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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 02-11-2008, 07:48 PM
54ford 54ford is offline
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Rough Idle and no WOT

We have an 89 F-150 that we had problems with it not starting so we replaced the TFI but when that didn't help we replaced the PIP sensor but still no luck. we had some oil leaks so we decided to check the timing chain. It was stretched a little so while we were there we put a cam in it and new timming set. Everything was done by the book. We knew speed density doesn't take cams well so we converted to mass air. Now the truck starts when I advance the timing but won't when it is set a 10-12 degrees with the SPOUT removed. It also runs good to half throttle but from there up it falls on it's face. It Idles extremely rough if it does at all. I had pulled the fuel filter off and It had some fine dust on the Inlet side. My question is if some of that dirt could have gotten into an injector and be causing our problems or if it is something else. PLEASE HELP, becomeing extremely frustrated and don't want to keep just throwing money at it because it isn't throwing any codes.
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Old 02-11-2008, 08:18 PM
DJdemon6696 DJdemon6696 is offline
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have you changed the fuel pressure regulator? and cheked the fuel pressure at the rail ?


and is the chek engine light on?
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Old 02-11-2008, 09:47 PM
MisterDave2 MisterDave2 is offline
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Fuel injectors are possible, they can make lots of trouble, I just had two blocked on my boat, made me crazy. Are all the cylinders firing? What motor, how many miles?
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Old 02-11-2008, 09:54 PM
DJdemon6696 DJdemon6696 is offline
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sounds more like a fuel pressure problem we had this same problem .. it was the fuel pressure regulator or the fuel pump .. i cant remember now.. it was 10 years ago.. when we bought the truck

so chek the pressure at the rail it should be 36 at idle ant 40 at WOT ( correct me on this im not 100 % )
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Old 02-11-2008, 10:20 PM
54ford 54ford is offline
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The check engine light isn't on. the truck has a 302 and 124,000 miles on it. I never even thought of the fuel pressure. How is the best and easiest way to check it? Should I buy a fuel pressure gauge to mount in the truck?
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Old 02-12-2008, 12:54 PM
DJdemon6696 DJdemon6696 is offline
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yes.. buy an pressure guage to chek fuel pressre or you can buy one that mount in the truck its up to you. the easiest is offcourse the one to chek the fuel pressure.. the way to chek it is on te fuel rail itself.. there is an schrader valve ( just like an tire valve ) ...

its something like this.. you can buy it at your local parts store
http://store.summitracing.com/partde...5&autoview=sku

then chek the pressure and see if its ok .. if its more than 40psi at wot your fuel pressure regulator is bad... if its less then your fuel pump is bad.. but dubbel chek the PSI for the 302. i know the psi for the 351w but not the 302 so dubbel chek it
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Last edited by DJdemon6696; 02-12-2008 at 12:57 PM.
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Old 02-12-2008, 01:09 PM
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quicklook2 quicklook2 is offline
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clogged exhaust?
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Old 02-12-2008, 01:12 PM
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What cam did you put in it? What is the firing order of the cam? Do your plug wires match this firing order?
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1990 5.0HO AOD XLT X-Cab F150 3.55LS, 1994 3.0L 5-sp x-cab Ranger 3.45, 2004 3.0L 5-sp X-cab Ranger Edge 4.10, 2004 2.5L 5-spd Subaru Legacy
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Old 02-12-2008, 02:23 PM
justa03 justa03 is offline
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Bump on both the firing order and fuel pressure. Even if its a HO 5.0 cam remember it still takes a 351 W firing order and not the regular 302 firing order. If you suspect a an injector you might be able to pull the plugs and see if any are lean.
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Old 02-12-2008, 06:11 PM
54ford 54ford is offline
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The cam has the windsor/HO firing order. I'm not sure which cam it is with out going to the shop and looking at the cam card. It was a cam the Comp cams guy recomended for a mostly stock engine with long tubes, dual 2.5 in exhaust, and converted to mass air. I already double checked my wiring and changed my plug wire order. I know the exhaust isn't pluged because we had hollowed out the cats when we got the exhaust work done 1 1/2 years ago. The truck sounds good at 2000 rpms. hopefully I can get a pressure gauge and check the fuel pressure this week.
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Old 02-17-2008, 06:58 AM
54ford 54ford is offline
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I checked the fuel pressure yesterday and I could only get 20 psi at the most so I thought I would replace the regulator first being that it costs less and that brought my fuel pressure up to where it should be. The truck still wouldn't run quite right so I thought I would replace the coil even though I had spark. The truck fired right up. I belive the old coil had enough power to show spark untill I reinstalled the plugs into the engine when it would then under compression fall short of what was needed. Thanks for all the help, It sure kept me from scratching a ballad spot on my head.
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Old 02-17-2008, 08:48 AM
DJdemon6696 DJdemon6696 is offline
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if the PSI is low.. it means your fuel pump s bad.. but first chek your fuel filter maybe its clogged... does it run like this on both tanks? did you chek the pressure of both tanks?

and btw the regulator brings the pressure down.. not up
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Old 02-18-2008, 09:25 PM
54ford 54ford is offline
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Since I put the new regulator on the fuel pressure is right where it should be, about 35-36 at Idle and right on 40 at WOT for both tanks. I believe the old regulator might have been stuck open causing it to bleed off pressure too fast. The fuel filter was replaced right before I checked the fuel pressure because I had been told it could have an effect on the pressure. It has been running realatively good since I replaced the coil and the idle is getting better the more we drive it.
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Old 02-18-2008, 09:34 PM
DJdemon6696 DJdemon6696 is offline
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thats good to hear .. try an injector cleaning or seafoaming it see how she runs maybe it just needs a clean up
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Old 02-18-2008, 09:43 PM
54ford 54ford is offline
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Thanks again for all the help without you guys I would have never thought of checking the fuel pressure. I might try some BG 44K injector cleaner that you get at a Ford Dealership I have heard it is some of the best out there or is there another kind you think would work better?
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Old 02-18-2008, 09:43 PM
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