runs poorly accellerating above 2500rpm

[tmbg]

I've been battling this problem with my car since I first started driving it with the MS installed. It idles great, and runs pretty good cruising through the neighborhood at low rpm, but the minute I try to bring it up to 3krpm, it starts running like crap. I don't know whether to tell you that it's stumbling or that it's surging, but it sounds like it's backfiring through the exhaust. I have tried richening it up, which made it worse, and I've tried leaning it out, which made it worse. I have a wideband, and it never really seems to get all that lean. It's generally under 14:1.

At this point, I don't know if I should be focusing on VE or on spark. The spark table I sort of duplicated from a stock map that a buddy of mine gave me, supposedly what the stock ECU uses. The one thing that I notice is that the areas where it starts running badly are the same areas where the spark advance gets up in the 40s. I've tried retarding the timing a good bit, and also advancing it, and neither seems to help.

I've read some stuff about dwell causing similar issues. I'm controlling the stock power transistor directly. Does this mean that MS has no control over dwell? I tried setting spark duration down to 1.4 from 2, and dwell up to 3.5 from 3.1, and it didn't seem to have an effect.

Attached are two datalogs. The first was a run with a 'normal' set of tables, the second is one where I shifted the whole VE table UP 20 (and you can see the resulting rich mixtures), then shifted it DOWN 30 from there. The areas where it runs jerky and badly are where the RPM ramps up to 3k or so, under load, usually with a little bit of boost.

hopefully someone can spot something in the datalogs that's eluding me.

[ae1969]

1st thing.... Verify timing.

1. Put the car at idle and check timing corresponds with what MS tells you.
2. Add or subtract timing on the idle cell and see that it moves properly.
3. At idle set timing around 10 to 15.
4. Reduce timing down from 40 to approximately 20-30. Keep it conservative until you can rev the car freely at idle.
5. Do you have AE on ?
DONT ADVANCE PAST 40 for now.


Can you post a pic of your timing chart and what the stock chart is supposed to look like.

>100Kpa timing must reduce

[tmbg]

1. I've verified timing, I'm running a 78 degree trigger angle, and I flattened the MS ignition table to 20 degrees in all bins, then idled it and put a timing light on it. It was jumping around a bit, but in general it stayed right around the 20 degree mark. I don't know if the jumpiness is normal or not, but I also don't know how to make it go away.

2. I'll double check, but I'm pretty sure moving the timing around in MS does in fact move the actual timing.

3. Right now I have idle timing at 20, I'll try moving it down, but it idles pretty well already.

4. I can rev the car freely, it'll run fine at 3k or 4k with no load. It's only under load that it starts having trouble.

5. Yes, AE is on, I may have it richening up too much under accel, could that be the problem?


I'll get some pictures of my timing up in a few minutes.

[tmbg]

Here's a couple of pictures. The 'stock' map came from NisTune, and it's a bit weird to read because it's RPM descending on the right and "TP" across the top. TP is sort of like load, it's a combination of all the input parameters, MAF, temp, whatever. I don't really know a ton about nistune, or how those TP values might correspond to MAP.

If timing is what's giving it problems, I'll try taking a bunch out tonight, but I already tried flattening the center down to 40 then shifting the whole table down 5 degrees, and none of it helped.

[ae1969]

Ok you may have too much timing over 100kpa.

Lets keep it conservative for now.........

A couple of things I did to make my life easier.

I only use the top 4 cells for on boost.

I use 100K, 135, 170, 225. BUT I set my max boost on my controller to 200kpa (for now). That way I extrapolate all the way to 225 on timing. Its nice if you overshoot when you get a little wild and crazy with the boost controller.

Timing is relatively linear at that point for me. So I don't go crazy trying to adjust every 15kpa. You are gonna fly past many of those cells. So the idea is to have a smooth transition.

BUT lets work with what you have.

FIRST POINT. STOCK maps ....or maps from other vendors sometimes have offsets built in. DANGEROUS. THey don't tell you. My stock motronic maps have idle maps, part throttle maps and WOT maps. BUT when deciphering them they are not actually exact timing. When ever you see someones map you really have to know what there system does with the values.

