850 Starts but Dies/will not start when up to Operating Temp

Csmiles · Post by **Csmiles** » 23 Nov 2006, 11:25

I have a 94 Volvo 850 with about 98K miles on it. My problem is that it starts fine when it is cold and idles very smooth, then (at idle in my driveway) as the engine temp comes up to normal (about midrange on the temp gauge) it starts to run a bit rough and if you give it any gas it stutters, gulps and stalls out. When you try to restart it the engine turns over but will not fire/start. At this point it acts as if it is out of gas. If you let it set/cool down for about an hour (when the coolant temp reads 1/4 scale or less) it starts up fine again. While it was in the no-start condition I have: checked codes-no fuel codes present, one time the "RPM sensor intermittent" code came up-cleared it, it did not come up the next times. Checked for spark to plugs (timing light in series with plug and plug wire)- good spark. Plugs had some black carbon but were not wet with fuel. Checked fuel rail pressure with fuel pressure gauge- shows 48psig. Replaced fuel relay in fuse box compartment with a spare/used one from a used volvo-this made no difference. Finally I replaced the cam shaft position sensor. Still the same problem. Tested coolant temp sensor with ohm meter, reads about 400 ohms when at operating temperature, ohms steadily increase as engine cools, to about 6,800 ohms when ambient temp is about 40 deg F. Checked RPM sensor, ohms are within spec when cool or hot. Can the RPM sensor or Coolant Temp Sensor be causing this problem and still read properly on an Ohm meter???
Thanks,
Thom.

Post by **MadeInJapan** » 23 Nov 2006, 11:43

I'd say your issues lie somewhere else. I'm stumped on this one myself. I'm hoping that others will give their opinions. Hopefully someone else has had the same issue and can give you his/her repair option. You have changed out your fuel filter right? Plugs are slightly fouled, but wires and rotors are okay? Still, you might change your pugs or at least take them out and clean them. Obviously the Air/Gas mixture is different after the car warms...plugs work with richer fuel for instance but not leaner after the engine has warmed...might also check the plug gaps (0.028 inches or slightly less if you have your car's ECU modified to boost more). I know you covered most of this but just double checking. Other issue that comes to mind is the MAF but that would set a code and you're not getting any. Otherwise a vacuum selenoid (near the top of your fan shroud on the driver's side) but that would also set a code. Hmmmm....someone help!

Sweet Wagon · Post by **Sweet Wagon** » 23 Nov 2006, 12:30

This is going to be quick, since I am just as stumped...

Have you checked your vacuum lines ? At that mileage, that would be an obvious issue. How old is the fuel in the car ? Don't laugh, but my lawnmower would do the same thing with bad fuel in the tank.

And finally, are your plug wires recent ? An issue with a plug wire may not be visible, for $40, you might fix your problem, or throw a little money towards a valuable cause...

I hope this helps, this one's gonna have me thinking for a while...

Post by **Ozark Lee** » 23 Nov 2006, 13:03

Checked RPM sensor, ohms are within spec when cool or hot. Can the RPM sensor or Coolant Temp Sensor be causing this problem and still read properly on an Ohm meter???

In a couple of words, Yes and No.

The RPM sensor / crankshaft position sensor cannot reliably be tested, other than completely shorted or open, with an ohm meter. It is a hall effect device that produces a dc pulse as the magnet passes by it. A proper, albeit difficult, test is to monitor the waveform coming off of the sensor. Both the crankshaft and camshaft position sensors can get "weak" in that they continue to send a pulse but the pulse is not large enough for the ECM to reliably read.

As far as your coolant temp sensor goes the ohm meter test is a good test and, based on your readings, it is OK.

...Lee

Csmiles · Post by **Csmiles** » 23 Nov 2006, 13:09

Thanks to MIJ and Sweet Wagon for the quick reply and suggestions. The fuel suggestion is interesting- the car had been sitting for several months before this problem showed up. One of the first things I did when this problem started was I put a fuel treatment/dry gas into the tank and added fresh gas, but I still only have about a quarter of a tank full, maybe I should try filling with fresh gas to "freshen" the tank mixture. I have visually tried to listen and look for any vacuum leaks, so far all hoses have looked good and no surprises there. I will also try new plugs and a fuel filter, can't hurt. Up until now I was assuming that if the plugs were bad or a fuel filter was plugged I would have cold starting problems or accelleration problems all the time. What baffles me is that on start up (from cold) it runs so fine -accellerates and shifts fine (automatic), for the first 10 to 15 minutes -untill it reaches operating temp. I'll try plugs, filter and fresh gas tomorrow and let you know.
Thanks,
Thom.

