4x4Wire TrailTalk

Died running, now no spark

Posted By: JAVYPRO

Died running, now no spark - 05/05/16 08:18 PM

I was on my way to work this morning on my 1990 LWB and 1/4 mile from home the engine died. Brought it home, cranked it and nothing, it has fuel as I can hear the fuel pump running but it shows no spark.

I tested the coil per the FSM. Tested the primary coil resistance (from + to Hight voltage terminal the standard value calls for .72-.88 ohms I get .9ohms.

Then tested the secondary coil resistance. Standard value calls for 10.3-13.9 Kohms, I am getting 11.

Also tested the power transistor also per the FSM and it tested fine. Still went to the auto parts and got a new one and still no spark (they were nice to accept it back).

So, what now? the ECU is freshly rebuilt. What else could it be?

I cannot enjoy driving this thing.

Javy
Posted By: TOASTY

Re: Died running, now no spark - 05/05/16 08:26 PM

Optical sensor in the dizzy is your next suspect. If you have a friend with an old DSM datalogger you can test while cranking to see what the tach is sensing for a signal (the stock gauge isn't sensitive enough to diag). If it's all over the place or not registering, there is your fault.
Posted By: JAVYPRO

Re: Died running, now no spark - 05/05/16 08:36 PM

Unfortunately I have no access to a data logger.

Javy
Posted By: fasteddy

Re: Died running, now no spark - 05/05/16 08:43 PM

MarkG had one.
Posted By: JAVYPRO

Re: Died running, now no spark - 05/05/16 09:27 PM

If it is the optical sensor the only way to replace it is by replacing the distributor unit, right?

Javy
Posted By: PajEvo

Re: Died running, now no spark - 05/05/16 11:46 PM

A friend (or junkyard) with a distributor to swap in would narrow it down for sure. I have evoscan and the cable here which can read MUT language but the turnaround time would be long...
Posted By: pcc

Re: Died running, now no spark - 05/06/16 10:45 AM

Originally Posted by JAVYPRO
I tested the coil per the FSM. Tested the primary coil resistance (from + to Hight voltage terminal the standard value calls for .72-.88 ohms I get .9ohms.


Did you check for actual primary voltage? I believe you can also connect a 12v test light to the primary and while cranking engine watch it blink as primary is switched off and on. If not blinking then it'll be the primary switch. I think the switch was the power transistor with signal from ECU.

Posted By: BottomFeeder

Re: Died running, now no spark - 05/06/16 01:46 PM

I picking up a 91 which had the ECU rebuilt. ECU took a crap again. Owner is tired of dealing with it.
My point is, see if you can borrow a ECU to rule out this theory.
Posted By: haztoys

Re: Died running, now no spark - 05/06/16 02:01 PM

Never do a reman ECU ... The ECU is wounded and they just fix what they see as bad then the ECU just keeps dying on some other part down the line in the ECU ... Get a good used ECU ..

I bet its the igniter "plug" at the igniter .. Not the igniter but the plug ...

Captain Gear Box

Hazardous Toys inc ..
Posted By: pcc

Re: Died running, now no spark - 05/06/16 04:39 PM

Originally Posted by haztoys
Never do a reman ECU ... The ECU is wounded and they just fix what they see as bad then the ECU just keeps dying on some other part down the line in the ECU ...


I must say my repaired ECU, done by avproecm.com, has been great. Repaired several years ago and no problems - great price and turnaround. Unfortunately the web address is not active any more. But there may be another one out there worth a try.
Posted By: TOASTY

Re: Died running, now no spark - 05/07/16 01:47 AM

Avproecm doesn't count as a reman, those guys are skilled craftsmen. Reman ECUs are junk though for sure, get a new one or figure out where they guys from Avpro are hanging out.
Posted By: pcc

Re: Died running, now no spark - 05/07/16 11:42 AM

This SITE looks like it may be resurrected AVpro? The technicians from AVpro must have gone somewhere.
Posted By: PajEvo

Re: Died running, now no spark - 05/07/16 01:29 PM

Great find!
Posted By: JAVYPRO

Re: Died running, now no spark - 05/11/16 11:04 PM

Guys,
I am going to check the primary voltage again. I am supposed to see 12v and here is why. I left the ignition switch on while looking at the fuses and such and all of a sudden the coil started to smoke shocked It got fried.

