Who knows their iron duke TBI?

Real tech discussion on design, fabrication, testing, development of custom or adapted parts for Pontiac Fieros. Not questions about the power a CAI will give.

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CincinnatiFiero
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Who knows their iron duke TBI?

Post by CincinnatiFiero »

Yeah, that's right TBI!

So I have one of these
Image

1972 Mercedes 220 gas. 72 makes it pre-DOT do it's got the euro style bumpers, taillights, big bakelite steering wheel, etc.

Ton of fun to drive... when its warm. It has a bastard of a Stromberg sidedraft carb on it that is hard to keep in tune (I've rebuilt it and cleaned it all out), the side draft with with the mechanical fuel pump loses prime when the car sits more than a couple of days. The automatic choke of course doesn't work and you've got to let it warm up for a while before you try to get on the road otherwise you're sputtering at backfiring at 7 mph pissing off all of traffic behind you. So,

I found this guy who put TBI on one.
http://www.peachparts.com/shopforum/vin ... rsion.html

He initially uses megasquirt to run the TBI, then uses the megasquirt to run a DIS system.

I was thinking, could this just be done with the stock "ecu" from an 80s GM iron duke tbi car? How many inputs does TBI really need to run? Seems like a coolant sensor, low pressure electric fuel pump, oxygen sensor, and map sensor is all that runs TBI. Its constant injection so there isn't a crank or cam sensor is there?

I would retain the stock Mercedes distributor and coil (probably go Pertronix or something at some point for further simplicity)

I have a spare 220 engine on the shelf to mock up a manifold on, but it seems like this could be done with a few wires, and a $50 raid on a Cavalier at Pick and Pull. Fuel pump, odds and ends, etc. Seems like it could be not all that complicated to do and be cheaper than having the automatic choke professionally rebuilt or replaced.

Is the TBI ECU as simple as I think it is?

This is a 105HP car 2.2L 4cyl car. I am not trying to make more power, just faster starts, shorter warm-up times, and probably smoother idle.

In that other thread he's running the TBI on its side, I would think the way TBI works it wouldn't be thrilled with being run sidedraft. I have access to an aluminum welder, I thought about welding a cast aluminum elbow onto the Mercedes manifold to be able to position the TBI like GM would have. But if you guys think it would work fine sideways, that's even simpler.
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Emc209i
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Re: Who knows their iron duke TBI?

Post by Emc209i »

You're on target except I think the TBI systems from GM use the distributor for injector timing like MPFI did, specifically: ignition pickup winding (AC analog signal) --> ignition control module --> digital square wave output to the ECM to trigger injector, coil, and tach. I'm away from home right now and don't have the diagrams with me, but if I'm right going off what's left over in my head from ten years ago (I might not be), you'd have to convert the dizzy as well. But I think that's right, in 1987 or 1988 they went to coil packs and a trigger wheel on the crank... so yeah, it must have had an ignition module. The injector not only needs to know when to fire but duration as well, it doesn't just stay open.

The cheap route would be getting the stock equipment retrofitted. Holley makes the Terminator series EFI carb's that essentially turn a carburetor intake into a TBI setup, but they're expensive, albeit plug and play and self learning. And yeah, I don't think the throttle body would play nice mounted sideways, you'd need to mount it to the manifold right side up.

Sure you can't just retrofit to a better/modern carb setup? That would be easier. TBI sucks compared to port injection on non direct injection engines. Plus you're killing the romantic part of owning old technology. Putting chevy TBI on a Merc is ... bleck.

Edit: Yeah, I looked up a picture of the Fiero dizzy, it's got the electronics on it.
CincinnatiFiero
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Re: Who knows their iron duke TBI?

Post by CincinnatiFiero »

I enjoy driving the car as is, in fact I drove it to work the past 2 days. But the warmup time and constant fiddling annoys me a bit. When this was a sub $200 junkyard fuel injection idea, it was cool. The fact of the matter is this car is worth like $3,000 on the sunniest of days, so going to true EFI or a Holley TBI in a box setup, just is realistic for the car.

The distributor thing makes perfect sense, I wonder if a signal created by the hall effect sensor in a Pertronix setup could somehow be used to replicate the signal the TBI ecu wants to see.

What I did today instead was or the parts necessary to install the 4speed manual gearbox I have on the shelf for this car. So I'll put in the 4speed first, then think more about the carb.

Another short run thought is an electric lift pump from rock auto to bypass the mechanical pump which should speed up priming and starts for $25 and minimal effort. Also would let me block off the mechanical fuel pump which is perpetually leaking oil out of its plastic spacer.
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Shaun41178(2)
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Re: Who knows their iron duke TBI?

Post by Shaun41178(2) »

Sensors the comp needs to see as far as I know are,

Map
Mat
Tps
O2
Coolant
Iac
The Dark Side of Will
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Re: Who knows their iron duke TBI?

Post by The Dark Side of Will »

Electric fuel pump sounds like a good idea.

Like EMC said, the TBI is pulsed injection, *NOT* constant flow, and requires electronic triggering. This can come from the distributor or a flying magnet (I think) style trigger wheel. It takes one pulse per ignition event.

You will *NOT* be able to get it to run well without retuning the stock ECM.

There are code masks for tuning a variety of TBI ECM's, as that's where the DIY GM tuning movement got started. You'll end up putting a good bit of time into tuning it to run right.

I haven't really looked intently at any TBI units, but I don't see why they wouldn't work side draft... The fuel spaces are sealed, so it's not like fuel will spill.
CincinnatiFiero
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Re: Who knows their iron duke TBI?

Post by CincinnatiFiero »

It quickly became much more effort than its worth. I'll do the electric lift pump, play with the water choke one more time, and then relegate it warm weather only driving.

Thanks for the insights!
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