1. When you log you can see if accel enrichment is on or not. When you play back your logs I would look at that. I try and disable AE when tuning the VE cells. Once you have VE dialed in I would start working with AE.

2. If you look at your high cells. YOu see how the cells at 3000 rpm are ~1 degree less. Normally you see a slight decrease in advance at peak torque. Once you get past peak torque you can increase advance slightly to get the most power out of it. Thats what you will normally see. For now keep that in the back of your head.

3. IF you were to do a 4th gear run it would look like an S curve. So if we are in 4th gear at 1000 rpm .....it would shoot straght up...........and slowly move to the right.

4. When troubleshooting keep timing conservative. Your EGTs will rise but occasional spikes should not cause too many troubles until we have a nice revving engine.

I hope the following makes sense.
AT 100KPA
2500 rpm I would use 30 all the way across to 6000 rpm
AT 200 kpa
2500 rpm I would use 15 all the way to 20 kpa at 6000 rpm

Create a new timing table with those values.... Try and taper the cells in between those values.
The timing map you have is aggresive as you are getting on boost. I would normally start pulling timing back as I got on boost.
Aggresive timing while you are off boost will give you nice throttle response.
Run a log and lets look at it again.

[ae1969]

........ I don't know whether to tell you that it's stumbling or that it's surging, but it sounds like it's backfiring through the exhaust. I have tried richening it up, which made it worse, and I've tried leaning it out, which made it worse. I have a wideband, and it never really seems to get all that lean. It's generally under 14:1.

I just re-read this.

PUt a timing light on that car at idle.....

According to your table it should read 20 degrees......... now rev it and make sure it changes. You can hold it at maybe 1500 rpm to see if you are now getting the timing that MS says you should have in that cell.

I am thinking you are actually not getting the right advance. The backfiring is telling me you are firing too close to TDC on load. IF timing is not changing you will backfire and have some nice high egts.

[tmbg]

thanks for the wonderful info, now I have some things to try when I get home this evening

I'll post some new logs afterward.

[tmbg]

Well, I played with it a bit more last night, ended up changing my trigger angle from 78 to 68, I noticed that reducing the trigger angle made the idle smoother. At 68, the timing light values match much better.

I dropped my maps down a good bit so that I'm only getting around 30 degrees of timing below 100kpa around 3000-4000, and it's getting better. It still gets quite hitchy around 4k and above. AFRs seem pretty good, possibly too rich, around 12:1 or so.

I don't have any datalogs right now, I left the house for work and forgot to grab my laptop. :/

[ae1969]

Well, I played with it a bit more last night, ended up changing my trigger angle from 78 to 68, I noticed that reducing the trigger angle made the idle smoother. At 68, the timing light values match much better.

I dropped my maps down a good bit so that I'm only getting around 30 degrees of timing below 100kpa around 3000-4000, and it's getting better. It still gets quite hitchy around 4k and above. AFRs seem pretty good, possibly too rich, around 12:1 or so.

I don't have any datalogs right now, I left the house for work and forgot to grab my laptop. :/

You may have had an extra 10 degrees built in to your offset.

Half the battle is making sure timing is dead on. Otherwise you are looking for a needle in a haystack.

So show us your timing table again. (we assume now that these are dead on) Thats the idea by verifying that timing is what it is at idle .......and if you rev it at idle you should see the change as entered in your timing cells.

Also if you have megatune .......... log the run.

You will be able to see the rpm spikes wear its starts to buck. We should be able to determine from the log wether it goes Rich/lean, PW is wrong, AE, timing is to aggresive etc etc...

[tmbg]

ok, so I made another run. I made two logs, one burst, one normal. Both times I made a couple long slow pulls to >6000rpm staying under 100kpa, and every time it'd have a tendency to buck at certain rpms. AFRs seem to look pretty good throughout, timing is not extravagant--it plateaus around 30 degrees.

It's very frustrating that everything I change has little effect on this particular problem. I know it's something stupid and I just can't see it.

I've posted both logs and my msq so you can see my timing map.