57 4520 FI unit guidance

[Mike E.]

I've rebuilt a good dozen or more 62 7360 units---never an issue.
This 4520 unit has me scratching my head.
The scenario:
Almost 3 years ago an engine connecting rod broke just below the wrist pin and took out the block/cam/crank/pan, etc. (realaly trashed everything but the heads). At that time, when I removed the FI unit it ran well, but was a little skittish about starting after sitting for a period of time. (More difficult than should be expected) I drained the unit of fuel.
I now have the new motor in, and timing is right, valves are set right, etc.
It is much harder to start. In fact, after fighting it to get anything from it, eventually it will start and run 5-10 seconds and die. NOT BALLAST RESISTOR RELATED. After about 20 or so repetitions of that, I can finally keep it running,and it runs strong.
Let it sit for a day, and it is the same fight all over again to get it to start.
My amateur diagnosis is that it is choke-related (and I have been wrong many times before). I have much FI manuals/documents, etc---but most/all deal with the 4360 unit rather than the 4520. I'm struggling a little bit with choke and cold start theory. Take away the microswith and give a good old cranking signal valve, and I'm much more competent.
Anybody got any good ideas for what to look at/for when I get the courage to tear into it?
Thanks in advance!

[David B.]

Re: 57 4520 FI unit guidance

Mike,

The "Rochester Fuel Injection Manual" covers the 4520. Specs are:
Power Stop @.5" H20 = 2.2 (stnd cam), 2.4 (spec cam)
Economy Stop = 1.2
Cold Enrich Index Setting 1-1/2R (Note: this is quite different than the 7360 at 3L which you are more familiar with.)
Float Level = 2-9/32, Float drop 2-27/32 (same as the 7360)

that being said....

The "Chevrolet Fuel Injection Shop Manual" says the following about starting operations, which I suspect may be related to the issue you are experiencing. Most of this I'm sure you know, but I will type it in case it helps.

"At cranking speed there is very little fuel pressure from the gear pump so that special provision must be made to feed sufficient fuel to the nozzle at cranking rpm so that the engine can start. To obtain the maximum amount of fuel at these low pressures, the fuel valve is mechanically forced off its seat so that fuel can bypass the valve and flow directly to the nozzles. This is accomplished by a solenoid which is energized by the starting circuit and which operates through linkage to force the spill plunger downward in contact with the fuel valve to force the fuel valve off its seat.... (which) uncovers a special bypass fuel line from the fuel meter intake which delivers fuel pump pressure to the metering chamber to combine with gear pump pressure in supplying sufficient fuel for starting. After starting, ... solenoid current is cut off and the fuel valve returns to normal position, shutting off all bypass fuel flow. To prevent difficulty in starting or any possible flooded engine condition, an unloading device is attached to the air meter."

So, anyway, I would check (1) vacuum leaks, especially to main diaphragm (2) fast idle cam adjustment and check ball in the sleeve (3)sticking spill plunger on the fuel meter (4)bypass solenoid operation (5)defective cranking signal valve.

I have a 4520 (SE#1897), but I am no expert. Hope this helps.

Dave

[John D.]

Re: 57 4520 FI unit guidance

Hi Rev. Mike, Stick to the 62's as they are a lot easier and better.
Hopefully you installed a siphon breaker kit on the 57 unit so you don't trash the engine again. Sounds like your starting solenoid is not working for sure. The 57's and the 64-65's are really fast starting FI's
The wiring on the 57's is tricky. In theory when you have you foot off the gas pedal and are holding the key in the start position the solenoid is energized and the engine fires. Not sure which Dave wrote you but I have to admit that finding a manual that covers 4520 is an impossible task. RP and GM skipped over the 4520's. They had a 4360 and a 4800 manual but that's it. But basically all those 57's start and run on the same principle.
As far as stopping and starting it could be a number of things. Your cold enrichment (choke) might not be working properly. Here is a cheater. Remove the rubber hose coming off the "goose" shaped vac. line on front of the choke housing. Get a longer piece of hose say a foot long as you are going to be putting it in your mouth. Now unloosen the three screws holding the choke cover on. Start blowing into the hose while turning the choke cover clockwise(to the right). Turn it until you hear air gushing into the choke housing. Now's the tricky part. You want to turn it just into the air sound start and then stop. Tighten up the screws and give it a try. You may have to tweak it a touch. If it were me doing it with your problem I would give it a little extra notch or so in the clockwise or rich condition. You can throw the notch instructions out the window today because the parts are old and the bi-metallic spring under the choke cover has seen better days.
Other problem may be happening. Get a flashlite and a magnifying glass. Remember we are old. Remove the fuel meter shield. Behind the shield you will see the starting solenoid. It's connected to a lever via a brass rod that is connected to the solenoid. Watch very closely now. WHen you put the juice to the starting solenoid make sure the lever is not loose on the peaned shaft. Rochester Prod. was famous for peening stuff. Trouble is after 50 years the peen broke loose. If the shaft lever moves (connected to the brass rod) and the shaft isn't turning you will never start the car easily. If you have this problem it's a major pain to fix. Call me for more info as I am out of space. John fingers sore too.

[John D.]

Re: 57 4520 FI unit guidance

Rev Mike, Just reread your letter. Your say not ballast resistor related. Stop right there. The starting solenoid is NOT wired to the ballast resistor. It should just plug into the harness but here is how the wiring goes.
IN theory there is a wire going from the starting solenoid to the micro switch. Then a wire from the micro switch goes to the engine starting solenoid. Trick is to find out which terminal on the engine start solenoid is hot ONLY when the key is held in the start position. Take your hand off the key and the key springs back. Then the power is off to the micro switch, etc.
64-65 7380 units have the same setup.
If you are using a really old repro wiring harness some of them weren't made correctly so test all your wires. Good luck, John
If all the above doesn't work see Jerry Bramlett. heeeee Or call JP.