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Discussion Starter #1
I am stumped and frustrated.

The engine in our '84 Spider is not running well. Idle speed has dropped slightly and there is a stumble on opening the throttle. It will pick up speed and rev to 5000+rpm but perhaps a little slower than usual. At first I assumed an intake air leak but I can find none. I cleaned the ECU's ground connections. Since it had been a while I bought some new spark plugs (Lodge HL) but no improvement. Checked the connectors at the AFM and the TPS. Also the flywheel sensors (and they both read about 900 ohms).

Cylinder #3 appears weak/dead. Pulling off the #3 spark plug wire makes no difference in the idle speed. Yanking any other spark plug makes a noticeable difference. I can see a good strong spark from the #3 spark plug wire. Just to be certain I swapped the #3 & #4 spark plugs - no difference - #3 still dead. Then I swapped the #3 & #4 spark plug wires (re-connecting them at the distributor so the firing order remained correct). #3 still dead. Distributor cap is recent andI can find no faults there.

Using a long handled screwdriver as a 'stethoscope' I can hear the #3 FI clicking - sounds the same as #4.

I disconnected the #3 fuel injector connector - no difference. Disconnecting the #4 FI connector makes it slow down noticeably. Connecting the #3 connector to the #4 FI returns the idle to previous speed/smoothness. Connecting the #4 FI connector to #3 makes no difference. Thus I am assuming the #3 wiring is OK as it seems to fire the #4 FI.

Compression is 180-185 psi in all cylinders. My el-Cheapo leak down tester (air hose @ 80psi screwed into spark plug hole but no gauges) reveals no sound of air leaking past valves, slight hissing from oil fill (sounds equal in all cylinders) and no bubbling in coolant or adjacent cylinders.

Thinking I must have a defective fuel injector, I positioned #3 such that the intake valve was open (visible via the spark plug hole) and pressurized the fuel rail (key on/off/on/off to cycle the fuel pumps) then I applied 12V to the FI's terminals. I could see/hear the injector squirting.

Finally ! - my question(s). 1) is that an adequate test for fuel injector function? B) am I missing something (beside my sanity)?
 

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1966-2013
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I'm reading your words and for the life of me can't figure out why it's doing what it is considering the tests you've done. (seems like you covered everything to me)

It just doesn't make sense that it doesn't do what it should.

This could require some extensive ponderment........
 

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Discussion Starter #4
check the clearance on the valves...
Good idea. I did check them within the past few months (all were OK and hadn't changed compared to last year). And the problem seemed to happen rather quickly. One day it was running fine, the next day it was not.

Is the injector test I tried - pressurize the fuel rail, apply 12V and see/hear the injector squirt via the open intake valve while peeking in through the spark plug hole - an adequate test of injector function? It'd squirt with 12V applied and stop when 12V was removed. Also, swapping the FI harness connectors (#3 to #4 and #4 to #3) did not change the location of the dead cylinder so I am assuming it is not a fault in the harness or connector.

Also, I installed another (used but servicable) distributor cap to rule out a hidden fault there. #3 still 'dead'.

Arrgh.
 

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1966-2013
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On that 'squirts with 12V applied':

Does it spray continuously (as long as there's pressure obviously) or does it pulse?

If it's a steady stream it seems to me that would be fine, but if it's got any kind of pulsation to it, then the injector would definitely be suspect as the only thing that makes them pulse is the ECU doing it's thing.
 

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1966-2013
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Secondary thought:

I'd not leave a steady 12V connected to one for too awful long a time or it may burn up the windings in it without a really substantial amount of fuel flowing to keep it cool.

No more that several seconds anyway.
 

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Discussion Starter #8
I only applied the 12V to it briefly. Touch - squirt, untouch - stop squirt. Starting with a pressurized fuel rail (but engine off), it'll do that 4-5 times in a row - then I assume fuel pressure drops and it doesn't squirt anymore. Re-pressurizing the fuel rail and it is repeatable. The squirting seems steady, not irregular/pulsing.

Valve clearances are good. Warm engine - I've been running it on & off this afternoon - the intakes are about 0.016", the exhausts about 0.018".
 

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1966-2013
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wanders back in between beers






You've got fuel, you've got fire, you've got intake valve motion, you've got lash, you've got compression, you've got rail pressure.

Here's a really big reach:

What if something silly happened like the exhaust port proper on that cylinder had something blocking it so that it messed up or totally eliminated the overlap and intake cycle?

Without a place to go, it there wouldn't be any real draw of mixture into the cylinder.

