1990 740 4 cyl single cam Wont start
 

was running ok wife barley made it home. haven't serviced it in a while my bad to many projects. cap was bad rotor was almost gone plugs changed but still wont start. fuel is there 40 psi spark is there timing belt ok but I did get it to run for awhile and then like someone turn the key off it die, and never restarted. today I was checking the injector electrical and could not get a light pulse with my test light voltage is there . Does the fuel pump relay have anything to do with injector firing or just fuel pump.???


this is flywheel sensor not hall effect dist. I would assume if I have spark sensor is ok doesn't that sensor also fire injectors at CPU ???


I have to double check spark when I cant see injectors firing. ok so theres a relay for injectors I pulled both one on each side Pass and drivers side looks ok pulled them apart, but I will clean contacts and reinstall. I did the resolder job on fuel pump relay afew years ago it still looks good but in that relay cube inside includes two contacts is one possible for injectors ????????
Any thoughts from you guys here, would app. it.
Thanks Douglas

any place here I can get electrical schematic on this car??
?

Oh buy the way I did check the resistor bank connector for the injectors, connector look good.

If you have spark but no pulse to the injectors, I would suspect the radio suppression relay. Search the forum here for location of such relay (I have only 240s which do not have the RSR).

relay is good as I do get 12vdc at injectors but when removing connector at injector and using a test light to signal wire I get nothing, shouldn't I see something ???????? or does it need the node light for a load???

I am using a test light to battery and to switching it to battery ground

Two good resources:

volvotips.com

volvowiringdiagrams.com

you should be see what drives the injectors - ie fuel pump relay, injector relay, ECU etc in Volvotips as well as what drives the spark - ie hall sensor, ignition control module, cap/rotor/wires/coil/plugs.

Does your fuel rail have a shrader valve to test pressure? (sorry no hands on with the 740s here)? What is your voltage at the battery? does it measure at 12.6 or less? have you tried some starting fluid to see if it gets some fire?

battery full charged 13.8 vdc, fuel pressure 40 psi always had manual gauge installed ,no hall effect flywheel sensor, tries with either. new cap rotor plugs, wires good spark ok. not sure on injector firing. supp. relay suppling 12vdc injector resistor bank ok, cam timing ok. going to store and buying nodes for better test

ok for me this is not a typical problem, something is screwy. have spark, tried my second CPU still same problem. probe light to batt - white wire or green wire both 12vdc, also measured with fluke same battery voltage. disconnect anything in circuit surpresser relay resistor bank turn off key battery voltage disappears, however white wire slowly drains away like a discharging capacitor mins. before zero. I bought some node testers plug them in cranking nothing. I can see why, any ideas on what wiring or component items would cause this. Ichecked for any wiring problems rats eating or varmints looks good checked connectors under hood looks good. Any ideas out there??????????????????????????

Pin 18 of cpu willnot pull down ground, ok grey is so light looks like white. Been looking at schematic in surpressor thread. I know my second cpu works as I used it before putting in trunk or compartment same results. I also noticed that if I unplug all the injectors 12dc + goes away at grey wire. plug any one of them in and there is problem again. Any thoughts ????????????????????

so is 2.4 ohms ok for injectors plus what 6 ohms from res bank is that correct?????????

anybody no ideas??

thanks for the tips though
 

Thanks for the info. anybody else alive around here????

Have some patience - there isn't a whole lot of activity on this board anymore as these cars are getting kind of old. Myself, I only can manage to get on once a day. You might want to try brickboard as there is more activity over there.

Having 12v at the injector would seem to confirm the functioning of the RSR - but I'm not sure since none of my 240s have one and I haven't looked at a wiring diagram for the 740. My understanding of the LH2.4 fuel injection (assuming that is what you got, it could be Regina system as well) is that when the key is turned to the II position, you should have 12v at the injector. As you crank, the ECU will send a ground pulse the injectors to complete the circuit and fire them. From your earlier post I assume you have checked this and found no pulse. Is this correct?

No pulse could be due to a failing crank position sensor. However, if that was the case I wouldn't expect no spark either as it runs of the CPS. Have you checked the CPS? If the wiring to it is cracked and flaking off then it needs replacement.

I was thinking about that prox switch last night maybe enough to fire IGN. model
but but not enough for CPU operation. Yea the wires are all frayed and falling apart. So its normal for the sinking output to be high until it fires would answer why both sides are high. I did try brick a lot of basic stuff nice site as well. And TIP.com.


Ok understand on lack of manpower and visits. The internet comsumes your life like my race car and tasks for everybody else.

I don't have the schematics specifically for a 1990 but it should be almost identical to a 1992 LH 2.4 fuel injection ECU, looks like...

https://photos.smugmug.com/Misc/Volv...vVcNcFC-X2.png

and EZ116k ignition ICU
https://photos.smugmug.com/Misc/Volv...m88jPBW-X2.png

unless its a Regina system, then both ECU and ICU are completely different.

all 4 injectors are wired in parallel, one side gets power from the RSR so will always be 12V when the car is on, the other side is selectively grounded by the ECU to fire the injectors... so if you unplug the injector, and try to measure the voltage, you won't see nayhting on this other pin.

all timing comes from the CPS, Crank Position Sensor. This is wired to the ICU, which in turn feeds a timing signal to the ECU. It provides timing for both spark and fuel injection.

tach jumps around when cranking, unplug crank sensor tach doesn't move when cranking. spark is there but no injecting firing. 12 vdc all over the place on feed side just no injector operation. Jetronics system.

with the crank sensor unplugged, there would be no spark, no injection

I am assuming that 413 is crank sensor connector E plug in snap connector ???? Is CPU pins 10,11,23 protected from short circuit if wiring is bad? If not then I blew out two cpu,s because of shorted pins to shield or ground. Why would tach and spark still work and not injectors? Will be interesting to find this problem. As these cars get older new problems always crop up not found in younger cars. Always that problem with all machines as they get older. Age vibration and rott always causes all kinds of new problems.

So is this the 1990 jetronics schematics ?????