hi sages- been considering a somewhat overlooked cause of ignition malfunctions on the board. since it is hidden away and not readily thought of in the number of recent ignition crapout discussions, i have a couple of questions about the cps. when all else fails the cps replacement seems to solve same. how do you quickly check this part. it appears to be a rotating magnetic switch which triggers the coil at the right time to fire the plugs, located in the backof the engine on the bell housing. sounds like there are no moving parts, which raises to question how does it do its job. does dirt or corrosion stop its signal. how tough is it to replace. dont want to go to the dealer and take out a mortgage to fix it when the day comes. would napa have the part and what would it cost. want to be ready next time.would like to hear from you folks who have had fat experience with this anomaly. thanks tons oldduke

Hi,

As far as replacing it goes, like Tony says if you have one of the 91 and up models you might be in for a treat. Not too bad though. It will be a plus if you have skinny arms not matter what model you are dealing with. I replaced both on our 90 244 and 92 245. Somehow I was able to pull a crazy "Stretch Armstrong" move and get the one off the 92 245 with a wrench-can't remember which I used either a stubby 10mm wrench or a Gearwrench XL flex head ratcheting wrench. The first time I did it on the 90 I used several extensions and a wobble joint. Both times I started the bolt with my left hand.

No matter what you do, have plenty of light and some PBlaster and remember the term "easy does it" applies here. Also if you can, get up on the passenger side strut tower I found that was easier than trying to lean into the engine compartment.

You can order a Bougicord CPS from either FCP Groton or FCP Euro-check both places the prices may be slightly different, both places are running free shipping for any order right now.

Good luck,

Travis

The primary winding in the coil finds its ground through the power stage AKA the ignition amplifier.

The flywheel on the LH 2.4 equipped engines has a ring attached to the outer rim. That ring has evenly spaced holes, which the CPS senses and indicates to the ECU, which in turn counts the holes. There is a void - an area without holes - in the ring, which, when sensed, tells the ECU to start counting. Every 14th hole, the ECU sends a signal to the power stage interrupting the ground path from the coil primary, thereby inducing the stored charged to seek a alternate ground path, which it does through the secondary coil windings and the distributor to the grounded spark plug.

Think of the ignition coil as an electronic point set, and the CPS/ECU as a high tech distributor shaft cam/interrupter block telling the points when to do and undo their thing.


The 700/900 FAQs has some good information on the problems and pitfalls of replacing the part. For price reference, the part is about $40-$45, and I recently had a local indy shop install one for $50.

As the ICU (ignition control) is separate from the ECU (fuel control), can the CPS system be replaced with the older Hall sensor system?
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1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

Theoretically I suppose it's possible, since the CPS and Hall sensor do the same job. But I'm not smart enough to address the electronics, such as the effects of pulse length and magnitude differences between the two systems. To say nothing of the physical wiring changes.



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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Often Fuel ECUs are built to revert to default mode if a signal is not received. Eg. An LH2.4 Volvo will run without an O2 sensor.

Am wondering if the Fuel ECU needs that signal from the ICU or can operate without it.

If it it can work independently, then a different ignition system could be substituted.
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1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

"Am wondering if the Fuel ECU needs that signal from the ICU or can operate without it."

I doubt it, because that ICU signal serves 2 purposes:

1) Safety — if no signal from the Ignition, no Fuel pumping is allowed.

2) Timing — The ICU pulses are needed to time the fuel injector operation.

There are non-ICU ways to satisfy the Safety requirement (K-jet samples the negative side of the coil). But with pulsed injection, the ECU's timing pulses have to come from somewhere, and using the ICU's version seems most efficient.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

That's a good description of the ignition sequence Chuck, with one exception -- The CPS has no connection to the ECU (FI controller), instead it works with Ignition Control Unit (ICU), which in turn gets the ECU active.

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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Agreed that it is the ignition computer that takes the signal from the CPS.

Actually, the Mitchell charts I use refer to those parts as the "Ign System ECU", and the "Fuel Inj ECU." Which is accurate, because they are both electronic control units.

http://www.volvowiringdiagrams.com/volvo/240%20Wiring%20Diagrams/Volvo%20240%201989.pdf

Page 19.

OK, uneventfully done. It helps to have a wobble head to the 10 mm socket but I was able to reach enough fingers down there ('89 244) to guide things back into place. No stall on the first hot restart.

With our '89's we get a break, the later ears they put some AC plumbing over by the #4 exhaust manifold. Blocking the reach under and around that I did to get my Bolt started before taking to the extension from the Top.

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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/

Changing one today due to a recurring hot start stall. I see the wire insulation is frayed on mine and it was last changed in '04. So, away it goes and we'll see if the stall goes too. I anticipate a short job, I use a long extension and do not have rust problems so its not a big deal. I will fix the 10 mm bolt to the socket with a bit of tape when replacing it, so I do not drop the bolt. Cost is $50-60 and will take about as much time as the thermostat I am doing too.

If the CPS fails you have no spark or fuel. They do fail but before replacing it I would check to make sure all your ignition related grounds are clean; particularly the grounding post that grounds the RSR and ignition module. With a poor ground you may get enough spark to visually confirm you have spark but it will not be strong enough to ignite a mixture. I went through this whole process with my 740 exactly a year ago...

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Dale