99 f250 5.4L runs rough on acceleration fall on its face - F150online Forums



99 f250 5.4L runs rough on acceleration fall on its face

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Old 03-22-2011, 02:01 AM
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99 f250 5.4L runs rough on acceleration fall on its face

My truck has been running really rough on acceleration. At an idle it doesn't seem to be miss firing at all it was throwing a code for the intake air temperature sensor so I replaced that and its not throwing any codes now and it didn't fix the problem I replaced the plugs and the fuel filter and the pcv valve and nothing I tested the ignition coils and they seemed to be working properly
It shakes really bad and you can hear it miss firing when I accelerate and there are no miss fire code please help have no idea what it could be maybe the PCM?
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Old 03-22-2011, 10:45 AM
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And it only does it when its warmed up never when cold
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Old 03-22-2011, 12:18 PM
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Update to Motorcraft plugs only and purchase a set of DG508's from Global Automotive on Ebay. Purchase the V10 pack. Tighten new plugs to 28'lbs/ Grease up your coils well and she should run like a new truck. You have to do exactly as I said tho, -for best results.
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Old 03-22-2011, 08:44 PM
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Thanks I will have to give it a try
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Old 03-30-2011, 01:22 AM
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Didn't work I have been to three mechanics and they have all told me different things I have replaced the fuel filter plugs cop's intake air temp sensor cam sensor fuel filter pcv valve checked vacuum lines there are no codes or anything the scan tool says everything is in working order and running fine but when engine is under load it spits and sputters like crazy so if the pcm has no codes and it says its all working right should I move to the transmission maybe torque converter I have been driving it everyday for the past three weeks and it will not throw a code for miss fire or anything just stumped what it could be definitely a challenge to figure out lol not giving up yet any ideas?
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Old 03-30-2011, 01:57 AM
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What was the pump pressure like?
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Old 03-30-2011, 02:16 AM
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At this point a fuel pump would be the next thing to look at. Buy a pressure gauge and see what ur fuel pressure is, like jbrew suggested. I would think if ur tranny was in that bad of shape it would throw a code. Cleaning the MAF sensor and EGR passages might help. Try and use a little punctuation also....

Last edited by ParnAZ; 03-30-2011 at 02:18 AM.
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Old 03-30-2011, 02:25 AM
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Originally Posted by bowhunter99 View Post
Didn't work I have been to three mechanics and they have all told me different things I have replaced the fuel filter plugs cop's intake air temp sensor cam sensor fuel filter pcv valve checked vacuum lines there are no codes or anything the scan tool says everything is in working order and running fine but when engine is under load it spits and sputters like crazy so if the pcm has no codes and it says its all working right should I move to the transmission maybe torque converter I have been driving it everyday for the past three weeks and it will not throw a code for miss fire or anything just stumped what it could be definitely a challenge to figure out lol not giving up yet any ideas?
wow that is a really long sentence. lol i couldnt breathe at the end of it. Good luck man!
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Old 03-30-2011, 02:12 PM
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Fuel pressure read 32 psi at and idle and when started read 40. Thanks for the help jbrew. Is there a way I can check voltage on the pump at all?
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Old 03-30-2011, 02:32 PM
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Its starting to miss fire at an idle now and does it when its cold to. still no codes or anything
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Old 03-30-2011, 02:45 PM
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Well, I'd check a few other things, then compression test it. You've been disconnecting the battery right? So you cleared the KAM KeepAliveMemory Right ?

1. Check all your fuses/relays in the fuse blocks. I just pull them check for corrosion or blown.

2. Check for harness chaffing directly above or on top of that connector @ the AC accumulator. Those models have problems with chafing and baring wires right at that location. It's a bad area for ignition mag field disturbance. If the the main harness/wires loose their foil insulation, that alone can cause havoc with these ignitions. So check for harness damage at that local.

3. There's always that possibility you still have a bad coil. New or not, it happens far to often lol. I try not to get that dielectric on the contact points, where the spring contacts the plug, - paranoid maybe, but I've changed allot coils , never a problem.

4. It doesn't hurt to go over your work, - forget a connector ? You can disconnect the coils/injectors then reconnect again. Bad contact can happen.

Other than all that, checking compression is your next step. #'s in my sig.
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Old 03-30-2011, 02:50 PM
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Are you loosing any coolant? Any leaks near a plug? Since you have replaced the COPs and plugs then maybe an injector is failing? These kinds of problems w/no CELs is awfully strange. Upstream O2s going bad? Keep us posted...
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Old 03-30-2011, 04:09 PM
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Originally Posted by bowhunter99 View Post
Fuel pressure read 32 psi at and idle and when started read 40. Thanks for the help jbrew. Is there a way I can check voltage on the pump at all?
32 @ idle = pumps in good shape. Below 28 = fail for both V8's. I'm not sure what you mean "when started read 40" - over my head lol.

You can check your VREF but why ? You can also check your relay, but again , why?
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Old 03-30-2011, 04:24 PM
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Originally Posted by bowhunter99 View Post
Its starting to miss fire at an idle now and does it when its cold to. still no codes or anything
That's a typical coil low grade misfire. A characteristic after KAM Clear/ battery reconnection.

It's coil or compression. Injector, -it's possible, but very doubtful IMO.

Since it's getting worse, try to identify the cylinder. DON'T RESET the KAM.

Bring the Misfire count up thru Drive Cycle. Go for a ride, give it hell when it's at it's worst. Right after the shift into OD under normal excel, then nail it! Do what you have to keep it missing until you get a blinking CEL. It will blink 4-6 times then shut off, watch for, check for DTC's even when CEL is off. Keep your scanner plugged in during drive cycle if you want.
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Old 03-30-2011, 05:05 PM
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Wow that's a lot lol. Thanks man I really appreciate all the help and I will have to do all of that and I will let you know what I find out, and no coolant that I have seen but will check again. once again thanks for all the help
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