'93 940 Starts, then dies...

[BEJinFbk]

I'm a little out of my element here, but trying to help out a friend.
This '93 940 sedan began running rough and now will not continue running.
It starts, idles briefly, then dies. The owner states that he sees approx 40
psi on the fuel rail valve and is getting a strong spark on all 4 cylinders.

It also appears that the IAC is functioning. He checked it with the OBD test
mode and tells me that it passes and blocks air flow when he's testing.

My first though was to get a meter on the fuel pump leads and confirm power.
Any access issues? MVS posts tell me that it's accessible via the trunk. Any pointers?

He also tells me that he hears it in position 2, but I suspect that it may be on it's way
out and dropping shortly after energizing. So - No gas, no run. I'm assuming that fuel
pressure should remain at around 40 whenever the key is on? Please advise.

It's been a while since I had my 240, so I'm a little rusty with the 230F...
Too much V70 I5 stuff in my head these days, I guess.
Any input or advice would be greatly appreciated.

Thanks!

[jimmy57]

A more thorough fuel pump check would be my first test. Disconnect the fuel line that goes to the fuel rail, 14mm on rail 17mm on the fuel line. Put the fuel line into a container and turn on ignition for 2 seconds three times in succession. You may find the fuel dribbles out. A very slow running defective fuel pump can build fuel pressure with little volume and not deliver enough for it to run but for a couple of seconds. A second way (maybe should be the better way...) to do this would be to take rubber clamped line off the fuel press regulator and do the same ignition on/off thing to get the pump to run 2-3 short cycles and see if any fuel comes out of FPR. A good pump will oversupply and there will be return line fuel flow.
I'm assuming non turbo with Regina/Rex fuel/ignition. RR has in-tank single pump.
A Bosch fuel system of that year would have under car main pump and an in tank pre-pump. The main pump being off for some reason can also behave like this as the prepump is capable of giving a little bit of fuel but will not run engine.

[Jonsmachine]

I am the friend with the 940 Volvo. Thanks for the help.

I put a line on the output of the pressure regulator and got about a cup of fuel with three activations of the key. I put a pressure gauge in the same place and get 60# plus. A pressure gauge on the fuel rail gives me 44 psi when cranking. It maintains pressure for a half hour or more. So, it would seem that my fuel pump and pressure regulator are functioning properly.

I connected the diagnostic lead to terminal 2 and got codes 223, 132 and 221 all of which should have been set when I was testing fuel pressure, the idle air control and had a battery charger on the battery. I cleared the codes and now get just 111 on both the fuel and ignition sides of the diagnostics.

On terminal 2 in the third mode I can hear the injectors and then the Idle air valve operate. I measured the resistance on the injectors and all have 14.1 ohms. In the second mode I got 333 after full throttle as should be and 332 after partial throttle. The motor does not start so I could not check the rpm signal from ignition to fuel system.

I do get good spark and the plugs look OK. If I let it sit overnight it will start for 10 or 15 seconds, rev normally and then just fall on its face as if running out of fuel. After testing and cranking the motor numerous times I would have thought that the plugs should be wet, but they are dry. It does not even try to fire now.

Is there some function or sensor to the ECU that will turn off the injectors if it gives a bad signal?
I am assuming that the timing is good as the motor seems to rev nicely and sounds good for the first ten seconds when it starts then misses a few times and dies. The air cleaner is new and I pulled it to make sure it was not the problem.
My wife is picking up intake manifold sensor cleaning spray and I will clean the air temp and flow sensors.
Any other hints or directions to head?
Thanks,
Jon

[Jonsmachine]

One more update on the problem. When I test the injectors and the Idle air valve with the diagnostics, and then try to start the car it fires for a couple of seconds and then dies. I believe that it is getting fuel in the testing stage, but not when normally trying to start the car. It will only fire after testing the injectors.
Jon

[BEJinFbk]

First off - This is a Regina system, not the Bosch.
I neglected to mention that in the first post. Sorry.

Jon and I monkeyed around a bit more with this today and learned a few things.
If the injectors were energizing before with the DTC box, they aren't now.
The 12 volts is there on the green wire, but the gray lead shows a very minor
pulsing deflection while cranking, on an analog meter set at 10x ohms ref'd to ground.
I may drag the scope out for this one for a better look. What impedence should be seen?

But the IAC still responds to the breaker check cycle with no problems.
When the DTC exercise cycle gets to the injectors, the 2/13 relay in the dash
operates, but the ECU's ground signal apparently isn't getting to the injectors.

Codes = 1-1-1, so that's no help.

Just to confirm that fuel could get to spark, we unplugged the #1 injector and
manually pulsed power and ground to it for a second or two to inject some gas.
This produced brief, limited chuffing when we tried to start it right afterwards.

So - We have spark, we have fuel pressure, and pulsing an injector and dumping
a little gas into #1 made it bark, but then it just cranks in a fuel free manner.
The injectors just don't seem to be getting ground pulses from pin 18 of the ECU.

The next step seems to be checking the harness/injector resistance from ECU
connector pins 9 and 18. Pulled the ECU to find no pin # markings on the plug. WTH?
I did find the pinouts for the REX box, though, and it looks like the same basic connector.
The day came to an end, so that next step with the ohm meter will happen later.

But confidence in finding a problem there is not high - I just can't help the feeling
that we're missing something frighteningly basic, like a bad relay or a dead sensor.

Any additional advice may help prevent me from doing something terrible to this
nice Volvo with some of the monster machine tools in Jon's shop...Could be fun!
If it comes to that, I'll be sure to post pics.

[Volvo1man]

I have a 1994 940 and may be able to help. I'm not an expert, but have you checked the rpm speed sensor on the back of the engine? I had a strange starting/idling/no run situation a few months back and it turned out the rpm speed sensor wires had cracked/missing insulation on the bottom 4 inches and was shorting out.

Maybe check that? It is easy to do. Just run your hand down the wire harness at the back of the engine wiring and feel for cracked insulation or exposed wires. It might be worth a quick check to mark it off the list of possibilities.

Take care.

[BEJinFbk]

I looked for a sensor back by the distributor and found nothing.
Either the '93 Regina is different, I missed it, or I need better light back there.

[billofdurham]

Sorry to say this, you need better light or someone else's eyes. On second thought am I really sorry?

The speed sensor sits in a bracket on top of the bell housing with the wire running up the back of the engine block. Usually, it is found by touch rather than sight.

Bill.

[Jonsmachine]

I have found it! The intermittent fault that has been driving us crazy. Turns out that the radio interference suppression relay had been corroded at one of the input wires and had melted the insides of the relay due to high resistance. This left the relay with 35 ohms resistance across the output terminals even when it was not actuated and was probably intermittently actuating when it should. We would still get 12 v at the injectors, just not enough current to always do the job. I threw a nice sealed icecube relay in it's place and we seem to be good to go. The good news is that I have learned a lot about my daughter's Volvo, did not spend any unnecessary money on parts I did not need, and it should be easier next time I have to go trouble shooting.
Thank you very much for the ideas and suggestions on the forum and many thanks to my friend Brian who sent me this way.
Jon

[BEJinFbk]

In the immortal words of Homer Simpson, "WooHoo!"