No spark from my optical pick up distributor

[2WDXT]

Hello there. I have been searching thruogh the threads here and have hit and missed on a particular problem. I own a 87 xt gl 1.8 mpfi 2wd that lost spark. I got the spark back about an hour after it first died even though I didnt work on it, then it died for good. I have replaced the coil, optical pick up, plugs, wires, cap, and rotor. i have the signal to what I believe is a transistor mounted on the coil bracket but have no spark. The two blade plug goin to this "transistor" has voltage until the signal comes around from the crank angle sensor like I think it should. I beleive this "transistor" may not be pulsing the coil like it should to build current and release it. I'm at my wits end and running out of cash. If someone out there has experienced a similar problem or can tell me where to purchase one of these " transisors" if thats what its called, I could sure use some help. the chiltons manual calls out a condenser, maybe this is what im thinking is the transistor.

[ruparts]

hi, from what you have described , it sounds like you found the problem . i had a similar experience with mine once. if you have any access to salvage yard parts try another one or two. these are expensive to buy new. any subaru from 87-91 i think is the same, the part is made-on to the coil bracket, so just plug & play. maybe someone on the board has a spare one to sell, post in the parts wanted section, or reply to ads parting out cars. let us know if it fixes it.

[idosubaru]

yeah that transistor - the FET I believe it's called - is likely hosed. just get a used one. post in the parts wanted forum here, someone will have one.

 

test for spark out of the coil - that rules out most of the disty, plugs, wire stuff if you don't have spark there. sounds like you got none out of the coil.

[GeneralDisorder]

That is the ignition amplifier - they are REALLY expensive from the dealer and it's pretty rare to see one fail (I've seen many factory units that work after 250k miles). Your best bet is a used one - sounds very lilkely that this is the problem.

 

GD

[john in KY]

May just be a broken timing belt.

[zacyork]

before you keep throwing parts at it you need to trace where you lose your spark. the ignition system system isnt that huge. get a decent wiring diagram and trace your wires.

[naru]

Since you have an ignition signal at the transistor and a known good coil,the transistor or its ground is bad.

[GeneralDisorder]

Since you have an ignition signal at the transistor and a known good coil,the transistor or its ground is bad.

 

I agree - and the fact that you lost spark, had it come back, and then lost it again would tend to rule out timing belt breakage. Thus why I didn't mention that. But easy enough to verify that the driver's side cam is turning when you crank it.

 

GD

[NorthWet]

... i have the signal to what I believe is a transistor mounted on the coil bracket but have no spark. The two blade plug goin to this "transistor" has voltage until the signal comes around from the crank angle sensor like I think it should. I beleive this "transistor" may not be pulsing the coil like it should to build current and release it...

(OK... First off, please pardon my non-precise terms for the transistor terminals. Their functions are probably more meaningful to most than the various names given to them based on hole-conduction theory and internal construction.)

 

You are showing voltage at the "input/power" terminal of the transistor, and then you see pulses at the "control" terminal? When the pulses appear, what happens to the voltage on the "input/power" terminal? Does it go to zero? Does it sag a bit? (Might be hard to tell with pulses anyways.)

 

Come to think of it, are you seeing voltage pulses on the "signal/control" terminal of the transistor? I think that the ECU grounds this terminal instead of giving a voltage pulse... pretty typical of power applications.

 

Regardless, the third terminal of the transistor will be it's ground through it's bracket mount to the body. If this ground is poor then you won't see much if any spark... and you shouldn't see the voltage sag on the "input/power" terminal.

 

Something you may want to consider is checking the coil terminals for steady voltage on one side and pulsing voltage on the other. (A dwell meter might also be useful.)

 

The basic circuit would be:

Ignition-switch power to one side of the coil, the other side of the coil going to the "input/power" terminal of the transistor, the "output/ground" terminal of the transistor being grounded to the chassis, and the ECU sending grounding pulses to the "signal/control" terminal of the transistor based on signals from the distributor.

 

BTW, and this may be a TOTAL false-trail, but I recently came across a no-start, seemingly no-spark situation after an engine swap. Both recipient and donor car had been sitting for many months, but both ran prior to storage. We were getting a single spark for every approximately 10 that we should have gotten. (10 rotor rotations yielded 4 sparks, evenly spaced.) Replaced disty, no joy; replaced coil/exciter transistor/bracket assembly, no joy; replaced ECU and it fired right up. These were all known working parts prior to sitting. ECU might have only required reseating the connectors, but that is 20/20 hindsight.

[2WDXT]

The ECU is a worry of mine. Where do I find it to check the connections and/or a new one if needed. I have constant voltage at the two bladed kinda rectangle plug that is on the "transisor" bracket and 1.7 volts constant at the round plug that goes into the wire harness who's mate goes to the coil terminals which doesnt pusle while cranking how ever I did get the 12 volts at the rectangle plug to pulse the other day while turning the motor by hand but not today. When i had the "transistor"(or ignitor whichever is correct) unsoldered and in my hand it read resistance in one direction but not the other and my electronics guy at the plant said that is correct and functioning. ALSO, IF THE KEY IS ON AND ALL HOOKED UP, I CAN PULL THE RECTANGULAR PLUG OFF THE COIL BRACKET WHILE HOLDING THE COIL WIRE NEAR GROND AND GET ONE SPARK JUST LIKE A BREAKER SET. It's the ECU isnt it? What the heck? Maybe this is why they didnt run this style long. It was great out of the gate but now I'm pulling my hair out.

