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Discussion Starter #1
Normally my 86 Alfa Spider runs like a champ. However, this is the second time where, for some unknown reason, it suddenly idles and runs like crud. It will even backfire through the exhaust

I have a presure gauge temporarily installed. The fuel pressure is a steady 40 psi (rules out fuel delivery issues). It's down to ignition or possibly a sticking valve (or maybe something else that I haven't thought of). Also the pressure takes a very long time to bleed down so I've ruled out leaky injectors.

I disconnected the battery to reset the ecu. No change.

It may also be a sticking exhaust valve. Anyone have any luck with oil additives formulated to free sticking valves?

This first happened about a month ago. I ended up having to nurse the car home. However, the next day it started right up and acted like nothing had ever happened. It ran fine for about three weeks until yesterday.

Any ideas guys?
 

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But Mad North-Northwest
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Fuel pressure on L-Jetronic should be (from memory, so double-check this) 36-37 PSl *minus* engine vacuum. That is, if you disconnect the vacuum line to the regulator it should be a steady 36-37. When you plug the hose back in the fuel pressure should drop by the amount of vacuum in the plenum.

(e.g., if you have 17 inches of vacuum at idle that's ~8 PSI, so the fuel pressure should read ~28-29 PSI at idle. It should go up if you open the throttle plate and decrease vacuum)

If the fuel pressure doesn't change with engine vacuum or as you open the throttle then you've likely got a bad fuel pressure regulator.

It may also be a sticking exhaust valve. Anyone have any luck with oil additives formulated to free sticking valves?
You've got mechanical valves so that's not the problem. Or at least you'd better hope it's not...
 

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Discussion Starter #3 (Edited)
Normally my 86 Alfa Spider runs like a champ. However, this is the second time where, for some unknown reason, it suddenly idles and runs like crud. It will even backfire through the exhaust

I have a presure gauge temporarily installed. The fuel pressure is a steady 40 psi (rules out fuel delivery issues). It's down to ignition or possibly a sticking valve (or maybe something else that I haven't thought of). Also the pressure takes a very long time to bleed down so I've ruled out leaky injectors.

I disconnected the battery to reset the ecu. No change.

It may also be a sticking exhaust valve. Anyone have any luck with oil additives formulated to free sticking valves?

This first happened about a month ago. I ended up having to nurse the car home. However, the next day it started right up and acted like nothing had ever happened. It ran fine for about three weeks until yesterday.

Any ideas guys?
It's an electric fuel pump (and fairly new) and the pressure is always a rock solid 40 psig. It has been 40 psig for a very long time. Doesn't change at all with vacuum.
I'm leaning towards sticky valve(s). Will look for an additive or maybe removing valve cover and directly lubricating valve with some type of p-oil.
However I am still always open for suggestions.
 

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But Mad North-Northwest
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It's an electric fuel pump (and fairly new) and the pressure is always a rock solid 40 psig. It has been 40 psig for a very long time. Doesn't change at all with vacuum.
Well it absolutely should not be a rock solid 40 PSI, assuming you're measuring at the rail. If you're measuring upstream of the pressure regulator or on the regulator return line, those are both the wrong places to measure and the pressure readings there are not really useful for any sort of diagnosis.

I'm leaning towards sticky valve(s). Will look for an additive or maybe removing valve cover and directly lubricating valve with some type of p-oil.
However I am still always open for suggestions.
I sure as crap wouldn't put anything in the oil, but it's your car.
 

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Discussion Starter #5
Also, I have not ruled out ignition problems either. Lack of proper spark will cause an accumulation of unburned gas in the exhaust.

Kaboom!

I'm digging into my info on fuel and spark controls now - and more towards spark. Between the factory manual and electrical schematics I got from this forum, I'll hopefully be able to troubleshoot (32 years as an instrumentation and controls specialist at major electrical generating stations).
 

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I disconnected the battery to reset the ecu.
I don't think there is anything in the ECU to reset. But it didn't hurt to try.

Since common things happen commonly, the first thing to check is for any intake air or vacuum leaks. Even seemingly tiny faults can have a dramatic effect on running. A loose intake duct or a split in the accordian section can cause a fault that comes & goes. See: http://www.alfabb.com/bb/forums/spider-105-115-series-1966-1994/41135-embarrassing-confession.html

IME, valves don't suddenly start to stick after working fine for thousands of miles. The times I've had that issue was shortly after a rebuild/valve job - when the machine shop did not follow my instructions for desired valve guide clearance.

Also, I think Tom is on to something as far your reported 'steady' fuel pressure. Attached is a snip from the shop manual.
 

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Discussion Starter #7
I see the light.

Didn't take long to see what you were referring to. That regulator looks old as crap so it will get replaced asap. I'll let you know what replacing regulator does. Why it started working again last time is puzzling. I guess internal shaft intermittently binding. Maybe I should whack it with a hammer (lol).
Usually these units just fail and die.

It does make sense though. I could see where pressure too high or too low for engine conditions can cause the incomplete combustion.

I just ordered one from Rock Auto. I'll know in about three days. Will let you know. If no success, then I'll be addressing the ignition module.

I absolutely hope all my valves are free and happy.

Thanks for info

Warren
 

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Discussion Starter #8 (Edited)
I'm reading pressure at fuel rail inlet (i.e pump outlet pressure). It reads 40 psig all the time. I can't explain why it remains steady as pressure inside the rail is obviously modulated (high vacuum opens return line) and you would expect the gauge to reflect it. Maybe some type of orifice in the piping?

The binary nature of the event - one minute day running perfectly and the next barely running at all and then the next running perfectly again usually says "module" to me.

We'll see. My new regulator should be here in a few days (Rock Auto).

Also the gauge did verify no problems with fuel pump and filter. I've had pump issues in the past.
 

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But Mad North-Northwest
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I'm reading pressure at fuel rail inlet (i.e pump outlet pressure). It reads 40 psig all the time.
That's the right place then. I had a brain fart and forgot the regulator is after the fuel rail. It really shouldn't be steady. Is the vacuum hose correctly hooked up to the regulator?

If it is, pull it off and check it for the presence of fuel. If the regulator fails internally you can get gas in the vacuum line.
 

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Discussion Starter #10
Update

The vacuum chamber of the regulator has an apparent diaphragm leak. Unless there is some type of internal bleed orifice, this has to be an issue.

This makes those few weeks that it began running fine again after the first failure even more of a mystery.
 

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But Mad North-Northwest
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Congrats, you just found your problem. That's a common failure mode. New regulator should fix you right up.
 

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Discussion Starter #12
I hope you are right sir. How it began to work flawlessly again for a couple weeks (with a leaking diaphragm no less) will be life mystery #48869.

I will post in a few as it will be installed asap after delivery.

$42.00 for a Beck Arnley regulator.

Cheap!

As for the control unit, $325.00 on Ebay. Hopefully not needed. But it's nice to see they are available - used but tested.
 
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