Fuel Injection questions

[jordan]

I have searched all of the theads on this subject and I have read most all of the way through, but I am unable to find answers to these questions.

-Where Do the thermostat hoses go? there are 3 medium sized ports and a small (3/8"?)

-What size should I use for the fuel pressure and return line? I have heard of people using brake line, doesn't seem like it would handle enough volume.

-Why is there a fuel pressure regulator needed by the pump? is it accurate and reliable? I was told to have it set at around 30 psi that seems too low considering the system needs more than that at the injectors.

-Is the fuel pressure regulator at the fuel rail reliable and accurate?

[Bill Hoffmann]

-Where Do the thermostat hoses go? there are 3 medium sized ports and a small (3/8"?)

The middle port bypasses water directly from the head to the water pump during warmup. The bypass hose is a short elbow-shaped hose with different sized ends. As the thermostat opens, it closes off a passage, which causes the water to flow from the head to the radiator inlet (top) through the opening closest to the head. Cooled water then returns from the radiator lower opening through the thermostat port furthest from the head, and flows to the water pump through the bypass hose. A hose barb on the block near the oil pressure sender supplies warm water for the heater (the '75 "E" block has a larger hole for this barb. Earlier blocks have a small drain hole). The small port on the water pump inlet returns water from the heater core.

-What size should I use for the fuel pressure and return line? I have heard of people using brake line, doesn't seem like it would handle enough volume.

Brake line would be way too small. Use 5/16".

-Why is there a fuel pressure regulator needed by the pump? is it accurate and reliable? I was told to have it set at around 30 psi that seems too low considering the system needs more than that at the injectors.

The fuel pressure regulator not only sets the pressure, but it also attempts to maintain a constant pressure differential between the fuel line pressure and the intake manifold pressure. You can see the effect if you pull the vacuum hose from the regulator at idle. The regulator "thinks" the manifold is now at atmospheric pressure and increases the pressure accordingly to maintain consistent fuel delivery. The car runs rich.

-Is the fuel pressure regulator at the fuel rail reliable and accurate?

In my experience, yes. Fuel pressure should be between 31 and 44 psi depending on manifold vacuum.

[David McCollam]

The stock Bosch Opel fuel pressure regulator for the L-Jetronic is non-adjustable. It is typically set for bypass at 45 PSI. The pressure as Bill Hoffmann indicated will vary for the Opel Bosch EFI from 31-44 PSI depending upon engine RPM and load conditions.

The fuel line should be 5/16 or 8mm multi-port fuel injection hose or solid line that will withstand that pressure. Copper tubing will work.

Just as an aside, that Bosch EFI pump can run the fuel pressure at the fuel rail up to about 100 PSI. Don't ask me how I know. You don't want it at the pressure by the way. Really bad things can happen. Once installed, it is a wonderful idea to check the pressure on the system at the fuel rail.

Good luck with that project.

Dave

[Rionart]

I make a point of adding a fuel pressure gauge to all my fuelie cars, just tee it into the rubber line before it gets to the solid line for the rear 2 injectors. I mount the gauge itself either on the air filter box or the bulkhead....nice way to troubleshoot real quick...

[tekenaar]

Originally Posted by Rionart I make a point of adding a fuel pressure gauge to all my fuelie cars, just tee it into the rubber line before it gets to the solid line for the rear 2 injectors. I mount the gauge itself either on the air filter box or the bulkhead....nice way to troubleshoot real quick...

. . . and I took that one step further by changing to an adjustable, rising-rate FI regular along with the FP gauge. Minutely adjustable and instant reaction to changes in vacuum (engine load) conditions. A bit pricey, but works awesome . . .

Here's one in my 2.4 GT:



and another in my 3.9 Bitter SC:

[tomking]

I think someone needs to JUMP on Otto's spelling(mis)!!

[Sportwagon75]

Years ago...I had a 75 Sportwagon in which I used a unique method for fuel pressure indication. The 75 rally instruments have an electrically driven oil pressure gauge. There's a separate sending unit for this that's screwed into the block and I had a spare one kicking around (and the gauge to go with it). Since the fuel is in the same pressure range as the oil pressure...I decided to use the spare sending unit I had to indicate fuel pressure. I removed the clock from the triple gauge cluster and had two oil pressure gauges. I just put a little sticker over the gauge to indicate it was "Fuel" pressure.