Long story short cold it will stall and hard restart, but will eventually start. Driving cold stalls same hard restart.

Was able to get it to a no start situation and there was no spark at the plug wire and at the coil. Well actucally I tested at the end of the coil wire to the coil so that wire could be bad.....


I was attempting the test for a trigger signal to the ignition module to rule out distributor, but there was nothing or I'm not doing something right.

My question is what kind of a signal should come out of the distributor, and what type of a signal to the module 0-5v DC square wave?

2nd question the fuel injection uses the dizzy too, correct? no injector pulse would lean more towards a dizzy.

 

I'm inclined to suggest you check your CTS, the coolant temp sensor, which is wired to both the ECU and ICU... if its bad, and the controllers don't know things are cold, they won't give it enough gas OR retard the spark enough to run reasonably.

I'd go down these various things to find possible matches.
Engine Tune and Performance


re your distributor signals, I assume yo mean the hall sensor... the hall sensor is a very low current differential kind of thing, it won't be easily read by a meter or a scope. its processed by the ICU (ignition computer), and a cleaned up version is sent on to the ECU (fuel injection control unit).

 

Well, Last night it turned into a compelet no start. So, it's not the ECT.

I'm assume a scope would be able to pick up the signal from the hall sensor and signal from ICU to ignition module. I need a scope.

 

if you have spark, you've got a working hall sensor.

 

True, I've heard the easiest way to check your hall effect sensor is turn it on, crank and watch the tach. It should read a little engine movement if the sensor works. Volvos official test requires pulling apart the connector to the ignition control unit and tapping into the wires from the hall effect sensor. The you turn it on (disconnect the coil) and have someone turn the engine slowly while probing the output of the sensor. You should see the signal go from about 0 to 5v I think. But I never ended up doing that. I tried to power one on a bench and ended up burning one up. I wrote something about it in another thread here.

 

probably easiest would be to disconnect the ECU connector, and probe it to see if the ICU is passing on the 'conditioned' signal.

I don't have a 1988 740 wiring diagram, but that should be LH2.2, and so it should be the same as a 1988 240, terminal 1 on the ECU connector is the timing signal from the ICU, so if you hook up a test light between that and ground, and crank the engine, you shoudl see blinks...

or, you can clip a test light to the ignition coil pin 1, same thing, should see blinks there if the hall sensor is working when you crank the motor.

 

so this problem persists. It was a complete no start that wouldn't start for nothing the other night, now it's back to intermittent stalls cold.

I know it loses spark and there's no control at the coil. Trying to determine if there's output from the distributor ie bad hall sensor.

I wanted to see if the injectors fire, but there's 12v on both sides of the connector as if they stay on constantly ??? I don't have a wiring diagram of the fuel system. I know the injectors need the dizzy signal / crank sig to work. If there not working ether I'm moving away from the ignition module.

I do have a graphing meter I can see a 0-5 volt sig from the dizzy when it's running.

 

When you pull a s park plug is it wet? If you take that pulled plug and ground it and turn the motor over do you get spark.. If you have both of these then unplug and replug the crank sensor.Then I would check the cold temp sensor. We assume that both fuel pumps are working and you have at least a half tank of gas. Next would be replacing the Radio suppression relay . .

 

88's don't have a CPS (crank sensor), they have a hall sensor in the distributor.

 

This must have been a change in 89 then. Didn't know that. Thanks

 

89+ non-turbos and 90+ turbos switched to LH 2.4, which uses the crank position sensor.

an 88 could be either regina or bosch lh 2.2, they work differently.

the hall sensor in the distributor is wired to the ICU (Ignition Control Unit), and the ICU passes the timing on to the ECU (Fuel Injection Control Unit). The ECU has various signals that turn on the 'radio suppression relay' (which powers the injectors) and the 2 halves of the fuel pump relay (one half switches on the ECU and assorted other stuff and comes on with the key, the other half switches the fuel pumps and comes on when the engine is turning over per the hall sensor pulses).

the ICU provides pulses to the power module(bosch only) or direct to the coil (regina) such that pin 1 of the coil is grounded for each spark. pin 15 of the coil gets power when the ignition key is on. a regina system has a square coil that looks like a transformer, while a bosch system has a conventional 'beer can' coil.

the ECU provides 'ground' pulses to the injectors to turn them on, wider pulses for more fuel. all 4 injectors are fired together.

the major difference between bosch and regina, regina uses a 'manifold air pressure' (MAP) sensor while the bosch LH uses a 'mass air flow' (MAF, sometimes called AMM) sensor that measures the airflow directly

 

well when I tested the injectors I seen 12v on both sides of the connector upplugged. ? As if they stay on all the time.

Do you have a wiring diagram for fuel system???

 

i don't have a 88 740 diagram, just 91+ 7/9's (and all year 2's)

one side of each injector is wired to power via the radio suppression relay. the other side 'floats' high when the injector is off, and is grounded by the ECU to turn on the injector.

 

it's a hall effect sensor, but it's still considered the crank sensor.
sensors can be ac relucatance or generator, hall effect, optical, etc.

 

the Crank Position Sensor (CPS) is a specific thing on the LH2.4 cars, it reads notches machined into the flywheel or flexiplate, such that it reads the crankshaft angle, not just one pulse per turn, and its used as the source to all timing. the hall effect sensor in the distributor of the LH2.2 cars just reads one pulse per quarter turn of the cam shaft (half turn of the crankshaft). Volvo service literature never refers to this hall effect sensor as a 'crank sensor', its most frequently referred to as 'Hall pick-up'

 

The frequency of the signal from the distributor is not 1 pulse per revolution I can say that as I had a scope on the signal wire the other day.

 

from the distributor, its one pulse per quarter turn of the distributor shaft, which is a half turn of the crankshaft.

 

Well I finally got it to act up with the right tools and diagnostic strategy to figure out the problem. The crank sensor is bad.

I bought an entire distributor as replacing just the hall sensor sounds intimidating and I haven't done the job before, I need the car on the road. Plus there is signs of oil. Yeah I know you can replace all the seals, I've done that and have had them still leak.

Will report back after replacing.
Volvo are one of the most unreliable, money spent during ownership cars out there......

 

how many other high mileage 26 year old cars have you worked on ?

our 87 is going strong at 400k+ miles of hard driving, we bought it new.

 

Toyota's, Honda's, Mercedes, Sun Beam imp, BMW, Jag's, VW, GM, Ford, +

400k on the engine, Yeah, I've seen it with my own eyes. My turbo wagon has 160k and it sounds like crap, all turbo wagons do. But everything around the engine on these cars goes out;