch had been flipped it ran perfect for a few hundred feet. The scanner was also showing no misfire even though the codes were set and the check engine light never came on on that trip. We only had access to an '03 Grand Marquis computer, it would make a test light on the ignition coils work perfectly where as it was a little random with the original computer, however, the Marquis computer would not let the fuel pump run (PATS???). The circuits from the PCM to the ignition coils have been tested fine. Also, we did a backpressure test and both sides were less than 1 psi. Thanks again for your time