Twinspark Conversion Questions

[lgowin]

I've been working on a twinspark conversion with the stock EFI setup in my GTV and I hit a couple questions tonight.

I realized that I didn't have a throttle position sensor. I used a Spica throttle assembly, so there's no visible rheostat unless it is somehow incorporated in the intake plenum. In any case, this set me off researching the Bosch Motronic system. I discovered that my twinspark is from an ’88 – ’92 75 with the ML4.1 system. I’ve since discovered some web pages discussing this system, but they’re non-Alfa specific. My assumption is that the inputs, wiring, etc are all consistent though certainly the spark/fuel maps are unique to the Alfa application. Can someone confirm this assumption? If so, it looks like I can rig up a Check Engine Light and do some other cool things (that is after I solve for the throttle position sensor, air flow sensor, etc). The specific page I'm referencing is here.

I’m finally hitting the hard part of the conversion, so I expect I’ll be hitting the board up with a lot of questions over the coming weeks. I’m going to keep the stock fuel injection, but I’ve got no experience in setting something like this up. I’ll apologize in advance for any painfully stupid questions I put forth.

Regards,
Lawrence
71 GTV

[Craig]

G'Day Lawrence,

You've got it pretty well right with minor exceptions like two coils.

The throttle position sensor is actually two switches in one enclosure (idle position and WOT).

See my site for more Alfa (and TS) specific info, in particular the "Twin Spark 'S' " manual and the "ECU info and diagnostics (Italian)".

Also the "Fuel quality plug" and the "Electrical & Electronic Diagnosis Section C (Motronic 4.1)".

[lgowin]

Thanks Craig. Last night I started laying in the wiring harness to figure out what I need/don't need. I've got a few pages from your website printed out to help with fuel line routing and the like, but thought there could be material differences between the different 75 twinspark engine management systems (i.e. with O2 sensor or without).

By the way, I went back out this morning and double-checked the underside of the intake plenum. There was a plug for what I believe to be be the TPS ;-).

Intake Support Rod
I did notice that the 75's intake support rod (carb support rod on the 105s) seems a touch too tall for the 105. It bolts into the right side engine mount and then fastens to the underside of the intake plenum and a branch bolts to the intake manifold. Picture an uplide down 'L'. The piece that bolts to the intake manifold seems to be about 1/8" too tall and would need to have some metal ground out to be bolted to the intake manifold. Has anyone else experienced this?

Clutch Slave Cylinder
Given that the standard 105 gearbox bolts up to the twinspark the same as the nord engine, the clutch slave cylinder should be a no-brainer. However, the 75 has a transaxle. When fitting the slave cylinder, I couldn't get the forward circlip into the groove that sits on the engine side of the gearbox. It seems like the twinspark has less clearance than the nord engine down there preventing the circlip from being put into position. The rear circlip that holds the slave cylinder went on fine. I don't think that the forward circlip does anything as the clutch arm prevents the slave cylinder from moving backward. I think this is a non-issue, but figured I would raise the question to be safe and document it for anyone doing this conversion in the future.

Regards,
Lawrence

[Capp]

lgowin-
I wouldn't worry yet about the plenum brace length 'cause you're probably going to have to modify it for hood clearance on a GTV
I'm confused when you say you're using the stock plenum but also spica throttle. Do you mean you're using the stock Spica throttle linkage bellcrank at the firewall? If so, you're on the right path BUT, you will need the stock TPS and AFM if you intend to use the original FI setup. Also, you'll have to fabricate a suitable throttle cable. The TPS is the black device bolted to the bottom of the throttle body, if you have it. This switch is pretty commonly available through numerous suppliers, and the AFM is common to some other same-era Alfas so finding a good used or rebuilt one shouldn't be too difficult. I can provide part nuimbers if needed. Keep hammering, and feel free to ask questions.

[lgowin]

I used the Spica standoff/throttle stop assembly that bolts to the firewall. I had the 'Rest-of-World' carb setup on my GTV, which is rod-actuated. So, I dusted off my old Spica parts to go back to a cable-actuated throttle assembly. I bought a cable & housing from Centerline. I swapped the inner cable with one that is a bit longer that had a end to fit into the TS throttle assembly. The inner cable came from a bike shop. The TPS is on the bottom of the EFI plenum. I haven't pulled the plenum back off to look for the AFM.

You mention having to modify the plenum brace. I was thinking that I would probably have to redrill the cable stop on the intake plenum to clear the hood. Will this not give sufficient clearance? If not, it wouldn't be too difficult to cut and reweld the plenum brace.

Regards,
Lawrence

[Capp]

lgowin-- Here's the problem: most of these swaps into 105/115 series cars using the stock EFI setup requires that you lower the intake side of the engine to gain sufficient hood clearance. Spiders are worse than GTVs because of the even lower hoodline. No, modifying the bellcrank at the throttle body on top of the plenum is not likely to gain you more than 1/4". Save that for the last little bit if you need it and, hopefully, you will not because it is important to maintain the correct geometry of the throttle as it swings through it's arc for linear throttle "feel", not to mention avoiding the possibility of binding issues
Usually this lowering of the engine is accomplished by using a shorter intake side motor mount, such as the one from an Alfetta. This in turn causes another but more easily fixed problem (on a GTV at least)-- as you lower and tilt the engine toward the right the intake plenum fouls the inner fender. The key to the whole task is juggling and modifying/adjusting a few pieces to get this hood clearance without hitting the inner fender.
I accomplished this by 1) making the plenum brace vertically adjustable by elongating the bottom mounting hole, 2) juggling the amount of spacers (washers, actually) underneath the other leg of the plenum brace which mounts to the cyl. head, 3) making sure the plate on which the fuel pressure regulator and pulsation damper are mounted is bolted UNDERNEATH the leg of the plenum brace that bolts to the bottom of the plenum, 4) cutting my own rubber intake connectors to the shortest possible length. This moves the whole intake array closer to the engine and away from the fender. All these things taken collectively gave me enough "adjustability" to get clearance in both places. This will make more sense as you get it all bolted up and generally in place.
Remember: YMMV! What works on some cars may not on others due to possible prior crash damage, factory build tolerances , and what we have come to know and love as the idiosynchratic nature of these cars. Rave on!