Csmiles · Post by **Csmiles** » 23 Nov 2006, 13:14

Thanks for the input Lee, seeing as I did get the RPM code one time I'll order the RPM sensor and try that. Appreciate the responses on a holiday.
Thom.

tca217 · Post by **tca217** » 24 Nov 2006, 02:36

Csmiles wrote:Thanks to MIJ and Sweet Wagon for the quick reply and suggestions. The fuel suggestion is interesting- the car had been sitting for several months before this problem showed up. One of the first things I did when this problem started was I put a fuel treatment/dry gas into the tank and added fresh gas, but I still only have about a quarter of a tank full, maybe I should try filling with fresh gas to "freshen" the tank mixture. I have visually tried to listen and look for any vacuum leaks, so far all hoses have looked good and no surprises there. I will also try new plugs and a fuel filter, can't hurt. Up until now I was assuming that if the plugs were bad or a fuel filter was plugged I would have cold starting problems or accelleration problems all the time. What baffles me is that on start up (from cold) it runs so fine -accellerates and shifts fine (automatic), for the first 10 to 15 minutes -untill it reaches operating temp. I'll try plugs, filter and fresh gas tomorrow and let you know.
Thanks,
Thom.

You can't really find a vacumn leak by looking or listening for it most of the time. Get yourself a can of spray starting fluid and start you engine and give it a couple of blasts around the vacumn tree, and all the other vacumn lines. There will be a noticable RPM change if there is a leak. Tim

Csmiles · Post by **Csmiles** » 24 Nov 2006, 19:24

SUCCESS!!! Wanted to post this to close the loop and report success. Yesterday I rechecked the codes after it failed again and the "RPM sensor intermittent failure" code was saved. I cleared it and today I bought a new RPM sensor and also a new set of plugs. Installed the new sensor and.......same problem, didn't make a bit of difference! Really getting depressed but figured since I had the new plugs I might as well put them in. Installed the plugs and......starts up and runs great! No stalling, restarts perfect when hot, etc. I was pleased but down right embarassed that the solution was so simple. Still, in my defense I have to say that my past experience has never been to have plugs work perfectly when the engine is cold- I live in Maine and it has been starting on 20 deg mornings perfectly, then shutting down when up to operating temp. And the Cam Position Sensor and RPM sensor code had been stored (why I am not sure unless it was all three items???) These components seemed to be electronic items that do often work when cold but not hot so I chased that (expensive) line of thinking. Yes, I had pulled a plug when the engine was hot and proven it was firing so I still had ruled out the plugs. Where did I go wrong? Well as I said, I just recently bought this car and my only guess is that the plugs in this vehicle might have been the wrong plugs for this engine-possibly the wrong heat range and as they became older/worn they were working in rich (start up) mixtures but failing in a lean operating mixture. The installed plugs were Volvo plugs, similar to Boch platinum plus (3 electrodes with a single center terminal ). I installed new Boch single electrode plugs gaped to .028". I'm going to call the dealer tomorrow and compare the number on these made in France Volvo plugs with what they say is the correct plug for this engine. Feeling foolish but this is a good example of how easy it is to get caught up assuming the problem is a complicated one when it is really a simple one. Thanks again to everyone who offered help. This is a great website!

Post by **MadeInJapan** » 25 Nov 2006, 07:39

Glad the plugs did the trick!

Post by **pebsham** » 24 Nov 2007, 04:01

I came across this topic via a search and I have the absolutely identical fault. Car starts perfectly from cold runs to the central "warm position" on the gauge and then if you touch the throttle it stalls immediately and will not restart until cooled down again. Only code is RPM sensor.

It ran fine until a couple of weeks ago and the starter failed. I finally got round to changing the starter and then this fault showed up.

I thought it may have been something to do with me disturbing something ie wiring from fan etc but it seems like it may just need a service with plugs.

Thanks for the pointers I'll give it a try!

1994 manual 855 with 145000 miles