Severe engine miss

[94tchikinv8]

The car is a 98 GT with an 02 explorer PI engine and a set of comp 262 cams.

I had a slight engine miss that was beginning to get worse and affect drivability so I figured it would be a good time to do a tune up and change the plugs and wires on my car. It had stock replacement motorcraft wires (I found that one was definitely bad and had corrosion in the plug boot) and autolite copper plugs. I changed them to NGK copper plugs and duralast wires from autozone. I went to start the car after changing these and it now runs like absolute crap. It has a dead miss on at least one cylinder. I was a little ticked and thought maybe I had gotten a bad plug or wireset from autozone. Apparently, that's not the case.

I have tried all combinations putting the old plugs in with the new wires; it currently has the new plugs with all of the old wires except for the one that was definitely bad (cyl 1). I checked the plugs, and they all looked the same except cylinders 2 and 3 looked a little darker like they had been running richer. I switched out the fuel injectors to those cylinders, no change. I have tried switching the coil packs out with ones known to work to no avail. I even did a compression test on the car and it was normal. The only CEL codes it throws are the ones for the rear O2 sensors that aren't hooked up and now the DPFE, which I imagine is a result of the way it is running. I even took the intake off and changed the gaskets, nothing really wrong there. I also cleaned the MAF, and ran the car with and without it connected and there was no change.

I am running out of ideas of what it could be that made it start running like this at the same exact time I decided to do a tune up. I'm going to go rent a noid light and fuel pressure gauge from autozone to cover those bases and possibly switch to a different set of injectors to make sure that's not a possibility.

Please help me out here, I'm almost at my wits end with this car. I need to get it running ASAP.

Thanks,
Rob

[JIMS SVT]

Do a compression check. Who installed the cams? Couldve accidently bent a valve when installing them?

[94tchikinv8]

Do a compression check. Who installed the cams? Couldve accidently bent a valve when installing them?

I already did a compression test as stated above and it was fine. I installed and degreed the cams myself when the engine was on a stand years ago and it already has about 50k miles on them.

Thanks,
Rob

[bobtsgt]

with the rear 02s throw a code you are running richer with less timing cause the computer is put into a "limp" mode. go over your harness and look for damaged connectors or pins. Also do what you said and check for proper spark and fuel pressure. The DFPE has to do with the EGR system. Chances are the little hoses that go from the sensor to the EGR tube are cracked or broke.

[redfirepearlgt]

I have a sticky EGR valve on a 93 Z28 (hate to admit that) that caused misfiring at high RPM.

[Blackout]

The car is a 98 GT with an 02 explorer PI engine and a set of comp 262 cams.

I had a slight engine miss that was beginning to get worse and affect drivability so I figured it would be a good time to do a tune up and change the plugs and wires on my car. It had stock replacement motorcraft wires (I found that one was definitely bad and had corrosion in the plug boot) and autolite copper plugs. I changed them to NGK copper plugs and duralast wires from autozone. NGK's are good but the stock replacements are a platinum plugI went to start the car after changing these and it now runs like absolute crap. It has a dead miss on at least one cylinder. I was a little ticked and thought maybe I had gotten a bad plug or wireset from autozone. Apparently, that's not the case.

I have tried all combinations putting the old plugs in with the new wires; it currently has the new plugs with all of the old wires except for the one that was definitely bad (cyl 1). I checked the plugs, and they all looked the same except cylinders 2 and 3 looked a little darker like they had been running richer. I switched out the fuel injectors to those cylinders, no change. I have tried switching the coil packs out with ones known to work to no avail. I even did a compression test on the car and it was normal. The only CEL codes it throws are the ones for the rear O2 sensors that aren't hooked up and now the DPFE, which I imagine is a result of the way it is running. I even took the intake off and changed the gaskets, nothing really wrong there. I also cleaned the MAF, and ran the car with and without it connected and there was no change.

I am running out of ideas of what it could be that made it start running like this at the same exact time I decided to do a tune up. I'm going to go rent a noid light and fuel pressure gauge from autozone to cover those bases and possibly switch to a different set of injectors to make sure that's not a possibility.

Please help me out here, I'm almost at my wits end with this car. I need to get it running ASAP.

Thanks,
Rob

OK, did you make sure that you got the wires down on the plugs good? ( I know its a stupid question but I have seen it before) make sure you are also using good wires andn also the you didn't get any water into the holes with the plugs. The next thing is, is that I would just check to make sure that you don't have wires crossed. It sounds that you are thinking too hard about this.

[94tchikinv8]

OK, did you make sure that you got the wires down on the plugs good? ( I know its a stupid question but I have seen it before) make sure you are also using good wires andn also the you didn't get any water into the holes with the plugs. The next thing is, is that I would just check to make sure that you don't have wires crossed. It sounds that you are thinking too hard about this.

I am absolutely 100% certain that the firing order is correct. I know the cylinder numbers and coil pack arrangement. The plug wells are dry with no moisture and I push each boot onto the plug until they "click" and seat properly into place. As stated in the original post, I have the NGK copper plugs in it currently with the motorcraft wires I had on it to start with. I have tried all combinations of old parts/new parts and have not had any success. The slight miss it used to have occasionally is not the same as the complete DEAD miss it has now at all RPMs. I have run copper plugs in this engine for 50-60K miles now without issue.

I have tried all of the obvious stuff; that's why it is baffling me.

-Rob

[Blackout]

OK..... does it throw any codes? Have you changed the TPS yet? Does it miss at idle, under a load, and make sure all vacuums are hooked up and sealed good ? Disconnect your vacuum to your fuel pressure regulator and see what it does. It should peg rich and fuel pressure should go through the roof. Do you have a stock fuel pump still installed and how many miles are on it.

Its frustrating,...I know. But we need some more info.

[graysonracin]

If you get a misfire code for a certain cylinder, try swapping the injector on that cylinder to a different cylinder and see if your miss follows it. Had this happen before, just something to check, good luck, also if you have the 2 coil pack set set up, try swapping them side to side if you can do that on those, i cant remember, see if your miss changes banks on the motor. Good luck.

[02mingryGT]

It is possible it is a plug even though you replaced them. I had a NGK plug take a dump on me about a month ago and after wasting my time switching cops around it ended up being the plug itself. Take one of your old plugs and switch them out one at a time. I would be surprised if your not getting a code like stated above.

[akagreg3]

iv bought plug wires/plugs/tps/alternators all kinds of stuff from autozone/advance auto parts and have them be bad right out of the box, i try and use o'reillys now days if i dont buy it online, one time i bought a set of plugs for a thunderchicken and why i was checking the gap i noticed that one was cracked?

[wolverine8490]

You need to get someone to hook it up to a scan tool. This will show missfires and outputs of all sensors even if there is no CEL. I had a truck one time that had over 25,000 registered missfires on a single cyl and it never threw a CEL. Rear o2's and anything EGR related should not cause a miss bad enough to feel or hear.

Also, are you sure the missifre is not just a vibration? I had a trans mount get out of wack and it made the car feel like it had a miss. Chased that around for quite a while before figuring it out.

Also, what were your compression testing results?