L-jetronic mods

[James Seabolt]

Hello. I'm new to the list (sort of), so forgive me this subject has been
covered before.

I installed a custom turbo system on my 1980 Fiat Spider. Building the
system was a task itself but getting the engine to resist detontation has
been an uphill battle. If detonation is as destructive as what everybody
describes, then my engine would have been toast months ago because my
engine has shown no ill effects. So far anyway.

I had been running a few band-aid solutions such as water/alcohol
injection, timing retard, etc. but these are getting old. My real problem
is fuel enrichment.

Here's some specs:

2 liter/twin cam/hemi design
C/R: 8.1:1 (factory), current unknown, head was resurfaced during the last
rebuild.
Bosch L-jetronic fuel injection system w/lambda sensor
Turbo: Rayjay 301
Boost: 7 pounds
gasoline : 93 octane (of course)

Fuel enrichement device, rising rate fuel pressure regulator and a 2nd cold
start valve mounted upstream triggered at around 2 pounds.

With these specifications, this engine should handle 7 pounds of boost with
no problems. That is with proper fuel enrichment, but I can't figure out
how to get more fuel into the engine. 

The most frustrating thing is, the potentional is there, I just don't know
how to unlock it.

The other day, I was able to trick the computer into dumping more fuel into
the motor than it could handle, to the point the car was smothering and
belching black smoke out out the exhaust at 7 pounds. The engine seemed to
handle the extra amount of fuel until the contacts in the throttle position
switch closed and dumped too much fuel.

I did this by installing a set of boost switches which adds resistance
(about 2000 ohms) between the computer and coolant temperature sensor. This
doesn't work on my car because I've got a rising rate fuel pressure regulator.

My latest experiment was to splice a Hobbs pressure switch between the
oxygen sensor and computer. As soon as I hit boost (.1 pounds) the control
loop is disrupted.

Today the temperature was near 80F and the car seemed to do OK.

Can someone tell me this:

I was under the impression that when the engine is under wide open
throttle, the throttle position switch breaks the control loop. Is this
correct?

Or no matter what, the engine is still in the control loop?

My theory is that any attempts to get more fuel into the engine are being
overiden by the oxygen sensor even under wide open throttle, but by
breaking the control loop, now I can get more fuel into the engine.

Seems like my latest attempt has worked by I would still be more
comfortable knowing that I am getting the most fuel I can get into my motor
without causing the car to choke.

Here's a rundown of my current setup:

1) rising rate fuel pressure regulator
2) 2nd cold start valve mounted upstream before the throttle body triggered
at around 2 pounds.
3) Oxygen sensor to computer broken at .1 pounds

I would like to do away with the 2nd cold start valve and use the injectors
as my sole source for fuel because I know they have the potential when the
fuel pressure is stepped up.

Also I want to point out that during the experiment where I got too much
fuel into the engine was done with the 2nd cold start valve disconnected.

What could I do to increase the pulse rate of the injectors? My attempt to
create my own boost switch didn't work. I tried rigging up another pressure
switch with several rated resistors (600-1000 ohms) in parallel but the CPU
didn't like this.

Also is there anything to my latest experiment by breaking the circuit
between the oxygen sensor and computer under boost?

If you guys need anymore details, just email me.

This fuel injection system has been around for 25 years so I am sure there
is someone on here that knows how to trick this system.

Should I just have the injectors remapped to flow more fuel and run a lower
fuel pressure so the engine won't run rich at idle and cruise?

Great Scott! I'm running out of options here. Someone help me!

Thanks.


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James Seabolt -----> mailto:jseabolt at intermediatn.net
Webpage: http://users.intermediatn.net/jseabolt/
ICQ # : 7344463

United States

1980 FIAT 2000 TURBO Spider injected (John Deere aspirated)
1981 FIAT 2000 Spider (Rest in Pieces)
1981 FIAT X 1/9 (Injected)
1994 JEEP Wrangler (2.5l )
1976 Chevrolet Pickup (454 Big block/7.3 liter) 
     
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