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Content dedicated to preserving the SAAB brand

Trionic 5 Conversion: What you need

A Definitive shopping list if your thinking about converting your classic 900 to Trionic 5

A major component in decision making is trying to give something a sense of value. Is something worth our time, money, or mental energy. When many heard of this Trionic 5 conversion, the natural skeptical response is, "What are they talking about and why do I want to spend more money on this car that doesn't seem to run right in the first place? OR "My car runs perfectly fine the way it is, I don't want a freakin' race car!". Which I will add, are all perfectly normal adult responses. Maybe you've seen some internet yahoos go on-and-on about how much better the car drives/starts/idles/boosts or that their engine harness isn't crumbling any more. Who knows, but the first step to making the right decision for you, is getting the details about what is involved.

What do I need?

  • Conversion Wire Harness
  • Red DI Cassette
  • T5 ECM (Any ‘94-99 SAAB Turbo), setup for a classic 900
  • Crank Position Sensor Trigger w/ sensor kit
  • 4x Bosch Red Top (431) NG900T, 94+ 9000 Injectors (OE # 9132449)
  • Coolant Temp Sensor (OE# 9357021)
  • Air Temp Sensor (OE# 8859886)
  • Intercooler Pipe modified for Air Temp Sensor mount (Sensor 10x1.25 Thread)
  • Throttle Position Sensor (OE# 8857195)
  • Throttle Position Sensor Adapter , 2.1 900 or 9000 Throttle Body
  • Throttle Body O-rings ( OE #7506264 and 7521875)
  • 3.0bar Fuel Pressure Regulator (From 2.1L Bosch #028016706 or 7486921 with adapter hose)
  • MAP Sensor (OE# 9132374)
  • Vacuum Line (3.5mm line of your choosing)
  • Vacuum "T" fitting
  • T7 Boost Control Valve (OE#55557331)
  • Air Idle Control Valve (2 pin 89+ 900 Turbo Bosch #0280140516)
  • Oxygen Sensor (Stock 3-wire works fine)
  • 4x NGK BCPR7ES Spark Plugs Gapped .039-.041”
  • Distributor Oil Plug (OE# 9135211)

Ok, so that is the bullet-point list , but I'll go deeper into each item as some need a little more explanation.

I also sell a COMPLETE T5 KIT so you don't have to worry yourself with part numbers or forgetting something, this is as turn-key as it gets.

Conversion Wire Harness

Ok so I'm totally biased here, but a custom-built new wire harness specifically for the classic 900 T5 conversion is what I bring to the table. Many, many, moons ago I began on this T5 journey modifying stock 9000/NG900 wire harnesses to adapt them to fit the classic 900. This required tearing down the old harness, wiping off all the nasty grime and grease that accumulates inside old tape and splicing each wire about ~24" out so that I could run it to the stock location. You find lots of crumbling insulation, broken connectors and there is still a significant amount of rewiring required. Many components are not in the same orientation between the classic and new generation models and the T5 main engine harness does not include the relays or boost control wiring like the original harnesses do.

Alt Text

Yes, there are some people who skip this step and drill a Big hole right through their firewall, or mount the ECM somewhere else in the engine compartment, but I like having a really clean install that was as good, if not better, than the original. This was quite a tiring excersize and ended up finding all sorts of broken/brittle connectors or suspect connections that I'd have to fix along the way. Later on, I decided to see if I could try to track down all the of the components as new and just buy colored wire to start fresh. The first new replacement T5 conversion harness was born and I never looked back. Now, If you enjoy pouring over wiring diagrams, I won't stop you from building or modifiying your own harness (heck I'll probably even help you if have questions), but the one I offer today is my 5th revision to make the best c900 Trionic 5 Conversion Harness possible. All NEW components, OBDII Diagnostics, and plug and play compatibility.

