I've been having some hesitation issues since a little while after I got the car. It began when I hooked up a boost controller. Every now and then at part throttle full boost, I'd get this weird hesitation like one of the cylinders wasn't firing. It wasn't a general "bogging" sort of hesitation. The car would buck a few times. the hesitation is not cyclical in any kind of pattern, and it it is very distinct like there is a sudden spike of no power, then back to normal, then another spike, and so on. no pattern at all. just frequent, distinct hesitations till I get out of full boost.
Also, I was getting the occasional "backfire" if I suddenly went WOT. I attributed the backfiring to unburnt gas being dumped on the cats all teh sudden (I also assumed the cats were hot at this point from the part-throttle-full-boost issues MBCs give). so I disconnected the MBC after a while figuring these weird hesitations were a bad thing. I never had a problem at part throttle before with teh stock boost controller, and now I was getting the hesitation at part throttle. Maybe I was getting it before but wasn't intune enough with my car since it was new to me, and didn't notice it.
Recently I got some Xylene and ran a gallon of it at around 10:1 or 12:1 or so with 93 pump gas. so I was around 95 octane. This cured my hesitation issues. I just didn't have the same hesitation at all. I tried hooking up the boost controller and running that at part throttle for kicks. still no hesitation. At that point I was convinced that this hesitation was the engine pulling timing because the air charge was so hot. I figured the upp'd octane was behaving better and not causing the car to pull timing. Even a few tanks after the xylene, my car was running better than ever. much peppier than normal. felt a bit torquier. I chalked it up to the xylene cleaning the cylinders, ports, injectors, and whatnot else.
Last weekend I went up to the Tim O'Neil winter driving school. on the way up it was rainy but warmer than usual. It's been below freezing around here a lot. I was driving up there for a couple hours and I noticed my hesitations were earlier than normal. meaning, I'd get them at a lower part throttle boost than normal. Usually I didn;t get it unless I was around 0.055 MPa. I was getting it as low as 0.04 MPa. I figured it was because of the warmer air, or maybe because it was so wet out. either way I didn't let it bother me. So I drove rally style all day learning winter driving techniques. my car was on for a good portion of the day running fairly hot, and near the end it was at idle for around an hour or so solid. on the way back the hesitation was really bad and I wasn't getting much power. I was having trouble accelerating uphill to over 85 MPh. given, the hills were really steep. This is in NH. I chalked it up to heat soak. not only was the air warmer, but if my engine and tranny (4EAT) were heat soaked, I'd have less power than normal and the intake charge would certainly be hotter.
At this point I was still thinking my hesitation problems are the engine pulling timing. I haven't had anyone that knows what that feels like ride in my car. I myself don't know what that's supposed to feel like, but people describe it as a very distinct loss of power. Anyways, I'm starting to wonder what my engine is going to do when it turns to summer out here and the intake charge is a solid 50 degrees higher to start with. Aside from that one power loss problem that I still believe was due to heat soak, my car is still running peppier since the xylene, despite the hesitations. one of my friends suggested that maybe the computer is running on a more aggressive fuel map since the xylene. I haven't reset it since and it's only been about a week. that would explain why she accelerates better in general. if the hesitation problem is timing related, it would also explain why I'm getting the hesitations earlier. if the timing is advanced more in general, it would make sense that it gets retarded earlier.
Yesterday I poured in another gallon of xylene. just for kicks. I mean, it's fun
. but I'm still getting hesitation. before, when I ran xylene I onl;y got one "puff" of hesitation and that was when the boost spiked to 0.08 MPa on the freeway during a downshift. now I was getting a little hesitation even under factory boost control. all this together is making me think whatever the problem is, it's getting worse. the xylene made it run better teh first time, but perhaps it accelerated the problem. this time, it's running better than without xylene, but I still feel the problem a little. I'm starting to wonder what it could be if it's not timing related. I mean, the air is going to get warmer... will I be unable to boost at all in warm air except at WOT or something? that's not right. so what could it be? maybe I just need to reset the ECU. maybe I have a bad coil pack or plug wire and what I'm feeling isn't the engine pulling timing. maybe it's misfires
. That'd suck, but a new coil pack or set of wires would help. any other ideas? I'm sorry for the story, but this is the only big problem my car is having and like half my posts here are me complaining about it in one way or another. Thanks for any help.PS - will the engine ping because of a charge that is too hot, or does that just cause pre-ignition knock?
? I'll try to see if my engine has some sort of hesitation like that. remember I mentioned I found it hard to accellerate past 85 MPh uphill that one time? well 85 MPh is around 5-5.3k RPMs at WOT in an auto. could be I hit the "sick spot." anyways I'll flog her a little on the freeway and see what's up. in the mean time I'll change out the spark plugs. let me thank you in advance if that helps 
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