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Hi guys I've found a wierd issue on my car not to sure what it is. When I am cursing on the highway 4th or 5th gear and I put my foot flat and the car starts to develop boost around 6 to 8 psi car starts to "bog/jerk" . It's hard to explain but it jerks and I can hear the turbo surging. But if i drop to third and rev through the gears there is no issue. AFR is running rich at that point and remains the same during the bogging. It's not a boost leak plugs or coils or dump valve opening. any ideas?

Which engine and ECU are you running?

one of our local entry level ecu called Spitronics

There are a variety of possibilities based on your description. It could be tune related - particularly if the engine is running too rich at that particular point of the rpm/load. Likewise if the ignition timing is exceptionally retarded at that point this will also cause poor running as described. A third option would be that you are suffering from a spark related misfire at that point. Usually this happens at the area of peak torque where the cylinder pressure is highest. Try new plugs or gap your existing plugs a little tighter and see if that helps.

The last possibility that comes to mind is that you will see this situation if you have a mismatched turbo on the engine. If the sizing of the compressor to turbine wheel is wrong, or the turbo is simply poorly sized for the engine, you may get a point (always low in the rpm), where the compressor is basically moving more air than the engine can consume and the turbo surges. This is not likely if you are running an OEM turbo.

Andre i have to pull you up on that as it may cause some misunderstanding. By design, the turbo is always moving more air than the engine can consume... thats what causes positive pressure. *Surge* happens when the turbo itself can't hold a certain amount of boost at that particular flow rate.

thank you for the ideas!

Welcome back Marek! We thought we had lost you :(

Thanks for your comment, and you're right, my description isn't technically accurate. I should have been a little more careful with my reply. Thanks for pointing it out as we are here to reduce confusion, not increase it!

I'm back!... and more pedantic than ever!. XD

We wouldn't want it any other way Marek :)

Hi all, I'd like to re-open this discussion.

I think I'm experiencing a similar problem with my map. The car is running quite a large turbo for the applications, perhaps too large, although I'm stuck with it now as it's on the car! It's a Borg Warner 7064, twin scroll, on a 3SGTE Toyota MR2 engine. We have oversize valves and 3inch pipework.

I have a problem where on exit of a corner, the power isn't "smooth". When it was first mapped, it was almost bunny hopping, spinning the wheels then not, then doing on exit of a corner (on a very smooth low grip kart track). Things are a lot better now, but it still isn't right.

The minimum the turbo will "target" is 1.2 bar on the springs. It's a lot smoother when on spring pressure alone.

Any tips for further diagnosis and ideas on how I can improve the setup - either with boost map, fueling, ignition?


Do you have a datalog of the unsmooth power? I'm trying to understand if this is a "problem" like too rich/too lean, misfire, etc or if it's a mismatch between the torque curve you get and the torque curve you need to achieve your goal.

Which data is important? Unfortunately I don't have the lambda sent to the data logger at the moment - it's on a separate non-integrated device. I do have logs but we're missing that.

Let me put it to you this way. What is it doing now, and what do you want it to do? See if you can figure out a way to express that in a chart.

It's more about the feel... so I guess the power curve isn't smooth at the moment - not sure how I'd show that from what is logged?

Also, some of the support people said on the outside they can hear it's not "smooth" - although I've not got experience on that, they just came to me and asked questions unpromted by me, but backed up what I felt.

Do you have a dyno run, or even virtual dyno run?

No, afraid not. We did an initial dyno run to get a baseline, but all other mapping is done on the road.

By "virtual" dyno, I presume you mean like an app based thing?

Things that will show up clearly in a log as a problem would include manifold pressure, air fuel ratio, throttle position, rpm and ignition advance. It's a little hard to understand exactly what you're experiencing and there could be a variety of issues causing the problem.

I have everything but AFR -- and I'm embarrassed to say, I thought I had igd advance on, but that appears to be missing... need to check my config.

Attached is a sample log file from a Motec - opens in i2.

Attached Files

You need to include the .ld file. The .ldx file is just an index of changes you've made to the .ld file.

Ok, I've added the .ld. Note that I had to change the filename from ._ld to .ld otherwise the browser couldn't "see" it.

Attached Files

Wondering if it could be way to much accell enrichment ? My engine had a big bog when standing on the accelerator when cruising slow - Turned out i had more than twice the accel fuel i needed . Progressively dialing it back in steps until it ran clean cured the problem .

I don't think it is.. I used to have that problem until I realised the default setting was too much for my car. It otherwise drives quite well.

I guess the engine trace isn't much use without the AFR readings - I'll have to get those wired in properly...

...that said, it's targeted between .85 and .80 as it gets into positive pressure, and from what I can see on the other software (for the AFR reading) it doesn't drop below that when accelerating off.

Time to open the wallet and go to the dyno.

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