I've been driving around and tuning for the last couple days, and am getting the car pretty good for driving around town... the only problem is that there's this hesitation/misfire type thing around 1500rpm once I'm past that point, it runs great, and below that it runs great. my fuel maps look really smooth in that area, and fuel is almost perfect all around that area. so what I'm thinking is the ignition maps? this is right at the point where it transitions from like -1 BTDC, and starts making its way rather quickly up to about 32 BTDC. could just simply the drastic change at this point in the map cause this problem? if so, what can I do to change that but still get up to a good level of advance for cruising? if no, what should I look into for causing that if fuel and iginition are both good... ?

 

Throttle pump maybe?


-Ted

 

I'll look into it... but it does it at any throttle position, even if I really ease into it, or if I'm decelerating...

 

Timing transition my be a problem. I think I am at ~15adv at 1k and then go to 32adv by 2.5k @0psi.

Something else I found that makes for a smoother transition is bumping the fuel here. I was trying to elimiate the hesitation I would get when bliping the throttle at a stop light before engaging the clutch. At this low of a TPS movement I dont think the throttle pump has much effect. I tuned for 11:1 AFR at 0psi at 1-1.5k rpm. This is easiest by putting the car in 5th and going about 30mph while watching manifold pressure. I also tuned as many bars to the left of 0psi, with exception of those that it idles on, to 11:1. I have found that the only time that I am in these bars is when the engine is accelerating up.

Justin

 

hmm.... cool. thanks for the info. I'm going to the dyno to tune tomorrow, so they should be able to get it all fixed up... I'll see what they do...

 

how did the dyno go?

 

dyno went good. here:

https://www.rx7club.com/time-slips-dyno-128/dyno-results-529636/

so, I've got more to add to this problem now. so the other night, I started to try and drive the car before it was 'completely' warmed up, which is the first time I had done this(it was still about 140 degrees or so). I soon found out the car wouldn't rev 'at all' past 1500 rpm. even when I went down the hill and put it in too low of gear, the engine would move up in rpm because it had to, but it wasn't actually firing or making any sort of power... it'd just slow the car down untill it got down below 1500 rpm. once it warmed up past 180 degrees, then it worked fine. it still had the little hesitation though...
so then I went to the dyno... it was warm the whole time on the dnyo, so it did good. it still hesitated just a tiny little bit, but not much at all. and I had a drift event to go to the next day so I didn't want to really screw anything up... just figured I'd make it safe to drive, and then fix the problem after the event. well, then day of the event, it took a while to warm up since it was a cool day, but one it did I drove up to the event no problem. then when I got there, I shut the car down. a little later before we were about to go out and drive, I started the car up to let it warm up. well, no matter how warm it got, it wouldn't rev past 1500rpm. it just backfired a little bit, shot some flames (some people told me that), and didn't do anything. it just like its hitting a rev limiter thats been set at that rpm.... a little while later, getting on to the highway to go home, it started to run good again. I made sure not to let it drop below 1500 just to make sure I wouldn't have to drive home in 5th at 35mph... so I don't know. I haven't had time to look at it since then. I thought it was probably something with coolant temp correction in the haltech, but now it seems like thats not the case since it warmed up a lot but still did this wierd problem. I have no idea. this is really wierd though...

 

Time to put the datalogging to good use!
Datalog the issue, then post it...

 

so I fixed the problem... although I'm not quite sure how... all I did was change the rev limiter from a 7500rpm hard cut, to a 6800rpm soft cut, and hard cut at 7300rpm. change the operating temp from 169 to 160, and change calibrate the coolant temp sensor. (using the stock sensor, it was like 10 degrees off before. and after that, started it cold, and revved just fine. I still have the slight hesitation, but its not bad. I'll do some datalogging and see what that is... but I think its probably just the jump in ignition advance.

 

okay, maybe not.... I dunno this is confusing as ****. I'll see if it still does it or not tomorrow...

 

so the problem is def. still there.

I did some datalogging, I don't see any problems... and I don't think there's any info I didn't log that could be causing this sort of problem...

anyone know how I can post the datalog on here? or I can email it to someone...

thanks

 

Try adding more fuel in that area. Sounds like you need more fuel to me...

 

okay... I'll give that a try.

I was actually thinking about maybe the fuel pump... like it has enough pressure at idle, but once you try and rev it, it won't flow enough... could this kinda go off and on? like maybe after it runs long enough to get warmer, then it starts working properly? I dunno.
I'm running a walbro right now... and I haven't heard the best of things about their reliability....

I guess I'll bust out the ol' fuel pressure gauge.

 

well, fuel pressure is good (well, probably a little high, but its not running out of fuel at least).

I tried increasing the injection time in that area as well, and it didn't help at all. I've also gone through and lowered the ignition advance in that area, but it really hasn't made any difference. its now at like 5* advance at 1500 rpm, and is only trying to go up to like 7 degrees for the next point (like 1750rpm).... I've tried with and without any sort of correction maps, or anything else I could think of to change, even if it wouldn't make any sense for that to be causing the problem, but it still does the same thing... I have absolutely no idea....

 

Have you ran a datalog while the problem happens?

 

yeah, I have.... I couldn't really find any problems....

I did another datalog yesterday while actually driving it through the problem, instead of just revving it. maybe it will reveal something, I haven't had a chance to look at it though.

I actually leaned it out a little bit in that area, and it kinda seemed to help a little... maybe just my imagination though...

 

okay, after looking at these new datalogs, and some info I gathered about my throttle pump maps while watching my a/f gauge, I think it just may be getting a lot too much fuel in that area. my throttle pump maps don't have enough enrichment right now, so it gets a big lean spot right as I step on the throttle. when its warm and does actually rev, I can find certain throttle inputs where it revs through that range without stumbline at all... if I rev it slow, it does it really bad, and it also stumbles a little if I step down on it a lot.

this would also make sense with the cold thing, as if its getting too much fuel in that area, it will be getting even more when its still cold....

I dunno, I'll try and lean it out a bit, but I won't be suprised it doesn't help at all. lol.