Well, the plot thickens here.. more dead ends..

I checked out the tech article on the ign system and determined the ign control module must be bad. So I pulled it and went to the parts store and had them test it on their fancy machine. It was wasted... So, I went to the junkyard and found on.. a new one is 90 bucks... [incidentally, I found a good 91 NA 740 cluster for 15 bucks.. for my 92 940 turbo..] I thought I had it licked and brought the part home to try.

I plugged it in and .... nothing... no fire.

I went in the garage here and actually found another I had in a junk box... tried it as well... nothing.

Frustrated with the possibility of TWO duds.. I pulled the one off of the nine... NOTHING..

Back to the nine... tried ALL THREE in my car and it fired right up! I'm really getting pissed by now.. lol..

So, now, it's back to the parts store to see if their machine is wrong or what on the other three spare I have.

The car is barely sparking.. all weak and yellow.

So, I yanked the coil off of the nine.. and tried it on the 740... same no start... What would cause a weak faint yellow spark?

It's like the coil is bad, but it was replaced with a known good one... nothing happened.. What the heck am I missing?

If the hall pickup was bad, the fuel pumps would not be triggered and there would be zero spark instead of the weak crappy yellow one...

Any ideas or pointers would be great.

Thanks,
Mike

More bad news.. the weak spark is now gone.. zero output from coil. It was weak and yellow before.. I guess the only thing left is the hall pickup in the distributor... Going to look into testing it..

M.

ummm, not necessarily. bad spark could EASILY be the ICU or the ignition power module. bad coil is much less likely, but not impossible.

I believe you have the Bosch EZ117K ignition system. that with other systems is covered here, http://www.k-jet.org/files/greenbook...incomplete.pdf

if you're getting fuel, then the hall sensor is working, as its pulses are required by the ECU to time the injector pulses. In fact, I believe on LH2.2, the hall sensor goes to the ICU first, THEN to the ECU, so if the ECU is generating fuel injection pulses, odds are pretty good the ICU is working, so I'd be looking at the power stage and the wiring from the ICU to power module to coil.

looking at a potentially dicey 1987 740 wiring diagram, it looks like the ICU has a grey wire to pin 5 of the power module, and a red-white wire goes from pin 1 of the power stage to the '1' terminal on the coil (red-white also goes to the tach on the dashboard). the coil '15' terminal goes to power.

Hmmm... I tried all 3 ign control modules and all of them started my car. And all 3 had identical weak/no spark output in the 740. I took the 3 modules back to the parts house for "checking" and all 3 "failed".. yet they all start and run in my car... [Naturally, the machine is made by the same company that makes the replacement ignition parts they sell....is it really bad or does everything "fail"..] :confused:

We found 12 volts with the key on at the + terminal on the coil. I even ran a dedicated single hot wire from batt + to the + on the coil to totally bypass all the internal wiring and to see if that would improve spark and it did nothing.

The key is, I guess, is to figure out why there is no spark at all now.. the weak yellow spark went away now and there is zero activity. 12 volts to the coil.... nothing from the high tension lead... I did swap out the coil from my car and nothing happened..

So with the coil wiring, the red-white wire goes to the - side of the coil? On the 740 all of the insulation has eroded away and the previous guy black taped up everything. What builds the field up in the coil? the hall sensor is supposed to discharge it as a spark at the plug... I'm out of ideas again... Thanks for your patience... I'm about out of it myself.. :o

Cheers, Mike

it goes hall sensor to ICU to power module to coil to sparkplug....

the ICU sends pulses to the power module, which switches off so the coil 'floats' to 12V, then grounds the '-' side so there's a current pulse through the coil which it transformers up to the multi-KV that sparks.

that PDF I linked has the whole 9 yards, how to ohm meter test the coil, etc.

Thanks Pierce,

I downloaded the link and began to read and look at the simplified diagram. This helped me out a great deal..

[I'm a picture guy.. LOL... I wish I had a good printer here and a way to bind it up. I've seen several nice pdfs I'd like to have printed. ]

Anyway, from reading and studying the diagrams I've got a new direction to try. I'll post the results...

The internet is LOADED with almost the same exact sequence of events and no spark out of the high tension side of the coil, despite the correct 12 volts in...

Thanks again for the pdf link.. it kicks A$$ .. :D

Cheers my friend,
Mike

Ok... more dead ends.. Replaced the hall sensor because of lack of spark... Got it sparking again, but weak.... better than before mind you, but still yellow. Tried spark out of coil tower.. bright blue! Changed over to a different main coil wire.. better spark at plug now. Still NO START... just cranks to the moon. How can it have spark... smell raw gas out of tailpipe, and not run? I know the next item up for replacement is the ignition control module on the inner fender near the resistor pack... been there, tried that... Took one from my running 940 and plugged it in with the same result. The owner is considering dumping the wagon now...

Drive it home fine... tho it did hit a bump and die.. but immediately restarted and ran fine to my place..

Then it ran good till it just quit the next day in my yard... from then on it's been a paperweight.

I have never ran into this before... gas spark and air equals running in every other car I've had.. or at least a sputter or two..lol

I tried shooting starting fluid in the throttle body and bottoned up the hose quick.. tried to start it.. NOTHING...