Could be a hung shut exhaust valve (even if the cam seems to indicate motion of the tappet, can you see the actual valve head in the cylinder moving what appears to be an equal amount as the other Ex valves when you roll it over?)

Could be a tennis ball or half a wad of shop rag jammed into the exhaust port :shrug:

I suppose you could see if there was draw at the intake by pulling the plenum (yea-ha...) and turning the engine over with with the starter (coil wire off) and your hand over that intake runner.

If it pulls strong, then not the issue.

If it pulses in and out or doesn't draw at all, (not likely as you do have compression, so there is at least some transference of cylinder volume), then chances are fair that something is wonky on the exhaust side of things.

Conversely, you might get away with leaving the plenum on and taking the plug out and feeling that with your finger while it's cranked. The pulsation feel won't be as true as actually putting your hand over the intake port, but it'll definitely feel different than a known working cylinder would.

Mind you, I am kinda grasping at straws here.
 

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I would like to offer these thoughts.

You have done a good job of eliminating most of the possible problems.
However, It still comes down to the basics. You have to have proper compression, properly timed spark and proper fuel air mix.

So... since #3 cylinder is still weak, one of the basic things needed is still missing.

Lets start with the easy stuff. Even though you have swapped sparkplug wires between 3 and 4 there is still the possibility of a faulty wire.

Go to the local parts house and by a set of wires. Never hurts to have new wires right? Why not go ahead and replace the cap and rotor as well?
While the distributor is open make sure the bushings are sound and there is no play in the shaft.

While you are there check the distributor alignment by removing all the sparkplugs, rotate the engine so that cylinder #1 in on compression stroke and at top dead center. The distributor rotor should point to the mark on the distributor body.

If this doesn't bring #3 back on line (and I suspect that it won't) you will have to go after the harder stuff.

You say you have done a compression test and a cylinder leakage test.
I would like to suggest that you review the results.

Even though the cylinder can reach 185 psi as you say in the results of your test, how many strokes did it take to reach this number?
The leakage test is also something to think about. If you can repeat the test with a tester that can give you numbers to compare it would be helpful.

Do the test with all the sparkplugs removed. This will allow you to hear a leaking exhaust valve via the manifold and open plug holes.

I really wouldn't suspect a faulty injector at this point. Other than sticking after long periods of non use and partial clogging they have proven to be quite reliable.

Which leads to what I really think is causing your problem.

The first symptom of a faulty (burned) valve is uneven idle. Car will seem to drive and perform respectfully at speed but will develop a uneven idle that gets worse until it make its self apparent.

I have seen people drive these cars for thousands of miles after being informed that a valve job is needed.

The valve seat is quite wide on the Alfa 2.0 engine and the angle is 30 degrees. Both of these can contribute to early failure (at least compared to more modern designs).

After reading your post, my first thoughts were:
-this guy has done the right tests
-the tests should have indicated the problem
-it sure sounds like the early stages of a burned exhaust valve
(the exhaust valve is much more likely to fail than the intake).

One last thought. Since all the plugs are out, turn the engine slowly and actually look at each exhaust (and intake) valve. You can sometimes see the start of a hole or small crack in the seat while the valves open and close.

I hope I am proven wrong, maybe there *is* a tennis ball or shop rag in your engine. It would be much cheaper to repair.

Hope this helps
ELM
 

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Discussion Starter #12
It was the fuel injector.

I loosened the fuel rail and was able to pull the #3 & #4 injectors out (leaving them attached to the fuel rail). Watching those two injectors while cranking the engine revealed a definite squirt from #4 and nothing from #3.

I replaced the #3 injector, put it all back together and it is now running right.

Thanks for all the replies and suggestions.

Interesting that the 'faulty' injector measures 2.5 ohms resistance and will click when 12V is applied. And I'm sure I was seeing fuel squirt when I tried the 'peek into the spark plug hole while the intake valve is open and apply 12V to the injector' test. But I guess that has little or nothing to do with whether the injector is functioning correctly in a running engine...
 

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You got it, cool.

For giggles, you might try putting, say, 10-11 volts through that known bad one as there's no telling what pssible small draw or voltage leak might be/have been occuring between the relay and the injector. (as in it may work at 12, but not at 11)

Do you have the little sealing boot thingy in the harness socket for that injector? (foam or rubber, I don't recall which right now, but it sits way up inside the socket in the groove around the inside and outside plastic bits)

Without it there's a fair chance for an intermittant connection too as the plug rattles around on the connection.
 
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