Massive Misfiring at 4k+ RPM

[yellowkyd278]

Hey everyone,

Over the past week I had my EPROM ECU swapped back with my original stock 98 ECU due to some maintainence problems. So the ECU is on its way to Thomas @ DSMLink but I've come across another significant problem. Once the car hits 4k RPM or above, no matter what gear or speed (it could be at 30 mph is 1st or 95 mph in 5th), the motor starts misfirining like crazy. During the misfiring the car bucks and does all sorts of nasty things - if anyone with DSMlink and a non-95 2g has changed to the EPROM while forgetting to swap the plug coil order, the misfiring sounds simliar.

I've confirmed w/ Thomas that the probability of this being an ECU issue is slim to none since all tuning changes went void once the ECU's were swapped. However, this problem didn't occur while I was running on the EPROM. I'm pretty convinced the issues are independent and it's just coincidence that they're happening at the same time, but there's no way to know for sure yet.

I'm in the process of changing the spark plugs (i'll need to pick up a tool for one plug since it was overtightened on accident during installation) and then the plug wires if the problem still isn't resolved. I really doubt this is the cause though since 1.) the car is fine until EXACTLY 4k+ and 2.) the plugs and wires were both changed a little over a year ago. The plugs are NGK BPR6ES's and the wires were Magnecores if anyones curious. I've never heard of an instance where the plugs fouled out so specifically to a point where they only have trouble firing at a certain RPM and beyond but maybe this has happened to one of you before.

It's also not boost cut and probably not entirely turbo related because I tested the car w/ very high and very low PSI pressures. With the boost turned up to a point where it hits 22 PSI well before 4k, there are no misfiring problems. Same goes when the boost is around 8 PSI - no problems until 4k+.

Sorry for the long post guys, but I just wanted to get all the info across. ANY insight would be greatly appreciated, I'm really stuck and my appointment w/ FFTec isn't for 2 weeks!

 

[4BangR-x]

Id say post back up when you get those plugs changed.

 

[firebirdvert305]

I can almost guarantee its either the plugs or plug wires....I experienced the same exact problem as you....i bought a new set of BPR7ES (ngk's) (gapped to .026) and a new set of accels plug wires and it solved the problem. Look into the basics first before you look deeper ex. coilpack, transistor...o yea btw the problem ended up being the plug wires which was only 2 months old...

 

[yellowkyd278]

I just finished changing the plugs, I was finally able to find a socket that would get down to the last chamber (hail to Duralast!!!). Anyway, the problems still there. Firebird, at what RPM did your car start misfiring?

I guess its off to prostreet or fftec for plug wires tomorrow (I shoulda listened to everyone when they said Magnecores were an overpriced piece of shit). It'll be my third 40 mile trip down there this week

UPDATE: I just swapped the plug wires and the problems still there.

Any idea what it could be now?

 

[Eclipsethis90]

I know you said it doesn't change with boost pressures , but did you do a boost leak check? You'd be amazed with the difference a small pinhole leak can make. I didn't look in you profile but do you have a logger? If so, is timing being pulled? Is there a CEL ? More information would facilitate more help in this case.

 

[mirkoelek]

You have the problem with Crank position sensor bro.... Try what is the easiest first, but I'm afraid You"ll have to take T-belt off and replace motherfuc*er

 

[yellowkyd278]

Thanks for the input guys.

Eclipsethis90: I did a boost leak test on all the significant connections. If it were a leak, it would have to be one which lets out all 17+ psi at once - it's not possible a minor pinhole leak can let out that much pressure. It would have to be a disconnection at a major pipe (i.e. sidemount to LICP etc...) and those were checked as well. All leak tests turned out neg which caused me to rule out a leak as a possible cause of the problem.

My logger was the DSMLink I mentioned. I wish I could have a look at a map of a pull to see exactly what's getting shitted up but as long as the EPROM ECU is being sent to Thomas for repairs, I'm stranded w/out a logger. There is a CEL but I've been living with a CEL ever since I replaced my cat w/ a test pipe without rewiring the rear o2 sensor. Again, I'd like to check DSMLink to see if a code other than the rear o2 sensor is causing the CEL, but I have no means of doing so until I get my EPROM back.

mirkoelek: What makes you think its the CPS? I've never touched it and don't really know what it does. Can you give me more info?

I've received a PM from Laysher91 telling me that it could be the TPS (throttle position sensor) and that he has had the same problem twice. The only difference w/ his problem was that his violent-bucking started at 3.5k+ instead of 4k+. Anyway, he said each time the problem was caused by a TPS gone bad. What's everyone else think about this? I have a remote idea of what the TPS does but can someone clarify its exact function?

As of now I'll start by replacing the TPS, and then possibly the CPS if I get more info about it... Post up if you guys want anymore info or an opinion

 

[mirkoelek]

Thanks for the input guys.

Eclipsethis90: I did a boost leak test on all the significant connections. If it were a leak, it would have to be one which lets out all 17+ psi at once - it's not possible a minor pinhole leak can let out that much pressure. It would have to be a disconnection at a major pipe (i.e. sidemount to LICP etc...) and those were checked as well. All leak tests turned out neg which caused me to rule out a leak as a possible cause of the problem.

