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4.2L high idle/1 bank rich/iffy power?

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Old 01-04-2015, 11:22 AM   #1
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Default 4.2L high idle/1 bank rich/iffy power?

My 2003 f150 seems to be running a bit weird. I recently bought the truck, and turns out the PCM was fried. So I got a replacement and Ford hooked me up so its working right now.
I was waiting for the ahah moment, like when I picked it up at Ford.lol Didn't get it.
So here is what it does. When you start the engine it revs up a bit more than I think it should, it will hit almost 2000 rpms and then settle down, sometimes it idles around 700 but mostly hangs around 900-1000 when hot. On top of that, the throttle response isn't very crisp at all. It will rev up but to me it seems to lag a bit. I had a 2000 f150 with 4.2 and it had a lot more snap than this 03 does. This just doesn't seem to have much for power either. It is OK but in 5th gear at 70 on a hill I have to drop a gear sometimes just to maintain speed. My older truck didn't need to do this.
Lastly, I had to pull 1 half of the exh off to re-tap an O2 sensor hole. I started it with left pipe off, and it smokes (fuel rich) on the right bank. Left side is clean. When driving, if you rev it up under load it blows smoke which I think it fuel smoke out the exhaust.
History on the truck. It is a 2003. 4.2. It has had the left head rebuilt so upper gaskets are new. I bought it this way so I don't know the ability of the guy that put it together. It has 75000 original miles, so it has sat around somewhere a lot. It only got about 3000 miles in a year and a half from the PO.
Wondering if I should just run some high octane gas for a tank or two and maybe a fuel injector cleaner and just run it and see how it fairs? Or pop the upper intake off and check IMRC and gaskets? I don't want to do work for nothing but it just doesn't seem to run right and I don't want to get 8 MPG with a 6 banger.lol
Any thoughts? I haven't driven it much since the PCM replacement but symptoms are the same before and after.
Reason for PCM, it was corroded(possibly from being under water). had KAM fault, PCM wasn't fix-able. Truck still ran, just wasn't doing much as far as tracking engine management, seems like it was running in default mode. Now it just doesn't seem much better. But maybe I need to meet certain conditions before PCM wakes up?
These electronic engines are nice when they run good but they sure suck when they don't! Well, when you have to learn it all the hard way!!
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Old 01-05-2015, 10:32 AM   #2
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nobody have these issues?
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Old 01-08-2015, 01:51 PM   #3
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Lots of help on this forum, lol. Must be all the other 4.2s run perfect.

I'm not liking this 03 truck. its a PIA. lol
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Old 01-08-2015, 03:09 PM   #4
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Lots of help on this forum, lol. Must be all the other 4.2s run perfect. I'm not liking this 03 truck. its a PIA. lol
my 4.2 runs perfect with 230,000 miles never had any problems lol so can't really help you out much
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Old 01-09-2015, 12:52 AM   #5
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At least I know there is one out there running good!lol
I had a 2000 that ran great. Traded it like a fool! This 03 isn't so hot.
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Old 01-09-2015, 02:19 AM   #6
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At least I know there is one out there running good!lol I had a 2000 that ran great. Traded it like a fool! This 03 isn't so hot.
yea man it happens lol
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Old 01-09-2015, 10:09 AM   #7
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I have gotten away with a lot of crappy trucks for a long time without issues. I was due for this. lol I don't think it is anything major. Maybe a vac. leak or something? Possibly the upper intake leaking if the gasket or bolt o-rings weren't done right when the PO did the left head rebuild. This truck doesn't run terrible, but I don't think it is right. I was just hoping someone here would say, hey I had this happen, check this! lol
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Old 01-09-2015, 11:09 AM   #8
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well the only thing i can think of for the throttle response would be, check your pedal make sure there isnt any play if it does ,do the zip tie mod. as for the idle id say check your pcv hose but thought would cause a low idle almost making it die,but also check all of your isolator bolts
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Old 01-09-2015, 02:02 PM   #9
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Any CEL or codes?
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Old 01-10-2015, 09:18 AM   #10
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No CEL or codes but the PCM was just replaced and it hasn't been driven more than 20 miles since. If the IMRC linkage has popped apart in the back, could that make it idle and run weird? I have to dig in there to see if I can verify that it is hooked up. Its nice how far back into the firewall they jammed this engine.
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Old 01-10-2015, 09:18 AM
 
 
 
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