04 Cobra miss at idle/low rpm bucking

[Jsantana91]

Hey guys since I bought the cobra I been having a low rpm/ idle miss and bucking. It came with the stock plugs I switched them over to the TR6s gapped at 35 that was no help. Next I closed the gap to 32 with some help but it didn't get rid off all my issues. My current plug is the TR6ix at 28 and I still have the low rpm miss and bucking. With my current tune I've noticed that with the tr6 plugs gapped at 35 the car runs lean the tip is white if I close the gap to 32 it runs a little rich at idle. And now with the tr6ix plugs gapped at 28 the car runs rich at WOT. My mods are BBK CAI, catted X pipe, 2.9 pulley. I've had the car checked by a mechanic and everything is working fine and there's no vacuum leaks. My question is what can I do next? The car pulls strong and I can definitely feel that with the tr6ix plugs it revs smoother. I am thinking of installing the tr6ix plugs with a gap of 30 next? If someone could please help me I'd appreciate it a lot.

Some other info is that with the gap at .35 on the tr6 plugs after a few pulls the engine would really start shaking. I haven't felt that since I closed the gap to .32, I haven't tried this with the tr6ix plugs

Here's another thread in which they had the same issue except their problem got fixed by changing to iridium plugs. http://www.svtperformance.com/forums/showthread.php?718422-TR6-Plug-Issue

 

[FortLewisCobra]

In between the blower and the firewall is a vacuum elbow that pretty routinely fails and most people miss it (I did at first). I would check it as that doesn't sound like a plug issue. Mine developed a crack in the side.

 

[Woody6799]

I pmd you but drop the IX plugs and go back to the tr6, then gap to .28. If it persists from there datalog it and contact a tuner.

 

[Jsantana91]

I pmd you but drop the IX plugs and go back to the tr6, then gap to .28. If it persists from there datalog it and contact a tuner.

In between the blower and the firewall is a vacuum elbow that pretty routinely fails and most people miss it (I did at first). I would check it as that doesn't sound like a plug issue. Mine developed a crack in the side.

Thank you for the replies. I've had all the vacuum lines checked with a evap gas machine. But I will check that elbow out tomorrow.

Hey woody I will do that tomorrow also. I've been using BAMA for my tunes. One issue that keeps persistent is that the car always goes back to running a little rich at idle and I believe also at the end of the RPM range. According to BAMA from the datalogs I've sent them

The car has 57k miles

 

[Woody6799]

Nobody with serious mods uses BAMA... there is a reason for that.... :beer:

 

[Jsantana91]

Nobody with serious mods uses BAMA... there is a reason for that.... :beer:

I believe you man just thought I'd give them a chance. Although the car used to have a Diablosport tuner with the same issue so I switched over to SCT X4 with a BAMA tune. My next things to try is the TPS voltage with a volt meter and disconnect the DPFE sensor and try everything you've told me. The misfire is coming from both tail pipes. I've not done a compression check if that matters

 

[Jsantana91]

So I pulled out my plugs and this how they look. I also did a compression check and these are the numbers I got for the driver side starting from the bumper to the firewall 155 155 154 163 the passenger side starting from bumper to firewall is 190 179 177 180

Any help is appreciated. The plug gap is .28

 

[Woody6799]

Looks like carbon fouling... do you have an AFR gauge? Can you datalog what your afr is at? or you may need a hotter plug... did gapping the tr6 to .28 help at all? Are all the plugs like that or just one?

 

[Jsantana91]

Hey woody I'll pm you a datalog file of just the idle in a bit see what u think. I do have a AFR gauge that I can datalog. All the plugs are like that I kept the tr6ix gapped at .032 this time and idle seems better.

 

[Jsantana91]

low rpm bucking is gone, new tune with egr shut off. low rpm misfire is still present.

 

[jblood37]

Have you checked connectors on coil on plugs? Does sound like a vacuum leak, but I saw you checked that. I wonder why your driver's side numbers for compression test are so low compared to passenger side.

 

[96gt02]

Do you have the stock aiR intake still? Try reinstalling that with the maf screen if so, turbulence could be the cause of your issues

 

[Jsantana91]

Do you have the stock ait intake still? Try reinstalling that with the maf screen if so, turbulence could be the cause of your issues

Have you checked connectors on coil on plugs? Does sound like a vacuum leak, but I saw you checked that. I wonder why your driver's side numbers for compression test are so low compared to passenger side.

Unfortunately I don't have the stock air intake.

Yeah I installed new COPs, I'm having a fueling issue I believe after talking to woody. Yeah I don't know why it's so low? I forgot to relive the fuel pressure when I started the compression check doubt that has anything to do with it though.

Thank you guys for your input I'll keep this thread updated as soon as I find my problem.

 

[jblood37]

Yeah, if you can datalog woody should fix you up quick. Datalogging is the key. I suggested looking at your cop connections bc my car was doing like yours, but worse, and replacing a broke connector fixed it. My car would go lean as hell all the sudden. I figured with no spark on a cylinder, the car would run rich, but I was wrong. I'm thinking that maybe if the car sees no spark on a cylinder it stops that injector from firing too. Could be way off base though haha. I'll be tuning in to see what woody finds.

 

[Jsantana91]

Yeah, if you can datalog woody should fix you up quick. Datalogging is the key. I suggested looking at your cop connections bc my car was doing like yours, but worse, and replacing a broke connector fixed it. My car would go lean as hell all the sudden. I figured with no spark on a cylinder, the car would run rich, but I was wrong. I'm thinking that maybe if the car sees no spark on a cylinder it stops that injector from firing too. Could be way off base though haha. I'll be tuning in to see what woody finds.

Yeah he's awesome man lol. I do have one COP the last one on the drivers head in which the connection is broken but I put tape and it's super tight I check it every time and it's still connected gotta fix it tho. Lol thanks man for your reply, no matter what it's a useful tip to know. I also thought it would go rich. Will post as soon as I get a chance to datalog.

 

[jblood37]

Dude fix that connector! Go to a junk yard and get one from a focus or something and repin it. Very easy fix. I had mine taped too.

 

[Jsantana91]

Dude fix that connector! Go to a junk yard and get one from a focus or something and repin it. Very easy fix. I had mine taped too.

Lol you know the struggle haha. I will fix it one day it's on my to do list, next to the VMP 2.3

 

[Jsantana91]

Quick Bump, spoke to BAMA and they think I have maybe a leaky injector, the fuel octane might be a problem so they want to start lowering spark degree, and they also think that my drivers side head compression numbers are to low and that maybe the headgasket is starting to go out. If anyone has any info on the compression number please chime in. Thank you

PS I did the compression on a cold block with the fuel pump fuse pulled out, starting with the drivers head. BAMA told me the engine should be warm/hot with the throttle body open? So I may retry that.

 

[Woody6799]

So I pulled out my plugs and this how they look. I also did a compression check and these are the numbers I got for the driver side starting from the bumper to the firewall 155 155 154 163 the passenger side starting from bumper to firewall is 190 179 177 180

Any help is appreciated. The plug gap is .28View attachment 64149

The plug is showing me by the deposits right on the edge of the threaded body that your car is slightly fat at idle

 

[Jsantana91]

Bump still have no fix for this problem. Tried race fuel with no fix. At this point I don't know what it could be. I'm going to be taking it to a knowledgeable shop around my area.