I found this interesting post by Twiggy144 on miata.net forum. Going to try this later today when I get home...
A faulty CAM pos sensor is hard to diagnose, it rarely triggers a CEL, but on the other hand, knowing it is hard to troubeshoot, we should suspect this part early in the diagnosis process, and unveiling it's failure becomes a faster process. The cam pos sensor sends a signal to the PCM, that will fire the spark plugs, AND activate the fuel injectors. It the engine cranks but does not start, first of all check the main relay, the 30 amp INJ fuse, (both under the hood) and the 15 amp engine fuse (in the cabin). Next, check for spark at the plugs. If no spark, and no unburnt fuel can be smelt coming out of the exhaust while cranking the engine, then strongly suspect either the cam pos sensor, or the crank pos sensor. I did these little tests on my 2002 to understand what the sensors control. Test 1. Disconnected the cam pos sensor connector and attempted to start the engine. Results: there was no spark, obviously the injectors were not activated ( the cam sensor's main purpose is to synchronize the fuel injectors through the PCM), but the fuel pump ran for three seconds, exactly as it is supposed to. ( The PCM activates the fuel pump relay for three seconds while starting the engine, to build fuel pressure in the fuel line. After these 3 seconds, if no signal from the cam pos sensor is received at the PCM, the fuel pump relay is shutoff. This is a safety system when the engine is not running to prevent a possible fuel feed fire in the engine bay). Test 2. Disconnected the crank pos sensor and attempted to start the engine.Results: there was no spark, and the fuel pump did not run at all, not even for the first 3 seconds. >From these tests, by listening at the humming noise the fuel pump makes, one can diagnose if either the camshaft or the crankshaft position sensor is faulty. If fuel pump noise is heard, the crankshaft pos sensor may be ok, suspect the camshaft position sensor. From: [email protected] [mailto:[email protected]] On Behalf Of Ken Bogart Sent: 10 March 2011 12:49 To: Bell, Richard (GE Energy Services) Cc: [email protected] Subject: Re: Non-starting 2001 help needed Correction - the Cam Position Sender on the 2001 is top of the cam cover, towards the front of intake side. It can prevent the car from running and more likely to fail that the CAS located on the crank pulley. Ken On Thu, Mar 10, 2011 at 7:42 AM, Ken Bogart <[email protected]> wrote: Fuel pump comes on for a few seconds when you turn the key to pressurize the system. No spark / no fuel indicates the ECU is not receiving a signal from engine rotation. >From my recollection, in a 2001, the Crank Angle Sensor is on the front of the engine and controls spark. The Cam Position Sensor on the top back of the engine controls fuel. No fuel and no spark point to the timing belt. Ken Bogart ----------------------------------------------------- 96 Montego Blue FFS Coldside (His) 97 Black & Tan (Hers) 90 Crystal White (sons) ------------------------------------------------------ http://www.miatacare.com http://www.cincimiata.com http://www.bcchallenger.org MiataMail.com list owner On Thu, Mar 10, 2011 at 6:55 AM, Bell, Richard (GE Energy Services) <[email protected]> wrote: Battery charged up to 12.6V and cranked well so think that is OK. I will check for cam belt today. I'm just wondering what could cut power to the fuel injectors but still allow the fuel pump to run? Thanks, Rich From: [email protected] [mailto:[email protected]] On Behalf Of Ken Bogart Sent: 10 March 2011 11:43 To: Bell, Richard (GE Energy Services) Cc: [email protected] Subject: Re: Non-starting 2001 help needed Could be weak battery... but sounds like a classic broken timing belt. Can you see the cam turning through the oil fill hole? Probably not, but simple to check for. Ken Bogart ----------------------------------------------------- 96 Montego Blue FFS Coldside (His) 97 Black & Tan (Hers) 90 Crystal White (sons) ------------------------------------------------------ http://www.miatacare.com http://www.cincimiata.com http://www.bcchallenger.org MiataMail.com list owner On Thu, Mar 10, 2011 at 4:23 AM, Bell, Richard (GE Energy Services) <[email protected]> wrote: Hi Folks, I wonder if anyone can shed some light on my issue as I'm getting nowhere at the moment. Car is a late 2001 and was running fine before sitting for a week. Battery wasn't great and went flat, however, I managed to get it back to full charge. Car cranks fine but refuses to fire. After cranking, I pulled a plug and it was completely dry and there is no spark when cranking with the plug against the cam cover. However, I do hear the fuel pump run for about 0.5 seconds after I stop cranking. I have no CEL and no fault codes logged. There is no key warning light on to suggest immobiliser issue. Can anyone suggest any possible causes? I'm going to borrow a crank and cam sensor to see if they are causing issues as I read sometimes they don't cause fault codes. But other than that, what else can I check? Can someone point me in the right direction of some wiring diagrams for a 2001? Thanks in advance, Rich _______________________________________________ Miatapower mailing list [email protected] http://list.miatapower.net/cgi-bin/mailman/listinfo/miatapower
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