HELP! 5.0L V8 Engine Miss/Stumble on Acceleration (Long)

Ok, here it goes, i'm gonna write out everything from day 1 cause mayeb someone will think of something that i have not. Also, thanks in advance for anyone that actuallly sits and reads through this whole thing for me, I really appreciate the help.

For starters, heres what i have:
1998 Explorer 5.0L V8 AWD

Last summer I installed the FMS headers that i had purchased a few months before. They are the ones that have no EGR port on the passenger side header. After installing the headers i noticed a slight miss under load, i sort of expected this being as there was no EGR hooked up. I had an Apten chip at the time andhad nto had it programed with EGR delete. Except for the slight miss the truck ran 99% perfect. I removed the EGR valve from the truck, plugged the vacum lines and blocked off the EGR hole in the intake. I removed my chip to send it in and have reprogrammed to delete the EGR and when i drove the truck it ran horribly. I had a terrible miss/hesitation problem when accelerating and especially when accelerating slowly on the highway. It would miss and stutter to the point of making the truck jerk a bit. So I put my chip back in since i had to drive a lot at the time and planned on sending it in when i went back to college and the truck would be sitting a lot.

Fast forward to january.

Being the procrastinator i am, i never got around to sending my chip in until febuary. When i removed it the truck ran like it had before, horribly. I sent it off to be reprogramed to delete the EGR. I traded my chip up for a dual program chip (given rising gas prices, premium was killing my wallet faster than i liked) and when i recieved the new chip back i installed it expecting the truck to run fine. It did not. The chip seemed not to make a difference at all, in any of the 3 switch positions. Faulty chip? Not sure yet, i've contacted apten and will send it in the coming week to check the programing.

Anyway, since i dont' seem to have a working chip, and i was home for spring break anyway, i decided to throw my old header and EGR valve back on so the truck was driveable until i got my chip back at least. That was yesterday. Once i got everything installed back i took her for a test drive. The problem was still there! I went back and checked all my vacum lines and connections and everything was fine. Test drove again and still the same, a very pronounced miss and stutter under acceleration, especially at lower engine speeds. Also, under heavy acceleration there is pinging/knocking.

What could be causing this problem? Was this ever an EGR problem or was it something else the whole time and i just assumed the EGR. What kind of problem would my original apten chip have covered up or muffled that would be much more aparent without the chip installed.

There is no CEL or no codes. I drove without the chip installed once and EGR codes came up after about 100-200 miles of highway driving. As soon as i install the chip there are no longer any codes, even though there is a slight miss. The apten chip seems to retard the CEL from lighting up for the slightest miss like it usually would. Even as horribly as it runs now there is still no CEL with or without the chip installed. I find it very hard to believe that as sensitive as the EEC-V is on these vehicles that the light has not yet come on but it has not. And the one time it did all it showed was EGR which is installed back in its entirety now.

Here's a list of things i have tried already:

--swapped MAF sensor out (replaced my Granateli with the factory one) - no effect

--spark plug wires are Bosch and less than a year old, still have facotry wires in box, will try changing them out but why would it run well with a chip and not without one

-- spark plugs all look pretty good, two cylinders on the passenger side show just a little bit of white on the plug ends which would indicate high combustion temps, expected with the pinging

--it idles almost perfect, maybe one little miss here and there, i assume a vacum leak large enough to cause the other problems would kill the idle as well

-- checked the resistance of the primary and secondary circuits on both coil packs, both are exactly midrange in specs

If anyone has any suggestions or things for me to check please let me know, this problem is really starting to get annoying and the miss is making the truck a bother to drive instead of a joy as usual.

Thanks

One addition to the above. The truck seems to run almost perfect when cold after first started. After it warms up about 1/8 the way on the temp guage is when the problems start. This is why i don't believe it is ignition related but have no idea what else it could be without a CEL.

This may seem silly, but did you check the coil packs after it was warmed up? I had a similar problem in an older car, it ended up being a bad coil that only went bad when it got hot. It would somehow expand and cause a short or circuit break with vibration. If you can, I would try replacing those, or at least testing them with the engine hot.

I've tested them warm, not too long after i drove the truck. I've thought about that and i'll ohm them out the next time i get the truck good and hot, but if i can't figure anything else out i think i'm going to replace them anyway. I don't like spending money i don't have to but i've gotta start somewhere and so far i've got nowhere with this problem.

Another question, are you SURE its the engine. I've been fighting this problem on my 5.0, all sorts of fun exhaust leaks. Specifically at the collector. It seems weird, but my guess is that with the leaks, the 02 is getting an incorrect signal and is adjusting accordingly. Just another thought as this is what I have right now and its incredibly frustrating because it keeps coming back.

