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2007 Loss of Power/Hesitation when cold

4K views 13 replies 7 participants last post by  bl817 
#1 ·
Hey guys, I'm hoping someone can help me with an issue with my 2007 GT modified with a Saleen Supercharger.

My car has a really bad hesitation/loss of power issue that occurs when the car is first warming up. The car starts great and everything seems great and it even drives well for the first minute, and then it starts hesitating badly until the engine warms up for another 3-4 minutes and everything seems fine. Note that if I shut the car off and go to drive it again within a few hours, there are no problems what so ever. This only happens when the motor cools down completely.

Fuel pressure looks good and is up around 40psi all the time.

I have replaced both upstream oxygen sensors (I was getting a O2 slow to respond about once a year and thought it might fix it, it didn't).

The vacuum gauge seems to indicate that the throttle body is opening up when I press the throttle and everything is cold when the hesitation occurs. Vacuum moves towards zero when I press the throttle.

I know that our cars don't have an EGR, so there is nothing to check there. Spark plugs were replaced last year with the same type of colder plugs that were in before.

Any ideas?
 
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#6 ·
I'm kinda doubting that it'd be the MAF. I think that if it was that it'd run crappy all of the time. Seems more likely that it'd be the coolant temp sensor or something along those lines. http://m.autozone.com/engine-management/coolant-temperature-sensor
I finally had time to clean the MAF last night and it didn't fix anything.

Do we have more than one coolant temperature sensors? I have a gauge that reads the coolant temperature for me off the OBD-II port and it is one of the parameters I watch, but I haven't seen anything unusual with it. Any idea what type of malfunction I should be looking for in that?

Any more ideas?
 
#8 ·
Is there any way to test the coolant or cylinder head sensors to see if they are working correctly? Because of the supercharger, getting to anything in the valley is not a trivial matter.

Also, I remember hearing once about keeping the throttle body clean. I have wiped mine down on the inlet side, is there anything else to do for that? Or would that cause problems all the time and not just when the engine is warming up?
 
#9 ·
I had the same issues on my turbo'd 06 GT this week. Try resetting your KAM (keep alive memory). After you reset it, start the car and let it idle for about 2 minutes without touching the A/C or turning the wheel. After that, turn on the A/C and let it idle for another 2 minutes. Then just drive it normally (whatever normal is for you) and it should be fine after about 50 miles.

I replaced my alternator last week and had the battery disconnected for about half an hour. After we got the new alternator in, we had to push-start it (no power in the battery). My dad was in the seat while I pushed it, car started, all was good. He wanted to hear the car though so he revved it a bunch. Taught the KAM to give it tons of gas whenever first touching the throttle, which is where my problem came from. It would idle fine, but as soon as you gave it gas, it would hesitate for a second or two before picking back up. I thought the same things, MAF, O2s, ignition, etc. before I remembered about the KAM. Reset it yesterday, made a world of difference.
 
#11 ·
I had the same issues on my turbo'd 06 GT this week. Try resetting your KAM (keep alive memory).
Actually, I just had to replace the alternator about a month ago, so the KAM was reset then. But I'll give it another go just in case!

Is this an all of a sudden issue or have you recently gotten a new tune?
because sometimes with tunes they are tricky to do with cold starts. Mine currently runs lean when cold and this causes the exact same issue you have. I'm set to go back to the Dyno shop for an update to fix this though.
This is an old issue that has just been slowly getting worse. So it is not due to a new tune or anything like that.

BTW I set my OBD-II gauge to monitor cylinder head temperature, and that appears to be working normally. It tracks the coolant temperature very well (i.e. a few degrees warmer than coolant). IAT looks normal and ambient temperature seems normal as well.

I will hopefully get time to reset the KAM and also try cleaning the throttle body about really well this weekend and post results. Thanks for the help guys, I appreciate the suggestions!
 
#10 ·
Is this an all of a sudden issue or have you recently gotten a new tune?
because sometimes with tunes they are tricky to do with cold starts. Mine currently runs lean when cold and this causes the exact same issue you have. I'm set to go back to the Dyno shop for an update to fix this though.
 
#12 ·
Alright, so I reset the KAM and cleaned out the throttle body with some cleaner. Still no luck, the problem persists :(. I cleaned the throttle body up to and just past the butterflies, removing the throttle body itself would require removing the fuel rails in this configuration.

I wish I could make sense of this.
 
#13 ·
For anyone else who runs into this, I was told that on these cars with the Saleen supercharger that hesitation can be caused by either spark plugs, dirty throttle body, or problems with the bypass actuator.

Spark plugs are not even a year old, so they are good. The bypass actuator seems to be working correctly when I test it manually. So I took everything off so I could remove the throttle body and cleaned it really well. The car runs much better now, although it still does hesitate a little bit. Next time I may try to take the intake plate off and just get in there and clean whatever I can reach.

I hope this helps someone else!
 
#14 ·
there is a thread on here somewhere about lagging and hesitation. the poster realized that the fan resistor was the problem. high fan resistor iirc, draws a lot of current away from the ignition causing hesitation. just a thought. SVTrider and his post is 13 or so down from this one, a good read and good fix, good luck
 
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