The guy who has the car suggested an inertia switch ? Do these cars have it and do they go bad? The bump and die event could be explained by that, I guess..

Much more trouble and it will likely be gone..

Any more ideas?

Thanks,
Mike

well, if you got a bright blue spark out of the coil, then its the spark plug wires, or the distributor cap + rotor, not hte power mdule.

I have no idea what an inertia switch is, and I'm pretty sure there's no such thing on a volvo redblock.

ok.. will try switching the cap rotor and wires over from my 940 tomorrow.. However the cap and rotor do look almost brand new on this 740... The wires don't appear too bad, but I'll just swap over the whole enchilada on the morrow. I dont understand all the wires bad at the same instant.. the main coil wire was replaced.. to no effect.. the only thing left is a defective cap to rotor connection..

I'll post the results.... fingers crossed..

Cheers,
Mike

On the topic of swapping my 940 cap rotor and wires... I looked up the cap and rotor.. They are the same part number... However, the wire set is different.. There is two sets for the nine, 44 and 54.... But the set for the 740 is 73! What's the big diff? So I guess I have to buy a wire set then.. Are they special or what? 30 bucks more makes me wonder. Any suggestions?

Thx, mike

the difference in wire sets has to do with the ignition system, where the coil is and what sort of coil it is. thats a pretty big price spread for just that, unless that last one is only available as a bougicord set or something, and those others are for cheaper sets. my experience is, the bougicord sets last for years, the others are mostly junk, and will be ligthing up like a christmas tree within a year.

Ok.. Tried the good bougicord coil wire from my car on the 740... No better. Getting a full 12 volt reading at pos side of the coil. Still a weak spark... Yellow. Plenty of gas now.. Gas is not an issue.

This car is loaded with the biodegradable wire cover.. There is all sorts of bare wires showing in a rats nest under the intake and behind the alternator. There seems to be a bit of buggery at the ign control module as well. I wonder if I'm going to have to find a good plug at the yard and try to splice and recover the rest.

A real shame, as the rest of the car is in great shape.

I'm running out of ideas and I reckon we're going to have to pull the wiring back to the "good" section and start adding new wires. I don't have the money for a new harness, so I guess this method will have to do.

After all the wires are fixed, then I'll try and look for the starting issue. I'll have to post pix as well.

Cheers, mike

yeah, fried wiring would definitely cause these sorts of issues. the weak spark could be the wiring between the ICU and power module, or between the power module and coil.

A few photos to give you an idea of the carnage I have to deal with...

The rats nest is just plain ugly.. thats going to take some time to fix, The insulation is just falling off in pieces.. Check out the plug wiring to the ignition control module.. I have no idea what some bonehead was doing there.. The splices and the bare wire? WTF?? No wonder it does not run right..

Any easier way to fix this crap other than a new harness? I'm going to have to try and replace the bad sections one segment at a time I guess.. :eek:

M.

BTW.. the cap and rotor look new as can be, and scope out the wiring to the coil.. Red and white go to neg side of coil? The wiring looks good that was protected in any sort of covering... go figure..

Cheers,
M.

Anyone happen to know the wiring harness year interchange with this 87 740 turbo wagon? There is an 89 760 turbo in the junkyard... Will this swap out? Also is there any main bulkhead wiring harness connectors to make easy removal.. I'm familiar with those, as my American vehicles are set up this way... Any other tips or tricks for harness removal or hidden connectors?

Thanks in advance,
Mike

760s have completely different dashboard harnesses, at least the later ones did. Not sure about the engine harnesses.

in 89 or 90, they switched to LH2.4, which would be totally different. I believe 1989 non-turbos were 2.4, as are 1990 turbos, but I only have a 87 240, a 1991 940SE (760 turbo of sorts) and a 1992 740 turbo at present to choose from.

87 is LH2.2, as are, I think, 85-88 and maybe 1989 turbos (unsure exactly).

yes, 740s have bulkhead connectors on the firewalls, left and right side.

Hi pierce, thanks for the reply! Come to think of it, it may have been a 740... I have been pulling so many parts from close years and models I'm getting confused. The dash looks the same as my sons 740 and it had the 2.3 turbo like both of out cars... It had the good exh manifold on it I grabbed. Did they make 760 with 2.3 turbo? Too many cars to keep track of .. The guy who has the car is headed to the junkyard right now to grab a harness... Hopefully it looks like his.. 87... It's an 89 in the heap...

Cheers, mike

the 760 turbo was a b230ft, same as a 740T/940T. late run 760s had a different dash like the early 960s. not sure when that happened.

Hi Pierce,

The harness is here.. only 5 bucks at the junkyard! This is confirmed to be from an 89 760 Turbo. The harness looks very close indeed.. and in very sweet condition too. It looks like the newer harness has just 3 more wires than the 740... The plugs look the same for the most part, but either may have been for abs or ??

I guess the thing to do now would be to somehow find both wiring diagrams for the 89 760 and the 87 740... and modify the 760 harness look like the 740...

Pics posted are of the plug ends.. as you can see the big plugs fit, wire position slightly different.. the other extra plugs may need to be swapped over?

Thanks for your help!
Mike