Chasing Fairies
 

93 LT1, no codes present.

Alright guys, been a while since I posted, mostly because of work and trying to chase down a misfire in the car. Initially, I thought it was the pump finally kicking it. Replaced the pump with a new Walbro 255 that I bought long ago. Pressure still holds about 40 psi, regardless of engine speed. I haven't yet checked to see what the pressure is when it misfires, but I will be doing that once I get the chance.

So after the pump didn't help, I turned to the next logical choice (aside from the fuel filter, which is a brand new AC Delco), the FPR. Replaced it and it didn't change anything. I've checked the injectors, none are leaking and using a long screw driver, I can hear them all pulsing.

Looked next towards the ignition. The wires are less than a year old, as well as the plugs. Thought maybe it was the opti going because the one in there was a cheapo reman'd one. So ordered a MSD one because I've heard mostly good things about their Opti. Got it torn apart and luckily I did it because the reman'd one had lost a screw on the rotor and the other one was backing out and a piece of the button broke. Any ways, the new opti helped a little, but the car still misfires at idle, and under light throttle. Any thing over roughly 2500 rpms and it's fine.

The spark plugs are next on the list even though their less than a year old as well, but I figure I might as well start with the least expensive thing next unless any one has other ideas to point me otherwise. I'll have to pull the current plugs and see what I have, but till then, I'm all hears.

check the coil wire on both ends, i had a issue once and the coil wire was roasted on one end. metal was eaten off completely.

Thanks Craby. I looked at the end going to the opti when I installed it, and seemed fine, but I haven't looked at the one on the coil. I'll try and get a video tomorrow to give an idea of exactly what I'm dealing with here.

I've had numerous ideas thrown at me, from a bad ground to not enough voltage at the pump.

So, I think I found part of the problem. I'll get a picture up of the plugs, but they were not in the greatest condition, and I'm not sure why even though they're only a year old. I also found that wire for cylinder number 6 was burned almost all the way through. Still has a slight misfire, but I'm thinking that's still the wire because I've only done a quick fix on it.

The pump still bothers me though. It stays at 40 psi, even at full throttle.

fpr is not working right, pressure should change with throttle. pull the fpr vacuum hose at idle to it and see if the pressure changes.

FPR is brand new. I'm still chasing this misfire and it's getting to the point where I don't want anything to do with the car.

New wires
New opti
New plugs
New fuel pump/filter
New FPR

I'm running out of ideas here. I checked the injectors and the engine gets worse if I unplug one at a time (as it should). It tends to stumble under load as well, mostly in OD. If I down shift or floor it, it will stumble for a second or two and then run like a raped ape.

i went through 3 fpr's before i got a good one. are you using a adjustable fpr

pick up a spark checker and make sure you have good spark. pull 02 sensors and see if there fouled. pull spark plugs,,, ugh,,, and see if they tell you something. test evap, test fuel pressure with gas cap off,,,, my vent was not working right and pressure would go way up on its own when tank pressure rose. I'm just running through some off the wall ideas.

I'm willing to take anything at this point. It's just down right annoying because there will be times where I'll be driving (I will try and get video) and you can just hear it misfiring and struggling to get up it while other times, she'll just cruise on.

I will check the FPR again, and it's a stock BWD replacement, and will try fuel pressure with gas cap off. I will pull the plugs this thursday and see what they say and see what kind of spark I'm getting. I would think the spark should be good, at least up until the plug with the new opti and wires. Coil is original as far as I know, so it is probably due for a replacement as well. 02 sensors are fairly old, so I will look at them and possibly pick up a new set.

The only good thing to come out of this is it is pushing me to get my Jeep done and on the road so I can pull the car back off and have some well deserved work done.

Thanks Craby for all the help.

Finally found it and not sure how it was missed the first time. Anyways, I had off thursday so I pulled the car in the shop and tore the TB off. Pull out the IAC valve and cleaned it well and made sure it operated has intended. It was stuck when I pulled it out causing my car to always idle a little high. So fixed that, checked the readings on the TPS, IAC, coil, and IAT with a multimeter and they all checked out fine. Pulled the plugs and all of them looked good with a brownish/gray tint to them.

Bought new O2 sensors, installed them and took it over to the bank to pull some cash to go to the local carnival. While waiting for the ATM to dispense my cash, I could here a real fast tick,tick, tick. Turns out I had a wire that was burned in two spots. It's funny cause I popped the hood multiple times while it was misfiring and never saw arcing. Anyways, replaced that wire and put some heat tape on it and tucked it out of the way so it wouldn't get burned again and now she runs just as good as the day I bought it.

Morale of the story, check the simple stuff more than once.