No, i havn't thought about that. I don't hear any of the 'ticking' that is common with exhaust leaks but i'll check out my pipes and see if i notice anything. This could also explain it happening only after it warms up although you would think that when it was cold the leaks would be more appartent and that the warming up would shrink their size, but when dealing with round pieces of metal it could go either way i guess.

Thanks for the suggestion, i'll check it out.

So, did you have luck finding your problem? I'm still hunting down the gremlins in my 5.0. I've had the Exhaust Manifolds replaced, the Collectors re-tightened twice, the gasket between the Cats and the Muffler replaced about 8 or 9 times. They just keep coming back.

I'm wondering if there's a blockage somewhere in the exhaust that's causing all these leaks because they keep coming back. Not sure what else I can do at this point since Ford has more or less told me to take a hike since they've had this car in under warranty now over 16 times. The answer I always get is, "There seems to be a problem, but we can't find it, so we can't repair it". Very frustrating, I'm at the point of getting the Ford Abbritrators involved and having them replace the whole damn thing... but don't know how that would work out.

Yeah, it ended up being a spark plug! I ran out of things to check so i just went ahead and replaced the plugs figuring the least expensive thing first. The problem dissappeared. I took a closer look at the plugs and one of them had a tiny hairline crack in it that i was barely able to see without a magnifying glass. I had missed it when i had the plugs out before.

I'm just wondering why my check engine light never came on since this would be considered a cylinder misfire and most cars will come on with the slightest burp.

Ya, spark plugs are actually my next change. I swapped in Bosch +2's when I changed the spark plugs, and come to think of it, this all kind of happened at the same time. I've heard some bad things about them (cracking and breaking off the insulator's), so that's going to be my next change, I'll swap in a set of the Autolite Double Platinums and see how those work (I looked at the Motorcraft Plugs for the X, $7.00 a piece *blech*). Hopefully I'll have the same luck you did.

Originally posted by CougarX
I'm just wondering why my check engine light never came on since this would be considered a cylinder misfire and most cars will come on with the slightest burp.

Click to expand...

i drove mine to and from work one day with no MAS or intake tubing on it and never threw a CEL.

Cali:
Try autozone, they are only 3.99 or 4.49 a piece. Although the Autolite double plats are prolly just about the same plug and they come pretty cheap in 2 packs at walmart i think.

james:
yeah, and the bad part is it will light up when nothing seems wrong at all then when you know something is wrong it'll never show itself!!

Cali,

This is EXACTLY what I suspect is the problem on my 97 XLT V8. Only, I get the occasional misfire at idle only. I suspect that at idle, there is not enough pressure in the maifold to "push" out all the air leaking through the hole in the gasket. I do not have any problems at higher RPM, load or driving. I'm going to replace the gasket this weekend and see if that fixes it.

Cali' Explorer said:

This may seem silly, but did you check the coil packs after it was warmed up? I had a similar problem in an older car, it ended up being a bad coil that only went bad when it got hot. It would somehow expand and cause a short or circuit break with vibration. If you can, I would try replacing those, or at least testing them with the engine hot.

Click to expand...

Sorry, I meant this quote:

Cali' Explorer said:

Another question, are you SURE its the engine. I've been fighting this problem on my 5.0, all sorts of fun exhaust leaks. Specifically at the collector. It seems weird, but my guess is that with the leaks, the 02 is getting an incorrect signal and is adjusting accordingly. Just another thought as this is what I have right now and its incredibly frustrating because it keeps coming back.

Click to expand...

schadler- did that solve your problem at all?

Well, it turned out the gasket was fine, it was the manifold that was cracked. A new one is between $500 and $800, so for a temporary fix, I used some repair putty and a fiberglass muffler patch for good measure...it's held up great! The engine sputtering is definitely a spark plug or wire problem. I was in the McD's drive thru, and could hear the arcing "bouncing" off the brick wall. I'll try crimping the wires better. If that dont fix er, I'll rip out the wires and plugs I just replaced and replace em again. The nice thing about Explorers, is you get damn GOOD at repairs when you do them more than once

bosch crap!!!

Cali' Explorer said:

Ya, spark plugs are actually my next change. I swapped in Bosch +2's when I changed the spark plugs, and come to think of it, this all kind of happened at the same time. I've heard some bad things about them (cracking and breaking off the insulator's), so that's going to be my next change, I'll swap in a set of the Autolite Double Platinums and see how those work (I looked at the Motorcraft Plugs for the X, $7.00 a piece *blech*). Hopefully I'll have the same luck you did.

Click to expand...

Id never run bosch plugs in our 5.0's!!! Ive tried all plugs and the best by far are Ngk irridium's. Best throttle response, and never seem to where out!!!

misfire

I'm having the same problem with misfire starting after warm up. My vehicle is stock. I know enough that it's probably ignition. I've replaced plugs and wires. The only thing I can think that's left is coil packs or whatever that pickup sensor is called that goes in the block. Any suggestions?