My logger was the DSMLink I mentioned. I wish I could have a look at a map of a pull to see exactly what's getting shitted up but as long as the EPROM ECU is being sent to Thomas for repairs, I'm stranded w/out a logger. There is a CEL but I've been living with a CEL ever since I replaced my cat w/ a test pipe without rewiring the rear o2 sensor. Again, I'd like to check DSMLink to see if a code other than the rear o2 sensor is causing the CEL, but I have no means of doing so until I get my EPROM back.

mirkoelek: What makes you think its the CPS? I've never touched it and don't really know what it does. Can you give me more info?

I've received a PM from Laysher91 telling me that it could be the TPS (throttle position sensor) and that he has had the same problem twice. The only difference was that his violent-bucking started at 3.5k+ instead of 4k+. Anyway, he said each time the problem was caused by a TPS gone bad. What's everyone else think about this?

As of now I'll start by replacing the TPS, and then possibly the CPS if I get more info about what it does etc... Post up if you guys want anymore info.

CPS controles your timing pretty much (it tells your ECU when to throw the spark on the sparkplug) , if it goes bad your timing is off, You could be retarded or advanced, mostly retarded....try to smell exhuast ... Does it feel that is runnig rich? TPS controles injector pulse, which i dont think you have problem with .... but its much easier to replace it ... If other people had problem with TPS and they had similar simptomes then its worth checking....I would like to know what caused problem, let us know ..... good luck

 

[yellowkyd278]

Awesome, thanks for the quick reply.

I'll start w/ the TPS since its only 15 bucks on eBay - I'm gonna place the order now.

I just had the 60k but I doubt Satan touched the CPS. How would you go about replacing it, how long does it take approximately, and how much does it cost?

The has been running rich, I was just getting around to tuning it before the ECU died. But I know for a fact on the stock ECU w/out any changes it'll definately be rich. Also, when I changed the plugs they were pretty black and sooty which points at the same thing. I'd smell the exhaust but w/ the testpipe its pretty much always smelled like the smog of death from hell . BTW, your car looks ####in amazing.

 

[mirkoelek]

Awesome, thanks for the quick reply.

I'll start w/ the TPS since its only 15 bucks on eBay - I'm gonna place the order now.

I just had the 60k but I doubt Satan touched the CPS. How would you go about replacing it, how long does it take approximately, and how much does it cost?

The has been running rich, I was just getting around to tuning it before the ECU died. But I know for a fact on the stock ECU w/out any changes it'll definately be rich. Also, when I changed the plugs they were pretty black and sooty which points at the same thing. I'd smell the exhaust but w/ the testpipe its pretty much always smelled like the smog of death from hell . BTW, your car looks ####in amazing.

Thanks bro, I know .....

The sensor is not that expencive, Probably in the range of TPS.... Its harder to replace... I not sure do you have to take T-belt off, probably you'll have to if that is the problem...One more time, check everthing else... before you start messing with it....Wait for DSMLINK, it will tell you for sure...

 

[yellowkyd278]

Sounds like a plan. Doesn't sound like a fun replacement job anyway. I just ordered the TPS. I'll do that, then wait for DSMLink to see if the timings retarded and I'll go from there. Hopefully I'll figure it out sooner than later.

I'll keep everyone updated when I start replacing things.

 

[DiamondStarM]

So did the TPS fix your misfire?

 

[boosted spartan]

i hope that you get it fixed, other ideas how old are your injectors? because my brother had an identical problem on his 240sx and we tried everything, from plugs, wires, cap and rotor, etc. Until it finally hit us, hmm we should try the injectors. Heres what he did, he started the car he then unplugged each wire carefully to see if it started to bug and try to die. Once it did he putted the plug wire back in and did the next one, until he noticed that plug on cylinder #4 when he pulled it out it did do anything, as in like i said the motor tries to bug and die. But it didnt meaning that the injector was clogged and probably ####ed. We changed it and VIOLA! problem solved.

I hope this can give you an idea as to what check before moving onto spending money where its not necessary.

i was misfiring on my last motor pretty bad did a compression test it went like this 165-0-170-165, i had to drive it to school the next day and BOOM! it blew up. my advice to you DONT DRIVE IT! i learned the hard way and hopefully your situation isnt this bad.

GOOD LUCK!

 

[IllEagl]

I had a very similar misfire, it was my coil pack. (Sorry if this was mentioned before)

 

[yellowkyd278]

Sorry for the long delay!

Turns out it was just good old fuel cut. When I got another EPROM in and DSMLink running it ran perfectly once it set the injectors to 650. Simple solution to a bitchin problem

Thanks for everyone's input though you guys are great

BTW, anyone have an idea why I got two warnings for "bumping" myself on this thread?! I don't think I ever posted twice in a row Oh well

 

[DSM90AWD]

BTW, anyone have an idea why I got two warnings for "bumping" myself on this thread?! I don't think I ever posted twice in a row Oh well

Only mods can issue warnings, so if you feel it was unjustified, PM one of them

 

[staticbrainwash]

Floating spring maybe? I don't know if it's been covered, but a weird miss like that is usually only electrical or mechanical. Check your springs though, it might be the problem.

HAHA, whoops, I missed that you found it. Good job getting it all worked out. And good luck.