01 Crown Vic Bucking/Stumbling Uphill

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My 2001 Crown Vic P71 SAP (with a little over 100k on her) is breaking up under a low RPM load. From a cold start it runs good then this problem gets gradually worse as the car reaches full temp, then heat soak. I'm pretty car savvy, this is not a trans shudder issue. The plugs are newer Motorcraft. I have a handful of spare COPs and have rotated them around. (with fresh dielectric grease) Weirdly this issue first showed up after I had my intake manifold off and then back on. (got a faulty replacement manifold and put my old one back on) then I had this stumble issue. After I put my new Ford Racing manifold on the stumble was gone, for about 700 miles. It seemed to show up gradually. I wondered if it was bumps in the road at first. Now, after a 25 minute drive, it's really bad. It will break up under wide open throttle too. Not getting any codes. I unplugged the DPFE sensor (EGR pressure sensor) and that didn't change anything (not sure if it would, I see lots of threads saying to replace that part) I'm kind of wondering if it could be something odd like an upstream O2 sensor or a fuel pressure sensor (I remember when I had my 03 Cobra, those would go and cause odd running issues). My little code scanner shows live data, TPS is consistent when it happens. I don't know enough about what to look for in other data to narrow the problem down further.
 
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Any chance it could be a clogged catalytic converter? I would expect one or more misfire codes if that were the issue, but you never know. I would be especially suspicious of a cat if your intake issue might have been causing unburned fuel to make its way into the exhaust.
 
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Originally Posted by fsdork
Any chance it could be a clogged catalytic converter? I would expect one or more misfire codes if that were the issue, but you never know. I would be especially suspicious of a cat if your intake issue might have been causing unburned fuel to make its way into the exhaust.
Clogged cat seems unlikely. I've driven a car before that was clogging, felt much different than this. I'll break out my heat gun and check.
Originally Posted by andyd
Symptoms of Intake manifold sucking air, creating a vacuum leak. You have R+R'ed the intake manifold 3 times. I would start there grin2
I want to say that is impossible, I've dumped a can of brakeclean under the hood looking for a vacuum leak. But, if it were an intake seal issue (new OEM intake, perfect mating surface, premium gaskets) I would expect it would be worse on cold start then get better as the engine warmed up, not worse. And also, would have expected the problem for the start after the new intake was on, I was driving it for over a month without an issue.
 
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Originally Posted by Surestick
Dirty MAF? Only occurs when the car is warmed up (closed loop), the intake manifold was off (chance to get contaminants on the MAF), doesn't appear to be ignition related...
Agree on closed loop. Maf was cleaned prior to this intake job and I just left it attached the intake tube while I was doing the job. I will re-clean it with my MAF spray. I can see MAF values on my handheld, but don't know what the numbers mean. It doesn't seem to fluctuate when it's stumbling.
 
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Have had this myself on my GM and it was coil packs. I have had a dirty MAF sensor that also caused a similar problem. For me the problem was prevalent when driving car long distances under load like climbing the hill. Much worse when hot out and car hot. No overheating going on but it would rise on temp gauge slightly.
 
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It could be the parts already mentioned and/or fuel injectors in need of a good cleaning. Hopefully Trav sees this thread and weighs in.
 
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Check mode 6 data for misfire counts. Although that year may not have the best data available. IMO I would look at ignition. What are you upstream o2 voltages at WOT?
 
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Pulled the MAF, cleaned it. Checked the cats after a 20-mile drive. Saw some side to side difference but nothing over 450 on the temp gun. Primary cats were cooler (200's) than the secondaries. It was breaking up before reaching operating temp, then warm intermittently ran solid or poor. I can't check mode 6, I just have a good parts store level scanner. It will show you some live data but that's it. Nothing will pop up in the Pending Codes (which will show up sooner than a CEL).
 
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Originally Posted by clinebarger
Coils, Coils, Coils! I would say something about Ford owners & their unbelievable reluctance to buy 8 OE coil packs, But that would be tacky grin
I am dying right now. Had a buddy with a 5.4 F150. Swore up it down it wasn't coils. He brought it over to my house. I replace the coils. That was 60,000 miles ago. smile
 
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Originally Posted by ls1mike
Originally Posted by clinebarger
Coils, Coils, Coils! I would say something about Ford owners & their unbelievable reluctance to buy 8 OE coil packs, But that would be tacky grin
I am dying right now. Had a buddy with a 5.4 F150. Swore up it down it wasn't coils. He brought it over to my house. I replace the coils. That was 60,000 miles ago. smile
I have 4 spare OEM coils, used but still. I circulated all of them around. Reluctance is real though. Unless I want the fakes on ebay/amazon, buying 8 OEM coils is over $300.
 
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Definitely sounds like COPs to me, which is a real nuisance with this engine. Back in 2012, Trav was able to find me a set of 8 Standard Red Box COPs, made in USA. Touch wood, I haven't had any issues with them since, but that's not to say it won't happen. Going to be buying a set of eight soon to have as back up, just in case. One goes out, the others are not too far behind; I always replace them in sets of eight.
 
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I was reluctant to buy new coil packs in my case there are 2 4 on each not COP. I went to junk yard and picked best 2 I could find for $10 and wow car feels like it gained 40 hp so now if it goes back I will break down and get new ones. Hard to beat the junk yard prices though.
 
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Well, 8 Bosch coil packs and it's running well again. I didn't expect such a simple solution but I guess the Ford computer really can't identify which cylinder has the issues. $17 each on RockAuto, amazing price. Coil knock offs are everywhere, Bosch puts coded hologram decals over the box ends so you can verify online that the part you bought is genuine.
 
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