S38B35 BorednStroked running hot

Specific conversations and info for the BMW E28 M5 and M535i.
Post Reply
SixEss
Posts: 13
Joined: Feb 14, 2022 12:50 PM
Location: Miami

S38B35 BorednStroked running hot

Post by SixEss »

This is a post I sent out some time ago but worth a revisit to see if there is any help for me.

Reaching out for some help here in Miami. I have bored and stroked S38 B35 motor running on an Autronic AQ-1 stand alone programmable EMS. This is an older stand alone installed in 2007. I've reached out to a few of the high performance shops which specialize in BMWs, have Dynos in house and have great reputations.....but none are familiar with, nor interested in looking at the car due to the EMS. A real Bummer. Fortunately, the car runs well, albeit, hot starts are inconsistent and long idle periods (namely traffic) run the car hot. Once i get rolling again, the temp drops quick and back to normal. Fan appears to be running normal too. Car has a lean/rich fuel light display and it appears to run the proper rich mixture at idle. So I'm at a loss as to where to look next

I know a full replacement of the EMS may be the most logical solution, in fact the California shop that built this car recommended the LINK Extreme ECU as a replacement of the Autronic. I was hoping to not have to spend $7-$10k. Anyone have any contacts, advice or any other useful info?

Many thanks.
athayer187
Posts: 1621
Joined: May 10, 2006 11:27 AM
Location: Cheshire, CT

Re: S38B35 BorednStroked running hot

Post by athayer187 »

My experience with a built M30 - get an ECU and tuning package that you have a local tuner who is comfortable with. Make sure they'll be around for as long as you plan on running the car. It's an expensive proposition, but that's a little bit of the cost of doing business with a built motor running an ECU.
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: S38B35 BorednStroked running hot

Post by Preyupy »

Do you have a copy of the tuning software and a computer that can run it (a system that old could easily run on XP or even Windows 98)? If not there isn't much anyone can do to help you.

If it only runs hot when stopped I would start by looking at the fan clutch and or radiator. Are you running a thermostat?
SixEss
Posts: 13
Joined: Feb 14, 2022 12:50 PM
Location: Miami

Re: S38B35 BorednStroked running hot

Post by SixEss »

I'll address my reply to you both, thank you for your thoughtfulness and interpretation of my situation. I only have the build records and the dynos while they sorted the car. One thing that I have not done is have a mechanic plug into the EMS to see if it may have downloadable software in the the EMS itself (if that is even possible). So software was not part of the purchase of this vehicle but access to older computer operating system software wouldn't be an issue for me.

The over heating is my most pressing issue and I do not know if the car is using a thermostat but my assumption would be yes. So changing that out would be cheap and easy so I'll confirm and change. The fan clutch appears to be good too. So it kind leads me to the fuel mix. athayer187, your point is well taken. It would seem that an EMS replacement, clearly newer tech and someone tweeking the motor may get me where I need to be for piece of mind, motor preservation and performance. Looks like you have a serious machine with your build and I suspect you have it all sorted. My other issues and difficulty with a hot restart sometimes (more often than not) and the car being a little jerky at low RPM in 1st and 2nd. Its a screamer and a lot of fun so it looks like its going to get a nice Xmas present under the tree this year.
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: S38B35 BorednStroked running hot

Post by Preyupy »

Start by getting in touch with Autronic and see if they still have the software available to talk to the AQ-1 ECU. It would be exceedingly rare that the ECU would have it stored and accessible just by plugging in a computer. I have never seen a system that you didn't have to have the software on your computer to even make contact with the ECU.

Has something changed recently, or is this the way it has always run? It could be something as easy as a failed temperature sensor. If it starts well cold but not hot the ECU could be thinking it is always cold and trying to start on a very rich setting. This could be just because the sensor is telling it that it is cold in error. It is also possible if it thinks it is cold the map might be trying to retard the ignition timing and this would cause the engine to run hotter as well.
jayjaya29
Posts: 188
Joined: Jul 30, 2014 12:53 AM
Location: Atlanta, GA

Re: S38B35 BorednStroked running hot

Post by jayjaya29 »

Sounds like a fan clutch failure and maybe a weak fuel pump.
SixEss
Posts: 13
Joined: Feb 14, 2022 12:50 PM
Location: Miami

Re: S38B35 BorednStroked running hot

Post by SixEss »

Unfortunately Autronic is now defunked. It was an Australian company making it even more challenging. Perhaps someone in the Forum may know who may have a copy of the software??

