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Fuel Injector Blow Out!

13K views 68 replies 11 participants last post by  msiert 
#1 · (Edited)
Last June I had a shop pull and send in my 10 year old injectors to flow test them, the test results where horrible with 3 out 4 injectors failing, they all were way way down on flow and dripping and the 4th was only able to get a fair rating with no drips but was lower then the rated flow rate. They were all repaired to flow like new and all was great. These are Bosch injectors!

Fast forward to today when I was pulling into my garage after a spirited hwy drive and all of sudden I heard soft knocking, turned the ignition off and pulled off the airbox and open the throttle bodies butterflies to find the #3 throttle body filled with bubbling boiling fuel on top of a closed valve.

Since I was wasn't at speed, just pulling into the garage I'm hoping nothing got bent, the engine didn't die or suddenly stop.

Inspecting the cylinder with a borescope everything looks fine, the cylinder was in the compression stroke with both intake and exhaust valves closed.

I have not tried to start the engine or turn the motor over by hand yet.

I did turn on the ignition to see if any codes came up on the ECU and when I did fuel shot out of the #3 injector till the fuel pump stopped, like the injector is stuck open acting as an open spicket.

I called the shop that did the work but they won't be able to look at it for 3 weeks. In the mean time about the only thing I can do is change the oil that's diluted with fuel now.

What all should be done to check that nothing got bent?
 
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#2 ·
Last June I had a shop pull and send in my 10 year old injectors to flow test them, the test results where horrible with 3 out 4 injectors failing, they all were way way down on flow and dripping and the 4th was only able to get a fair rating with no drips but was lower then the rated flow rate. They were all repaired to flow like new and all was great. These are Bosch injectors!

Fast forward to today when I was pulling into my garage after a spirited hwy drive and all of sudden I heard soft knocking, turned the ignition off and pulled off the airbox and open the throttle bodies butterflies to find the #3 throttle body filled with bubbling boiling fuel on top of a closed valve.

Since I was wasn't at speed, just pulling into the garage I'm hoping nothing got bent, the engine didn't die or suddenly stop.

Inspecting the cylinder with a borescope everything looks fine, the cylinder was in the compression stroke with both intake and exhaust valves closed.

I have not tried to start the engine or turn the motor over by hand yet.

I did turn on the ignition to see if any codes came up on the ECU and when I did fuel shot out of the #3 injector till the fuel pump stopped, like the injector is stuck open acting as a opens spicket.

I called the shop that did the work but they won't be able to look at it for 3 weeks. In the mean time about the only thing I can do is change the oil that's diluted with fuel now.

What all should be done to check that nothing got bent?
I don't have a good answer for your problem, but I've never heard of an engine being hydrolocked with fuel.
 
#4 ·
Shoulda sent them to Cruzin Performance!!! Teasing aside, without a compression gauge and turning over engine at speed, I would try getting #3 at the bottom of the compression stroke and turning the engine over with your finger over the plug hole and see if you feel pressure. That would assure your valves are seated.... from your description though I would lean toward a bad injector with no real damage, but I'm kind of a newbie to the Alfa scene!
 
#5 · (Edited)
Been reading up on stuck open injectors, some say it could be a grounding short that would cause it, others are saying its a mechanical failure in the injector?

It's unclean right now if it fixable or if I need to buy a new one. From what I read you dont just replacing one you replace them all?

Sure glad it didn't happen at speed, the engine would be a goner. Fuel can hydro lock just like water.
 
#7 ·
You need to get some oil in the cylinder. The gas washes all the oil off the cylinder wall and surface rust can start within a couple of days.
 
#8 ·
Since all the injectors fire at the same time, just swap leads with another and see if it just sprays continuously too, then you will know whether it is the injector or electrical lead...
 
#10 ·
normally if I wanted to "try" unstick a stuck injector I'd remove the connector and touch the injector on/off with current (9V DC battery)....see if that makes it click on and off....maybe in between some short sharp taps to help it along!

I seem to recall your S4 has a completely modified injection system ('black spider project' thread of 10+ years ago!), so not quite sure what you have.
 
#14 ·
skibum said:
The Bosch FI fires all injectors simultaneously.
Are you guys serious? Are you meaning that they all squirt fuel together, or the same time in the 4 cycle combustion process?

If they all squirt fuel together, then for every revolution of the engine they would ALL have to squirt 4 times with only 1 time being actually when wanted per cylinder (i.e. when the inlet valve is open and air is being sucked in). Fuel would be pooling on the back of the closed inlet valve.

What is the advantage of fuel injection then? A carburetor or a single injector into the manifold would be more efficient. Crazy design. Cannot believe it. The fuel wastage is enormous
Pete
 
#16 ·
Well, if you think about it, maybe these 4 "microbursts" equal what is needed for a combustion stroke. The first three are sitting in stasis until the intake valve opens, sucking all four bursts into the combustion chamber. Seemed strange to me when I learned that, but it works! And think about how fast all this is happening....
 
#24 · (Edited)
I have an Autronic SM2 for my fuel injection it can control each injector individually, the injectors fire just once during the compression stroke for each cylinder. I can trim fuel to each cylinder but one would need an O2 sensor for each exhaust manifold runner to do that.

Anyway there's not too many ways for injectors to fail. I'm guessing the return spring got broken or jammed which would leave the pintle stuck open. That would cause quite a bit of excessive fuel at idle, and then when you turned the car off all the residual pressure in the line would dump fuel though that injector.

