indeed, 413 is the CPS... pin 11 is ground, pins 10 and 23 are low level voltage pulse outputs from the CPS, I think that stuff is all pretty short proof.

 

I have 4 Volvos 95-850 turbo, 90 740 turbo 93 940 and a 94 940 turbo I love the last three, hate front wheel drive cars.

 

"Jetronic" is the generic name for ALL Bosch EFI systems prior to "Motronic"... There's multiple varieties of Jetronic, including K-Jetronic (aka CIS), LH-Jetronic (EFI using a hot wire mass air flow sensor), etc. and even within a tyle like LH there's different versions of it, Volvo used LH-II, LH 2.2, and LH 2.4 in different years.

these are the schematics for a 1992 LH 2.4 system. your 1990 is also LH 2.4, and as I said above, should be very very close to this (changes would probably be limited to an occasional wire color difference).

 

 

That's a wealth of info there thank you. My 93 has distributer up front with crank trigger in back. another eng. idea.


which line is pulling to ground at cpu 10 or 13 ? witch one is low voltage sinking I would think. ?

 

correction pin 23 , so I am looking for 5 vdc at connector then correct

 

wont start even if I plus injectors manually. I am going to drop the exhaust on this one and see. I couldn't get it but to putter when hit with starter fluid. Must be multi problems. but still sensor is working tach, spark but no injectors.

 

if you're asking about the CPS connection to the ICU, pins 10 and 23 are 'differential'. the CPS is an inductive pickup, think magnetic coil, and when the notches on the flywheel passes under it, it generates a low level AC signal... this is probably fed into a differential amplifier inside the ICU that turns it into digital square wave pulses...

are you sure the fuel pumps run when you crank the car over? when you switch the ignition on, normally they run about 1 second and stop, then when you crank the car, they should run until about 1 second after the engine stops turning. I believe I'd check the fuel pump relay next. this is a dual relay, one half provides power to the ECU and stuff and is on with the ignition switch. the other half powers the fuel pumps (and O2 sensor heater circuit) and is only on when the engine is turning over.

 

Yes thanks for info. The fuel pumps run and work correctly, I installed a manual gauge system in the car 10 years ago to watch out for fuel pump problems so I am on top of that game.
So as I said has spark and tach operation but no injector operation as tested with nodes. Also temo wired trigger to low side and fired injectors manually.
Aw has spark should have tested with high voltage tester could not find my tester anywere to be sure and guess what?
Installed a new coil and bang car started. Now what the heck does the coil have to do with firing injectors?????
It seems secondary voltage was to low and yet high enough to fool you into you have spark and not let injectors work.
Please help me under stand how the coil keeps the injectors from firing, because I was chasing the WRONG logic here. I am missing something.


But yes car runs now Thanks for being here but I need to understand what I am missing here.

 

The rotor was in terrible shape when I changed it never seen a rotor so bad and still allowed car to run, I mean bad nothing left of plastic, I am sure that's what took out coil.

 

Yea I am guilty of not taking care of my car maint. while helping everybody else. I am always last.

I just don't understand how I got so side tracked on not getting injectors to fire. I pulled coil wire and pulled a good enough spark.
Oh well if you can help me understand that one it would be a great mental nourishment for sure.
I build 10,000 and 11,000 RPM race motors and here we are bach to the basics.


Thanks

 

have you tested it with a noid light plugged into an injector? if its as you say, and the fuel pumps start when you crank it, so we know the ECU's processor is working and the ECU is seeing timing pulses, and you have injector power, but there's no blink on a noid light, then I'd have to suspect your ECU's injector output pin has failed, and you might actually need a new ECU.

this is a non-turbo car, right? turbos use different injectors that require load resistors in series, this load resistor is on the left fender, near the RSR.

 

The engine runs now please read previous posts, Yes I used a node light for testing. And I installed a spare CPU that I know works and it still did not run. Not until I changed the coil did the car start. Car is turbo model. what does the coil have to do with injectors not working. ????????????????????????????????

 

So I still don't understand why a weak coil problem will not allow the injectors to fire ??????


Can anybody explain that one to me ?????


Never ran into that problem..


There was enough high voltage to arc a coil wire to ground and enough high voltage to fire a plug external of combustion chamber, but in the cylinder it would foul right away and never fire withing the combustion chamber.

 

I am still looking into find the answer to why a weak coil will not allow the injectors to fire. It seems that there would be 5 vdc involved with coil circuit and coil would be pulling 5 vdc supplied by ECU down to the point injectors would not have 5 vdc to play with. Anybody have any logic to this understanding the internal logic of the ECU ?????


Douglas

 

the 740/940 injectors are powered by 12V from the radio suppression relay, the ECU has 'open collector' output which selectively ground the injectors to fire them. note all 4 injectors are fired together, they fire twice per crank rotation, and 4 times per engine cycle, each time squirting in 1/4th of the total fuel required per intake cycle, the fuel air mixture collects in the intake runners until the intake valve opens and sucks it in.

 

Thanks Mr. Pierce


Ok that part is understood so how would the coil get involved with pulling down the 5vdc to that transistor ?and cause that circuit not to operate????? Thanks for burning your brain.

 

if the coil is fried, maybe its acting as a short, drawing too much current and causing the system voltage to drop.

where exactly are you measuring this 5V? under what conditions ?

 

first coil wasn't fried but it was strong enough to fire a gap 1/2 inch or so (coil wire to ground) and plugs out in to open grounded at .040 but to weak to fire a gap under compression with fuel added. This would not allow injectors to fire. The moin I put a good coil in the circuit car started right up. Go figure. The only thing that COULD be going on is the coil trigger from CPU using 5 vdc was getting overloaded and causing 5 vdc not to trigger injectors or pulling down transistor. PNP or NPN which ever it is.
so my question is how does the coils circuit tie into the cpu,s 5 vdc circuit. Has to be somehow. My rotor is what took out the coil as I was amazed it still worked so long.

 

I know for a Fact that injectors wernt firing as I used Nodes to check circuit and watched with meter and I manully fired them and car still wouldn't start. But at first I did the either spray routine and still wouldn't start so I went into diff direction checking all the wiring and relays and resistor bank for injectors, After pulling all my hair out I just did the old parts changer routine until I changed coil and bam started right up. changed back all the old parts backwards until I got to the coil and wouldn't start again. so tested 200%. I have another 740 as well running so it was the doner for test parts. Bad coil has typical res values Pri and sec. but I don't know exactly what them values should be from new.