E46 M3 not always hitting 100% throttle. 3 month nightmare

[e36seanp]

Hi guys,

Recently I swapped an s54 into my e36. I am down to my last issue that has taken me 3 months to finally pinpoint what it may be.

Symptoms: car is fast sometimes and other times slow. (Not sluggish, hesitating, missing etc.)

After narrowing it down, i have realized that the car is not hitting 100% throttle all the time. Since then I have changed throttle position sensors, maf sensor, brand new e46 M3 pedal w/ sensor. And the issue still remains. On the live readings it shows my pedal usually hits about 60% full throttle. I first thought it was an issue with the obd iphone app and it was fine. But the difference between full throttle being “50%” or “100%” on the reader is very dramatic.

For example, I will leave it in 2nd and pin it to the floor. throttle will open usually to about 60%. If I keep it in the same gear and take it to higher revs and then let it come down, it seems the throttle will open up more. If I do it enough I can get 100% throttle And 100% throttle is amazing. But it is very inconsistent.

The last thing I’m thinking it could be is the throttle actuator itself. Any other ideas? I’m lost at this point unfortunately.

Thanks for the read

Take care
- SP

[MarcoZandrini]

What app are you using? OBDFusion seems to be the app of choice. It’s throttle by wire, correct?

[e36seanp]

Yes that is correct, using drive by wire. I’m using the blue driver app. I thought it could be the app but at the same throttle position in the same gear and the same rpm, the car performs different.

Last night I took it for a few more runs. It seems like the throttle will open about 50-60% and if I keep punching the throttle after a few runs in the same gear, I notice the absolute throttle position will begin to open up more. It will then hit around 80% and if I keep doing pulls, it will get to 100% but not easy to.

So I’m thinking And hoping it could either be;
1. Throttle actuator is messed up causing an inconsistency in throttle position
2. I’m running the stock base map and have a short ram/catless headers/AA catback. Was thinking it could be this and the computer is limiting throttle to run as optimal as possible. And maybe after I floor it a few times, it wakes the dme up and gets it to run on par to give 100% throttle.

i am getting a tune this week, fingers crossed that it helps. I’ve noticed -20 Long term fuel trims at idle. Which I think means I’m running too rich. I’ve also had an oil analysis by Blackstone and everything checks out. I know that’s not the be-all-end-all but I’m just trying to cover my tracks.

I appreciate your time

[dworthy]

Do you have any codes, pending or otherwise?

What E-36 has this motor gone into? Year/model

Did you do the install or a shop?

What wiring harness did you use?

[MarcoZandrini]

I recommend you get the OBDFusion app. It lets you see a lot of different data streams.

[e36seanp]

Hey thanks for the response,

I have one pending code p0418 which is an “open circuit in sap relay” (even though I’ve deleted sap codes and used the block off plate) Still trying to figure that out.

My friend and I put it in, its a 97 328 coupe using Andrews harness.

Just seems like if I want 100% throttle, I need to beat on it for a few minutes. I’m wondering if its the big intake/catless headers/exhaust that I have and the base map is just trying to make it run as optimal as possible and after beating on it, it starts to compensate and learn the values to allow 100% throttle but only for a short while and once I stop driving aggressive, it seems to go back to the issue. Hopefully I’ll be doing a remote tune with AA today.

If that doesn’t fix it then perhaps the actuator is going bad (~175k miles) and if that’s the case then I’d possibly look into going to drive by cable.

[bmwdirtracer]

What have you done with your ABS/DSC ? Any chance that the DME is perceiving wheel slippage, and electronically trying to prevent it by limiting throttle opening?

On the other hand, you say that live readings show the PEDAL at ~60%...is this correct, are you reading pedal position or throttle position? If you're reading pedal position, then the problem is between the pedal and the DME, not with the engine throttle apparatus, or even the tune.

There are two self-checking potentiometers in the pedal unit; a good diagnostic program should be able to show both.

My guess is that your pedal unit, new or not, isn't achieving full throttle.

[dworthy]

+1

I was thinking along the same line as the ASC+T will limit the throttle if it detects slippage. Wanted to know which harness was used to see if they connect.

[e36seanp]

I was able to get the tune installed yesterday and it is much better. I am now seeing 90%+ throttle on full throttle pulls, have only driven it about 30 miles with the new tune, I imagine it gets even better.

I believe, the theory about the dme not being able to keep up with the mods is what the issue was. My guess is that the car was getting full throttle but the throttle would only open so far as the stock base map on the dme was trying to make it as optimal as possible given it was up against uncharted territory with the new mods.

To whoever may be reading this, if you get intake/exhaust mods and you don’t get a tune, your car will still feel like it’s pretty fast but a tune will get you where you need to be. I’m sure it’s a no brainer to some but I didn’t realize how badly an intake and catless headers could throw it off.

Thanks for the responses everyone!

[dworthy]

Yes, any mods made to most motors will need a tune. You can use a cookie cutter tune, and it will get you about 50-75 percent. That is why most builders will want you to get the car tuned on a dyno to get the most out of mods.