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1987 XT: No spark, except one spark while turning off? WTF?


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43 replies to this topic

#1 misledxcracker

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Posted 30 April 2011 - 10:43 PM

1987 XT MPFI EA82, non-turbo :)

A little background: Car dies on me at random. Had it towed home... next day I got it running, albeit a little rich and misfiring a bunch. Then randomly one day later on in the week I go to try and start it, and it runs great! I'm driving it around, she got a little hot so I decide to turn on the heater to dissipate some of the heat.... and wow, whaddaya know, the minute I turn on the heater, the car dies completely. Have not been able to get it to fire since.

There is no spark while cranking... I pull the coil wire off the disty cap and put the lead near a ground, get no spark whatsoever while jumping the starter with a screwdriver and the key on, but once I take the screwdriver off the starter it sparks once. I don't get it!

Cleaned, checked, replaced the CAS in the disty to no avail. (Amazing how easy the distributors are to disassemble!) Also replaced the coil and power transistor to no avail.

Checked the wiring from the ECU to the coil, the power transistor and the CAS. Everything seemingly checked out...

Cleaned pretty much all the grounds, even added a good one from the coil bracket to the negative battery terminal. Cleaned up the coil bracket really good as well. On there nice and tight.

I'm clueless on what to do now... ECU? I'm really hoping not.... Not exactly the easiest ECU to find in the world :-\

ECU is throwing no codes. Threw a crank angle sensor code at one point, virtually worthless though as replacing the thing didn't do a thing.

This is fun! :rolleyes:

#2 Cougar

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Posted 30 April 2011 - 11:28 PM

Check to see if you are getting voltage on both sides of the ignition coil when the ignition is on. If you have voltage on both sides then see if there are voltage pulses on the minus side of the coil when you crank the engine. If there aren't any pulses then something is wrong with the CAS circuit. If you are sure the things you replaced are ok and the wiring to the ECU is ok then the ECU would seem to be the suspect.

#3 grossgary

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Posted 30 April 2011 - 11:36 PM

drivers side timing belt broken?

have you tried another distributor? you replaced the CAS in it, but what about the wheel and other bits in there, all good you think?
i've had strange issues with distributors twice where swapping in another fixed a no-start. i can't recall if they had spark or not but both vehicles sat for a few months.

Edited by grossgary, 30 April 2011 - 11:39 PM.


#4 misledxcracker

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Posted 30 April 2011 - 11:43 PM

Crap! I knew I forgot something! The timing belt is not broken!

I have no timing covers, and my driver's side T-belt is fine. The rotor spins, it looks nice, I even took the danged distributor apart and cleaned it all out pretty (not a millimeter of bushing play!)

Again, and to cover the third or fourth timing belt related reply, it's not broken nor stripped! :)

Gary, I replaced the CAS in the original disty, from an SPFI disty. You can get the CAS out of Isuzu Troopers and Mercury Villagers too, tripped me out anyway! Very surprised how simple it is to disassemble one.

Cougar, how do I check the pulses? I get 12V when I check the negative side of the coil, but not the positive. Maybe I'm doing something wrong?

Can the ignition relay or ignition switch possibly be an issue?

Edited by misledxcracker, 30 April 2011 - 11:47 PM.


#5 Cougar

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Posted 30 April 2011 - 11:45 PM

What about the voltage to the coil?

#6 misledxcracker

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Posted 30 April 2011 - 11:48 PM

I'm trying to figure out how exactly I do that.... Last time I went prodding with the DMM, I fried a fuse :lol:

#7 Cougar

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Posted 30 April 2011 - 11:51 PM

The ignition circuit should tie to the plus side of the coil not the minus side. I think the power wire to the coil is black and it should tie to the plus side. Once you verify that is ok then make sure there is voltage on the minus side of the coil also. If there isn't any then the coil is open or the CAS is making a ground connection to it. Remove the wire to the minus side and check for voltage again. If you now have voltage then the CAS may be bad.

Edited by Cougar, 30 April 2011 - 11:59 PM.


#8 misledxcracker

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Posted 01 May 2011 - 12:00 AM

Okay, I have roughly 11.80V going to both sides of the coil... without disconnecting anything.

Can't try starting it at all until tomorrow, complaining neighbors :mad:

Bad 2nd CAS? This is getting very annoying :-\

#9 Cougar

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Posted 01 May 2011 - 12:05 AM

The voltage is a little low, most likely due to a low battery. The voltages readings are what you would expect to see. Have you checked all the fuses and made sure they are ok?

#10 misledxcracker

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Posted 01 May 2011 - 12:06 AM

Fuses all look great, and I replaced the fusible links with some nice-looking newer ones I grabbed from the SPFI wagon at the junkyard.

Yeah, the battery is on the low side for sure.

#11 Cougar

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Posted 01 May 2011 - 12:09 AM

It would be a good idea to measure the voltage on the fuses to make sure they are getting power. Also make sure the CEL light is working. You may need to check power to the ECU next.

