Engine break up

cet · Post by **cet** » 09 Jul 2012, 10:41

Had noticed a post start roughness (irregardless of engine temp) which self resolved on 3 occaisions over the past week.Left a store this morning, the roughness got so bad the car would not move. It would start and idle well but any throttle opening made it break up.Unplugged and plugged the connector on the mass airflow sensor and cam sensor which allowed it to run about a mile before dying compleatly. Took advantage of local hills to make it the 2 miles back to home.Any Ideas? Will try spare MAF first. cannot read codes because circuit 15 (interior lights/diagnostics) blows fuses as you insert them(which needs fixed to pass PA inspection). BTW hats off to IPD for saving me money on the exact same lower controll arms.saved 20 a side even with shipping...........Put in spare MAF sensor, better start and initial idle, ideled well for 30 sec then started breaking up. it sounds like it is drifting on timing

Post by **jblackburn** » 09 Jul 2012, 11:40

Does fuse 15 continue to blow even if you turn off all interior lighting via the rocker switch at the top? I believe finding out what's wrong there should be first priority before you begin throwing parts at the car.

It could be a MAF sensor, crank position sensor, or cam position sensor. Or possible even others.

Is this a turbo or just a regular 850?

cet · Post by **cet** » 09 Jul 2012, 13:02

If rocker is neutral, no.As soon as rocker goes to the light position, or door opens or glovebox opens it blows in spectacular fashion, Once the fuse has blown any action that should give you interior lights, gives you instead, the "you left your keys in the ignition bell". would love to cure this but the car did run just fine for a year like this.

installed my spare MAF, car started right up, idle smoothley surged up to 2000rpm like the computer was "seeing" the new MAF ,droped back to its normal 850ish, held for 30 sec, then before i could open throttle to test it broke up to the point where i had to shut it off. It sounded like the point of detonation shifted from the cylenders to the exhaust manifold to the cat.......

went out to hit fuel rail shraeder valve good preasure tryed to start , started right up got on the gas, flew up to 5000 sounded great, put it gear stayed smooth for about 30 sec, then just before it started breaking up the temperature gauge dropped tp zero. Now the temp gauge has dropped out occaisionally since i bought the car in 2009 but i just thought it strange that the engine ran fine for almost a min and a half, then the gauge tanked just as it broke up.

Thanks for jumping in

Post by **jblackburn** » 09 Jul 2012, 13:06

Based on those symptoms, I can think of 2 possibilites:

1) Feel the battery cable heading to the fusebox once the car begins to die. Is it hot? The cable may be bad and choking up current like a kinked off garden hose as it gets hot.
2) The ECT (coolant temp sensor) has gone bad or the plug is corroded up. This can cause the computer to choke the engine with fuel since it thinks it's cold.

cet · Post by **cet** » 09 Jul 2012, 13:19

will police up terminal crud and check for heat. Would you have a location and ballpark resistance for the temp sensor?
Both sound like plausable theories, will report back.

Post by **jblackburn** » 09 Jul 2012, 13:22

Follow the upper radiator hose to the thermostat housing. You'll see a wire going into a brass plug just under that.

Resistance values:
ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE TABLE
Temperature F ( C) Ohms
32 (0) .............................................. 7300
68 (20) ............................................. 2800
176 (80) ............................................. 300
212 (100) ............................................ 150

Post by **rmmagow** » 09 Jul 2012, 14:38

Can one run the Ohms test by removing the ECT and testing at the various points in a pan of hot water?

Post by **jblackburn** » 09 Jul 2012, 14:38

Sure. Need to crack open the thermostat housing on a pre-99 to get the ECT sensor out, though.

cet · Post by **cet** » 09 Jul 2012, 15:03

Is the fuel pump relay up on the fan gaurd? and can it be swaped with anouther similar bosch relay? after cleaning terminals, taking temps, checking R's, I starting checking the shrader at the END of every run and the preasure stunk. put meter on fuel pump feed and shure shootin had a 3 sec. no volt which caused a little stumble and then a 30 sec no volt which brought it down. It runs the pump to prime at start but is cutting out during run. I guess there is little room for pressure reserve so the pump must run continuousley.

Post by **jblackburn** » 09 Jul 2012, 15:08

Hmm!

FPR is under the fuse cover near the windshield. 3 screws around the edges, and it comes off.

Remove relay 103 and stick a paperclip between pins 15 and 87. See if it will STAY running - if so, you've found your culprit.