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Discussion Starter · #21 ·
Well, you're actually taking me back now about 30 years to something that my brother managed....
He'd just rebuilt the 429 Police Interceptor engine that was in a Thunderbird (well, he hadn't JUST done it, but he hadn't fired it up yet. It sat for a few years).
He told me that something had dropped a nut into the carb, something like a #10 or #8 nut. He claimed it was a mouse, but the fact that he knew it was a nut suggests otherwise...
So, he had 2 options: pull the engine apart, and go looking for that nut, or fire it up and pray the nut just made its way through without any damage. He opted for the second choice. That thing rattle for a few seconds, and the rattle went away. Sure enough, the nut worked its way through the engine safely.
In my situation, I doubt there is, or was, a chunk of anything remotely solid in the chamber; the noise would have been horrific. I'm beginning to wonder if somehow something else didn't make its way into the intake (a mouse maybe?). I'm not sure how it would have gotten that far in, but there was a mouse nest on the engine last winter, before all of this started. My immediate thought was a mouse chewed on a wire and cause the misfire, but all wiring appears to be intact, since voltages are ok and there's no visible damage to any of the wire looms.
If something strange is going to happen, it'll happen to me, or I'll at least wind up working on it (25 years as a computer technician has brought a lot of stories; the stuff of tech support nightmares). So, impossible is not a word I use too much anymore. I've seen, and had to fix "impossible" too many times to leave it in my vocabulary.
I'm still at a loss as to what, so far, has happened with this engine, but I certainly don't mind having the power back, even if it is still missing (although not totally consistently) on the same cylinder. Even the spark plug is cleaner than it was before.
 

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2000 grand marquis ls with handling package, magnaflow mufflers,dual exhaust, 3.55 rear axle
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Well, you're actually taking me back now about 30 years to something that my brother managed....
He'd just rebuilt the 429 Police Interceptor engine that was in a Thunderbird (well, he hadn't JUST done it, but he hadn't fired it up yet. It sat for a few years).
He told me that something had dropped a nut into the carb, something like a #10 or #8 nut. He claimed it was a mouse, but the fact that he knew it was a nut suggests otherwise...
So, he had 2 options: pull the engine apart, and go looking for that nut, or fire it up and pray the nut just made its way through without any damage. He opted for the second choice. That thing rattle for a few seconds, and the rattle went away. Sure enough, the nut worked its way through the engine safely.
In my situation, I doubt there is, or was, a chunk of anything remotely solid in the chamber; the noise would have been horrific. I'm beginning to wonder if somehow something else didn't make its way into the intake (a mouse maybe?). I'm not sure how it would have gotten that far in, but there was a mouse nest on the engine last winter, before all of this started. My immediate thought was a mouse chewed on a wire and cause the misfire, but all wiring appears to be intact, since voltages are ok and there's no visible damage to any of the wire looms.
If something strange is going to happen, it'll happen to me, or I'll at least wind up working on it (25 years as a computer technician has brought a lot of stories; the stuff of tech support nightmares). So, impossible is not a word I use too much anymore. I've seen, and had to fix "impossible" too many times to leave it in my vocabulary.
I'm still at a loss as to what, so far, has happened with this engine, but I certainly don't mind having the power back, even if it is still missing (although not totally consistently) on the same cylinder. Even the spark plug is cleaner than it was before.
At this point , as long as it is not making any strange noises, I would probably just drive it like is for a while. If it gets better, great. If not, maybe it will behave in a way that will help you diagnose the real problem.
 

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I was just wondering if anything new has happened with this car. I have done everything except the compression test on my 01 and I'm having the same issue. Mine started as a misfire and I replaced all coils and plugs checked voltage and I still have a cylinder 4 misfire. The car put itself in limp mode driving down the highway, I have removed the back two and hallowed out the front two cats. Still running super rough with power loss and only codes are for the 02 sensors and cylinder 4 misfire.
Any assistance would be greatly appreciated because I am at a loss as to what could be causing this issue.
 

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Gutting a catalytic converter is dangerous and should not be done! Cats contain heavy metal carcinogens. I hope you wore a respirator and disposed of the contents safely. Additionally, gutted cat(s) will not provide the correct feedback to your DPFE and the car will likely go into limp mode.
 