#12 misledxcracker

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Posted 01 May 2011 - 12:12 AM

CEL is functioning normally to my knowledge, with no connectors plugged in all I get is a 6. I connect the black connectors, I get a 13, I think it was.

I'd love to know how to check ECU power, I can do so tomorrow morning, gotta run off to work here in a while :lol:

#13 misledxcracker

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Posted 01 May 2011 - 12:15 AM

What's really baffling me is that one spark from the coil upon shutdown... Why would it do that, just spark once like that yet not spark at all when cranking? Also, if it makes any difference, any time I disconnect and reconnect the CAS plug from the main harness, it throws out a spark. :confused:

#14 Cougar

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Posted 01 May 2011 - 12:17 AM

To check for power set your meter to read DC volts. Then tie the common black probe to a good ground point. Then touch the red probe to each side of the slits on top of the fuses. You should have voltage on each side of the fuse. You will have to turn on the ignition switch for the dash fuses since some are powered after the ignition switch connection.

#15 Cougar

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Posted 01 May 2011 - 12:23 AM

What's really baffling me is that one spark from the coil upon shutdown... Why would it do that, just spark once like that yet not spark at all when cranking? Also, if it makes any difference, any time I disconnect and reconnect the CAS plug from the main harness, it throws out a spark. :confused:


That happens when the CAS circuit isn't working. When it is shutdown or grounded it triggers the coil and a spark is made. There may be a fuse problem causing the CAS circuit to fail so we need to check that out.

Edited by Cougar, 01 May 2011 - 12:26 AM.


#16 naru

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Posted 01 May 2011 - 02:30 AM

The single spark after removing your screwdriver jumper from the starter is a little mysterious as the coil is still powered up w/the key on.

This combined w/the weird blower action suggests to me that the ECU is not receiving full voltage.IIRC,the wiring harness has some crimped connections in the rocker area that corrode.

I would measure ECU input voltages by backprobing the connector.

#17 misledxcracker

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Posted 01 May 2011 - 09:27 AM

I'll go check the fuses now. Will this tell me if I have a bad circuit somewhere or something?

And where do I check for the voltage being supplied to the ECU?

#18 Cougar

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Posted 01 May 2011 - 10:27 AM

If there is a blown fuse we will most likely have to track the trouble down. I am try do find some info in my data about the ECU wiring so that can be checked.

#19 misledxcracker

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Posted 01 May 2011 - 10:37 AM

All fuses seem to check out OK, none blown, checked for voltage on both ends of them all. Like you said, some required the key to be in the on position, but checked out.

#20 Cougar

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Posted 01 May 2011 - 10:41 AM

Ok, well I guess the next step is to verify power is getting to the ECU. I am still trying to get my software running to check it. I think I need to reset my computer.

#21 Cougar

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Posted 01 May 2011 - 11:30 AM

I finally got my service software to load up. It shows power to the ECU comes from the Ignition Relay on a wht/r wire to pins 27 and 35. Power also supplied from the ignition switch on pin 24. The green fusible link supplies direct power to pin 62 via a red wire.

The CAS wires should tie pins 7,8, and 17. The forth blk/r wire should tie to shielded ground.

One thing that may make things easy is to just put the ECU into the test mode and see if that works ok. If that checks out then the ECU may be ok though I suppose the ignition section of it still could be at fault.

Edited by Cougar, 01 May 2011 - 11:33 AM.


#22 misledxcracker

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Posted 01 May 2011 - 06:47 PM

OK, now I plug in the black connectors, put the key in the on position, and I get...

11, 23, 32, 33, 35, 42, 51

I think I may be retiring this one.... this problem is a bit too much. All I did was drive the thing... get it running again and the friggin heater kills it for good... Seen too many XT ECU failure stories and I am frankly tired of sinking money into what's seemingly becoming a money pit...

#23 naru

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Posted 01 May 2011 - 07:31 PM

That many codes at once is an almost sure sign of an ECU power supply or grounding issue.Likely to cost nothing but time to fix.

Check ECU power by putting your meter negative lead on battery negative and the positive on the backside of the ECU plug at the relevent location.

Check grounds by moving the positive lead to the ECU grounds at the plug.All should be 0 volts.

My money is on failed wiring harness crimp connections in the rocker under the sill plate.Gloyale has posted some good photos,IIRC.You might want to search for those.

ECU failure is doubtful,but,if so,they can be had for $25-$50 at Car-part.com depending on your build date.

#24 Cougar

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Posted 01 May 2011 - 07:51 PM

I agree with Naru. This appears to be a power problem of some sort and it shouldn't be to hard to pin down the trouble.

#25 misledxcracker

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Posted 01 May 2011 - 08:09 PM

That's relieving, thanks :grin:

Alright, I'll go look for those pictures and figure out exactly where those connections you're talking about are...




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