Hi guys, ok, i've got a real issue that i am realllly needing help with. I have a 1998 f-150 with a 4.6 winsor motor. Initial problems were misfire codes after a hard rain. Well, i dried everything out and the misfiring went away but the engine idles rough and hesitates constantly thru all rpm range, in and out of gear. after drying out, i got no more codes. i also had what sounded like a dieseling noise coming from passenger side valve cover. I took it to the ford house and they said timeing was off, probably too much chain slack. so, i bought the $300 timing set and changed it out. engine still doing the same thing. brought it back, they said i put it on wrong.... i have done alot of timing chains and also had a certified mechanic help me so i know it was done right. i also changed the coil packs, wires, plugs and even pcm. engine was still doing same thing. I have another identical truck so i checked the maf sensor and tbp sensor from my truck on the other truck and both were fine. all other sensors were changed out. engine was still doing the same thing. I checke compression and all cylinders were the same, a bit low, but the same across the board... engine has 200,000 miles so I replaced engine with a blueprinted crate engine. new engine doing same thing as old engine.... hesitation, rough idle... checked over intake and vacuum lines for leaks/cracks. it checked out ok.. cleaned tb and IAC. still same issues.... even went thru entire wiring harness on engine side and checked continuity and cross continuity for any shorts.. it also checked out ok. I am at a total loss. I have taken to 4 different mechanics including back to the ford house and no one can tell me what the issue is. Has anyone run into this kind of issue??? any help would be much appreciated.

 

Fuel pressure? Fuel filter...? Could be fuel related. Also could be related to accessory parts you changed over to the new engine.

What coil packs and plugs did you use?

 

Check the EGR valve. If it's hanging open just a little bit, it will always run that way. It's can be difficult to determine and DOES NOT always promote a DTC when if it's sticking.

So, - bi-pass it. If that's the problem, you'll know right away. That might narrow it down for yuh anyway.

You can try just pulling the green line (vacuum) from the valve and see if that changes things. If so, the EVR is faulty.

Yea, they'll run like garbage when that valve acts up.

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Dieseling sound can be two things. Either #4 cylinder is misfiring or it's the PCV valve. I bet it's the valve. Make absolutely sure the PCV system is tight as well. Most likley it's tight enough or you would be getting PO171/174 DTC's.

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If all that fails to remedy the problem or give you a clue, - Then examine the engine harness, passenger side, between the MEGA 175 fuse/harness cradle and top of the AC accumulator.

The harness in this location can drop/sag over time. Contacts the accumulator, severs the foil and bares the wires. Once the foil is compromised, magnetic interference causes havoc with our ignition systems. Basically, they run as you described. Check the harness at that location. Make sure everything looks alright.

 

ok, Toyz, i did change the fuel filter and am getting good fuel pressure, used ford original motorcraft parts for plugs/ wires/ coil packs.

Brew, i did the test on egr by pulling the green vacuum line, no change... The dieseling sound was on old engine, not getting it on new one. I did check the harness also, all the way from the pcm to the mega plug then the mega plug to every sensor/coil pack/ injector, etc.. i also checked the sheath that surrounds the harness and it appeared fine.. i made sure its not sagging over the accumulator...

Latest.. i had a mobile electronics mechanic come out to the house today, (had several people tell me he was great at tracking down headaches like this one).. anyhow, he hooked up the computer and it threw a 1137 code, lean on bank 2, bad O2 sensor after the cat... and a 1157, lean on bank 1, bad O2 sensor after the cat... i changed that, he reprogrammed pcm and ran self test again... all codes clear but still have that hesitating... he thinks its the other two O2 sensors before the cat... what do yall think? could the O2 sensors be doing this? Is it likely? also, i want to explain what i mean by hesitating, it almost sounds like a misfire. its just a constant stuttering of enging in and out of idle. the more rpms, the worse it gets. at about 2000rpm, the engine shakes pretty bad. mobile mechanic's computer said that it is firing on all cylinders tho... Thanks and i really appreciate the info

 

The O2's after the cats don't affect the way it runs much at all. If the pigtails are long enough, I'd move the new sensors up front and put either the old ones or the existing front ones back in back.

Lean codes both banks USUALLY mean too much unmetered air (air getting in after the MAF) such as would be caused by vacuum leaks or a leaky intake tube.

 

Thanks glc. After I replaced the one after the cat, we could no longer get any codes.. i will go over whole intake/vacuum lines tonight and see if i am getting any leaks.

 

I still check the EGR valve, just the way I've said . By passing will eliminate it totally from the picture. it completely out of the picture. I don't trust those valves. And it's about impossible to tell if it's screwing with yuh. If it is, it will just as described..

So this is a new engine right ? You were serious?

 

Hi Brew, yes, it is a new engine. I was still planning on checking out the egr valve. when i take the tb apart this weekend to clean it, i will clean egr ports also. oh, and you said to bypass egr... how do i do that? also, wanted to ask if i should replace the front oxygen sensors? never did get any codes for the front ones, but the diagnostic guy said thats what he believed it was.. have you ever run across an engine that ran that bad caused by bad o2 sensor?

 

Front O2's have a lot more to do with how it runs than the rear ones. The rears primarily report on catalyst efficiency. As long as the pigtails are long enough, they are interchangeable. That's why I suggested you put the new ones up front, then put good used ones in the rear. For best results, use only Bosch or Motorcraft O2's.

 

Thanks glc. I will be switching out the front sensors tonight.

 

ok guys, i have replaces all the o2 sensors, cleaned the tb, egr, iac,maf... one of the egr ports was completely clogged in the tb, but the valve was closing completely, so i thought... hmmm this could be whats causing the problem, but nope, put it all back together and getting same result. it seems to idle a little better now, but still stuttering. when up around 2-3k rpm, it really shakes...

 

Crazy thought, but could it be the torque converter?

 

Hi lariat, no, not torque converter, when i pulled engine, i brought tranny to a bud who does trannys and he checked it out... it is doing the stuttering and hesitation in or out of gear. just sitting in park and reving the throttle makes it stutter/ misfire pretty bad, but its not throwing any codes...

 

Ok.

 

hi guys, ok latest update, i cleaned the fuel injectors, no change in symptoms. i bought a vacuum kit and checked every vac line on engine. all good. Started hearing that dieseling sound again so changed the pcv valve, that helped with that noise but not with the stuttering. had computer reset again, drove it for about an hour to pass all the testing senarios, passed all self test/ self diagnosis but still has the stutter.. one thing i noticed is that when i romp on it, once it drops down a gear it accellerates properly for about 2 seconds, then it starts to buck and stutter. so i thought fuel issue, but pressure is checking out fine, and it still has the stutter when in idle.... so... still lost on this one. oh and had yet another mechanic look at it this weekend.. so the list is up to 6 mechanics now who dont know what is doing this....