I have a 1988 740 wagon. . i always loved it, but lately It stopped loving me back ;(

all was fine until I started having issues with random dying.. so random troubleshooting was difficult. eventually I found it , The hall sensor in the distributor went bad.

then 6 months later it won't start. It has no spark at the coil.
I replaced the entire distributor with a cheap knock off from Ebay and pretty much exhausted my troubleshooting skills with it.. maybe I can check if there is a pulse from the ignition control module to the diode near the driver side headlight, maybe that would narrow it down to weather I am getting the low voltage pulse telling it to spark. I tried a different transistor, no change.

I did what any other normal thinking volvo nut would do and bought a $300.00 1990 740 sedan. that was parked 10 years but still runs. that one has a busted windshield , nice mags with rotten 14" tires, and it spurts oil out the dipstick so |I think the flame trap is plugged up. the headliner is falling down.. rotors need turning as they probably have some rusty spots and are pulsating. it's higher milage than the others, but it runs just to bug me.. i cleaned the engine and thought I might tackle the flame trap and make it a runner at least.

unfortunately this "new" 1990 740 spare parts car also has the newer style ignition with a crankshaft position sensor and not the hall sensor. i think that makes the ignition module different. Is it possible to use the same one? would the central computer be different too? I can;t imagine trying to rewire it to update it to 1990 style wiring , If I could I would have the parts but it seems overwhelming. Has anyone ever tried to change from hall sensor to crankshaft sensor?

I can tow it to my mechanic and he has test boards but I think that will be more expensive than I can afford..he'll want thousand bucks before he lets me go for sure.. I'm tempted to try a new ignition control module.. the wreckers near me seem to have very few 240/740 anymore.

Can I troubleshoot the issue further? i got ahold of the volvo factory ignition troubleshooting guide but when it started talking about the connector for the ignition control module the pinouts seemed different.

somewhere on the internet I did find info on what ignition modules and what computers go to what years,, I left off meaning to check that out a bit further to at least know what years I can steal an ICU from.

the 88 does not have diagnostics, there are some procedures to use an LED but that's for an already running car.

im ashamed to admit it but at one point in dealing with it I went to charge the battery and hooked the charger up bass ackwards and plugged it in. I immediately unhooked it and hope that didn't' fry the central computer as well or something.. it wouldn't start , no spark before that so I can't tell if I made things worse.

I do have an oscilloscope , is there a way I can follow the signal from the hall sensor and to and from the ICU to see if it seems to function or not before I spend on a new one? i'm sure the hall sensor is ok now seeing I put in a new knockoff distributor.

i sold my brother my older 1990 240 wagon. his fix was to throw all that junk off and put carbs and an old school distributor and did away with all the complicated computer stuff.. it's a little less powerful but his car still starts ;-)

I have a 122s as well at one point I git sick of playing with the points and stuck a distributor and ignition box from a 1974 240 in it and that has run since for 20 years without ever touching the timing so that wasn't' a bad mod for me. i think I turned the vacuum retard into a vacuum advance to get a bit more movement out of it and after I did that it seemed to lug ok and go up the the redline without any pinking or anything. I love that car.

I'd really like to get the 1988 740 wagon running but I don't know if the ICU is the only issue or if I am putting good money after bad.. It is good mechanically I have kept it all up with maintenance and it was my daily driver.. now Ihave three volvos I cant; drive and I can't drive my 122 to work unless i drop the collector status.. so I have an 88 ford van and it works but I seem to be lining up all these sick volvos.. mostly it's these electrical issues. the mechanical stuff I can usually tackle.

i made a separate post about my 1990 volvo 240. I rebuilt the engine 20 years ago in that one and parked it about 7 years now I have it working nicely.. its rough and a bit rusty but it runs so beautifully,, I threw a lot into the rebuild, new pistons, overbore, new cam , oil pump and the lot so if I can just sort out the flickering lights issue I'll drive it till they pry it out of my hands ;-)

the van is an econoline, also 88 last year for low back bucket seats. I put seats from a delica in it. the low backs are cute but so hard on my back, straight 6 cyl, 300 cu it's nice it purrs after 5 minutes once the fan belt stops squealing;-) , only 100K since it was a wheelchair van and didn't get used. It has some early form of fuel injection,, anyway you guys don't want to hear about fords ,, lol ;-)

 

yeah, the 1990 is LH 2.4, and fairly different than the LH2.2 88. As you said, CPS instead of hall sensor, new/different ECU, new/different ICU. different distributor, etc. I think the fuel pressure regulator is different, as are the injectors. The ignition power module could well be the same. I dunno what this 'diode' is near the headlight, I don't remember anything like that in the circuit, but I only have the wiring diagrams for 1991+ 740/940, not the earlier ones. I do have all the 240 wiring diagrams.

