Car begins to sputter after 65 mph, can't figure out what is it???

[black97GSX]

A while back after a put about a 1000 or so miles on my new motor the car would sputter after about 65 mph. Only maybe once or twice a week. Right around the same time the sputtering started the alternator belt loosened up a bit and started to make that high pitch noise upon starting, then it would stop. Then my car sat for about a month and a half during my college winter break. When i began to drive it again it wasnt doing the sputtering at all. The alternator belt was still loose and i tightened that up. After almost 2 months of driving after sitting for that month and a half it started doing the sputtering once and a while above 65 mph. Not bad, only once and while up till last night. I was driving my car for about a 15 min drive and it was doing it real bad. If i was doing about 65 mph for a couple mins it was would start to sputter, then i would have to drop it in neutral for a bit, rev it then pop it back in 5th and usually it would stop. But it did this about 10 times during the 15 min drive. The weird thing is, it only does it at or after 60 mph. I'm still in vaccum also, so its not boost creep at all. Also my alternator belt is loose again, i dont know if i just have a bad belt so im going to replace that anyway. Also i just noticed this today, that i guess for about the past week my AC belt has been rubbing my timing belt cover. I'm going to go over the brackets to see if any of them are loose. Either today or tomorrow i will replace the belts. See if that helps at all. Also i will check my plugs to see how they are doing. Clean out my air filter also and maybe get a new fuel filter. The sputtering also makes it seem like the car isnt getting either enough air or fuel. I'm trying a bunch of stuff but if anybody has any other ideas post them and maybe they could be very helpful, thanks a lot.

 

[black97GSX]

Also to add something, my car wasnt doing the sputtering very often till last night. Up till last night i could rip up to 130 mph if i wanted to had usually had no problem at all. Then last night it was running horrible and im trying a bunch of stuff but nothing yet.

 

[Doug99RS]

What's the history on the plugs and wires? What brand and how old? Double check the gap or maybe close them up a bit just to see if you can change the condition. Check your IC and air filter to turbo clamps just in case there's a post MAF leak.
Doug

 

[Agent Ezzard]

If you have a 6 bolt then it sounds like the Random Misfire condition. If you just had your motor put in or your ECU reset by a battery change then it takes a while for the criteria to be met before the condition occurs. That is probably why you drove it like a DSM before it starting sputtering and sounding like a mean WRX. Do some research on it. I bet that is what is happening to you. It happened to me but that was a while ago.

 

[black97GSX]

The plugs are Denso and i put them in when the 6 bolt was put in almost 3000 miles ago and the wires are NGK, which i used on my 7 bolt for a little while till the 6 bolt was swapped in. I have checked the champs on the intercooler piping and the intake before for leaks but ill check again. Thanks for the info guys.

 

[Defiant]

Take a look at the plug wires in the dark.

 

[aaron93tsi]

Originally posted by Agent Ezzard
If you have a 6 bolt then it sounds like the Random Misfire condition. If you just had your motor put in or your ECU reset by a battery change then it takes a while for the criteria to be met before the condition occurs. That is probably why you drove it like a DSM before it starting sputtering and sounding like a mean WRX. Do some research on it. I bet that is what is happening to you. It happened to me but that was a while ago.

Could you please explain more on this because i cant figure my problem out either...

 

[Agent Ezzard]

Well your problem is different then black97gsx's. The problem that I think he is encountering is very coming for when a 6 bolt motor is swapped into a 2g car. The problem is called the RM or Random Misfire. No one knows for sure what causes the problem but it stems from the use of the camshaft angle sensor from a 1g for the crankshaft position sensor input needed for a 2g ECU.

When driving the car the condition might not make itself know for sometime depending on the car because as we all know, every car is different. Certain conditions have to be met in order for the RM to surface. These conditions can be found HERE .
It is very weird the first time it happens because you don't know what to do or what is happening. The reation most people take is stepping on the clutch and letting the RPMs drop and come back up and the RM goes away but only for a little bit.

The only way to cure this is by getting some sort of standalone or DSMLink.

There are a few ways around it but thy do have their drawbacks. The first one I will explain is the potentiometer mod. It is also explained on the magnus page. What it does is throw one of the criteria needed for the ECU to look for the RM out of range so the ECU doesn't wory about RMs. The potentiometer will alter the barometric pressure. You will need some kind of fuel controller to add the fuel back that the ECU is pulling from seeing less air pressure. This has to be done carefully otherwise you could melt your motor.

The second fix is unplugging the TPS (throttle position sensor). That also causes the ECU not to look for RMs. The drawback to this is that If you are using an AFC that needs TPS input to modify fuel delivery for Hi and Lo maps, your TPS will stay at zero. Another small quirk with this method is that since you have no TPS input, idle control is loss so stalling could result if you take your car out of gear at high RPM (like the end of a run down the track or street racing from stop light to stop light). The ECU will go into open loop mode without the TPS.

I have done both of these methods and since I was on stock injectors I utilized the TPS method for a few months. Now I have a DSMLink and use that to disable the ECU's ability to look for RMs.