[mikael82]

Time to time someone asks about this and how I do it, this might not be correct way to do it, but it is similar what I adjust carburetors and Diablo in it's way works like it got two carburetors.

Tool you need is manometer, it is more accurate then any other gauge you might have and it is only tool to use in my opinion, even factory manual says it is tool to use.

1. idle car so auxiliary air valves (aluminium part on valve cover each side) are closed, you can take intake tube along with air bypass tube out by now and check with mirror, through tube that valves are closed. On later cars Carter devise is not touching accelator shaft.

2. with T-connection, connect you manometer (I have four lines in mine, but two will do) to small tube that come from intake to fuel regulator, remember you need T-connection as you need fuel pressure system to work and not to leak through air anywhere, you can not just pull out one vacuum tube and let other end loose.

Here you can see how lines are connected, how black vacuum line changes to bluy pneumatic line after T-connection.

IF YOU NEED TO ADJUST:

3. close both bypass screws, brass screw under throttle body

4. adjust balance from those long bars side of plenums (remember one side got lefthand thread so they leght alteres) make it even, by adjusting BOTH sides (remember to make sure what side controls what side of engine they cross, but you get it). Adjust balance even on +900rpm, catch this low RPM with both sides throttle stop screws, so both sides are even when all slack from mechanism is resting. (find it little hard to get so low rpm, so closer 1000rpm is as good.)

5. have a friend in car lift up rpm's to 1500-2000rpm see that balance is even when accelator mechanism slack is out. adjust intake balance even as you friend keep STEDY rpm with gas pedal, it's difficult, but take time and practice. (remember to watch those temperatures, if you got issue with with cooling system you can stop any time and continue after while) use earplugs...

6. now car got air balance correct, but you still need to lift rpm to 1150rpm idle. You do this by opening up those bypass screws you closed at first; open them little from both sides and get idle to correct rpm. VERY carefully close locking nut so you do not alter balance and you do not brake threds.

(if you are not able to get balance, you have air leak somewhere, check all vacuum connections, there are plenty)

7. open one 35pin ECU connector and take connector casing out, there is a small screw at end and undoing this you can slide connector open, two rails will drop, don't worry, you get them back
Connect a multimeter to terminals 1 and 17 on the unplugged lie harness or pluged harnes like I do:

Voltage with no throttle should be 0.5v
Voltage at full throttle should be 5.0v (+ or - .5v)
(here we all should thank you "Sledge4.2" for reading original LM console for correct angle of throttle valve and using multimeter to how much voltage it is on wire, without it no-one could ever adjust idle and getting TPS sensor adjusted so ECU will know where idle is. this is one of most important service anyone have ever done to Diablo owners around world; Thank you.)
without car runing, you rotate by hand actual TPS sensor so multimeter says exactly 0.5v and bolt it carefully tigh. (bolting down can actually affect value, so keep multimeter "on" while you doing this.)
I have changed flathead bolts to hex bolts, because they are easier to use.

8. drive a bit and connect manometer back to see all is good, sometimes new angle of throttle linkage might settle in wrong. Remember to have warm car to see results, auxiliary valve mixes things up and can close little differently.

There you go, hopefully this help people to run their car without two red "check engine" -lights on dash from lean or rich mixture.

 

[Rayman]

Excellent write up.

 

[mikael82]

Couple of tips for manometer building;
Fluid is automatic transmition fluid, that is not harmfull if engine sucks it in, also it has nice color, easy to see.

I placed mig welder tips in inside tube, it restricts flow and calms fluid movement. Diablo intake vacuum is strong and without restriction fluid will be gone in seconds...

 

[Sledge4.2]

Thank for taking the time to write this up. I have stumbled around quite a bit finding the exact procedures, so this is very helpful.

How sensitive are the air by pass screws? They are fine-threaded, how many (approximately) turns to bring idle to specs from fully closed?

 

[mikael82]

Thank for taking the time to write this up. I have stumbled around quite a bit finding the exact procedures, so this is very helpful.

Of cource this is my version of setting air balance, I converted it from carburetors where mechanism slack is important and idea is that you kind of hang butterfly valves with by mechanism and thorttle wire. When car is let down to idle and all slack settles down to throttle stop (screws) so both idle and throttle is even.
My version is little more wider from what factory workshop manual gives.

How sensitive are the air by pass screws? They are fine-threaded, how many (approximately) turns to bring idle to specs from fully closed?

Diablo throttle valves are like Bosch K-jetronic's you find in injected Countach or Testarossa, where you have to have air by pass part of funktion, you can not run them so tight you would use carbs, where only one half is open other is closed, it would stall engine. With Diablo and injected Countach by pass air keeps idle runing when you drop from high rpm, thorttle valves let so little air through.
(I have to check this next time I adjust, I have couple of parts coming in that need adjusting same time)
I think by pass screws are 1-3 compleat turns open, other one little more from other.

 

[Sledge4.2]

Thank you. What about the rest of the mechanical adjustment on the butterflies. When would you use those?

 

[k-works]

I had used other way, because I'm not that cool to have an actual vacuum tube board. 🙂

I thought, the way ECU knows about vacuum is by means of MAP sensors. So I went to a car parts shop and bought few cheap Bosch style crank/cam angle sensors with the same style connector like MagnettiMarelli MAP to use as male connectors and few female pigtails. So I've built 3 male-female short harnesses to plug in between the sensors and the main harness.

I've also got 2 identical Multimeters to watch the MAP readings.

As for the tuning itself:
- 3rd harness was used to plug in between the main harness and TPS
- checked the TPS (thanks Sledge4.2!)
- took off the throttle rods
- let the TB sync by the MAP readings, tried to get them low and watch the idle
- took the rods on the TBs
- adjusted them so that they read identical as before (when rods were off)

That's it, probably, It was done on LM FI though.