Red DI Cassette

This is the heart of Trionic 5, don't buy aftermarket, ever. Should you buy new? Old DIs work just fine, but don't expect them to last forever. Date codes can be read on the SAAB sticker on the bottom of the DI next to the connector. It is a 4-digit code above the "SAAB" logo that is year of manufacture followed by week of manufacturer. In otherwords 1605 would be 2016, 5th week or February. Can I use the black one? Can you? Yes, Should you? Not really. Although somewhat backwards compatibile, the Black DI cassette (stock on Trionic 7 cars) has some different calibrations and uses AC vs DC spark, that may not work optimally with the T5 brain. If your in a pinch, sure, but use the red one!


Trionic 5.5 (the .5 is important!) ECMs actually come in two flavors with some subtle differences in hardware. Rather than bore you with the details, I will just say that the OBDII versions which came on MY97+ SAAB turbo models are preferred and the most compatibile. If you can only scrounge one up from a 94-96, no big deal, but just know what you have. My foreshadowing about the .5 being important is all due the fact that there was also a 1993 only Trionic 5.2, that shares a similar world view to 5.5, but that is about it. 94-99 turbo cars (and even the 9000 non-turbos!) all had Trionic 5.5. So once you have a unit, it still needs to be programmed to run on a c900 correctly. Some of them have VSS (Vehicle Security System) enabled, some are set up for 2.3L motors, all will not give you a correct speed calculation based on your speed signal (if you have one), so you'll likely be set up for base boost. For all these reasons, (and more) your T5 ECM should be tuned specifically for the c900, and your cars own setup or modifications. The B202 in the c900 does have different flow characteristics than the B204 engines so although they are similar enough to run the car, you'll find some lean/rich areas as well as some sub-optimal performance.


Another topic of slight contention is how to get the crank position signal. This sensor is missing from the the stock Jetronic system, it gets around this by using batch-fire. Instead of injecting fuel for each cylinder, once per combustion cycle, it blindly squirts fuel into multiple cylinders each rotation. The factory Trionic cars use a "toothed" (reluctor) wheel bolted right to the crank inside the block. That isn’t really going to work for an easy conversion. The modified flywheel option is my go-to because it allowed the most straight forward installation and has very few disadvantages. The flywheel can only be mounted one way and is bolted directly to the crank making it perfect for accurately referencing the crank angle. Another option is to bolt something to the crank pulley side, but being “in-backwards” make for tight quarters for making adjustments needed to get the sensor and trigger wheel lined up perfectly. Due to lack of space, usually the A/C pulley is sacrificed which is a non-starter for many. Most alternatives I’ve seen also make belt changes challenging and general “front” engine service requires removing the setup completely. The biggest challenge is maintaining accuracy as the smaller diameter of the pulley wheel has a much larger margin of error. When the stock sensor is mounted into the block and fixed to the crank , this isn't much of a concern. However, the reluctor being mounted from the crank, to the pulley, to an adapter, allows for concentricity and alignment errors. This is why they can't just bolt right on, they need to be tweaked until proper timing is set. Trionic is fairly tolerant of some of these misalignments, so you may not even know your timing is off, but even a degree or two can make a huge difference in performance.

Fuel Injectors

The path of least resisitance is to use the standard T5 injectors and a 3.0bar regulator, since the software mapping is already setup to use these components. The question is often asked, why can't I use the standard 900 Turbo injectors? The reason is that the stock classic 900 injectors are sized @ 21lb/hr where T5 injectors are sized as 33lb/hr. The reason why they are so much larger is that Trionic 5 will inject fuel only once per combustion cycle. The Bosch Jetronic system has no idea where it is in the combustion cycle (no CPS), so it will inject smaller amounts mulitple times in multiple cylinders. The end result being a similar amount of fuel, but just done more efficiently with T5. The stock injectors I found to be good for about 260whp (300 crank). After that they can't keep up , and larger injectors should be fitted. This for most is plenty so no reason to change. I will also mention there are alternative, modern injectors that could offer some additional benefits, but again, the software would need to be recalibrated to take full advantage of this.

