Build Thread: 1991 325ic Restoration + engine swap

[JimBobs 91E30]

I have removed Megasquirt (MSPNP Gen 2) from my car. First, let me say that Megasquirt is a great idea and it works very well. It is also cool to be able to monitor and adjust all the various parameters on the ECU. It was installed in my car with the idea of future performance upgrades; in particular, turbocharging. At this point in the build I am most likely going to keep it nearly stock. With that in mind I have some thoughts on Megasquirt. I am no expert so this is just MY humble opinion:

1. MS on a stock engine is probably not worth any minimal power increases. The German engineers did a pretty good job of optimizing the DME (ECU) for the engine.
2. If you are going with major performance then MS is a must for you.
3. You really need some dyno time with a pro to set up the fuel and timing tables. I have used the auto-tune feature extensively but my setup still tends to be on the rich side.
4. Getting the startup sequence and idle to work as well as the stock system is very difficult to achieve.

Certainly there are those out there who have achieved near perfect results but I have done extensive online research and have found many like me who are still trying to find the best tune.

With all of this in mind I decided to experiment by reinstalling the original Motronic 1.3 ECU. That basically involved installing the distributor cap and rotor and the plug wires, as well as the original TPS with a minor wiring change to restore it to stock. I also had to install the stock AFM.

As soon as I started the car the difference was obvious. The engine started faster and quickly settled into a very smooth idle around 800 rpm. The acceleration felt about the same but everything seemed smoother. The MS may have had a slight edge at higher load in 5th gear but there was no dramatic change. As the engine is run for a little while the DME adjusts itself for the ambient conditions. Any time the battery is disconnected the DME goes through the same adjustment cycle.

I plan to drive it for a while to see how I like it. The only other change I might consider is the Miller MAF conversion. I would not want the W.A.R. chip because that gets back into adjusting the fuel tables, which is really something for the pros.





MSPNP Gen 2 ECU - IGN-6 coil pack - MAF IAT sensor - TPS (true rheostat type) - AC idleup solenoid - Ethanol sensor - Bosch knock sensor - QuadSpark coil driver - LC-2 O2 sensor controller

[JimBobs 91E30]

After going back to the stock ECU, ignition, and AFM the engine ran very smooth except for the low rpm performance and idle. Starting off from idle the engine would hesitate and the low end acceleration was not smooth. The car would "buck" sometimes when maintaining a low constant speed, like cruising 25-30 mph in 2nd gear. I suspected that the dual grind performance cam was too aggressive for the stock ecu. It had a 280/274 degree duration which caused a bit of overlap with intake and exhaust valve opening. I installed a new stock cam (264 degrees) and the car ran great, with very smooth starts and low end acceleration and no bucking at low steady speeds and deceleration. The only issue that remained was a surging issue at idle. The car would start and idle fine but after the engine warmed up the engine would develop a rhythmic surge pattern between 700-1200 rpm. Some research indicated that this is a very common issue and some of the common causes are the AFM, temperature sender in the t-stat housing for the ECU, and the oxygen sensor. When I was running Megasquirt I used a wideband O2 sensor but when I removed MS and went back to stock I installed a used oem sensor. I bought a new one and installed it and that solved the problem.

[E34DIYer]

Fellow Bimmers, just a quick heads-up that we will be putting our beautiful E30 restomod up for sale. I'm not sure yet on pricing, but PM me if you are interested or have feedback.

[Zawiggins]

Hey there I've been building my own m20 turbo and I can't seem to find any information on which bosch 42lb injectors physically fit could you please let me get a part number 🙏