Strange behaviour of Tiptronic after installing LPG on S4

[stanoev94]

Hello colleagues.
After installing LPG system on the Audi S4 B7, the tiptronic began to behave a little stranger when the car is stable at any speed below 2400 rpm. In the period of 10-15 seconds it shifts down to the previous gear for like a second and it goes up again.
This came as soon as I picked it up from the LPG service, there was no such behavior before.
Here is a video example of 100km / h on cruise control on a flat road.
https://streamable.com/0p4q3
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If I drive it with 130-140 on the highway, there are no problem as it's after 2500 RPM.
Otherwise, the car is well tuned for gas, I see no difference in accelarating or expense. There are no interruptions. This is the only difference I see in behavior for now.
By the way, when I move the gear to the right, turn on the tiptronic, there is no problem.It doesn't shift down. But if I go to D, this issue still appears. Could it be because of wrong data about the fuel mix, giving wrong signals to the ECU?
Has anyone encountered such a problem?

[mad70sx]

Hmm...interesting. I really don't have an answer but I can't see how changing the fuel should effect the way the trans shifts. Do the ECU & TCU even talk to each other? I honestly don't know. Maybe something (a sensor, cable, plug, etc) may have been knocked loose in the course of doing the conversion?

I'm really interested in your LPG conversion as well. Have you posted anywhere about it so I can read up on it?

[stanoev94]

I'm really interested in your LPG conversion as well. Have you posted anywhere about it so I can read up on it?

I haven't. Here in Bulgaria it's normal and usual to install LPG on engines which could work properly on it.This engine works like a charm. Almost every car with normal injection engine in Bulgaria has LPG by the way because it's almost 3 times less expensive and the car works the same way. LPG is 0.40EUR per litre while A95 petrol is 1.1EUR.
I have been driving my old A3 8L 1.8 125hp on LPG for the last 6years(140k km). It still works like a charm tough
But for example FSI models require very special liquid-phased LPG installation which works 90% LPG and 10% petrol, because it has to cool the injectors. This system is very expensive and it has very long Return-on-investment.

Still , if anyone has seen such a strange behaviour from this tiptronic, please let me know.

[mad70sx]

I've seen a few LPG conversions here is the States but they are not too commonplace. I think it's a great idea, though.

Best of luck with your transmission issue. I hope you get it sorted out soon.

[ven0m]

I've seen a few LPG conversions here is the States but they are not too commonplace. I think it's a great idea, though.

Best of luck with your transmission issue. I hope you get it sorted out soon.

Most Eastern European countries tend to convert anything 3 liter petrol or above to LPG.

Stanoev, what kind of control module does the LPG system have and how does it handle cooling of the valves? Some LPG systems have a 3:1 ration of combined fuel use. So on every 3x injecting LPG it wil then inject 1x petrol to keep the valves lubricated and cool (since LPG has a higher flame point than petrol). Maybe there is something on the LPG control that is not correctly giving info to the ECU.

In your place I would take it back to the shop who installed the LPG system before something goes wrong with the car and you're stuck on an expensive repair bill.


Cheers from Slovenia bud!

[Eye_In_The_Sky]

Sadly I dont have any input on your problem but how expensive is a lpg conversion? Does it have a drastic impact on engine performance?

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[stanoev94]

Sadly I dont have any input on your problem but how expensive is a lpg conversion? Does it have a drastic impact on engine performance?

Skickat från min VOG-L29 via Tapatalk

Mine conversion for powerful V8 worths 1050EUR. The setup is that good that you don't feel the difference between LPG and GAS. You only feel when better when you go to the gas station

[Kaiga]

I also have a similar problem, but when mine does it you can see it flicker into tip mode. Any ideas?
https://www.audizine.com/forum/showt...6#post13775376