1993 Cobra Misfire

[93_SVT_Cobra]

I have a '93 Cobra which has been in storage for a couple of years. Although it has been in storage, I started the car on a regular basis up until about ten months ago. So, the car has been sitting for about ten months. A few weeks ago, I decided to take it out of storage and I found that the fuel pump had stopped working. So, I replaced the fuel pump and filter along with plugs, wires, oil and filter. I purged all of the old fuel that I could. So now, I am been experiencing a partial throttle misfire. If I am in a higher gear running around 1000 - 2000 rpm, the engine will misfire until I down shift and increase the throttle. Once I am running around 2500-3000 rpm, the engine doesn't seem to miss... Under a WOT condition, it seems to perform like a Cobra should. From what I have noticed, it does seem to be running a bit rich. Yesterday, I was sitting at a stop sign waiting on traffic. I sat there for a bout three minutes and when I pulled off from the stop sign, the engine bogged really bad, and backfired through the exhaust. The car has 78k on it. The engine has stock internals, stock GT40 heads, stock cobra intake, stock 65mm TB. It does have a set of BBK shorty headers and an off road x pipe with flowmaster mufflers/tailpipes, and also a K&N filter. I have recently removed the clutch fan, and added a electric fan and a 3-row Aluminum Radiator. The smog equipment has been removed.

Since I started experiencing the misfiring, I have cleaned the EGR valve, MAF Sensor, IAC valve, and the throttle body. I still have a misfire.... Any help or advice out there will be greatly appreciated!!!

 

[Hockeyman48]

Replace plugs,check plug wires,check/clean injectors and check TPS voltage.Probably one of those items.

 

[93_SVT_Cobra]

Yeah, I checked the wires last night, which are newly installed. I could not see any of them breaking down. Do you think it is possible a plug or two is fouled even though they are new? I was headed to the injectors next. I ran a bottle of seafoam through it.... Still missing. When you say clean the injectors, do you advise that I should remove the rail and clean them all individually? Any good advice on cleaning the injectors and what products are good?

 

[buddha93]

The bog and backfire was due to it loading up really bad, and then igniting the unburned fuel through the exhaust. Now the only question is why.

It really sounds like an ignition thing to me but it sounds like you've addressed all of that. I personally don't think you have an issue with an injector from what your describing. The only thing I may have checked out would be the TFI module at this point, just to eliminate it from the equation.

 

[93_SVT_Cobra]

I really appreciate all of the good advice! I will take a look at the TFI also.

 

[fivestangs]

Originally I typed in all of this: "You might want to try to do...what do they call it now....a "cylinder balance test" I believe.... it's a self-test built into the EEC-IV that is supposed to help pinpoint what cylinder is misfiring....the procedure to do it should be somewhere on the internets (sorry, I don't have a link or anything)"


..then I thought about it some more.....you should try to get a mechanical fuel pressure guage on that thing and verify your fuel pressure is correct. Too high or too low will cause the car to load up on fuel.

 

[93_SVT_Cobra]

To test the fuel pressure, should I just connect the gauge to the port near the fuel rail on the passenger side? Also, In what range should I be in? It is a 190 lph pump, stock rails, 24lb. stock injectors... Thank you for the great advice!

 

[93_SVT_Cobra]

Also, if the pressure is too low/high, how can I solve the problem? The stock regulator is not adjustable, is it?

 

[fivestangs]

The pressure with the car running at idle with the vacuum line connected will be around 32-34psi I believe..I think it will be around 38psi with the line disconnected (at idle). By 'way off' I mean like 20psi (for the low side) or 50+psi (on the high side)...and you're right, the factory regulator is not adjustable, so you would need to replace it.

The reason I brought up the fuel pressure is that I have a kirban adjustable regulator on mine. When I don't drive my car for a while (like, say, 3-4 weeks), it has a tendency to 'stick' and my fuel pressure is off. Since you stated your car has been in storage for a good bit of time, I'm wondering if the rubber diaphram in the regulator has hardened or developed an internal leak or something of that nature.

And yes, use the port on the fuel rail.

Keep in mind that a guage that you can actually see while driving is preferable to the ones that screw directly into the test port....but if that's all you have, you'll at least be able to check the pressure at idle.

 

[93_SVT_Cobra]

Thank you! I wil take a look at this tonight and see what I have...

 

[WillyB93]

Besides that I would check the timing and at least do a visual look at all the plugs. You may have cracked one putting it in and didn't realize it, or do may have one fouling up its not firing.

 

[fivestangs]

any luck?

 

[93_SVT_Cobra]

I pulled the injectors, cleaned them, soaked them in Sea Foam and put them back in this morning. I also replaced the fuel pressure regulator. I checked the timing again and it is set at 10* BTDC. I started the car, let it idle for fifteen minutes while checking for any fuel leaks. I then drove the car and the missing is still present..... my current instinct is to replace the spark plugs (new three weeks ago) or the ignition module. But i have heard the ignition module is like a light switch, it either works or it doesnt.... what do you all think?

 

[WillyB93]

I have seen ignition modules be tepmermental, like I said be fore check the plugs and make sure you didn't crack one putting it in. Ignition modules are decent price so it wouldn't hurt to try one, they normally act up in high heat or cold weather.

 

[fivestangs]

It's probably a plug...the ignition modules are usually working or not (from my personal experience).

 

[buddha93]

Have you checked the cap and rotor? I didn't see that in your post anywhere.

 

[93_SVT_Cobra]

I have replaced the cap/rotor with an MSD version. Also, i have a MSD coil. I am going to change the plugs tomorrow and see if this helps... if not i am going to start looking toward egr, o2, tps, tfi, iac, etc.... trouble is i havent any codes flashing. Does anyone know if you can still determine which cylinder(s) are misfiring without having a code flash? Also, how do you go about determining this?

 

[buddha93]

To my knowledge, you can't even identify the bank, let alone the cylinder. Even though the MIL isn't on, run a Quick test using the Self Test Output. You can either get a tester, or just run a jumper wire and read the flashes of the MIL on the dash and see what it flashes.

You can run the test with the key on engine off, and with the engine running. I'll bet it pulls a few codes and might tell you what's going on.

 

[buddha93]

I found this over on the Corral. No pics, but goes into more detail on how to do it:

EEC-IV Testing

 

[Farmer-Ted]

Nevermind, you already did.