Some mis-firing input please.... - Page 2

93Cobra#2771 · 07-12-2005, 12:25 PM

The MAF you swapped with - was it a known working MAF off a working car? If not, it does indeed sound like classic MAF issues.

Any detonation occuring at the same time?

coupe · 07-12-2005, 12:43 PM

Not really detonating. Just sputtering EXACTLY like timing or a vacuum leak. The MAF was a stocker from a working car. Checking into the vacuum & distributor today.

93Cobra#2771 · 07-12-2005, 12:48 PM

In that case, I'm leaning towards a vacuum leak as well...

Disney Lincoln · 07-12-2005, 02:37 PM

A vacuum leak will usually show up at idle as well, and cause a rough/missing idle.

Try something else. Get it to misfire/bobble like normal, then put it into open loop and see if it still exists. Easiest way to do that is just go WOT when it's happening.

Wicked · 07-12-2005, 04:04 PM

[Quote=Coupe]
Give it more gas (ie: roll into it hard) and it is not noticable...

Still a bobble/sputter up to 2400...unless you're about 1/2 throttle or better.[/Coupe]

Sounds like he has already done that which is why I suspected vacuum leak...there is no vacuum at WOT.

Italian LX · 07-12-2005, 05:56 PM

Quote:

Originally Posted by Wicked

...there is no vacuum at WOT.

That doesn't matter when it comes to vaccum leaks. What makes a leak so problematic is that it allows unmetered air into the motor. Even though there is no vacuum at WOT, it still is allowing air into the intake that hasn't gone theough the MAF which can cause issues.

However, I'm sure it is unlikely to be noticable since a vacuum leak is usally very small compared to the 58+mm opening into the intake.

Disney Lincoln · 07-12-2005, 09:16 PM

If it goes away at open loop then I wold suspect something in the 02 sensors or harness.

Wicked · 07-12-2005, 09:31 PM

Quote:

Originally Posted by Italian LX

That doesn't matter when it comes to vaccum leaks. What makes a leak so problematic is that it allows unmetered air into the motor. Even though there is no vacuum at WOT, it still is allowing air into the intake that hasn't gone theough the MAF which can cause issues.

Yep, thanks, I know how it works.

My point was also that the small leak compared to the TB will be negligible at WOT.

Italian LX · 07-13-2005, 05:28 AM

Quote:

Originally Posted by Wicked

Yep, thanks, I know how it works.

Sorry, I couldn't tell by your post.

Quote:

Originally Posted by Wicked

My point was also that the small leak compared to the TB will be negligible at WOT.

Well, maybe next time you should word it that way.

coupe · 07-13-2005, 07:29 AM

Found a bad ground for the MSD-type (other brand) ignition...STILL didn't fix it! I replaced distributor with a known working piece...Still didn't fix it. Cannot find vacuum leak; it's a cobra intake with only a small vacuum tree under the plenum. Seems to be fine. The 2400 RPM thing has made me think the ignition box...but the stock ignition does not fix anything. Overall; changing these things has slightly improved the problem...but not repaired it...I'm thinking O2 now...

Or maybe plug gap??? Checking it next.

07-12-2005, 12:25 PM	#11
93Cobra#2771 The Kocky One Join Date: Dec 2004 Location: Yeah, but those cutters won't bust any walnuts.â„¢ Posts: 1,948	Re: Some mis-firing input please.... The MAF you swapped with - was it a known working MAF off a working car? If not, it does indeed sound like classic MAF issues. Any detonation occuring at the same time? __________________ *For Sale: Reproduction Window Stickers, 87+ Mustangs, Cobras, Lightnings, and HD F150!* Richard White 93 Cobra Kocky will be back!

07-12-2005, 12:43 PM	#12
coupe Super Moderator Join Date: Dec 2004 Posts: 6,313	Re: Some mis-firing input please.... Not really detonating. Just sputtering EXACTLY like timing or a vacuum leak. The MAF was a stocker from a working car. Checking into the vacuum & distributor today. __________________ " If you can't explain it simply, you don't understand it well enough. " - Albert Einstein

07-12-2005, 12:48 PM	#13
93Cobra#2771 The Kocky One Join Date: Dec 2004 Location: Yeah, but those cutters won't bust any walnuts.â„¢ Posts: 1,948	Re: Some mis-firing input please.... In that case, I'm leaning towards a vacuum leak as well... __________________ *For Sale: Reproduction Window Stickers, 87+ Mustangs, Cobras, Lightnings, and HD F150!* Richard White 93 Cobra Kocky will be back!

07-12-2005, 02:37 PM	#14
Disney Lincoln Senior Member Join Date: May 2005 Posts: 290	Re: Some mis-firing input please.... A vacuum leak will usually show up at idle as well, and cause a rough/missing idle. Try something else. Get it to misfire/bobble like normal, then put it into open loop and see if it still exists. Easiest way to do that is just go WOT when it's happening.

07-12-2005, 04:04 PM	#15
Wicked Friends Join Date: Dec 2004 Location: Pell City, AL Posts: 1,371	Re: Some mis-firing input please.... [Quote=Coupe] Give it more gas (ie: roll into it hard) and it is not noticable... Still a bobble/sputter up to 2400...unless you're about 1/2 throttle or better.[/Coupe] Sounds like he has already done that which is why I suspected vacuum leak...there is no vacuum at WOT. __________________ 2001 Cobra 'Vert Procharged and Intercooled 455rwhp/441rwtq Work Car: 2005 Honda Odyssey 400 whp Turbo V6, 6-speed, full cage, H&R Suspension, Brembo Brakes

07-12-2005, 09:16 PM	#17
Disney Lincoln Senior Member Join Date: May 2005 Posts: 290	Re: Some mis-firing input please.... If it goes away at open loop then I wold suspect something in the 02 sensors or harness.

07-13-2005, 07:29 AM	#20
coupe Super Moderator Join Date: Dec 2004 Posts: 6,313	Re: Some mis-firing input please.... Found a bad ground for the MSD-type (other brand) ignition...STILL didn't fix it! I replaced distributor with a known working piece...Still didn't fix it. Cannot find vacuum leak; it's a cobra intake with only a small vacuum tree under the plenum. Seems to be fine. The 2400 RPM thing has made me think the ignition box...but the stock ignition does not fix anything. Overall; changing these things has slightly improved the problem...but not repaired it...I'm thinking O2 now... Or maybe plug gap??? Checking it next. __________________ " If you can't explain it simply, you don't understand it well enough. " - Albert Einstein