Misfire. A pattern?

[911teo]

This past weekend it was the second time that my check engine light (the yellow one) came on.

The first occurrence was at the track. Light came on at full throttle and the engine cut back.

I obviously ended the track day early, brought it to Ford where they diagnostic showed misfire at Cyl #2 and #6.

At Ford they changed both the coils and plugs and sent me away.

This past weekend whilst driving on the Autobhan it happened again...

I was chasing a Gallardo and there was traffic so we were both pushing hard when the traffic would clear...

Well the light came on at 100% throttle and 170mph (as per diagnostic).

This time the light stayed on even after I let the car cool off....

The following day (after the 3rd start with no fault as per the manual) the light went off.

At Roush (in the UK) they again detected misfire on cyl #6.

They are going to change coil and plugs again, but I wonder if it could be something else.

Injectors maybe?

What do u guys think?

 

[nota4re]

The likelihood that it was and is again a coil pack may be remote now - but it was probably a logical move with your first symptom. Make sure the plugs are correct for the GT and that they are gapped correctly. If too large of a gap, high boost pressure can prevent a good arc and subsequent cylinder burn.

However, I think your suspicion of an injector problem could be on target. I would replace both injectors on cylinder 6. Alternatively, you can swap injectors from an adjacent cylinder. If the fault moves over to that cylinder, then you know it is an injector problem.

 

[ThatPhilBrettGuy]

Did it actually miss or was it just the light?

 

[BlackICE]

Besides the coils and injectors themselves, it could be the electronics driving thoses devices. The coils I believe are driven from the ECU and the injectors from the injector control module. Good luck, you are in good hands with Roush.

 

[911teo]

It did actually miss.

It felt like power was cutting off and the light was flashing on both occasion.

This time though the light stayed on even after a cool down period.

Now the car runs great (self fixed? light is off) but I am heading to the Ring next week and would not want for it to happen again.

I will follow nota's advice and swap the injectors to see if we can track the fauld down.

 

[ThatPhilBrettGuy]

Hhhmmm, the reason I asked about the miss is that mine did something like this, but more extream. It happened under full load and once the miss started any touch of the throttle resulted in rough running.

It happened in Denmark at the time. I took it to a Ford dealer and with Roush on the other end of the phone and the garage ODBII system plugged in, we reset the ECU totally clearing all the adaptives.

Since then it's been fine....

 

[FordFanStan]

What type of mods do you have? Pulley? Tune? ... Stan

 

[nota4re]

It happened under full load and once the miss started any touch of the throttle resulted in rough running.

The ECU assigns differnet severity to different faults and conditions. When the ECU believes that it has a fault with a critical input that compromises it's normal closed-loop operation, it reverts to a pre-programmed "limp mode" where input from outside sensors is ignored. In limp mode, the car will feel terrible and will generally run like crap. The ECU is in engine preservation mode (first priorirty) but still allows running - enough to get you out of a bad neighborhood (second priority).

Less severe faults will be recorded but will not trigger limp mode (on the first occurance). There is also logic within Ford ECU's (as in almost all other OBDII compliant autos) that will allows the ECU to turn off the check-engine light after so many successful re-starts without a fault occurence. Other codes, like airbag codes, for example, cannot even be reset by disconnecting the battery. Suffice to say that there's a lot going on in the electronics of a modern day vehicle.

 

[fjpikul]

Why can't it be just some bad gas? Run some injector cleaner through your next tank of gas.

 

[911teo]

Bad gas... MMMmmm I doubt it as it would have happened earlier.... we were with less than 1/4 tank left.

No mods... the car is completely stock.

Roush now cleared and reset the ECU. We'll see next week. I am planning on pushing it a little on the way to and at the 'Ring...

 

[BlackICE]

Bad gas... MMMmmm I doubt it as it would have happened earlier.... we were with less than 1/4 tank left.

No mods... the car is completely stock.

Roush now cleared and reset the ECU. We'll see next week. I am planning on pushing it a little on the way to and at the 'Ring...

Whipple doesn't recommend pushing the limits of the car without at least 1/4 of a tank. But if you were sucking air instead of gas I would think you would get a low fuel pressure code.

 

[FordFanStan]

First I would run injector cleaner through your system. Adding a bottle of cleaner to a tank of fuel will not clean your injectors, it will not be potent enough. You need to find a shop, (dealerships should have them), that have a injector cleaner setup. It simply has a bottle that you fill with fuel system/injector cleaner (Berryman B12 Chemtool), with one inlet for compressed air with a regulator, and one outlet for the liquid to attach to your fuel rails schrader valve. When doing this you must activate your fuel pump inertia switch so the vehicle will only run on the supplied bottle of cleaner. After it uses all the fluid, then reactivate your fuel pump interia switch disconnect the tool, and done...

Even though stock, you may also want to think about running a NGK Tr6 or Tr7 plugs. They are one and two heat ranges colder accordingly, and they may help you from receiving spark blow out if that is what is occuring. I would have someone datalog during your short WOT blasts... Stan

 

[Mase]

What fuel are you using?

98 RON?

I often visit UK to tune cars several times a year, and I've noticed the fuel is quite different from what we have over here in the states.

I had a clients car shipped to me from the uk to florida. did a full build on it, and tuned on the gas we have here in florida (our 93 which is measured RON + MON/2) at first. once i sent it back over, flew over to UK, tuned it on the gas over there (98 RON). it was quite suprising the differences in overall fuel curve not to mention ign timing.

I also noticed another UK owner had misfire issues. I'm curious to see if this is a trend with the GT's over there.

 

[911teo]

The first time it misfired was at Rockingham oval track in North Carolina.

The second time in Germany near Aachen.

The fuel in the car when it misfire the first time was 93 American octane. For the second time it was probably French gas.

If it was a fuel quality issue I doubt the fault would have been on the same cylinder.

I think this information is key.

Anyway at Roush they swapped the injectors for cyl #6 and #4 (as per nota4fre's suggestion). Since I am going to the Ring on Tuesday I will push it and see if it happens again.

At Roush they think it may be something to do with the second injector on cyl #6.

I will keep you posted.

 

[911teo]

Little update....

After having swapped the injectors the engine still misfired on Cyl #6 under heavy load.

Roush solution was to install ITR6 Iridium tipped NGK spark plugs.

We'll see if this solves the problem.

 

[FLASH]

Anyone who has boosted their cars and dynoed them has probsably noticed the jagged graph line from the dyno print out. Kenne Bell says that with boost they have noticed the supercharger blowing out the spark. Their recommendition it to install a Boost-A-Spark. Has anyone had any experience with this? Bony do you have any problems with a Whipple and 21 lbs. of boost?
Flash

 

[B O N Y]

My pulley is a custom one off 20lbs pulley. I was corrected when I stated 21lbs in error.
No I don't have a boost-a-spark or any modifications in that area.
I know that the plugs and carefully set gaps are a needed change.

 

[somelee]

since we're on the subject (sort of)....what is the correct gap size...I thought I remember it being .044 ....but a friend told me something slightly different.....

 

[Silverbullitt]

My Terminator had the same problem. New plugs and coils fixed the problem. There was a tsb out at the time. MSD also makes an aftermarket coil on plug. It might be worth a look.

 

[Ed Sims]

misfire

My GT did the same thing. It was incorrect gapped plugs.

Ed