Not starting - no spark coming out of coil, replaced with radio relay with one from my 240 for cooling fan -exact same number, also replaced coil with new one. What to try next? Thanks.

maybe the cap or rotor are worn??

Gary, at first reading I mistakenly thought you had replaced the coil/power pack. Now thinking otherwise, I suggest the following based upon my own 740 Rex experience.

Cleaning the up the Rex/Regina coil pack fixed a no-start problem I had. Whether it was due to dirty internal contacts or oxydation on the mating surfaces I really don't know. All I know is that I cleaned everything and then the car ran fine. I do have to say that the internal contacts had what appeared like some hardened crud on them kinda like 100 year old dielectric grease. Unplug the high tension lead and the other harness connection. The pack separates by removing a couple of fragile Torx screws that secure the coil in place. Once apart, you'll see the (three I believe) internal "springy" contacts. Scrape any accumulated crud off of the cantacts and the pins that mate to them. I've even bent the springy contacts a bit to assure good contact with the pins when re-assembled. Also clean up the mating surfaces of the two halves of the pack to assure good grounding. There is some argument as to the importance of cleaning up the pack-to-chassis interface, but I do it just to be a good boy, besides, you're there anyway. A light coating of dielectric grease on any mating surfaces isn't a bad idea.

I did replace the coil pack to no avail. But I will clean up mating surfaces and especially clean the pack to chassis interface. Thanks.

Hi,

Doesn’t the 700 series engines use a CPS, Crank Position Sensor?

It seems to me, from my experiences of how the 240’s, starting in 1989, use a CPS that has to put out a signal first to the ICU to get anything to turn on and operate.
Spark and fuel are almost simultaneously but it’s really the spark timing generation that the ECU needs before any relays close for reasons of safety!

The engine can turn for days but the electronics needs to know exactly when that happens!

Are you checking for the spark, right straight from the coil to ground?
This is so you eliminate the distribution system from the distributor out.
Doesn’t sound like you are flooding the engines cylinder either!

The Rex system is different but is it really that hard to troubleshoot without exchanging parts?
The CPS is not one of those items that are 100% without faults and there is not a way to test them easily. A change out is the best option and carry a spare, I do for my three 240’s.

Phil

I have used aluminum heat tape to wrap around the cps wire for a temp fix

91 with Rex .When I had a no start problem it was the crank position sensor and a faulty coil. I installed a new cps and still no start. I then installed a new coil and still no start. I reinstalled the disintegrating ( outer plastic? shield ) cps and walla , the car started. The new cps was faulty so I returned it for a refund. All this after I put in another good computer and put the old one back in , even swapped radio relays and and a new ignition module to boot. Basically throwing in parts blindly .And it is running great ever since. I plan on renewing the cps ...someday. So now I have a back up computer and an ICM

I will replace CPS, see if that works, thanks

Thanks everyone!
Replaced the Crank Position Sensor and started right up and
runs like a champ!!

Bonzo, bought a cps from amazon and it did not work. Where did you get your cps ? Last time I checked fcpeuro was out of stock

Ignition module heat sinking paste has dried out and module has fails due to overheating ??????? Then again your system might not have an Ignition module.

“.... Ignition module heat sinking paste has dried out and module has fails due to overheating ??????? Then again your system might not have an Ignition module....”

FYI - unlike the Bosch system, that uses a module pasted to the inner fender, the Rex system uses a combined coil/power stage unit. No paste involved. Rumor has it that some Jeep models from that era use the same coil/power stage.

Does the engine turn over??Do you have spark? If so try the Fuel injector relay / on the right fender,,

The engine turns over. I do not have spark.

clean all grounds everywhere..

Sorry for the ignorance...can you please specify location of grounds that need cleaned?

You'll need to research wire harness ground location for your 1991 740 with Bendix Rex ignition / Regina injection.

Wire harness info can help.

http://www.v8volvo.se/mekartips/volvo/index.html

Find the Mitchell Service diagram for 1991 740. See PDF page 23.

Have you checked for fault codes?
https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm

Also, the fuse and relay box behind the ashtray is a serviceable item as described on this page by forum member John Sargent.
https://www.brickboard.com/FAQ/700-900/ElectricalCircuitsRelays.htm

Check for melted plastic around high current relays and fuses. DeoxIT-D helps greatly.

At 30 years of age, your 1991 740 will require more frequent or vigilant care as my 1991 240 does.

The relay location info in 740 on Dave Barton's site may help.

Merely relays:
https://www.davebarton.com/pdf/700-900relaylocations.pdf

--
Beh.

Thanks for the info! I think I will replace CPS but will also look at fault codes and fuse block

The radio suppression relay provides power to the injectors and does nothing for the ignition. Read out the OBD fault codes and see if there are any codes pointing to an issue with the Crank Position Sensor. The 700/900 FAQ section on this set is your best friend right now.

Curious.... when you are cranking the starter does the tachometer needle jump or quiver with each revolution?