pi swap misfire issue

SlvrBullet98 · Nov 29, 2010

so, i recently did a pi swap on my 98 gt, and since then ive had a misfire which seems to be on cylinder #4, i unplugged one injector at a time and cylinder number 4 was the only one with no change in the idle, i started with a compression test 180-190lbs across the board, i replaced the spark plugs with new ngk tr6's, i have brand new plug wires, heads are fresh from the machine shop, i even pulled the valve cover and put compressed air in the cylinder and it held, then removed the lash adjusters and tried wiggling the valves in the guides, no air leak at all, pushed the valves down with a pry bar and they seated as soon as i released them, so i replaced the lash adjusters, put it all back together same thing. replaced the injector with a new one, same deal. im lost here. any ideas?

SlvrBullet98 · Nov 29, 2010

also has a popping noise from the exhaust on the passenger side which i beleive is the misfire

dirtysnowball302 · Nov 30, 2010

do you have a coil pack?

SlvrBullet98 · Dec 1, 2010

yup, tried swapping out the coils for known good ones, no difference, im thinking?? that maybe one of the valve guides is too tight and its hanging the valve open a bit when its up to operating rpm, any one have any ideas?

Ninety8stang · Dec 1, 2010

Did you use new timing components or did you reuse your old ones?

dirtysnowball302 · Dec 1, 2010

take your spark plug out an get a leak down gauge an see. i highly dought u have a valve guid stuck. you could have a stuck open inj causing the plug to foul out dumping fuel into ur exhaust causing it to explode(popping noise) ohm the inj out. or swap inj...

SlvrBullet98 · Dec 2, 2010

i put a new injector on the suspect cylinder, i reused my old timing components, but they all looked good and figured the car has 80k on it so why not. also i would think if it was a timing issue wouldnt the compression be up on one bank and off on the other? all the cylinders are between 180-190 lbs on both banks. ive also noticed that when you start the car in the morning from a cold start it cranks like it has a cylinder with no compression (un even cranking speed, it like surges and slows) but if you start it warm it doesnt do this, and the skip seems much worse when the engine is cold, once it warms up it almost goes away at idle. im honestly thinking it has to be an issue in the heads, i just had the machine shop check the deck on them, valve job, bronze valve guides, and new seals, and reassemble, the car had no issues before the swap. but the machine shops anwser when i asked if he had any input was "pull the head and ill check it over"... much easier said than done of course

duff daddy · Dec 2, 2010

yea you need to get the head off and start checking to make sure its not an internal issue. Get the cam tools out again and get rippen.

SlvrBullet98 · Dec 2, 2010

anyone know what the proper valve spring seat pressure and guide tolerances are for this thing? i guess im gonna have to pull the heads again.. FML thinking maybe aftermarket springs and cams this time idk... anyone have any experience with the tfs stage 1 cam and spring combo? or the mhs stage 2 blower/ nitrous cam? and pac springs? i mean shit if im doin it all over again, winters pretty much here, might as well get something out of the deal

Ninety8stang · Dec 2, 2010

if you plan on going with some aftermarket cams hop on corral.net. there's always some sweet deals on 2v cams on there. i actually just saw a couple sets on there. normally around 300-400 for the set. And how much did you have your heads decked? I've heard you really dont want to deck them just a slight surface job is sufficient enough just to ensure that the surface of the head is flat and will mate with the surface of the block. Also out of curiosity what type of head gasket did you use?

SlvrBullet98 · Dec 2, 2010

i didnt have the heads decked really, just a surface check, a couple thousandths tops, to clean it up and make sure it was square, i used the ford MLS gaskets from the head changing kit. im thinking im going to go new with the cams, after this whole experience, i think id rather spend an extra few $ and make sure i dont have to do this project a third time. i still want to know whats actually wrong with this damn thing, im 80% sure it has to be a mistake on the machine shops part :angry4:

GrnGt · Dec 3, 2010

Check into hitech stage 2 cams, ive seen good results from those

SlvrBullet98 · Apr 11, 2011

well, not to drag up a dead thread, but i figured id update the situation, after much aggravation i said screw it and parked the car for the winter, now that the spring thaw came around i finally dug back into the mustang and tore everything down again, dropped the heads at the machine shop friday, got a call today, apparently some how one of my new bronze valve guides was letting the valve walk around a bit and was causing the misfire issue, but was still sealing enough for me to register good compression (dont know how?). regardless ill have them back tomorrow and will be putting them on soon along with new trickflow springs and modmax stg 1 cams and a (matched to pi and ported) svo intake manifold. along with ditching the egr stuff. should be fun