With the assistance of a knowlegable friend (Richard Brodeur), I just installed a 4900R unit into my car this weekend. The installation went pretty well without incident however it took some cranking to get it started up (probably took a while to get fuel into the cylinders) but when it started it ran so rough it sounded like it was running on half the cylinders. The point gaps were set to .018 and the timing to 18 degrees. I also noted that it was running very rich as black carbon was on the exhausts. Does anyone know if this is normal? I have been told that this is normal and the FI cars need to be warmed up for 5 -12 minutes before use.
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Re: fuel injection unit installation/startup
For it to be that rich on starup, I'd suspect a bad cranking signal valve. Start the car and pinch shut the rubber line coming out of the cranking signal valve. If it cleans up, there's your problem. With a 4900, you should be able to drive a stone cold engine after a 30 second warmup. (I used to do it in michigan at -10 F!) -
Re: fuel injection unit installation/startup
i would pull all the plugs to see if any carbon fouled.Comment
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Re: fuel injection unit installation/startup
Definately NOT normal. If the cranking signal valve is OK check to make sure the enrichment lever is on the economy stop. If it is, then lean out the ecomomy stop setting until the smoke clears up.
Dale.Comment
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What do you know about the FI unit?
Tom -
Have you witnessed this particular unit running correctly on an engine with the same camshaft grind that you're using? If it ran right on someone else's Corvette, then it can be made to run right on your car without too much effort. However, if it's a mystery unit that you just bought at a swap meet or off eBay, then you may be in for a lot of work.
Could you explain what you know about the condition of the unit? Then maybe I can give you some diagnostic steps to try.
JerryComment
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Re: What do you know about the FI unit?
Jerry,
The unit is a "mystery unit" as you put it. It was purchased from a gentleman named Joe Marquez who resides in california and apparently deals in FI units. He sold it as is, but indicated that the party he had purchased it from indicated it was as rebuilt- and I believe them. If you saw the unit you would think the unit was brand new. All visible gaskets have been changed out and are supple. The unit itself is immaculate...including the number tag. It is really a nice unit from a visual perspective. Thats about all I know about the unit at this time, other than it makes the car run like !@$%. Regards, TomComment
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Here's what I would do.
Tom -
I don't know Joe, and I certainly mean no disrespect to him by my comments. Maybe you got a sweetheart of a unit that just needs little tuning.
But that hasn't been my experience with non-running units. I advise people shopping for FI units to view it this way: if the seller won't guarantee that it will run right, it won't. External cleanliness and a recent "rebuild" just mean that somebody has been messing with it. It is unlikely that they repaired it properly.
There is no way to ascertain that a unit will run correctly by inspecting it from the outside. The best check is to bolt it to a good engine and see what happens. You did that, so now what?
If it was mine, I would do a few basic checks before removing it. Dale's suggestion is good. See if the enrichment lever is popping over to the lean stop. If it isn't, find out why. I assume you're running a stock 097 cam that generates plenty of vacuum. The tension on the enrichment lever diaphragm is somewhat adjustable.
If the lever is on the lean stop and the stop is sticking out a quarter inch or less, then I would give up on tuning. Next I would remove the unit to look for drilled out nozzles, warped gasket/diaphragm surfaces, and incorrect or damaged fuel meter parts. While it's off I would install a solenoid upstream of the spider as a syphon breaker.
Tom, with all due respect, please do not attempt to fix this unit yourself if you don't understand the terms I'm using. And if you send it to someone else, ask if they can test run the unit before they ship it back. Being the test monkey for somebody's FI work is dangerous. You could really hurt your engine.Comment
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A Good Test
This requires a little effort but is something I would have done before installing the unit.
Set up a one gallon gas can with inline filter. Put the doghouse portion (leave the adapter plate manifold on the car) on a suitable test stand out of doors with a BIG fire extinguisher nearby. Using the high pressure drive cable and a hand drill, spin the pump at various speeds with gasoline supplied from the 1 gal can. Use a small hose to provide oral vacuum to the control diaphragm and place eight water tumblers, one under each nozzle. Run at least a quart or two of gas into the tumblers while experimenting with different oral vacuums. You will be able to see the fuel being squirted into the glasses and by comparing the amount of fuel in the glasses after finishing, a faulty injector or screen can be identified.
Every six months or so I test my driver in this fashion and always test any fuel unit I trouble-shoot or rebuild as well. Be careful however because you are working with gasoline.
I like the smaller nozzle sizes on the street because they provide better resolution of the enrichment function. Instead of "all-on" or "all-off" enrichment necessary for racing, you get a wide range of richness for optimum part throttle operation.
Please post Joe Marquez's phone number or e-mail. Also study the ST-12 and you can be an expert just like everybody else. Jerry's advice here is very good.
Dale PearmanComment
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Re: A Good Test(Jerry & Dale)
Jerry / Dale,
I actually did perform the static test off vehicle before I put the unit on and it worked flawlessly and met the criteria in the manuals. I also installed a solenoid valve just upstream of the spider connection to the fuel meter fuel line as you indicated Jerry and it works fine.
Jerry no offense taken on your comments. I readily admit I am in unchartered waters on this project and I realized I was taking a chance but figured I could always get the unit reworked by someone if I had to. Thank you both for your ideas, and I would welcome any other thoughts you might have. I will post the outcome when I get there! Regards, Tom
PS Joe Marquez phone number (805-929-3910)Comment
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Good test, but use mineral spirts
Whenever I bench test fuel system componets, I use mineral sprits. It's much less likely to cause a fire. GASOLINE IS VERY DANGEROUS, especially in a FI bench test where the material is highly atomized by being forced through a small orifice at high pressure. After I've run the paint thinner through the system I just dump it into my parts cleaning bucket. Paint thinner is an excellent solvent for cleaning parts and drys without leaving a greasy film like kerosene.
DukeComment
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Choke function
Tom -
As you probably know, the choke on your model is a pretty funky design. I believe that it cuts off vacuum (through the large plunger) to the enrichment diaphragm when it is engaged. It also sends some manifold vacuum (through the small plunger) to boost the venturi signal.
If the enrichment lever isn't held on the lean stop when the choke is hot, make sure the large choke plunger has popped out and is passing vacuum to the enrichment diaphragm. At the same time, make sure the small plunger is pushed in and not allowing any manifold vacuum to go to the main diaphragm.
JerryComment
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Re: Choke function
Jerry,
Would it be possible to get your phone number? I may want to call you as I get further into this problem. TomComment
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