TBI to semi-sequential MPI (VW Passat)

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kuchen
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Joined: Tue Oct 25, 2011 12:38 pm
Location: Stuttgart/Germany

TBI to semi-sequential MPI (VW Passat)

Post by kuchen » Sun Oct 30, 2011 1:22 pm

Hi,

this is our MY88 VW Passat Variant family hauler powered by the unbreakable 1.8L 90hp TBI engine, 300Tkm on the odometer.
The car itself is uninteresting, but the conversion might be of interest to those of you who want to convert a TBI engine like the 305 OR 350 Chevys from the early 90ies using a sequential system.

Basically, all 4 petrol Injector hookups were soldered together, so the LPG controller handles the signal as it would handle a full-group system.
My favorite LPG controller, the AC Stag 300 has an option to drive the LPG injectors semi-sequentially on full-group petrol systems. This means the frequency is split into half, the injection time is doubled, plus on that particular inline four the LPG injectors are grouped in 2x2, 2 firing at the same time. An important feature, as the petrol injection time is 1.7ms at idle on that Bosch Mono-Jetronic single injector, and no known LPG injector can handle that.
overview.JPG
Stag connection schematics
schematics.png


Frank
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Re: TBI to semi-sequential MPI (VW Passat)

Post by Frank » Mon Oct 31, 2011 3:38 pm

I thought that it would be much better to convert a TBI engine with an injection conversion rather than a mixer conversion. However, I have not been able to get any advice from the factory as to how this may be accomplished. I think there may have been an issue with matching injector coil impedances.

If I read your posting correctly, you spliced the four petrol injector wires from the LPG system into the single petrol injector's wiring. I thought this could also be done for 2-injector TBI systems found on American V8 engines. That is, each petrol injector could drive 4 LPG injectors (ie, semi-sequential or bank-fire) and the placement of the injector nozzles at each intake port would eliminate the need to find obsolete Impco/Gann mixer adapters and Dual Curve controllers.

Do you know of anyone who has converted a 305 or 350 TBI engine to semi-sequential LPG injection?

kuchen
Posts: 79
Joined: Tue Oct 25, 2011 12:38 pm
Location: Stuttgart/Germany

Re: TBI to semi-sequential MPI (VW Passat)

Post by kuchen » Sat Nov 05, 2011 11:13 am

Hi Frank,

no I don't know anybody who owns a TBI V8, as they are pretty uncommon over here. The Haynes manual I have for my 88 Brougham also covers those engines, as they were available in later model years. I just figured that the way these systems work is almost identical to the Bosch TBI, hence a conversion is possible.

Frank
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Re: TBI to semi-sequential MPI (VW Passat)

Post by Frank » Sat Nov 05, 2011 1:06 pm

After some inquiry, I've learned that some multi-port injection conversions have already been done with V8 TBI engines. I don't have specific examples though.

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