So the running hot in standstill traffic is somewhat new in that it has gotten worse. Here is a detail regarding my cold start, which may help you guys with your diagnosis, which by the way, are all appreciated and I'm taking note of all, in order to get a good cold start with one turnover, I "Cycle" my key in the ignition twice, letting the fuel pump pressurize the lines. Without doing so it tries to kickover but it seems like its starved for fuel. Was thinking this may be a bad fuel regulator?
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: S38B35 BorednStroked running hot

Post by Preyupy »

That is a really simple test. Get a fuel pressure gauge and put it in the feed line to the fuel rail. When you turn on the key it should go to at least 35psi immediately. If you have to cycle the key you probably have a weak fuel pump. With it running what pressure are you seeing? If it is running the stock fuel pressure regulator you should have 35 psi at idle and 42-45 if you remove the vacuum line from the regulator. If not, you probably have a bad FPR
SixEss
Posts: 13
Joined: Feb 14, 2022 12:50 PM
Location: Miami

Re: S38B35 BorednStroked running hot

Post by SixEss »

Cool thanks, I got my marching orders, much appreciated. On another note, i connected with someone who directed me to a place to download the Autronic software. So i'm making a lot a progress, appreciate the help.
Preyupy
Posts: 326
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: S38B35 BorednStroked running hot

Post by Preyupy »

If you can get the software you are 50% of the way there. Anyone that is good at tuning Megasquirt, MoTec, AEM, Halltech etc systems should be able to figure it out. Once they can look at the tuning software and figure out what parameters are adjustable on that system and how to actually make the changes then they should be able to monitor and adj as needed.

They all do exactly the same thing they just do it in a different "language". The systems just need to squirt the right amount of fuel at the right time and fire the spark plugs at the right time. They need to see engine speed and where the crankshaft is in its rotation. It needs to see coolant temperature and some reading of how much air is going into the engine (MAF, MAP, throttle position etc). It is not needed but really nice to have a wide band O2 sensor, even better if you can get the ECU to look at it and try to help you maintain a proper Air Fuel Mixture.

There are just graphs that compare Load (lets use throttle position just to make it easy 0-100% in 5% increments) to engine speed (RPM 0-7000 in 200rpm increments) and on the graph you just need to tell it how much fuel the engine needs at each point on that graph. That is 700 individual points that need to have a value (this is the number of milliseconds of injector pulse you need to deliver the correct amount of fuel) Then you have another graph just like it and every one of those 700 points need a number of degrees BTDC you want to fire the spark plug. Then you have silly things like modifiers for things like cold start and change in altitude. Thank goodness we are not dealing with Variable Valve Timing or even Variable Intake Runner length, each one with it's own 700 box graph that needs to be filled in.

A tuner knows what to do, they just need the proper software to gain access to the ECU and some time to learn the "language" of this system so they actually talk to it.

If you switch to a different system you have to do exactly the same thing all over anyway. If it runs now I would at least try to get someone to look at it and decide if you are having a "System" problem and the ECU/Wiring/Sensors ect need to be replaced or you just have a "tuning" problem and you need to get someone to do it correctly. At least right now you have a place to start, change everything and you start from SCRATCH.
SixEss
Posts: 13
Joined: Feb 14, 2022 12:50 PM
Location: Miami

Re: S38B35 BorednStroked running hot

Post by SixEss »

Hey preyupy, you have been really helpful and I appreciate it. I spoke to the tuner who last worked on the car 2 years ago in Colorado. He directed me to a site where I now have downloaded the software (saved to a hard drive and thumb drive). So I agree, I'm in a much better starting position. Following your logic, I need now only convince someone that works with other aftermarket EMS units that this would be a similar methodology.

To make life easier for the tuner, my EMS (Autronic) has an "Autotune" feature in the software that uses "a complex combination of interpolation, extrapolation, statistics and adaptive algorithms to intelligently adjust fuel delivery tables" making the tuning process 5 times faster than manual means. Its diagnostics facilities allows simultaneous operation of both PC based data logger and the ECU internal data logger. While this may all be similar to the other systems, it certainly validates the reason for a tuner with experience on the other systems to give this one the good ole college try.

So now I offer a challenge to someone in Miami that does have aftermarket EMS tuning experience to help me with this very worthy vehicle.

S38 B35 3.8L, 94.5mm Bore 90.0mm Stroke 10.5:1 Compression Ratio JE forged pistons Ported & Polished Head Shrick cams 50mm throttle bodies MSD/Rochester 50 pound injectors
Post Reply