Fortunately the coil has a lifetime warranty at Oreilly's. Well I went ahead and installed the new one and guess what? It got so hot that shortly after it went up in smoke too mad mad At this point I am so F pissed that I wanted to hit it with a sledge hammer. I sat for a second and thought about the only electrical update I had done to it, the tach filter. A couple of days back I had to fix a broken wire and in order to do so, as it was so close to it's frame, I had to melt some of the rubber back plane, I welded the wire and got the tach working. So now, I disconnected the filter from the wiring harness and turned the ignition switch, the same fried coil remained normal and it did not get even warm. I wonder if that was the culprit.

Well I got me a third one from Advance, it was cheaper, so I guess that I will plug it in without the filter to see if it start to get hot.

I calmed down and started to analyze the scenario. Only 12v come into the coil and there is now way that more than that is been produced so it has to be a short of some sort, I don't know where. I checked the plug on the coil primary and there is just power on the expected side. 2) I need to have a pulse coming in as the ignition control module pulse will produce, what if I have a constant and no pulse, will it burn the coil? and 3) the filter I mentioned before.

Guys I have to admit that this is getting on my nerves and I am working on this issue while in a really bad mood and it doesn't help because I cannot think straight that way.

Deep breath, uhhmmmm, uhhmmmm.

Ok

Back at it.

Javy
Posted By: 4x4Wire

Re: Died running, now no spark - 05/11/16 11:57 PM

Javy:

The max should ever have is 12 v. The heat was generated by a short -- low resistance, high current, high heat.

You should have popped a fuse before the coil burned. Your tach filter repair sounds like the problem source.

Melting some of the rubber backplane doesn't sound good. Your are better off slicing with an Exacto knife or fine grit grind with Dremel. tool to expose the connector without heat. If the backplane is multilayer, it can be messed up with with excess heat.

Sorry, in a former life I was Micro-Miniture Electronic Repair Certified.....
Posted By: pcc

Re: Died running, now no spark - 05/12/16 10:38 AM

Originally Posted by JAVYPRO
I am supposed to see 12v


Not necessarily. Some systems use 12v for cold start then switch to say 9v for running. Some coils have internal resister while some use external. It's important to determine which coil you need.
Posted By: JAVYPRO

Re: Died running, now no spark - 05/14/16 01:24 PM

GENTLEMEN...IT IS ALIVE, IT'S ALIVE...

The issue? the tach filter. As I mentioned before, on the positive incoming into the primary side of the coil I saw the 12v +/- coming in but i also noticed a parasitic mV on the negative so something was feeding this into the wiring harness.

I disconnected the tach filter and indeed, that was the culprit. It had shorted out when I attempted to solder the wire that had broken off. Hey, not because I did a lousy job, it is because i attempted the impossible. The rubberized backpacking is old and was too hard to make a cut with a blade and successfully pull a bit of wire for the soldering job. it simply was not worth even to try to begin with.

So, I am tach-less and I am not sure how easy it is to find this part. Any pointers?

Thanks Y'all,
Javy
Posted By: 4x4Wire

Re: Died running, now no spark - 05/15/16 09:59 PM

One trick to soften old and hardened rubber is heat. I have a heat gun that is left over from days when I used a lot of heat shrink tubing. A hair dryer will get you almost enough heat if you take your time.
Posted By: Mudraider

Re: Died running, now no spark - 05/16/16 02:54 AM

I had to find a used one.
Posted By: fasteddy

Re: Died running, now no spark - 05/16/16 05:25 PM

You can buy a new general use LC filter that should work. I Googled LC filter for tachometer and came up with a couple including wiring directions. Once I started researching these are fairly common parts.
Posted By: JAVYPRO

Re: Died running, now no spark - 05/19/16 12:09 AM

Thanks Eddy

Javy
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