Coolant Temp Sensor

When I build my harnesses I retain the stock connector for the coolant temp sensor. If you have your own modified harness from a T5 car there is a good chance it has a different style of connector. Just make sure you match the sensor to the plug you have. Also note with the sqaure-style connector, there are a few oddball 9000 coolant temp sensors on TCS cars, you want the ones that are blue, not white or black.

Air Temp Sensor

The same info applies to the air temp sensor as the coolant temp sensor above regarding the connectors. It should be added that there is no air temp sensor in the Bosch Jetronic system because it uses a MAF (Mass Airflow Sensor) to read incoming air mass. T5 uses the combination of a MAP (Manifold Absolute Pressure) & Air Temp to calculate air mass. These two sensors are most critical for accurate fuel calculations. To fit these I prefer to have them installed into the intercooler pipe before the throttle body just as the 9000 has. This isolates the sensor from having its temperature affected by engine heat soak. More importantly, it keeps it out of the turbulent zone of the throttle body which can phyically destroy the sensor. Since there are two versions of intercooler piping, cast aluminum (85-88) and aluminum tubing (89+) installation varies. The cast aluminum pipes are thick enough to be drilled and tapped, where the aluminum tubing should have a a bung welded to it. The sensor is M10x1.25 thread. Remember, oil also collects in these pipes, so it is best not to mount the sensor on the bottom.

Throttle Position Sensor

The throttle position sensor is a fairly straight forward swap with a couple of options. T5 uses the same sensor that was used on 2.1 liter 900, so if you have the parts cache, you can simply swap the throttle body. Make sure to replace the o-rings behind the throttle body as well as the coolant passage o-ring behind the sensor while you have it i out. It is also a good idea to epoxy the brass fittings in place as they are not used to seeing positive boost pressure and commonly blow out. The second option is to use the MCS TPS Adapter. The adapter allow you to use the T5 sensor on the stock throttle body. It's also recommended to change your throttle body o-rings (while you're in there).

MAP Sensor

You need this. Max resolution for this sensor is 1.5bar above sea-level (~22psi boost) If you plan to exceed 20psi often, you should consider a 3bar sensor, but that is a different article. The sensor should be mounted with as short and rigid a hose as possible with a thick sidewall to prevent ballooning. Ideally, it should have a dedicated hose right from the manifold and not shared with other components.

T7 Boost Control Valve

The boost control valve from Trionic 7 cars offers more reliable performance at a cheaper cost. I make all of my wire harnesses and c900 ECM tunes setup for the T7 BPC so no other modifications need to be made.

Spark Plugs

NGK BCP*R*7ES-11. The -11 means they are pre-gapped to 1.1mm. If you get them without the dash, they should be re-gapped to the proper spec which is 0.9-1.1mm (.035-.041in). Spark plugs are exteremly important for Trionic to function properly, so it is best to stick with the book.

Stock Oxygen Sensor

Replace your o2 Sensor if you don't know how old it is. The o2 sensor constantly monitors & adjusts your air-fuel mixture to get the best economy and efficiency, so it is vital that it functions well. Within Trionic 5, it is confusing because some sensors have three wires and some have four, meanwhile the stock c900 sensor has three wires, but two connectors. The truth is that all the (LH & T5) sensors are all functionally the same with different connection styles. I make my T5 conversion harness with the stock connector in mind, but any of them will work. There is a difference between the three and four wire sensors , which has to do more with wiring configuration than anything else. Again, the sensors are the same, but the four wire uses an "extra" ground wire to run directly from the ECM where as the three-wire is just grounded to the chassis through the exhaust system. Four-wire systems are a little more robust, but the three-wire work just fine as long as the sensor contact surfaces are in good shape.

Distributor Oil Plug

One of the benefits of the conversion is all of the components that get consolidated. The distributor is one parts that when removed, makes you feel good. But in its place there are a couple options. SAAB at first used a nice spun aluminum block off plate held in with the factory distributor retainer, but later changed this to simple rubber coated steel plug. The rubber coated plugs tend to leak after a while, so a small amount of sealant around them before installing will least for a little while.

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Welcome to Modern Classic SAAB

Yes, It IS an Oxymoron.