Saabscene Saab Forum - Saab Technical Information Resource banner

1 - 6 of 6 Posts

·
Registered
Joined
·
623 Posts
Discussion Starter #1
I have a '87 9000T, and when I try to reach the full boost I notice a cutout that lowers my boost pressure. I believe that it's the APC that feels the knock, and lowers to the base boost. I tweacked a bit the APC, turning the P and F pots. Now the turbo gauge needle reaches the half red, but then the APC cuts it down, as I saied.
When I tweacked the APC I thought I had no problems with knock, since I was running on LPG, and I didn't had until I did a head gasket job and a hidraulic lifter rebuilding (valves were leaking).
The question is: is it possible that I really have knock on LPG, boosting half red gauge, and that it didn't occurr before the head job because the valves were leaking, so I had a low compression? The car's performances aren't increased too much after the job, actually they are worse because of the APC cut.
If I have knock, what's the best way to get rid of it? I tried to enrich the mixture (more LPG), but no results. Water injection? Water cooled intercooler?
Or is it better to just put back the pots where they were?
Thanks in advance.
 

·
Registered
Joined
·
14,305 Posts
Stefano,

Assuming you have a standard ECU, then it sounds like you're reaching the overboost fuel cut off point- did the boost get that high before?
 

·
Registered
Joined
·
12 Posts
For what it's worth LPG is about 105 octane and unleaded is 95. So LPG should run considerably more boost than on petrol. IT sounds as if the performance is being limited by something else such as fuel cut out or the mixture being wrong. Is it a closed loop system? What type of kit do you have, gas injection? Can you not monitor the mixture from a laptop? If you don't know it's right I'd be very worried about melting the engine. What do you get to a gallon on gas compared to petrol? Greg.
 

·
Registered
Joined
·
1,676 Posts
I'm not the LPG expert here - but it occurs to me water injection would be a very desirable thing to have on an lpg converted car because you basically cannot dump excess fuel into the combustion chambers on full throttle as a coolant medium like with petrol fuel.
 

·
Registered
Joined
·
623 Posts
Discussion Starter #5
I have a very simple kit, just a pressure reducer and a venturi to mix the air and the gas. No injection, no closed loop ince there's no lambda sond (no cat). So there's no fuel cut off, since the injectors don't work anymore. My engine now works like if it had a carburettor, everything is mechanical. The only ECU controlled is APC. In fact, the engine doesn't "jerk" badly as it hadn't fuel, it just "bucks" because the boost fluctuates. My ECU, BTW, is stock, but it does very little when the car is running.
I can't monitor the mixture since I have not even a lambda sond, because my car has no cat. Petrol injection worked open loop before I fitted the kit, now it's even more open loop since there's no ECU controlling the mixture. To control it, I can turn by hand two screws, that control two calibraed nozzles (one for the idle and one for other situations).

What do you think?
 

·
Registered
Joined
·
623 Posts
Discussion Starter #6
water injection would be a very desirable thing to have on an lpg converted car because you basically cannot dump excess fuel into the combustion chambers on full throttle as a coolant medium like with petrol fuel.[/b]
I hadn't thought of it, thanks. Anyway, I thought I had not to be so knock prone on LPG
 
1 - 6 of 6 Posts
Top