Poor man's injector tester

[91Saleen#15]

I have a 93 325is that sat with the intake manifold off for 6 months or so because somebody wanted to look under the manifold to see how the wires were run so he could wire up his m50 swap. After I put it back together, the engine fired with starting fluid, but was totally dead without the fluid. I assumed the wiring to the injectors was screwed up, but testing it with a test light showed that the injectors were drawing power. After eliminating everything else, the only thing I could conclude was that all of the injectors weren't working. That seemed unlikely, because if even one of the injectors was working, I would have gotten some sort of pop. The only way I could be sure was to come up with some way to see that the injectors were actually firing.

I borrowed another running 325is and routed the incoming fuel line to a fuel rail that I took off of 96 325is. I chose that rail, because the pressure regulator is not built into the rail. I then routed the return of that late model fuel rail to inlet of the 325is fuel rail. Since I had released the fuel pressure of the car, and had added a complete another fuel rail, it required 5 or 10 seconds of cranking to flush the air, but then the car started and ran just as it did before.

Here is a picture of the fuel rail hanging off of the 325is engine.


Note that the added fuel rail has a full complement of injectors. This is important because there would be a massive fuel leak if any of the injectors are gone.

I then scavenged an injector connector off of one of our butchered e30 harnesses, and use it to apply 12v to the far left connector. You can see in the picture the injector spray leaves the injector. It was interesting to compare the spray patterns of all 6 injectors. Some were better than others. These injectors, BTW, were working injectors that I had laying around. As to the injectors of my dead car: EVERYONE of those damned things were plugged. Rusted.... as near as I could tell. I sprayed carburetor cleaner through them backwards and was able to clear a couple of them. A large amount of rusty cleaner came out the inlet side.

Well.... don't know what you guys do to see how your injectors work, but this worked for me. Before anyone panics about the fire hazard, I should point out the spray from an injector looks larger than it really is because it breaks the fuel up into such a fine mist. There was hardly enough fuel to wet the ground. We managed not to self-immolate ourselves.

[nando]

uhm. a fine mist of fuel is FAR more dangerous than a pool of it..

cool, but I wouldn't do it that way.

[91Saleen#15]

uhm. a fine mist of fuel is FAR more dangerous than a pool of it..

cool, but I wouldn't do it that way.

not so sure.... a fine mist in an enclosure will explode, in the open it will flare like a propane barbecue, but a pool of it will make a fire you can't put out easily.

[10Toes]

Gas can cause fires

[AndrewBird]

Yeah, not the smartest to just spray fuel on the ground. At least spray it into a container of some kind. A glass jar or even a soda bottle would be better than the ground.

[greg1333]

i like the soda bottle idea...its a safer than squirting gas all over the place..and you can measure if your injectors are all flowing about the same...

[AndrewBird]

I used 4 glass jars glued to a 2x4 to check for equal flow rate on a VW Jetta I had. Worked great.

[91Saleen#15]

You guys slay me. Do you know how much comes out of an injector? A car going 60 mph gets 30 mpg. In an hour it runs 2 gallons (256 oz) of gas through those injectors. If the car is turning 2000 rpms, that's 120,000 revolutions with 3 firings per revolution makes 360,000 injector pulses of gas. That's less than a thousandth of an ounce of gas every time an injector fires. That mist that you saw in the picture never even made it to the floor. It evaporated before it went 2 feet.

Whenever I change a fuel filter, I end up with a cup or more of gas on the floor and usually some all over me. That's why I have a fire extinguisher in my shop. Any time you work on a fuel system, you end up with spilled gas. It's an every day event around my place.

[TurboJake]

You forgot to include that there's 6 injectors taking from that 256 oz, and that it's 1 fire per 2 revolutions. (These engines are 4 strokes...)

So, 256/6 = 42.6 oz per injector of the course of 60 miles..

Now, a car turning 2000 RPMS is pretty damn low at 60. Mines at about 2500. So, 60*2500/2 = 75,000 pulses per injector. (They only fire once per 2 revolutions, dunno where you got 3 per...)

Now, 42.6oz/75,000 fires: .00568 oz per spray. Multiply that by say, 300 rpm for cranking, 150 fires of the injector.

.00568 oz * 150 pulses

.085 oz, or 2.5 mL.

Per injector, for one minute of 300rpm cranking, you're dumping 1/2 tsp of atomized fuel. Roughly.

I could keep going, but I've already wasted enough time on this just to be mildly annoying and emphasize that when dealing with fuel, it's much better to have math that's correct.. FWIW, calculating it this way is pretty well pointless. Too many generalizations.

Just don't get near any heat or spark source. Atomized and evaporated fuel vapors expend their energy much faster than pooled fuel in a tablespoon. :p

To test my injectors, I just hook them up to a function generator with a 12v power source running an inline fuel pump that pulls from a bucket. Spraying into a hose that just dumps back into the bucket. Easy peasy. To clean them, Heptane in the bucket.

[91Saleen#15]

Now, 42.6oz/75,000 fires: .00568 oz per spray.

My calculator says that equals .000568 oz per spray

You're off by a factor of ten. almost just a half a thousandth of an ounce.

Gee, I try to show you guys a ten minute way to set up to test your injectors, and all I get is a bunch of quibbles about fire hazard. Didn't anybody think that was useful?

[TurboJake]

My calculator says that equals .000568 oz per spray

You're off by a factor of ten. almost just a half a thousandth of an ounce.

Glad to know you got the joke ;)

[91Saleen#15]

Glad to know you got the joke ;)

Too subtle for me... did you figure out where the factor of 3 came from? 3 cylinders fire per revolution on a 6 cylinder car.

[willworkfore30s]

Ed China puts a zip-loc bag around his injectors when he test them.