By what sensor does the fuel pump run for a sec & stop when key is turned on before engine is turned over? I believe this is to pressurize the system before the pump runs constantly once the engine is running.

I first replaced the pump relay, then the pump & accumulator but still have this intermittent no start situation which must be a sensor or, heaven forbid, a wiring issue? TD

 

How intermittent is it? Does turning the key off and then try again cause the engine to start or do you have to wait a day?

 

The fuel pump does not run if there is no spark (or signal from the engine speed sensor) Pump runs for a sec then turns off if engine is not spinning.

Your no start - I trust that means it spins over and won't catch?

You will need to determine if it's not getting spark or fuel when this occurs. Test light on the flashing side of the coil is an easy check, fuel pressure gauge another easy check.

If this is a turbo car there is a noise suppression relay that like the fuel pump relay develops cracks in solder joints. Also that relay is mounted under the hood and the "bullet" connectors are prone (at this age) to have bad connections.

Google volvo noise suppression relay - it's rectangular and black with 4 connections on your car (some cars have 2 on those under the hood, the second is for the electric cooling fan.)

Turbo cars have ballast resisters for the injectors that can have bad connections and the ign amp could have a bad connection also causing starting problems. (also check the small positive wires at the + battery terminal - there's a Volvo 740 or 940 (can't remember which one) that if those become loose will cause problems

This guy has all sort of replacement electrical connector to be able to fix those old wires.

https://www.prancingmoose.com/

 

Very unpredictable. Sometimes it will restart, other time it seems to take a long time to "recover"(??)

 

Thanks Hoonk for all the ideas. No start means it turns over normally but not starting. Checked spark first thing when it first happen and there is plenty. By speed sensor are you referring to crank position sensor? This is a turbo engine I put in a few years ago when some clown ran the car out of oil and blew a 3" hole in the block.. I can't remember if the old engine was a turbo or not but since I haven't been able to find that 2nd relay on the hood I suspect not? To complicate maters, the '91 SE was a one year only as it was made as a 960 but apparently the 6cy engines were ready in time??

As a test, I've put a switched hot wire in parallel to the pump power wire to switch it on manually next time the situation occurs. TD

 

Latest is that when hot wire is switched on, engine starts/runs fine, when switched off, engine soon stalls i.e. runs out of gas. So it's definitely in the voltage supply sequence of sensors in that circuit. I think I have a spare crank position sensor so I'll start with that. TD

 

If the crank sensor was bad - you would not have a spark. It is the only sensor that provides timing/engine position info to the ignition and fuel computers. The crank sensor is tested with an ohmmeter. And if the insulation is in poor condition, replace it anyway. (forgot what ok is, compare the 2 to see if they are the same)

There is a Fuel injection control unit that is known to fail by not turning the fuel pump on. (don't remember the years it was used, but I use to stock one for I sold so many of them) Have replaced many - but they are not erratic.

Do you have any codes stored? and have checked the basics (plugs, cap, rotor, wires, etc?)

https://www.volvoclub.org.uk/faq/EngineOBDCodes.html

 

Yes, I did check all the basics, plugs, cap, rotor, etc and all are within a couple years old, including Crank Position Sensor, Fuel Pressure Regulator, and a couple other sensors.

I have no fault codes, but, I did just find two identical relays that were hanging down near the back of the alternator, part of the 91 SE car wiring harness that obviously wasn't attached to the '93 Turbo engine that I installed from our rolled 93 wagon four years ago. One of these relays must be the "infamous" Radio Suppression Relay (#899931) that is also tied into the FI system? How do I determine which one? I gather one is related to the cooling fan sensor? I'll pick-up one of those and see if that solves the lacking voltage supply to the Fuel Pump. One more verse to the Old Volvo Song, ...Just getting newer part by part! TD
https://www.shazam.com/track/91072629/an-old-volvo

 

I had a similar problem in my 89 740 GL. Did some hard wiring to the fuel pump to resolve but ended up finding the problem . It was the ECM that was intermittent . I bought one on e-bay for $30 and problem solved. That was about 75K miles ago. I just turned 416,000 and blew the waterpump. Just waiting for parts now.

 

2/12 is where the noise suppression relay (in a 1994 don't have a diagram for a 1991) near the booster. That relay powers the coil, not the injectors. So if you have spark - it's not the noise suppression relay (as long as a 1991/1993 is he same as a 1994) If you think the injectors are not firing when it won't start use a noid light to verify that. If you have no codes - it's probably not a component that's erratic. It's going to be a connection or power problem.

 

Do you mean ICM (Injection control Module) instead of ECM?

 

Engine control or Injection control?

In 1993 Volvo calls the computer for the fuel injection " control module LH jetronic"

and calls the computer for the ignition system "Control module Ez K"

 

Well, as the Brits would say, "I've jury-rigged the ole' Swedish Brick!" But I've done it in a very proper way. I've got a switch and a 25 amp fuse in the hot wire from a spare bus in the fuse panel that is switched by the ignition. If car stalls or the ignition is on without the engine running the pump will be switched off. With this in place the car runs perfectly.

So now it's on to a methodical tracing of the voltage path upstream starting at the fuel pump. Hoonk I believe you've provided me with adequate wiring diagrams. Thanks for that and I'm open to any sleuthing tips in this adventure. TD

 

Hoonk,
Looking at the wiring diagram you posted (LH-Jetronic 2.4), the first thing I see working upstream in the voltage supply to the fuel pump, is a "Bulkhead Connector" and the Lambda (O2 sensor?) is also connected to that same "Bulkhead Connector". Where is that connector and could a bad O2 sensor cut off the voltage to the fuel pump? TD

 

No.... If you think it is - unplug it and drive the car. You may not notice the difference. And this bulkhead connector? where it is on the diagram.