Motronic motor turbos- 'The Tuoma Mod'

[genphreak]

No doubt many have heard of the Tuoma Mod, but I've never heard it discussed here... just found it on when I saw this awesome turbo M30 page and this one.

Looks to be useful on M102 and M106 and Porsche turbo setups for increasing boost pressures above 8.0 PSI, I suspect it has good info for anyone turboeing an M30 or other car whilst retaining the Motronic EMS.


Date: Thu, 7 Sep 2000 15:42:48 -0400
From: "jhstein" <jhstein@mindspring.com>
Subject: 745 w/ Tuoma Mod, a users report

To all:

I have had several people ask to see this again. Why, I don't know, but here it is.....

"I have been waiting to write this report until I had a few months experience with the modification.

Just a quick note.

The Tuoma mod comes in 2 parts:

1. A modification to the wastegate (much like the Porsche crowd uses, and
2. A modification to the Motronic which eliminates the 10 psi over boost shutdown. The package can be seen in detail at http://www.tuoma.com/referenc.htm.

My experience with the Tuoma mod is favorable..... But ONLY with these caveats- I would only consider / recommend the modification under these conditions:

1. A boost gauge must be installed. It is essential.

2. A 3 or 4 wire o2 sensor and a mixture monitor such as the HALMETER AFR30 http://www.halmeter.com/ should be installed. This is also essential. A 1 wire can be used but I prefer the 4 wire.

3. For boost levels above 9 inches, a fuel system modification which enriches the fuel mixtures based upon boost level is absolutely essential to avoiding blown pistons. The stock BMW injectors and stock FPRs run out of capacity at 8 psi and start to lean out the engine with potentially catastrophic results if the knock sensors are not fast enough. I use a Cartech unit.(http://www.cartech.net/fmu.htm ). This raises the fuel pressure by progressively blocking the fuel return line, thereby providing up to 80 psi to the fuel rail versus the 42 psi with the 2.5 bar FPR. This unit is very effective because it lets the fuel rail operate at the stock mixtures whilst in the range of idle to max normal boost (6 psi). Over sized injectors can be used to deliver more fuel but are a very problematic solution because they screw up the entire fuel delivery profile.....

Obviously 80 psi on the fuel rail also requires the fuel system hoses be fresh, or better yet, fresh AND steel braid clad.

Having said all that..... The Tuoma mod is everything they advertise. In the past, I have played with elevated boost pressures up to 10 psi by bleeding the wastegate line (using fish tank air valves). I had good success. The nemesis is the 10 psi over boost shutdown in the Motronic. The Tuoma mod to the Motronic completely solves that problem, with no adverse effects on derivability. While the Motronic was at Tuoma, I had them give it a full health check.

This was also money well spent.

They replaced several components which were failing at ambient temps above 85 degrees F. ( A very common problem in Atlanta...) So far, all my problems are solved. I also replaced the 2 flywheel sensors while I had the car off the road.

Just took the car on a 1000 mile trip. No problems.....Fun to drive.... All as advertised..

[Jon K]

Here's the deal about the RRFPR - I had one... still do (on shelf ) and they do what they claim, bump that fuel pressure up. But, what happens to an injector valve at 90 psi of fuel pressure is they get pinned open or closed occasionally. It's hard as HELL trying to figure out if you have a misfire, lean fire, rich fire, etc, when an injector is sticking shut or open. That's why I am bring my fuel pressure back down to 43 psi, putting 42# injectors in, custom ECU, and letting the 1:1 FPR handle its thing.

[genphreak]

Here's the deal about the RRFPR - I had one... still do (on shelf ) and they do what they claim, bump that fuel pressure up. But, what happens to an injector valve at 90 psi of fuel pressure is they get pinned open or closed occasionally. It's hard as HELL trying to figure out if you have a misfire, lean fire, rich fire, etc, when an injector is sticking shut or open. That's why I am bring my fuel pressure back down to 43 psi, putting 42# injectors in, custom ECU, and letting the 1:1 FPR handle its thing.

Sounds like the right thing now one has the luxury of new ECUs. It was a funky read though. I was more worried about the thought that the poor fuel delivery rail and squished up o-rings, pesky clamps and so on are holding back 90PSI.

We get enough fuel rail troubles on these cars! And one engine fire and you really never want to go near one again.... I like the line they had about checking the system was perfectly operational before doing the mod, i mean, how reliable would it be as you drive round and use different fuels and use the car from day to day...