View Full Version : Hesitation with high RPM shifts??

04-15-2005, 01:57 PM
My car will sometimes has a hesitation when shifting from one gear to the next when letting it rip. If I go from 2nd to third under WOT conditions and shift above 5k rpms the car will hesitate when I get the clutch out after the shift.

I find it annoying. The acceleration of the car almost seems to “hiccup”.

Any suggestions?

I should mention the only power mods are the X cats, exhaust and K&N CAI. The car has 20k miles on it.

04-15-2005, 04:08 PM
I think it's just losing a little boost when you shift, then coming back up real quick...since you dont have a chip/tune, it's more than likely ok...you could also try the clutch firewall adjuster, your clutch could be slipping a little bit...good luck and when all else fails, take it to the dealer :thumbsup:

04-25-2005, 07:15 AM
watch your shift RPM. If it gets high enough the timming will retard or injectors will shut off. It is possible the engine speed may exceed the rev limiter when you disengage the clutch. I have had that happen on occasion especially when not paying attention to RPM before shifting. Just a thought. If it is doing it before red line, you may have a sticky Idle control valve or a dirty MAF sensor. Once you release the throttle, it is the idle control valve that regulates engine speed. I had that issue with my 01 until I cleaned the entire intake plenum. It is possible it is related or perhaps not even the issue.

04-25-2005, 08:37 AM
It happens before redline and I think I have my foot out of the gas pedal in plenty of time before shifting. (I am not that bad a driver :rolleyes: LOL) I'll check the MAF first when I get a spare moment. After watching every 03' Cobra video I think that the car hesitates or shudders just as I let the clutch out and hit the gas again.

Thanks for the info.

04-26-2005, 07:12 AM
I did not intend to attack your driving skills. I appoligize if I did.

I do know that if the MAF sensor gets any oil deposits on it (namely from the filter element). The result of an oily film could cause hesitation and poor performance. The MAF element is extremely sensitive, even the screen if placed incorrectly will cause a change in the air flow that may also effect the sensitivity of the MAF sensor.

My thoughts on your issue may be related to the PCV valve. They do not last very long and should be replaced regularly with every or every other oil change. Perhaps at higher RPM it may not be much of a factor, however due to its construction, the plastic elbow will eventually loosen up from heat which will lead to a mild vaccum leak which will effect idle speed and possibly cause hesitation or rough performance when shifting. My PCV valve crapped out at around 6k miles and is due for replacement anytime soon.

I did have a oil separator filter to remove oil from the PCV line, but recently removed it and went back to the stock arrangement (I noticed that after adding the Lucas oil stabilizer I did not get any oil build up in the filter so I decided it was not needed). What a difference that made, especially at start up when the engine was warm. The PCV is next for replacement (I ordered a matching canister type similar to the SHM intake filter which is probably not necessary).

Another issue, related to PCV and EGR arrangements, oil mist from the PCV line will cause a build up in the intake assembly (typically in the vaines of the intercooler). Along with oil change intervals, throttle body cleaner can be used to remove deposits accumulated in the intake but should be done with care since the engine must be running to get the cleaner into the intercooler. If you fear that would cause any damage, as it could if you get vapor lock, you may want to use the MOTORVAC service offered by FORD. That is supposed to remove all carbon deposits and varnish in the intake, but it is not cheap.

I can only hope that any of this is helpful.

04-26-2005, 08:06 AM
Do you drive with the traction control on? If so it can cause you to lose power under hard acceleration when shifting.;)

04-26-2005, 08:26 AM
I am the one attacking my driving skills :rotf: All of your help is appreciated. I will replace the PCV valve and use an electronic spray cleaner for the MAF. The car has 20k on it so if the PCV valve is that bad it certainly needs replacing. I will also check all of the vaccum lines to be sure they are on good.

I usually turn the TC off. The hesitation comes at high speeds and before any wheel spin would occur.

BTW: Does the stock setting of rev limit match the redline on the tach?

04-27-2005, 06:48 AM
The redline is the point of no return in most cases, but since ours is electronically limited it is the point of full timming retard and fuel shut off (injectors stop injecting fuel). If the easy things do not fix the issue, it could be related to fuel pressure. The fuel pressure regulator is controled by engine vacuum. The connection to the fuel regulator is connected near the bottom of the throttle body or in that general area. As for the fuel return line, there is a T secion on the vacuum line that ties into the PCV feed at the back of the motor. I was curious as to what the T was for and I got answers from asking. A drop in fuel pressure could be a result of many things. Usually the Fuel filter may be the leading cause if it cloggs up. You may get fuel but the pressure will drop off due to the flow rate of the filter. About the same amount of milage I had on my 01 (18k) is when I had the filter changed.

From what you said is that the throttle response is not instant when you mash down on it once you get it into gear. Question to you is... does this occur all the time or after a period of hard driving? I do recall the term "limp mode" which is related to engine temperature and timming. I think the Cobras will go into limp mode if the engine temps exceed a specified temperature to avoid detination. That may be difficult to remedy besides letting the motor cool down. If there is trapped air in the cooling system, and if the coolant is not circulating into the motor here is what to look for. Drive for a short period (a few miles or so). Turn off the engine. If the Expansion tank is still cold or if the drivers side of the radiator is cold that would indicate lack of coolant in the block. The water pump is not capable of compressing air or displacing it. I had this issue after replacing my expansion tank even after filling up the coolant (since I could not get the bung off I thought the air would be pushed out, wrong) I found that the expansion tank and entire radiator was ice cold except for the return side. Hence no coolant in the block. At least once the bung was warmed up was the only time it would come off without breaking my tools. If you had experienced popping the radiator cap, it it likely you my have air in the cooling system. That may not be the case with your Cobra, just an after thought of what I had issues with mine.

I do not want to miss lead you in all directions, I am just expressing possibilities. Food for thought. Since I am no expert, call it junk food.

Come to think of it, since out supercharges have a boost-bypass valve, and since all of the gasses from EGR and PCV may flow throught that port it is probable that it may be gummed up. It operates on a vacuum motor and opens at low RPM as well as the point the boost drops off at high RPM. Watch the boost gauge as you accelerate. If it is sluggish and not quick in building up boost, you may have a dirty boost by-pass valve. To clean it is much the same way when cleaning the throttle body. Since there is no direct means other than taking off the supercharger, it can be cleaned with TB cleaner while the engine is running at idle. If someone has a better approach, I am all ears. Come to think of it, mine is ready for a dose of TB spray and an oil change to go with it.