The chain of events, the what and how of a getting a car on the dyno.

A clean 1990 E30 BMW in for a tune. Engine rebuilt with a set of 268 Clive cams, Forged pistons, rods and ITBs. The engine was running very poorly with soot out the tail pipe. Fact is it was only running on 4 or 5 or the six cylinders.

This car was put together nicely. Had fruit from Hillside, racing hardware developments carbon fibre inlet, Quick rack, fresh suspension arms and coil overs, new extractors and full exhaust  and a Haltech Sprint 500 ECU in piggyback. An old ECU for sure. The plan was getting the car running correctly and iron out any bugs prior to upgrading the ECU and stepping up to a PDM or two.ITB E30

 The sanity check (a sanity check is a look over the readings from the sensors to confirm readings are rational) of the Sprint 500 showed the ATS (air temp sensor) was reading -10, a clear sign of an issue and no response for the TPS (throttle position sensor) during a pedal sweep. The ECU was not locked so we were able have a look around the Tune and Maps. For clarity, the ECU is the physical part, the Tune all the settings and Maps combined. The Maps are the individual settings for each aspect of the tune. An example the VE (volumetric efficiency) Map. 

base maps

When talking locked ECUs, the only reason I see to lock an ECU is to prevent changes being made either accidentally or deliberately. If a person is inclined to take a copy of a map and use it because their car is similar, good luck. Several brands of ECUs do flash a warning if a different laptop has been connected since yours was, you know instantly if someone has plugged in. With a locked tune you will be able to see sensor outputs and limited settings. You will not be able to see the Maps or make changes.

ECU locked

We keep a copy of every Tune. Lucky we do, one ECU manufacturer has a firmware issue. Firmware is a type of software that allows the ECU hardware to operate. With this issue if battery voltage gets low the firmware corrupts and the ECU will not boot. At least the fix is simple. Load the latest firmware, reload the tune and you are good to go.
I personally like to have the latest firmware installed and update every ECU whenever I plug in. Some will argue if it isn’t broke don’t fix it. I will also check the logs and trims. The trim tables record the small adjustment the ECU has been making to the Maps. Several trim tables are available for use. Fuel trims, knock trims, idle speed and boost to name a few.

OK back to the E30. The Tune was not locked. The engine capacity had been set incorrectly to 3000cc instead of 2500cc. All other settings were as expected. No wide band sensor installed. The TPS issue was checked before going for engine start. It was found the sensor had not been installed correctly with the pin or the backside of the sensor instead of the front. Simply fix.
On engine start the engine ran poorly and was missing on two cylinders. Using the infrared thermometer to check the header temperature. Four of the 6 were reading 350 degrees or so with the remaining 2 at under 100 degrees indicating those cylinders not firing.

Spark plugs removed showing all plugs were fouled. Perfect time to complete a compression and leak down test. Yes, rebuilt engine, but we are chasing an issue and need to be confident the engine is sound. Both compression and leak down came back with passing results. Spark plugs were cleaned and refitted. Fouled spark plugs and tuning go hand in hand. Base Maps always run rich. Rich running fouls sparks plugs. Those first few minutes when warming up the engine on a base map can foul plugs. Often you burn the soot off and reuse the plugs. When the engine is at operating temperature the plugs are less likely to foul and you can get the idle section of the map close enough to stop fouling occurring.

Fouled spark plug

Engine did run better after the plug cleaning. While the engine was running it did sound lean, popping in the intake and sluggish to rev. The dyno wide band connected at the tailpipe showing the engine running 20-25% lean. Getting the Lambda to read correctly by adjusting the VE Map, wild figures resulted. Injector size and dead times were correct in the map. Wild VE numbers and good data for injectors and dead times (Dead time being the amount of time between the point where the ECU tells the injector to open before being fully open and when told to close and before being fully closed), data being correct it is time to check fuel pressure.

Fuel pressure gauge connected showing fuel pressure of <15 PSI. Regulator return was blocked to evaluate maximum possible fuel pressure. Result of 20PSI. Fuel pressure spec being 43 Psi, we have a fuel pressure fault.

The fuel pump was located under the rear seat which is a good thing. No need to drop the tank. The plug connected to the fuel pump was cracking. This poor connection generated heat due excessive resistance at the pump. The pump removed to find the in tank wiring insulation deformed due to this heat.
In tank pump and wiring replaced along with the fuel filter. The cracked plug  replaced and wiring for the fuel pump main circuit and relay upgraded. Beautiful thing was we were able to swap in a fusible relay and block at the same location of the original fuel pump relay. All new wiring on the main circuit and new plug connecting to the fuel pump gave fuel pressure as expected close to 43PSI.

Fuel Pressure Gauge

Engine ran so much better with the original numbers in the VE Map. Now onto the cause of the ATS reading -10 degrees. Five volts was present at the sensor and continuity was good back to the ECU on the signal wire. Removing the GM style (common to us GM style ATS and CTS with aftermarket ECUs) ATS showed an abnormal rattling noise. Possible damaged due to the backfiring that was occurring when the engine was lean.
ATS sensor replaced and reading correctly.
With idle lambda set and the VE looking as expected. Very slight miss was present. Swapped out the original plugs and time to Dyno.
All when well on the dyno. No more running rough, no black soot and a nice lumpy idle as you want with a cam. Cold start all retested the next morning and good to go.

With dyno tuning, the tune is often the simple part. It is making sure everything else is working correctly that makes the tuning straight forward.

Congratulations you made it to the end.  Give yourself a gold star.

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