Intermittent no start, doesn't quite fit LMS symptoms

conceptchris · Post by **conceptchris** » 14 Sep 2016, 08:14

Hey all, I have been working on Volvos for 15 years and this is the first stumper that I haven't been able to work out. You all are the best group I've found online and am happy to be a part of it, so here goes.
I have a '95 850 Turbo wagon that has close to 500K on the odometer. It is in great shape and I have slowly been fixing and replacing about everything on the car since I got it in a poorly maintained mechanical state. I am a good mechanic and usually very good at diagnosing issues, but this one has me stumped. Things that I have personally replaced in the past 4 years that may apply to the situation:
Cam position sensor
Crank Position Sensor
Coolant temp sensor
Cap/rotor/wires/plugs
PCV system/vacuum lines
Intercooler hoses
Rebuilt head
Fuel Pump
Fuel pressure regulator
Turbo control valve
MAF sensor

Here are my symptoms. The car runs great, no hesitations, plenty of power. It never stalls while running, which seems to be something that a lot of these posts regarding CPS or TPS have in common is stalling or poor performance while running. Mine doesn't. Always starts great when cold. 99.9% of the time the no-start occurs after driving for a few minutes, shutting off, then trying to start after another 5 minutes up to an hour later. The car turns over normally, no sign of compression or timing issues, but just sounds like there is no ignition signal and doesn't try to fire and catch. It is getting fuel because there is pressure at the rail that I can release, try cranking it again for a bit, and the pressure is back. I can take the main wire from the coil to the cap off and I seem to not be getting any spark signal. I can crank and crank and crank with no luck, then sometime in the midst of my cranking it all of a sudden fires up with no issues and runs perfectly. This doesn't sound like the old "lawn mower syndrome" to me. ALSO, no additional codes appear after this happens typically.
If this issue were a cam or crank sensor, I would expect it to be something that would continuously get worse like a sensor failure. This is a completely random case of getting juice or not it seems. I bought another ECU thinking maybe with all of those miles my brain box was getting worn out. I plugged in the different ECU after running with no issues and the car wouldn't start at all. Plug the old ECU back in and it would start fine. . . . . . until it decides to happen again. . .
The car laid down on me again yesterday and this time it would not restart no matter what. I had to trailer it home, tried starting again, crank crank crank with no sign of firing, and then all of a sudden it just came to life, ran great, no issues. Drove it up to my garage, seemed to be fine. Let it run for a while to recharge the battery, shut it off and tried to restart, nothing again, just turns over and doesn't try to fire. Annoying.
I have checked codes again both ways since it is a '95. The self diagnostic obd1 underhood unit gave me the 314 code for cam position sensor. The OBD2 reader told me there was a code for the throttle position sensor. Not sure why they don't match. The TPS clicks as it should when opening and the cam sensor is a little over a year old and still clean as can be. I will investigate the codes later today and clean the sensors and make sure things are doing what they should.
Thoughts anyone? I love this car and it runs so well, but this gremlin always rears it's ugly head at the worst possible times (usually the rare times that my wife rides with me in it) I can't wait to get this figured out an conquer the demon, please help!

Post by **tryingbe** » 14 Sep 2016, 09:47

Have you check the fuel injectors relay and its connector? It's the grey relay on top of the radiator fan.

conceptchris · Post by **conceptchris** » 14 Sep 2016, 09:59

No, I haven't done that yet, good idea thanks for mentioning it. Whats the best way to test that?

Post by **abscate** » 14 Sep 2016, 11:57

Once the no start occurs, starter fluid will help isolate the fault in either fuel (starts) or ignition/other (if it doesn't start)

Then you troubleshoot on the correct system instead of bouncing around.

conceptchris · Post by **conceptchris** » 14 Sep 2016, 12:43

I have tried starter fluid, initially it did nothing for the problem at all. There was some popping and cracking like detonation from compression with a lot of fluid, but there wasn't an actual ignition fire happening. Later on I tried again and it tried to fire, but I believe that between the constant cranking and low battery by this point, it was flooded when the spark returned. I will definitely look at the injector relay just to cover my bases, but as I said, I pulled the coil wire and got no spark when cranking.

Post by **Clemens** » 14 Sep 2016, 13:12

Are the cps and tps sensor oem?
Are the plugs Volvo?
Could it be a corroded connection that drops the voltage too low for the coil to engage? 500K is alot and wires just fail sometime. I had that happen to my 83 Opel the other day. Suddenly a connection to the starter was bad. Antiseize fixed the problem.

volvooh · Post by **volvooh** » 15 Sep 2016, 08:37

I am very curious what you find out about this. I am having the exact problem with my 1999 C70. I did some internet research and changed out the fuel pump relay...admittedly when I was having the no start issue I did not bother to get a psi reading and the fuel rail, but I have not been able to duplicate the problem since the last episode.

conceptchris · Post by **conceptchris** » 15 Sep 2016, 08:56

Ok, I haven't tried this yet, but there could be something here. This is a video link about a faulty fuel injection relay. This makes total sense to me and is giving the symptoms that I have. I know that my pump is working, but the injection side of it I am not sure. However, after cranking forever and ever I would expect my cylinders to be flooded and take a long time to clear out with lots of smoke and such. BUT, whenever the car does decide to start running, there is no smoke, no coughing, no signs of it having been flooded. This really leads me to believe that this relay could be the answer. I will post back later and let you all know what happens. In the meanwhile, here is the link I found showing this happening.

Post by **tryingbe** » 15 Sep 2016, 09:41

My connector was making poor connection. I wiggled the injector relay connector when it didn't start, then it started right away after that.

I replace the connector and now my starts every time.

Post by **polskamafia mjl** » 15 Sep 2016, 18:31

abscate wrote:Once the no start occurs, starter fluid will help isolate the fault in either fuel (starts) or ignition/other (if it doesn't start)

Then you troubleshoot on the correct system instead of bouncing around.

Starter fluid straight into the TB? (For future reference

)