[GeneralDisorder]

ALSO, IF THE KEY IS ON AND ALL HOOKED UP, I CAN PULL THE RECTANGULAR PLUG OFF THE COIL BRACKET WHILE HOLDING THE COIL WIRE NEAR GROND AND GET ONE SPARK JUST LIKE A BREAKER SET.

 

Still sounds like a bad ignitor to me. ECU's on these almost never fail. I have never even seen it.

 

It's the ECU isnt it? What the heck? Maybe this is why they didnt run this style long. It was great out of the gate but now I'm pulling my hair out.

 

What do you mean they didn't run that style long?!? They ran it from '86 to '94 - that's 8 years. And they are dead reliable systems - ignitor failure and CTS failure are about the only things you see and even those are rare.

 

Just pickup a used coil bracket with the ignitor and try it.

 

Even if it does turn out to be the ECU - they are common and cheap since they never fail. People are always ready to blame the ECU for stuff - they just don't really fail. I highly doubt that's your problem.

 

GD

[2WDXT]

With the optical pick up crank angle sensor?

[GeneralDisorder]

With the optical pick up crank angle sensor?

 

Yes - all the optical distributor systems are the same from '86 to '94. I know for a fact you can use any of the optical distributors and you should also be able to use the coil and bracket assembly from any '87 to '89 DL/GL with fuel injection and any '90 to '94 Loyale.

 

The ECU itself is slightly different because yours is an MPFI system. But that ignition should be the same.

 

GD

[2WDXT]

But I'm having trouble finding any of these ignitors for sale. I'm new to this site and have a hard time navagating it. Do you know what the resistance readings should be for the ignitor? Also my alarm has stopped working on this vehical. The chiltons manual doesn't show it but its bred right into the factory wiring. I cant get the dealer to admit that this vehical had a factory valey( if thats how its spelled) alarm but its there. Normally when the door is opened a clicking starts which is the timer and it gets faster after a short period and if the key is not turned to on within maybe 30 seconds a relay is engaged to pulse the horn. I inspected the connectors on the ECU in the trunk and found no melted or corroded connections. It seems like every week there is something else not working with this unit. I posted about the voltage pulse on one of the originals but cant get back to it to quote.

[2WDXT]

Does anyone know what the 4 numbers on the ECU that are what seem to be spec or sub-numbers on a silver section of the label on the ECU mean? They seem to be different on every one.

[GeneralDisorder]

Being you have an XT - there is a higher probability of wireing harness problems between the ECU and the engine bay - this is due to the ECU being in the trunk on that model vs. under the dash on all other models.

 

People have found issues with the wireing harness factory crimp joints under the door sill trim, etc. Water can get in there and can cause corrosion of the wires and crimp joints - IIRC that typically results in a no spark situation. The thread I saw a few years back had pictures of the culprit connection which I beleive was located under the passenger side door sill/rocker trim.

 

Perhaps grossgary will chime in with more info here - he has owned more XT's than probably any member on this site.

 

Here's a site that details how to test a transistor (amplifier, or in igntion system terms they are called an "ignitor").

 

http://www.kpsec.freeuk.com/components/tran.htm

 

As you can see a resistance test is not the only thing used to verify that a transistor is functional - they are more like a diode than a resistor and will only conduct in one direction so you have to be mindful of the direction you test and to fully test them you need to switch them on and off.....

 

But I think it more likely that you have wireing troubles.

 

As far as ECU's - any XT4 ECU from one with the same type trasnmission will work - the numbers don't matter.

 

GD

Edited November 16, 2010 by GeneralDisorder

[naru]

Plenty of ignitors at car-part.com.$10 up.

 

As long as the white/yellow wire at the square connector carries ignition pulses from the ECM while cranking,you can forget about ecm/harness issues.Use a low current LED type test light/dmm to avoid damaging the ecm w/too high current draw.

 

Resistance measurments are meaningless when applied to transistors.

The "diode check" function of a multimeter can however provide useful info.

[2WDXT]

Wow! You are all awesome with the information you have and can provide. I will check the rocker tomarrow and get a more sensative meter for the ignitor test. Thanks in advance. I feel confident that we will overcome this issue because appearently we Subaru lovers never say CAN'T! I try to encourage all the mechanics in our facility that CAN'T never could and CANT doesn't work here. Again, thank you!

[2WDXT]

Just so we all are on the same page, this is not my first subaru. I have owned, and sold them still running, two 1977 1600 standards as well as a 92 dl NA wagon and have never had any problems more than axles and clutches. I guess if you can rag 'em' you will. I had one head gasket problem from a 1600 standard but like I said, when you beat the brakes off of them, some maintenance should be expected. I also own a 69 Rambler Wagon and a 68 Montego. They all work great, but every thing needs attention right? We wont talk about the wife's '05 Taurus.......Not yet sure how to make a new post so forgive me for replying to every thing. It's just right there...

Edited November 17, 2010 by 2WDXT
Not familiar with the site quite yet