misfiring? kinda stumped

paintballpyro1 · Mar 21, 2012

I have a 96 gt, just hasnt been running right. When i first start it up it idles alittle rough and then smooths out after about 15-20sec. I can hear a slight tick,tick in the exhaust and when i push the gs down the car just bogs down, gets no power and sounds like a massive exhaust leak almost. Ive just replaced the coil packs,spark plugs and wires. Thought it was a ignition problem but not sure where else to go other then compression check which i have to go rent one.
Any ideas?

Superhereaux · Mar 21, 2012

Should we assume the check engine light is on? An exhaust leak, especially a massive one like you said, will throw the o2 sensors for a loop, change up the A/F ratio and dump loads of fuel into the engine. Does the vehicle smoke on start up or WOT?

Does it completly go away after it's warmed up and then run fine? Is it every time or intermittent? Cold startup only? The more details we get, the better.

paintballpyro1 · Mar 21, 2012

No check engine light. It sounds like an exhaust leak but when I push the gas down but doesn't show signs while just idling(plus ive check for leaks,most annoying sound in the world). Doesn't smoke on start up(maybe little from condensation,longtube headers) haven't noticed any smoke otherwise.

The rough idle was just on cold start and then smooths out after. I can't drive the car really cause there is no power and doesn't really wanna move withput the pedal to the floor.

Last time I drove it, it drove fine and idled for 30min no problem but I hammered it on the way back home and now its been constint and can't seem to find the problem.

tricep · Mar 21, 2012

Spark plugs, wires, etc.... ? Time for a tune up.

paintballpyro1 · Mar 21, 2012

Yea just did new coil pack,wires and plugs today and made no difference in how it runs. I bought a compression tester but I gotta take it back since there isn't enough threads to catch in these deep plug wells. Next I may do a fuel filter,clean maf and check plug gap again.

paintballpyro1 · Mar 22, 2012

Hopfully doing compression test today, I'm really hoping that its just low and doesnt have a dead cyclinder. While doing the test are u suppose to relieve the fuel pressure so it doesn't just dumped a bunch of gas in the cyclinders while u crank?

Superhereaux · Mar 22, 2012

Just pull the fuel pump relay and crank away.

paintballpyro1 · Mar 22, 2012

All plugs come out at once or one at a time? I've read both ways.

paintballpyro1 · Mar 22, 2012

All right just did fuel filter.and am about to start compression check. Noticed it idle ok but if I gave it more gas over 1k it started to break up

paintballpyro1 · Mar 22, 2012

well here is the compression test. Not sure if its 100% accurate since this was my first time and i had to do it a couple times cause i missed a step before haha. Ran the tests twice to see how close they were, cylinder #6 is the worst. Where should i go from here? probably rebuild since car does have 195k on it.....

#1 1st-160psi, 2nd-162psi
#2 1st-152psi, 2nd-152psi
#3 1st-155psi, 2nd-155psi
#4 1st-170psi, 2nd-170psi
#5 1st-165psi, 2nd-160psi
#6 1st-120psi, 2nd-140psi
#7 1st-163psi, 2nd-165psi
#8 1st-155psi, 2nd 155psi

hotcobra03 · Mar 23, 2012

are you sure the check engine light works?...i would check for codes even if light isnt on....

sounds like a bad o2..but i dont like guessing

paintballpyro1 · Mar 24, 2012

. Car has longtubes and o/r x-pipe. O2 are installed but turned off with a tuner and has been like that for over 2yrs no problem.

paintballpyro1 · Mar 24, 2012

Ok so i used my code scanner and came up with 2 codes...po353 and po354. igniton coil c primary/secondary circuit malfunction and igniton coil d primary/secondary circuit malfunction. I replaced the coil pack that sits on the right side of the motor(facing car).

I reset the codes and the car idle ok then would start shaking alittle and idling kinda crappy and it kept going back and forth for about 2min and then smoothed out and stopped.

My code reader also does live data so i took some notes down as im not sure where it should be at etc.

abslt tps(%) was at 18.8 and i noticed when the idle would get crappy this jumped up to 50-70%
02s11 volts were at .290 and -14.8%
o2s12 volts were .690 and n/a%
ign adv(deg) was at 25.5 but was at 27
iat (degree C) 16
maf(gm/sec) 7.320

i tried measuring the resistance of the packs which i read should be between .03 and 1.0 which i did both mine and they were over 1 including the new one so either my multimeter is shot or i have it turn on the wrong thing(Rx1,Rx10)

1987stangman · Mar 25, 2012

Simple proof that just because there is no check engine light does not mean there are no codes.

Are you still getting the codes now that you replaced the coil packs? Test the alternator out put.

paintballpyro1 · Mar 25, 2012

No codes yet but didn't run it to long once I reset them. Still idles weird and has that slight tick tick in the exhaust.

joshjwc9 · Mar 25, 2012

If I am right the O2 sensor shouldn't really ever read in the negative. The fact that you saw it at -14.8 means it could be your problem. It is fouled up.

wmburns · Mar 25, 2012

Sorry a little late to this party. Did you fix the exhaust leak? If not, continued parts replacement is just plain silly IMO. Why? Any exhaust leak ahead of the front O2 sensors will allow unmetered air to enter. This will make the O2 sensor "think" the motor is running lean.

The PCM will respond by adding fuel. This results in a rich AF mixture and all the problems that a chronically rich AF will bring. For proof, monitor the LTFT values for large positive values which shows the PCM adding fuel.

Also, a slight tick could be spark plugs backing out. But since the plugs have been replaced, it seems reasonable to me to rule this out.

While you are at it, confirm that the fuel pressure regulator intake vacuum reference line is connected and leak free.

Confirm that the spark plug wires have been routed following the factory layout. Have all factory standoff and looms been used? Are the wires touching ANY metal parts?

Try this old racer's trick. Run the car in a totally dark location. Look for the blue hue of escaping spark. Inspect the wires for white spots which is evidence of arcing.

paintballpyro1 · Mar 25, 2012

Would it matter if the o2 sensors are turned off in a tune tho? If wasn't an exhaust leak sounded that way cause of a misfire on 2 cyclinders. Ill have to check the fuel pressure intake line later today. I did try searching for arching already and didn't see anything, used all factory looms and went over my book and did and traced every plug wire 1 by 1. I think next thing I might well try is taking out all the injectors and cleaning and rebuilding them since I heard the filter in the top can get clogged and they do have 195k on them.

paintballpyro1 · Mar 25, 2012

I do ssee what you mean tho with the o2 the 1 does read half the voltage and so far neg but why doesn't the other read? I'm assuming since it says o2s11 that would be sensor 1 bank 1 which is what side again?

joshjwc9 · Mar 25, 2012

Now it is just the rears that are turned off in the tune correct? I would think about checking the wiring for the passenger side upstream one because of the negative voltage reading that came up..

misfiring? kinda stumped

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