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Discussion Starter · #26 ·
Digging up my own thread… Things still don’t work right, but there’s now a few more ideas.
Not long after I posted this issue, I discovered the gas tank was leaking. It had rusted out. Tank replaced, fuel filter changed, but the car is still a mess.
Looks like there’s no schrader valve under the hood, so testing the fuel pump requires splicing a gauge in.
Should have insisted on having the pump replaced while the tank was out.
 

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Discussion Starter · #28 ·
I hooked up my brother's code reader to the car earlier today; it came up with the usual message, which is a misfire on cylinder D. Since I've already replaced the plug, injector, coil, and even rewired the coil on cylinder D, I was more interested in what else it would give me, which in this case was just flashing indicators saying something was going on with the EGR, EVAP, and O2 sensors, but nothing specific.
I then shut the fuel pump off using the switch in the trunk and started the car up again; it ran for about 2 seconds, which is far less than I would usually expect.
So, the fuel pump tester is on the way, and this particular tester is just a pressure gauge, so I can also check compression on the missing cylinder, as well as the rest of the cylinders. It's strange, but I'm glad in a way that I've been largely stuck working from home, so I'm not putting miles on whatever is going on with that thing.
By the way, has anyone else shut off their fuel pump and seen how long the engine ran? I suspect the pump is at least draining back and losing pressure with only a couple of seconds of run time, but then again maybe this car should only run that long?
 

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Without the pump, there's nothing to draw the fuel other than vacuum and with the size of the orafices in the injectors, fuel can be dragged from the tank, pressure drops off immediately, and the car goes dead. Could also be a gasket leak. I chased a cylinder missing for months on a Pontiac about that old. When I noticed that the coolant reservoir was empty when the misfire had gotten worse, it clued me in. Turned out it was the intake manifold, which was also a blessing since pulling the heads would have been a nightmare.
 

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Discussion Starter · #30 ·
Well, I'm starting to think the issue is not just one thing, but several. If I had to guess, I'd say this car was in a flood at some point, based on the rusted tank, among other things.
But at this point I'm finding that there's nowhere to plug the new fuel pressure gauge into, as all the lines are plastic. I may have to remove the line that links the passenger and driver side fuel rails and splice into that, or I'll have to buy an adapter for the spring lock at the main line to the passenger side fuel rail. That runs about as much as the fuel pressure testing kit I bought, but is probably still worth having as it just fits inline and doesn't require replacing lines. I have yet to determine which I'd rather do.
 

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Discussion Starter · #31 ·
I finally got time to hook up the gauge to my fuel system. It reads 28 PSI at the rail. I doubt that's enough pressure to run all 8 cylinders consistently.
Now the work begins.
 

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Yes that is pretty low. Most likely from a failing pump. I don’t remember if you did it yet but have you tried a new fuel filter? That could be a cause of low fuel pressure.
 

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Yes, I replaced the filter first, so that should not be the issue. I don't look forward to pulling this tank, but since it was replaced a year ago, at least I'm not dealing with 16 years of corrosion.
The tank isn’t that bad to drop. With it low on gas it’s pretty light. I R&R’d the fuel pump on my 87 Grand Marquis a little while back on ramps by myself in a couple hours. The longest part was messing with the lock ring.
 

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Discussion Starter · #35 ·
Local mechanic told me that with a manual gauge, this vehicle is supposed to be fine as low as 25 PSI. If that's the case, should I have any leakback as it sits? I've currently had the gauge connected for just over half an hour, and lost at least 4 PSI so far.
 

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No it should be around 40psi.

The fuel pump will lose its prime as it sits. I wouldn’t say it’s excessive but could be an avenue to explore. Does it crank excessively before starting? Another thing to remember is that it may be an injector leaking or a fitting and not necessarily the check valve in the pump.
 

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If the fuel pump has a screen / filter , it could be that partially choked . , Be careful dropping the tank you dont have any hand lamps under the car that could ignite any spilled fuel , safety tip
 

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Discussion Starter · #39 ·
I just did a longer run of the engine, and watched the fuel pressure drop to 20 PSI at idle. It would seem the pump is losing pressure the warmer it gets, which certainly could make sense.
Without starting the engine, after the pump is primed, it hits about 45 PSI, then just after starting goes to 28, but slowly goes down.
 
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