having some serious "bucking" issues with the Cobra. The car is down for the count

[01SVT2894]

ok, long story short, on a couple of occasions while driving the Cobra, it would just jerk, maybe once or twice and then go away. :dw:

well, yesterday, when i got in the car to go home from work, it started doing it from the get go! it happens in all gears and it did not go away. I barely got the car home. The RPMs just magically drop and rise again. totally sucks. This happens at idle too.

now, i'm mostly a cosmetic guy... so my tech skills are limited, but i'm learning. after talking with a few guys on my own site, i've learned to look at 3 things... Air. Fuel. Spark (before talking to anyone, i thought it was a transmission issue).

Here is what i've done so far guys...
-cleaned the Idle Air Control
-cleaned the EGR valve
-cleaned the MAF
-bypassed the Crane Cams Fireball ignition in favor of the stock set up
-installed new fuel filter

NONE of these things have done anything. I still have new plug wires, new plugs and a new Ignition Module to install.

I'm hoping maybe some of you guys have seen this before and can point me in a specific spot! i'm including a link to a vid of the gauges from tonight...
at idle, you can see that when the RPMs drop, so does the voltage. When the RPMs jump up to around 2, that is me pressing the gas.

here's the vid...
[ame="http://www.youtube.com/watch?v=TCsqGaN2PAg"]YouTube - bad idle[/ame]

 

[01_OXFORD_SVT]

My girlfriends 95 Cobra did this same thing to the point of it being totally un-drivable. She had two issues. (1) The TFI module was slowly taking a dump and (2) the MAF was toast. We tried cleaning the MAF and it worked for a little while but it ended up pooing in the end. Hope this helps man. I spent literally hundreds of dollars on various components before finding these two culprits.

 

[fivestangs]

After watching that video, I would definitly check the TPS.

 

[BlueOvalBolt]

Maybe this will help.

http://www.fordmuscle.com/archives/2002/01/tenpin/index.shtml

 

[93Cobra#2771]

Have you made any changes recently? Any vacuum or exhaust leaks? Pulled engine codes?

 

[01SVT2894]

thanks for the replies dudes...

no changes... other than a few cosmetic things... nothing under the hood.

BlueOvalBolt, thanks for the link, i'll check that out.

 

[04MystiCobra]

Battery posts clean of corrosion?
MAF element in good condition?
Did you wash the engine recently?

 

[93Cobra#2771]

Really sounds like the TFI, or possibly a bad plug or wire - look for arcing inside the plug ends.

Typically the TFI will quit altogether, as opposed to just a miss or whatever. TFI failures are almost always heat related, and often difficult to diagnose.

I'd also check electrical connections in the engine compartment, especially the MAF connector.

You do need to check for engine codes - they can be present even if CEL isn't lit.

 

[fivestangs]

I don't think a bad plug or wire is going to cause the idle to jump up to 2000 rpms and stay there....I've had my fair share of bad wires and plugs and the EEC-IV doesn't make the rpms go up that high just for a miss (at least, not on any mustang I've owned).

I think it's definitely electrical, a bad TPS, corrosion in the black/white 'salt and pepper shaker' connections at the firewall, perhaps a bad (read: broken) ground wire (specifically, the ground wire that connects to one of the intake manifold bolts near the firewall).

If you have a buddy with a *good running* 5.0, borrow his TPS (and perhaps his TFI while you're at it), swap it to your car and see if that does any good.

 

[Hockeyman48]

Its electrical check TFI , clean coil 12 volt wire contacts, check coil, check coil wire to distributor (high voltage) you're losing spark somehow in primary or secondary circuit. Basically check/clean all electrical connections, then start swapping parts if available. Good Luck

 

[93Cobra#2771]

I don't think a bad plug or wire is going to cause the idle to jump up to 2000 rpms and stay there....I've had my fair share of bad wires and plugs and the EEC-IV doesn't make the rpms go up that high just for a miss (at least, not on any mustang I've owned).

I think it's definitely electrical, a bad TPS, corrosion in the black/white 'salt and pepper shaker' connections at the firewall, perhaps a bad (read: broken) ground wire (specifically, the ground wire that connects to one of the intake manifold bolts near the firewall).

If you have a buddy with a *good running* 5.0, borrow his TPS (and perhaps his TFI while you're at it), swap it to your car and see if that does any good.

I don't see where he said anything about the EEC bumping the idle to 2k rpm. From the video, it sounds like its missing on a single cylinder, which leads me to believe a plug or wire is the primary culprit. Bad tps Is a possibility but it really sounds like a single cylinder miss to me.

If you have aftermarket exhaust, look closely at the plug ends on the wires. I had a very similar misfire and found my header had heated the plug end enough to harden and crack the insulation. New wire, some fiberglass wrap and problem solved.

 

[01SVT2894]

no no, i pressed the gas to make the RPMs shoot up to 2000.
the battery is BRAND NEW, not even a week old.. this was happening before i bought a new battery.
i did wash the engine bay... but this happened before i did that.

 

[Hockeyman48]

You might want to also check distributor spout connector wire connections. Pull spout and see if rpm drop/ miss stops. It appears from listening/watching the video that your getting an rpm instantaneous drop not necessarily a miss. If it was my car, I'd be checking as many wire connections possible before I took it to a shop.

Good Luck

 

[670 of 4993]

could it be fuel related?

 

[fivestangs]

no no, i pressed the gas to make the RPMs shoot up to 2000.

ahh..okay, my bad...I thought it did that *on it's own*

 

[Hockeyman48]

Dan When you eventually get this problem worked out let us know what it was!!

 

[01SVT2894]

Dan When you eventually get this problem worked out let us know what it was!!

i'll be sure to. right now, getting ready to install new upper and lower intake gaskets. we'll see what that does.

 

[Red Turtle]

maf is toast.

 

[01SVT2894]

maf is toast.

think so? i don't have a check engine light or anything...

 

[cobr96]

maf is toast.

this is what I what thinking also, just didnt want to say it , cause if he buys a new one and it dont fix it , he would be mad at me.