 

[Cuda Cody]

Very nice write up!!!

 

[mikael82]

I had used other way, because I'm not that cool to have an actual vacuum tube board. 🙂

I thought, the way ECU knows about vacuum is by means of MAP sensors. So I went to a car parts shop and bought few cheap Bosch style crank/cam angle sensors with the same style connector like MagnettiMarelli MAP to use as male connectors and few female pigtails. So I've built 3 male-female short harnesses to plug in between the sensors and the main harness.

I've also got 2 identical Multimeters to watch the MAP readings.

As for the tuning itself:
- 3rd harness was used to plug in between the main harness and TPS
- checked the TPS (thanks Sledge4.2!)
- took off the throttle rods
- let the TB sync by the MAP readings, tried to get them low and watch the idle
- took the rods on the TBs
- adjusted them so that they read identical as before (when rods were off)

That's it, probably, It was done on LM FI though.

That is interesting way to do it, specially when you use MAP sensor to read vacuum.

 

[mikael82]

Thank you. What about the rest of the mechanical adjustment on the butterflies. When would you use those?

Basicly you do not touch throttle stop screws, they should be close enaugh from factory and I like to keep adjustment prosedure easier, and by pass valve will take care of rest, that is what they do. If you are sure you do not have air leak, if you suspect someone had touch them you can adjust lower (smaler) valve stop screws or you want to make some odd behaviour transition from idle to throttle what you can not take out with regular adjustment;

-You take out both long linkages.
-Close both by pass screws.
-Use manometer to adjust throttle stop screw vacuum even.

After this you need to adjust everything compleatly again, rule of thump is; if you touch anything, everything have to adjust again. I would not even remove long throttle linkages, in carburetors it means adjustment is off, Diablo is not that sensitive, but good thing to keep in mind; if you touch anything, everything needs to adjust again.
Larger valve stop screw is not to adjust, it is just to keep valve not striking against throttle body, larger valve can not be adjusted in relation to smaler one.

I like to note that I do not get any engine warning lights in my car if I start and go, only when you start car again after half an hour and auxiliary valve have started to open again, I get lean mixture warning both sides (this is because I have ECU's in my car that are ment to be used with leded fuel and there for car runs lean with unleded fuel) Auxiliary air valves work so that ECU powers heater inside them and this closes valve that feed extra air to intake so your car will run higher rpm when you start your car cold. they are also heated from engine itself in some F-cars they are even bolted to coolant tank so they would heat up faster, when coolant heats up. In lamborghini they are over valve cover, not ideal place for out side heating kept in mind, but good.

 

[k-works]

The reason was that I thought if MAPs read different, the fuel trim between banks would be different as well.

Nothing is really perfect, if you have a big manifold, there would be some unbalance anyway due to air charge robbing by the adjacent cylinders.

 

[mikael82]

And only with electronic gas pedal, it was possible to make plenums with multiple throttle bodies, like in Murcielago, they got that plenum vacuum issue sorted. Also need for adjustment was gone, as car can do it itself.

 

[k-works]

With electronic throttle bodies you lose the throttle response that you have with the Diablo style racing-derived EFI or carbs. You know that carbs may not have a perfect fuel mixture curve throughout the RPM thus making racing style EFI the only daily-friendly driver's car engine fuel supply system.

K/KE-Jetronic is also quite nice if tuned right, though you lose a lot of torque at low RPM, until the air metering plate opens.

New electronic throttle body systems are torque-based environment, which means the actual gas pedal is just a torque demand tool, not a real value that opens throttle bodies.

It's virtually impossible to comply with Euro 4+ emission norms without having torque demand ECU algorithm.

 

[mikael82]

I got this question asked time to time in other forums and social media; "how do you adjust Diablo air intake balance" and I would think this write up should be marked as "sticky" on first page, since most cars got issues with air balance adjustment with "check Engine" -lights burning on dash and these instructions will keep them out regarding on fuel mixture and lambda related, did with my car and most people report that it helps them.
Also like to note that mechanics today seem to overlook manometer as a tool and adjusting these cars seem to be bit lost know how.

 

[DiabloClyde]

Mikael, which number (blinks) check engine lights would be on as a result of this imbalance? Random misfire 20?

 

[mikael82]

Imbalance will cause.
2 - Lambda, weak fuel misxture
3 - Lambda, rich fuel mixture
7 - Air pressure sensor

More general note for casual reader;
Two "check engine" lights will shut off after while, but issue does not go a way. So that regard Diablo engine managment system works differently from modern systems where you need plug some sort of computer to delete "engine lights".

 

[SPGlass]

I got this question asked time to time in other forums and social media; "how do you adjust Diablo air intake balance" and I would think this write up should be marked as "sticky" on first page, since most cars got issues with air balance adjustment with "check Engine" -lights burning on dash and these instructions will keep them out regarding on fuel mixture and lambda related, did with my car and most people report that it helps them.
Also like to note that mechanics today seem to overlook manometer as a tool and adjusting these cars seem to be bit lost know how.

Sure is a more useful write up these days than the sticky thread "Napa Ignition Parts on Diablo". Literally every Diablo owner should check this and adjust if out of balance. I've done a write up on how I have done it as well which is sort of a culmination of all of the write ups I have seen on it including yours Mikael. It's buried somewhere in my project thread somewhere. I totally agree that this should be a sticky and everyone who has done it posts their own process or adds some tips and tricks.

 

[Sledge4.2]

Agreed. I wonder how many people have wound up with Jaguar caps on thier cars disgarding the brass caps for garbage?

there are three ways to balance the banks.
Manometer (measuring vaccum)
Airflow meter (measuring airflow)
Console readings (measuring manifold pressure from the Lamborghini Console).

Maybe all shoudl be written up and included?