 

sorry I refered to diode incorrenctly meant to say transisitor,, or ignition power module is the corect term I guess.

so in laymen's terms .. basically I think the hall sensor is used instead of points. so it is putting out 4 pulses per rotation, then that goes to the ignition module, and the ignition module is communicating with the central computer.. they together are monitoring engine speed, input from CO sensor mass meter etc and electronically adjusting the timing, rather than the former system of weights in the distributor..

the pulse signal from the ignition control unit sends the pulse to the ignition power module which amplifies it to a pulse of current which in turn causes the primary coil in the distributor to rise and collapse and as it collapses the spark (or power spike) is created in the secondary coil and to the distributor to be sent to the appropriate spark plug..

so If I could test for a pulse between the hall sensor and the ignition module or between the ignition module and the ignition power module , the thing I called a diode,, then maybe i could narrow my search for the cause?

if the hall sensor lost it's power or ground it could cause the issue I guess.. It only has three wires , they must be power. ground and pulse signal but maybe they are actually like 3 volts 5 volts and power signal or something like that. I can follow the schematic somewhat but I quickly seem to get mesmerized by it and confused by changes and updates to the system used. this car has no code reader, that came the next year unfortunately because it might help if it was there.

the other way to approach it might be to bite the bullet and order a new ignition module and hope the central computer isn't cooked,, but obviously this is an expensive way to troubleshoot . I have a spare main computer and ignition module from a 1990 240 but I guess they aren't compatible.

Ive also got a 1989 740 ignition module part number 0 261 201 012 it also has numbers 1346 469 and a blue label
and the central computer from an 89 740 part number 0 280 000 541 Jetronic 1 367 487 they both have another number 810 on them..

but my car is an /88

 

there are two 'computers', the ICU for ignition(spark) and the ECU for fuel injection.

the hall sensor goes to the ICU, which calculates the optimal time for the spark and pulses the ignition power module which fires the coil which makes the spark. the ICU also sends a 'copy' of the hall sensor timing to the ECU which uses it to calculate when and how much fuel to inject.

the 1988 740 Bosch should have ignition power module Volvo pn 3501921, Bosch 0.227.100.124. Per a couple Volvo specific parts webstores, this power module is the same as the one used on later LH2.4 cars, The ICU/ECU most certainly are NOT the same.

but, I really don't see any mechanisms where the ignition system would make the headlights flicker like you describe, at a constant speed regardless of RPM.

 

no the headlight flickering issue is in my 1990 240 this problem is a no start issue in my 740. I appreciate the Help Pierce. \I did swap the power module with an unknown one I got at a wrecker and no change so I am assuming its an issue with the ICU or ECU.. since this car is dead< I'm tryign to get the 240 going which is why I had two posts going. the 240 is still running ok but it has an engine light on flickering headlights and now dead signal lights.. but I made separate posts for those issues.

I guess unless I can troubleshoot more.replacing the ICU is the next logical step for this 740. Ive got an 89 740 that runs that I can steal from but other than relays and stuff I guess no parts from it will help solve this issue. same with the 1990 240. i seem to be going in circles with volvo electrical issues lately and a little low on cash so just trying to do what I can to get to work. ;-)

 

the ECU and ICU are under the dash inside the car. the ECU is near the lower hinge of the passenger front door, and the ICU is on the firewall, either behind the glovebox, or on the firewall depending on version and stuff.

so... you have no spark? is the wiring in good shape to the hall sensor in the distributor ? that provides all the timing... its wired to the ICU, which then sends a signal to the ECU.

before replacing the ICU, you've tested and confirmed there's no spark? hook a test light to the coil pin 1, and it should blink when you crank the motor.

wait, did you say something about the distributor rotor having been completely trashed ? what condition was the insulator disk thats under the rotor? what condition was the hall sensor plate thats under said insulator disk ?

 

No spark is highly likely this part: Bosch 0.227.100.124 same as my 1993 240 that I spent a month to find. Bosch said reason for failure is the computer heat sink grease (that I used on other used "final stage") dries out. It probably also failed due to bad plug wire and bad rotor.
Let us know what you find