osu_p51

I ask this because ever since the weather has turned cold I have noticed at WOT (in 2nd, 3rd and 4th gears) around 3500-4000 rpm's my car stutters almost like the engine wants to die. It lasts for a second or two and I immediately up shift to get out of that rpm range. In the next gear it will do it again. No codes are thrown at all. I have datalogged the occurrence but don't see anything unusual. I have updated my tune and upgraded my fuel pumps to the dual gt500 setup and it still happens. Now, I can take the car slowly through that rpm range and no stuttering occurs. Same thing when the weather is warmer (50 and above) no issues slowly or at WOT. I added a Cali dream hood in October and I started noticing the issue in November. Not sure if it is coincindence or not but I never had an issue over the summer. It is really annoying me. Anyone have similar issues or have any suggestions? Thanks

mvon919

It's possible. Cold air's density is bigger, meaning already "compressed" and your S/C compresses it more... who's tunes are you running? I currently have JDMs COLD tune, which is designed for cold weather.
Give JDM a call!

osu_p51

I have spoken with Jim jr. on a few occassions about this. He re-did my tune a couple weeks ago (don't think I have a COLD tune though). He was surprised as well when I told him the problem was still there after I re-flashed my pcm. I was just hoping that someone else out there has had a similar issue and found an easy fix.

mvon919

Check your Vacuum connections, maybe there's a leak somewhere...

mikes rx

It might be because the engine is still cold. I know that upon startup, if you attempt to "floor it", the car will bog down because the engine is still cold.

osu_p51

I am pretty good about letting the car warm up before going nuts. The last time this happened was after about a 30 minute ride home from work. I got the car into the rpm range then slowed down then put her back in the rpm range. I did this 2 or 3 times to make sure I wasn't imagining it. Each time she stuttered. Since these cars are so reliant on the computer I would think that some kind of code would have been thrown: too lean, too rich, something. I have switched gas stations, used fuel system cleaner. I am running out of ideas.

don_w

Just a wild guess here, but are you getting any belt slip?

70MACH1OWNER

It's hard to tell from your description if your are kinda getting on it ( mucho gas pedal) when this happens or not. If yes i'd say turn off your traction control and try it again. If you are accelerating enough in this cold weather to slip a tire then the traction control will shut you down for a few seconds. I am not even SC'ed and I can promote this kind of problem in this cold weather with the TC on. Just a thought.
Scott

RadBOSS

I don't think its air too cool. Cool air makes more power (denser), computer compensates mixture to keep it in range.

Checked plugs lately? Changed heat range? May need a step cooler?

All else failes you might want to get it on a chassis dyno, then monitor all the parameters and see what happens when you hit that spot. Might be expensive, but you might have to spend so bucks to find th root problem.

94tbird

getting enough fuel at high rpms? do you have a fuel pressure gauge? you may have a defective stock fuel pump if you havent upgraded your fuel system

osu_p51

Don - When this first started happening (Nov. or so) I did think it was belt slippage. Wouldn't this cause a surge in RPM's? The car chokes to the point of stalling when I get to 4000 rpms, no surge.

70mach1owner - The traction control setting was another step that I tried. I had read earlier this week on another thread that someone suggested turning it off. For my problem, turning it off did not help. Stomping on the gas is the only time it occurs. When I gradually build the rpm's up not stuttering occurs.

RadBoss - The plugs came new with the S/C. I beleive they are FRPP.

94tbird - I do not have a fuel pressure gauge but I have used my XCal2 to dattalog the pressure drop across the injectors. Is this sufficient or should I invest in a fuel pressure gauge? I recently installed the dual gt500 fuel system from JDM. Jim has been extremely helpful but he would need the car to really diagnose the problem.

I am hoping to find a simple solution before going to a local dyno. My biggest fear with taking it to a dyno is that they won't be able to reproduce the problem (or blowing it up if it is a fuel problem).

S197 GT

Hmmm, did you also use octane booster?

Check your plugs first. Sounds to me like you may have fouled the plugs. Does it do it every single time?

Bullitt995

How cold are the air tempuratures? Superchargers have small tolerances and have been known to be a little tempermental in very cold weather.

osu_p51

No octane booster, just good ole 93 octane. Of course with all of the ethynol they are adding these days it may not really be 93. It does it when its cold, below say 40F, and yes everytime at WOT. No problems when going slowly through the rpm's.

70MACH1OWNER

OSU P51,
Have another thought for you. This comes to mine because I am having issues with a 98 Explorer that has a dealer installed black box attached to record some wierd events going on. I wonder if your MAF sensor is not quite right. If your MAF sensor is not keeping up with the sudden air flow changes at WOT could explain your issue. I don't know if you can datalog just the MAF sensor or not but we have been trying to find a problem with our Explorer for a month and it is acting similar to your stang with some other things going on. Only after the dealer installed their black box with record button so we could drive it normally but record the event did we finally find the problem. The MAF sensor. It is the sensor that tells your computer how to adjust fuel and timing for every condition after the car has been started. Just another thought.
Scott

Cobrakev

Yes I would invest in a fuel pressure gage,especially since you have a S/C. I would also look to see what your A/F ratio is at. Last, I would get a good dyno tune done to the car. This will really set your A/F ration where it needs to be during the high rpm runs.

osu_p51

Interesting thought. I will look to see what data I can log with regards to the MAF. Was your Explorer acting funny only in the cold? Thanks

osu_p51

I just got a re-tune from JDM but haven't taken it to a dyno since I had the S/C installed (A/F then was around 12:1). Can you reccomend a good fuel pressure gauge and gauge pod? Are the guages hard to install? Thanks!

70MACH1OWNER

Well ..the problem with the Exporer only developed since the week before Xmas. But that is probably just concidence.

RadBOSS

If its sensitive to temperature, perhaps you have a engine management temp sensor out of calibration or with a bad connection? O2 sensor could be suspect too. That could confuse the engine management system. I am shooting from the hip on this because I am not totally familiar with the sensors on this engine. My turbo Merkur does monitor water jacket as well as inlet air temperature to manage required fuel and boost.

The reason I asked about the plugs was if they were a heat range too hot, under load they would probably break down. Short of that it sounds like a lean out problem which goes back to sensors or a fuel delivery problem.

Might still be worth your while to look at a few of the plugs.