[lgowin]

I played around with this tonight a bit. I pulled the throttle body off and remounted it upside down (the bolt pattern allows a 180* turn, but not 90* or 270*). Unfortunately the coolant inlet with a hose attached will take up at least as much room as the throttle stop.

I've pulled the plenum brace and am letting the intake sag a bit for the time being. After I get things sorted out, I'll modify the plenum brace to put the intake at the best height for my 105 engine bay.

BTW, my car has decent clearance with the inner fender. The Spica intake was similarly sized to the twinspark plenum.

Now, does anyone have an AFM from a TS 75 or a 90-94 Spider (Bosch P/N 0 280 202 202) they're willing to sell?

Lawrence

[Philip Hehir]

Hi Lawrence

I have a TS AFM I could sell you for $100 USD. But I'm in New Zealand, so would need to check postage costs to ensure it's cost effective.

What is your address? and I'll get a quote for you if you still need the part.

Regards
Phil.

[lgowin]

Thanks for the offer Phil, but a local Alfista called me today with an AFM from a 75 TS.

Regards,
Lawrence

[lgowin]

Here's a couple more and an update to a prior question...

It appears that my twinspark was from a non-catalytic converter market (maybe Italy?). The wiring harness doesn't have the 2 leads that go to the O2 sensor. I would hope that the ECUs would be able to run in closed loop mode if the O2 sensor were wired into the 35 pin connector. I Googled the part number (0 261 200108) and it only came up with Alfa Motronic ML4.1 applications. I wouldn't expect that they would have O2/No O2 variations such as this within the same part number. There is another tag on the ECU with three lines of numbers and bar codes that could be a serial number and/or a sub-variant to the main part number. This is as follows:

*751*02*
*26RT2517*
*0112000308*

Will this ECU work for O2 or non-O2 sensor applications?

The next question is should I care? Polar bear extinctions aside, it seems like the engine would have better performance in a closed loop mode, but it seems that they would have used O2 sensors in all markets for the performance benefits. If I don't have to run an O2 sensor, I may not mess with it. If nothing else, I may use an O2 sensor to feed a mixture meter.

Finally an update to the intake plenum support rod...I cut the lower two thirds of the rod off and replaced it with a turnbuckle. This made the rod adjustable on the car so that I could keep the intake as close to the stock height as the 105 engine bay will allow.

Next challenge - Finding a pair of ignition modules and coils and mounting the ECU.

Regards,
Lawrence

[NZAlfa75]

Again, check Craig's page for info on the O2 sensor. The ECU is the same you just have to put a jumper in the plug.

The non-O2 maps will yield a little extra power and take advantage of higher octane 98 RON fuel.

I have spare coils/ignitors. I'm sure Phil Hehir (also in NZ) will too. Postage will be the killer.

[Craig]

G'Day Lawrence,

The ECU's are (I believe) the same. There are three(?) different 'chips' but nobody knows why (but someone tested and reported no difference in power).

You could run without an O2 sensor, the mapping is very good. However I think an O2 sensor (closed loop) could help with Denver's altitude (just a guess).

See this thread for some info.

Does you harness have the red relay base (S30) hanging off the ECU connector?

[lgowin]

I didn't catch the info on Craig's page about the O2 sensor, but I've been pouring through the manuals posted there. I'm still somewhat in the discovery phase of the project (I guess that lasts until you get the car running), but I haven't spent much time looking at the fuel quality plug section of Craig's site.

My harness doesn't have the red plug. I've compared it with the manual section showing the harness and its connections. The kids are in bed, so I'm going to spend some quality time tonight with a multimeter, some tape for labels, and the injection harness.

Regards,
Lawrence

[lgowin]

Update...My wife voiced her displeasure when I laid the injection wiring harness out on the kitchen island, though she wasn't too upset. In any case, there was no fuel quality relay plug. However, there was a 9 pin female connector that when I toned it out now seems like it might have originally plugged into a tail with this and the T2 connector.

The good news is I can leave it open to run in open loop. I still like the idea of running closed loop, so at some point I'll need to figure out what the pinout is on the connector diagrams to figure out what connections to short out. Does anyone know the ECU pinouts that correspond with the blue, yellow, or red plugs?

I also found a set of ignition module/coils from a 75 TS. Someone here in Denver has done a TS conversion with carbs and has some leftover pieces. That's also where I got my AFM that I mentioned I was missing earlier.

On a side note, it struck me funny tonight that I was flipping through manuals and other info I found on the internet trying to master 20+ year old technology. Its a bit different from my day job where a number of us work on IETF standards and the like.

Regards,
Lawrence

[Bruce Colby]

Here are a few links I found helpful when working through TS conversion projects:

This one includes pictures of the connectors:
http://alfaimola.free.fr/twinspark/c...urs/index.html

This one includes a picture of the wiring harness:
http://alfaimola.free.fr/twinspark/schemas/index.html

If you're rebuilding a TS motor, there are some other helpful pages at this site as well.