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Discussion Starter #1
Can someone explain to me the systems that make the distributor advance between 2000 and 2400 rpm? I know it's vacuum determined, but unfortunately, that's all I know. Is it computer controlled? if so, which one?
Thanks.
Charlie
 

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Assuming a USA version with L-jetronic, the distributor is nothing more than a four-way switch. The computer controls timing based on signals it gets from the flywheel sensors (one for speed/rpm, the other for position/timing). There is also a MAP (Manifold Absolute Pressure) sensor to measure intake vacuum. The MAP sensor is located behind the right side panel - behind the door.

Click on the link in my signature for a page of info about the L-jet system in our cars.

If you have a non-USA Spider then none of this applies. You can go to your User Control Panel and add the relevant info.
 

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Discussion Starter #3
Thanks Eric. Can you recommend someone to check/repair my ECU, if needed?
Thanks,
Charlie
 

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Charlie,
presume it is the old problem "around the 2400 range" that you had back then?
https://www.alfabb.com/bb/forums/8373892-post36.html

check the VSD as Eric says....check the vacuum hose from that to plenum is intact, the electrical connector is good and make sure it is not whistling (if it is, the bellows is holed)

your question as to which computor: it is the Ignition computor
 

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Discussion Starter #6
It's the same problem from before. When you step on the gas, the engine chugs through the 2000-2400 rpm range, unless you accelerate slowly through the range. It appears to me the distributor is not advancing. I keep coming back to it, hoping to get to the bottom of it. I've checked the vacuum hoses, the plenum, the electrical connections, replaced the flywheel sensors....and I'm left thinking the ECU is not causing the distributor to advance.
Is there someone who checks/ repairs 1986 ECUs?
Thanks,
Charlie
 

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That could very well be the problem. Like Eric says, the dizzy is just a 4-way switch that's basically just there to fire the plugs in the right order. The rotor needs a wide tip so it has a wide range of rotation it can fire in, and then let the computer determine the precise timing. It's going to be weird otherwise. It should look like this (more or less):

 

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have you checked the VVT is working?...not just the simple test where you test if the solenoid clicks/moves, but testing that the VVT itself is actually advancing the cam?

if the solenoid doesn't even click, then you can open it and clean the plunger, like here:
https://www.alfabb.com/bb/forums/spider-105-115-series-1966-1994/415594-vvt-solenoid-really-dead.html

to test the VVT is advancing:
completely remove that electronic plug (contraption) from the end of the VVT, start the engine then apply 12V (9V battery will do) for a few seconds to the two contacts.....the engine should almost stall, if not, the VVT is not working.
 

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It’s a good thing to check, but a non-functional VVT won’t cause this problem.

Sounds like you may have the wrong rotor. Start there.
 

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Discussion Starter #12
OK...just ordered a new rotor from Centerline. Will let you know what happens.
In the meantime, does anyone know of someone that checks/repairs 1986 ECUs...you know, just in case?
Thanks, Charlie
 

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Rich Andrade at Electronik Repair in Arizona worked on mine. He usually only does Porsche so I do not know if he did me a favor by doing the one on my 1985 because he has done Porsche 928 ones for me in the past or he will work on yours if needed. You can always ask.
A rotor is a lot cheaper. Let's see if that works before you shell out more money
 

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Discussion Starter #14
Thanks. Will certainly give the rotor a go, before contacting any repair-people!
I'll be sure to let everyone know what happens.
Charlie
 

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Discussion Starter #15
OK, Gents...I changed the rotor, and no improvement. When looking at the old rotor, it appears it was the wide one after all, but when looking directly at the tip face that fires the pins in the distrib cap, there is a dark area on the left face of the tip that's about 2/3 of the width of the tip from the left edge to just past the center of the tip. It appears to be firing on this area exclusively.
I think now, that instead of the distributor not advancing, I think that its stuck in the advanced position. This would explain why I had to adjust the Air Flow flapper valve 8 clicks in order to get the car to start and idle. It would also explain why, when I remove the vacuum hose to the sensor by the computer, that nothing happens.
So....how do I check whether that its the computer sending the wrong advance signal to the distributor, or that the distributor has failed in the advanced position?
Thanks, Charlie
 

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But Mad North-Northwest
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Does the '86 L-jet distributor even have any mechanical advance? I could be wrong, but I thought at that point the advance was all electronic and there were no weights.

In any case, you should be able to tell if it's advancing (and how much and when) with an advance timing light. Just look at the pointer and rev the engine and see how much it advances at each RPM. That'll tell you if you have an advance problem or some other problem (and I'm leaning towards "some other problem," myself.)

You sure you don't have an air leak? Did you check everywhere? Did you check the four rubber intake runners? Did you check again after checking the first time?
 

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Discussion Starter #17
Tom,
There are no weights in the distrib. I checked my vacuum hoses and also checked I was getting vacuum to the sensor... and no change happens when there is vacuum, and when I pulled the hose off the sensor and there was no vacuum. So either the distributor is advanced and won't retard, or it's retarded and won't advance. (At this point that may be a more appropriate description of me!) I think it is advanced and wont retard because the Air flow meter had to be adjusted 8 clicks just to get it to start and idle. I have a new air flow meter that I've left at the factory settings. When I put that in, it won't even start. If it was retarded and won't advance, it should start and idle at the factory settings....yes? Which leads me to think it's in the advanced position and won't change.
Charlie
 

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There is no advance (or retard) mechanism inside the distributor. The distributor is supposed to be installed in one specific position (see info from shop manual) and left there. All further timing adjustments are computer controlled. A timing light should reveal where the timing is and how much it avances. The MAP sensor (intake vacuum sensor) are known to fail. Usually the internal diaphragm fails and it makes a whistling sound. Even with failed MAP sensors the engine will run fine - you just may sacrifice some fuel economy as the computer won't advance the timing under part throttle/light load conditions (e.g. highway cruising).

If you are not getting any vacuum at the hose attached to the MAP sensor then check for a kinked hose or clogged fitting on the intake plenum. The hose runs through the firewall then under the carpeting along the floorboard/sill area.

That you had to mess with the AFM should have nothing to do with ignition timing. Something else is is wrong. Air or vacuum leaks?
 

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Discussion Starter #19
Eric,
The MAP is not whistling. There is vacuum to the MAP, and increases as the engine RPM increases. Is there a way that I can check that the MAP is sending the correct signal at the appropriate rpm, or during a sudden increase of RPM?
The only time there is no pressure is when I pulled the hose to the MAP off while the engine was running. It had no effect on the engine, from low to high RPMs. Which tells me that either the distributor is incapable of changing, or that it's not getting the signal to change. Am I on the right track?
I will certainly pull the distributor cap again and check that the rotor is lined up correctly after I find TDC.
Thanks,
Charlie
 

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But Mad North-Northwest
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Don't worry about the MAP just yet. that's unlikely to be the cause of your problem.

If you think it's not advancing, you should get a timing light and actually check what's happening with the timing. Most auto parts stores will loan you one for free. If you don't do this you're just assuming that the advance is a problem

Honestly I doubt that's your problem, and you should really go through the whole L-jetronic guide. The symptoms you're describing could be an air leak, fuel pressure, bad temperature sensor...whole bunch of stuff.

https://www.hpsimotorsports.com/l-jetronic--spider-
 
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