Hi guys,
I just joined the forums but I've had a constant check engine light problem. It's on a 1996 850R and has been on for the past few years, mostly on but sometimes off. I have taken an OBD II scanner many, many times to see if I could diagnose the problem, but most of the times it did not result in a problem code. However, sometimes I did manage to find code P0303 for a misfire in engine 3, so I tried doing compression and leakdown tests to find the cause. It turned out to be a burnt valve, so I took apart the head and replaced the head gasket, PCV system, exhaust manifold gaskets, did a valve job, head resurface, and various other gaskets. That seemed to fix the problem... for about 100 miles. The check engine light came back on, and I tried to read the code but there turned out to be no code. What are some other things that can throw off a check engine light? The car has about 120,000 miles, and I have done a lot in the past few thousand miles to restore the engine to stage 0. I've done the timing belt, thermostat, distributor cap and rotor, cam seals, all the gaskets, water pump, coolant, synthetic motor oil, tranny oil, and brake fluid within the past 3000 miles. I also cleaned out the fuel injectors and made sure that they weren't clogged up. When I took the head off, I cleaned the pistons, valves, intake manifold, and everything of carbon buildup. After replacing the PCV system, and putting everything back together, I also made sure that all the vacuum lines were tight and in the right place. I just can't understand what is causing this check engine light! All of the cylinders have about 180 psi compression, and a leakdown test shows no leaks. Does anybody have any information about what could be the cause of this check engine light?

 

Sounds as if you could have similar problems as me with your Evap/emissions system. Purge solenoid, charcoal canister, gas cap, etc....However, normally you would see a code stored in the memory of the ECU. I would suggest checking all of your connections (vac lines, electrical, etc) there first, then work your way forward from there. Could also try replacing the all too often overlooked O2 sensors as well.

Good luck and hopefully this helps

-Z-

 

Thanks, I'll take a look at the Evap system... are there any symptoms that may show a bad purge valve or a bad charcoal canister (bad mpg, rough idle) or maybe vacuum leaks? I forgot to mention that I replaced the O2 sensors a few thousand miles ago, in an attempt to fix the check engine light. I've had this really annoying light for years now and I've tried pretty much everything, I just want to make sure it's the right problem before I pour more money into a new item. I've read that the o-ring inside of the purge valve sometimes hardens and prevents a tight seal, but what problems do people usually have with the charcoal canister?

 

Ck engine light (CEL) should only come on if a code is set. If you can't read it, try taking it to a place where they can read it. If truly no codes are set, you may have a wiring problem to the CEL itself.

 

What he said about it should only be on if the computer is actively seeing a problem and it should be stored.

If it's intermittent you need to try and read it while the CEL is on. Swing by an Orielly, autozone .... anytime you have the light on and see if they can pull it.