DFWGrant

iTrader: (6)

Does anyone have any ideas of where to start with some issues I've been having?

First issue: Rough idling, I had it hooked up to the computer and it showed that it was misfiring intermittently on all cylinders basically. The car will run fine, it just runs like crap..and when you try and get on it from say around 45+, it basically stalls for a few seconds and then goes.

The o2's were checked and they said they registered fine.

I've already put new plugs/wires on it, new MAF, new MAF sensor in the lid. It's not de-screened. I've also changed the fuel filter.

It's an '02 with 30,353 miles on it, basically bone stock, with SLP MAF, SLP lid, cut-out.

Any help would be appreciated!

Grant

Jenns01TA

Hmmmm okay so you are getting an intermittent misfire on all cylinders. We know that is going to be from air/fuel, loss of ignition (spark) or compression. So, starting with the easy stuff and working up later: you have already nearly ruled out an ignition issue in the cylinders with the replacement of plugs and wires. If an injector was going bad, it would be isolated to a single cylinder, unless you got contamination in the tank which was able to spread and foul all 8 injectors. If your injectors have fouled (it happens - happened to the Cobra) you would be encountering a lean misfire in all banks.

You can also get a lean mixture misfire on all banks from low fuel pressure from a weak or failing pump, a clogged fuel filter or a leaking pressure regulator.

Intermittent misfire on all banks can also be caused by air leaks. Since our cars do not have an EGR system, we can rule out a failure or leak in the EGR system. lol :woot: Two down.

If it is due to compression loss then we can look for failing head gasket. It would not be a blown valve since that would register in a single cylinder or adjacent cylinders if the failure was between them. Have you noticed if the engine is running hotter than normal when this occurs? If the engine is overheating or losing coolant, then we can look to the head gasket as the problematic turd.

Hope this helps. Look for the easy stuff first and if all this returns negative then we go to electronic calibration issues.

Good luck.

~Jenn~

DFWGrant

iTrader: (6)

Hi Jenn - thanks for the response.

To answer some questions:

I replaced the fuel filter, it was happening before and still after.

The weird thing is, in october when it was still stalling at high speeds when I floor it, we went to our local dragway and it ran very good times.

Also, when I dyno'd it, it dyno'd at 309rwhp and 330 rwtq to the wheels, with a broken lid (since been replaced) and a cut-out. It was also 108 in the shop..the weird thing about it was unlike my 99z, around 3500rpm, it was showing running really rich, but around 4500 it was perfect the rest of the way up. Consquently, with the exact same mods as my 99, with basically same mileage, it made less.

I've never got an SES light or anything like that though, always 93 octane.

Jenns01TA

Roger that - Rich misfire. Like I just placed in the other thread to the member having misfire issues on banks 5 and 7, these are never easy to diagnose. Sometimes linked articles like this can be of use. So peruse through here and see if it helps.

I hope it does. Let me know if it doesn't and we can brainstorm a couple other things.

http://www.aa1car.com/library/misfire.htm

DFWGrant

iTrader: (6)

Thanks, Jenn - that read was helpful, I'll follow-up with a few of the points illustrated in that read and see what I find.

Take care,

Grant

DFWGrant

iTrader: (6)

So, I did some testing today to see if I could better explain the lack of power issues.

When I'm accelerating mildly (not stomping on the gas, but steadily increasing the throttle) I don't really feel like I have any power loss, it pulled all the way to 130mph with no problems.

HOWEVER,

Say if I'm driving at around 40,50,60mph and then floor it, it'll immediately shoot the RPM's up to redline like it is supposed to, and then it'll start to go and then just stall for about 4-5 seconds and then start accelerating.

Does that sound like maybe there's an issue with too much fuel, or not enough fuel?

Thanks in advance.

shaun

could be to much fuel.my car has a catback/lid/ported maf/tune. and before the tune the car used to feel like it would lose power at higher rpms and at half gas it would feel like a slight miss. then i had the car tuned and it would be fine till about 3500 rpms then the a/f ratio would jump to about 17 so i would run real rich at higher rpms. i had it tuned and its now at 13 for the whole power band. and the wierd stumbling is gone.
try you factory maf and see if that helps.

DFWGrant

iTrader: (6)

I guess I should say it was happening before I bought the new MAF. I de-screened and ported my old one..it may have happened then, however I completely replaced it with the SLP one.

Jenns01TA

Have you checked to O2 sensors? They may be starting to fail and the conditions in which the fault occurs is not within the monitoring parameters of the OBD to report it as an O2 sensor issue. Just a guess.

DFWGrant

iTrader: (6)

How would I check them without having to replace them? I don't mind replacing them, but just curious.

Thanks for your continued help.

Jenns01TA

Linkie-link.... lol

http://www.autozone.com/servlet/UiBr...3d8004f602.jsp

tomustang

Did you get a tune for the MAF?

GMRL

Can you record a log with whatever your using to scan the car?

Have you checked the MAP sensor and TPS?

Seems it only does it under extreme load when the throttle is wide open and vacuum is zero right?

DFWGrant

iTrader: (6)

Yes, when it was hooked up to a scanner, whenever we put load on the car and even during just idling, it would randomly show misfire on basically all cylinders.

When I'm driving the car, if it's a smooth, even acceleration, I can basically go as fast as the car is capable of, with no apparent issue.

However, if i'm driving the car around 45+ at a constant speed and then floor the gas, it stalls for a few seconds or more and then starts accelerating, almost every single time. I tried it around 10 times in a row and 6 out of the 10 showed the same issue.

I don't have any logs, it was just some scanner a buddy of mine used from his work that plugged in below the dash.

Thanks for the help.

qwk93ta

iTrader: (13)

it's got to be the opti..... j/k

DFWGrant

iTrader: (6)

Interested in hearing more if you were going somewhere with what you typed out.

Thanks.

GMRL

Well, check the throttle position sensor for proper operation. On my scan tool, with the key on-engine off, with the throttle closed it will read 0% and as I steadily increase throttle angle. It will go up all the way to 100% when the gas is to the floor. I would check for proper operation, if there is something wrong, your readings may be off since you say it only does it at WOT.

Also, under WOT, vacuum should be right around 0. So depending on what value your scanner presents MAP data, check that for proper readings corresponding with whatever it should be at. At idle a stock cammed car should pull around 16-18 inches of vacuum, and decrease as you open the throttle.
Assuming the MAF is working properly since you replaced it. The TPS and MAP are what would calculate load and may be casusing the problems you described.
Good luck.

Toes

iTrader: (1)

Have you tested your fuel PSI yet?

food nd cars

try injector cleaner and get rid of that k&n, oil in your intake system = problems, i trust fram paper filters more than oil based filters, dont go wasting all your money just yet.

letsrun97z

iTrader: (7)

*Ahh damn just missed above GMRL was talking about map and tps (Read slower lol)*

MAP sensor? issue my pig tail was bad on mine and couldnt figure out for the life of me. my neighbor has a tech 2 and with the car off he was wiggling wires and all of a sudden me moved the map wires and bam the needle spiked