So my guess is the chances of having hydrolocked are low, given that the liquid fuel you saw likely flowed out after the engine was turned off. But let us know what you find.
The injectors are Disc type not Pintle if that makes a difference?

I going to check the wiring between the ECU and the injector for continuity, I believe that the injector is looking for a ground to fire?

Everything thing checks out fine, the engine turns freely, the leak down test showed 7 % loss thru the rings which is normal for that cylinder (since starting doing monthly leak downs from the end of last year in my quest to clean the carbon off the # 4 intake valve) and there are no visuali signs of contact between the Pistons and valves.

What save me from blowing the engine up was it happen at idle not at speed on the hilly highways I was on a 1/2 hour before the injector craped out on me.

I don't see any reason to pay to tow the Spider to the mechanics shop to pull the fuel rail to send the bad injector or all the injectors back to be check out again.

Think the fastest and cheapest way to get the Spider back on the road would be for me to pull the fuel rail and injectors (after checking the wiring) and take them to the shop for them to mail off to California.

It's not the mechanics fault that the injector went bad so I'm pretty sure I would be billed for the time to pull and reinstall plus most likely a new injector?

That way the car stays at my shop where I can work on other things and I save 3 weeks waiting to get her in and another 2 weeks to getting her back.
 
#22 ·
Anyway there's not too many ways for injectors to fail. I'm guessing the return spring got broken or jammed which would leave the pintle stuck open. That would cause quite a bit of excessive fuel at idle, and then when you turned the car off all the residual pressure in the line would dump fuel though that injector.

So my guess is the chances of having hydrolocked are low, given that the liquid fuel you saw likely flowed out after the engine was turned off. But let us know what you find.
 
#23 ·
Sequential firing is of marginal benefit except when you are trying to squeeze the last bit of performance out of an engine. When we were developing our last couple of competition engines, we used AFR and thermal sensors for each cylinder and used a Megasquirt system that allowed us to trim each individual cylinder for spark timing and fuel needs. Not something necessary for everyday engines.

When we built a turbo 4-cylinder for roadracing it still used batch firing, and at full chat the injector was open for a full 600 degrees of rotation. To provide enough fuel, you fire the injectors for much more than the time while the intake valve is open. If you only had that time, you would need humongous and inefficient injectors. Also, you wouldn't have enough time to condition the intake charge. It's quite normal to use the injector to spray on a closed valve in order to both cool the valve and vaporize some fuel. The intake runners and plenum are a chaotic environment, there are waves that are dancing back and forth as valves open and close, and it's quite normal for cylinders to rob intake charge from each other.

To really dive deep, you also have to consider injector placement and inception of injection timing. We tried three different locations, and did rounds of timing changes, all to try to eke out a couple of more points.
 
#26 ·
Just a thought, is there a quality issue with injectors today, I'm thinking that there quite of few China made injectors now a days and to me they should stay within spec for longer the 10 years.

In 10 years 3 out of 4 injectors where just horrible with the 4th not far behind. Before this I had one injector go bad after a year of the rebuild.

Right now I don't think I would go over a year without pulling them and having them checked.

Sorry just ranting.
 
#27 ·
My experience with FI is with V6's but I expect the individual fuel flow to be similar for high performing engines. Al Mitchell builds Megasquirt conversions using Red Top (I think) injectors. He buys them used, cleans them up, measures the flow rate and selects sets of six that are similar. That is what I had on my hot 3L GTV6 with no problems and AFAIK they are not a reliability issue on the many other Megasquirt conversions that Al has done.
I did have a leaking Bosch injector once, on the Verde I think but it just caused rough running at low rpm.
 
#29 · (Edited)
Update

The shop that pulled the injectors and sent them in last June asked that before I pulled the fuel rail and injectors to run a couple of tests to see if the ECU was the problem not the injector.

Test #1: The turn on the ignition with the #3 injector plugged in.
Results where the #3 injector starting buzzing as soon as the fuel pump started and it sounded like it was sprayed gas like the last time but the throttle body was dry.......odd, it's like it was releasing pressurized air?

Or maybe it was just buzzing but it started as soon as the fuel pump started and ended as soon as the fuel pump stopped.

Test #2 Unplug the #3 injector and turn on the ignition.
Results where the same, buzzing from the #3 injector but the throttle body was dry, same deal on what sounded like pressurized air releasing.

Test #3 Unplug all the injectors and turn on the ignition.
Results where the same with the #3 buzzing as soon as the fuel pump started but the throttle body was dry.

Ok, I'm pretty convinced it's the injector but the shop tech still thinks it has to be something to do with the computer

Odd that it doesn't spray gas anymore but it's certainly making a racket whenever the fuel pump starts.

The fuel pressure gauge goes up to 43 lbs then rapidly drops to zero as soon as the fuel pumps stops.

He wanted me to run some more tests but I said I'll pull entire rail with pressure req. so he could do some more testing if he wanted but I willing to take the gamble to have the injectors sent in today.

Here are some pictures of my days work.
 

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#32 ·
I've used RC numerous times. And plan to use them again here shortly.
 
#34 ·
so only #3 injector was making that odd noise? If so, that injector obviously has a fault.

"Test #2 Unplug the #3 injector and turn on the ignition.
Results where the same, buzzing from the #3 injector but the throttle body was dry"


just turning on the IGN wouldn't show fuel in the throttle bodies as the engine needs to crank or run for an injector to spray, so not sure why all those tests....
 
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