Crazy misfire problem!

[1fast97gsx]

I finally installed an aeromotive afpr after over running my stocker for about a year. At this time I also installed a manual boost controller. I adjusted it as best I could just guessing it's set for around 20 psi and I set my base fuel pressure to 43 psi with the vac. hose off. The car hesitates a lot now when giving it moderate throttle even though my useless blinky a/f guage pegs lean for a second on 2 and then the car start's building boost. At this point the guage pegs rich which I expected and it hits 20 psi. Once it hits full boost it's fine for roughly 1/2 second or so then it misfires badly several times. During this time the a/f guage goes all across the board ( it's usually right on lean when the misfire happens ). It almost feels like fuel cut, but it's not since fc is eliminated in my eprom chip.

For reference : walbro 255 hp, aeromotive afpr ( 43 psi ), maft set for stock injectors, +2 on idle, 0 on mid and -1 on wot. I have a dsmchips chip with 780 injectors compensation anf fuel cut eliminated, that's why the maft is set for 450s.

Please help, I can't figure it out. Couldn't find any boost leaks up to 20 psi.

 

[GVR4592]

What does the datalogger say? What plugs are you using and what gap?

 

[kazzam]

check your spark plug gaps. gap them to .026 and check your spark cables. gap alone should help with missfire

 

[1fast97gsx]

I don't have a working logger right now. PLugs I gapped at .026 ( 6es plugs ) and wires check out fine as well. This problem started right after I installed a mbc and an aeromotive afpr so it's got to have something to do with that.

 

[GVR4592]

Why are you messing with that stuff without a working logger? It's probably a shit load of knock if you just increased the boost with no other changes. What are you using to tune with? Just the MAFT?

 

[dnhieu]

I finally installed an aeromotive afpr after over running my stocker for about a year. At this time I also installed a manual boost controller. I adjusted it as best I could just guessing it's set for around 20 psi and I set my base fuel pressure to 43 psi with the vac. hose off. The car hesitates a lot now when giving it moderate throttle even though my useless blinky a/f guage pegs lean for a second on 2 and then the car start's building boost. At this point the guage pegs rich which I expected and it hits 20 psi. Once it hits full boost it's fine for roughly 1/2 second or so then it misfires badly several times. During this time the a/f guage goes all across the board ( it's usually right on lean when the misfire happens ). It almost feels like fuel cut, but it's not since fc is eliminated in my eprom chip.

For reference : walbro 255 hp, aeromotive afpr ( 43 psi ), maft set for stock injectors, +2 on idle, 0 on mid and -1 on wot. I have a dsmchips chip with 780 injectors compensation anf fuel cut eliminated, that's why the maft is set for 450s.

Please help, I can't figure it out. Couldn't find any boost leaks up to 20 psi.

this sounds to me like a tuning problem not a miss fire for say. get your logger working and see what your trims look like. since your logger isnt working check your spark plugs and see if your running rich as shit. thats the very same problem i have with the MAFT (always running rich).....

hope that helps
david

 

[dnhieu]

Why are you messing with that stuff without a working logger? It's probably a shit load of knock if you just increased the boost with no other changes. What are you using to tune with? Just the MAFT?

with my experience with phantom knock it doesnt make my car buck and kick and break up like the original poster is having. it just simply slows my car down and it feels like its not pulling nearly as hard as it should. every time i seem to look at the logger when the car is doing this it sure is pegged at 43 counts....

 

[1fast97gsx]

I have an autometer blinky guage which gives me somewhat of an idea of where my O2 voltage is although not close to exact. I also have a dsmchips chip that uses my stock boost guage as a knock guage and I get 0 knock during this condition. I'm almost positive it has something to do with the fpr messing up for some unknown reason. Phantom knock won't cause the car to hesitate like crazy and go to basically 0 volts on the O2 sensor, then kick to 1 volt and misfire like crazy at 4000 rpm. Seems like a fuel problem having to do with the fpr, but I'm not sure how I can check it.

For fuel control I'm using a chip with 780 injector compensation as well as a maft. I don't care to get it perfect, I just want it smooth and driveable for now.

 

[1fast97gsx]

I got a logger on it today and played around with it. I had to change the base to 430 injectors and richen up the mid 3 clicks. Wot is set at 1 click richer at this point. It doesn't hesitate anymore and it builds boost good, but still misses under wot at 5000 + rpm. The logger's capture rate sucks because I couldn't see sh!t as far as the miss coming into play. O2 voltages were around .96 at full boost and timing went 12, 14, 16, 17 to redline. Can feel it really miss, but the logger doesn't hint what it could be at all.

 

[dnhieu]

it really sounds like you got a bad tune on the car man. post a log so we can see whats going on. also when was the last time you changed your spark plugs? my buddys 95gsx is always fouling plugs....

 

[1fast97gsx]

Well the tune is way off at this point, however that would have shown up in the datalogs if that was causing the miss. The car seems rich from the stock narrowband, but no way to know for sure. Timing increases normally and O2 voltage stayed at .96 across the board. Could just be bad spark plugs, I will try that tomorrow. Coilpack resistances check out fine, wires are fine too. Maybe just low gas ... the car squats a LOT and the tank is at 1/8th or so. I'll so some more testing tomorrow.

 

[ITSME4G63]

Hmm, so what happens when you adjust the base fuel pressure with the vaccum line in? We did that on my friends car just a coupel days ago, but hasnt really moved it around, adjusted the base fuel pressure to 38 psi with the vaccum line in. Let me know.

 

[1fast97gsx]

Sure the pressure will go up if you do that but you wouldn't know what the true pressure is. You have to unplug the line, adjust, look at your reading, then plug it back in. Generally speaking I hear your fuel pressure with the line off would be the same as your pressure with the line plugged in + 1/2 * manifold vaccum. For a car with stock cams and no leaks it should be right around 9 psi more with the hose unplugged than with it plugged in.

 

[RickClarke23]

im having the Exact same problem but i dont have a FPR or bigger injectors and i think its electrically related...im trying to source it right now.....ill keep you updated and if you fix it please update me but it seems to be the exact same problem and i have a datalogger as well which tells me nothing that would create this problem

 

[spyderturbo007]

What wires are you running and how old are they? I have seen many wires that look fine and are actually the cause of the problem. The spark tends to sneak out the side of the wire inside the spark plug well.

Also, Eclipses are know for leaking oil and capturing condensation inside the spark plug well, which compounds the problem. Might want to check those things out.

 

[RickClarke23]

my wires are new stockies and are only a few months old (like 2) and also i have checked the oil in the spark plug area and there is none....dont know what else to do

 

[RickClarke23]

I have also changed the coil pack, power transistor, plugs/wires, tps, iac, knock sensor (unplugged to see if timing was the issue), and ecu